Subinternship Surgery · Year 4 · from Subinternship Surgery

Case 2: Post-Operative Respiratory Complications

Patient Presentation

Demographics: 67-year-old male

Chief Complaint: Increasing oxygen requirement on POD 2 following open abdominal aortic aneurysm repair

History of Present Illness: Mr. Davis underwent elective open AAA repair for a 6.2cm infrarenal aneurysm. The procedure took 4.5 hours with an estimated blood loss of 800mL. He was extubated in the OR and transferred to the surgical ICU. He has been requiring increasing supplemental oxygen.

Past Medical History:

  • AAA (now s/p repair)
  • COPD (FEV1 58% predicted, on tiotropium)
  • Former smoker (quit 2 months ago, 45 pack-years)
  • Hypertension
  • Obesity (BMI 32)

Post-Operative Course:

  • POD 0: Extubated, stable on 4L NC
  • POD 1: Required 6L NC to maintain SpO2 >92%
  • POD 2: Now on 10L high-flow NC, SpO2 90-92%, mildly dyspneic

Physical Examination:

  • Vitals: T 38.0C, HR 102, BP 145/88, RR 24, SpO2 91% on 10L NC
  • General: Alert, speaking in short sentences
  • Lungs: Diminished breath sounds at bases bilaterally, scattered rhonchi
  • Cardiovascular: Tachycardic, regular, no murmur
  • Abdomen: Midline incision intact, soft, mildly distended
  • Extremities: 1+ bilateral lower extremity edema, SCDs in place

Laboratory Studies:

  • WBC: 14,500
  • Hgb: 9.8 g/dL (from 11.2 pre-op)
  • ABG on 10L NC: pH 7.38, pCO2 42, pO2 62, HCO3 24
  • BNP: 450 pg/mL (mildly elevated)

Imaging:

  • CXR: Bilateral lower lobe opacities, small bilateral pleural effusions, mild pulmonary vascular congestion

Clinical Questions

  1. What is the differential diagnosis for his hypoxemia?

Differential Diagnosis: | Diagnosis | Supporting Features | Against | |-----------|--------------------|---------| | Atelectasis | Post-op, poor inspiration, basilar findings | Should improve with IS | | Pulmonary edema/fluid overload | Received blood products, elevated BNP, congestion on CXR | BNP only mildly elevated | | Pneumonia | Fever, leukocytosis, productive cough | Early for hospital-acquired PNA | | Pulmonary embolism | Post-op, tachycardia, hypoxemia | On prophylaxis, no pleuritic pain | | ARDS | High-risk surgery, bilateral infiltrates | P/F ratio ~62/0.5 = 124 (moderate ARDS criteria) |

  1. Calculate his P/F ratio. Does he meet ARDS criteria?

P/F Ratio Calculation:

  • PaO2 = 62 mmHg
  • FiO2 on 10L NC ~ 0.44-0.50 (estimate 0.50)
  • P/F ratio = 62/0.50 = 124

Berlin Criteria for ARDS:

  • Timing: Within 1 week of insult - YES
  • Imaging: Bilateral opacities - YES
  • Origin: Not fully explained by cardiac failure - UNCLEAR (needs echo)
  • Severity: P/F 100-200 = Moderate ARDS

Assessment: Meets criteria for moderate ARDS, but cardiogenic component must be excluded with echocardiogram

  1. What interventions should be implemented?

Respiratory Support:

  • Transition to high-flow nasal cannula (40-60 L/min, FiO2 titrated)
  • Aggressive pulmonary toilet: IS q1h, chest PT, early mobilization
  • Consider BiPAP if not improving on HFNC
  • Prepare for intubation if continued deterioration

Fluid Management:

  • Assess volume status carefully (elevated BNP, edema, but major surgery)
  • Consider diuresis if truly fluid overloaded
  • Maintain euvolemia - avoid additional boluses

Other Interventions:

  • Continue DVT prophylaxis
  • CT-PE if suspicion remains high
  • Echocardiogram to assess cardiac function
  • Sputum culture if productive cough
  • Bronchodilators for COPD component
  1. What are the principles of lung-protective ventilation if intubation becomes necessary?

Lung-Protective Ventilation Settings: | Parameter | Target | Rationale | |-----------|--------|-----------| | Tidal Volume | 6-8 mL/kg IBW | Prevents volutrauma | | Plateau Pressure | <30 cm H2O | Prevents barotrauma | | PEEP | 8-15 cm H2O | Maintains alveolar recruitment | | FiO2 | Lowest to achieve SpO2 >92% | Prevents oxygen toxicity | | pH | Accept >7.20 | Permissive hypercapnia |

Ideal Body Weight Calculation:

  • Male: 50 + 2.3 (height in inches - 60)
  • If 5'10" = 70 inches: 50 + 2.3(10) = 73 kg IBW
  • Target TV: 6 mL/kg = 438 mL (round to 450 mL)

Clinical Image

Image: Sequential compression devices (SCDs) for DVT prophylaxis. These should be applied to all post-surgical patients and continued throughout hospitalization. Source: Wikimedia Commons. License: CC BY-SA 3.0.

Image Attribution: Sequential compression device. Wikimedia Commons. CC BY-SA 3.0.

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