Mechanical Ventilation
Lecture Outline
 Pulmonary Terminology.
 Mechanical Ventilation:
 Indications. Types. Mechanics.
 Modes of Mechanical Ventilation.
 Mechanical Ventilator Alarms.
 Weaning.
 Reading Assignment
 Brunner 11th ed., chapter 25
 Mechanical Ventilation: Indications.
 Classification of ventilators.
 Complications with mechanical ventilation.
 Weaning parameters.
Pulmonary Terminology
Respiratory Rate (f)
 Breaths per minute.
 Patient Normal: 12 – 20 breaths/minute.
 Rates > 30:
 Rates > 40:
 Ventilator Normal: 8 – 12 breaths/minute.
 Ventilator can provide ALL of patient’s breaths, OR the patient may be able to breathe
spontaneously between ventilator breaths.
Tidal Volume (Vt)
 Volume in one breath. POSITIVE PRESSURE
 Volume of gas delivered with each ventilation.
 Normal is 5 – 8 cc/kg (ideal body weight).
**too much can cause volutrauma. It will often be set a higher rate lower volume
Minute Volume / Minute Ventilation (VE)
 Volume of air that is moved through the lungs over 1 minute.
**This regulates CO2 and acid/base
 Vt x Rate (ventilator / patient).
 Normal: 5 – 10 liters. (Never < 5L)
 Increased VE: Hyperventilation.
 Decreased VE: Hypoventilation.
 Example: Vt x Rate (ventilator / patient).
 0.4 L x 8 breaths = 3.2 L/min.
 0.7 L x 12 breaths = 8.4 L/min.
 0.8 L x 24 breaths = 19.2 L/min. – look at ABG you will see alkalosis
Vital Capacity (VC)
 Maximum amount of air exhaled after a maximum inspiration.
 Normal 65 cc/kg (IBW).
  before extubation.
 Diaphragm function.
Fraction of Inspired Oxygen (FiO2)
 Amount of oxygen being delivered (%).
 Usually the FiO2 will be adjusted to keep the SaO2 > 90% OR PaO2 > 60 mm Hg.
 Remember oxygen toxicity!
 Occurs with FiO2 > 50% – 60% for > 24 hours.
Negative Inspiratory Force (NIF)
Negative Inspiratory Pressure (NIP)
 How much negative pressure change can the patient generate with maximum inspiratory effort.
 Normal range:
 -80 cm to -100 cm H2O.
  before extubation.
 Need at least -20 cm to maintain minute ventilation (VE).
Peak Inspiratory Pressure (PIP)
 How much pressure is reached in the lung at the peak of inspiration (after giving set Vt).
 Do not want high pressures.
 Volutrauma in 50+ pressures.
 Stiff lungs = High pressure.
 Very important parameter to measure – because of compliance – if compliance is down pressure
increases-this will put a pt a great risk for pneumothorax
PEEP
 Positive End Expiratory Pressure
 Low PEEP = 1 – 5 cm H2O.
 Moderate PEEP = 5 – 15 cm H2O.
 High PEEP = > 15 cm H2O.
 Optimum PEEP =
 Helps with oxygenation
 Keeps alveoli open
 Minimizes shunting
 Caution at high levels
 AUTOPEEP – a nautrual change in PEEP setting due to the fact that pt is not exhaling as much as they
were before (AIRTRAPPING)
PIP & PEEP
 High levels
- increase volutrauma
- increase chances for pneumothorax
- decrease venous return to heart
- may cause hypotension
- increase auto PEEP
Sensitivity
 Sensitivity function controls the amount of patient effort needed to initiate an inspiration.
 Measured by negative inspiratory effort.
 Usually set at minus (–) 2.
Indications-Types-Mechanics
Indications
 Supporting gas exchange.
 lung volume.
 work of breathing.
 Reverse hypoxemia & resp. acidosis.
 Relieve resp. distress.
 Preventing resp. muscle fatigue.
 Permit sedation & neuromuscular blockade.
 Stabilize chest wall.
 Decrease oxygen consumption.
Types of Ventilators
 Negative Pressure Ventilators:
 Applied externally to the patient.
 Example: Ventilator or iron lung.
 Positive Pressure Ventilators:
 Forces air into the lungs via endotracheal tube or tracheostomy.
 Iron Lung – Polio Patient
Ventilator Mechanics
Trigger.
 Event that begins inspiration.
 Patient-initiated respiratory effort.
 Machine-initiated positive pressure.
Limit
 Limits / maintains airflow during inspiration.
 Flow-Rate (IFR).
 How fast is air pumped into lungs?
 Set Pressure (Pressure Control) (PIP).
 How much pressure is reached at peak of inspiration?
 Volume-limited (Volume control) (VT).
 How much volume of air is given with each breath?
