SEDATION IN THE INTENSIVE CARE UNIT

The major goals of sedation in the ICU are to provide anxiolysis and to improve the patient’s perceptual experience during this physiologically and emotionally stressful period (Box 30-1). Secondarily, sedation reduces the physiologic stress response and attendant cardiovascular work, may facilitate the maintenance of circadian rhythms, and lessens delirium and agitation. These goals are distinct from those associated with analgesia, which are the alleviation of pain through nonpharmacologic and pharmacologic means and to facilitate diagnostic and therapeutic procedures. Although sedation and analgesia are separate therapeutic goals usually provided by individual drugs, there is often synergism between anxiolytic and analgesic drugs; and some newer agents provide elements of both analgesia and anxiolysis, thus blurring the distinction in clinical practice.

The Society of Critical Care Medicine (SCCM) published guidelines for sedation,² which emphasize the need for the goal-directed delivery of psychoactive medications. Goal-directed sedation is supported by an increasing body of literature that shows that daily interruption of sedation, intermittent sedation, and sedation protocols all reduce the duration of mechanical ventilation and in some instances decrease ICU length of stay.³

There are several scoring systems available to assess a patient’s degree of sedation in the ICU and facilitate goal-directed therapy (Table 30-1). The Riker Sedation-Agitation Scale (SAS) was the first scale proved to be reliable and valid in critically ill adults. The SAS score is assigned by choosing a score from a seven-item scale that best matches a patient’s behavior. Another scale, the Motor Activity Assessment Scale (MAAS), has seven categories to describe patients’ behavior in response to stimulation. Like the SAS, it has been validated in critically ill adults. Most comparative clinical studies of sedation in critically ill patients have used the Ramsey scale. This scale is a six-point scale of motor activity that ranges from 1 (“patient anxious, agitated or restless, or both”) to 6 (“no response to light glabellar tap or loud auditory stimulus”) (Table 30-2). This scale was originally designed as a research tool but has been used for decades in clinical practice. Although no scientific consensus exists about which level of sedation using the Ramsey scale is optimal, recent literature frequently cites sedation goals of Ramsey 2 to 4, reflecting more realistic levels of sedation as part of goal-directed therapy. Other sedation scales that have been validated in critically ill adults include the Vancouver Interaction and Calmness Scale (VICS), the COMFORT Scale, and the Richmond Agitation-Sedation Scale (RASS). The SCCM’s guidelines do not advocate one specific scoring system. Instead, they advocate defining a specific sedation goal or endpoint for each patient and then regularly assessing and documenting the patient’s level of sedation in response to therapy.

Table 30-2 The Ramsey Sedation Scale

Sedative Agents

Neuromuscular Blocking Agents

Occasionally, some patients are so critically ill that they cannot be adequately sedated to receive appropriate care. This most commonly happens in an agitated patient requiring mechanical ventilation in whom the level of sedation would mimic a general anesthetic and whose hemodynamic status does not tolerate this degree of deep sedation. In these circumstances, neuromuscular blocking agents (NMBAs) are used.

If these medications are used, it cannot be overemphasized that the patient must be adequately sedated before the initiation of the NMBA. Once an adequate degree of sedation (usually to include an analgesic medication such as an opioid) is achieved, the patient is administered a bolus and then a continuous infusion of an NMBA. Although there are several drugs available, the drugs most commonly used in the ICU are the aminosteroidal compounds (pancuronium, vecuronium, and rocuronium) and the benzylisoquinolinium compounds (doxacurium, atracurium, and cisatracurium). Pancuronium and doxacurium are long-acting NMBAs, whereas rocuronium and vecuronium are intermediate-duration medications and atracurium and cisatracurium are short-acting medications, at least when given by bolus. Because these drugs are infused continuously, this attribute is not as important, but it does become important when the medication is discontinued and the physician is assessing the return of the patient’s neuromuscular function. When infusing these medications, a twitch monitor should be used and the physician should strive to achieve a train-of-four of one or two twitches.⁶ If there are no twitches observed, then the patient may be overdosed and may be at risk for development of acute quadriplegic myopathy syndrome (AQMS), a situation that develops in patients receiving NMBAs in which, when the medication is discontinued, the patient remains flaccid for much longer than would be predicted simply based on pharmacokinetics of the medications that were infused. The etiology of this syndrome is unknown but is most likely secondary to the destruction of myosin by the NMBA or one of its metabolites. Often, it is difficult to differentiate between AQMS and critical illness polyneuropathy, but in the latter profound muscle necrosis as is seen with AQMS would not be expected to occur.

Another way to minimize the likelihood of this syndrome is to institute a daily drug holiday. Not only is this beneficial in decreasing the incidence of AQMS, but in patients receiving opioids and benzodiazepines the incidence of drug withdrawal also decreases with the discontinuation of the medication. When using NMBAs in the ICU, the algorithm as shown in Figure 30-1 is recommended.

Figure 30-1 Use of neuromuscular blocking agents (NMBAs) in the intensive care unit. Monitor train-of-four ratio, protect eyes, position patient to protect pressure points, and address deep venous thrombosis prophylaxis. Reassess every 12 to 24 hours for continued NMBA indication. ICP = intracranial pressure.

(Redrawn from Murray MJ, Cowen J, DeBlock H, et al: Clinical practice guidelines for sustained neuromuscular blockade in the adult critically ill patient. Crit Care Med 30:142, 2002.)