UNSW School of Medicine Liverpool Clinical School Year VI Critical Care Rotation Anaesthetics Study Guide Blair Munford, BMedSc, MB,ChB, FFARACS, FANZCA Senior Specialist Anaesthetist, Liverpool Hospital Aims of Anaesthetic Attachment To understand the scope of the practice of anaesthesia. To understand the role of the anaesthetist as part of the surgical or procedural team. To gain exposure to airway management and other procedural skills To understand the importance of the perioperative process including pre-anaesthetic assessment, investigations, and optimisation. To understand post anaesthetic care including pain management, and the indications for specialised postanaesthetic monitoring & support. To revise/enhance key concepts & simple competencies in emergency assessment and resuscitation, including CPR/BLS/ALS. For those interested, to acquire insight into anaesthetics as a medical career option. Introductory Case Study “Don’t play with that!” … A simple paediatric case - NOT My first ever weekend on duty as an anaesthetics registrar . . . Case transferred from country hospital for theatre: 3 year old girl, previously well Mixed total/partial toe amputation (From playing with grandfather’s axe!) 18 hours ago, fasted since IV in situ, IV fluids running. Has had antibiotics/narcotic analgesics. No problem, even for a junior registrar, right? What happened next . . . To OT as scheduled. Rapid sequence induction, uneventful anaesthesia. Extubated near awake at end (in hindsight, too soon) Vomited undigested food, developed laryngospasm, desaturated. Re-paralysed, intubated, pharynx sucked out, suction down ET tube – no evidence aspiration Awoken & re-extubated uneventfully. The lessons from this: 1. 2. Specific: Beware occult delayed gastric emptying – predictable in hindsight. General: There is minor surgery but there is no minor anaesthesia! Anaesthetic practice is more than just being able to give an anaesthetic – just like being a 747 captain is more than just holding the controls! Part I: Scope & Development of Anaesthetic Practice Imagine a world without anaesthesia . . . What medicine was like prior to the invention of anaesthesia: Surgical operations performed rarely & only as a last resort. Death was the expected and usual outcome, from shock, haemorrhage, or infection. When surgery unavoidable, patient was held down by assistants & surgeons operated as fast as possible. The first incision was often deliberately brutal in the hope that the patient would faint, allowing less haste. No analgesia in labour & interventional/operative obstetrics essentially unknown – except post mortem (original meaning of Caesarean Section) Without anaesthesia . . . Surgical advances would have been minimal. Childbirth would remain a major risk for baby and/or mother. Concepts of intensive care & resuscitation would not have developed. Pain - acute and chronic - would have remained an inevitable part of life. Without doubt the development of anaesthesia has been one of the top ten medical advances of all time. Some have even ranked it as the most important medical invention ever. Others rank it amongst greatest discoveries of any type in human history. But what is anaesthesia? A state that encompasses (1)analgesia plus (2) arreflexia (muscle relaxation or lack of movement) and (in the case of general anaesthesia) (3) hypnosis; enabling painful or distressing procedures to be performed humanely. This is the “Triad of Anaesthesia” The other triad of anaesthesia 1. THE MISSION IS (in order of importance): Preserve life 2. Relieve suffering 3. Provide optimum conditions for procedure (Any fool can do the third by ignoring the first. Doing the second by ignoring the first is called euthanasia. The art is in being able to provide all three.) Anaesthesia can be: Cerebral Sedation/analgesia General Inhalational/spontaneous ventilating Balanced/controlled ventilation Neuro-interruptive (Or some combination of Local two or more of these) Regional Neuraxial Classification of Anaesthetics Anaesthesia General Alternative Regional Dissociative Surface/topical Controlled ventilation Intubated Spontaneous ventilation Intubated infiltration Auditory Nerve/plexus block Electrical Spinal blocks Hypnosis LMA Epidural: Manual Mechanical Mask Subarachnoid cervical, thoracic, lumbar, caudal Acupuncture Single shot, intermittent, continuous Local anaesthetic, narcotic/adjuvant, combination But wait . . . there’s more: Scope of Anaesthetic Practice Anaesthesia for surgery Sedation/anaesthesia for other procedures Obstetric analgesia/anaesthesia services Pre-anaesthetic assessment & perioperative medicine Acute & Chronic Pain Services Vascular access services: Central venous lines, et al. Resuscitation: Trauma team/MET/Prehospital Teaching: Procedural skills/resuscitation/analgesia Intensive Care practice/cover/support Operating theatre management/coordination Critical care transport (It’s a broad church!) Part II: Perioperative Medicine “The way of the future” What is perioperative medicine? “Integrated multidisciplinary management of the surgical or procedural patient’s hospital admission & stay.” Perioperative system includes: Identification of patient requiring procedure Referral to perioperative service Screening for level of workup required Pre-anaesthetic assessment/plan Referral & investigations as required. Admission at appropriate pre-op interval Post-operative drug/fluid/other therapy Appropriate post op level of care & stay Discharge at earliest appropriate point But why? Minimize unnecessary pre-op bed days. Minimize preoperative cancellations Enable more predictable bed occupancy Minimize pseudo-urgent blood tests & other investigations Improve post operative care & shorten post operative stay The Pre-anaesthetic Consultation What? Targeted history & examination, & formulation of anaesthetic/perioperative plan. Who? Ideally by the anaesthetist for the procedure (not always possible). Whom? All patients should have some form of this. When? At the earliest appropriate opportunity (Obviously this varies on a case by case basis) Why? To enable optimimum pre-anaesthetic preparation, risk minimisation, informed consent, and allaying of anxiety. Pre-operative preparation may include premedication Use if required, not “one size fits all” Aims: 1. 2. Ameliorate anxiety Usually with a benzodiazepine such as temazepam Relieve pain – predominantly in the acute setting – usually with narcotics. 3. 