Pulmonary Risk Assessment

Postoperative pulmonary complications (PPCs) are a leading cause of perioperative morbidity and mortality, particularly in orthopaedic surgery, where patients are often elderly with multiple comorbidities. They include pneumonia, respiratory failure, atelectasis, bronchospasm and pleural effusion.

The cost. PPCs occur after 2-5% of elective orthopaedic procedures and in 10-40% of high-risk patients. They increase 30-day mortality 2-20 fold depending on severity, prolong hospital stay by 5-10 days on average, and cost an additional $20,000-50,000 per episode. They are also largely preventable through systematic risk assessment and optimisation.

The tools. Risk is stratified with:

• ARISCAT - validated PPC prediction, and the most widely used
• Arozullah score - respiratory failure prediction
• STOP-BANG - OSA screening, an 8-item questionnaire
• Gupta MICA - myocardial infarction or cardiac arrest
• Clinical assessment - exercise tolerance is the most predictive

Postoperative pulmonary complications arise from a predictable chain of physiological insults. Understanding them explains why each risk factor, and each preventive measure, works.

Reduced functional residual capacity. General anaesthesia, supine positioning and abdominal or thoracic incisions reduce functional residual capacity by 15-20%, promoting alveolar collapse (atelectasis). Atelectatic lung is poorly ventilated but still perfused, which creates shunt and hypoxaemia and leaves a nidus for infection.

Impaired cough and clearance. Pain-related splinting, opioids and residual neuromuscular blockade impair deep breathing and cough. Retained secretions plus atelectasis progress to pneumonia, especially in smokers and COPD patients with baseline mucociliary dysfunction.

Ventilatory depression. Opioids and sedatives blunt central respiratory drive, and OSA adds dynamic upper-airway obstruction. Together they produce hypoventilation, hypercapnia and obstructive hypoxaemia, peaking on postoperative nights 1-3 during REM rebound.

Fixed and modifiable risk. Risk is the product of patient factors (age, COPD, OSA, anaemia, baseline SpO2), procedure factors (site, duration, urgency) and anaesthetic and care factors (technique, opioids, mobilisation). Only the modifiable elements can change the trajectory, hence the focus on optimisation.

Site of surgery. Proximity of the incision to the diaphragm is the single strongest procedural predictor. Upper abdominal and thoracic surgery impair diaphragmatic excursion and carry the highest PPC rates, while peripheral limb surgery, which is most of orthopaedics, is comparatively protected. This is why ARISCAT assigns 15 points to an upper abdominal or thoracic incision, and why neuraxial lower-limb surgery is so favourable.

View larger

View larger

The patient who desaturates or becomes breathless after orthopaedic surgery is a classic viva and ward scenario. Pulmonary complications must be distinguished from cardiac, embolic and mechanical causes, and the management of each differs sharply.

View larger

View larger

View larger

View larger

View larger

View larger

View larger

View larger

Atelectasis is the most common PPC, alveolar collapse from hypoventilation and secretions. Pneumonia is the most serious, with a 30-day mortality of 20%. Respiratory failure (hypoxaemia requiring reintubation or NIV) is associated with OSA, bronchospasm is an exacerbation of reactive airway disease in COPD or asthma, and pleural effusion is common after upper abdominal or thoracic surgery. Early mobilisation and physiotherapy prevent most of them.

View larger

The prevention bundle. Prevention starts weeks before surgery and runs into the ward days.

Neuraxial anaesthesia reduces pulmonary complications by 30% compared with general anaesthesia in lower-limb surgery.

Choosing the technique. Prefer neuraxial anaesthesia for:

• High pulmonary risk (ARISCAT over 44)
• Severe OSA (STOP-BANG 7-8)
• Severe COPD (FEV1 under 50%)
• Lower-limb surgery (TKA, THA, femoral fracture)
• Obesity (BMI over 40)
• Patient preference for awake surgery

General anaesthesia is needed for:

• Upper limb or spine surgery, which is not amenable to neuraxial
• Patient refusal of neuraxial
• Anticoagulation preventing neuraxial (recent DOAC or LMWH)
• Haemodynamic instability (severe AS, dehydration)
• Infection at the injection site
• Coagulopathy or platelets under 70

View larger

View larger

Orthopaedic populations are increasingly elderly, obese and comorbid, exactly the profile that drives pulmonary risk. Assessment exists to identify the high-risk patients who need enhanced monitoring and intervention, to optimise modifiable risk factors before surgery, to guide the choice between neuraxial and general anaesthesia, and to decide between ward and HDU/ICU care afterwards.

