Basic Practice of Anesthesiology Hany El-Zahaby, MD Preoperative Evaluation 1. History -Current problem -Other known problems -Medical history (allergies, drug intolerance, present therapy, tobacco and alcohol intake) -Previous anesthetics, surgeries, deliveries -Family history -Review of organ systems -Last oral intake Preoperative Evaluation 2. Physical Examination -Vital signs -Airway (Thyromental distance, Malampati sign) -Heart -Lungs -Extremities -Neurological examination Preoperative Evaluation 3. Routine Laboratory evaluation (healthy asymptomatic) Hematocrite: All menstruating women, age >60 y, anticipated significant blood loss S. glucose, creatinine: age >60 y ECG: age >40 y Chest radiograph: age >60 y Pregnancy test: fertile women American Society of Anesthesiology Risk Classification ASA Class Description 1 Normal, healthy (0.06-0.08%) 2 Mild systemic disease (0.27-0.4%) 3 Severe systemic D, not incapacitating (1.8-4.3%) 4 Severe systemic D that is a constant threat to life (7.8-23%) 5 Moribund, not expected to live 24h (9.4-51%) 6 Care for organ donation The Anesthetic Plan Premedication Type of anesthesia General (airway, induction, maintenance, relaxant) Regional (technique, agents) Intraoperative management Monitoring, positioning, fluids, MABL, special techniques Postoperative management Pain control, ICU (ventilation, monitoring) Preoperative Evaluation Informed consent Gives the patient explanation of the options for anesthesia and its realistic risks (general, regional, local, topical, intravenous sedation) Regardless of the technique chosen, consent must always be taken for GA if other techniques prove inadequate e.g. LA The Anesthetist-Patient relationship Is The Patient Scared? Surgery (cancer, physical disfigurement, pain, death) Anesthesia (loss of control, not waking up, waking up during surgery, nausea, confusion, paralysis, headache) Preoperative Evaluation 1-Unhurried, organized interview 2-Calm reassurance and expression of interest in the patient’s well being 3-Informing about: NPO (no solids after m.n., clear fluids up to 2-3 h unless GER) Time of surgery Premedication and other daily medications Tasks to occur on the day of surgery Postoperative recovery or ICU Premedication Benzodiazepines: Diazepam (5-10 mg PO 1-2 hours before surgery), never IM (pain, unpredictable) Lorazepam (1-2 mg PO), intense prolonged amnesia and sedation Midazolam (1-3 mg IV or IM) at the receiving area, 0.5 mg/kg PO for pediatrics Premedication Narcotics: painful fractures, planned extensive awake invasive monitoring devices Morphine 5-10 mg IM 60-90 min before surgery Anticholinergics (rare): Not Routine Glycopyrrolate 0.2-0.4 mg IV to reduce oral secretions (fibreoptic intubation) Premedication Prophylaxis for pulmonary aspiration: Pregnant, hiatal hernia, GER, difficult airway, ileus, obesity, CNS depression H2 blockers (ranitidine, 150-300 mg PO before bedtime and early morning) Nonparticulate antacids (sodium citrate 30-60 ml) Metoclopramide (10 mg IV 1h before surgery to enhance gastric emptying) Premedication Goals: Reduce anxiety, pain during vascular cannulation and regional blocks, facilitate smooth induction Reduce the dose or withhold in elderly, debilitated, upper airway obstruction or trauma, central sleep apnea, neurologically obtunded, severe pulmonary or obstructive valvular disease Monitoring Standard monitoring for GA: ECG, non-invasive BP, respiratory rate, oxygen saturation, end-tidal carbon dioxide, inspired oxygen concentration Standard monitoring for regional anesthesia: ECG, non-invasive BP, respiratory rate, oxygen saturation IV access IV access: (14-16 G if rapid fluid or blood transfusion or continuous drug infusions, better under local anesthetic infiltration) Components of GA Loss of consciousness Loss of reflexes (Movement to pain) Analgesia Amnesia Relaxation Induction of