Using Bispectral Index Monitoring to Detect Potential Breakthrough Awareness and Limit Duration of Neuromuscular Blockade

Optimizing clonidine dosage for sedation in mechanically ventilated children: A pharmacokinetic simulation study

BACKGROUND

Clonidine is in widespread off-label use as a sedative in mechanically ventilated children, despite limited evidence of efficacy. A variety of dosage regimens have been utilized in clinical practice and in research studies. Within these studies, clonidine has inconsistently shown useful sedation properties. One of the reasons attributed to the inconsistent signs of efficacy is suboptimal clonidine dosing.

AIMS

This study aims to propose a target plasma concentration and simulate clonidine pharmacokinetics (PK) in a cohort of mechanically ventilated children to evaluate the adequacy of clonidine dosage regimens used in clinical practice and research studies.

METHODS

A literature search was undertaken to identify a clonidine pharmaockinetic-pharmacodynamics (PKPD) model, from which a target concentration for sedation was defined. Using a previously published PK model, the projected plasma concentrations of 692 mechanically ventilated children (demographics taken from a recent study) were generated. Doses from recently published clinical studies were investigated. Adequacy of each regimen to attain therapeutic clonidine plasma concentrations was assessed.

RESULTS

A target plasma concentration of above 2 µg/L was proposed. Nine dosage regimens (four intravenous boluses, four intravenous infusions, and one nasogastric route boluses) were evaluated ranging from 1 µg/kg eight hourly intravenous boluses to a regimen up to 3 µg/kg/hr continuous intravenous infusion. Regimens with a loading dose of 2 µg/kg followed by variable continuous infusion of up to 2 µg/kg/hr titrated according to sedation score appear most suitable. Doses should be halved in neonates.

CONCLUSION

The variety of dosage regimens in the previous studies of clonidine along with difficulties in the conduct of interventional studies may have contributed to the lack of efficacy data to support its use. Simulations of clonidine plasma concentrations based on known population pharmacokinetic parameters suggest a loading dose followed by higher than current practice maintenance dose infusion is required to achieve adequate steady-state concentrations early in treatment. Further PKPD studies will aid in the determination of the optimal clonidine dosage regimen.

Perceived safety and efficacy of neuromuscular blockers for acute respiratory distress syndrome among medical intensive care unit practitioners: A multicenter survey

PURPOSE

Neuromuscular blocking agents (NMBAs) are frequently used in patients with acute respiratory distress syndrome (ARDS). The purpose of this survey is to describe providers' knowledge and perceived efficacy and safety of NMBAs in patients with ARDS.

MATERIALS AND METHODS

We performed a prospective, multicenter survey of medical intensive care unit intensivists, fellows, nurse practitioners (NPs), physician's assistants (PAs), and pharmacists at 5 tertiary care centers between July 2012 and May 2013.

RESULTS

A total of 335 surveys were sent to providers, with a 47% response rate. Ninety-eight percent of providers correctly identified that NMBAs lack anxiolytic and analgesic properties. The effect of end-organ damage on NMBA clearance was less commonly identified by NPs/PAs for both hepatic (P=.0077) and renal (P=.0272) dysfunction compared with physicians. More NP/PAs identified the association of consciousness with the use of NMBAs than physicians (P=.047). Forty-two percent of prescribers reported always or frequently using continuous-infusion NMBAs in patients with severe ARDS, with 89% initiating NMBAs because of ventilator dyssynchrony. Prescribers perceived continuous NMBAs to be more effective than inhaled prostaglandins (74% vs 56%) in severe ARDS but less safe (45% vs 84%). Train of 4 was identified by 54% of prescribers as their primary method for titration.

CONCLUSION

Providers are knowledgeable about NMBAs, but educational opportunities exist. Perceptions about the efficacy and safety of NMBAs varied among prescribers, and inconsistencies existed in the prioritization of management strategies for ARDS.

Role of the Bispectral Index in Sedation Monitoring in the ICU

Objective:

To review and critique evidence for the use of the bispectral index (BIS) in intensive care unit (ICU) patients.

Data Sources:

A computer search of English-language articles in MEDLINE (1966–July 2005), International Pharmaceutical Abstracts (1971–July 2005), and Scientific Citation Index Expanded (1980–July 2005) was conducted. A manual search of abstracts was also performed using the key search terms BIS, sedation, and critical care.

Study Selection and Data Extraction:

Case series, letters, editorials, and clinical studies that evaluated BIS in ICU patients were considered for inclusion.

Data Synthesis:

Nineteen studies comparing the BIS with sedation scales were evaluated, revealing that the BIS trends lower with increasing sedation. The BIS appeared to correlate better when sedation scores were grouped rather than individual values. However, correlations between BIS and subjective scales were low in most studies (r2 0.21–0.93). Additionally, there was poor correlation between drug dosage and the BIS. Randomized, controlled trials demonstrating improved outcomes with BIS monitoring have not been reported.

