|Pharmacologic Adjuncts to Intubation|
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Pharmacologic Adjuncts to Intubation
Laura R. Hopson Steven C. Dronen . 2004
Endotracheal intubation in the acute care setting presents a challenge distinct from that associated with intubation of the fasted, premedicated patient in the operating room (OR). The emergency department (ED) patient is frequently uncooperative and unstable and may have medical problems that are completely unknown to the treating clinician. Often within a matter of minutes, the clinician is expected to simultaneously accomplish many formidable tasks: assess and control the airway, as well as to diagnose and manage other life-threatening problems.
Table 5-1 -- Rapid-Sequence Induction Protocol
In 1979, Taryle and colleagues reported that complications occurred in 24 of 43 patients intubated in a university hospital ED. They called for improved house officer training in endotracheal intubation, as well as "more liberal use of the procedures used in the OR, such as sedation and muscle relaxation." Since the report of Taryle and others, training programs in both critical care and emergency medicine have been greatly expanded, resulting in significant improvement in the expertise of clinicians who provide acute airway management. Simultaneously, the use of established pharmacologic adjuncts to intubation previously available only in the OR has increased. In addition, new drugs that are potent, rapid-acting, and safer have been developed, giving the clinician greater ability to tailor therapy to specific clinical problems. Because of these developments, clinicians now may not only concentrate on the manual skill of intubation, but also skillfully use drugs to achieve specific objectives. These objectives may include (1) immediate airway control necessitating induction of anesthesia and muscle relaxation; (2) provision of analgesia and sedation to the awake patient; and (3) minimization of intubation adverse effects, including systemic and intracranial hypertension.
This chapter reviews the pharmacology and use of the drugs that are currently available to facilitate intubation in the acute care setting.
RAPID-SEQUENCE INDUCTION OVERVIEW
In the critically ill patient who may be hypoxic, hemodynamically unstable, agitated, uncooperative, and at risk of further deterioration, it is frequently necessary to gain immediate control of the airway. In recent years the technique of rapidly inducing anesthesia (rapid-sequence induction [RSI]) as a means of airway control has gained broad acceptance among emergency clinicians. RSI as practiced in the ED is a modification of the process initially described in the anesthesia literature and used to minimize the risk of aspiration in patients with full stomachs who require anesthesia. There is also a subtle but significant modification of the intent of RSI as practiced in the ED. Whereas anesthesiologists have used RSI to intubate patients requiring anesthesia, emergency clinicians commonly use RSI to induce anesthesia in patients requiring intubation.
Airway control in the ED is obviously not the same as planned intubation prior to general anesthesia in the OR. While some techniques and medications are similar, ED airway control cannot simply be accomplished by "calling anesthesia." The anesthesia team may serve as backup, but it is not standard that airway control await the arrival of an off-site team. What is standard is that the total process is accomplished with the personnel and resources available in the ED, with the prudent use of anesthesia specialists in select cases and for procedures and equipment not available in all settings. As described by Stept and Safar, general anesthesia RSI includes 13 steps, several of which are not practical or relevant to the ED setting. In the ED, RSI is begun by placing the patient on 100% oxygen, for at least 2 to 3, and ideally 5, minutes. The intent is to denitrogenize the lungs and build an oxygen reserve that will last several minutes should intubation prove to be difficult. Under optimal conditions, breathing 100% oxygen for 3 minutes has been demonstrated to maintain acceptable oxygen saturation for 8 minutes. The same study demonstrated that 4 maximal breaths of 100% oxygen from a face mask maintained acceptable saturation for 6 minutes. Comparable results should not be expected in the ED setting because of differences in the underlying health and cooperation of the patient population. While preoxygenation should be maintained for the longest period practical prior to beginning intubation, the ideal situation and circumstances are not always present, and clinical judgment is the deciding factor for this portion of RSI.
During the period of preoxygenation, the airway should be assessed to determine the likelihood of a difficult intubation while establishing an intravenous (IV) line, placing the patient on cardiac and pulse oximetry monitors and assembling all necessary equipment for oral intubation and potentially cricothyrotomy. A defasciculating dose of a non-depolarizing neuromuscular blocking agent is commonly recommended 2 to 3 minutes prior to administration of succinylcholine, although the advantages of this time-consuming step are poorly documented and generally overstated. General anesthesia is then rapidly induced with one of the agents discussed later in this section, followed immediately by muscle paralysis with succinylcholine at a dose of 1.5 to 2.0 mg/kg. Cricoid pressure is applied by an assistant as consciousness is lost. After the onset of adequate relaxation, orotracheal intubation is performed, and correct tube placement is verified. Cricoid pressure can then be released and ventilation with 100% oxygen begun. Mask ventilation prior to intubation is unnecessary if adequate preoxygenation occurs. In fact, mask ventilation should be avoided because of potential gastric distention and passive regurgitation. Mask ventilation should be used only if adequate oxygenation cannot be ensured and then should be performed gently in association with cricoid pressure. If a first intubation attempt is unsuccessful, bag-mask ventilation with cricoid pressure may temporize until a repeat orotracheal attempt or an alternative approach to intubation is made. In the event of failure to expeditiously accomplish orotracheal intubation, cricothyrotomy generally should be performed in order to secure the airway. The protocol for ED-based RSI is described in Table 5-1 .
Endotracheal intubation and RSI have also expanded beyond the ED into the prehospital setting. Using an RSI protocol of a sedative plus paralytic for non-cardiac arrest patients, success rates at intubation in the field have ranged from 92% to 98%, which is similar to rates achieved in the ED. As in the ED setting, without a full complement of medications, prehospital intubation becomes significantly more difficult with success rates dropping to approximately 60% largely due to patient combativeness, preexisting muscle tone, and intact airway protective reflexes.
The impact of prehospital intubation on outcome remains controversial. Gausche and colleagues compared prehospital bag-mask ventilation and endotracheal intubation for critically ill and injured pediatric patients. Their protocol did not include the use of sedatives or paralytics and had a 57% intubation success rate. A total of 820 subjects were analyzed for survival and neurologic outcome. The two groups were statistically equivalent (26% to 30% survival with 20% to 33% of those having a good neurologic outcome). Rates of vomiting, aspiration, and airway trauma were likewise similar. This study was performed in an urban environment with short Emergency Medical Service (EMS) transport times, which may limit its generalizability. Nonetheless, it has raised important and as yet unanswered questions about the necessity of prehospital endotracheal intubation if the airway is able to be adequately managed by other means.
In contrast, Winchell and Hoyt, in a retrospective review of 1092 blunt trauma patients with a Glasgow Coma Scale (GCS) score of less than 9, showed that prehospital intubation reduced mortality from 36% to 26% with the impact most pronounced among the most severely injured. As with the previous study, this one also evaluated orotracheal intubation without any pharmacologic adjunct with 66% of subjects able to be intubated in the field.
Bochicchio and colleagues compared brain-injured patient outcomes in patients with and without prehospital RSI.[18a] They found that patients receiving prehospital intubation versus those intubated at the hospital had a higher mortality rate and more ventilator days. Although the equivalence of the patient groups upon paramedic arrival is unknown, this study does suggest that prehospital RSI and intubation may adversely affect outcomes. Further prospective evaluation with evaluation of prehospital physiology and notation of preexisting aspiration will be required for resolution of this prehospital controversy.
The two general types of drugs used most commonly as part of RSI protocols are anesthetic agents and neuromuscular blocking agents. These are discussed in greater detail in the following section.