Anesthesia The environment in OR should be warm with minimal noise and all attention focused on the patient Supine position with extremities in neutral position and head on firm pillow raised to ‘’sniff’’ position Induction of Anesthesia Techniques: 1- IV induction preceded by oxygen via face mask until loss of consciousness using thiopentone or propofol 2- Inhalational anesthetics either by low concentration with incremental increase every 3-4 breaths or by a single vital capacity breath technique using sevoflurane or halothane Intravenous Induction Thiopentone Propofol 3-5 mg/kg 2-2.5 mg/kg --- IVI 6-10 mg/kg/h --- Painful injection Slower onset, slower recovery Rapid induction, rapid clearheaded recovery Hypotension ++ Hypotension +++ Depress respiration Depress respiration Contraindicated in porphyria Less N,V Airway Management Face-mask with: Oro-pharyngeal airway Naso-pharyngeal airway LMA ETT with a muscle relaxant (depolarizing as succinyl choline or non-depolarizing as tracrium, cistracrium, rocuronium) Muscle Relaxants Depolarizing MR (succinylcholine) mimics the action of acetylcholine i.e. causes depolarization of the motor end plate and muscle membrane but for longer time than Ach. Used for rapid-sequence induction in patients with full stomach Non-depolarizing MR produce reversible competition with Ach at the motor end plate that produce relaxation for longer duration Succinylcholine Dose:1mg/kg produce relaxation in 1 min Side effects: Muscle pains, ganglionic stimulation, increase S. K+ level by 0.5-1 mEq/L, increase intraoccular pressure, increased intragastric pressure, increase intracranial pressure, prolonged block due to decrease or inhibition or atypical plasma cholinesterase, malignant hyperthermia Non-Depolarizing MR Atracurium: 0.5 mg/kg, Hofmann elimination Cisatracurium (Nimbex): 0.15 mg/kg, Hofmann elemination, less histamine release Vecuronium: 0.1 mg/kg, hepatic metabolism Rocuronium (Esmeron): 0.5 mg/kg, hepatic metabolism (short duration) TOF Twitch Height After Succinyl Choline Twitch Height After Non-Depolarizing Clinical Assessment of the Blockade Evoked response Clinical correlate 95% -- single twitch Good intubating condition TOF response =1 Surgical relaxation without inhalation anesth. TOF response =3 TOF ratio > 0.75 Surgical relaxation with inhalation anesth. Possible extubation TOF ratio = 1 Normal VC Laryngoscopy and Intubation Profound sympathetic responses (hypertension, tachycardia) can be attenuated by hypnotics, inhalation anesthetics, opioids, lidocaine, or beta blockers ETT Size Premature: 2.5-3 Full term: 3 6 M -1 y:3.5 2 Y: 4.5 Over 2y: 4+(age/4)► 4 +(6/4) ►5.5 Length (at mouth cm): 10+(age/4) ► 10 +(6/4) ►11.5cm Positioning Movement of supine anesthetized patient into another position may cause hypotension due to lack of intact compensatory hemodynamic reflexes. Patient’s head and limbs should be protected and padded. Hyperextension or over-rotation of the neck and limbs must be avoided. Maintenance Depth of anesthesia (surgical anesthesia) +Muscle relaxation Signs of inadequate depth of anesthesia: Somatic responses (movement, coughing, changes of respiratory pattern) Autonomic responses (tachycardia, hypertension, mydriasis, sweating, tearing) Stages of General Anesthesia Stage I Amnesia From induction to loss of consciousness, pain perception is maintained Stage II Delirium Exaggerated responses to noxious stimulus, dilated pupils, divergent gaze, irregular breathing Stage III Surgical anesthesia Central gaze, constricted pupils, regular respiration, no somatic or autonomic responses Stage IV Overdosage Depressed respiration, dilated fixed pupils, marked hypotension Maintenance If spontaneous breathing is needed, minimal opioids with nitrous oxide and inhalation anesthetic If muscle relaxation is needed, nitrous oxide-opioidrelaxant with minimal inhalation anesthetic