mechanical ventilation weaning from mechanical ventilation

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Mechanical Ventilation Weaning from Mechanical Ventilation Kathia Ortiz-Cantillo, MD

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Mechanical Ventilation

Weaning from Mechanical Ventilation

Kathia Ortiz-Cantillo, MD

Mechanical VentilationWeaning

• When is a patient ready to be disconnected from the ventilator?

• 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.

Weaning

• How often will the patient need to be re-intubated?

• Accepted rate: 5% - 15%

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

Mechanical VentilationSudden Airway Pressure

• Tension pneumothorax

• ETT/tubing obstruction• Mucous plugging - common

• Acute bronchospasm

• Mainstem migration of ETT