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American Journal of Critical Care. 2008;17: 133-140
Copyright © 2008 by the American Association of Critical-Care Nurses.
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CE Article

Comparison of Sleep and Mood in Patients After On-Pump and Off-Pump Coronary Artery Bypass Surgery

By Christine Hedges, RN, PhD, APRN, BC, CCNS and Nancy S. Redeker, RN, PhD. Christine Hedges is a nurse researcher at Ann May Center for Nursing, Meridian Health, Neptune, New Jersey. Nancy S. Redeker is a professor and associate dean for scholarly affairs at the School of Nursing, Yale University, New Haven, Connecticut.

Corresponding author: Christine Hedges, RN, PhD, Ann May Center for Nursing, Jersey Shore University Medical Center, 1945 Rte 33, Neptune, NJ 07754 (e-mail: chedges{at}meridianhealth.com).


   Abstract
Top
 Abstract
Off-Pump CABS
 Mood and Sleep Disturbance...
 Methods
 Results
 Discussion
 Recommendations
 References
 
Background Off-pump coronary artery bypass surgical procedures have been advocated to reduce the adverse effects of cardiopulmonary bypass on the brain.

Objective To examine differences in objective and subjective characteristics of sleep and mood disturbance between patients after on-pump and off-pump coronary artery bypass surgery.

Methods In a secondary analysis of pooled data from 2 previous studies, sleep characteristics and mood disturbance on postoperative night 2 after transfer to the cardiac surgery step-down unit were compared in patients who had on-pump and off-pump cardiac surgery. The sample included 129 coronary artery bypass patients: 48 on-pump patients from one hospital and 81 off-pump patients from another hospital. Data were obtained with wrist actigraphs. Subjective characteristics of sleep were determined by using the Pittsburgh Sleep Quality Index and a sleep diary; mood disturbance was evaluated by using the short form of the Profile of Mood States.

Results Off-pump surgery was associated with better objective sleep continuity (decreased percentage of wake time after sleep onset and fewer awakenings) but not longer sleep duration after controlling for age and sex. The 2 groups of patients did not differ overall in subjective sleep characteristics, mood disturbance, or preoperative sleep quality.

Conclusion Use of off-pump coronary artery bypass surgery may improve sleep continuity during the early postoperative period. Prospective longitudinal studies are needed to evaluate the potential long-term benefits of this procedure during the different phases of recovery.

Notice to CE enrollees:
A closed-book, multiple-choice examination following this article tests your understanding of the following objectives:
  1. Describe the objective differences between characteristics of sleep in on- and off-pump coronary bypass patients.
  2. Identify the types of mood disturbances experienced by on- and off-pump coronary bypass patients.
  3. List 2 components associated with better objective sleep continuity in the off-pump coronary artery bypass group.
To read this article and take the CE test online, visit www.ajcconline.org and click "CE Articles in This Issue." No CE test fee for AACN members.

The recovery period after coronary artery bypass surgery (CABS) is characterized by disturbances in sleep1–4 and mood5,6 that are associated with decreased quality of life.5 Researchers have attributed disturbed sleep to a variety of factors, including the hospital environment; individual differences in age, sex, and comorbid conditions; and the effects of treatment.7,8 However, the impact of differences in surgical and anesthetic techniques on sleep and mood disturbance have been understudied.9

Compared with traditional CABS performed with a cardiopulmonary bypass pump, CABS performed on a beating heart without use of a bypass pump may reduce the occurrence of neurological syndromes after cardiac surgery.10 Reducing the adverse impact of cardiopulmonary bypass on brain function also may markedly affect postoperative sleep and mood, which are profoundly affected by brain function. Therefore, the purpose of this study was to examine differences in objective and subjective characteristics of sleep and mood disturbance during the early postoperative period between patients who had on-pump and those who had off-pump CABS.


Coronary artery bypass surgery recovery often is associated with disturbances in sleep and mood.

