Postoperative hypoxia
- Lack of alveolar ventilation
- Hypoventilation (airway obstruction, opiates)
- Bronchospasm
- Pneumothorax
- Arteriovenous shunting (collapse, atelectasis)
- Lack of alveolar perfusion
- Ventilation-perfusion mismatch (pulmonary embolism)
- Impaired cardiac output
- Decreased alveolar diffusion
- Pneumonia
- Pulmonary oedema
Atelectasis
- Hypoxaemia is often seen during the first 48 hours after most major operations
- Due to a reduction in functional residual capacity
- Significant atelectasis is more often seen
- In those with pre-existing lung disease
- With upper rather than lower abdominal incisions
- Obese patients
- Cigarette smokers
- The basic mechanisms leading to atelectasis are:
- Increased volume of bronchial secretions
- Increased viscosity of secretions
- Reduced tidal volume and ability to cough
Clinical features
- Postoperative pyrexia - usually presenting at about 48 hours
- Often accompanied by tachycardia and tachypnoea
- Examination shows reduced air entry, dullness
on percussion and reduced breath sounds
- X-ray shows consolidation and collapse
Treatment
- Intensive chest physiotherapy
- Nebulised bronchodilators
- Antibiotics for associated infection
Pneumonia
- Nosocomial pneumonia occurs in 1% of all patients admitted to hospital
- Occurs in 15-20% of unventilated ITU patients
- Occurs in 40-60% of ventilated ITU patients
- Organisms involved include
- Gram-negative bacteria (Pseudomonas aeruginosa, Enterobacter)
- Staph. aureus
- Anaerobes
- Haemophilus influenzae
- No evidence that prophylactic antibiotics reduce the risk of pneumonia
Aspiration pneumonitis
- Aspiration of gastric contents results in a chemical pneumonitis
- Most commonly seen in apical segments of right lower lobe
- If unrecognised or inadequately treated it can result in a secondary bacterial
infection
- Secondary infection is usually with gram-negative and anaerobic organisms
Treatment
- Tilt table head down and suck out pharynx
- Consider intubation and endotracheal suction
- Prophylactic antibiotics should be given
- No evidence that steroids reduce inflammatory response
Bibliography
Johnson J L, Hirsch C S. Aspiration pneumonia: recognising and managing a potentially
growing disorder. Postgrad Med 2003; 113: 99-112. |