4. Prevent reflux/aspiration - in at risk patient Usually (a) H2 blocker or PPI 6-8 hrs preop if possible, then (b) non particulate antacid immediately preop. Treat other medical conditions e.g. asthma prophylaxis. Most regular medications are continued, including on the day of surgery (b) Exceptions include: (a) Oral hypoglycaemics Antithrombotic agents (mostly) ASA Physical Status ASA 1 – Healthy patient ASA 2 – Mild or controlled systemic disease ASA 3 – Significant systemic disease ASA 4 – Severe systemic disease – current or constant threat to life ASA 5 – Moribund patient unlikely to survive with or without procedure ASA 6 – Brain dead patient (organ donor) +/- E = Emergency procedure Relevance of this? Risk stratification Workload/resource utilisation planning Remuneration aspects Perioperative (Preanaesthetic) Clinic Surgical clinic Nurse Clinic Checked up, satisfied as fit & suitable Decides to proceed with planned time, date & procedure Surgeon refers case Satisfied with it; decides to send it back to her for mx Not certain;sends only case notes to anaesthetist to review it Decides to further investigate. May cancel, postpone, refer case or decide to do it Not quite satisfied; takes over review & mx Preanaesthetic Clinic The Doctor takes a quick history, leading questions are allowed as major diagnoses should already be known Asks for hypertension, diabetes, asthma,epilepsy, previous anaesthetics, allergies, complications, medications being used A quick examination is done, Ix like Xray, ECG, UES & Blood ix are done ASA categorised, anaesthesia decided Explained to patient about anaesthetics, risks, PCA & possible complications Preanaesthetic Clinic Based on: History Examination, Investigation . . . Decision: To do the planned procedure To postpone the procedure till fully investigated optimised To cancel the procedure CASE STUDY II Perioperative management Diabetic patient for vascular surgery History 65 year old man, BMI 35 Type II DM, 15 yrs, on OHGs, poor control Smoker 60+ pack years Hypertension Hypercholesterolaemia Ischaemic heart disease Diabetic nephropathy, (eGFR ~ 30mls/min) For (R) femoro-popliteal bypass What are the issues and risks here? 1.What are the issues and risks here? 2. How can we optimise him preoperatively? 1. What are the issues and risks here? 2. How can we optimise him preoperatively? 3. What are our anaesthetic options & problems? 1. What are the issues and risks here? 2. How can we optimise him preoperatively? 3. What are our anaesthetic options & problems? 4. How do we manage him postoperatively? Part III: Safety & Monitoring in Anaesthesia Safety in anaesthesia is paramount “When it goes right, no-one remembers. . . When it goes wrong, no-one forgets” . . . So the aim is to make anaesthesia as forgettable as possible! Safety Initiatives in Anaesthesia Anaesthetists have been the leaders in safety initiatives in medicine – e.g. : Privileged reporting & investigation of deaths under or associated with anaesthesia in most states. Systematic reporting of incidents and near misses Collegial policies on minimum standards for facilities, equipment, monitoring, staffing, & training. Publication of algorithms – e.g: difficult airway management; malignant hyperthermia Simulation & contingency training e.g. difficult airway workshops, emergency management of anaesthetic crises (EMAC) course. Principles of Safety Recognise risk – pre anaesthetic consultation Avoid risk if possible – e.g. can procedure be done under LA? Mitigate risk – optimise patient condition, select safest technique/agents/resources – e.g “cardiac” anaesthetic & postop ventilation. Plan & be prepared for emergencies – e.g. predrawn emergency drugs, backup airway plan. Observe/monitor for deviations & crises. Respond in a timely& appropriate fashion. Call for help/backup if required. “The price of safety is eternal vigilance” “Clinical observation is the cornerstone of patient monitoring” - ANZCA Policy statements (several) OR . . . “The best patient monitor is still the one between your ears – so make sure it’s switched on” – my take on the above. Monitoring in anaesthesia Basic (all/most patients) Pulse oximetry ECG Noninvasive (cuff) BP Capnography Oxygen concentration Agent monitoring Airway pressures Temperature Others as indicated Invasive arterial BP Precordial stethescope Ventilator alarm(s) Nerve stimulator BIS/entropy Spirometry CVP “Swann Ganz” (PAP) Transoesophageal echo Pulse oximetry First monitor I put on most patients & first I usually look at. If this is OK, then patient has a pulse, a survivable blood pressure (at least 60/) and is oxygenating their blood. But if it’s not right, it’s not very specific – i.e. it may be as simple as a dislodged probe, or as serious as a cardiac arrest. Doesn’t guarantee tissue oxygenation – may be relatively normal in extreme anaemia, carboxyhaemoglobinaemia, cyanide posoning, etc. Electrocardiogram Good monitor for: Arrhythmias/ectopics Some electrolyte abnormalities (K+ & Ca++) Ischaemic/strain changes (Provided leads are placed correctly!) Does not monitor: Volume status Cardiac output Blood pressure Remember: it is entirely possible to die with a relatively normal ECG! Noninvasive arterial blood pressure (NIBP) monitoring Usually automated Convenient but not reliable: Dependant on correct cuff size & position Not continuous Usually under-estimates true hyper-& overestimates true hypotensive values. Interferes with IV infusions & pulse oximetry Should not be placed on limb with AV fistula or lymphoedema. Capnography “Gold standard” for verification of ETT placement. Can also give information on: Dead space/V-Q mismatching Adequacy of ventilation Spontaneous respiratory effort during controlled vent’n. Rebreathing: circuit problems or inadequate gas flow. Venous return, RV function & pulmonary blood flow e.g. thrombotic, gas or fat embolism Oxygen monitoring Monitors machine rather than patient. The only specific monitor of oxygen supply (Other safety features assume/depend on the gas from O2 outlets & cylinders actually being oxygen) N.B. Before adoption/mandating of oxygen monitoring, all reported (& thankfully very rare) “wrong gas” anaesthetic incidents (misconnected pipelines or incorrectly filled cylinders) resulted in the death of the first patient exposed in every case. Anaesthetic agent monitoring Identifies (hopefully confirms!) anaesthetic agent being used Measures inspiratory & expiratory concentrations Expiratory (alveolar) concentration enables calculation of MAC fraction or multiple – i.e. estimation of anaesthetic depth. Now mandatory when inhalational anaesthetic agents are used. Temperature monitoring Anaesthesia promotes hypothermia by: Patients may need temperature support Decreased metabolic rate -> decreased heat production Redistribution of blood flow -> increased heat loss Passive (prevent heat loss) Active warming: forced air/ heated IV fluids What you support you must monitor Ideally monitor core temperature: Nasopharyngeal/oesophageal/bladder/PV Better than Skin/axillary/oral/rectal Airway manometry Usually analogue gauge on circle circuit Monitors inflation pressure With IPPV can help identify: Airway obstruction Bronchospasm Circuit leaks/faults Ventilator monitor Mandatory when mechanical IPPV employed. Usually integrated into ventilator w/automatic activation. High (overpressure) & low (disconnect) functions Precordial stethescope “Traditional” monitor Still used in some paediatric cases Can monitors: Heart & respiratory rate Breath sounds presence & quality. Only as good as the person listening to it! Direct arterial pressure monitoring Invasive procedure, but: Gold standard for real time haemodynamic assessment Accurate, reliable. Immediate warning of hypo/hypertension of any aetiology. Depth of Anaesthesia monitoring Nerve stimulator Used with muscle relaxants (neuromuscular blockers): Electrical stimulus to nerve then observation of innervated muscle. Commonest site: Ulnar nerve Nondepolarising block characterised by “fade” – weakening of contraction with (4) successive impulses “train of four.” Assesses: - Density of block - Return of function - Point of safe reversal Uses simplified EEG recording & algorithm to produce number related to level of conciousness (lower no=deeper anaesthesia) Two methods: bispectral edge (“BIS”) and entropy. Role/value still controversial Probably indicated for: TIVA (as no MAC to monitor) Patient with a history of awareness Where lightest possible plane of anesthesia essential Other monitors Central venous line. - Mostly used for drug infusions but can also measure CVP as a (not very accurate) guide to volume status. Has become the gold standard cardiac function monitor. Able to estimate: Ejection fraction/stroke volume/cardiac output LV & RV Preload/pressures Diastolic dysfunction (early index of ischaemia) Pulmonary artery (Swann Ganz) catheter - - Can estimate LV filling pressure (preload) – a better guide to functional volume status than CVP Also can measure cardiac output by thermodilution. Trans-Oesphageal Echocardiography (TOE) Spirometry Measurement of pressure volume loops & hence work of breathing in controlled, spont. & ass’t’d ventilation CASE STUDY III Gynaecological laparoscopy Patient with polycystic ovaries for laparoscopic cystotomies as day case procedure History 25 year old woman Height 165cm, weight 80kg BMI 29.5 Typical PCOS history/findings. Allergies nil Rx: Metformin 0.5G b.d. Previous GA – E/O wisdom teeth – OK O/Ex: Overweight, otherwise unremarkable. Common lies told by surgeons - number 2: “Just a quick laparoscopy”! What are the issues and risks here? Anaesthetic issues Medical condition Prolonged surgery Laparoscopy/pneumoperitoneum Trendellenberg Analgesia PONV “Quiet victory” Largely uneventful anaesthesia/surgery Problems maintaining normocarbia without excessive airway pressures when head down Mild permissive hypercapnoea, corrected at end Polymodal antiemetic therapy – no PONV Comfortable on combined analgesia Home as day case. A typical “straightforward” case that was expected to go well - & did - so is not memorable to anyone but the anaesthetist who worked hard to make it that way. “There are a million stories in the naked city, this is one of them.” - The Naked City, US crime drama series The practice, safety & reputation of anaesthesia is built on thousands of such cases – far more so than the glamorous emergency cases & heroic saves. Part IV: Anaesthetic Equipment & Airway Management Introduction to/overview of the Anaesthetic Machine Consists of three main parts: 1. “A cocktail bar” This is the backbar – which blends piped &/or bottle gasses: O2, N2O & air, and the vapour of (usually one only) volatile anaesthetic agent (liquid) to produce the desired blend. 2. “A delivery service” This is the breathing circuit – which delivers the fresh gas mixture to the patient and removes carbon dioxide. (There are three main classes of circuits – discussed later) 3. “A bunch of hangers on” These are all the ancillaries attached to the anaesthetic machine but not part of its core function: typically suction system, patient monitors, drawers/trays for airway equipment, and a mechanical ventilator for hands-free controlled ventilation. A Note of Caution: Modern anaesthetic machines are complex devices that require special knowledge to operate. In particular, knowledge of the pharmacology of inhaled anaesthetic agents is essential. Undetected mishaps can be rapidly fatal. A thorough check prior to use, appropriate for the particular machine, by an experienced person, is vital. Some parts of the circuit e.g. filters & hoses, need to be changed after every or certain cases, or a different type of circuit may be selected & attached. An abbreviated recheck must be carried out after any such change. Anaesthetic Circuits Three principal types: 1. 2. 3. Drawover or “semi-open” systems: where non-rebreathing valves are used to ensure unidirectional flow of gas. Principally now used in resuscitation & field anaesthetic systems, because of the ability to use ambient air instead of (some or even all) pressurised gas supply. Simple or “semi-closed” systems with pressurised fresh gas inflow, reservoir tube & bag in one of several different configurations. (Sometimes called Maplesen systems, after the man who classified & evaluated the different configurations). The patient breathes ‘to & fro’ through the reservoir tube & bag & the system relies on an adequate fresh gas flow to minimise rebreathing. Commonest example: the “Jackson-Rees T-piece (Maplesen “F”)” paediatric circuit. Circle, or closed circuit systems which use one way valves to direct expired gas through a carbon dioxide absorber. This gas can then be supplemented with only enough fresh gas mix to replenish the oxygen and anaesthetic agents taken up, and then rebreathed. This is the commonest type of anaesthetic circuit in modern practice. Remember: The commonest anaesthetic circuit most medical & nursing staff will ever use is the non-rebreathing resuscitation bag (“Laerdal bag” or similar) . . . . . . to give the commonest anaesthetic and resuscitation drug of all: Oxygen Another rule of three: The triad of resuscitation A – AIRWAY B – BREATHING C – CIRCULATION Or . . . Alternatively: (The triad of resuscitation – my own version) 1. 2. 3. Air goes in & out Blood goes round & round Variations on the first two are a BAD THING Note that airway always comes first Airway isn’t everything . . . . . . but without it everything else is nothing. This is why anaesthetists are good people to have around at a resuscitation – and why a grounding in anaesthesia is good training for emergencies. Airway Control – Why? Prevent obstruction Anatomical/foreign body Protect against aspiration Vomit/blood/secretions Permit controlled ventilation With paralysis/deep anaesthesia Where ventilatory support required Enable special manoeuvres e.g IPPV & PEEP for thoracotomy, laryngeal surgery with microlaryngeal tube, single lung deflation with double lumen ET tube. Classification of airways SUPRAGLOTTIC TRANSGLOTTIC SUBGLOTTIC Oropharyngeal airway Nasopharyngeal airway Laryngeal Mask Airways (various) Combitube/PTL * Orotracheal tube (85% of placements oesophageal) - if one of the 15% placed tracheally Cricothyrotomy Nasotracheal tube Transtracheal jet catheter Intubating LMA Tracheostomy (w/ETT placed thru it) (Combitube/PTL) The winner, and still champion: Endotracheal intubation (usually oral), remains the gold standard for airway management, . . . but . . . It is also the most difficult to master and carries the highest risk. Remember: An unrecognised oesophageal intubation has a 100% mortality Emergency Airway Management (in anaesthesia & resuscitation) >90% <10% Rapid sequence intubation Other techniques: [or unmodified (“cold”) intubation if apnoeic & arreflexic] Supraglottic airway Fibreoptic intubation Surgical airway Rapid Sequence Intubation: How to do it properly Preoxygenation: 3mins or 5 VC breaths. IV induction agent – titrated to effect Cricoid pressure – 30N. Suxamethonium 1.5mg/kg (IBW). or Modified RSI: 0.9mg/kg rocuronium No bag mask ventilation (unless hypoxic) Intubation & confirmation of placement (then & only then) Cricoid pressure released. Remember (1) : every intubation attempt is a potential failed intubation. You should always have a backup plan - i.e. a failed intubation drill. Backup begins even before you start - with preoxygenation for every IV induction Remember (2): People don’t die of failure to intubate, but of failure to oxygenate FAILED INTUBATION DRILL FIRSTLY MAINTAIN OXYGENATION! CAN YOU MASK VENTILATE? [With Geudels &/or nasopharyngeal airway if necessary] YES 1. Bag mask ventilation 2. Repeat attempt &/or alternate technique to intubate NO NO Supraglottic rescue airway e.g. LMA SUCCESSFUL? NO