mechanical ventilation weaning from mechanical ventilation
TRANSCRIPT
• Numerous trials performed to develop criteria for success weaning, however, not useful to predict when to begin the weaning.
• Physicians must rely on clinical judgment.• Reversal of initial process that led to respiratory
failure• Daily screening may reduce the duration of MV
and ICU cost
Mechanical Ventilationfactors that should be corrected before weaning
• CNS; Absence of cough, gag, level of consciousness
• CVS; Shock, arrhythmias
• Renal; Correction of acid-base/electrolyte disorders
• Hematologic; Anemia
• Infections;• Nutrition; Poor nutritional status, low phosphorus,
excessive nutrition.
Mechanical VentilationWeaning Parameters
• Respiratory Muscle Strength:• NIF; maximum inspiratory pressure:
• PImax generated by a patient from FRC approximately 20 sec after occluding the inspiratory circuit.
• Index of Rapid Shallow Breathing:• RR/TV. Inspiratory muscle weakness leads to rapid
shallow breathing
• Paradoxical Breathing:• Chest and abdomen move outward on inspiration.
• Intercostal muscle fatigue, diaphragmatic fatigue.
Mechanical VentilationWeaning Parameters
• Respiratory Muscle Strength• Vital Capacity VC >15mL/kg body weight
• The maximum amount of gas that can be inhaled from residual volume or exhaled from total lung capacity
• Requires patient cooperation
Mechanical VentilationWeaning Parameters
• Respiratory Muscle Demand• Minute Ventilation VE;
• the amount of air that must be moved in or out of the lungs over 1 min to maintain a given PaCO2. <10L/min
• VE will be determined by CO2 production
• Increased on critical care illness, high fever, over feeding, excess carbohydrate load, Increase death space.
• RR;• Muscle fatigue, patient resorts shallow breathing >35
Mechanical VentilationWeaning Parameters
• Respiratory Muscle Demand• Maximum Voluntary Ventilation; MVV >2 times
the VE• Requires a motivated and cooperative patient• The maximum amount of air that can be inhaled or
exhaled over 1 min.
• Respiratory Compliance >33ml/cmH2O• Work must be performed by inspiratory muscles to
overcome the elastic properties of both the lungs and chest wall.
Mechanical VentilationWeaning Parameters
• Respiratory Gas Exchange
• Significant hypoxemia constitutes a relative contraindication.
• A PaO2 <60mmHG with and FIO2>.040.• Arterial to Inspired O2 ratio (PaO2/FIO2)
• >200
Mechanical VentilationWeaning Parameters
• Respiratory Rate < 30/min
• Spontaneous Vt > 4 ml/kg
• Inspiratory Pressure > - 30 cm H2O
• Breathing Index (f/Vt) < 105
• PEEP < 8 cmH2O
• PaO2/FIO2 > 200
• FIO2 < .50
Mechanical VentilationMethods of weaning
• No one or method of weaning has been definitely found to be superior:• Initial Trial of Spontaneous Ventilation
• T-piece trial
• Spontaneous trial on ventilator (CPAP = 0)
• Gradual Weaning• SIMV
• Pressure Support Ventilation (PSV)
• SIMV + PSV
• Extubation + noninvasive ventilation
WeaningPressure Support Ventilation (PSV)
• Fixed pressure during inspiration
• Patient initiated and terminated
• More comfortable• Depth & length of breath controlled by patient
• Counteract work/resistance of ETT & ventilator circuit
SIMV Protocol
• Switch to SIMV from assist mode or decrease RR
• Begin with RR 8/min decrease SIMV rate by two breaths per hour unless clinical deterioration
• if assume to fail, increase SIMV rate to previous level, until stable
• if stable at least 1 hour of rate 0/ min extubate• in patient without respiratory disorders,
decrease rate with half an hour interval, 2 hr extubate
WeaningACCP/AARC
A. Stable/resolved pulmonary process
B. PEEP < 8; FIO2 < .50
C. Cardiovascular stability
D. Spontaneous breathing trialA. T-piece or PSV (~ 5 cm H2O)
B. Up to 2 hours every 24 hrs.
Failed to Wean
• Associated with intrinsic lung disease
• Associated with prolonged critical illness
• Increased risk in patient with longer duration of mechanical ventilation
• Increased risk of complications, mortality
WeaningFailure Criteria
• Rapid shallow breathing• RR > 35/min or > 10/min increase
• Tachycardia • > 120 bpm or > 20 bpm increase
• BP change > 20%
• Mental status change
WeaningFailure Criteria
• Clinical signs of distress:• Increased dyspnea• Diaphoresis• Accessory muscle use• Paradoxical breathing
• Hypoxemia and/or hypercapnea
•Hypoxia (PaO2 < 60, SpO2 <90%) 11 (31%)
•Hypercarbia (PaCO2 > 50 mmHg) 9 (25%)
•Pulse rate > 120/min 17 (47%)
•SBP > 180 or < 90 mmHg 2 (6%)
•Respiratory rate > 30/min 33 (92%)
•Clinical respiratory distress 27 (75%)
Fatigue Criteria
Evidence-based medicine
• Patients receiving MV who fail an SBT should have the cause determined.
• Once causes are corrected, and if the patient still meets the criteria of DS, subsequent SBTs should be performed every 24 hours.
WeaningFailure to Wean
• Auto-PEEP • Cardiac disease
• CHF, ischemic heart disease
• Nutrition and electrolyte imbalance• Inadequate rest following previous trial
• May need up to 24 hours
• Muscle weakness• Paralysis or polyneuropathy of critical illness
Mechanical VentilationComplications
• Barotrauma• 4% - 15%• Highest in ARDS
• Reductions in cardiac output• Impaired right ventricular preload
Mechanical VentilationComplications
• Renal effects
• GI bleeding• 20% - 30% without prophylaxis
• DVT• 40% - 80% without prophylaxis
• Ventilator induced pneumonia