A 72-year-old woman with a history of chronic obstructive pulmonary disease (COPD) on home oxygen therapy and an FEV₁ of 35% of predicted presents for elective abdominal aortic aneurysm repair. She has no prior pulmonary function testing. Which investigation is most appropriate to assess her perioperative respiratory risk and guide anesthetic management?

Explanation

## Rationale for Pulmonary Function Tests (PFTs) **Key Point:** In patients with known or suspected significant pulmonary disease (COPD, restrictive lung disease) undergoing major surgery, formal pulmonary function tests including spirometry and diffusing capacity (DLCO) provide objective quantification of respiratory reserve and predict perioperative pulmonary complications. ### Why PFTs Are Indicated Here This patient has: - Severe COPD (FEV₁ 35% predicted = GOLD Stage IV) - Home oxygen dependence - Planned major surgery (AAA repair = high-risk procedure) - No prior objective pulmonary assessment **High-Yield:** PFTs provide: - **FEV₁** — predictor of postoperative pulmonary complications - **FVC** — detects restrictive disease - **DLCO** — assesses gas exchange; low DLCO increases risk - **FEV₁/FVC ratio** — differentiates obstructive vs. restrictive patterns ### Investigation Comparison | Investigation | Purpose | Yield in This Patient | |---|---|---| | **PFTs (spirometry + DLCO)** | Quantify airway obstruction, gas exchange; predict complications | **HIGH** — objective risk stratification | | **ABG** | Assess current oxygenation, ventilation, acid–base status | Moderate — snapshot, not predictive | | **Chest X-ray** | Detect acute infection, pneumothorax, acute decompensation | Low — does not quantify functional reserve | | **HRCT** | Characterize parenchymal disease, rule out malignancy | Low for risk prediction; useful if diagnosis unclear | **Clinical Pearl:** Patients with FEV₁ < 40% predicted have significantly increased risk of postoperative respiratory failure, prolonged ventilation, and ICU admission. PFTs guide decisions on preoperative optimization (bronchodilators, steroids, smoking cessation), intraoperative ventilation strategy, and postoperative monitoring intensity. **Mnemonic — When to Order PFTs Pre-op:** **COPD-RISK** - **C**hronic obstructive pulmonary disease - **O**bstructive or restrictive disease suspected - **P**rior respiratory symptoms or dyspnea - **D**iagnosis unclear; need objective assessment - **R**esection surgery (lung, esophageal) - **I**nterstitial lung disease - **S**evere asthma or COPD exacerbation history - **K**nown low FEV₁ or DLCO ### Role of ABG in This Context ABG is useful **after** PFTs to assess current gas exchange (baseline PaCO₂, PaO₂) and guide intraoperative ventilation, but it does not predict complications or quantify reserve. [cite:Barash Clinical Anesthesia 8e Ch 7; ACC/AHA Perioperative Evaluation Guidelines]