1. Mechanical Ventilation

2. Epidemiology 28 day international study –361 ICUs in 20 countries –All consecutive adult patients who received MV for > 12 hours –33% Patient admitted to those ICUs received mechanical ventilation Mean age 59 M > F (61 v. 39%) Esteban et al. JAMA 2002

3. Indication for mechanical ventilation –Acute respiratory failure 68% Post-op (21%) Pneumonia 14% CHF 10% Sepsis 9% Trauma 8% ARDS 4.5% Aspiration 2.5% Cardiac arrest 1.9% –Acute on chronuic respiratory failure COPD 10% Asthma 1.5% Chronic respiratory disease (non_COPD) 1.8% –Coma 16.7% –Neuromuscular disease 1.8%

4. Copyright restrictions may apply. Esteban, A. et al. JAMA 2002;287:345-355. Ventilator Modes Used Each Day During the Course of Mechanical Ventilation

5. Duration of mechanical ventilation –Overall 5.9days –COPD pts 5.1 days –ARDS pts 8.8 days ICU LOS: 11.2 days Hospital LOS: 22.5 days

6. Mortality: –ICU mortality 30.7% –Hospital mortlaity 39.2%

7. Copyright restrictions may apply. Esteban, A. et al. JAMA 2002;287:345-355. Kaplan-Meier Curves of the Probability of Survival Over Time of Mechanical Ventilation

8. Mechanical ventilation Physiology: –Positive pressure ventilation versus naturanl negative pressure ventilation Effects: –Heterogeneous ventilation Preferential ventilation of the non-dependent regions –Increased physiologic dead space –Improvement of physiologic shunt causes by atelectasis and/or alveolar filling –Rapid disuse atrophy of the diaphragm –Impairment of mucociliary clearance

9. Cardiovascular effects: –Decreased venous return Exacerbated by: –Auto-PEEP –Applied PEEP –Intravascular volume depletion –Cardiac tamponnade –Increased right ventricular afterload: Compression of the pulmonary vascular bed  Increased PVR –May decrease left ventricular afterload Lung exansion decreased extramural pressure

10. Mechanical ventilation Benefits –Improves gas exchange by improved V/Q matching predominantly be decreasing shunt –Decreased work of breathing

12. Mechanical ventilation: Complications Barotrauma –Incidence ~3% –To Avoid: Keep plateau pressure < 35 cm VILI –Over stretch –Atelectotrauma Auto-PEEP Asyncrhony

15. Mechanical ventilation: Modes Choices: –Mandatory v. non-mandatory Mandatory –Volume v. pressure limited ventilation –Mandatory rate –Modes: »SIMV »Assist Control »PCV »Hybrid Modes: PRVC, SIMV/PRVC Non-mandatory or assisted breaths –PSV

16. Variables: some default values Trigger sensitivity: -1 to -3 cm Tidal volume: 6-8mg/kg/IBW Rate: 10 to 14 PEEP: 5 cm H2O Flow rate: 60 L/min I to E ratio

17. Volume limited v. pressure limited Volume limited –Physician sets: Tidal volume Rate –Guaranteed constant tidal volume –Guaranteed minute ventilation –High peak pressures Pressure limited –Physician sets: Peak airway pressure Inspiratory time –Tidal volume and minute ventilation depends entirely on patient factors: compliance and airway resistance –Associated with lower peak airway pressure –Associated with more homogenous gas distribution No difference in mortality, oxygenation, or work of breathing

18. P = Vt/C R + Vt/T i * R + PEEPtotal Where CR = compliance of the respiratory system, Ti = inspiratory time and V T /Ti = Flow, R R = resistance of the respiratory system and PEEP total = the alveolar pressure at the end of expiration = external PEEP + auto (or intrinsic) PEEP, if any. Auto PEEP = PEEP total – P extrinsic (PEEP dialed in the ventilator) adds to the inspiratory pressure one needs to generate a tidal breath.

19. Peak pressure Plateau pressure –Surrogate for peak alveolar distending pressure Peak – Plateau –Resistive pressure Mean airway pressure –Pressure applied acorss the lung and chest wall averaged throughout the ventilary cycle

20. Patient factors: –Airway resistance –Compliance of the respiratory system Chest wall recoil Lung recoil

21. Assist-Control Set variables –Tidal volume –Flow rate or Ti –PEEP FiO2 –Mandatory rate Spontaneous breaths –Additional cycles can be triggered; they are identical to the mandatory breath

22. SIMV Set variables –Targeted volume –Flow rate –Manatory frequency –PEEP –FiO2 –PS augmentation for spontaneous breaths Spontaneous breaths –Unrestricted and aided by the selected level of pressure support

23. PCV Set variables: –Peak pressure –Inspiratory time –Frequency of mandatory breaths Spontaneous breaths –PCV (AC): same as mandatory breaths –PCV/SIMV: unsupported or pressure supported

24. Tidal volume during PCV Changes in mechanics –Increased airway resistance –Decreased respiratory system compliance Increased auto-PEEP Decreased inspiratory time

25. Waveforms

28. Ventilator change Flow (lpm) Pressure (cm H2O) Volume (mL)

29. Waveforms 40 30 20 10 0 Airway pressure Time Pause

30. Waveforms Pause

31. What changes on the ventilator should you make for hypoxemia? What changes for hypercapnia and respiratory acidosis? Hypotension on the ventilator?