Weaning from Mechanical VentilationWeaning from Mechanical VentilationMazen Kherallah, MD, FCCPMazen Kherallah, MD, FCCP

Consultant IntensivistConsultant IntensivistKing Faisal Specialist Hospital & Research King Faisal Specialist Hospital & Research

CenterCenterAssistant ProfessorAssistant Professor

University of North Dakota, USAUniversity of North Dakota, USAwww.icumedicus.comwww.icumedicus.commkherallah@msn.commkherallah@msn.com

ObjectivesObjectives

Discuss physiologic variables that are used to Discuss physiologic variables that are used to indicate readiness to wean from mechanical indicate readiness to wean from mechanical ventilationventilationContrast the approaches used to wean patients Contrast the approaches used to wean patients from mechanical ventilationfrom mechanical ventilationDiscuss the use of protocols to wean patients Discuss the use of protocols to wean patients from ventilatory supportfrom ventilatory supportDiscuss the criteria used to indicate readiness Discuss the criteria used to indicate readiness for extubationfor extubationDescribe the most common reasons why Describe the most common reasons why patients fail to wean from mechanical ventilationpatients fail to wean from mechanical ventilation

IntroductionIntroduction

75% of mechanically ventilated patients 75% of mechanically ventilated patients are easy to be weaned off the ventilator are easy to be weaned off the ventilator with simple processwith simple process10-15% of patients require a use of a 10-15% of patients require a use of a weaning protocol over a 24-72 hoursweaning protocol over a 24-72 hours5-10% require a gradual weaning over 5-10% require a gradual weaning over longer timelonger time1% of patients become chronically 1% of patients become chronically dependent on MVdependent on MV

Readiness To WeanReadiness To Wean

Improvement of respiratory failureImprovement of respiratory failure

Absence of major organ system failureAbsence of major organ system failure

Appropriate level of oxygenationAppropriate level of oxygenation

Adequate ventilatory statusAdequate ventilatory status

Intact airway protective mechanism Intact airway protective mechanism (needed for extubation)(needed for extubation)

Oxygenation StatusOxygenation Status

PaPaO2O2 ≥ 60 mm Hg ≥ 60 mm Hg

FiFiO2O2 ≤ 0.40 ≤ 0.40

PEEP ≤ 5 cm HPEEP ≤ 5 cm H22OO

Ventilation StatusVentilation Status

Intact ventilatory drive: ability to control Intact ventilatory drive: ability to control their own level of ventilationtheir own level of ventilation

Respiratory rate < 30Respiratory rate < 30

Minute ventilation of < 12 L to maintain Minute ventilation of < 12 L to maintain PaPaCO2CO2 in normal range in normal range

VVDD/V/VTT < 60% < 60%

Functional respiratory musclesFunctional respiratory muscles

Intact Airway Protective MechanismIntact Airway Protective Mechanism

Appropriate level of consciousnessAppropriate level of consciousness

CooperationCooperation

Intact cough reflexIntact cough reflex

Intact gag reflexIntact gag reflex

Functional respiratory muscles with ability Functional respiratory muscles with ability to support a strong and effective coughto support a strong and effective cough

Function of Other Organ SystemsFunction of Other Organ Systems

Optimized cardiovascular functionOptimized cardiovascular function– ArrhythmiasArrhythmias– Fluid overloadFluid overload– Myocardial contractilityMyocardial contractility

Body temperatureBody temperature– 11◦ ◦ degree increases COdegree increases CO22 production and O production and O22 consumption by 5% consumption by 5%

Normal electrolytesNormal electrolytes– Potassium, magnesium, phosphate and calciumPotassium, magnesium, phosphate and calcium

Adequate nutritional statusAdequate nutritional status– Under- or over-feedingUnder- or over-feeding

Optimized renal, Acid-base, liver and GI functions Optimized renal, Acid-base, liver and GI functions

Predictors of Weaning OutcomePredictors of Weaning Outcome

PredictorPredictor ValueValue

Evaluation of ventilatory drive:Evaluation of ventilatory drive: P 0.1P 0.1 < 6 cm H2O< 6 cm H2O

Ventilatory muscle capability:Ventilatory muscle capability: Vital capacityVital capacity Maximum inspiratory pressureMaximum inspiratory pressure

> 10 mL/kg> 10 mL/kg < -30 cm H< -30 cm H22OO

Ventilatory performanceVentilatory performance Minute ventilationMinute ventilation Maximum voluntary ventilationMaximum voluntary ventilation Rapid shallow breathing indexRapid shallow breathing index Respiratory rateRespiratory rate

