Anaesthetic Physiology & Drug Principles
Relate oxygen delivery, ventilation and drug effects to changing physiological reserve.
Quick revision ↓ Medical Dictionary
01Oxygen delivery
Tissue oxygen delivery depends on cardiac output and arterial oxygen content, which is influenced by haemoglobin and saturation. A normal saturation does not prove adequate delivery in severe anaemia or low flow. Interpret circulation and oxygenation together rather than treating one monitor as a complete assessment.
02Ventilation and gases
Alveolar ventilation affects carbon dioxide elimination, while oxygenation also depends on gas exchange and inspired oxygen. Hypoventilation may be masked initially by supplemental oxygen on pulse oximetry. Assess breathing and carbon dioxide where indicated instead of assuming a high saturation proves adequate ventilation.
03Drug effects
Anaesthetic drugs can affect consciousness, pain, circulation and breathing in different ways. Dose requirements vary with age, organ function, physiology and interacting medicines. Hypovolaemia or frailty can increase adverse effects, so administration requires trained titration and appropriate monitoring.
04Neuromuscular blockade
Neuromuscular blockers produce paralysis without providing unconsciousness or analgesia. Their use requires an anaesthetic and ventilation plan, appropriate monitoring and assessment of recovery. Apparent movement or its absence does not reliably establish awareness, pain control or complete recovery from blockade.
05Recovery and accumulation
Drug effect can outlast a procedure, especially with repeated dosing or impaired clearance. Review temperature, organ function and interactions in delayed recovery. Reversal agents have specific indications and limitations and do not remove the need for continued physiological observation.
High-Yield Revision
- Oxygenation and ventilation are different.
- Paralysis does not provide anaesthesia.
- Drug effects depend on physiology and clearance.
Common Pitfalls
- Equating normal saturation with normal tissue oxygen delivery.
- Assuming a reversal drug ends the need for monitoring.
References & Further Reading
Read the relevant guideline sections alongside these original clinical teaching cases. Local pathways, available services and individual patient factors determine care.
Reference review: 29 September 2026. Consult current local protocols for prescribing, procedures and escalation.