During rapid sequence intubation, physicians sometimes administer premedications, those drugs given before the induction agent and paralytic with the intention of reducing the patient's adverse physiologic responses to the subsequent medications and intubation. To be effective, all classes of premedications require at least three minutes of circulation time in the body before subsequent medications are given or intubation is performed.
This often limits their usefulness in emergent airway cases, but more importantly, none of these premedications should be considered standard of care. The biggest errors I see during critical airway encounters are focusing on premedications and complicated RSI sequences rather than focusing on basic principles and simple, universal RSI medication algorithms.
Infants and young children may develop bradycardia during RSI from laryngoscopy, hypoxemia, and direct medication effects. Infants and children may rarely develop profound bradycardia from succinylcholine, as can anyone, young or old, receiving a second dose of succinylcholine. It is often recommended that atropine be given “prophylactically” before succinylcholine is administered to any child under age 6.
Some sources recommend bradycardia to pretreat any infant under a year being intubated, regardless if succinylcholine is used. Potential risks of atropine include dysrhythmias and masking hypoxemia. There is little evidence to support or refute atropine pretreatment. The bottom line: Skip the atropine, but have it immediately available, and avoid succinylcholine entirely in kids when possible. If using succinylcholine, use large enough doses that re-dosing is never necessary.
In a patient with underlying stable reactive airways disease (i.e., status asthmaticus), intubation may provoke bronchospasm. There are no trials, however, that have looked at this rare population of patients.
The best current evidence is limited and somewhat contradictory. It is impossible to make any evidence-based recommendation on the role of lidocaine in this scenario. Pending further research, lidocaine may be considered as a pretreatment for any patient with a history of severe asthma, with detectable wheezing, and being intubated for status asthmaticus. The bottom line: Use 1.5 mg/kg for unstable asthmatics when time permits.
Minimizing Hypertension, Tachycardia
Patients with healthy brains tolerate elevations of intracranial pressure (ICP) very well. Consider that ICP goes up every time you cough or bend over to tie your shoes. Patients with unhealthy brains, particularly ischemic brain tissue or elevated intracranial pressure from head injury or stroke, is at constant risk of secondary injury from anything that decreases perfusion of injured neurons. Rises in ICP adversely affect cerebral perfusion pressure, and may rarely cause brain herniation.
Most patients also are tolerant of elevations of blood pressure and heart rate. Many undergoing emergent intubation are only alive because their sympathetic flight-or-fight system has kicked in full blast. Occasionally patients undergoing RSI, such as those with severe coronary artery disease, may not be so tolerant of tachycardia and hypertension.
The airway contains a wealth of nerve endings, and stimulating these with a laryngoscope may cause elevations of ICP. For this reason, a variety of premedications have been advocated to block or blunt these nerve stimulation mediated rises in heart rate, blood pressure, and ICP for patients at risk of secondary injury.
Among the most commonly used but least validated cerebro-protective premedications is lidocaine. There is little evidence that it produces the desired effects, at least when given intravenously, and there are legitimate concerns about hypotension and allergic reactions. Intubation should never be delayed to give lidocaine if the patient is moribund, combative, or hypoxemic because these conditions are far more dangerous to nervous system tissue than the rise in ICP associated with well-performed RSI.
Beta blockade for cerebral and cardiac protection is usually attempted only with esmolol (Brevibloc), a unique beta-blocker because it is administered intravenously, has a rapid onset and short duration, and is selective for the B1 receptor. Esmolol is among the best studied and validated agents to blunt the hemodynamic response to intubation though it is unknown if this truly equates to less elevation of ICP.
Esmolol is rarely used in emergency settings because of cost and concerns for precipitating hypotension or bronchospasm. Intravenous metoprolol (Lopressor) makes sense as an alternative for patients with severe coronary artery disease and hypertension, especially those who have missed routine oral doses of their beta-blockers, but this has not been validated. The bottom line: Don't bother with lidocaine, but beta-blockers are a nice touch for hypertensive patients with coronary artery disease, time permitting. Otherwise just say no.
Opiates, Defasciculating Agents
High-potency, fast-acting synthetic opiates, especially fentanyl, have been evaluated extensively for this indication for more than 25 years. The results are not surprisingly contradictory. A nonscientific meta-analysis suggests that doses higher than 2 mcg/kg, up to 6 mcg/kg, are most likely to be effective. Patients with normal to high blood pressure, such as most patients with isolated severe head trauma, will rarely become hypotensive from these doses. Use caution, however, in critically ill and sympathetic-dependent patients, such as those with severe multisystem trauma. These patients may be alive only because of their sympathetic drive. The bottom line: Opiates are generally safe, and provide analgesia if nothing else. Go for 3 mcg/kg if possible.
Fasciculations are chaotic contractions of muscle fibers that may be produced in some adult patients receiving succinylcholine. At least one small study of patients in the OR with cerebral pressure monitors demonstrated that blocking fasciculations minimized the elevation of ICP that occurred following succinylcholine administration.
Many studies have shown that fasciculations may be minimized or eliminated by pretreatment with a small dose of a non-depolarizing paralytic; rocuronium appears to be among the most effective. Succinylcholine also has been evaluated as its own defasciculating agent in small doses, but it appears less effective than a non-depolarizing paralytic. The clinical significance of this in acute elevations of ICP is unknown. The effect is time-dependent with up to five minutes required for maximal effect. Unfortunately, there also is some evidence that the effectiveness of succinylcholine is reduced following pretreatment, and the dosage may need to be increased.
The bottom line: On balance, defasciculation does not seem worth the drawbacks and delays, and is not recommended. If you are that worried about ICP and have a non-depolarizing agent available to use for pretreatment, you should probably just use it for the intubation and skip the succinylcholine altogether.