< 10 L/min< 10 L/min > 3 times V> 3 times VEE

< 100< 100 < 30 /min< 30 /min

Maximal Inspiratory PressureMaximal Inspiratory Pressure

Pmax: Excellent negative predictive value if less Pmax: Excellent negative predictive value if less than –20 (in one study 100% failure to wean at than –20 (in one study 100% failure to wean at this value)this value)

An acceptable Pmax however has a poor An acceptable Pmax however has a poor positive predictive value (40% failure to wean in positive predictive value (40% failure to wean in this study with a Pmax more than –20)this study with a Pmax more than –20)

Frequency/Volume RatioFrequency/Volume Ratio

Index of rapid and shallow breathing RR/VtIndex of rapid and shallow breathing RR/Vt

Single study results:Single study results:– RR/Vt>105 95% wean attempts unsuccessfulRR/Vt>105 95% wean attempts unsuccessful– RR/Vt<105 80% successfulRR/Vt<105 80% successful

One of the most predictive bedside parameters.One of the most predictive bedside parameters.

Measurements Performed Either While Patient Was Receiving Ventilatory Support or During a Brief

Period of Spontaneous Breathing That Have Been Shown to Have Statistically Significant LRs To Predict the

Outcome of a Ventilator Discontinuation Effort in More Than One Study*

RefertencesRefertences

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

Approaches To WeaningApproaches To Weaning

Spontaneous breathing trialsSpontaneous breathing trials

Pressure support ventilation (PSV)Pressure support ventilation (PSV)

SIMVSIMV

New weaning modesNew weaning modes

Do Not Wean To ExhaustionDo Not Wean To Exhaustion

Spontaneous Breathing TrialsSpontaneous Breathing Trials

SBT to assess extubation readinessSBT to assess extubation readiness– T-piece or CPAP 5 cm H2OT-piece or CPAP 5 cm H2O– 30-120 minutes trials30-120 minutes trials– If tolerated, patient can be extubatedIf tolerated, patient can be extubated

SBT as a weaning methodSBT as a weaning method– Increasing length of SBT trialsIncreasing length of SBT trials– Periods of rest between trials and at nightPeriods of rest between trials and at night

Frequency of Tolerating an SBT in Selected Patients and Rate of Permanent Ventilator Discontinuation

Following a Successful SBT*

*Values given as No. (%). Pts patients.†30-min SBT.‡120-min SBT.

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.

Pressure SupportPressure Support

Gradual reduction in the level of PSVGradual reduction in the level of PSV

PSV that prevents activation of accessory PSV that prevents activation of accessory musclesmuscles

Gradula decrease on regular basis (hours Gradula decrease on regular basis (hours or days) to minimum level of 5-8 cm H2Oor days) to minimum level of 5-8 cm H2O

Once the patient is capable of maintaining Once the patient is capable of maintaining the target ventilatory pattern and gas the target ventilatory pattern and gas exchange at this level, MV is discontinuedexchange at this level, MV is discontinued

SIMVSIMV

Gradual decrease in mandatory breathsGradual decrease in mandatory breaths

It may be applied with PSVIt may be applied with PSV

Has the worst weaning outcomes in Has the worst weaning outcomes in clinical trialsclinical trials

Its use is not recommendedIts use is not recommended

New ModesNew Modes

Volume supportVolume support

AutomodeAutomode

MMVMMV

ATCATC

ProtocolsProtocols

Developed by multidisciplinary teamDeveloped by multidisciplinary team

Implemented by respiratory therapists and Implemented by respiratory therapists and nurses to make clinical decisionsnurses to make clinical decisions

Results in shorter weaning times and Results in shorter weaning times and shorter length of mechanical ventilation shorter length of mechanical ventilation than physician-directed weaningthan physician-directed weaning

Daily SBT

<100

Mechanical Ventilation

RR > 35/minSpo2 < 90%HR > 140/minSustained 20% increase in HRSBP > 180 mm Hg, DBP > 90 mm HgAnxietyDiaphoresis

30-120 min

PaO2/FiO2 ≥ 200 mm HgPEEP ≤ 5 cm H2OIntact airway reflexesNo need for continuous infusions of vasopressors or inotrops

RSBI

ExtubationNo

> 100

Rest 24 hrs

Yes

Stable Support StrategyAssisted/PSV

24 hours

Low level CPAP (5 cm H2O), Low levels of pressure support (5 to 7 cm H2O)“T-piece” breathing

