Sedation and neuromuscular blockade in the ICU.

A the key innovations of critical care medicine is treatment directed by continuously measured objective physiologic data. A prime example is the dosing of vasopressors using continuous measurements of systemic arterial pressure acquired from an indwelling arterial catheter. Similarly, the settings of mechanical ventilators are based on pressure and volume measurements of airway gases and arterial blood gas analysis. However, not all of the care provided in ICUs is so carefully monitored and titrated. This is especially true concerning sedation and analgesia, which are widely used in ICUs, as reported in this issue of CHEST (see page 496), by Arroliga and colleagues. These investigators analyzed data from a prospective, multicenter, international cohort of 5,183 adult ICU patients who received mechanical ventilation for 12 h in 361 ICUs. Sixty-eight percent of these patients received sedation while being mechanically ventilated, while 13% also received a neuromuscular blocker for at least 1 day. The latter patients had a 50% mortality rate. The sedated patients had longer durations of mechanical ventilation, weaning time, and ICU stays than nonsedated patients. These results are not unexpected since patients receiving sedation and neuromuscular blockade tend to be the most severely ill. However, there is always the lingering question as to whether sedation, analgesia, and administration of neuromuscular blockers contribute to the morbidity and mortality of such patients or are only indications of severe illness. Critically ill patients are constantly subjected to noxious stimuli, unpleasant experiences, and pain. They require sedatives, amnestics, and analgesics to reduce anxiety and suffering, to control pain, and to manage agitation. Despite the frequent use of these pharmacologic modalities, there is a lack of consensus as to the following: (1) when to administer these drugs, (2) which drugs to administer, (3) the depth of sedation required, and (4) how to monitor the depth of sedation and adequacy of analgesia. This lack of consensus is occasioned by the absence of welldesigned and conclusive studies examining these issues.1 Additionally, there are relatively few studies examining when and how to use neuromuscular blocking agents in critically ill patients.1 Much of the knowledge and many of the drugs used to sedate, reduce pain, and pharmacologically paralyze patients in the ICU have been adapted from the operating room environment.1 However, there are many differences between the critical care and operating room environments that make it difficult to transfer these experiences. In the operating room, there is usually the need for short-term deep anesthesia, amnesia, and total immobility in the face of intensely painful and noxious stimulation. This requires high doses of very potent, relatively shortacting drugs and, frequently, the use of muscle relaxants. This situation differs considerably from the ICU where there is a need for long-term sedation (rather than anesthesia) in patients who frequently have multiple organ system failure and hemodynamic instability. Total immobilization is only rarely needed. Ideally, ICU patients should receive the minimum amount of sedation (ie, sufficient sedation and analgesia for them to be pain free and to tolerate noxious stimuli [eg, endotracheal tubes and suctioning]) while still being safely arousable when stimulated. This is a tall order, considering the ever-changing clinical conditions and degrees of stimulation when patients can rapidly go from being asleep to undergoing chest physical therapy, which is a rather uncomfortable treatment.2 These situations require the ability to rapidly change the levels of sedation and analgesia to prevent oversedation and undersedation while still maintaining hemodynamic stability.3 However, instead of a titration approach to sedation, similar to that used for BP control, there is often an extrapolation of the operating room experience to the ICU, which may result in oversedation, deep paralysis, and additional hemodynamic instability. Continuous sedation has been associated with prolonged mechanical ventilation and longer hospital and ICU stays.4 Moreover, it is recommended that sedation be interrupted daily to permit the evaluation of the patient’s neurologic and respiratory functions. Such an approach leads to a reduction in the duration of mechanical ventilation and ICU stay.5,6 CHEST editorials