SUCCESSFUL? Subglottic (surgical) airway Non endotracheal airways There’s more to anaesthetic airways than just ET tubes! Laryngeal masks (of various types) are the most widely used airways in modern anaesthetic practice: Classic (original) & its various copies – reuseable or single use. Reinforced – kink resistant & more flexible upper lumen to permit alternative positioning after insertion for oral/facial procedures. Proseal - second lumen to communicate with oesophagus & allow drainage of gastric contents or placement of gastric tube. Intubating – modified shape, more rigid, & lacking apeture bars – to enable passage of a special ET tube through it. Non endotracheal airways II Advantages of laryngeal masks: Hands free (compared to face mask/oral airway) Easier to insert & become proficient at compared to ETT Tolerated at lighter plane of anaesthesia than ETT. Good protection against “top” aspiration - of saliva/mucus. Pressure support & in some cases IPPV can be given. Disadvantages of laryngeal masks Less secure airway - more prone to dislodgement than ETT No protection against laryngospasm Poor protection against “bottom” aspiration – of gastric contents (Except “Proseal”) Not guaranteed to permit satisfactory IPPV – especially where high pressures required. Remember, the traditional facemask/chin lift +/- Geudel’s airway is still an acceptable – possibly even underutilised – technique for short simple cases. Part V: Anaesthetic Drugs: Pharmacology, Use & Related Issues Classification of drugs used for anaesthesia “The Big Five “ Inhalation anaesthetic agents – gasses/vapours IV anaesthetic agents alias “Hypnotics” or “induction agents” Narcotic (& other) analgesics Muscle relaxants – neuromuscular blocking agents Local anaesthetic agents Other agents are often given as part of anaesthesia – e.g. antiemetics & autonomic agents, but are not conventionally regarded as anaesthetic agents per se. Pharmacology 1: Inhalational Anaesthetic Agents Inhaled – therefore delivered via apparatus Gasses or volatile liquids Moderate to high lipid solubility – “solvents” Effects related to physical properties (rather than to a generic chemical structure) Effects on multiple organ systems Actual mode of action not yet fully elucidated, but thought to be by dissolving into cell membranes & causing secondary changes in configuration of ion channels. Currently Used Inhalational Anaesthetics (shown in their international colour codes): Nitrous oxide (N20)– a gas. Insufficiently potent to produce full anaesthesia on its own, but is rapid acting, pleasant to inhale & is the only currently used agent that is also analgesic. Sevoflurane Desflurane Isoflurane all liquids that are flourinated ethers Earlier volatile agents such as ether, chloroform & halothane have been superceded due to issues such as flammability, slow recovery, & toxicity. Practical Pharmacology of Inhalational Agents Used for induction sometimes (predominantly in children) & maintenance of anaesthesia in the majority of cases - either alone, or in combination with narcotics & muscle relaxants. Modern flourinated agents are good hypnotics, & provide a degree of muscle relaxation at high doses, but not analgesia. In contrast, nitrous oxide is analgesic, but doesn’t decrease muscle tone, and is a poor hypnotic except at very high (i.e. hypoxic) concentrations. The combination of a volatile agent, e.g. sevoflurane, with a 50:50 nitrous oxide/oxygen mix is a useful combination that combines the attributes of both agents. Practical Pharmacology of Inhalational Agents (2) Sevoflurane has superceded isoflurane as probably the most widely used agent, & has also superceded halothane as the agent of choice for inhalational induction in children. All currently used agents have relatively low solubility in blood & tissue – meaning that their partial pressures rise & fall quickly, producing more rapid induction & emergence. The classical stages of anaesthesia are still seen with modern agents – including the delerium phase – characterised by restlessness & risk of laryngospasm. This stage is usually seen on emergence, or with inhalational inductions in children. Practical Pharmacology of Inhalational Agents (3) Nitrous oxide, as a gas is delivered by a flowmeter (as are O2 & air – the 3 flowmeters on a typical modern anaesthetic machine). A linkage between the N20 & oxygen flowmeters stops the delivery of any mixture <25%O2. Most anaesthetic machines also only allow delivery of either N20/O2 or air/O2, not all 3 & none allow air/N2O (a hypoxic mixture). Volatile agents are delivered by vapourisers – devices which add a precise percentage of vapour to the gas mixture. Modern vapourisers are agent specific and colour coded/labelled accordingly. They have numerous mechanisms to ensure accurate delivery, plus safety measures such as “keyed” filling systems that match only the correct bottle; and machines that can have more than one vapouriser fitted must have interlocks that prevent more than one being turned on. Pharmacology 2: IV anaesthetic “induction” agents Used for: Induction of anaesthesia Sole agent for brief procedures By infusion for longer procedures - in place of inhaled agents – i.e. total intravenous anaaesthesia “TIVA” Classification of intravenous agents – Thiopentone Benzodiazepines – Midazolam Dissociative agents – Ketamine Others- Propofol Barbiturates + Alpha-2 agonists – Dexmetomidine . . . maybe “the next big thing” General features of IV agents Lipid soluble High volume of distribution (Vd) Initial distribution to VRG Offset of (initial) effect predominantly by redistribution More complex when used as infusions (Computerised multicompartment pharmacokinetic modelling required) Propofol Most widely used agent now Rapid(ish) onset & offset Shorter elimination halftime Less CVS & respiratory depression Doesn’t predispose to laryngospasm ED50 for induction: ~ 2 mg/kg Suitable kinetics for infusion Other IV agents THIOPENTONE First widely used agent Rapid onset & initial offset by redistribution Long elimination halftime CVS & resp depressant Laryngospasmogenic ED50: ~ 5mg/kg Still used for RSI “The correct dose of thiopentone is enough” (and no more!!) MIDAZOLAM Low CVS & resp depressant Anxiolytic, good initial adjuvant agent, not often used as sole agent KETAMINE “Dissociative” agent Phencyclidine derivative Cardiorespiratory stimulant (in vivo) Maintains airway reflexes Analgesic in subanaesthetic doses “The disaster anaesthetic” Total intravenous anaesthesia “TIVA” Not practical until introduction of propofol , with its short elimination half life, meaning minimal accumulation with infusion. Usually target controlled infusion using computerised algorithm in syringe pump software. Operator enters patient weight, age, & desired blood level. Often used in combo with remifentanil & cisatracurium infusions for long cases (these also have good kinetics for use by infusion). TIVA –good & bad Advantages Good for cases of long or uncertain duration Less effects on CBF & ICP than volatile agents Less likely to cause PONV then either volatiles or N2O. Disadvantages Long setup time More expensive Multiple syringe pumps required No direct measure of blood or effect site concentration Pharmacology 3: Narcotic Analgesics & Acute Pain Management A Definition of Pain: “An unpleasant localised sensory experience perceived as actual or potential tissue damage.” May be acute or chronic