 


   Off-Pump CABS
Top
 Abstract
 Off-Pump CABS
Mood and Sleep Disturbance...
 Methods
 Results
 Discussion
 Recommendations
 References
 
Since the 1950s, cardiac surgeons have been able to operate on the heart and great vessels while a cardiopulmonary bypass pump, also known as extracorporeal circulation, maintained blood circulation and gas exchange.11 As a result, CABS with cardiopulmonary bypass is considered the reference standard and has been performed on millions of patients with a high degree of safety and success.12

However, patients who have CABS with cardiopulmonary bypass are likely to experience a variety of transient metabolic, hemodynamic, and neurohormonal postoperative alterations that may be manifested as neurocognitive alterations or disturbances in mood or sleep.1,13 Therefore, procedures have been developed to perform cardiac surgery on the beating heart by using mechanical stabilizers. This procedure is thought to be less traumatic because inflammatory responses associated with use of a cardiopulmonary bypass pump are reduced.14

Cerebral hypoperfusion and embolization are likely mechanisms of brain injury due to the use of a bypass pump.15–17 Reducing these pathophysiological processes by using off-pump CABS may decrease neurocognitive impairment and postoperative delirium in the early postoperative period.12 Because both sleep and mood are neurophysiological phenomena, disturbances in these 2 entities may be associated with potential damage to the brain by altered cerebral perfusion. However, little is known about the potential differences in characteristics of sleep and mood disturbance associated with the use of a cardiopulmonary bypass pump.


   Mood and Sleep Disturbance After Cardiac Surgery
Top
 Abstract
 Off-Pump CABS
 Mood and Sleep Disturbance...
Methods
 Results
 Discussion
 Recommendations
 References
 
Mood disturbance, including anxiety and depression, is common after on-pump CABS.6,18–21 Although prevalence rates varied depending on the time frame of the study, the study population, and measurement methods, rates of anxiety have ranged from 34% to 45% and rates of depression from 20% to 65% for men and women in the first postoperative week.6,22 However, previous studies primarily included patients who had undergone CABS with traditional cardiopulmonary bypass and did not compare mood disturbances of on-pump and off-pump CABS patients.

Following surgery, CABS patients experience disturbed sleep cycles with no or reduced REM sleep and reduced delta or slow-wave sleep.3,23 The objective and subjective characteristics of sleep include decreased duration, frequent awakenings, and poor self-reported sleep quality.2,4,7,24,25 In CABS patients, as much as 50% of total daily sleep may occur during the day.4 Sleep is poorer during the early postoperative period after on-pump CABS than at other times during recovery,4,26 and the resulting acute sleep deprivation may have important consequences for postoperative recovery.26 However, little is known about differences in the characteristics of objective or subjective sleep associated with variations in procedures used to perform CABS, particularly off-pump vs on-pump techniques.

Because sleep is profoundly influenced by changes in brain function, decreasing the alterations in cerebral perfusion and inflammation associated with use of cardiopulmonary bypass may result in improvements in objective and subjective characteristics of sleep and in mood disturbance when patients have off-pump CABS. We hypothesized that patients who had off-pump CABS would have less mood disturbance and better objective and subjective characteristics of sleep in the early postoperative period than would patients who had on-pump surgery.


   Methods
Top
 Abstract
 Off-Pump CABS
 Mood and Sleep Disturbance...
 Methods
Results
 Discussion
 Recommendations
 References
 
Study Design
The study was a secondary analysis of pooled data from 2 previous studies.26,27 A 2-group retrospective comparative design was used.

Sample and Setting
The participants in the original studies were male and female cardiac surgery patients recruited from 2 tertiary care cardiac surgery programs in the northeastern United States. Participants were recruited by using convenience sampling methods for 2 separate studies in which identical methods were used to measure sleep and mood disturbance.26,27 None of the participants had cognitive impairment, as determined by clinical impression, and all could speak and read English. Exclusion criteria included history of cerebrovascular accident, unstable psychiatric disorder, chronic alcohol or drug use, documented sleep disorder, and neuromuscular disorders that impaired limb movement and would preclude use of wrist actigraphy.

Instruments
Sleep is a multidimensional patterned biobehavioral phenomenon with objective and subjective (perceptual) attributes. Wrist actigraphy and sleep diaries were used to evaluate sleep during the hospital period, and the Pittsburgh Sleep Quality Index (PSQI) was used to retrospectively evaluate preoperative habitual sleep quality.

  Wrist Actigraph.   Duration of nocturnal sleep, frequency and duration of awakenings, and percentage of wake after sleep onset (ie, the percentage of time spent awake between the time of sleep onset and the time of final awakening) were measured by using a Mini-Motionlogger Actigraph (Ambulatory Monitoring Inc, Ardsley, New York). The actigraph contains an accelerometer that detects wrist movement. Actigraphs provide reliable estimates of sleep time and distinguish being asleep from being awake28 by using commercially available computerized scoring algorithms to derive sleep parameters. High correlations have been found between electroencephalographic measures of sleep and actigraphy for total sleep time, sleep efficiency, and sleep latency.29 The actigraph has 87% sensitivity and 90% specificity in distinguishing sleep from wakefulness.30 Automatic scoring algorithms29 have indicated high agreement (88%) between actigraphy and polysomnography for sleep and wakefulness.