Cycle.
 Event that ends inspiration.
 Volume cycled ventilation.
 Pressure cycled ventilation.
 Pressure support ventilation.
Modes of Mechanical Ventilation
 Assist Control (AC).
 Initial mode of choice!
 Synchronized Intermitted Mandatory Ventilation (SIMV).
 Pressure Support Ventilation (PSV).
 Continuous Positive Airway Pressure (CPAP).
 Bilevel Positive Airway Pressure (BIPAP).
Assist Control (AC)
 Set Vt, RR, FiO2, &/or PEEP.
 Trigger that initiates inspiration can be either ventilator or pt’s respiratory effort.
 If pt initiates breathes faster- receives set Vt, FiO2 & PEEP from the ventilator.
 If pt breathes slower ventilator delivers set Vt, at set rate, FiO2 & PEEP.
 ALL breaths are delivered by ventilator at set Vt, FiO2 & PEEP.
 Synchronized Intermittent Mandatory Ventilation (SIMV)
 Vt, rate, FiO2, PEEP, & sensitivity are preset.
 All breaths taken above the set rate are spontaneous breaths. **
 Trigger may be spontaneous or mandatory
 the ventilator delivers breaths at set Vt, rate, FiO2 &/or PEEP.
Synchronized Intermittent Mandatory Ventilation (SIMV)
 All breaths are synchronized.
 Mandatory breaths – set tidal volume
 Spontaneous breaths – patient tidal volume
SIMV Advantages:
 Strengthens respiratory muscles.
 PSV can be added.
 Lower mean airway pressure.
Disadvantages:
 Increased WOB.
 Not tolerated well by some patients.
Pressure Support Ventilation (PSV)
 No set Vt or rate. (this is a weaning mode)
 Patient’s effort determines RR, IFR, Vt.
 Delivers air to a set pressure early in inspiration.
 Pressure is maintained throughout inspiration.
PSV Advantages:
 Increased patient comfort.
 Decreased muscle fatigue.
 Respiratory conditioning.
 Can be added to SIMV to enhance weaning.
 Decreased WOB/O2 consumption.
Disadvantages:
 DO NOT over sedate.
 Monitor closely.
 Can be difficult for patient.
Continuous Positive Airway Pressure (CPAP)
 Spontaneous breathing mode.
 Positive pressure that is maintained throughout respiratory cycle.
 Usually 5 to 10 cm H2O pressure.
 Patient generates own rate & tidal volume.
 Similar to PEEP.
 Used for intubated & non-intubated patients.
 Used as weaning mode.
 Used for nocturnal ventilation.
 Same as SIMV with PEEP.
 Often used for obstructive sleep apnea.
 CPAP Mode
BiPAP
 Noninvasive, noncontinuous, Bilevel Positive Airway Pressure.
 Provides both inspiratory & expiratory pressure support.
 Weaning.
 Hypoventilation.
 Sleep apnea.
Mechanical Ventilator Alarms & Humidification
Ventilator Alarms
Low pressure alarms. (tube disconnected may be a common cause)
High pressure alarms. (coughing, tube kinked)
 Peak Inspiratory pressure (PIP)
Apnea alarm:
 ALWAYS have AMBU bag at bedside.
 Pressure Alarms
Peak Inspiratory Pressure:
 Decreased compliance.
 Kinked ET tube
 Mucous plug.
 Increased secretions.
 Water in circuit.
 pneumothorax
 MONITOR trends.
Low pressure alarms:
 Cuff leak.
 Dislodged ET tube
 Broken circuit.
 Troubleshooting?
 Remember DOPE
 Dislodged
 Obstructed
 Pneumothorax
 Equipment failure
 Always check the patient, not the monitor!!!
Patient-Ventilator Dysynchrony
 Patient appears to be fighting or “bucking” the ventilator.
 Decreases effectiveness of mechanical ventilation, development of auto-PEEP, psychological distress.
 Adjust ventilator settings to accommodate patient’s spontaneous breathing pattern.
 Sedation or neuromuscular blockade.
 E.g., Diprivan drip.
 Humidification




Why should we humidify & warm air delivered by artificial airways?
What would happen if there was no humidification?
100% humidity at 37 oC.
Prevent water condensation build up – tubing needs to be drained.
Ventilator Complications
 Aspiration:
 Before, during & after intubation.
 ARDS & Pneumonia (VAP):
 Risk Factors:
 Brushing Teeth: Ventilator Patient
 Volutrauma (Barotrauma):
 Mechanical ventilation & PEEP can over distend & rupture alveoli air leakage.
 GI Complications:
 Distention.
 Ileus (Gastroparesis).
 Stress ulcers.