Where it changes management. A structured, low-cost assessment alters four decisions:

• Level of monitoring. A high ARISCAT or high STOP-BANG score moves a patient from the ward to HDU or continuous oximetry, where early respiratory deterioration is caught before arrest.
• Anaesthetic technique. Lower-limb arthroplasty and hip-fracture surgery are amenable to neuraxial anaesthesia, which reduces pneumonia and 30-day mortality and is especially valuable in COPD and OSA.
• Timing of elective surgery. An active respiratory infection or COPD exacerbation is a reason to defer, and deferral is one of the highest-yield interventions available.
• Analgesic strategy. Identifying OSA mandates an opioid-sparing, multimodal and regional plan, directly reducing the most lethal complication, respiratory depression.

The Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score is the most validated tool for predicting postoperative pulmonary complications. It was developed from a multicentre cohort of 2,464 patients undergoing noncardiac surgery and identifies seven independent risk factors.

Stratification. The total places the patient in one of three bands, each with its own PPC rate and level of care.

Validation. ARISCAT was derived and validated within the 2,464-patient cohort, split into development and validation subsamples, with excellent discrimination: area under the ROC curve 90% in development and 88% in validation. It predicts respiratory infection, respiratory failure, bronchospasm, atelectasis, pleural effusion, pneumothorax and aspiration pneumonitis.

Obstructive sleep apnoea (OSA) affects 24% of men and 9% of women in the surgical population, and 80-90% are undiagnosed. Untreated OSA increases perioperative complications, including respiratory failure (2-3x risk), cardiac events and ICU admission, and undiagnosed OSA is a major cause of postoperative respiratory failure. The STOP-BANG questionnaire is the validated screening tool.

The questionnaire. Eight questions, one point for each yes, for a total of 0-8:

1. Snoring - do you snore loudly (louder than talking, or heard through a closed door)?
2. Tired - do you often feel tired, fatigued or sleepy during the daytime?
3. Observed apnoea - has anyone observed you stop breathing during sleep?
4. Pressure - do you have, or are you being treated for, high blood pressure?
5. BMI - is your BMI greater than 35 kg/m2?
6. Age - are you older than 50 years?
7. Neck - is your neck circumference greater than 40 cm, measured at the cricothyroid level?
8. Gender - are you male? Men carry twice the risk of OSA of women.

In the derivation study its sensitivity was 84%, 93% and 100% for an AHI over 5, over 15 and over 30.

The perioperative pathway. OSA care runs from 2-4 weeks before surgery to 72 hours after it.

The payoff. This pathway reduces OSA-related respiratory complications from 20% to under 5%.

Chronic obstructive pulmonary disease (COPD) affects 10-15% of patients over 65 undergoing orthopaedic surgery. It increases postoperative pulmonary complications 2-5 fold, particularly pneumonia and respiratory failure, and its severity guides optimisation.

View larger

View larger

Bronchodilators. Ensure adequate bronchodilation, starting 4-6 weeks before surgery for maximal benefit:

• Short-acting salbutamol as required, as the rescue inhaler
• Long-acting tiotropium (LAMA) daily if FEV1 is under 60%
• A LABA/LAMA combination if symptomatic despite a single agent
• Verify inhaler technique; incorrect use is a common error

Inhaled corticosteroids. Add ICS for frequent exacerbations: they are indicated if FEV1 is under 60% and there are 2 or more exacerbations a year. ICS reduce inflammation and exacerbation frequency but are not indicated for stable COPD without exacerbations. They are given as a LABA/ICS combination (for example fluticasone/salmeterol) and continued through the perioperative period.

Smoking cessation. A minimum of 4 weeks is essential: mucociliary clearance has improved by 4 weeks and pulmonary benefit is maximal at 8 weeks. Offer nicotine replacement or varenicline plus structured counselling, and document the pack-year history.