  Sleep Diaries.   Sleep diaries were used to gather self-reported information about sleep quantity and quality and to assist in validating actigraphic data. Variables included sleep duration, frequency of awakenings, and sleep quality; a numeric rating scale of 0 (worst sleep) to 10 (best sleep) was used. Numeric rating scales are reliable and valid measures of symptoms such as sleep disturbance.31 High levels of agreement have been reported between sleep diaries and sleep scored on the basis of electroencephalographic data ({kappa} = 0.87).32

  Pittsburgh Sleep Quality Index.   The PSQI33 was used to retrospectively evaluate habitual sleep quality for the month preceding hospitalization. The PSQI consists of 19 self-rated questions and is used to assess 7 components of sleep: sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleep medications, and daytime dysfunction. A global PSQI score is used to distinguish "good" from "poor" sleepers and has adequate internal consistency (Cronbach {alpha}= .80–.85). A global cut-off score of PSQI greater than 5 is considered indicative of poor sleep and had 89.6% sensitivity and 86.9% specificity ({kappa}=0.75; P <.001) in a sample of elderly patients.34


Mood disturbance, including anxiety and depression, is common after on-pump CABS.

 

  Profile of Mood States.   Mood disturbance was measured by using the Profile of Mood States short form,35 a 30-item self-report instrument used to assess 6 components of mood states (tension-anxiety, depression-dejection, anger-hostility, fatigue-inertia, vigor-activity, and confusion-bewilderment) over a period of 1 week. The short form rather than the 65-item Profile of Mood States was used to reduce demands on the respondents. The 30-item short form has high internal consistency reliability (Cronbach {alpha} = .75–.90)36 and has been validated in a wide variety of patients.37,38 Higher scores indicate more total mood disturbance.

Procedure
Approval was obtained from the appropriate institutional review boards. A member of the research team visited CABS patients during their preoperative visit to the hospital, described the study, and obtained informed consent from those who expressed interest.

A member of the study team visited each participating patient on postoperative day 2, applied the actigraph to the patient’s nondominant wrist, and gave the patient the packet of study materials that included instructions for wearing the actigraph and completing paper-and-pencil instruments. Patients were instructed to wear the actigraph at all times, to depress the "event marker" at the time they intended to go to sleep (corresponding to "lights out"), and to depress it again when they woke in the morning ("lights on"). Participants were specifically instructed to depress the event marker when they woke rather than when they "got up," because patients recovering from surgery may not get out of bed immediately upon awakening.

Patients were instructed to complete the sleep diaries in the morning after the night they wore the actigraph. Diary entries were used to validate event-marker data or as a surrogate for missing event-marker information. Research assistants visited each patient the next morning to ensure that the actigraph was being worn, determine that the event marker was being used, answer questions, and assist in filling out data collection materials. At the end of the data collection period, questionnaire packets and actigraphs were collected, and the patient was thanked for participating in the study.

In the 2 larger studies26,27 from which the data for our study were pooled, researchers collected data for either 2 or 3 contiguous 24-hour periods. Because data were not complete for all patients for postoperative day 3, only the data from the 24 hours representing postoperative day 2 were used in the current analysis.

Data Analysis
Wrist actigraph data were downloaded to a personal computer and analyzed by using Action4 software (Ambulatory Monitoring Inc). The sleep segments were partitioned according to the patient-initiated event marker recordings to detect the primary nocturnal sleep period. This method was used rather than predetermined nocturnal sleep periods because of the potential for wide variability in patients’ bedtimes and wake-up times. When event-marker recordings were not available, diary entries were used to determine time in bed. Data transformations were performed as appropriate to meet assumptions of normality. Descriptive statistics were computed. For group-related differences in the primary study variables, multivariate analysis of covariance (MANCOVA) was used for correlated variables and analysis of covariance for single variables. For each analysis, controls for age and sex were used because of the potential influence of these 2 factors on the primary study variables. Significance level was set at P < .05. All data were analyzed by using SPSS, version 14.0 (SPSS Inc, Chicago, Illinois).


