Special Feature

Sedation During Mechanical Ventilation

By Leslie A. Hoffman, RN, PhD

Clinicians have been criticized for prescribing too much, as well as too little, sedation for critically ill patients, especially patients who require mechanical ventilation. Over-sedation may prolong weaning from ventilatory support, increase ICU and hospital lengths of stay, and predispose to development of ventilator-associated pneumonia.1 Inadequate sedation predisposes the patient to pain and discomfort and can evoke a stress response that compromises recovery.2 Therefore, it is important to strive to achieve the proper balance when administering sedation to mechanically ventilated patients. This essay reviews ways to achieve this balance through bedside assessment, establishing patient oriented sedation goals, using reliable and valid scales to monitor goal achievement, and implementing protocols in ways that are likely to promote clinician acceptance.

Bedside Assessment: Investigate Before Sedating

Agitation is a common problem in ICU patients of all ages. It is also a problem with multiple potential causes. Causes that can lead to devastating problems, if missed, include hypoxemia, hypercarbia, hypoglycemia, visceral pain (eg, myocardial infarction, intestinal ischemia, tension pneumothorax), central nervous system infections, and drug intoxication and withdrawal. Other potential causes include other pain, uncomfortable bed positions, inadequate ventilator flows, fear, and anxiety.1 When patients are agitated or anxious, the first priority should be to conduct a thorough assessment to identify and treat any underlying physiologic or environmental causes. Non-pharmacologic measures may be appropriate, eg, reassurance, repositioning, and decreased light and noise levels.3 Withdrawal from alcohol or drugs can be an unrecognized cause of agitation. For this reason, all patients admitted to the ICU should be assessed for signs and symptoms of withdrawal on admission and for several weeks thereafter.2 Using this approach, sedatives become the end of a chain of thinking rather than the beginning. The complexity of the analysis requires a bedside assessment, rather than the more simple solution of a telephoned order.

Sedation Protocols—The First Key to Consistency

It is important that a sedation goal be established for each patient, regularly reassessed, and changed when indicated.2 The need for established goals is particularly important in academic institutions and other settings where frequent rotation of covering physicians is the norm. Beyond ensuring comfort, the most compelling goal is to improve ability to tolerate mechanical ventilation.1 For most patients, the optimum state is lightly asleep, or awake, alert and able to communicate, cooperate and tolerate the care regimen.

When patients are awake and arousable, they are better able to participate in their care and assist health team members in assessing their problems and progress.1 In a study designed to compare the sedative effects of midazolam and propofol, Kress and colleagues4 achieved this goal while sedatives were infusing in 60% of patients receiving morphine and midazolam. With a regimen of propofol and morphine, this percentage decreased to 30%. In some instances, heavy sedation is required, eg, during poorly tolerated mechanical ventilation modes such as inverse ratio ventilation and permissive hypercapnia or during neuromuscular blockade.

Treatment goals are most easily accomplished if they are directed by a protocol that identifies target sedation levels, the medications used to achieve these goals, administration route (such as IV bolus vs IV continuous infusion), and adjustments in dosage to maintain target sedation levels.1,3 In addition to ensuring a uniform approach, protocol-directed sedation has been shown to accomplish other important goals. Brook and colleagues5 randomly assigned 321 mechanically ventilated patients to receive protocol-directed sedation (n = 162) or non-protocol directed sedation (n = 159). Patients in the protocol-directed group required fewer days of mechanical ventilation and were discharged more quickly from the ICU and hospital. Patients randomized to protocol-driven sedation also had a lower tracheostomy rate, compared to non-protocol patients. Findings of this study are consistent with others that have shown benefits when protocols are used to guide care, eg, weaning from mechanical ventilation. The success of protocols appears to be related, in part, to their ability to facilitate more timely and consistent assessment and speed decision-making. They enable the bedside nurse and respiratory care team to implement care in a more efficient manner.

Regardless of their benefits, protocols may not be enthusiastically accepted. Some have suggested that change is best facilitated if supported by an "opinion leader." Kaufman and colleagues6 developed a nurse-driven sedation protocol and tested this premise using three different strategies: 1) daily bedside audit with 24 hour feedback by an ICU physician; 2) weekly audit and feedback by a RN opinion leader; and 3) twice weekly bedside audit with immediate feedback by a RN opinion leader. Use of IV sedatives was not significantly affected by the first 2 strategies. The third strategy substantially decreased overall sedation administration without negatively impacting patient comfort. The findings of this study suggest that protocol success can be enhanced by weekly audits and nursing feedback

Objective Measures of Sedation: The Second Key to Consistency

Sedation scales provide objective validation of subjective impressions regarding sedation goals. An ideal sedation scale should be simple to complete, accurately describe sedation or agitation using clearly defined categories and have documented reliability and validity.1-3 Of available sedation scales, the Richmond Agitation-Sedation Scale (RASS) appears to best meet these goals.7,8 The RASS uses a 10-point scale ranging from +4 (combative) to 0 (calm) to -5 (unarousable) based on observation of patient behavior and response to verbal and physical stimulation (see Table 1).1,8 It requires less than 20 seconds to perform8 and has been shown to be highly reliable when used by nurses and intensivists.

