The term induction refers to the production of a deep level of unconsciousness. Rapid-sequence induction is the classic anesthesia term pertaining to the induction of anesthesia. In emergency medicine parlance, rapid sequence intubation (RSI) most commonly involves the combined administration of a sedative and a neuromuscular blocking agent to facilitate tracheal intubation ( Table 15-2). This technique is a component of standard airway management in the emergency department.11 Tracheal intubation follows laryngoscopy, while cricoid pressure is maintained to prevent aspiration. The principal contraindication is any condition preventing mask ventilation or intubation, since this may be the only way to ventilate a patient once the patient is paralyzed.
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Patient care is optimized if emergency physicians are adept with all methods for managing standard and difficult airways in nonfasting patients. Otherwise, the incidence of cricothyrotomy will exceed the current 1 to 2 percent of patients when RSI is selected and fails. 12 The prime goal is to avoid placing the breathing patient in the "can't ventilate, can't intubate" predicament.
Topical laryngeal and intravenous lidocaine (1.5 mg/kg) is a useful adjunct during RSI. Lidocaine suppresses coughing, and adverse airway reflexes. The efficacy of pretreatment with intravenous lidocaine during tracheal intubation of patients with reactive airway disease is unclear. Lidocaine levels achieved through an ET tube side port designed to administer medication may not be therapeutic, and will be lower than than those achievable intravenously or via the ET tube's main lumen.
There is no single initial agent of choice for achieving hypnosis and sedation during rapid-sequence induction in the ED. Pharmacotherapy must be tailored to the patient's unique circumstances. All of the commonly used agents offer distinct advantages in specific clinical conditions. Each agent, however, also has signifcant potential side effects, and specific contraindications (T§MeJ..5.-3).
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TABLE 15-3 Sedative Induction Agents
Thiopental (Pentothal) is a short-acting barbiturate sedative. An intravenous dose of 3.0 to 5.0 mg/kg will induce unconsciousness in 30 to 60 s and last 10 to 30 min. It is a widely used induction agent. Hypotension is commonly observed because of myocardial depression and venous dilatation. An ultra-short-acting barbiturate option is methohexital (Brevital). It is twice as potent as thiopental with onset of action in 60 s, and a duration of action of 5 to 7 min. These cerebroprotective agents should be avoided if systemic hypotension is a problem. This is a major consideration in the multiple trauma patient. Thiopental and methohexital can cause laryngospasm. A more feared but very rare complication is trismus, or masseter muscle spasm, which has also been reported with fentanyl and propofol, often with rapid bolus administration. Methohexital reduces the seizure threshold.
Another pharmacologic alternative is a short-acting benzodiazepine, such as midazolam (Versed) at a dose of 0.1 mg/kg. This drug has valuable amnesic and anticonvulsant properties and is reversible with the antagonist flumazenil. One disadvantage is that it has a wide therapeutic index.
Some agitated and combative patients can be reasoned with only by using rapid-acting major tranquilization. The combative multiple trauma patient is the most common example. Repeated intravenous aliquots of haloperidol (Haldol) 5 to 10 mg will eventually control severe agitation. Another butyrophenone, droperidol (Inapsine), titrated with aliquots of 2.5 to 5.0 mg IV, is a more potent and rapid-onset agent. Droperidol can blunt the cardiovascular response to intubation. Hypotension is rare, and there are fewer dystonic reactions than with haloperidol. Since it is a potent antiemetic, it is an ideal option as a premedication or for neuroleptanalgesia.
Ketamine, a phencyclidine derivative, is a potent bronchodilator to be considered particularly in difficult hypotensive or bronchospastic patients. This agent is indicated for refractory status asthmaticus. Since ketamine increases the blood pressure, it is an appropriate choice in hypovolemic patients. It can, however, increase the intracranial pressure (ICP) in patients with head injuries. Owing to its inotropic and chronotropic cardiac effects, it should be used with caution in the elderly. As ketamine wears off and consciousness returns, the patient may experience "emergence phenomenon" in the form of nightmares, visual hallucinations, and dissociative sensations. Benzodiazepines (e.g., midazolam 0.5 mg aliquots limited to a maximum of 4 mg) may attenuate this phenomenon.
Etomidate is a nonbarbiturate nonreceptor hypnotic. It significantly inhibits adrenocortical function with continuous infusion. For single administration as an induction agent, however, this is not a major concern. The advantages of etomidate in the ED include protection from myocardial and cerebral ischemia, minimal histamine release, a stable hemodynamic profile, and short duration of action. This is another drug to consider if patients are hypovolemic or with closed head injury. Myoclonus, nausea, and vomiting do occur, and seizure foci may be stimulated. The incidence of severe etomidate-induced myoclonus can be decreased by pretreatment with diazepam or fentanyl. Etomidate lacks analgesic efficacy and does not blunt the sympathetic response to intubation.
Another option is propofol, a highly lipophilic, rapid-acting sedative. During RSI, this agent provides effective hypnosis. Propofol has a more rapid onset of action than etomidate and a shorter duration of action. Some of the pharmacologic advantages include its anticonvulsant and antiemetic properties and its ability to lower intracranial pressure.
While not first-line selections, opioids are also potent reversible induction agents. Fentanyl has an onset of action of less than 2 min. The ideal dose is highly variable
(Table 15-3). Fentanyl is popular because of its sedative and analgesic properties. This agent provided the most neutral hemodynamic profile during RSI in a randomized double-blind study on sedatives and hemodynamics in the ED.13 Rapid injection of high doses may cause chest wall rigidity. A related compound, alfentanil, is more potent and has a more immediate onset of action.
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