   Results
Top
 Abstract
 Off-Pump CABS
 Mood and Sleep Disturbance...
 Methods
 Results
Discussion
 Recommendations
 References
 
The sample consisted of 129 patients: 48 (37.2%) from one site who had on-pump CABS and 81 (62.8%) from the other site who had off-pump surgery. Table 1Go gives the demographic characteristics of the 2 groups. The majority of patients were white (n = 125, 96.9%) and male (n = 95, 73.6%). The off-pump group was significantly older than the on-pump group (P = .009) and had more women, although the sex difference was not statistically significant.


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  		Table 1 Characteristics of sample (n = 129)

 
Descriptive statistics (means and standard deviations) were computed for the primary study variables (Table 2Go). In these bivariate analyses, the off-pump group had significantly fewer actigraph-recorded awakenings, a lower percentage of wake after sleep onset, and higher ratings of sleep quality than the on-pump group did, but the 2 groups did not differ significantly in the other sleep variables.


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  		Table 2 Descriptive statistics for primary study variables (n = 129)

 
Two MANCOVA procedures were performed to evaluate the difference between off-pump and on-pump surgery for the objective and subjective sleep variables. MANCOVA was used because of the inter-correlations among these variables. The first MANCOVA was used to evaluate differences between the off-pump and on-pump patients for the cluster of objective sleep variables (duration of nocturnal sleep, number of awakenings, duration of awakenings, and percentage wake after sleep onset) with controls for age and sex. The overall difference in objective sleep characteristics between the groups was significant (Hotelling trace [df = 4,122] = 2.96, P = .02). Follow-up analysis revealed significant differences in frequency of awakenings and percentage wake after sleep onset (Table 3Go).


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  		Table 3 Post hoc differences in objective sleep characteristics between on-pump and off-pump coronary artery bypass surgery patients, MANCOVA with controls for age and sex

 
The second MANCOVA was used to evaluate differences between the off-pump and on-pump patients for the 3 self-reported sleep characteristics (duration of sleep, frequency of awakenings, rating of sleep quality) with controls for age and sex. The overall difference was not significant (Hotelling trace [df = 3,101] = 1.57, P = .20). Post hoc analysis revealed a univariate difference only in frequency of awakenings (Table 4Go).


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  		Table 4 Post hoc differences in subjective sleep characteristics between on-pump and off-pump coronary artery bypass surgery patients, MANCOVA with controls for age and sex

 
Finally, differences between on-pump and off-pump patients for mood disturbance and subjective report of preoperative sleep were evaluated with controls for age and sex. Analysis of covariance revealed no significant difference between the 2 groups for habitual sleep quality (PSQI score; F1=0.156; P =.69; confidence interval=–1.03 to 1.55). The 2 groups did not differ significantly in total mood disturbance (F1=0.221; P =.64; confidence interval=–9.09 to 5.61).

Data transformations performed for nonnormally distributed data yielded similar P values; therefore, any violation of assumptions did not affect the results.


   Discussion
Top
 Abstract
 Off-Pump CABS
 Mood and Sleep Disturbance...
 Methods
 Results
 Discussion
Recommendations
 References
 
Our findings suggest that patients who have off-pump CABS may have better objective sleep continuity, as indicated by frequency of awakenings and percentage awake after sleep onset, than do patients who have on-pump CABS. Although the difference in sleep duration did not differ significantly between the 2 groups, the mean nocturnal sleep duration of the off-pump patients was 48 minutes longer than that of the on-pump group, a large and potentially clinically important difference. Frequency and duration of awakenings and percentage wake after sleep onset were from 1.4 to 1.5 times greater in the on-pump group than in the off-pump group.

Although we found no between-group differences in subjective sleep variables, after controlling for the potential influence of age and sex, frequency of awakenings was 1.5 times greater and rating of sleep quality was 1.3 times greater in the on-pump patients than in the off-pump patients. Therefore, these differences appear to mirror the differences in the objective sleep characteristics. Discrepancies between the objective and subjective sleep findings may be due to the greater sensitivity of the wrist actigraph to differences between sleep and wakefulness or may be due to the variability in the measures.

The 2 groups did not differ in preoperative habitual sleep quality. Therefore, postoperative sleep disturbance probably was not due to preexisting sleep disorders such as insomnia and sleep-disordered breathing, which are common among middle-aged or older adults, especially those with coronary artery disease.


Patients who had off-pump surgery had fewer awakenings and reported better sleep quality than did on-pump surgery patients.

