A 63 year old male smoker undergoes routine coronary artery bypass surgery. He remains ventilated on 10 cmH2O PEEP and FiO2 60% the following morning with a PaO2 of 63 mmHg. Outline your diagnostic and therapeutic approach
3 - 4 key features
• Hypoxaemia post-cardiac surgery is common, most commonly due to basal atelectasis, but need to consider other possibilities such as pneumothorax, haemothorax, acute lung injury, airflow obstruction, pneumonia. Intra-cardiac shunt and PE unlikely unless specific history.
• Diagnosis by history (?smoker, chronic lung disease), examination (asymmetry of movement, air entry), search for posterior basal bronchial breath sounds (common) and chest radiograph (basal atelectasis may not be obvious on CXR – but can be on clinical exam), CT scan shows much more atelectasis but rarely justified
• Drain pneumothorax/haemothorax, bronchodilators for airflow obstruction, may need antibiotics for infection, consider ‘marginal’ extubation – often well tolerated in CABG patients but this patient probably too hypoxaemic. Basal atelectasis need time and try recruitment with specific manoeuvres and or higher level PEEP if tolerated (likely to depress BP so need careful supervision)
Causes of hypoxia in the post-bypass patient are explored in a brief summary hidden among the "Required Reading" notes for the topic of cardiothoracic ICU. They are separated into four major groups:
A systematic approach is called for:
Ng, Calvin SH, et al. "Pulmonary dysfunction after cardiac surgery." CHEST Journal121.4 (2002): 1269-1277.
Tenling, Arne, et al. "Atelectasis and gas exchange after cardiac surgery."Anesthesiology 89.2 (1998): 371-378.