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Weaning from Mechanical Ventilation

Weaning from Mechanical Ventilation. Mazen Kherallah, MD, FCCP Consultant Intensivist King Faisal Specialist Hospital & Research Center Assistant Professor University of North Dakota, USA www.icumedicus.com mkherallah@msn.com. Objectives.

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Weaning from Mechanical Ventilation

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  1. Weaning from Mechanical Ventilation Mazen Kherallah, MD, FCCP Consultant Intensivist King Faisal Specialist Hospital & Research Center Assistant Professor University of North Dakota, USA www.icumedicus.com mkherallah@msn.com

  2. Objectives • Discuss physiologic variables that are used to indicate readiness to wean from mechanical ventilation • Contrast the approaches used to wean patients from mechanical ventilation • Discuss the use of protocols to wean patients from ventilatory support • Discuss the criteria used to indicate readiness for extubation • Describe the most common reasons why patients fail to wean from mechanical ventilation

  3. Introduction • 75% of mechanically ventilated patients are easy to be weaned off the ventilator with simple process • 10-15% of patients require a use of a weaning protocol over a 24-72 hours • 5-10% require a gradual weaning over longer time • 1% of patients become chronically dependent on MV

  4. Readiness To Wean • Improvement of respiratory failure • Absence of major organ system failure • Appropriate level of oxygenation • Adequate ventilatory status • Intact airway protective mechanism (needed for extubation)

  5. Oxygenation Status • PaO2≥ 60 mm Hg • FiO2 ≤ 0.40 • PEEP ≤ 5 cm H2O

  6. Ventilation Status • Intact ventilatory drive: ability to control their own level of ventilation • Respiratory rate < 30 • Minute ventilation of < 12 L to maintain PaCO2 in normal range • VD/VT < 60% • Functional respiratory muscles

  7. Intact Airway Protective Mechanism • Appropriate level of consciousness • Cooperation • Intact cough reflex • Intact gag reflex • Functional respiratory muscles with ability to support a strong and effective cough

  8. Function of Other Organ Systems • Optimized cardiovascular function • Arrhythmias • Fluid overload • Myocardial contractility • Body temperature • 1◦ degree increases CO2 production and O2 consumption by 5% • Normal electrolytes • Potassium, magnesium, phosphate and calcium • Adequate nutritional status • Under- or over-feeding • Optimized renal, Acid-base, liver and GI functions

  9. Predictors of Weaning Outcome

  10. Maximal Inspiratory Pressure • Pmax: Excellent negative predictive value if less than –20 (in one study 100% failure to wean at this value) An acceptable Pmax however has a poor positive predictive value (40% failure to wean in this study with a Pmax more than –20)

  11. Frequency/Volume Ratio • Index of rapid and shallow breathing RR/Vt • Single study results: • RR/Vt>105 95% wean attempts unsuccessful • RR/Vt<105 80% successful • One of the most predictive bedside parameters.

  12. Measurements Performed Either While Patient Was Receiving Ventilatory Support or During a BriefPeriod of Spontaneous Breathing That Have Been Shown to Have Statistically Significant LRs To Predict theOutcome of a Ventilator Discontinuation Effort in More Than One Study*

  13. Refertences 2 Tobin MJ, Alex CG. Discontinuation of mechanical ventilation. In: Tobin MJ, ed. Principles and practice of mechanical ventilation. New York, NY: McGraw-Hill, 1994; 1177–1206 4 Cook D, Meade M, Guyatt G, et al. Evidence report on criteria for weaning from mechanical ventilation. Rockville, MD: Agency for Health Care Policy and Research, 199910 Lopata M, Onal E. Mass loading, sleep apnea, and the pathogenesis of obesity hypoventilation. Am Rev Respir Dis 1982; 126:640–645 16 Hansen-Flaschen JH, Cowen J, Raps EC, et al. Neuromuscular blockade in the intensive care unit: more than we bargained for. Am Rev Respir Dis 1993; 147:234–236 18 Bellemare F, Grassino A. Effect of pressure and timing of contraction on human diaphragm fatigue. J Appl Physiol 1982; 53:1190–1195 20 Roussos C, Macklem PT. The respiratory muscles. N Engl J Med 1982; 307:786–797 24 Le Bourdelles G, Viires N, Boezkowski J, et al. Effects of mechanical ventilation on diaphragmatic contractile properties in rats. Am J Respir Crit Care Med 1994; 149:1539–1544

  14. Approaches To Weaning • Spontaneous breathing trials • Pressure support ventilation (PSV) • SIMV • New weaning modes

  15. Do Not Wean To Exhaustion

  16. Spontaneous Breathing Trials • SBT to assess extubation readiness • T-piece or CPAP 5 cm H2O • 30-120 minutes trials • If tolerated, patient can be extubated • SBT as a weaning method • Increasing length of SBT trials • Periods of rest between trials and at night

  17. Frequency of Tolerating an SBT in Selected Patients and Rate of Permanent Ventilator DiscontinuationFollowing a Successful SBT* *Values given as No. (%). Pts patients. †30-min SBT. ‡120-min SBT.

