Sedation is a vital component of critical care practice. When defining sedation in the intensive care unit, four words come to mind: analgesia, anxiolysis, hypnosis and amnesia. The choice of drugs used to reach these clinical endpoints and the assessment of adequacy of therapy have always been a substantial challenge for clinicians taking care of patients in the intensive care units. This paper will discuss the role of various sedation assessment tools to help clinicians provide a satisfactory level of sedation for their patients.

The goals of sedation are allowing the patient to be pain-free, calm, minimizing the recall of the stress and fear experienced during his ICU stay¹ and synchronizing breathing with mechanical ventilation if mechanical ventilation is warranted.² While numerous drugs are available, no one drug has been shown to be useful in all circumstances. Sedatives such as benzodiazepines and propofol provide anxiolysis, hypnosis and amnesia but do not offer adequate analgesic effects, whereas opiates offer potent analgesia. Therefore, combination therapy is frequently used to reach a satisfactory level of sedation.

The complications of undersedation (self-extubation, dysynchrony with the ventilator, severe anxiety, ischemic events,) and oversedation (respiratory depression, bradycardia, failure to wean from the ventilator, increased risk of infection) may have serious impact on a patient's outcome, leading to prolonged ICU stay and increased costs.^3-4 Therefore, the need to assess the depth of sedation is crucial and is one of the most challenging tasks for intensivists.

In clinical practice, both subjective and objective methods are used to assess a patient's level of sedation. The subjective methods used in ICU settings are mainly sedation scales. Among the 25 instruments developed, only 4 have been tested for both reliability and validity: the Ramsay scale, the SAS (Sedation-Agitation Scale), the MAAS (Motor Activity Assessment Scale) and the COMFORT scale.^5-9

The Ramsay scale, considered as the prototype by many investigators, is shown below:

Since the Ramsay scale was first published in 1974, the attempt to define and reach an "optimal level" of sedation has compelled investigators to develop several sedation scoring instruments.

All of the scales use observer ratings which are not normally examined for inter- and intra-observer differences. For instance, a clinician could document a patient as deeply sedated when another clinician could describe the same patient as unarousable or unresponsive. The reliability of such scales over time is diminished by this lack of consistency. Although the comparative analyses showed a high correlation among many of the subjective scales ⁵, they still have limitations. For example, the COMFORT scale studied only pediatric patients, whereas the MAAS studied surgical patients. Therefore, in an attempt to better quantify the depth of sedation, a presumably more objective assessment tool, the BIS monitor, was introduced.

The Bispectral Index (BIS) is a statistically-derived value created to describe changes in the EEG. The BIS monitor analyzes a raw EEG signal and converts it into an easy-to-use number: the BIS. When two adhesive sensors are applied to the forehead, the BIS monitor will display the BIS value that reflects the patient's level of consciousness. The BIS value ranges are shown in the table below:¹⁰

Recent studies showed that the BIS provided a good correlation with the loss of consciousness after administration of propofol, isoflurane, midazolam, but not alfentanil.¹¹ Hence, the BIS only measures the hypnotic state of the brain, not analgesia. This feature may allow a more "evidence-based" titration of sedatives and potentially limit the harmful consequences of either excessive sedation or uncontrolled agitation. However, only a few studies to date have shown that the use of the BIS monitor improves patient's outcome or decreases length of ICU stay or mortality; further investigation is needed.

One potential application of BIS monitoring is in patients undergoing neuromuscular blockade. Due to the inhibition of motor activity in these patients, clinicians are less able to assess sedation with subjective observational methods. Therefore, the BIS can provide valuable information about the level of sedation and help rational drug titration to ensure patient comfort. The BIS monitor is currently being used in the Burn Unit at MGH in patients receiving neuromuscular blockers.

Another promising role of the BIS monitor is in assessing the level of consciousness in brain trauma patients requiring barbiturate coma. A number of studies conducted on a very small number of patients evaluated the utility of the BIS as an outcome predictor of consciousness recovery in comatose patients. Patients who showed higher BIS scores during their ICU stay seemed to have better chance of recovery than patients with lower BIS scores.^12,13

The data using the BIS to monitor sedation in the ICU seem promising.^14,15,16 The BIS showed good correlation with subjective scales such as the Sedation-Agitation Scale¹⁷, but it still does not meet all goals for an ideal monitor. Larger randomized trials are needed to better validate its use in critically ill patients and investigate its impact on clinical outcome and costs in the intensive care unit.

In order to maintain a satisfactory level of sedation in critically ill patients, one may consider the following general recommendations:

1. Choose agents based on pharmacodynamic and pharmacokinetic properties and the patient's hemodynamics.

2. Provide analgesia before sedative therapy is initiated since pain causes anxiety and stimulates the sympathetic nervous system, which may compromise a patient's condition.

3. "Total paralysis can be a terrifying experience!"² Patients undergoing paralysis are unable to verbalize their pain, anxiety or fear. Sympathetic excess such as increases in heart rate, blood pressure and sweating are signs of inadequate sedation. Therefore, it is imperative to administer sedatives and analgesics prior to neuromuscular blockers.

4. Titrate pharmacotherapy to a defined clinical endpoint, not to a dosage regimen.

5. Reconsider daily the drug and the quality of sedation provided, and adjust the regimen to a patient's needs.

6. Consider using both subjective scales and objective methods (such as the BIS monitor) to assess the depth of sedation; more information is available to better guide and tailor therapy.

7. Communicate effectively among all caregivers to guide decision-making.

From Ramsay to the BIS, tremendous efforts have been employed to assess the depth of sedation/analgesia in the critically ill and, although the findings are promising, quantifying sleep remains a mastered art, not a science.

Author's note: I appreciate the careful review of this manuscript by Rick Dew, RPh and Harold DeMonaco, MS.

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