Classification of Analgesics Conduction blockade Opiods Paracetamol NSAIDs & COX2s Miscellaneous agents Complementary/Non pharmacological An opiod is a drug that exhibits agonist activity at opiate (endorphin/enkephalin) receptors. A classification of opiods includes: Opiates (naturally occuring constituents of opium) & their derivatives: e.g. morphine, codeine, diamorphine (heroin) Synthetic opiods e.g. pethidine, fentanyl cogeners, oxycodone Partial agonists e.g. pentazocine “Fortral”, buprenorphine N.B. This classification does not include the narcotic antagonists e.g. naloxone “Narcan” & naltrexone; however these are closely related, being n-allyl substituted derivatives (hence their names)of opiods Properties of opiods Analgesia Spinal ( μ/κ) & supraspinal (μ) Respiratory depression Sedation/euphoria (addiction potential) Emesis Depression of GI motility Neuraxial route Pruritis predominantly Urinary retention } No difference in respiratory depression between equi-analgesic doses of any narcotic agonists So the differences between opiods are less in their analgesic efficacy than in: Onset Duration Potency/dose Histamine release Autonomic effects Chest wall rigidity Effective routes of administration Routes of administration of opiods: Intravenous: (a) Boluses – titrated to effect – e.g recovery pain protocol (b) Infusions – require close monitoring due to potential for overdose as narcotic requirements fall away. (c) PCA – now widely used. Intrinsically safer than infusions, plus positive psychological effect of patient knowing they are in control. Neuraxial - Epidural or intrathecal (spinal) – usually in combination with regional anaesthesia, but may also be stand alone technique for postoperative analgesia. Risk of late onset respiratory depression if agent migrates into intracranial CSF in significant amount (highest with morphine, but this is also the longest acting) IM/SC – decreasing importance with availability of PCA & better oral agents, & multimodal therapy. Oral – variable bioavailability: e.g. oxycodone high, morphine ~ 15% due to first pass metabolism. Sublingual(buprenorphine) /Intranasal(fentanyl) – lipid soluble agents fairly rapidly absorbed & this route avoids first pass effect (& injection) Transcutaneous – e.g. fentanyl patches for chronic pain Problems with opiods Respiratory depression/cough suppression Tolerance Abuse/addiction potential Accountability/access/supply difficulties - consequent to abuse potential. Nausea & vomiting Constipation Multimodal analgesia options Regional/local blockade (if possible) Paracetamol NSAID or COX2 Basal opiod (e.g. oxycontin); or tramadol (or both) prn or PCA opiod Other Clonidine or ketamine Pharmacology 4: Neuromuscular blockers Purely paralysing agents – no analgesic or hypnotic activity. Two types based on modes of action: Depolarising (Suxamethonium) Versus Nondepolarising (NDNMBs, several available) Why use paralysing drugs at all? Permit procedures at a lighter plane of anaesthesia – hence less CVS depression Intubation & ventilation Surgery Permit IPPV without interference Lower airway pressures by increasing chest wall compliance. Lower O2 consumption in critical periods Properties of NMBDs Highly polar molecules Low VD ( ~ ECF volume) Do not cross BBB/placenta Renally excreted (with exceptions) Range of actions at other ACh receptors Histamine releasers (most) Decrease VO2 /ATP & heat production “Sux” versus the NDNMBDs Nondepolarisers Suxamethonium Rapid onset (30s) Fasciculations Transient rise in ICP, IOP, IAP/IGP, K+. Rapid offset (usually) by hydrolysis in plasma Unpredictable effects in repeat dosing Slower onset (3-7m) No fasciculations Little to no effect on ICP, etc. Varying durations with different drugs OK for prolonged use by boluses or infusion Nondepolarising relaxants First generation Curare/tubocurarine Alcuronium Metocurine Gallamine Pancuronium “Modern” agents Vecuronium Atracurium cisAtracurium Rocuronium Mivacurium Brown = curare derivatives Blue = aminosteroids (the “oniums”) Green = benzisoquinolines (the “uriums”) Side effects of suxamethonium Myalgia MH trigger Masseter spasm Phase II block Raises ICP Raises IOP Bradycardia (Usually in infants or with 2nd dose) Raises serum K+ Exaggerated action & K+ rise in denervation, burns, muscle injury Prolonged action with pseudochlinesterase variants/deficiency. Histamine release Anaphylaxis (1:5000) Problems with nondepolarisers Slow onset – not usually a major problem Slow offset (situation/agent dependant) Awareness Hypothermia –reduced heat production Autonomic side effects Interactions Failure to reverse/recurarisation Paralysis obviously mandates controlled ventilation Modern anaesthetic machines are all equipped with ventilators. Usual mode is volume controlled (delivers a set size of breath, a set number of times a minute) with or without PEEP. Most can also give, or be adapted to give, pressure controlled ventilation, which is the mode of choice for paediatric patients (who usually have uncuffed tubes, and hence a small leak). The Physiology of Controlled Ventilation “Spontaneous ventilation sucks; Controlled ventilation blows” Maintains constant minute volume & enables titration to desired pCO2 – vital in neurosurgery & acidotic patients. Uptake of volatile agents therefore usually higher than in spontaneously breathing patient -> more CVS depression. Recruits alveoli & prevents collapse: minimises shunt. Raises mean intrathoracic pressure – & hence RAP, so reduces venous return & cardiac output – especially in head up position & with pneumoperitoneum – e.g. laparoscopic cholecystectomy. Risk of barotrauma – esp. w/high tidal volume or pressures. Pharmacology 5: Local anaesthetic agents Local anaesthetics are membrane stabilisers that block depolarisation in nerves Non specific blockers of: All sensory fibres (not just pain) Motor fibres Autonomic fibres (mainly sympathetics in most blocks) Hence can produce analgesia & arreflexia in the distribution of the nerves blocked. Lower concentrations of LA agents effect predominantly smaller axons: pain (Aδ & C fibres), temperature, & autonomic (unmyelinated sympthetic post-ganglionic fibres) “Your friendly local anaesthetic molecule” Think of a person standing in the water – keeping their head high & dry H+ N A- Head: benzene ring (lipophilic) Body: (intermediate chain) with either ester or amide link. Tail: (feet) – hydrophilic due to tertiary nitrogen capable of accepting proton & rendering molecule water soluble. (This is the form it is in in the ampoule) “The voyage of the molecule Lignocaine” ECF ICF Sodium channel Lignocaine hydrochloride injected N H+ N ClTissue buffering H+ Lower intracellular pH leads to reionization HCO3- H+ N N H2O + CO2 Freebase lignocaine diffuses across cell membrane Understand this, and you will know: Why local anaesthetics sting on injection (because of the low pH needed to maintain ionised state) Why their onset of action is not immediate (because of the buffering/diffusion/reionisation steps) Why local anesthesia is poorly effective in inflamed/ infected tissue (because of the lack of buffering capability in acidotic tissue) Why LAs exhibit tachyphylaxis (exhaustion of buffering capability) (& why cocaine users end up needing nose reconstructions – from repeated insult to the nasal septum from an acid substance that is also a vasoconstrictor - which inhibits circulatory dilution of the acid load) Local