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Program Information. Mechanical Ventilation #2. Alain Broccard, MD John Marini, MD University of Minnesota Regions Hospital St Paul, MN. Objectives. To understand: Pressure Control ventilation Inverse Ratio Bi-Level pressure ventilation Auto PEEP How to measure and correct

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Program Information

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  1. Program Information

  2. Mechanical Ventilation #2 Alain Broccard, MD John Marini, MD University of Minnesota Regions Hospital St Paul, MN

  3. Objectives To understand: Pressure Control ventilation Inverse Ratio Bi-Level pressure ventilation Auto PEEP How to measure and correct Venilator weaning

  4. Pressure Controlled Ventilation Key set variables: Pressure, TI, and frequency PEEP and FIO2 Mandatory breaths Ventilator generates a predetermined pressure for a preset time Spontaneous breaths PCV-AC mode: same as mandatory breaths PCV-SIMV mode: unsupported or PS

  5. Key Parameter to Monitor is VT Change in mechanics  airway resistance: e.g., bronchospasm  respiratory system compliance .e.g, pulmonary edema, pneumothorax AutoPEEP  What Causes a Decreased VT During PCV?

  6. Auto-PEEP (Intrinsic PEEP, PEEPi) -The pressure applied to the alveoli due to trapped volume Marini, Wheeler. Crit Care Med. The Essentials. 1997.

  7. Total PEEP Pressure PEEPi PEEPe Time Suspecting and Measuring AutoPEEP Suspect AutoPEEP if flow at the end of expiration does not return to the zero baseline. End expiratory pause AutoPEEP is commonly measured by performing a pause at the end of expiration. In a passive patient, flow interruption is associated with pressure equilibration through the entire system. In such conditions, proximal airway pressure tracks the mean alveolar pressure caused by dynamic hyperinflation.

  8. Bi-Pap & Airway Pressure Release Characteristics • Allow spontaneous breaths superimposed on a set number of “pressure controlled” ventilator cycles • Reduce peak airway pressures • “Open” circuit / enhanced synchrony between patient effort and machine response • Settings:Pinsp and Pexp (Phigh and Plow)Thigh and Tlow

  9. Inverse Ratio Airway Pressure Release (APRV), and Bi-Level (Bi-PAP)

  10. Unlike PCV, BiPAP Allows Spontaneous Breathing During Both Phases of Machine’s Cycle

  11. Bi-Level Ventilation

  12. Bi-Level VentilationWith Pressure Support

  13. Automatic Tube Compensation The endotracheal tube offers resistance to ventilation both on inspiration and on expiration. A low level of pressure support can help overcome this pressure cost, but its effect varies with flow rate. Automatic tube compensation (ATC) adjusts its pressure output in accordance with flow, theoretically giving an appropriate amount of pressure support as needed as the cycle proceeds and flow demands vary within and between subsequent breaths. Some variants of ATC drop airway pressure in the early portion of expiration to help speed expiration. Supplemental pressure support can be provided to assist in tidal breath delivery.

  14. External and Tracheal Pressures Differ Because of Tube Resistance ATC offsets a fraction of tube resistance

  15. Discontinuation of Mechanical Ventilation To discontinue mechanical ventilation requires: Patient preparation Assessment of readiness For independent breathing For extubation A brief trial of minimally assisted breathing An assessment of probable upper airway patency after extubation Either abrupt or gradual withdrawal of positive pressure, depending on the patient’s readiness

  16. Preparation: Factors Affecting Ventilatory Demand

  17. Other Factors Secretions How frequent is suctioning occuring? Consistancy Base line Chronic COPD CO2 retention

  18. Measures to Enhance the Weaning Process

  19. Extubation Parameters Respiratory Rate <40/min Tidal Volume 5 ml/kg Minute Ventilation < 10L/min Vital Capacity 10 ml/kg PaO2/FiO2 ratio >200 NIF -25cmH2O

  20. Rapid Shallow Breathing Index Resp Rate -------------- Tidal Vol If RSBI > 105: 95% extubations failed If RSIB < 105: 80% extubations successful

  21. Three Methods for Gradually Withdrawing Ventilator Support Although the majority of patients do not require gradual withdrawal of ventilation, those that do tend to do better with graded pressure supported weaning than with abrupt transitions from Assist/Control to CPAP or with SIMV used with only minimal pressure support.

  22. Extubation Criteria Ability to protect upper airway Effective cough Alertness Improving clinical condition Adequate lumen of trachea and larynx “Leak test” during airway pressurization with the cuff deflated

  23. Extubated Add supplemental oxygen Watch for signs of decompensation Avoid over sedation Encourage coughing Incentive spirometer Out of bed

  24. Self Assessment The following case study provide you with the opportunity to review the current and previous modules on mechanical ventilation. Review Skip

  25. MV Case

  26. References and Suggested Readings Hubmayr RD, Abel MD, Rehder K. Physiologic approach to mechanical ventilation. Crit Care Med. 1990;18:103-13. Tobin MJ. Mechanical ventilation. N Engl J Med. 1994;330;1056-61. Marini JJ. Monitoring during mechanical ventilation. Clin Chest Med. 1988;9:73-100. Brochard L. Noninvasive ventilation for acute respiratory failure. JAMA. 2002;288:932-935. Calfee CS, Matthay MA. Recent advances in mechanical ventilation. Am J Med. 2005;118:584-91.

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