Failure to WeanFailure to Wean

Weaning to exhaustionWeaning to exhaustionAuto-PEEPAuto-PEEPExcessive work of breathingExcessive work of breathingPoor nutritional statusPoor nutritional statusOverfeedingOverfeedingLeft heart failureLeft heart failureDecreased magnesium and phosphate levesDecreased magnesium and phosphate levesInfection/feverInfection/feverMajor organ failureMajor organ failureTechnical limitationTechnical limitation

Weaning to ExhaustionWeaning 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

Work-of-BreathingWork-of-Breathing

Pressure= Volume/compliance+ flow X resistancePressure= Volume/compliance+ flow X resistance

High airway resistanceHigh airway resistance

Low complianceLow compliance

Aerosolized bronchodilators, bronchial Aerosolized bronchodilators, bronchial hygiene and normalized fluid balance hygiene and normalized fluid balance assist in normalizing compliance, assist in normalizing compliance, resistance and work-of-breathingresistance and work-of-breathing

Auto-PEEPAuto-PEEP

Increases the pressure gradient needed to Increases the pressure gradient needed to inspireinspireUse of CPAP is needed to balance Use of CPAP is needed to balance alveolar pressure with the ventilator circuit alveolar pressure with the ventilator circuit pressurepressureStart at 5 cm H2O, adjust to decrease Start at 5 cm H2O, adjust to decrease patient stresspatient stressInspiratory changes in esophageal Inspiratory changes in esophageal pressure can be used to titrate CPAPpressure can be used to titrate CPAP

0

-5

Gradient

0

-5

0

Auto PEEP +10-5

Gradient

-15

PEEP10

Auto PEEP +105

Gradient

-5

Left Heart FailureLeft Heart Failure

Increased metabolic demands that are Increased metabolic demands that are associated with the transition from mechanical associated with the transition from mechanical ventilation to spontaneous breathingventilation to spontaneous breathingIncreases in venous return as that is associated Increases in venous return as that is associated with the negative pressure ventilation and the with the negative pressure ventilation and the contracting diaphragm which results into an contracting diaphragm which results into an increase in PCWP and pulmonary edemaincrease in PCWP and pulmonary edemaAppropriate management of cardiovascular Appropriate management of cardiovascular status is necessary before weaning will be status is necessary before weaning will be successfulsuccessful

Nutritional/ElectrolytesNutritional/Electrolytes

Imbalance of electrolytes causes muscular Imbalance of electrolytes causes muscular weaknessweakness

Nutritional support improves outcomeNutritional support improves outcome

Overfeeding elevates CO2 production due Overfeeding elevates CO2 production due to excessive carbohydrate ingestionto excessive carbohydrate ingestion

Infection/Fever/Organ FailureInfection/Fever/Organ Failure

Organ failure precipitate weaning failureOrgan failure precipitate weaning failure

Infection and fever increase O2 Infection and fever increase O2 consumption and CO2 production resulting consumption and CO2 production resulting in an increase ventilatory drive in an increase ventilatory drive

Points to RememberPoints to Remember

The primary prerequisite for weaning is reversal of the indication of The primary prerequisite for weaning is reversal of the indication of mechanical ventilationmechanical ventilationAdequate gas exchange should be present with minimal Adequate gas exchange should be present with minimal oxygenation and ventilatory support before weaning is attemptedoxygenation and ventilatory support before weaning is attemptedThe function of all organ systems should be optimized, electrolytes The function of all organ systems should be optimized, electrolytes should be normal, and nutrition should be adequate before weaning should be normal, and nutrition should be adequate before weaning is attemptedis attemptedThe most successful predictor of weaning is RSBI < 100The most successful predictor of weaning is RSBI < 100Maximum inspiratory pressure is the best predictor of weaning Maximum inspiratory pressure is the best predictor of weaning failurefailureVentilatory discontinuation should be done if patient tolerates SBT Ventilatory discontinuation should be done if patient tolerates SBT for 30-120 minutesfor 30-120 minutesPatients who fail an SBT should receive a stable, non-fatiguing, Patients who fail an SBT should receive a stable, non-fatiguing, comfortable form of ventilatory supportcomfortable form of ventilatory supportUse of liberation and weaning protocol facilitates the process and Use of liberation and weaning protocol facilitates the process and decreases the ventilator length of staydecreases the ventilator length of stay