Pulmonary Function Tests and Preoperative Assessment: What Does Spirometry Actually Tell You?
FEV₁ 58% predicted, FVC 71%, FEV₁/FVC 0.68 — what does this mean before major surgery? When spirometry changes the plan, when it doesn't, and how it connects to ARISCAT risk stratification.
My patient has FEV₁ 58% predicted — how does this change perioperative risk?
Spirometry alone does not predict PPC well. ARISCAT — integrating SpO₂, surgical site, and other factors — is the validated model. PFTs characterise the severity of underlying disease.
Key Points
Spirometry identifies obstructive and restrictive patterns but does not predict postoperative pulmonary complication (PPC) risk well in isolation. ARISCAT integrates SpO₂, surgical site, and other variables into a validated risk model. PFTs are most valuable when the clinical question is whether COPD is present, how severe it is, and whether it is optimised before surgery — not as a standalone risk score.
Frequently Asked Questions
- Should all patients have spirometry before major surgery? No. Routine spirometry is not recommended for unselected patients. Targeted testing is indicated when undiagnosed or inadequately characterised obstructive or restrictive disease is suspected.
- Does FEV₁ < 80% predicted mean the patient is too high risk for surgery? Not alone. Absolute FEV₁ thresholds matter most for resectional thoracic surgery. For non-thoracic procedures, severity of obstruction informs but does not determine fitness.
- How does spirometry interact with ARISCAT scoring? ARISCAT uses preoperative SpO₂ — which reflects the functional consequence of lung disease — rather than spirometry directly. A patient with COPD and SpO₂ 92% will score differently from one with SpO₂ 97%.
Clinical Scenario
A 67-year-old ex-smoker presents for elective laparoscopic colectomy. SpO₂ 94% on room air. His GP requested spirometry 6 months ago: FEV₁ 62% predicted, FVC 78% predicted, FEV₁/FVC 0.67. He uses a salbutamol inhaler occasionally. The anaesthetist must determine: is obstruction optimised, what is the PPC risk, and does the spirometry change the plan compared to SpO₂ alone?
Reading a Spirometry Report: What the Numbers Mean
| Parameter | What it measures | Perioperative relevance |
|---|---|---|
| FEV₁ (% predicted) | Forced expiratory volume in 1 second — effort-dependent peak flow marker | Severity of obstruction; <50% predicted = severe; guides bronchodilator need |
| FVC (% predicted) | Forced vital capacity — total exhaled volume from full inspiration | Reduced in restriction and severe air trapping; isolated FVC fall suggests restriction |
| FEV₁/FVC ratio | Fixed ratio < 0.70 post-bronchodilator defines obstruction (GOLD criteria) | Distinguishes obstructive from restrictive pattern; normal ratio with low FVC = restriction |
| DLCO (% predicted) | Diffusing capacity — gas exchange at alveolar level | Best single predictor for post-thoracotomy complications; not routinely measured |
| Reversibility | FEV₁ increase ≥ 12% and ≥ 200 mL after bronchodilator | Significant reversibility suggests asthma component — ensure optimised pre-surgery |
Obstructive vs Restrictive Pattern: Clinical Interpretation
| Feature | Obstructive pattern | Restrictive pattern |
|---|---|---|
| FEV₁/FVC | < 0.70 (post-bronchodilator) | Normal or elevated (≥ 0.70) |
| FVC | Normal or mildly reduced | Reduced (< 80% predicted) |
| FEV₁ | Reduced | Reduced proportionally |
| Common causes | COPD, asthma, bronchiectasis | Obesity, pulmonary fibrosis, pleural disease, neuromuscular weakness |
| Preop optimisation | Bronchodilators, steroids if indicated, smoking cessation | Weight optimisation (obesity), treat underlying cause; often less reversible |
| Primary perioperative risk | Air trapping, bronchospasm, hypercapnia, difficult extubation | Atelectasis, reduced FRC, hypoxaemia especially after upper abdominal surgery |
GOLD Severity Classification
| GOLD Grade | FEV₁ % predicted | Symptoms / Perioperative implications |
|---|---|---|
| GOLD 1 (Mild) | ≥ 80% | Often asymptomatic; PPC risk modestly elevated; ensure bronchodilator optimised |
| GOLD 2 (Moderate) | 50–79% | Dyspnoea on exertion; SpO₂ may be borderline; confirm optimised therapy pre-surgery |
| GOLD 3 (Severe) | 30–49% | Significant air trapping; PaCO₂ may be elevated; consider ABG; ARISCAT score likely high |
| GOLD 4 (Very Severe) | < 30% | Functional impairment; high PPC risk; multidisciplinary preoperative evaluation warranted |
When Spirometry Changes the Plan
- Undiagnosed COPD: patient reporting 'just a smoker's cough' — spirometry reveals GOLD 2–3 obstruction, prompting inhaler initiation and respiratory physiotherapy referral before elective surgery
- Inadequate optimisation: known COPD but spirometry shows significant reversibility — suggests undertreated airway inflammation; a course of oral steroids and optimised bronchodilators before surgery may reduce intraoperative bronchospasm risk
- Suspected restriction vs obstruction: obese patient with SpO₂ 94% — spirometry showing normal FEV₁/FVC with low FVC (restrictive pattern) changes the focus from bronchodilators to pre-induction CPAP, optimal positioning, and lung recruitment strategy
- Thoracic surgery planning: for lung resection, FEV₁ and predicted postoperative FEV₁ (ppoFEV₁) are essential — ppoFEV₁ < 40% predicted is a threshold for further exercise testing or cardiopulmonary exercise testing (CPET)
Spirometry does not predict PPC risk well in non-thoracic surgery
Multiple systematic reviews have found that spirometry performs poorly as a standalone predictor of postoperative pulmonary complications in non-thoracic procedures. Validated multivariable tools like ARISCAT incorporate surgical site, SpO₂, anaemia, recent respiratory infection, and other variables that outperform spirometry alone. Use spirometry to characterise disease — use ARISCAT to estimate risk.
