Cigarette Smoking - MD Anaesthesia pg exam - major question
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Cigarette Smoking - MD Anaesthesia PG Exam
Overview
Cigarette smoking is a major question in anaesthesia PGs because it affects virtually every organ system relevant to anaesthetic management - from preoperative assessment to intraoperative hazards to postoperative recovery.
Constituents of Tobacco Smoke
Tobacco smoke is a toxic mix of >7,000 chemicals. The three most anaesthesiologically relevant are:
- Nicotine - sympathomimetic stimulant
- Carbon monoxide (CO) - causes carboxyhemoglobin formation
- Tar/Irritants - cause airway inflammation and mucociliary dysfunction
Physiological Effects Relevant to Anaesthesia
1. Respiratory Effects
| Effect | Mechanism | Clinical Consequence |
|---|---|---|
| Increased carboxyhemoglobin (COHb) | CO binds Hb with 250x affinity vs O2 | Tissue hypoxia; left shift of OHb dissociation curve |
| Decreased mucociliary clearance | Irritant damage to cilia | Retained secretions, increased infection risk |
| Increased sputum production | Goblet cell hyperplasia | Airway obstruction |
| Airway hyperreactivity | Inflammatory mediators | Bronchospasm under GA |
| COPD (long-term) | Alveolar destruction | Impaired gas exchange, air trapping |
- COHb levels in chronic smokers: 5-15% (vs <1% in non-smokers)
- Elevated COHb causes tissue hypoxia - wound oxygen tension falls, impairing wound healing and resistance to infection
- Pulse oximetry falsely reads COHb as oxyhemoglobin - actual SpO2 is overestimated
2. Cardiovascular Effects
- Nicotine stimulates catecholamine release - causes tachycardia, hypertension, increased myocardial O2 demand
- Nicotine causes peripheral vasoconstriction
- Smoking is a major independent risk factor for coronary artery disease, atherosclerosis, and stroke
- Polycythemia (secondary to chronic hypoxia) - increased blood viscosity, thrombotic risk
- Up to 20-fold increased risk of esophageal and lung cancers
3. Pharmacological Interactions
- Smokers have enzyme induction (CYP1A2) - altered drug metabolism
- Nicotine has ganglionic stimulant effects - potential interaction with neuromuscular blocking agents
- Increased analgesic requirements reported in some studies
Pack-Year Correlation
- Pack-years = (packs smoked/day) x (years of smoking)
- Increasing pack-years = increasing frequency of postoperative pulmonary complications - a positive dose-response relationship
- Smokers without chronic lung disease already show increased airway reactivity, elevated COHb, and decreased mucociliary function
- Smokers with COPD have additional risks: cor pulmonale, right ventricular dysfunction, hypercapnic drive
Preoperative Smoking Cessation - Critical Exam Topic
This is the most heavily tested aspect in PG exams. Know the timeline precisely:
| Duration of Cessation | Effect |
|---|---|
| 12-24 hours | COHb returns to near-normal; nicotine levels fall; improved peripheral blood flow |
| 48 hours | COHb normalized; mucociliary clearance begins to improve; cardiovascular effects (tachycardia, vasoconstriction) start resolving |
| 2 weeks | Tracheal ciliary function recovering |
| 4-8 weeks | Significant reduction in postoperative pulmonary complications |
| >8 weeks (some say 4-6 weeks) | Optimal - reduction in wound complications, respiratory complications |
| Long-term | Reduced lung cancer risk; return toward normal lung function |
Key Controversy (Exam Favourite):
- Short-term cessation (<8 weeks) does NOT increase pulmonary complications - there is no "rebound" increase (Miller's Anesthesia)
- Some older teaching suggested short-term cessation paradoxically increased secretions - this is NOT supported by current evidence
- Therefore: stopping smoking at any time before surgery is beneficial - never advise a patient NOT to quit
- Optimal benefit for pulmonary complications requires 4-8 weeks cessation (Barash Clinical Anesthesia)
- Even 12 hours off smoking reduces CO and nicotine - improving oxygen delivery
Smoking Cessation Interventions:
- Intense programs with pharmacological aids (nicotine replacement therapy) + counseling for 3-4 weeks produce better results than brief interventions (Morgan & Mikhail)
- A meta-analysis showed preoperative smoking cessation for any surgery reduced overall postoperative complications by 41%, wound healing complications by 52%
- Nicotine transdermal patches and e-cigarettes during the perioperative period remain controversial
Intraoperative Considerations
- Airway hyperreactivity - smokers benefit from preoperative inhaled bronchodilators
- Increased risk of laryngospasm and bronchospasm at induction/extubation
- Regional anaesthesia preferred where feasible to avoid airway instrumentation
- Pulse oximetry may overestimate true oxygen saturation due to COHb
- Increased secretions - require more frequent suctioning
Postoperative Considerations
- Higher incidence of postoperative pulmonary complications - pneumonia, atelectasis, prolonged mechanical ventilation, reintubation
- Impaired wound healing - tissue hypoxia from COHb and vasoconstriction reduces wound O2 tension
- Higher risk of surgical site infection
- Importance of chest physiotherapy and early mobilization
- Patients must be strongly advised NOT to smoke postoperatively - smoking postoperatively prolongs tissue hypoxemia
Vaping / E-Cigarettes
- No large studies yet, but case reports document increased airway reactivity and complications under GA
- Pulmonary interstitial changes noted from e-cigarette use (EVALI - e-cigarette/vaping product use associated lung injury)
- Treat as high-risk airway for perioperative management (Barash Clinical Anesthesia)
Quick Recall Table for MCQs
| Question | Answer |
|---|---|
| COHb normalized after cessation | >12-24 hours |
| Nicotine effects abolished | 12-48 hours |
| Mucociliary clearance improved | 48 hours - 2 weeks |
| Optimal cessation for pulmonary complications | 4-8 weeks |
| CO affinity vs O2 for Hb | 250x greater |
| % of lung cancers attributable to smoking | ~90% |
| Relative risk of perioperative complications (smoker vs non-smoker) | 1.4 to 4.3x |
| Smoking cessation reduces complications by (meta-analysis) | 41% overall |
| COHb in chronic smokers | 5-15% (vs <1% in non-smokers) |
Sources:
- [Barash, Cullen & Stoelting's Clinical Anesthesia, 9e](Barash Clinical Anesthesia), pp. 1775-1776 & 3138
- [Miller's Anesthesia, 10e](Miller's Anesthesia), p. 7108
- [Morgan & Mikhail's Clinical Anesthesiology, 7e](Morgan & Mikhail), p. 2101-2102
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