Postoperative Pulmonary Complications (PPCs)

Definition

• Miller's Anesthesia, 10e - p.3959; Murray & Nadel's Respiratory Medicine - p.822

Classification / Types of PPCs

Pathophysiology

1. Reduced FRC (Functional Residual Capacity): General anesthesia induces diaphragmatic cephalad displacement, reducing FRC by up to 20%. This leads to dependent lung atelectasis within minutes of induction.
2. Impaired mucociliary clearance: Anesthetic agents and endotracheal intubation suppress ciliary function, causing secretion retention.
3. Diaphragmatic dysfunction: After upper abdominal surgery, reflex diaphragmatic inhibition via splanchnic afferents reduces tidal volume and cough efficacy.
4. Opioid-induced respiratory depression: Reduces hypoxic and hypercapnic ventilatory drive; suppresses protective cough reflex.
5. Residual neuromuscular blockade (RNMB): Residual blockade at a train-of-four ratio <0.9 impairs upper airway tone, increases risk of aspiration, and weakens respiratory muscles.
6. Pain-induced splinting: Inadequate analgesia leads to shallow breathing, reluctance to cough, and retained secretions.
7. Aspiration: Reduced laryngeal reflexes during emergence, full stomach, or nasogastric tube placement increases aspiration risk.

Risk Factors

A. Patient-Related Risk Factors (Odds Ratios from Smetana et al. 2006)

B. Procedure-Related Risk Factors

Risk Scoring: ARISCAT Index

Prevention Strategies

Preoperative

1. Smoking cessation: Optimal benefit requires 4-8 weeks before surgery. Recent meta-analyses confirm no increased risk from cessation <4 weeks before surgery; cessation should be encouraged at any stage. Use the "5A's" model: Ask, Advise, Assess, Assist, Arrange.
2. Optimization of chronic lung disease: Treat COPD exacerbations, asthma, or respiratory infections; use bronchodilators, corticosteroids as indicated.
3. Prehabilitation: Inspiratory muscle training + cardiopulmonary rehabilitation before major abdominal or cardiac surgery reduces PPCs by up to 50% (NNT = 7). A 1-2 week program with an inspiratory threshold device is most studied.
4. Oral hygiene: Daily tooth brushing and antiseptic mouthwash for 2 weeks preoperatively reduces postoperative pneumonia after cardiac surgery and lung resection.
5. Nutritional optimization: Correct hypoalbuminemia.
6. OSA screening: Use STOP-BANG questionnaire (score ≥5 = high risk); ensure PAP therapy compliance. - Murray & Nadel's - p.822

Intraoperative

1. Lung-protective ventilation (LPV):
   • Low tidal volume: <6-8 mL/kg IBW (certainly <10 mL/kg)
   • Adequate PEEP: ≥5 cmH2O (optimal ~5 cmH2O)
   • Plateau pressure: <30 cmH2O (lowest risk ≤16 cmH2O)
   • In a study of ~70,000 patients (Ladha et al.), LPV significantly reduced PPCs. - Miller's Anesthesia, 10e - p.9316
2. Recruitment maneuvers: Periodic lung recruitment to reopen collapsed alveoli.
3. Avoid residual NMB: Use sugammadex for reversal of rocuronium/vecuronium rather than neostigmine; ensure TOF ratio ≥0.9 before extubation.
4. Regional / neuraxial anesthesia: When appropriate, associated with significantly lower pulmonary risk vs. general anesthesia; thoracic epidural provides excellent analgesia after abdominal/thoracic surgery.
5. Multimodal analgesia: Minimize opioids; use acetaminophen, NSAIDs, gabapentin, regional blocks, and glucocorticoids.
6. Minimize surgical duration: <3 hours when feasible.
7. Aspiration prophylaxis: Rapid sequence induction for full stomach, antacids/H2 blockers, avoid supine position.
8. Avoid long-acting benzodiazepines: Associated with prolonged intubation.

Postoperative

1. I COUGH Protocol (validated pulmonary bundle):

1. Early ambulation: Reduces atelectasis, VTE, and ileus.
2. Chest physiotherapy: Percussion, postural drainage, and breathing exercises.
3. Opioid-sparing analgesia: Essential for adequate tidal volume and cough.
4. Non-invasive positive pressure ventilation (NIV/CPAP): For high-risk patients, OSA, or those with early respiratory deterioration.
5. Enhanced recovery after surgery (ERAS) protocols: Bundled interventions including regional anesthesia, minimally invasive surgery, goal-directed fluid therapy, and early mobilization demonstrably reduce pneumonia and respiratory complications.
6. Continuous postoperative monitoring: Automated ward monitoring can detect early respiratory deterioration.

Specific PPCs: Recognition and Management

Atelectasis

• Most common PPC; often asymptomatic but can cause hypoxia and fever (within 24-48h)
• Treatment: incentive spirometry, deep breathing, chest PT, CPAP, bronchoscopy for lobar collapse

Aspiration Pneumonitis / Pneumonia

• Mendelson's syndrome (chemical pneumonitis) from acid aspiration vs. bacterial pneumonia from particulate aspiration
• Prevention: RSI, antacid premedication, avoid premature extubation
• Treatment: supportive oxygen, antibiotics if bacterial component

Bronchospasm

• Often in asthmatics/COPD patients; can occur during intubation, extubation, or light anesthesia
• Treatment: deepen anesthesia, inhaled salbutamol, IV magnesium, IV ketamine, IV epinephrine in severe cases

Postoperative Respiratory Failure

• Defined as need for mechanical ventilation >48 hours or unplanned reintubation
• Management: NIV as first step; optimize analgesia; treat underlying cause

Pulmonary Embolism

• Risk elevated postoperatively; classic triad: dyspnea, plexiric chest pain, hemoptysis
• Prevention: early mobilization, LMWH, compression stockings
• Treatment: anticoagulation, thrombolysis in massive PE

Summary Table: Prevention by Phase