Pulmonary Complications

Aspiration Syndromes - Gut Gone Wrong

• Aspiration of gastric contents → pulmonary injury. Types:
  • Chemical pneumonitis (Mendelson's): Gastric acid ($pH < \textbf{2.5}$, volume $ > \textbf{0.4} \text{ ml/kg}$ or $ > \textbf{25} \text{ ml}$). Rapid onset (1-2 hrs).
  • Bacterial pneumonia: Infected aspirate. Slower onset (24-48 hrs).
  • Particulate aspiration: Airway obstruction.
• Risk Factors: Full stomach, emergency surgery, GERD, obesity, pregnancy, ↓LOC, difficult airway.
• Prevention: Fasting (solids 6-8h, clears 2h), RSI, cricoid pressure, prokinetics, antacids, H2 blockers, PPIs.
• Management: Airway suction, O₂, PEEP, bronchodilators. Antibiotics for pneumonia, not routine for pneumonitis.

  ⭐ Mendelson's: chemical pneumonitis from gastric aspirate (pH < 2.5, volume > 0.4 ml/kg or > 25 ml).

Airway Obstruction - Choke Hold Horrors

• Laryngospasm: Reflex glottic closure.
  • Causes: Irritation (secretions, blood), light anesthesia, pain.
  • Signs: Stridor, "rocking horse" breathing, ↓SpO₂.
  • 📌 Mnemonic: Larson's maneuver, Oxygen (100%), Suction, Suxamethonium.
  • Mgmt: 100% O₂, PPV, Larson's maneuver, deepen anesthesia (Propofol 10-30mg), Succinylcholine 0.1-1 mg/kg IV or 4-5 mg/kg IM.
• Bronchospasm: Lower airway smooth muscle contraction.
  • Causes: Asthma, COPD, allergy, aspiration, drugs.
  • Signs: Wheeze, ↓SpO₂, ↑Peak Airway Pressure, ↑EtCO₂ (early) then ↓.
  • Mgmt: 100% O₂, deepen anesthesia (volatiles, ketamine), β₂-agonists (Salbutamol), IV Hydrocortisone 100-200 mg. Consider Aminophylline, MgSO₄.

⭐ Laryngospasm is most common in children during Stage 2 anesthesia or with airway irritation.

Lung Collapse & Fluid - Soggy Sponges

• Atelectasis (Collapse): Alveolar collapse, ↓ lung volume.
  • Types: Resorption (post-op mucus plug), compression, adhesive (↓surfactant).
  • Risks: Anesthesia (↓FRC), surgery, immobility.
  • Signs: ↓Breath sounds, dull percussion, hypoxemia.
  • Prevention/Tx: Incentive spirometry, PEEP, mobilization. 📌 SIGH - Spirometry, Inspiration (deep), Get moving, Hydration.
• Pulmonary Edema (Fluid): Excess fluid in alveoli/interstitium.
  • Cardiogenic: ↑Hydrostatic pressure (LV failure, fluid overload).
  • Non-cardiogenic: ↑Permeability (ARDS, sepsis, TRALI).
  • Negative Pressure Pulmonary Edema (NPPE): Forceful inspiration against obstructed airway.
  • Signs: Dyspnea, crackles, pink frothy sputum.
  • Tx: O2, PEEP, diuretics (cardiogenic), address cause.

⭐ Negative Pressure Pulmonary Edema (NPPE) can occur within minutes to hours after relief of acute upper airway obstruction_

Barotrauma & Hypoxia - Pressure Problems

• Barotrauma: Lung injury from excessive positive pressure during mechanical ventilation.
  • Manifestations: Pneumothorax, pneumomediastinum, subcutaneous emphysema, pneumoperitoneum.
  • Risk factors: High Peak Inspiratory Pressure (PIP), Plateau Pressure (Pplat) > 30 cm H₂O, large tidal volumes ($V_T$).
  • Prevention: Lung Protective Ventilation (LPV): $V_T$ 4-8 ml/kg Ideal Body Weight (IBW), Pplat < 30 cm H₂O.
• Hypoxia: Arterial $O_2$ saturation ($SpO_2$) < 90% or $PaO_2$ < 60 mmHg.
  • Key Causes: 📌 Hypoventilation, V/Q mismatch (e.g., atelectasis, PE), Shunt, Low $FiO_2$, Diffusion limitation.
  • Management: ↑ $FiO_2$, ensure patent airway, optimize ventilation (PEEP), treat specific cause.

⭐ Plateau pressure (Pplat), reflecting alveolar pressure, is a more critical determinant of barotrauma than PIP. Keep Pplat < 30 cm H₂O.

High‑Yield Points - ⚡ Biggest Takeaways

• Aspiration pneumonitis: high risk with full stomach, GERD. Mendelson's syndrome: pH < 2.5, volume > 0.4 mL/kg.
• Atelectasis: most common post-op pulmonary complication, often from hypoventilation.
• Bronchospasm: triggered by airway irritation, drugs, or reactive airway disease.
• Negative Pressure Pulmonary Edema (NPPE): follows laryngospasm or upper airway obstruction.
• Pneumothorax: risk with central line insertion, supraclavicular block, barotrauma.
• Post-op hypoxemia: common causes include atelectasis, diffusion hypoxia (N2O).