Running head: A CRITICAL REVIEW OF A RANDOMIZED CONTROLLED TRIAL
A Critical Review of a Randomized Controlled Trial of Postoperative Delirium
Angelique Davis
Kansas University Medical Center
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A CRITICAL REVIEW OF A RANDOMIZED CONTROLLED TRIAL
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A Critical Review of a Randomized Controlled Trial of Postoperative Delirium
Overview
This paper is a critical review of an article written by Radtke et al., 2013, titled
Monitoring Depth of Anesthesia in a Randomized Trail Decreases the Rate of Postoperative
Delirium but not Postoperative Cognitive Dysfunction. The authors proposed the use of
bispectral index monitor (BIS) would reduce the incidence of postoperative delirium related to
anesthesia. The aim of this parallel study was to determine if monitoring the depth of anesthesia
would more accurately guide the anesthesia provider to a sufficient level of anesthesia. The
bispectral index is an analysis of an elecentroencephalogram (EEG) and presents this information
as a single value of awareness. The values for BIS range from 0-100, with zero referring to no
brain wave activity and 100 being fully awake. The goal range for anesthesia for routine surgery
is 40-60. The goal of using the BIS monitor is to ensure anesthesia for patients is neither too
deep nor too light, thus potentially reducing the incidence for postoperative delirium. The
sample size included 1277 patients and each patient was assessed for postoperative delirium
according to the Diagnostic and Statistical Manual of Mental Disorders (DSM IV). The study
concluded that the use of the BIS monitor did indeed reduce the incidence of postoperative
delirium (Radtke et al., 2013). This article has its strengths and weaknesses, but overall I believe
this a poorly conducted research trial.
Summary
A significant concern when administering general anesthesia is the recovery. According
to Radtke et al., 2013, “Postoperative delirium is a frequent complication, especially in elderly
patients, and is associated with poor outcome.” (p.98). Currently, postoperative delirium does
not have a specific treatment. The use of an objective measuring tool, such as the BIS monitor,
A CRITICAL REVIEW OF A RANDOMIZED CONTROLLED TRIAL
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during general anesthesia may serve to reduce the incidence of postoperative delirium. The BIS
monitor is used now to monitor the depth of anesthesia and provides the anesthetist to titrate
drugs accordingly. The purpose of this study is to determine whether BIS assisted anesthesia
versus routine anesthesia will reduce the incidence of postoperative delirium in elderly patients.
The objective of the study with BIS guided anesthesia is to maintain patients within the values of
40-60 via a bilateral forehead electrode that continuously monitors a patients EEG activity
throughout the case. This randomized controlled trial included a blinded group and an unblinded
group to develop results. (Radtke et al., 2013)
Critique
Introduction
According to Radtke et al., (2013), the purpose the study was to conduct a randomized
controlled trial that compared the use of a BIS monitor versus routine monitoring of anesthesia
among elderly patients undergoing surgery. The purpose of the study was easily located, clearly
stated and pertinent to anesthesia. The independent variable was the use of the BIS monitor and
the dependent variable was the incidence of postoperative delirium, which was measured in
accordance with the DSM IV. The use of the BIS monitor and its function is clearly defined in
this study and is an overall strength of the study. The study does not, however, provide a
sufficient literature review on the background of postoperative delirium. This article discusses
little about the current research on the problem. The Radtke et al., (2013), offers a single
statement referring to current literature, stating “An influence of depth of sedation on delirium
has been suggested; however, the influence on postoperative delirium remains unclear” (p. 99).
This is a weakness of the article. The author plainly states the objective of the study, but does
not define a clearly stated hypothesis. The hypothesis can be inferred, but a stance is not stated.
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Methods
The study is a parallel group that is an electronically randomized controlled trial
conducted at two different campuses at the Charite-Universitatsmedizin Berlin, Germany. The
study was conducted between March 2009 and May 2010, with follow up until August 2010.
The study appropriately gained approval from the institutional review board and ensured all
patients were given written informed consent. This is an apparent strength of the study. A
power analysis is not provided in study and does not provide the reader with an understanding of
if the population is appropriate for the study. The study adequately defines the inclusion and
exclusion criteria for the study. The inclusion criterion involves patients greater than or equal to
the age of 60 undergoing elective surgery that lasts longer than 60 minutes. The surgical
procedures that are allowed in the study are appropriately listed. Exclusion criteria eliminate
patients with cognitive impairment or neurological deficits. Two groups for the study are
defined as BIS guided anesthesia, with the anesthesia provider proficient and knowledgeable
about the use of the device and a BIS blinded group that describes the anesthetist as providing
routine anesthesia care without the knowledge of the BIS value throughout the case. (Radtke et
al., 2013)
Results
Radtke et al., (2013), used statistical tests that were appropriate for the author’s results,
but Cronbach’s alpha was never reported. This in particular displays a weakness in the article
due to the reader being unable to assess internal consistency. The author did report a confidence
interval of 95% in the logical regression analysis and a two-tailed P-value of <0.05 was
considered statistically significant. This is considered a strength of the study. According to
Radtke et al., (2013), “All numerical calculations were performed with SPSS, Version 19. Forest
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plots were created with Microsoft Excel 2003.” (p. 100-101). The tables and figures were
appropriately integrated throughout the article. The tables and figures are easy to read and
follow. This is a strength of the study. The results did display the main objectives of the study.
The results of Radtke et al., (2013), displayed “Postoperative delirium was detected in 191
patients (18.8%). Of these, 95 patients (16.7%, 95% CI: 13.9-20.0) belonged to the open group
while 124 patients (21.4%; 95% CI: 18.3-24.9%) were in the blinded group (P=0.036).” (p. 101).
The study showed that the blinded group BIS values showed more values below 20, which is
associated with sedation that is too deep.
Discussion
The author’s conclusions are drawn from and consistent with the results. The results
suggest that the use of the BIS monitor during general anesthesia is beneficial to patients to
reduce postoperative delirium. The author suggests that the use the BIS monitor will prevent a
“roller coaster” type of anesthesia, which would improve patient outcomes. Confounding
variables are mentioned in the study to provide another motive to the incidence of postoperative
delirium. Confounding variables included duration of surgery and age. Limitations of the study
also included a scenario when the blinded group had to become an open group due to the safety
of the patient. The patients that were unblinded for this purpose still remained in the blinded
statistics, thus not giving an accurate analysis of the results. The study did not offer any
additional suggestions to future studies or modifications. This is an apparent weakness of the
article.
Conclusion
Overall Radtke et al., (2013), provided moderate evidence that the use of the BIS monitor
will reduce the incidence of postoperative delirium. The results were skewed due to a group of
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patients’ having to become the unblinded group. If this group of patients were resulted in the
open group, the results would have less validity. The evidence presented in the study may be
helpful for anesthesia providers when providing care for patients with an extended surgery
length, past history of delirium, and the age of the patient.
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A CRITICAL REVIEW OF A RANDOMIZED CONTROLLED TRIAL
References
Radtke, F. M., Franck, M., Lendner, J., Kruger, S., Wernecke, K. D., & Spies, C. D. (2013,
March 28). Monitoring depth of anesthesia in a randomized trial decreases the rate of
postoperative delirium but not postoperative cognitive dysfunction. British Journal of
Anesthesia, 98-105.
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