Anaesthetic Agents AGENT Max dose: Plain (+Adr) 4 (7) mg/kg Lignocaine (“Xylocaine”) 2 mg/kg Bupivicaine (“Marcain”) 3-4mg/kg Ropivicaine (“Naropin”) Levobupivicaine (“Chirocaine”) 4 mg/kg 7(9) mg/kg Prilocaine (Citanest”) Local Anaesthetic Problems Failed block - multiple causes High block (spinals/epidurals) CNS toxicity at high dose or with inadvertent IV injection Selective cardiotoxicity (bupivicaine) Needle/injection trauma Nerve damage Other – e.g pneumothorax Adjuvant agents used with LAs Adrenaline – prolongs blockade, allows increased dose (lignocaine/prilocaine) Bicarbonate – Decreases acidity - speeds onset of block Hyaluronidase –Aids diffusion (Eye & brachial plexus blocks) Glucose (spinals) – to produce hyperbaric solutions Narcotics (neuraxial) – synergistic analgesia Other analgesics – e.g clonidine in neuraxial blocks. Modes of Local Anaesthesia (a) Peripheral Surface Topical (incl EMLA) Nebulised Intrapleural/peritoneal Infitration Intravenous regional Nerve/plexus blocks Multiple types (b) Neuraxial Epi(extra)dural Single shot vs catheter Bolus vs infusion LA only vs combinations Includes caudal blocks Spinal/subarachnoid Usually single shot LA only or LA/narcotic Combination (CSE) Some common nerve/plexus blocks Eye blocks: Peribulbar, retrobulbar, Sub-Tenons Superficial cervical plexus block Brachial plexus blocks: Axillary, supraclavicular, interscalene Paravertebral blocks Intercostal blocks Ilio-inguinal block Dorsal penile nerve block Pudendal nerve block Femoral (+/- LCNT) block Ankle blocks Spinal Anaesthesia Relatively quick, defined end-point for placement Small volume of LA Usually single shot – “fire & forget” Block level depends on spread – varies with: Volume Speed of injection Baricity Minimal respiratory effects – unless high block Autonomic effects: - Vasodilatation @ T12 & up - Bradycardia @ T4 & up Epidural Anaesthesia Alone, or with GA, or as CSE. Cervical (rare), thoracic, lumbar, caudal Usually catheter placement (except caudal) High volumes LA +/- adjuvants. “Band” phenomenon. Autonomic effects similar to spinal, but slower onset Considerations in regional blockade Consent/communication IV access Adjuvant sedation/analgesia Time involved Failed block/backup plan Management of side effects/reactions Part VI: Sub-Specialty Anaesthesia INCLUDES: 1. Paediatrics 2. Obstetrics 3. Cardiothoracic 4. ENT/Head & neck 5. Neurosurgery Subspecialty Anaesthetics A: Paediatric “They’re not just small adults” . . . But . . . “Nor are they all just big neonates, either” Case Study IV Paediatric Hypospadias Repair History 4 year old boy (obviously!) Grade III hypospadias & chordee For EUA/repair Background: Mild asthma & ADHD Issues Preop assessment & stabilisation Premedication Induction & IV insertion Prolonged surgery Postoperative analgesia Postoperative IV & IUDC Adult-Paediatric Differences Psychosocial CNS Respiratory Airway Other Cardiovascular Renal/fluids Gastrointestinal Hepatic/metabolic Endocrine Haematological Immunological Musculoskeletal Integument The Psychosocial Dimension There are (almost) always two patients – child and parent(s). If you don’t keep the parents happy, or at least reassured, the child won’t be either – no matter how good the anaesthetic. Children don’t understand that you are there to help – only that you are a stranger. Children hate needles. Parents hate their children having needles. Even without this, cannulation can be difficult. Anything that ameliorates this is good: such as premedication, EMLA to cannula sites & inhalational inductions. Parental presence at induction can be a good idea – as long as the parent is going to cope. If in doubt, a generous premed & a goodbye outside may be a better option. Anatomical Differences 1 Body proportions Head larger Limbs smaller Increased surface area to volume ratio CNS differences Brain & spinal cord relatively larger Anatomical Differences 2: Airway Head larger Nares (relatively) larger Larynx higher C3 in neonate -> C6 in adult Epiglottis longer (& softer) Cricoid ring narrowest part of airway Paediatric Respiratory Physiology Chest wall mechanics & tracheobronchial tree “floppier”. Tidal volume/dead space same as adults in mls/kg Respiratory rate & minute volume higher FRC similar to adult in mls/kg, but vO2 higher, so desaturate more quickly when apnoeic. Control of respiration immature till ~ 15/12 post conceptual age – up till then vulnerable to apnoeas – especially post GA &/or narcotics. Paediatric CVS Physiology Refresher Fetal circulation/Postnatal transition -predelivery: systemic & pulmonary circulations in parallel, with oxygenation via placenta & high pressure/low flow on (R) side. -Transition at birth to systemic & pulmonary circulations in series with fall in PVR & closure of shunts. Haemodynamics Neonates & infants have fixed stroke volumes: CO dependant on HR – i.e. bradycardia = hypotension & shock. Autonomic control Different in neonates & children – response to hypoxia is bradycardia (“Diving reflex”) rather than tachycardia. Blood & body fluids Blood volume 80-90 mls/kg (adult ~ 70) Birth Hb 180-200 g/L (adult 120-160) Falls to ~ 110 @ 6/12 then rises. Fetal haemoglobin (HbF) Different chains Lower p50 (Hb-O2 curve shifted left) 75% of Hb at birth minimal @ 6/12. Body water 75-80% in neonate (adult 65%) ECF compartment larger than ICF (crossover @ ~ 4/12) Paediatric Thermodynamics Infants at higher risk of hypothermia Higher surface area to volume ratio Remember the four modes of heat loss: 1. 2. 3. 4. Conduction Convection Radiation Evaporation All four occur more when the surface area to volume ratio is higher Heat production & regulation Controlled in hypothalamus Balances heat loss & heat production Heat production Shivering – poorly developed in neonate/infant Metabolic thermogenesis (brown fat) Thermoneutral environment; Point of minimum O2 consumtion e.g. for unclothed term baby is ~ 33°C Subspecialty Anaesthetics B: Obstetrics Remember, once again you have two patients – but this time they are physically connected Case Study V Caesarian Section History 38 yr old lady, P0G1 Booked LSCS IVF pregnancy Moderate PIH/pre-ecclampsia History of back pain Wants to be awake for delivery Needle phobic Issues Preop consultation Investigations Premedication Choice of anaesthetic technique Choice of IV fluids Backup anaesthetic plan Postoperative monitoring Analgesia plan Principles Pregnancy is a normal, but vulnerable condition. The prregnant patient is different Delivery is hazardous Operative intervention may be required Labour & delivery can be agonisingly painful Anaesthesia inevitably has (at least some) foetal effects/implications. Differences in Pregnancy Psychosocial CNS Respiratory Airway Other Cardiovascular Renal/fluids Gastrointestinal Hepatic/metabolic Endocrine Haematological Immunological Musculoskeletal Integument Drugs & the Placenta General rule: If it crosses the blood brain barrier, it crosses the placenta! Placental transfer: Narcotics/Sedatives/GA agents - HIGH Muscle relaxants -Essentially nil Local anaesthetics – Significant (in freebase form) . . . but peak maternal plasma levels usually post delivery Scenarios Analgesia for labour Anaesthesia for operative delivery Emergency Semiurgent Planned Anaesthesia for post partum complications Neonatal resuscitation Analgesic options Inhalational – N2O as Entonox (50:50 N20/O2) or via blender (up to 70% N2O – Caution!) Narcotics IM/SC prn – pethidine favoured by midwives Infusions – not often used PCA – remifentanil drug of choice. Epidural – usually initial bolus then either: (a) Infusion [&/or] (b) bolus top-ups [or] (c) PCEA Other regional/local blocks – e.g. pudendal block for second stage. Anaesthetic Options for Caesarean Regional Spinal vs Epidural Spinal quicker – unless epidural already in situ & only needing top-up. Most mothers want to be awake. Beware the failed or patchy block. General Technique of choice for emergency LSCS Fastest Better in hypovolaemia Riskier for mother on raw figures, but: GA population includes failed regionals & most emergency cases. So are we comparing apples to oranges? No difference (surprisingly) in foetal outcomes between GA & RA Subspecialty Anaesthetics C/D: Cardiothoracic & ENT What do these surgical disciplines have in common? Remember the basic rules: 1. 