Post-Lobectomy FEV1 Calculation
For lobectomy, calculate the estimated postoperative FEV1 using the anatomical segment counting method: multiply the preoperative FEV1 by (19 minus the number of segments removed) divided by 19. 1, 2
Standard Calculation Formula
The British Thoracic Society provides the definitive formula for lobectomy:
Estimated postoperative FEV1 = Preoperative FEV1 × (19 - segments removed) / 19 1
Lung Segment Distribution
The total lung contains 19 segments distributed as follows: 1, 2
- Right upper lobe: 3 segments
- Middle lobe: 2 segments
- Right lower lobe: 5 segments
- Left upper lobe: 3 segments
- Lingula: 2 segments
- Left lower lobe: 4 segments
Modified Formula for Obstructed Segments
When segments are obstructed by tumor or atelectasis, use this adjusted calculation: 1
Estimated postoperative FEV1 = Preoperative FEV1 × [(19 - a) - b] / (19 - a)
Where:
- a = number of obstructed segments
- b = number of unobstructed segments to be resected
This modification accounts for the fact that obstructed segments contribute minimally to baseline lung function. 1, 3
Essential Requirements for Calculation
Preoperative Measurement
- Use post-bronchodilator FEV1 as the baseline value 1
- Measure in liters, not just as percentage predicted 1
Expression of Results
The calculated postoperative FEV1 must be expressed as a percentage of predicted normal values to properly assess surgical risk, particularly to avoid denying surgery to women and elderly patients who may have lower absolute values but adequate functional reserve. 1, 2
Risk Stratification Thresholds
After calculating the estimated postoperative FEV1, apply these risk categories: 1, 2
- >60% predicted: Low risk, proceed with surgery 2
- 40-60% predicted: Average risk, acceptable for surgery 1
- 30-40% predicted: Moderate risk, perform exercise testing 2
- <30% predicted: High risk, requires cardiopulmonary exercise testing and consideration of limited resection 2, 4
Critical Additional Assessments
Transfer Factor (DLCO)
Calculate estimated postoperative DLCO using the identical segment counting formula as both FEV1 and DLCO are independent predictors of perioperative mortality. 1, 2, 5
Both estimated postoperative FEV1 AND estimated postoperative DLCO must exceed 40% predicted for acceptable surgical risk. 1, 2
Oxygen Saturation
Measure room air oxygen saturation at rest, as SaO2 <90% indicates significantly increased postoperative complication risk regardless of spirometric values. 1, 2
Important Clinical Caveats
Underestimation of Actual Function
The anatomical calculation consistently underestimates actual postoperative FEV1 by approximately 250 mL for lobectomy, making the estimates conservative and safe for surgical decision-making. 1, 6
Research demonstrates that measured postoperative FEV1 is typically 8% higher than predicted at 3 months, 11% higher at 6 months, and 13% higher at 12 months after lobectomy. 7
When NOT to Use This Method
Do not use the anatomical segment counting method for pneumonectomy—instead, use quantitative perfusion scanning to determine the fractional contribution of each lung. 1, 2 The segment counting method underestimates pneumonectomy outcomes by approximately 500 mL. 6
Absolute Value Thresholds
If preoperative FEV1 exceeds 1.5 liters for lobectomy, no further respiratory function testing is required unless there is evidence of interstitial lung disease or disproportionate dyspnea. 1
Special Populations
Patients with COPD may experience a "lobar volume reduction effect" resulting in paradoxically improved respiratory function after lower lobectomy, with minimal FEV1 loss. 5
Combined surgery and radiation therapy results in additive lung function loss, with approximately 5.47% FEV1 loss per segment versus 2.84% for surgery alone. 6