Airway - Ventilation

Ventilation

• Avoiding high PIP is important in limiting lung injury from barotraumas.  Keep PIP < 30cm H₂O
• Maintain normocapnia (PaCO2 35-45) and tolerate PaCO2 up to 55
• Maintain oxygenation ie; SaO₂>, 95% (Registrar to be notified if F_iO₂ > 0.5)
• Notify IC Specialist if PEEP >10, SaO₂, 90 on F_iO₂ > 0.5 & PIP >30

Weaning Ventilation

• Routine post cardiac surgical patients are usually weaned and extubated within 2-6 hours.
• In all other post cardiac surgical patients, weaning and extubation should be discussed with the Intensive Care specialist.
• Weaning should be attempted in all patients who meet the criteria, which may be as soon as 1 -2 hours post surgery.
• The Intensive Care Nurse and the Intensive Care Registrar will manage the patient's ventilation, weaning and extubation.  The Nurse will contact the Registrar prior to extubation and will confirm the timing of extubation so the registrar is present to deal with any unexpected complications post extubation.
• Extubation should not be delayed once the patient has met criteria.
• Patients with underlying lung disease should be weaned according to the guidelines, and if they meet criteria, consider extubation to mask CPAP.
• If criteria are met, reintubation following extubation is extremely uncommon.
• If the patient is known to be a difficult intubation, discuss with the Intensive Care specialist prior to extubation.

Wean once:

• Chest closed
• Normothermic (Temp > 36°C)
• Minimal bleeding (<150 mls/hour)
• Awake, obeying commands
• Adequate oxygenation SaO₂>95 on F_iO₂ < 0.5
• Haemodynamically stable, (Cardiac output satisfactory clinically HR, BP, UO & CRT),  or
  if PA catheter or PICCO, CI>2.5 l/min/m²)

 
The need for moderate inotropic support (<5-10mls/hr dopamine/Dobutamine) is not a contraindication to weaning of ventilation if the patient is haemodynamically stable.

1. Uncomplicated:
• Reduce SIMV rate to ½ the initial rate, observe for spontaneous ventilation for 2 minutes, if present change mode from SIMV to CPAP.
• Put on pressure support (PS) 5 cm H₂O
• Observe for 10-20 minutes and extubate provided:
• Adequate oxygenation SaO₂>95 on FiO₂< 0.4
• Adequate spontaneous ventilation RR > 10 and <20, TV > 5mls/kg (lean or ideal body weight)
• Awake and cooperative
• If respiratory depression present, use a low rate of SIMV until more awake
• If low TV or increased respiratory effort on PS, try PS 10-15 cm H₂O.  This should be weaned to 10cm H₂O before extubation.
2. Complications ie; marginal cardiovascular, respiratory or neurological function:
• Use SIMV (volume control) plus pressure support
• Wean rate as tolerated
• If haemodynamically stable, the need for moderate inotropic support is not a contraindication to weaning of ventilation.

Failure to wean

Consider:

• Pulmonary
• Oedema: fluid overload, cardiac dysfunction (see below)
• Atelectasis
• Pleural effusion
• Bronchospasm
• Pneumothorax
• Phrenic nerve injury
• Abdominal distension, obesity
• Cardiac
• Residual left to right shunt
• Low cardiac output
• Pericardial effusion
• Pulmonary hypertension
• Neurological
• Residual narcotic/sedation (especially if renal/hepatic impairment)
• Pain
• Brain injury / CVA
• Residual neuromuscular blockade
• Metabolic
• Electrolyte abnormalities (low Na, K, PO₄)
• Metabolis alkalosis
• Increased metabolic rate (increasing CO₂ production)
• Fever, sepsis, carbohydrate excess

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