2. 3. Air goes in & out Blood goes round & round Variations on this are a BAD THING . . . BUT (you knew there had to be a “but” somewhere, didn’t you) . . . ENT, Thoracic, & Cardiac anaesthesia all require some flexibility of these rules! Anaesthetic Factors in ENT/Oral Surgery: the A to E A. Airway - shared with surgeon . . . And they’re not good sharers sometimes! B. Bleeding – even a little in the airway is a BAD THING C. Children – make up a large proportion of patients D. E. Disruptions – see Airway! Extubation strategies – deep versus awake: deep prevents coughing but leaves patient without airway protection; light ensures airway protection but patient coughing may exacerbate likelihood of bleeding. (No easy answer to this – has to be case by case basis) Airway Management Options in ENT/Oral Surgery None (!) Venturi ventilation Nasal tubes RAE tubes MLT tubes Laryngeal masks (yes!) Subglottic airway i.e tracheostomy Anaesthetic Factors in Thoracic Surgery Open thorax – mandates IPPV +/- PEEP Pre existing lung disease Lung isolation requirements Intraoperative hypoxia (lung isolation by definition creates a major shunt) Postoperative issues Respiratory support Analgesia Lung separation techniques: Endobronchial intubation (but this time not inadvertent!) Double lumen ET tubes Bronchial blockers Other (generally bodgie) methods Anaesthetic Factors in Cardiac Surgery Cardiopulmonary bypass Cardiopulmonary bypass! Cardiopulmonary bypass!! (Scary, scary, scary stuff) Cardiopulmonary bypass (“CPB”) for dummies Pump plus oxygenator (“Heart lung machine”) Cardioplegia (High K+ solution to cause cardiac standstill) Hypothermia (Enables prolonged ischaemic times) Problems with CPB Non-pulsatile flow – can cause paradoxical circulatory responses Hypothermia/pH issues – What is the right pH in hypothermia to maintain acid base status? Red cell trauma – from pump rollers impellers, & (especially “bubble” type) oxygenators Cardiac restarting/Weaning from bypass Post CPB syndrome – confusion & cognitive impairment, sometimes long-term or permanent. Other Anaesthetic Factors in Cardiac Surgery Pre-existing cardiac disease – well, obviously! Co-morbidities - high incidence CVD, PVD, diabetes, renal impairment, etc. Concurrent medications – likely to be multiple Monitoring – In patient on CPB: there is no ECG, pulse (oximetry), conventional BP, or expired CO2 there to monitor. Can monitor MAP generated by bypass, ABGs, & BIS/entorpy Subspecialty Anaesthetics E: Neurosurgical It’s not rocket science . . . . . . but it is brain surgery Special considerations in neurosurgical anaesthesia: Airway – secure, as access to it intraoperatively may be impossible. Breathing - may need to manipulate CO2 to control intracranial pressure/volume. Circulation - maintain appropriate BP for desired cerebral perfusion pressure Disability & Exposure - special positioning may be required – e.g. sitting or prone, all of which carry particular risks. Part VII: Emergencies, Complications & Problems. Anaesthetic Emergencies Anaesthesia for emergencies Emergencies from (or during) anaesthesia A: Emergency Anaesthesia Obstetrics Trauma Gen. Surgical Vascular Neuro-surgical/-radiological Cardio-thoracic Threatened airway Considerations in Emergency Anaesthesia First: How much of an emergency is it, really? Then: Airway assessment Cardio-respiratory status Full stomach/fasting status Pre-existing medical conditions Medications/allergies Assessment may itself be difficult because of haste, patient compromise, etc. Anaesthetic management Assessment Management plan/scheduling Stabilisation & preparation (as much as the urgency of the presenting problem permits) Pain management Then (& only then) commencement of anaesthesia Emergency Anaesthesia: Maintenance Includes ongoing resuscitation & Rx Monitoring: More not less Postanaesthetic management plan? “LITTLE SHOP OF HORRORS” Selected excerpts from my trauma casebook Trauma scenes are an everyday sight: When racing a train to a level crossing, coming first equal is not a good idea! Airway Management I “Seasonal Goodwill” 28 year old male 3 days prior to Christmas Hit in face . . . with a frozen turkey (?!!) Le Fort III and mandibular #s Anaesthetic Management Topical airway anaesthesia with nebulised lignocaine – (then) Attempted Fibreoptic assisted awake oral intubation – failed due blood in airway & restless patient Plan B: RSI with head up position till induction then Trendelenberg till airway secured Lesson: In a crisis - do what you do best and you are comfortable with. Airway Management II “Young & Silly” 19 yr old female Unrestrained backseat passenger in MVA Hx of EtOH +++ GCS 9, HR 120, BP 90/60, distended abdo . . . . . . Priorities? Anaesthetic management Hi-flo O2 by mask, 2x large bore IV access. Fluid bolus, then rapid sequence intubation. To OT for laparotomy/splenectomy. Midazolam/ketamine/suxamethonium In line Cx spine stabilisation Fentanyl/N20/relaxant Circulatory support: Fluids/blood to MAP of 90 Then CT scan – NAD. Lesson: “Head injury + hypotension + hypoxia = Death”. i.e. Secure the airway but oxygenate the brain too! Airway Management III “There are old motorcyclists and there are bold motorcyclists . . . but are there any old and bold motorcyclists?” 56 yr old male motorcyclist Morbid obesity (approx 155kgs) Fractured ribs/pulmonary contusions Borderline hypoxia (SaO2 90-91% on high flow O2 via NRBM) Suspected Cx/Tx spine #s Do you think that this just might be a difficult intubation? Anaesthetic management Topicalisation of airway Awake fibreoptic nasal intubation Surgical insistence on supine posture due potential spinal #s. Extremely technically difficult & patient hypoxic throughout procedure. Improved after intubation & IPPV/PEEP. Lesson: Although satisfactory result, could very well have been a failed intubation due to failure to insist on optimal conditions for airway management. Airway Management IV “And Judas went and hanged himself” 18 yr old male; Hx of depressive illness Found hanging Cardiac output always present GCS 3, pupils fixed & dilated, Spontaneous respirations, trismus Neck swollen, but no palpable subcutaneous emphysema. Anaesthetic Management Inhalational anaesthesia O2/sevoflurane Laryngeal mask placed Bronchoscopy via LMA: No evidence of laryngeal/tracheal fracture. Then relaxant, LMA replaced with ETT. Lesson: Beware the potential airway disruption - the one time a correctly placed endotracheal tube can result in fatal loss of the airway. Respiratory Management I “Guns don’t kill people” (. . . it’s the bullets fired out of them that do that, sometimes). 