and controlled ventilation (Balanced anesthesia) TIVA: Continuous infusion of propofol-opioid + muscle relaxant (nothing through inhalation) Inhalation Anesthetics Blood-gas partition coefficient is inversely related to the rate of induction MAC: minimal alveolar concentration that prevent movement in response to a skin incision in 50% of patients Inhalation Anesthetics Blood/gas PC MAC Nitrous oxide 0.47 104 Halothane 2.3 0.74 Isoflurane 1.4 1.15 Sevoflurane 0.69 2.05 Desflurane 0.42 6.0 Ventilation Spontaneous/assisted: All inhalation anesthetics depress respiration and moderately increase PaCO2 Can be affected by positioning, peritoneal insufflation, open chest, surgical packing and opioids Ventilation Controlled Ventilation: Initial setting with TV=10-15 ml/kg, RR=10-12/min, notice the PIP, If>30, decrease TV and increase RR A sudden drop in PIP → circuit leak A sudden increase in PIP → kink, endo-bronchial intubation, peritoneal insufflation IV Fluids Maintenance: first 10kg→ 4ml/kg/h Second 10 kg → 2ml/kg/h After 20 kg → 1 ml/kg/h Third-space loss: Tissue edema and evaporation, varies from 5-10 ml/kg/h Blood loss: Replaced in 1:3 with isotonic crystalloid, or 1:1 with blood IV Fluids (60 kg fit adult fasting for 6h) 1st h 2nd h 3rd h Fasting 300 150 150 Maintenance (100ml/h) 100 100 100 3rd space 5x60=300 5x60=300 5x60=300 Blood loss -- -- -- Total 700 550 550 Estimated Allowable Blood Loss 70 kg, Hct 35 EABL = EBV X (Hctstart-Hctallowable) Hctstart EABL = 4900 X (35 – 27)= 980ml 35 Estimating Volume of Blood to be Transfused 70 kg, with present Hct of 23 Volume=EBV X (Hctdesired - Hctpresent) Hct transfused blood Volume=4900 X (30-23) =490ml 70 Emergence from GA Goals: awake, responsive with full muscle strength so he can maintain patent airway, cannot aspirate and can be assessed neurologically Technique: withdraw anesthetics near the end of surgery, reverse muscle relaxation with neostigmine (0.03-0.06 mg/kg) and atropine (0.2-0.4 mg/kg) Emergence from GA Environment: Warm and calm Positioning: Supine, tonsillectomy if full stomach Mask ventilation: 100% oxygen, avoid stimulation of the airway during stage II Emergence from GA Extubation: 1-Awake (desirable) with fully recovered protective reflexes, follow simple verbal commands, breathe spontaneously with good oxygenation and ventilation (lidocaine 1mg/kg IV) 2- Deep extubation (during stage III) reduce risk of laryngospasm and bronchospasm (in asthmatic) avoid coughing ( eye surgery, hernia repair) Emergence from GA Agitation: due to hypoxia, hypercarbia, airway obstruction, full bladder, pain or sevoflurane and desflurane anesthesia. Treated by treating the cause, fentanyl 25μg IV or morphine 2mg IV increments Delayed awakening: Continue ventilatory support and airway protection and reverse the etiology Transport Stable patient can be transferred without oxygen or monitor to PACU Unstable patient should be transferred with oxygen, monitors, tools for re-intubation to PACU or ICU Anesthetist should give concise but thorough summary to PACU or ICU staff Acute postoperative pain management Optimal pain control is an integral component of accelerated recovery Although opioids are the most effective, acute postoperative pain management is now based on multimodal analgesia and opioid sparing Acute postoperative pain management Psychological Preparation Assessing Pain (0-10 Verbal Analogue Scale is now the fifth vital sign to be recorded in the record) Preemptive Analgesia (peripheral injury ►central sensitization ►increase pain sensitivity Acute postoperative pain management Treatment Options: 1- NSADs: Oral alone ► mild to moderate pain, begin preop., gastric irritation, coagulopathy, mask fever Oral with opioids ►reduce opioid intake Parentral ►keorolac 30 mg then 15-30 mg/6h, expensive, can replace opioids Paracetamol (Perfalgan), 1 gm/6h Acute postoperative