In 38 mechanically ventilated ICU patients, the RASS demonstrated excellent inter-rater reliability among nurses, intensivist physicians, and neuropsychiatric experts.8 RASS scores also demonstrated the ability to distinguish between levels of consciousness and correctly identified fluctuations within patients over time when comparisons were made between clinician scores and assessment by neurospsychiatric experts. The RASS also demonstrated excellent construct validity when compared with an attention screening examination, Glasgow Coma Scale scores, the quantity of medications administered, and ratings using bispectral electroencephalography (BIS). There was also high acceptance by nursing with 92% of respondents agreeing with the RASS scoring scheme and 81% agreeing that the instrument was effective in guiding goal-directed sedation therapy.8

There are several additional scales that have been used for sedation assessment. Although not intended for use as a clinical monitoring tool, the Ramsey Scale has been used extensively to monitor sedation levels in both clinical practice and research studies.8 This scale categorizes patients into 3 awake states and 3 asleep states, ranging from alert and agitated to asleep and unresponsive. The definitions of the various scores are not very useful, eg, the scale groups mildly anxious, agitated and severely agitated patients into one category. Notably, it has never been objectively validated. The Sedation-Agitation Scale expands the 6-point Ramsey scale by adding one point and more detailed descriptions.9 It has been shown to have acceptable reliability and validity in critically ill patients. However, it does not provide direction in crossover situations, eg, when patients appear sedated but become agitated once aroused. The Motor Activity Assessment Scale, adapted from the SAS, has also been shown to be reliable and valid when used in critically ill patients.10 However, it has not been extensively tested.

Strategies for Administering Sedatives: Less is More

In 1998, Kollef and colleagues11 reported findings of a study that indicated that continuous infusion of sedatives prolonged mechanical ventilation, ICU and hospital lengths of stay when compared with intermittent sedation strategies or no sedation. The study did not use a randomized design, which is a limitation, but did alert clinicians to previously unrecognized complications of continuous sedative infusion. In 2000, Kress and colleagues12 reported findings from a study in which patients were randomized to receive a daily interruption in sedative infusion, which allowed them to awaken, vs continuous infusions interrupted only at clinician discretion. For intervention patients receiving paralytic drugs, sedative infusions were stopped after administration of the paralytic drug had been stopped. The median duration of mechanical ventilation was significantly less in the group that awakened daily (7.3 vs 4.9 days), as was the median length of stay in the ICU (9.9 vs 6.4 days). In addition, complications (such as removal of the endotracheal tube) occurred less frequently in the daily awakening group. Findings of this study changed practice as they supported daily interruption of sedative infusion as a easy to implement, cost-effective intervention that could improve patient outcomes. Daily awakening has the additional advantage of allowing a daily neurologic examination and reevaluation of sedation needs.

While daily awakening may have short-term advantages, there were concerns regarding adverse psychological reactions. However in a follow-up study, Kress and colleagues13 reported fewer, rather than more, problems in the intervention group. None of the patients in the intervention group recalled awakening, despite daily attempts to awaken them. There were fewer signs of post-traumatic stress disorder in the intervention group and a lower incidence of chronic anxiety. The intervention group also had lower depression scores. Thus, in contrast to the initial perceptions of many, patients in the group that underwent daily awakenings fared significantly better than control patients on all measured variables.

Summary

Available evidence indicates that it is less important what drugs are administered than that they are properly titrated to optimize patient comfort and minimize complications using goal-directed therapy. Key components include a thorough bedside assessment when patient response indicates, goal-directed sedation, use of protocols, and objective assessment of sedation levels using validated, reliable instruments.

References

1. Siegel MD, et al. Clin Pulm Med. 2002;9(4):221-228.

2. Jacobi J, et al. Crit Care Med. 2002;30(1):119-156.

3. Kress JP, et al. Am J Respir Crit Care Med. 2002;166: 1024-1028.

4. Kress JP, et al. Am J Respir Crit Care Med. 1996;153: 1012-1018.

5. Brook AD, et al. Crit Care Med. 1999;27(12):2609-2615.

6. Kaufman DA, et al. Am J Respir Crit Care Med. 2004; 169:A630.

7. Sessler CN, et al. Am J Respir Crit Care Med. 2002; 166:13338-1344.

8. Ely EW, et al. JAMA. 2003;289:2983-2991.

9. Riker RR, et al. Crit Care Med. 1999;27:1325-1329.

10. Devlin JW, et al. Crit Care Med. 1999;27:1271-1275.

11. Kollef MH, et al. Chest. 1998;114:541-548.

12. Kress JP, et al. N Eng J Med. 2000;342:1471-1477.

13. Kress JP, et al. Am J Respir Crit Care Med. 2003;168: 1457-1461.

Leslie A. Hoffman, PhD, RN, Department of Acute/Tertiary Care, School of Nursing, University of Pittsburgh, is Associate Editor for Critical Care Alert.