Introduction

Most anesthesiologists take care of emergency patients in the operating room (OR) or as part of a “code team” in their hospital. Whether dealing with a surgical crisis in the OR or a trauma patient in the emergency department (ED), the anesthesiologist must have a plan for rapid and safe induction of general anesthesia. Box 18-1 is a list of potential pitfalls that can be encountered in the emergency situation. Whereas elective patients have a known medical history, optimized medications, hemodynamic stability, and an empty stomach, emergent patients may lack all of these things. Indeed, an older trauma patient brought to the ED with severe injuries might present anatomic challenges to intubation, might be hypovolemic, might have limited cardiac reserve, might be taking unknown long-term medications, have a potentially full stomach, and have a potentially unstable cervical spine. Induction of general anesthesia and successful endotracheal intubation will be critical to the long-term survival of this patient, but how are these best accomplished?

Options/Therapies

By definition, emergency induction is needed when the severity of the patient’s presentation does not allow for the normal preoperative anesthetic assessment. Nonetheless, the anesthesiologist must take advantage of every opportunity to learn about the patient’s condition while formulating a plan for his or her care. Box 18-2 is a list of suggested questions. At a minimum, the anesthesiologist should determine why the patient requires emergent induction (e.g., urgent surgery for hemorrhaging, airway protection or ventilatory support, or septic shock) and as much about the patient’s history as time allows. Usually this information can be gleaned from the physicians or nurses already caring for the patient. If possible, these providers should be asked whether the patient has any allergies and what medications the patient is taking. A quick look at the medical record may be helpful. Any recent anesthetic record is especially useful, as it will provide information about the ease of intubation and the patient’s tolerance of medications. A brief survey of relevant laboratory values can also help to avoid pitfalls: hematocrit (hemodynamic stability), creatinine (acute or chronic renal failure), arterial blood gas (ventilatory difficulties, acidosis), serum potassium (potential for hyperkalemia), and coagulation studies (potential for bleeding).

Physical examination of the patient must be abbreviated but is still important. It takes only seconds to assess the patient’s level of consciousness by asking the patient to extend his or her neck and open the mouth, which also provides valuable insight into the airway anatomy and potential for a difficult intubation. Vital signs should be noted. New sources of pain, external hemorrhaging, or visible deformity should also be recorded.

Once this brief survey is accomplished, the anesthesiologist is ready to consider various options. Box 18-3 lists important questions that should be addressed. The first has to do with optimizing the emergency induction. If the patient is not in the OR, success can sometimes be improved by moving there, assembling more equipment, or calling for assistance but only if the benefit of doing so will outweigh the risk of delay to the patient. The second consideration is the manner of anesthetic induction and the technique for securing a definitive airway. Although a rapid-sequence approach leading to direct laryngoscopy and endotracheal intubation will most often be correct, there are situations where a more gradual induction or even awake fiberoptic intubation may be more appropriate. Finally, the anesthesiologist must consider the medications to be used, and the dose of each.

Evidence

There is substantial evidence to support the use of rapid-sequence intubation in most cases in which emergency induction is required. Neuromuscular blockade provides the best intubating conditions on the first approach to the airway and leads to the highest “first pass” success rate. A rapid transition from awake to anesthetized reduces the patient’s exposure to intermediate stages of anesthesia in which complications such as laryngospasm, pain, hemodynamic lability, combative behavior, and aspiration are most likely to occur. Several large case series have examined the use of neuromuscular blockade to facilitate rapid-sequence intubation outside of the OR, with highly favorable results. A recent retrospective study from my institution documented the need for surgical airway salvage in only 21 of 6088 patients who underwent rapid-sequence induction within 1 hour of hospital arrival, which yielded a rate of 0.3%.

The choice of neuromuscular blocking agent is determined by the clinical situation and the practice environment. Succinylcholine is the most commonly used medication for rapid-sequence intubation because it produces the most rapid onset of paralysis and thus the best intubating conditions in the shortest amount of time. Succinylcholine also has the advantage of being short acting, with return of neuromuscular function in approximately 10 minutes after usual doses. In the elective situation when a difficult airway is unexpectedly encountered, this may be beneficial in allowing the patient to wake up and resume spontaneous ventilation while other plans are considered. This will seldom be an advantage during emergency induction, however, because the conditions creating the emergency will still be present. Rapid resolution of paralysis after succinylcholine administration may enable subsequent neurologic assessment. Succinylcholine is contraindicated in patients with neuromuscular conduction abnormalities of greater than 24 hours’ duration (e.g., spinal cord injury, amyotrophic lateral sclerosis, Guillain-Barré syndrome) and in patients with recent severe burns. Excessive numbers of postsynaptic choline receptors can cause a fatal hyperkalemia in these patients. Although at least one article has downplayed the potential for succinylcholine to trigger malignant hyperthermia in susceptible patients, the catastrophic nature of this complication makes it prudent to avoid the use of succinylcholine in patients potentially at risk. Succinylcholine will also produce transient elevation of intracranial and intraocular pressure. This has the theoretic potential to put some patients at risk, although it has never been proved in the scientific literature. In reality, avoidance of succinylcholine may make intubation harder, thus contributing to hypoxia during induction and intubation that is of far more relevance to the patient’s outcome.

Rapid-acting nondepolarizing neuromuscular blocking agents can produce intubating conditions almost as good as succinylcholine, almost as quickly. The use of high-dose rocuronium or vecuronium is appropriate when contraindications to succinylcholine exist, with the understanding that the patient will remain paralyzed for a longer period of time. In most emergent situations this is not a major concern, and even if a difficult intubation is encountered, it is unlikely that waking the patient up will be a viable option.

Although complete neuromuscular blockade is the key to a rapid transition to mechanical ventilation and should be used in almost all emergency inductions, the use of sedative/hypnotic agents should be approached on a case-specific basis. Amnesia to the events of induction and intubation is desirable, as is prevention of extreme sympathetic stimulation in response to airway manipulation. Some degree of sedation is therefore appropriate in almost all emergency inductions, yet careful titration is required. Patients in shock have increased sensitivity to the central effects of sedative agents: less medication is required to achieve a similar depression in awareness. Hypovolemia in patients is especially troublesome. Reduction in compensatory sympathetic outflow, reduced cardiac filling in association with positive pressure ventilation, and the direct vasodilatory and negative inotropic effects of sedative agents may all lead to profound hemodynamic instability and cardiac arrest after normal induction doses of thiopentol, propofol, or midazolam.

A number of recent reports have advocated the use of etomidate for induction of anesthesia in emergency situations because it is not a vasodilator or negative inotrope. As with ketamine, however, a normal induction dose of etomidate may still lead to profound hypotension in patients in hypovolemic shock because of interruption of sympathetic outflow. Several recent reports have also described the subsequent development of adrenal insufficiency in patients receiving even single doses of etomidate for emergency induction.

The choice of induction agent is thus less important than the dose selected. In general, the least amount consistent with amnesia is appropriate, unless there is reason to be concerned about a hypertensive response to intubation (e.g., a patient with an isolated traumatic brain injury has the potential for increased intracranial hemorrhage). Additional doses can always be given if the first dose is well tolerated. Familiarity with the medication chosen is also important, enabling greater precision in titration. For example, deaths attributed to the use of sodium thiopental in soldiers injured at Pearl Harbor were the result of unfamiliarity with the drug rather than with its specific function.