 

Past studies have indicated that as much as 50% of early postoperative sleep in CABS patients occurs in the daytime hours,2,4 that sleep becomes more consolidated during nocturnal hours during the early postoperative period,4 and that sleep patterns, as measured with wrist actigraphy, improve during the course of hospitalization and afterward.4 Because our study was retrospective, we did not have consistent data available on sleep that occurred during the daytime and evening hours. Therefore, our findings probably are marked underestimates of the total daily quantity of sleep.

Possibly, differences exist in the circadian pattern of sleep and wakefulness that are associated with off-pump vs on-pump CABS. These differences may be associated with other outcomes relevant for recovery. For example, Bucerius et al10 concluded that off-pump CABS may protect patients against postoperative delirium and the concomitant altered sleep-wake cycles in the early postoperative period. Prospective longitudinal studies may reveal differences in the changes in sleep continuity and circadian rhythmicity during recovery between patients who have off-pump CABS and those who have on-pump surgery.

Our findings suggest that off-pump CABS does not confer any benefits relative to mood disturbance during the early postoperative period. This lack of benefits is particularly surprising, because an earlier study1 indicated associations between sleep disturbance and mood among cardiac surgery patients.

Many factors, including patient demographics, comorbid conditions, medical and surgical treatment, and characteristics of the hospital environment,7,39 may affect characteristics of sleep after CABS. As suggested by other researchers,12 off-pump CABS patients are more likely to be older, be female, and have peripheral vascular disease or history of stroke than are patients who undergo on-pump CABS. Our results reflect these demographic characteristics, but we did not have detailed information available on the occurrence of peripheral vascular disease and we excluded patients with a history of stroke. Therefore, we cannot determine the potential influence of these factors. In addition, it was not possible to prospectively randomize patients to either the off-pump or on-pump conditions. Because our study was retrospective, we were only able to consider the potential influence of age and sex on the primary study variables.

Inclusion of study participants from 2 different hospitals and the recruitment of all of the off-pump CABS patients from a single institution were limitations of the study. Therefore differences in nursing practices, unit design, or other environmental factors may have contributed to our findings. In addition, the study participants were a convenience sample of patients. Future studies should be designed prospectively to address these factors.

Other limitations were the availability of usable data for only a single postoperative night and the lack of detailed information on environmental and treatment-related variables. Post hoc power and effect estimates indicated that the study was under-powered to detect a significant difference. The identified trends in the data suggest that differences might be statistically significant with a larger sample. The clinical relevance of the size of these differences also should be examined in a larger study.


   Recommendations
Top
 Abstract
 Off-Pump CABS
 Mood and Sleep Disturbance...
 Methods
 Results
 Discussion
 Recommendations
References
 
To our knowledge, this study was the first in which differences in objective and subjective characteristics of sleep and mood disturbance between off-pump CABS patients and traditional on-pump CABS patients were examined. Our findings suggest that the objective characteristics of sleep differ between the 2 groups; patients with off-pump CABS have better sleep continuity and trends toward better self-reported sleep quality than do on-pump patients, but no less mood disturbance. Future longitudinal randomized clinical trials should be designed to prospectively evaluate these differences and the potential role of improved sleep characteristics as mediators of the effects of off-pump CABS on improved cognitive functioning, functional performance, and other relevant clinical and quality-of-life outcomes. These studies should account for potential multivariate influences on postoperative sleep characteristics, such as treatment, demographic and clinical factors, and hospital environment.


   ACKNOWLEDGMENT
 
We thank Yen-Hong Kuo, ScM, MS, for assisting with this study.

To purchase electronic or print reprints, contact The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656. Phone, (800) 809-2273 or (949) 362-2050 (ext 532); fax, (949) 362-2049; e-mail, reprints{at}aacn.org.

SEE ALSO
To learn more about cardiac surgery outcomes in the ICU, visit http://ccn.aacnjournals.org and read the article by Donna Rosborough, "Cardiac Surgery in Elderly Patients: Strategies to Optimize Outcomes" (Critical Care Nurse, October 2006).

eLetters
Now that you’ve read the article, create or contribute to an online discussion about this topic using eLetters. Just visit www.ajcconline.org and click "Respond to This Article" in either the full-text or PDF view of the article.

FINANCIAL DISCLOSURES
Portions of this project were funded through an NIH grant NR00102 (Dr Redecker) and the Rutgers University College of Nursing Dean’s dissertation fund.


   REFERENCES
Top
 Abstract
 Off-Pump CABS
 Mood and Sleep Disturbance...
 Methods
 Results
 Discussion
 Recommendations
 References
 

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