Conclusions:

Interpreting literature on the usefulness of the BIS in the ICU is difficult for reasons that include heterogeneous populations, different methods of collecting BIS data, and use of different versions of BIS software and hardware. Outcomes data are lacking. The 2002 Society of Critical Care Medicine Sedation Guidelines recommendation that more data are needed before the BIS should be used routinely in the ICU remains unchanged. We recommend that further studies be conducted to determine the optimal method of obtaining BIS data and evaluate the impact of the BIS on relevant patient outcomes.

Arousal time from sedation during spinal anaesthesia for elective infraumbilical surgeries: Comparison between propofol and midazolam

Background and Aims:

Studies have already compared propofol and midazolam as sedatives during regional anaesthesia. A few studies have focused on recovery characteristics and very few have utilised both instrumental and clinical sedation monitoring for assessing recovery time. This study was designed primarily to compare arousal time from sedation using propofol with that of midazolam during spinal anaesthesia for infraumbilical surgeries, while depth of sedation was monitored continuously with bispectral index (BIS) monitor. The correlation between the BIS score and observer's assessment of awareness/sedation (OAA/S) score during recovery from sedation was also studied.

Methods:

A total of 110 patients were randomly assigned to receive either propofol (Group P, n = 55) or midazolam (Group M, n = 55). Patients in the Group P received bolus of propofol (1 mg/kg), followed by infusion at 3 mg/kg/h; Group M received bolus of midazolam (0.05 mg/kg), followed by infusion at 0.06 mg/kg/h and titration until BIS score 70 was achieved and maintained between 65 and 70. OAA/S score was noted at BIS 70 and again at BIS 90 during recovery. The time to achieve OAA/S score 5 was noted. Spearman's correlation was calculated between the arousal time from sedation and the time taken to reach an OAA/S score of 5 in both the study groups.

Results:

Arousal time from sedation was found lower for Group P compared to Group M (7.54 ± 3.70 vs. 15.54 ± 6.93 min, respectively, P = 0.000). The time taken to reach OAA/S score 5 was also found to be lower for Group P than Group M (6.81 ± 2.54 min vs. 13.51 ± 6.24 min, respectively, P = 0.000).

Conclusion:

A shorter arousal time from sedation during spinal anaesthesia can be achieved using propofol compared with midazolam, while depth of sedation was monitored with BIS monitor and OAA/S score. Both objective and clinical scoring correlate strongly during recovery from sedation.

Bispectral index score and observer's assessment of awareness/sedation score may manifest divergence during onset of sedation: Study with midazolam and propofol

Background:

Correlation between the clinical and electroencephalogram-based monitoring has been documented sporadically during the onset of sedation. Propofol and midazolam have been studied individually using the observer's assessment of awareness/sedation (OAA/S) score and Bispectral index score (BIS). The present study was designed to compare the time to onset of sedation for propofol and midazolam using both BIS and OAA/S scores, and to find out any correlation.

Methods:

A total of 46 patients (18-60 years, either sex, American Society of Anesthesiologists (ASA) I/II) posted for infraumbilical surgeries under spinal anaesthesia were randomly allocated to receive either injection propofol 1 mg/kg bolus followed by infusion 3 mg/kg/h (Group P, n=23) or injection midazolam 0.05 mg/kg bolus followed by infusion 0.06 mg/kg/h (Group M, n=23). Spinal anaesthesia was given with 2.5 ml to 3.0 ml of 0.5% bupivacaine heavy. When sensory block reached T6 level, sedation was initiated. The time to reach BIS score 70 and time to achieve OAA/S score 3 from the start of study drug were noted. OAA/S score at BIS score 70 was noted. Data from 43 patients were analyzed using SPSS 12 for Windows.

Results:

Time to reach BIS score 70 using propofol was significantly lower than using the midazolam (P<0.05). Time to achieve OAA/S score 3 using propofol was comparable with midazolam (P=0.358).

Conclusion:

A divergence exists between the time to reach BIS score 70 and time to achieve OAA/S score 3 using midazolam, compared with propofol, during the onset of sedation.

Impact of bispectral index monitoring on sedation and outcomes in critically ill adults: a case series

In situations in which clinical assessment of sedation level is compromised, such as deep sedation/analgesia with and without neuromuscular blockade (NMB), electroencephalogram-based monitoring may potentially assist in achieving balance between inadequate and excessive levels of sedation. To validate the bispectral index (BIS) for use in clinical practice, correlation and possible differences in outcome using clinical assessment versus clinical assessment augmented by electroencephalogram-based monitoring were determined. BIS monitoring was decisive in ICU care in 9 of 15 patients in this series. The most significant potential benefit was obtained in the subset of patients receiving NMB.