  18. Criteria Used in Several Large Trials To Define Tolerance of an SBT* *HR heart rate; Spo2 hemoglobin oxygen saturation. See Table 4 for abbreviations not used in the text.

  19. Pressure Support • Gradual reduction in the level of PSV • PSV that prevents activation of accessory muscles • Gradula decrease on regular basis (hours or days) to minimum level of 5-8 cm H2O • Once the patient is capable of maintaining the target ventilatory pattern and gas exchange at this level, MV is discontinued

  20. SIMV • Gradual decrease in mandatory breaths • It may be applied with PSV • Has the worst weaning outcomes in clinical trials • Its use is not recommended

  21. New Modes • Volume support • Automode • MMV • ATC

  22. Protocols • Developed by multidisciplinary team • Implemented by respiratory therapists and nurses to make clinical decisions • Results in shorter weaning times and shorter length of mechanical ventilation than physician-directed weaning

  23. Rest 24 hrs PaO2/FiO2 ≥ 200 mm Hg PEEP ≤ 5 cm H2O Intact airway reflexes No need for continuous infusions of vasopressors or inotrops > 100 RSBI <100 Stable Support Strategy Assisted/PSV Daily SBT 24 hours 30-120 min RR > 35/min Spo2 < 90% HR > 140/min Sustained 20% increase in HR SBP > 180 mm Hg, DBP > 90 mm Hg Anxiety Diaphoresis Extubation No Yes Mechanical Ventilation Low level CPAP (5 cm H2O), Low levels of pressure support (5 to 7 cm H2O) “T-piece” breathing

  24. Failure to Wean • Weaning to exhaustion • Auto-PEEP • Excessive work of breathing • Poor nutritional status • Overfeeding • Left heart failure • Decreased magnesium and phosphate leves • Infection/fever • Major organ failure • Technical limitation

  25. Weaning to Exhaustion • RR > 35/min • Spo2 < 90% • HR > 140/min • Sustained 20% increase in HR • SBP > 180 mm Hg, DBP > 90 mm Hg • Anxiety • Diaphoresis

  26. Work-of-Breathing • Pressure= Volume/compliance+ flow X resistance • High airway resistance • Low compliance • Aerosolized bronchodilators, bronchial hygiene and normalized fluid balance assist in normalizing compliance, resistance and work-of-breathing

  27. Auto-PEEP • Increases the pressure gradient needed to inspire • Use of CPAP is needed to balance alveolar pressure with the ventilator circuit pressure • Start at 5 cm H2O, adjust to decrease patient stress • Inspiratory changes in esophageal pressure can be used to titrate CPAP

  28. Gradient 0 -5 0 -5

  29. Gradient 0 -5 Auto PEEP +10 -15

  30. Gradient PEEP 10 5 Auto PEEP +10 -5

  31. Left Heart Failure • Increased metabolic demands that are associated with the transition from mechanical ventilation to spontaneous breathing • Increases in venous return as that is associated with the negative pressure ventilation and the contracting diaphragm which results into an increase in PCWP and pulmonary edema • Appropriate management of cardiovascular status is necessary before weaning will be successful

  32. Nutritional/Electrolytes • Imbalance of electrolytes causes muscular weakness • Nutritional support improves outcome • Overfeeding elevates CO2 production due to excessive carbohydrate ingestion

  33. Infection/Fever/Organ Failure • Organ failure precipitate weaning failure • Infection and fever increase O2 consumption and CO2 production resulting in an increase ventilatory drive

  34. Points to Remember • The primary prerequisite for weaning is reversal of the indication of mechanical ventilation • Adequate gas exchange should be present with minimal oxygenation and ventilatory support before weaning is attempted • The function of all organ systems should be optimized, electrolytes should be normal, and nutrition should be adequate before weaning is attempted • The most successful predictor of weaning is RSBI < 100 • Maximum inspiratory pressure is the best predictor of weaning failure • Ventilatory discontinuation should be done if patient tolerates SBT for 30-120 minutes • Patients who fail an SBT should receive a stable, non-fatiguing, comfortable form of ventilatory support • Use of liberation and weaning protocol facilitates the process and decreases the ventilator length of stay

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