 Cardiac Complications:
 Mechanical ventilation & increased PEEP increased intrathoracic pressure decreased venous return to
right heart decreased preload decreased CO decreased hepatic, renal, CNS (increased ICP) perfusion.
 Anxiety:
 Dependent on machine to breathe & unable to speak.
Nutritional Support
 Why should we feed our ventilated patients?
 Respiratory muscles need energy to work muscle fatigue & decreased tidal volume.
 Body cannibalizes intercostal & diaphragmatic muscles for energy.
 Long-term mechanical ventilation patients need 2000 - 2500 kcal/day.
 Begin by 3rd day of intubation. Malnourished – within 24 hours of intubation.
 Enteral route vs. TPN.
 Prerequisite for weaning!
Weaning
 Gradual withdrawal of mechanical ventilation & reestablishment of spontaneous breathing.
 Begin only after cause for respiratory failure is corrected & patient is stable.
 Factors to Consider:
 Length of time on ventilator.
 Sleep deprivation.
 Nutritional status.
 No sepsis.
 Adequate respiratory muscle function.
Readiness to Wean
 LOC, spontaneous breathing, respiratory rate & pattern.
 Physiologic & hemodynamic stability.
 Adequacy of oxygenation & ventilation.
 Rested with no suppressant drugs.
 Breathing Trials:
 Ø accessory muscle use, retractions, or paradoxical breathing.
 ABG: Ø rising CO2 or falling pH.
 Secretions? Cough?
Weaning Criteria
 PaO2: > 60 – 80 mmHg.
 FiO2: 50%.
 PEEP: 5 cm H2O.
 SaO2: > 90%.
 PaO2:FiO2 ratio: > 150 or 200.
 Vital Capacity: 10 to 15 ml/kg or > 800 cc.
 Negative Inspiratory Pressure (Force) (NIP or NIF): Minus (-)30 cm H2O or less.
 Respiratory Rate (f): > 12 & < 30
 Tidal Volume: > 5 cc/kg.
 Example: Pt weighs 80 kg.
 80 X 5 = 400 cc.
 Minute Ventilation: 5 – 10 L/minute.
 Examples:
 RR 30. VT 900 cc
 RR 8. VT 300 cc
 Ratio of Resp. Rate : Tidal Volume (liters) = Rapid Shallow Breathing Index (RSBI)
 < 100* is predictive of weaning success.
 RSBI = f / Vt
 Examples:
f = 40; Vt = 300. f = 20; Vt = 400. f = 18; Vt = 600.
f = 35; Vt = 250.
Weaning Methods: SIMV
 Place ventilator in SIMV mode & slowly decrease rate until zero (4).
 Obtain ABG 30 minutes afterwards.
 Can increase work of breathing.
 Monitor for signs of respiratory muscle fatigue PSV.
 Benefit:
 Ventilator backup if patient fails to breath.
 Alarms will sound.
Weaning Methods: T-Piece
 Remove patient from the ventilator & have patient breath spontaneously on a T-piece.
 Monitor patient's response & tolerance.
 Duration of T-piece is dependent on MD.
 After a set amount of time, the patient is placed back on ventilator (trials of increasing frequency & duration).
 May add CPAP.
Weaning Methods: PSV
 Augments patient’s spontaneous breathing with positive pressure “boost” during inspiration.
 Gradually decrease level of PSV while maintaining spontaneous tidal vol. (Vt) of 8 – 12 ml/kg & RR < 25
breaths/minute.
 If the patient is able to maintain adequate spontaneous breathing at this level – extubation is considered.
Example: COPD Exacerbation
8/22/05: On Vent.
 Time: 0659
 FiO2: 40%. VT: 700. SIMV: 4. PEEP: 3.
 pH: 7.36
 PCO2: 52.1
 HCO3: 28.6
 PO2: 81.1
 Interpretation:
 Respiratory acidosis. Full compensation.
8/23/05: T-Piece Trial
 Time: 0556
 FiO2: 40%
 pH: 7.28
 PCO2: 66.2
 HCO3: 30.4
 PO2: 107
 SaO2: 97%
 Interpretation:
 Respiratory acidosis. Partial compensation.
 Would you wean this patient at this time?
8/23/05: CPAP
 Time: 0816
 FiO2: 40%
 pH: 7.32
 PCO2: 54.7
 HCO3: 33.3
 PO2: 74.8
 SaO2: 94.8%
 Interpretation:
 Respiratory acidosis. Partial compensation.
 Would you wean this patient at this time?
8/24/05: T-Piece Trial
 Time: 0658
 FiO2: 35%
 pH: 7.35
 PCO2: 47.9
 HCO3: 29.8
 PO2: 126
 Interpretation:
 Respiratory acidosis. Full compensation.
 Would you wean this patient at this time?
 Patient weaned off ventilator & extubated.
 2L NC.