SpO₂ as the Bridge Between PFTs and ARISCAT
ARISCAT does not use FEV₁ or FVC directly. Instead, it uses preoperative SpO₂ on room air — which reflects the functional consequence of lung disease, whether obstructive, restrictive, or mixed. A patient with GOLD 3 COPD and SpO₂ 93% will score higher on ARISCAT than a patient with GOLD 2 COPD and SpO₂ 97%, even if the FEV₁ values are similar.
| Preoperative SpO₂ | ARISCAT points | Implication |
|---|---|---|
| ≥ 96% | 0 points | No contribution to risk from oxygenation |
| 91–95% | 8 points | Moderate contribution — investigate underlying cause |
| ≤ 90% | 24 points | Major contribution — COPD/restriction likely; further workup warranted |
Preoperative Optimisation Based on Spirometry Findings
- Smoking cessation: the single most effective intervention — benefits on airway secretion and ciliary function begin within days; risk reduction requires at least 8 weeks before elective surgery when possible
- Bronchodilator therapy: ensure SABA and LABA/LAMA are prescribed and patient-educated on inhaler technique before surgery
- Respiratory physiotherapy: preoperative inspiratory muscle training improves postoperative lung function in high-risk patients; referral 4–6 weeks pre-surgery is ideal
- Treat active infection or exacerbation: schedule elective surgery at least 4–6 weeks after resolution of acute respiratory exacerbation
- Oral corticosteroids: consider a short course if significant reversibility is present on spirometry and the patient is not already on inhaled steroids
Clinical Pitfalls
- Using spirometry as a go/no-go threshold for non-thoracic surgery — no absolute FEV₁ cut-off reliably excludes acceptable surgical risk in general surgery; context and multivariable risk tools are required
- Ordering spirometry routinely for all patients — current evidence supports targeted testing for patients with suspected or known respiratory disease; routine pre-operative spirometry in low-risk patients adds cost without improving outcomes
- Failing to check for reversibility — a GOLD 2 patient with significant bronchodilator response is not the same as one without; the former warrants optimisation before proceeding
- Not revisiting spirometry findings at pre-assessment — results from months or years ago may not reflect current functional state, particularly after exacerbations or disease progression
Related Tools
- ARISCAT Score — Pulmonary Risk
Calculate postoperative pulmonary complication risk — integrates SpO₂, surgical site, anaemia, duration, and other validated variables
- Perioperative Oxygenation Assessment
Classify SpO₂ against age-adjusted expected PaO₂ — useful when spirometry results are borderline and functional status is uncertain
Continue Learning
- ARISCAT score and PPC risk — clinical interpretation
How ARISCAT's seven variables combine into a risk score — and what the three risk tiers mean for management
- Why is my patient's preop SpO₂ low? COPD, atelectasis, or measurement error?
Differential diagnosis of reduced preoperative SpO₂ — structured approach to identifying the cause
- Residual neuromuscular blockade and postoperative respiratory arrest
Why TOF ratio 0.9 matters in the COPD patient — how incomplete reversal compounds respiratory failure
Written by
Kozo Watanabe, MD
Chief of Anesthesiology
Practicing anesthesiologist specializing in cardiovascular anesthesia and perioperative management. Clinical focus includes perioperative risk assessment, respiratory and hemodynamic management, and decision support for high-risk surgical patients.
- Cardiovascular anesthesia and cardiac surgery
- Perioperative critical care
- Perioperative respiratory management (oxygenation, ventilation, ABG interpretation)