16 yr old male, accidental GSW to chest. (7.62mm NATO [.308”] calibre – high velocity rifle) Entry & exit wounds (R) chest. (R) haemopneumothorax. Haemodynamically unstable. Anaesthetic Management High flow O2/large-bore IV x2/chest drain. Rapid sequence induction Narcotic, low dose thiopentone/suxamethonium. (L) double lumen tube placed Checked clinically, confirmed w/bronchoscope. Other options: Univent tube; bronchial blocker. Lesson: Must have a plan for rapid placement and checking of lung separation device; and strategies for oxygenation with one lung ventilation: e.g. upper lung CPAP, or intermittent inflations. Upper lung CPAP device on a double lumen ET tube Respiratory Management II “Just another holiday weekend” 9 yr old girl, MVA with associated fatality GCS 7, initial haemodynamics & SaO2 OK Rapid sequence induction – sBP fell to 50mmHg Abdo distension noted Fluid challenge 20mls/kg crystalloid – improved BP but SaO2 fell to 90% Where to from here? Anaesthetic Management PEEP 5 then 10cm – improved SaO2 but BP fell again. Further volume expansion with colloid & blood 30° head up tilt once BP adequate, to: Reduce ICP rise from PEEP Improve ventilation/perfusion matching To OT for laparotomy: Oversewing liver lacerations & mesenteric tear. Lesson: Beware the occult lung injury: contusion, haemo- or pneumothorax . . . they all get worse. Circulatory management “Off with his head!” 23 yr old male, partial beheading with machete Severed (R) neck muscles, carotid & subclavian arteries, probable phrenic/vagal/accessory nerves HR 140, peripherally shut down, BP 65 systolic Conscious, semi-orientated, distressed. Decreased R chest movement, SaO2 90% Brought straight into theatre (2 mins warning). Anaesthetic Management Continued direct haemostatic pressure on wound. IV access & arterial line (L) arm. Rapid sequence induction: (ketamine/suxamethonium) Anaesthetic maintenance with ketamine/fentanyl Volume support with crystalloid/blood: to systolic BP of 65mmHg only. Until surgical haemostasis obtained Lesson: Resuscitation to normotension may not be indicated – or possible Circulatory management: Principles Good (large) IV access vital Peripheral: exchange/cutdown Central: femoral/jugular Consider controlled hypotension until haemostasis Exceptions to this: Neurotrauma Elderly/hypertensive Pregnancy “Appropriate BP theorem” Early arterial line & IABP where indicated Warm all fluids Early use of blood Monitor what you do: Arterial gasses Haematocrit Platelets/coagulation (+clinical consultation) Other problems: Hypothermia 34 year old man “Accidental” rectal insertion of vibrator Perforated sigmoid colon Faecal soiling & peritonitis/sepsis/MOF Prolonged laparotomy Significant hypothermia Hypothermia in Trauma Common problem Increases morbidity & mortality Decreases coagulation & injury response May be therapeutic in isolated neurotrauma Be aware of risks Practice passive heat conservation Active warming: Surface IV fluids Gas humidification Other problems: Coexisting disease “In the line of duty” 29 yr old man, bartender Gunshot wound to stomach during armed holdup Obese, smoker, moderate to heavy EtOH. Conscious, distressed ++++ HR 160, BP 180/120 Anaesthetic Management Analgesia titrated against pain, hypertension & tachycardia. To OT for urgent laparotomy. Intraoperative arrhythmias & arterial desaturation. No evidence ballistic damage to/near diaphragm Post op diagnosed with extensive anterior AMI. Surgical recovery but ongoing poor LV function. Would earlier analgesia have prevented this? Lesson: (a) Beware of occult disease even in the young. (b) Pain does matter. Recreational drugs “High on cocaine – in both senses” 38 yr old woman IVDU, formerly heroin, now IV cocaine On naltrexone Sex industry worker, Hep B/C +ve 3 story fall while under influence of cocaine 100% subluxation/# T12-L1 Complete neurological deficit at T10 Severe neuropathic pain Difficult IV access The geriatric trauma patient “Somebody’s grandma” 86 yr old woman, Fractured NOF Hypertensive on Rx (enalapril/diltiazem) Fall secondary to ?TIA? Ex smoker, mild to moderate CAL Exercise tolerance limited by arthritis For Austin Moore hemiarthroplasty Anaesthetic Management Potential problems: Attempted spinal Respiratory complications with GA Hypertension/tachycardia with airway manipulation Hypotension +/- cerebral ischaemia with regional Technically difficult due calcification of spaces Abandoned after several failures to locate space Converted to GA: - uneventful. CVA 2/52 post op – died 1/52 later. Lessons: - Sometimes there is no “right” anaesthetic - Just some may be less wrong than others The Pregnant Patient “Your next two patients are . . . “ 38 year old female P2G1 - 31/40 pregnant MVA with #’d femur For femoral nailing. B: Anaesthetic Emergencies & Complications “BIG ONES” Arrest Anaphylaxis Failure to intubate Ventilator disconnect Laryngospasm/NPPO Aspiration Nerve damage “Little ones” Agitation/delerium Sore throat PONV Pain Urinary retention Atalectasis Cognitive dysfunction Post Operative Nausea & Vomiting (PONV) “The Big Little Problem” Still affects up to 30% of patients. Major subjective concern – studies suggest most patients prefer pain to N&V. Most common cause of prolonged recovery stay, & delayed discharge in daystay patients Multifactorial: Patient factors: ♀ > ♂; Non smoker > smoker. Surgical: High incidence in eye, ENT, & gynaecological laparoscopic surgery. Anaesthetic: Narcotics, volatile & N2O all potentially emetic. (Propofol usually not) Treatment approach to PONV Prevention is better than cure General Identify at risk patient Anaesthetic history Identify & ameliorate precipitant if possible e.g. narcotics General supportive Rx: IV hydration, narcotic sparing, multimodal analgesia Consider TIVA Antiemetic agents: HT3 blockers - e.g. ondansetron. Pre-emptive or reactively. Dexamethasone – mode of action unknown. Most effective premptively. Dopamine antagonists - e.g. droperidol. Good for narcotic related N&V Others: - Anticholinergics - Antihistamines/phenothiazines - Prokinetics – metoclopramide Anaesthetic Risk In Perspective Risk of anaesthetic death (due to the administration of the anaesthetic) < 1:50,000 No paediatric anaesthetic deaths in Australia in the last reported quinquennium. Typical healthy elective surgical patient probably at more risk of death or serious injury from car trip to/from hospital The figures are good but may lead to: Overconfidence amongst anaesthetists Complacency by surgeons & under-appreciation of risk of coexisting disease factors (which do kill patients). Anaesthesia & sedation services becoming a target for cost cutting measures by politicians/managers with consequent erosion of safety margins. The Eternal Triangle (In all health services, not just anaesthetics) QUALITY QUANTITY Pick any two! ECONOMY (And if one of these is economy, are you sure it’s not a false economy?!) The Bottom Line Safe anaesthesia may not prevent the patient dying of the disease. It will however help prevent them dying of the treatment. Think as a potential surgeon: Isn’t this what you would want for your patient? Think as a health consumer: Isn’t this what you would want for yourself or your family? The End If you have any questions about the course material, or about anaesthesia as a potential career choice, feel free to contact me: docblair@optusnet.com.au