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Preoperative Evaluation of the Respiratory System Before Surgery

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I. INTRODUCTION

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II. CHANGES IN PULMONARY FUNCTION WITH SURGERY

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III. POSTOPERATIVE PULMONARY COMPLICATIONS (PPCs)

1. Pneumonia
2. Respiratory failure (mechanical ventilation >48h or unplanned reintubation)
3. Atelectasis
4. COPD exacerbation
5. Bronchospasm
6. Respiratory arrest due to sleep-disordered breathing
7. Perioperative pulmonary mortality

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IV. RISK FACTORS FOR PPCS

A. Patient-Related Risk Factors (Fishman's Table 102-4; Murray & Nadel's Table 34.1)

1. Chronic lung disease (COPD): Increased airway resistance, secretion retention, and blunted hypoxic/hypercapnic drive all contribute. Despite being significant, COPD is less important than age or ASA class.
2. Smoking: Significant when tobacco use exceeds 20 pack-years. Cessation for ≥8 weeks significantly reduces risk. Mucociliary function and pulmonary function may remain abnormal for months after cessation.
3. Obesity: Reduces total respiratory compliance by >60%; reduces ERV; promotes V/Q mismatch and atelectasis. In the absence of concurrent cardiopulmonary disease, obesity alone does not substantially increase PPC risk—however, obesity is a strong risk factor for undiagnosed OSA.
4. Nutritional status: Malnutrition → reduced ventilatory response to hypoxia, diaphragmatic weakness, impaired immunity. Serum albumin <36 g/L associated with increased PPCs.
5. Age: Independent predictor with each decade >50 years. Should not be sole reason for withholding surgery—decisions must be individualized.
6. ASA classification (Fishman's Table 102-7):

B. Procedure-Related Risk Factors (Murray & Nadel's Table 34.2)

• Emergency surgery (higher risk than elective)
• Prolonged surgery (>3–4 hours)
• General vs. neuraxial anesthesia: General anesthesia has OR of 2.4 for PPCs; neuraxial (spinal/epidural) anesthesia reduces PPCs with OR of 0.38 vs. general anesthesia in meta-analyses (Murray & Nadel's)

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V. PRINCIPAL ELEMENTS OF PREOPERATIVE EVALUATION

1. History and Physical Examination

1. Smoking history (pack-year quantification)
2. Respiratory symptoms: cough, chest pain, dyspnea, symptoms of sleep apnea
3. Extent of pre-existing lung disease (COPD, asthma, ILD)
4. History of recent respiratory tract infection

2. Chest Radiograph

• Routine preoperative CXR is NOT indicated in patients without cardiopulmonary disease or symptoms
• Even in patients with known cardiopulmonary disease, the CXR usually only confirms previously known abnormalities and rarely changes management
• Indications (Fishman's):
  • New or unexplained symptoms/signs
  • Known underlying lung disease without a recent CXR
  • Planned thoracic surgery
• American College of Surgeons/ACR (Choosing Wisely): CXR only for patients with evidence of acute cardiopulmonary disease, OR patients >70 years with chronic stable cardiopulmonary disease without imaging within 6 months (Murray & Nadel's)

3. Arterial Blood Gas Analysis

• Elevated PaCO₂ is associated with increased postoperative respiratory morbidity in significant chronic lung disease → ABG should be done preoperatively in these patients
• Standard practice: obtain ABG in all patients undergoing lung resection (even without significant lung disease) as a baseline for intra/postoperative comparisons
• Indicated when history or physical examination reveals a new significant pulmonary process
• Data do NOT support routine ABG as a preoperative screening test

4. Pulmonary Function Tests (PFTs)

• Increased risk of PPCs demonstrated only with obstructive disorders—not restrictive disease
• Therefore, spirometry for airway obstruction is all that is required to screen for PPC risk
• A complete PFT battery (including lung volumes) is useful when restrictive disease is suspected
• Normal PFTs do not guarantee a complication-free course

1. Cough or unexplained dyspnea
2. History of chronic lung disease
3. Cigarette smoking history (>20 pack-years)
4. Planned lung resection

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VI. RISK PREDICTION TOOLS (ARISCAT Score)

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VII. EVALUATION FOR LUNG RESECTION

1. What is the surgical morbidity/mortality for the patient with underlying lung disease?
2. Will postoperative lung function support acceptable quality of life?

