15.2 Coexisting Disease I: Asthma, COPD, Obstructive Sleep Apnoea, Obesity, Liver and Renal Disease
Key Takeaways
A STOP-Bang score of 5-8 indicates a high probability of moderate-to-severe obstructive sleep apnoea; such patients are sensitive to opioids and sedatives and should use their CPAP device after surgery.
In obesity, induction doses of propofol are based on lean body weight, suxamethonium on total body weight, rocuronium on ideal body weight (with sugammadex on actual weight), and tidal volume on predicted body weight.
The Child-Pugh score (bilirubin, albumin, INR, ascites and encephalopathy) and the MELD score predict perioperative mortality in cirrhosis; elective surgery in Child-Pugh class C carries very high mortality and is usually avoided.
In chronic kidney disease, avoid suxamethonium if potassium is high, prefer atracurium or cisatracurium, avoid morphine and pethidine (active metabolites accumulate), and protect arteriovenous fistula arms.
In COPD, avoid hyperoxia in patients with chronic hypercapnia, use long expiratory times to limit gas trapping and intrinsic PEEP, and consider regional anaesthesia to reduce postoperative pulmonary complications.
15.2 Coexisting Disease I: Asthma, COPD, Obstructive Sleep Apnoea, Obesity, Liver and Renal Disease
Asthma
Assessment: frequency of symptoms, nocturnal waking, reliever use, previous hospital or intensive care admissions, recent oral steroids and current control. Elective surgery should be deferred if asthma is poorly controlled or after a recent exacerbation (often 4-6 weeks).
Optimisation: continue inhalers including on the day of surgery; give a bronchodilator before induction in symptomatic patients; consider a short course of oral steroids for poorly controlled disease.
Intraoperative management:
- Avoid airway instrumentation when possible (supraglottic airway or regional technique).
- Propofol and ketamine cause bronchodilation; volatile agents (sevoflurane) are bronchodilators; desflurane is irritant.
- Avoid histamine-releasing drugs (morphine, atracurium in large doses) where alternatives exist, and use NSAIDs only in patients known to tolerate them (aspirin-exacerbated respiratory disease affects about 5-10% of adults with asthma).
- Ventilate with a low rate, long expiratory time and moderate tidal volume to avoid gas trapping.
- Intraoperative bronchospasm: deepen anaesthesia, 100% oxygen, exclude mechanical causes (kinked tube, endobronchial intubation), salbutamol via the circuit, then intravenous salbutamol, magnesium, adrenaline or ketamine; consider anaphylaxis.
Chronic Obstructive Pulmonary Disease (COPD)
- Assessment: exercise tolerance, sputum, exacerbations, home oxygen, right heart failure (cor pulmonale), arterial blood gas if severe (baseline ), spirometry.
- Smoking cessation reduces wound and pulmonary complications; benefits increase with longer abstinence, but stopping at any time helps. Carbon monoxide levels fall within 12-24 hours.
- Ventilation: use a low respiratory rate and long expiratory time (I:E 1:3 or longer) to prevent dynamic hyperinflation and intrinsic PEEP, which reduce venous return and can cause hypotension and pneumothorax.
- Oxygen: in patients with chronic hypercapnia, target of about 88-92%, because high inspired oxygen can worsen hypercapnia by releasing hypoxic pulmonary vasoconstriction (V/Q mismatch) and through the Haldane effect, rather than solely by loss of hypoxic drive.
- Postoperative: regional analgesia, early mobilisation, physiotherapy, non-invasive ventilation for hypercapnic respiratory failure.
Obstructive Sleep Apnoea (OSA)
OSA is recurrent upper airway collapse during sleep. Severity is graded by the apnoea-hypopnoea index (AHI): mild 5-14, moderate 15-29, severe 30 or more events per hour.
STOP-Bang Screening
| Letter | Criterion |
|---|---|
| S | Snoring loudly |
| T | Tiredness during the day |
| O | Observed apnoeas |
| P | Pressure: treated or untreated hypertension |
| B | BMI above 35 kg/m² |
| A | Age above 50 years |
| N | Neck circumference above 40 cm |
| G | Male gender |
Score 0-2 low risk, 3-4 intermediate, 5-8 high risk.
Implications: difficult mask ventilation and intubation, sensitivity to opioids and sedatives, postoperative hypoxaemia (worst on nights 2-3 because of REM rebound). Patients should bring and use their CPAP device after surgery; use multimodal opioid-sparing analgesia, extubate fully awake in a semi-upright position, and monitor with continuous oximetry.
Obesity
Obesity is defined by body mass index (BMI): 30-34.9 class I, 35-39.9 class II, 40 or more class III (severe).
Physiological Changes
- Respiratory: reduced functional residual capacity (especially supine and anaesthetised), atelectasis, rapid desaturation, increased work of breathing and oxygen consumption; obesity hypoventilation syndrome (BMI above 30 with daytime above 6 kPa) indicates high risk.
- Cardiovascular: increased blood volume and cardiac output, hypertension, heart failure, atrial fibrillation, pulmonary hypertension.
- Gastrointestinal: reflux and fatty liver disease; gastric volume is not reliably increased in fasted patients.
- Venous thromboembolism risk is increased.
