CHOICE OF INDUCTION AGENT

Different clinical scenarios lend themselves to the use of certain induction agents when rapid sequence intubation (RSI) is needed.

Head injury or stroke — In the patient with potentially elevated intracranial pressure (ICP) from head injury or stroke or other conditions, adequate cerebral perfusion pressure must be maintained to prevent secondary brain injury. This means avoiding elevations in ICP and maintaining adequate mean arterial pressure. For these reasons, etomidate or ketamine are used for induction of these patients.

If the patient is hypertensive at the time of induction, etomidate is preferable, as it will not further elevate the blood pressure. In normotensive or hypotensive patients, either agent can be used. In the severely hypotensive patient, ketamine is preferable. Ketamine's analgesic effects minimize the adverse sympathetic stimulation of laryngoscopy, while etomidate lacks such effect.

Pretreatment with a low dose of fentanyl (3 mcg/kg given three minutes before the induction agent) for patients with suspected elevated ICP, particularly if etomidate is to be used for sedation, to mitigate catecholamine release caused by laryngoscopy. If the patient is hypotensive, however, fentanyl should be avoided.

Midazolam and propofol have been used in head-injured patients, but the risk of hypotension-induced brain injury must be considered. If these agents are used, the dose should be reduced to minimize the risk of hypotension.

Status epilepticus — Midazolam is used for the rapid sequence intubation (RSI) of patients in status epilepticus. Reduced doses should be used in the unusual circumstance of seizure with hypotension.

Propofol is acceptable. Etomidate can cause myoclonus, and has a slightly higher rate of EEG-documented seizure activity compared with other medications, but may be used for RSI in status epilepticus when the patient manifests hemodynamic compromise. We suggest ketamine not be used because of its stimulant effects.

Reactive airway disease — For hemodynamically stable patients with severe bronchospasm requiring intubation, we suggest ketamine or propofol be used for induction, because of their bronchodilatory properties. Etomidate and midazolam are acceptable alternatives. In hypotensive patients, we prefer ketamine or etomidate. None of these agents causes histamine release.

Cardiovascular disease — We suggest etomidate for induction of the patient with significant cardiovascular disease requiring RSI. The hemodynamic stability it provides and the absence of induced hypertension make it preferable to other sedatives. Patients with coronary artery disease or suspected aortic dissection should receive fentanyl (3 mcg/kg) as a pretreatment agent to mitigate the catecholamine release associated with laryngoscopy and intubation.

Shock — We suggest ketamine or etomidate for induction of the patient in shock requiring RSI. 

Ketamine causes a sympathetic surge that may augment endogenous catecholamines but may also elevate intracranial pressure. Etomidate has been scrutinized because of its transient suppression of endogenous cortisol. More research is required in this area before a firm recommendation can be made. These issues are discussed in detail above.

Source: UpToDate