[Inhalation induction]

Abstract

Objectives: To clarify how pharmacokinetics explains the speed and quality of mask induction with sevoflurane alone or associated with adjuvants. To describe the various techniques to obtain adequate anaesthesia for laryngeal mask or tracheal tube insertion. To give the indications, contra-indications and complications of this technique.

Data sources: Data were obtained from Medline and authors clinical experience.

Data synthesis: Inhalation induction in adults affords rapid loss of consciousness similar to the intravenous route if high concentrations of sevoflurane are delivered to the patient. Time of laryngeal mask or tracheal tube insertion is longer but may be reduced by adding N(2)O and/or a low opioid dose. The interest of benzodiazepine as premedication is not established but is highly probable when considering its potentiating effect on halogenated agents. Without any adjuvant, inhalation induction maintains spontaneous ventilation better than propofol. This justifies favouring this technique when difficult intubation is anticipated. This technique is associated to less or similar cardiovascular effects than intravenous propofol. However, some patients exhibit dramatic tachycardia and arterial pressure increase that should lead to caution in cardiovascular disabled patients. This sympathetic hyperactivity occurs with epileptiform EEG activity that was never associated with postanaesthesia mental dysfunction. In aged or cardiac patients, by reducing sevoflurane concentrations from 8% to 2% (or by 2% decreasing steps), the cardiovascular effect of this inhalation induction is better than propofol. This technique is contra-indicated in HMS susceptible patients and those suffering from a myopathy, or patients with intracranial hypertension, a full stomach or active gastro-oesophageal reflux.

Conclusion: Inhalation induction in adults remains little used in common clinical practice. Technical improvement by adding opioids and education of anesthetists should increase the diffusion of this alternative method to intravenous induction of anaesthesia.