Weight Scalars for Drug Dosing
| Drug | Weight used | Reason |
|---|---|---|
| Propofol (induction) | Lean body weight | Initial distribution to the central compartment |
| Propofol (maintenance infusion) | Total or adjusted body weight | Larger volume and clearance |
| Thiopental, fentanyl, remifentanil | Lean body weight | |
| Suxamethonium | Total body weight | Increased plasma cholinesterase and extracellular fluid |
| Rocuronium, vecuronium | Ideal body weight | Limited distribution into fat |
| Sugammadex | Actual (total) body weight | Per licence |
| Low molecular weight heparin (prophylaxis) | Increased doses by weight band |
Practical Management
- Positioning: "ramped" with the external auditory meatus level with the sternal notch, head-up 25-30°, to improve laryngoscopy and FRC.
- Preoxygenation with head-up position and CPAP or high-flow nasal oxygen prolongs safe apnoea time.
- Ventilation: tidal volume 6-8 mL/kg predicted body weight, PEEP and recruitment manoeuvres.
- Regional anaesthesia may be technically difficult; use ultrasound and longer needles.
- Extubation fully awake, head-up, after full reversal confirmed with quantitative monitoring.
Liver Disease
Assessment of Severity
| Child-Pugh variable | 1 point | 2 points | 3 points |
|---|---|---|---|
| Bilirubin () | Below 34 | 34-50 | Above 50 |
| Albumin (g/L) | Above 35 | 28-35 | Below 28 |
| INR | Below 1.7 | 1.7-2.3 | Above 2.3 |
| Ascites | None | Mild | Moderate to severe |
| Encephalopathy | None | Grade 1-2 | Grade 3-4 |
Class A 5-6 points, B 7-9, C 10-15. Reported perioperative mortality for abdominal surgery has been about 10% (A), 30% (B) and 75-80% (C) in older series. The MELD score (bilirubin, INR, creatinine, often with sodium) is also used.
Anaesthetic Implications
- Hyperdynamic circulation with low systemic vascular resistance; portopulmonary hypertension and hepatopulmonary syndrome.
- Coagulopathy and thrombocytopenia, though the haemostatic balance is "rebalanced"; viscoelastic testing guides correction better than the INR.
- Drug handling: reduced albumin increases free fraction of acidic drugs; reduced hepatic clearance prolongs midazolam, morphine and aminosteroid relaxants; increased volume of distribution may raise initial requirements. Atracurium and cisatracurium (Hofmann degradation) and remifentanil (esterases) are useful.
- Hepatic encephalopathy: avoid benzodiazepines; sedation may precipitate it.
- Hepatorenal syndrome: functional renal failure from splanchnic vasodilation; avoid nephrotoxins and hypotension.
- Maintain hepatic blood flow by avoiding hypotension; isoflurane and sevoflurane preserve hepatic arterial flow better than older agents.
Chronic Kidney Disease (CKD)
CKD is staged by estimated glomerular filtration rate (G1-G5; G5 below 15 mL/min/1.73 m²).
Systemic effects: hypertension, accelerated atherosclerosis, left ventricular hypertrophy, anaemia (reduced erythropoietin), uraemic platelet dysfunction, metabolic acidosis, hyperkalaemia, delayed gastric emptying and renal osteodystrophy.
Perioperative management:
- Time surgery about 12-24 hours after dialysis, when volume and potassium are optimal; check potassium on the day.
- Suxamethonium raises potassium by about 0.5 mmol/L and should be avoided if potassium is already high.
- Prefer atracurium or cisatracurium; rocuronium and vecuronium action is prolonged. Sugammadex-rocuronium complexes are not recommended in severe renal impairment (creatinine clearance below 30 mL/min) because their excretion is renal.
- Opioids: avoid morphine (morphine-6-glucuronide and morphine-3-glucuronide accumulate) and pethidine (norpethidine causes seizures); fentanyl, alfentanil and remifentanil are safer.
- Avoid NSAIDs and nephrotoxins in patients with residual function.
- Protect arteriovenous fistulas: no cannulas or blood pressure cuffs on that arm; check the thrill after surgery.
- Uraemic bleeding responds to desmopressin, dialysis and correction of anaemia.
A patient with a BMI of 52 kg/m² is anaesthetised for laparoscopic surgery. Which dosing approach is appropriate?
Rocuronium according to total body weight, because it distributes widely into fat
Propofol induction according to lean body weight and suxamethonium according to total body weight
Suxamethonium according to ideal body weight, because plasma cholinesterase activity is reduced in obesity
Tidal volume of 8 mL/kg total body weight to recruit atelectatic lung
A patient with cirrhosis has bilirubin 60 micromol/L, albumin 26 g/L, INR 2.5, moderate ascites and grade 2 encephalopathy. What is the Child-Pugh class?
Class A (5-6 points)
Class B (7-9 points), suitable for most elective surgery
Class C (14 points)
It cannot be calculated without the serum creatinine
A haemodialysis patient with end-stage renal failure needs an urgent laparotomy. Which choice is most appropriate?
Morphine PCA for postoperative analgesia, because its metabolites are inactive
Suxamethonium for rapid sequence induction regardless of the serum potassium
A blood pressure cuff on the fistula arm, because the other arm has an arterial line
Cisatracurium, because Hofmann degradation does not need the kidneys
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