pain management 2- Opioids: PO (chronic pain) IM ( morphine 0.1mg/kg, pethidine 1mg/kg) painful, unreliable IV-bolus (morphine 2mg every 5 min, max 10-15mg) IVI ( morphine 10- 20 μg/kg/h) Monitor the respiratory rate Acute postoperative pain management 3- PCA: Provide analgesic doses immediately based on patient needs using microcomputer-controlled infusion pumps which avoids extreme swings in plasma levels. Special order sheet is needed with detailed pump setting (demand dose, start dose, delay time, basal rate) and monitoring (pain level, sedation level, verbal response) Acute postoperative pain management 4- Epidural Analgesia Abdominal , vascular & L.L. surgery Contraindications: patient refusal, coagulopathy, LMWH, bacteremia, local infection 0.1% Bupivacaine + 1-2 µg/ml Fentanyl ►5-10 ml/h ▼Bupivacaine if hypotension or motor block ▼Fentanyl if pruritis Complications: Inadequate analgesia, PDPH, epidural hematoma or abcess Acute postoperative pain management 5- Neuraxial Morphine (preservative-free) Epidural: 1-4 mg Intrathecal: 0.1-0.4 mg (Respiratory depression) 6- Intraoperative Neural Blockade (esp. children) Local Anesthetics Ester/ Amide Aromatic Ring Amine Local Anesthetics Esters: procaine, chloroprocaine, tetracaine (metabolised by plasma esterase, allergen) Amides: lidocaine, bupivacaine, ropivacaine (liver metabolism) Local Anesthetics Potency ►lipophilicity Duration ► protein binding Onset ► pKa (pH at which 50% are uncharged ions ► diffuse to nerve membrane) Local Anesthetics Sequence of block: Sympathetic ►pain & temp. ►proprioception ►touch & pressure ►motor Additives: Epinephrine 1:200,000►prolong duration, ▼systemic toxicity, ▲intensity of block, ▼surgical bleeding Sodium bicarbonate: 1 meq:10ml lidocaine, 0.1meq:10 ml bupivacaine (avoid ppt)►fasten onset LA: Systemic Toxicity CNS Light-headedness, tinnitus, metallic taste, visual disturbance, cicumoral numbness, muscle twitching, seizures, loss of consciousness Treatment: stop injection, oxygen, midazolam 1-2 mg, thiopentone 50-200 mg CVS ▼contract., ▼ conduct., VD ►collapse (esp. Bupivacaine) Treatment: oxygen, volume, vasopressors ►ACLS Local Anesthetics: Spinal Anesthesia Spinal Needle: 25G pencil point with 19G introducer Position: Sitting or lateral Level: L3-4, L4-5 Approach: Midline or paramedian Drugs: Bupivacaine (Heavy) 0.5% 2-3 mls Local Anesthetics: Spinal Anesthesia Complications: Hypotension►0.5-1L of LR before the block, ephedrine 5-10 mg boluses Bloody tap► if does not clear rapidly, withdraw & reinsert Nausea & vomiting ►treat hypotension Apnea (total spinal) ►support ventilation PDPH: bed rest, IV fluids, analgesics, caffeine 30mg, epidural blood patch Local Anesthetics: Epidural Anesthesia Epidural Needle: 17G Tuohy needle Position: Sitting or lateral Level: L3-4, L4-5 Approach: Midline or paramedian Drugs: Bupivacaine 0.125- 0.25% 15-20 ml Techniques: Loss of resistance Hanging drop method Test dose: 3 ml lidocaine 1% with epinephrine 1:200,000 Local Anesthetics: Epidural Anesthesia Drugs: 1.5 ml/segment Decrease dose 50% in old age Decrease dose 30% in pregnancy Epinephrine increase duration Opioids (fentanyl 50-100 µ) improve the quality Sodium bicarbonate speeds the onset Local Anesthetics: Epidural Anesthesia Complications: Dural puncture 1% ► Convert to spinal ► Reinsert one space above Inability to thread the epidural catheter (too lateral, partial bevel insertion) Insertion into a vein (withdraw) Catheter break off (inform patient & leave it) Local Anesthetics: Combined Spinal-Epidural Anesthesia Combine advantages and avoid disadvantages of both techniques Rapid onset, solid sacral block, less volume Longer time, more control on level Local Anesthetics: Caudal Epidural Through the sacrococcygeal membrane Can reach high level in children: 1 ml/kg Bupivacaine 0.2-0.25% with 1;200,000 Epinephrine reach T6-8 level THANK YOU