Bispectral index-controlled anaesthesia for electroconvulsive therapy*

BACKGROUND

The suggested induction dose of methohexital for electroconvulsive therapy (ECT) varies widely influencing efficacy of ECT and safety of anaesthesia. Bispectral index (BIS), a monitor of consciousness, may be useful to assure adequate hypnosis with optimized methohexital dose.

METHODS

Patients with medically resistant major depression (ICD10), scheduled for multiple ECT's, were studied. Depth of anaesthesia was BIS controlled. ECT was not performed until BIS dropped below 50. Initially anaesthesia was induced with methohexital 1.0 mg kg(-1), and stepwise reduced by 0.1 mg kg(-1) during consecutive treatments. If BIS did not drop below 50, the methohexital was supplemented by further boluses of 0.5 mg kg(-1), until the desired level of hypnosis was reached. The adequacy of the anaesthetic recommendation for methohexital (1.0-1.5 mg kg(-1)) as well as the psychiatric recommendation (0.75-1 mg kg(-1)) was investigated.

RESULTS

One-hundred and nine ECT's in 14 patients were studied. The recommended anaesthetic dose (1.0-1.5 mg kg(-1)) was inadequate in 40% of the treatments, with 12% exceeding 1.5 mg kg(-1), and 28% below 1.0 mg kg(-1). Psychiatric recommendation (0.75-1.0 mg kg(-1)) was inadequate in 49%, with 39% exceeding 1.0 mg kg(-1) and 10% undershooting at 0.75 mg kg(-1).

CONCLUSIONS

Methohexital for ECT showed a great variability, exceeding as well as undershooting the dosage recommendations widely. BIS monitoring may be useful to secure adequate hypnosis during muscle relaxation and treatment and may optimize ECT efficacy.

Patients’ Recollections of Therapeutic Paralysis in the Intensive Care Unit

• Background Neuromuscular blocking agents used for therapeutic purposes, such as facilitating mechanical ventilation and relieving life-threatening agitation, paralyze patients but leave them fully conscious. Aggressive sedation or analgesia is necessary to reduce awareness, relieve fear, produce comfort, decrease anxiety, induce unconsciousness, and minimize possible complications such as posttraumatic stress syndrome. Little information is available on the extent to which patients experience awareness during therapeutic paralysis.

• Objectives To determine and describe the remembered experiences of critical care patients who were given neuromuscular blocking agents and sedatives and/or analgesics to facilitate mechanical ventilation, improve hemodynamic stability, and improve oxygenation.

• Methods A phenomenological approach with in-depth interviews with 11 patients was used. Data were analyzed by using the constant comparative approach.

• Results A total of 4 themes and 3 subthemes were identified. The first theme was back and forth between reality and the unreal, between life and death; the subtheme was having weird dreams. The second theme was loss of control; the 2 subthemes were (1) fighting or being tied down and (2) being scared. The third theme was almost dying, and the fourth theme was feeling cared for.

• Conclusions Patients can remember having both negative and positive experiences during neuromuscular blockade. Steps to improve the experiences of patients receiving neuromuscular blockers include improving assessment parameters, developing and using sedation/analgesia guidelines, and investing in quality improvement programs to provide assessment of awareness during therapeutic paralysis and follow-up and referral as necessary. Ways to decrease the use of neuromuscular blockers would also be useful.

Sedation, analgesia, and neuromuscular blockade for high-frequency oscillatory ventilation

OBJECTIVE

To provide a comprehensive review of the issue related to the administration of sedative, analgesic, and neuromuscular blocking agents (NMBA) to patients who are receiving ventilatory support for acute respiratory distress syndrome (ARDS) with high-frequency oscillatory ventilation.

RESULTS

Sedative, analgesic, and NMBA are used with great frequency in patients with severe ARDS who are undergoing high-frequency oscillatory ventilation. In particular, the use of NMBA has been higher than for other ARDS populations. Important considerations for effective treatment include careful patient evaluation, patient-based medication selection, identification of treatment goals with periodic re-assessment, titration of medications to objective parameters such as sedation scales and peripheral nerve stimulation, use of intermittent therapy when feasible, implementation of drug interruption strategies, and discontinuation of medications at the earliest possible time. It is important to recognize that patients evolve from severe ARDS through phases of recovery to the resolution of respiratory failure and that ventilatory management, as well as sedative and related medication requirements, will vary markedly over the course of this process.

CONCLUSIONS

A multidisciplinary, structured approach that is based on the considerations described should help achieve optimal results in this challenging patient population.