Sevoflurane basics

What it is (core concept)

Sevoflurane is a volatile (inhaled) anaesthetic agent delivered via a calibrated vaporiser into the breathing system.
Used for: inhalational induction (especially in children) and maintenance of general anaesthesia.
Often described as “non‑pungent” (less irritating to breathe than some other volatiles), so patients tolerate the mask better.
Key idea: the brain effect relates to the alveolar concentration (end‑tidal agent) rather than the vaporiser dial alone.

Key numbers to know (approximate, exam-friendly)

MAC (Minimum Alveolar Concentration) in adults: ~2% (varies with age; lower in older patients).
Blood:gas solubility: low (~0.6) → relatively fast onset and offset compared with more soluble agents.
Typical maintenance: often ~1–2% end‑tidal (adjust to clinical effect and analgesia).
Vaporiser output is in %; end‑tidal agent on the monitor is your best guide to delivered effect.

How it behaves clinically

Fast wash-in/wash-out: changes in dial settings are reflected relatively quickly in end‑tidal readings.
Causes dose-dependent: unconsciousness, reduced airway reflexes, reduced blood pressure (vasodilation), and some respiratory depression.
Provides hypnosis/amnesia but weak analgesia: you usually still need opioids/other analgesics for painful surgery.
Can be used with oxygen/air or oxygen/nitrous oxide (local practice dependent).

Inhalational induction (first-time practical steps)

Preparation: check machine, vaporiser filled/locked, scavenging connected, circuit leak test done, suction available, airway plan ready.
Monitoring before starting: ECG, NIBP, SpO2; capnography once breathing via circuit; consider agent monitoring early.
Explain simply to patient (or parent/child): “breathe normally through the mask; it may smell a bit sweet.”
Start with high fresh gas flow (e.g., 6–8 L/min) to speed wash-in; increase sevo gradually (or use a single-breath technique if trained and appropriate).
Maintain a good mask seal; watch for loss of eyelash reflex/regular breathing; support airway with jaw thrust as needed.
Be ready for airway obstruction/laryngospasm: have CPAP, jaw thrust, suction, and a clear escalation plan.

Maintenance: what to watch and how to adjust

Use end‑tidal sevo (and MAC display if available) plus clinical signs (BP/HR, movement, tearing) to guide depth.
If hypotensive: reduce sevo, check volume status, consider vasopressor; ensure adequate analgesia (pain can also drive tachycardia).
If patient “light”: check circuit/vaporiser, end‑tidal agent, fresh gas flow, leaks, and IV access/analgesia before simply turning the dial up.
Remember: high sevo can worsen hypotension and delay wake-up; balance with analgesia and other agents.

Airway effects and laryngospasm (common new-starter scenario)

Sevo is relatively non-irritant, but laryngospasm can still occur (especially during induction/emergence, secretions, airway stimulation).
Early signs: inspiratory stridor, paradoxical chest movement, no capnography trace, falling SpO2.
Immediate actions: remove stimulus, jaw thrust, 100% oxygen, apply CPAP, deepen anaesthesia (e.g., more sevo or IV agent if appropriate), suction if secretions/vomit.
If persistent/severe: call for help early; consider small dose suxamethonium and proceed to controlled ventilation/intubation per local protocol.

Cardiovascular and respiratory effects (safe basics)

Blood pressure commonly falls due to vasodilation; heart rate may rise slightly or remain stable.
Respiratory depression: reduced tidal volume and ventilatory response to CO2; support ventilation as needed.
Bronchodilation can be helpful in reactive airways, but airway obstruction from reduced tone is common during induction.
Always interpret physiology in context: depth of anaesthesia, analgesia, volume status, and surgical stimulation.

Emergence and recovery

Because it washes out relatively quickly, wake-up is usually smooth if analgesia and antiemetics are planned.
Common issues: agitation (especially children), nausea/vomiting, airway obstruction, coughing/bucking if too light with airway device in place.
Plan extubation/LMA removal based on patient and surgery; ensure adequate oxygenation/ventilation and airway reflex strategy.
Continue monitoring in recovery: SpO2, airway patency, pain, nausea; document agent used and any events (e.g., laryngospasm).

Safety, equipment, and environmental points

Vaporiser safety: correct agent, correctly seated/locked, adequate fill level; avoid tipping; check for leaks/smell of agent.
Scavenging must be connected and functioning to reduce staff exposure.
Agent monitoring (inspired/end‑tidal) and capnography are key safety tools—use them early and interpret trends.
Be cautious with high fresh gas flows for long cases (waste and environmental impact); reduce flows once stable if appropriate and local policy allows.

Special considerations (intro level)

Age: MAC decreases with age—older patients need less for the same effect.
Malignant hyperthermia (MH): sevoflurane is a triggering agent—avoid in known/suspected MH susceptibility and use a trigger-free technique.
Renal considerations: sevo metabolism produces fluoride; clinically significant renal injury is uncommon in routine practice, but avoid unnecessary prolonged very low-flow techniques unless you understand local guidance and monitoring.
Pregnancy/obstetrics: volatile agents relax uterus at higher doses; use only with appropriate supervision and indication.

What does MAC mean in simple terms?

– MAC is the end‑tidal concentration that prevents movement in 50% of patients to a surgical stimulus. – It’s a population guide; individuals vary. – MAC falls with age and rises with some stimulants (e.g., chronic alcohol).

Why do we look at end‑tidal sevo rather than just the dial setting?

– The dial is what you intend to deliver. – End‑tidal is what is actually reaching the lungs/brain (affected by fresh gas flow, ventilation, leaks, uptake, and circuit issues).

Typical sevo settings for induction and maintenance?

– Induction (mask): often higher dial settings with high fresh gas flow to speed onset (local practice varies). – Maintenance: commonly around 1–2% end‑tidal in adults, adjusted to effect and analgesia.

Patient becomes hypotensive after increasing sevo—what should I do first?

– Check depth/need: reduce sevo if appropriate. – Ensure adequate analgesia (don’t treat pain with more volatile alone). – Assess volume status/bleeding. – Consider vasopressor (e.g., metaraminol/phenylephrine per local practice) and ask for senior help if unstable.

The patient is moving/tachycardic—how do I troubleshoot “light anaesthesia” safely?

– Check end‑tidal agent and capnography trace. – Check vaporiser on/filled/locked and fresh gas flow. – Look for circuit leak/disconnection. – Consider inadequate analgesia (give opioid/regional/top-up local as appropriate). – Then adjust sevo if needed.

What are the early signs of laryngospasm during sevo induction?

– Stridor or silent airway with no ETCO2. – Increased work of breathing/paradoxical movement. – Falling SpO2. – Often triggered by secretions, airway stimulation, or light anaesthesia.

Immediate first-line actions for suspected laryngospasm?

– Call for help early. – 100% oxygen, jaw thrust, remove stimulus. – Apply CPAP. – Deepen anaesthesia (agent/IV) and suction if needed. – Escalate to suxamethonium if not resolving promptly or if severe.

Does sevo provide pain relief?

– Not reliably. – It provides hypnosis/amnesia; you still need analgesia for painful surgery (opioids, regional, paracetamol/NSAIDs if suitable).

When should I avoid sevoflurane?

– Known/suspected malignant hyperthermia susceptibility (use trigger-free technique). – If you cannot provide safe scavenging/monitoring. – Use caution and seek senior input in complex physiology (severe shock, critical aortic stenosis, etc.).