Stopping late. Cessation under 4 weeks may worsen sputum production, and the classic teaching is that it may paradoxically worsen outcomes through increased secretions. That concern rests largely on older observational data, and several subsequent analyses have not confirmed early harm. The pragmatic consensus is that any cessation is beneficial and should always be encouraged, with the largest complication benefit from cessation 4 or more weeks before surgery.

Pulmonary rehabilitation. Physiotherapy begins before surgery and continues daily afterwards:

• Incentive spirometry training, started preoperatively
• Breathing exercises and pursed-lip breathing
• Ambulation and building exercise tolerance
• Secretion clearance techniques

The payoff. This optimisation protocol reduces postoperative pulmonary complications in COPD patients by 40-50%.

View larger

Pulmonary function tests. PFTs rarely change management in elective orthopaedics unless disease is severe, and spirometry rarely reclassifies risk in a patient with good exercise tolerance, so they are not a routine screen. The indications are:

1. Known moderate-severe COPD without recent spirometry (over 6 months old), to assess current status
2. Unexplained dyspnoea disproportionate to comorbidities, to diagnose underlying lung disease
3. Smoking history over 40 pack-years with symptoms (cough, sputum, wheeze), to screen for COPD
4. High ARISCAT score with unclear aetiology, to identify modifiable factors
5. Planned lung resection, to assess candidacy (not applicable to orthopaedics)

Do not order them for asymptomatic patients with good exercise tolerance (able to climb 2 flights), for known COPD with recent spirometry on optimal therapy, or for low-risk peripheral orthopaedic surgery in healthy patients.

Global Epidemiology

Postoperative pulmonary complications are among the most common serious perioperative events worldwide, affecting roughly 2-5% of unselected surgical patients and a higher proportion of elderly and high-risk patients. OSA is estimated to affect up to a quarter of men and around 10% of women in the surgical population, the large majority undiagnosed at the time of surgery. COPD prevalence rises sharply with age and smoking exposure and is a leading global cause of morbidity, with substantial regional variation driven by tobacco use, biomass-fuel exposure and air quality.

Side-by-side Society Guidance

Registry and Surveillance Signals

• Large national surgical-quality registries (e.g. ACS NSQIP in the US and equivalent audit programmes in Europe) consistently identify pneumonia and unplanned reintubation as high-impact, partly preventable pulmonary complications, and are used to benchmark institutional performance.
• Surgical-quality collaboratives have shown that untreated OSA, rather than OSA per se, drives excess cardiopulmonary events - supporting screening that leads to actual CPAP treatment.

High- vs Limited-resource Practice Variation

• High-resource settings: routine STOP-BANG screening, ready access to CPAP/BiPAP, HDU/ICU step-up beds, formal smoking-cessation services and inhaled COPD therapy, continuous postoperative pulse oximetry.
• Limited-resource settings: emphasis on low-cost, high-yield interventions - clinical risk screening, smoking-cessation advice, incentive spirometry, chest physiotherapy, early mobilisation, head-up positioning, and pulse oximetry (a WHO-prioritised safety standard). Neuraxial anaesthesia is often preferred for lower-limb surgery where it both reduces pulmonary risk and conserves scarce ventilatory and critical-care resources.

Documentation Principles (Global)

• Record the pulmonary risk assessment (ARISCAT, STOP-BANG, COPD severity) in the preoperative note.
• Ensure informed consent reflects patient-specific pulmonary complication risk.
• Document any patient declining optimisation (smoking cessation, CPAP) and the risks discussed - unrecognised OSA and failure to optimise COPD are recurrent themes in adverse-event reviews internationally.

Mandatory sleep studies. Whether a positive STOP-BANG screen should trigger formal polysomnography before elective surgery remains debated. Most perioperative guidance favours proceeding with an empirical OSA-precautions pathway rather than delaying surgery, reserving sleep studies for selected high-risk or symptomatic patients.

Strength of the neuraxial benefit. The pulmonary advantage of neuraxial over general anaesthesia is consistent for pneumonia, but its magnitude varies between meta-analyses, and many constituent trials predate modern enhanced recovery and lung-protective ventilation. The benefit is clearest in high-risk, lower-limb surgery.