Pulmonary Function Thresholds

Prediction of Postoperative Function

ppoPFT = Preoperative FEV₁ or DLCO × (lung function remaining after resection)

1. Ventilation-perfusion (V/Q) scan: measures relative blood flow/ventilation; more accurate, especially for pneumonectomy
2. Segment-based calculation: uses anatomic segments (10 right, 9 left); tends to underestimate function after pneumonectomy

Lung Resection Algorithm (Fishman's, Fig. 102-3):

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VIII. SLEEP-DISORDERED BREATHING (OSA) — Special Consideration

• Moderate/severe OSA found in up to 40% of surgical patients, undiagnosed in the majority
• OSA increases risk of: infections, respiratory failure, cardiac events, mortality
• STOP-BANG questionnaire is the recommended screening tool:

• Score 0–2 = low risk; 3–4 = intermediate; ≥5 = high risk
• Delay surgery only if elevated STOP-BANG score PLUS: uncontrolled systemic disease, hypoxemia, or evidence of CO₂ retention (elevated PaCO₂ or serum bicarbonate)
• Patients with known OSA should bring their PAP device to hospital for perioperative use

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IX. PREOPERATIVE PREPARATION (Risk Reduction)

Preoperative Interventions:

Intraoperative Strategies (Murray & Nadel's):

• Neuraxial/regional > general anesthesia for PPCs (OR 0.38 vs. general)
• Avoid long-acting neuromuscular blocking agents (e.g., pancuronium)
• Lung-protective ventilation: tidal volume 6–8 mL/kg with PEEP and recruitment maneuvers; avoid VT ≥10 mL/kg; plateau pressures <16 cmH₂O associated with lowest PPC risk

Postoperative Strategies:

• Early and frequent ambulation
• Adequate pain control (epidural or PCA to limit systemic opioids)
• Incentive spirometry, deep breathing exercises, chest physiotherapy
• I COUGH protocol: Incentive spirometry, Coughing, deep breathing, Oral hygiene, Understanding (education), Getting out of bed, Head-of-bed elevation

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X. SUMMARY TABLE

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• History and physical examination remain the cornerstone—a negative history predicts a negative examination
• PPC risk is greater with procedure-related factors (especially surgical site) than patient-related factors
• FEV₁ <2L (or <80% predicted) is the critical threshold for pneumonectomy risk
• DLCO is an independent predictor of complications, separate from FEV₁
• The ARISCAT score is the most clinically useful multivariable PPC predictor
• Neuraxial anesthesia is significantly superior to general anesthesia for PPC prevention
• Smoking cessation ideally ≥8 weeks pre-surgery; inspiratory muscle training for ≥1–2 weeks with NNT of 7

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Preoperative Evaluation of Respiratory System

15 Marks — High-Yield Exam Answer

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DEFINITION

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POSTOPERATIVE PULMONARY COMPLICATIONS (PPCs)

PPCs are the most costly perioperative complications; 90-day mortality 24.4% with PPC vs 1.2% without (Murray & Nadel's)

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4 PRINCIPAL ELEMENTS OF PREOPERATIVE EVALUATION (Fishman's)

1. History & Physical Examination (Cornerstone)

• Smoking history (pack-years)
• Respiratory symptoms — cough, dyspnea, chest pain, sleep apnea symptoms
• Pre-existing lung disease (COPD, asthma, ILD)
• Recent respiratory tract infection

Physical exam is rarely helpful when history is negative — serves mainly as a baseline

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2. Chest Radiograph

• New/unexplained respiratory symptoms
• Known lung disease with no recent CXR
• Planned thoracic surgery
• Age >70 with chronic cardiopulmonary disease (no CXR in last 6 months)

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3. Arterial Blood Gas (ABG)

• Significant chronic lung disease (elevated PaCO₂ = increased PPC risk)
• Planned lung resection (as baseline)
• New significant pulmonary process on examination

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4. Pulmonary Function Tests (PFTs)

Only obstructive disorders (not restrictive) have proven correlation with PPCs → Spirometry alone sufficient for screening

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RISK FACTORS FOR PPCs

Patient-Related (Murray & Nadel's Table 34.1)

Procedure-Related (more important than patient factors)

General anesthesia OR = 2.4 for PPCs vs neuraxial anesthesia (OR 0.38)

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EVALUATION FOR LUNG RESECTION (Fishman's — HIGH YIELD)

ppo FEV₁ = Preoperative FEV₁ × (remaining lung function after resection) (by V/Q scan — more accurate than segment-counting method)

• Pneumonectomy risk rises sharply when FEV₁ <2 L or <80% predicted
• Lobectomy critical threshold: FEV₁ <1.5 L
• DLCO <60–80% predicted = independent predictor (separate from FEV₁)

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OSA SCREENING — STOP-BANG (Murray & Nadel's)

• Score ≥5/8 = High risk
• Delay surgery only if high score PLUS hypoxemia, CO₂ retention, or uncontrolled systemic disease

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PREOPERATIVE PREPARATION (Fishman's Table 102-8)

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QUICK SUMMARY BOX

History & PE  →  Cornerstone (always)
CXR          →  Only if symptoms / known disease / thoracic surgery
ABG          →  Chronic lung disease / lung resection baseline
PFTs         →  Obstruction suspected / >20 pack-years / lung resection
CPET         →  Borderline lung resection candidates (ppoFEV₁ 30–40%)
STOP-BANG    →  Screen ALL patients for OSA

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