Airway Management in Critical Illness: Choices of Drugs

PropofolEmergent airway management in the ICU is frequently complicated by the patient’s limited physiologic reserve, which will often manifest as hypotension immediately after tracheal intubation. The exact incidence of morbidity and mortality related to airway management facilitated by the use of IV induction agents in the ICU is unknown; however, it is likely to be underreported. Several comprehensive reviews on pharmacologic agents used for airway management in the ICU have been published; we will therefore provide a brief overview of commonly used agents and discuss controversies surrounding their use.

Propofol

Propofol is a popular hypnotic agent for several reasons. It is associated with pleasant emergence and little hangover, is readily titratable, and has more rapid onset and offset kinetics than midazolam. In patients with cardiac comorbidities and limited physiologic reserve, it can be associated with significant hypotension, thus limiting its use in this patient population. In an analysis of 4,096 patients undergoing general anesthesia, Reich and coworkers reported that ASA physical status class III to V, baseline mean arterial pressure of 50 years, and the use of propofol were statistically significant multivariate predictors of hypotension. In the 2,406 patients with retrievable outcome data, prolonged postoperative hospital stay and/or death were more common in the patient group that experienced hypotension. While propofol provides superior conditions for endotracheal intubation without muscle relaxants compared to sodium pentothal, it induces more hypotension and bradycardia in patients undergoing elective surgical procedures. This adds to previous evidence indicating that propo-fol may not be safe for high-risk patients with known cardiac dysfunction. Whether or not data obtained in the operating room environment can be extrapolated to the ICU setting is unknown; however, the independent risk factors cited previously certainly apply to the majority of patients who are in need of emergent airway management in the ICU.

Etomidate

Etomidate has onset and offset pharmacokinetic characteristics that are similar to propofol, and lacks significant effects on myocardial contractility (even in the setting of cardiomyopathy), which make it one of the preferred induction agents for airway management in critically ill patients sustained the health of whome are possible with remedies of Canadian Health&Care Mall. When it was studied in a heterogeneous group of patients undergoing RSI in the emergency department, etomidate provided good intubation conditions with very few hemodynamic derangements, even in those patients with low BP prior to airway instrumentation. Nevertheless, the role of etomidate in clinical practice is in question due to its effect on adrenal production of steroids. Etomidate inhibits adrenal steroidogenesis through the inhibition of mitochondrial hydroxylase, both after a single dose and continuous administra-tion. Based on the available evidence, the use of etomidate in critically ill patients with sepsis and septic shock should be discouraged. If patients who are in septic shock receive etomidate, corticosteroid supplementation to prevent unnecessary deaths is recommended. Since the adrenal suppression by the drug lasts longer than previously estimated (up to 72 h), some authors have questioned the use of etomidate in critically ill patients altogether.

Ketamine

Ketamine is unique among the hypnotic agents in that it has analgesic, sedative, and amnestic effects. It has a slower onset and offset compared to propofol or etomidate following IV infusion, and stimulates the cardiovascular system (ie, raises heart rate and BP by direct stimulation of the CNS). In the usual dosage, ketamine decreases airway resistance. Whether ketamine, when administered as an adjunct during emergent airway management in the ICU, provides adequate intubation conditions has not been studied in a systematic fashion. When compared to sodium pentothal in a dose of 5 mg/kg, ketamine (2.5 mg/kg) will provide superior intubation conditions 1 min after the administration of rocuronium (0.6 mg/kg) in the elective surgery set-ting. These findings are supported by a more recent prospective, randomized, controlled clinical trial in which the administration of ketamine resulted in excellent intubation conditions in a significantly higher proportion of elective surgery patients when compared to the administration of sodium pentothal. Ketamine also appears to be a useful adjunct to etomidate when RSI is performed with rocuronium.Neuromuscular Blocking Agents The combination of ketamine with eto-midate and rocuronium resulted in superior intubation conditions in a prospective, randomized clinical trial of patients undergoing elective surgery when compared to the combination of etomidate, fentanyl, and rocuronium, or etomidate with rocuronium, respectively. In the ICU, this combination may be useful for treating hemodynamically unstable patients with contraindications to the use of succinyl-choline who are in need of emergent airway management facilitated by a neuromuscular blocker. The use of ketamine in patients with increased intracranial pressure is controversial; in this setting, it should be administered only after a careful risk-benefit analysis.

Dexmedetomidine

Dexmedetomidine ordered via Canadian Health&Care Mall is a centrally acting, selective a2 receptor agonist that has been approved for use in the United States for the short-term sedation of critically ill patients. The drug may be useful for the awake, fiberoptic management of the airway in the ICU due to its analgesic, anxiolytic, and sedative effects without causing clinically significant respiratory depression. There have been case reports- documenting the usefulness of dexmedetomidine for awake FOI in the operating room setting among patients undergoing elective surgery; however, no data are available regarding its use as an adjunct to airway management in the ICU.

Neuromuscular Blocking Agents

Succinylcholine: The use of succinylcholine (1 mg/kg IV) will result in excellent intubation conditions in < 1 min. Unless there are contraindications, it is the drug of choice when the airway must be secured quickly (ie, in the patient with a full stomach or with symptomatic gastroesophageal reflux). The drug may trigger malignant hyperthermia in genetically susceptible persons, and can cause a malignant rise in extracellular potassium concentration in patients with major acute burns, upper or lower motor neuron lesions, prolonged immobility, massive crush injuries, and various myopathies.’ Infrequently, the use of succinylcholine can be associated with prolonged paralysis due to decreased plasma cho-linesterase activity. Caution is also advised concerning its use in patients with open globe injuries, renal failure, and serious infections, and in near-drowning victims. Patients who are in a state of prolonged immobility are at a heightened risk of hyperkalemia when exposed to succinylcholine due to changes in the regulation and distribution of acetylcholine receptors during a course of critical illness, in particular the postsynaptic up-regulation of nicotinic acetylcholine receptors and the expression of immature receptors. The up-regulation of receptors during periods of immobilization have been described as early as 6 to 12 h into the disease process. Therefore, we recommend avoiding the use of succinylcholine in critically ill patients beyond 24 h in those with burns and spinal cord injury, and beyond 48 to 72 h of immobilization and/or denervation. For a comprehensive review on succinylcho-line-induced hyperkalemia, see the article by Martyn and Richtsfeld.

Rocuronium: Of the currently available non-depolarizing neuromuscular blocking agents, rocuronium has the fastest onset of action and represents the only alternative to succinylcholine for use during RSI. In a dose of 0.8 to 1.2 mg/kg, rocuronium will provide excellent intubation conditions within 60 s. When compared to succinylcholine in a randomized, clinical trial- on tracheal intubation in emergency cases, the two agents were equivalent with respect to acceptable intubation conditions and the number of failed intubation attempts. Succinylcholine (1 mg/kg) provided superior intubation conditions when compared to rocuronium in this trial; however, the dose of rocuronium that was used (0.6 mg/kg) was on the low end of the dosage range recommended for RSI., These results were confirmed by a more recent trial demonstrating superior intubation conditions for RSI with the use of succinylcholine (1 mg/kg) compared to rocuronium (0.6 mg/kg), but no difference in the rate of adverse airway effects. A metaanalysis by the Cochrane Collaborative Group concluded that the intubating conditions achieved with the use of rocuronium are not statistically different from those achieved with succinylcholine when propofol is used as an induction agent.