Early mobilization is incorporated into many enhanced recovery pathways. Inadequate analgesia or excessive opioids may restrict postoperative mobilization. The authors tested the hypotheses that in adults recovering from abdominal surgery, postoperative pain and opioid consumption are inversely related to postoperative mobilization, and that postoperative mobilization is associated with fewer potentially related complications.
The authors conducted a subanalysis of two trials that enrolled adults recovering from abdominal surgery. Posture and movement were continuously monitored for 48 postoperative hours using noninvasive untethered monitors. Mobilization was defined as the fraction of monitored time spent sitting or standing.
A total of 673 patients spent a median [interquartile range] of 7% [3 to 13%] of monitored time sitting or standing. Mobilization time was 1.9 [1.0 to 3.6] h/day for patients with average pain scores 3 or lower, but only 1.2 [0.5 to 2.6] h/day in those with average scores 6 or greater. Each unit increase in average pain score was associated with a decrease in mobilization time of 0.12 (97.5% CI, 0.02 to 0.24; P = 0.009) h/day. In contrast, there was no association between postoperative opioid consumption and mobilization time. The incidence of the composite of postoperative complications was 6.0% (10 of 168) in the lower mobilization quartile, 4.2% (7 of 168) in the second quartile, and 0% among 337 patients in the highest two quartiles (P = 0.009).
Patients recovering from abdominal surgery spent only 7% of their time mobilized, which is considerably less than recommended. Lower pain scores are associated with increased mobility, independently of opioid consumption. Complications were more common in patients who mobilized poorly.
Early mobilization is a central component of enhanced recovery pathways
Pain and opioids may each reduce postoperative mobilization
The authors combined data from two abdominal surgery trials and evaluated pain, opioid use, and mobilization
Pain was associated with less mobilization, but opioid consumption was not
Overall mobilization was low, and complications were more frequent in those who mobilized poorly
Postoperative mobilization is an important component of enhanced recovery after surgery programs.1–3 Typical enhanced recovery after surgery programs recommend many hours per day out of bed starting the day of surgery4–7 —although the recommendations are largely based on recognized deleterious effects of bed rest8–10 rather than strong evidence that postoperative mobilization improves outcomes.6,11–23
Postoperative pain remains common,24 with about half of surgical patients reporting inadequate postoperative analgesia.25,26 Inadequate analgesia impairs functional recovery and promotes postoperative complications.27,28 In an attempt to address this problem, adequate analgesia was introduced as a quality measure,29 which predictably increased opioid administration and the consequent opioid-related adverse events.24 Opioid-related adverse events including nausea and vomiting, lightheadedness, and oversedation seem likely to reduce postoperative mobilization,27,28,30,31 although there is currently little evidence to support the theory.
Surprisingly, there is no clear evidence of association between impaired postoperative mobilization and postoperative outcomes.11,14,16,17 One explanation may be that assessment of mobilization remains imprecise and largely based on patient or nursing subjective reports rather than objective quantitative measurement. Furthermore, patient mobilization is frequently skipped or poorly implemented.10,32,33
The extent to which postoperative pain and opioid consumption influence postoperative mobilization remains unknown.16–18 We therefore tested the primary hypothesis that in adults recovering from abdominal surgery, postoperative pain is inversely associated with postoperative mobilization, defined as the number of hours per postoperative day spent sitting or standing during the initial 48 postoperative hours. Secondarily, we tested the hypothesis that postoperative opioid consumption is inversely associated with postoperative mobilization. Finally, we tested the exploratory hypothesis that postoperative mobilization is associated with fewer complications potentially related to inadequate mobilization, defined as a composite of myocardial injury, stroke or transient ischemic attack, venous thromboembolism, pulmonary complications, and all-cause mortality.
Materials and Methods
We conducted a retrospective analysis of data from two randomized trials: Effect of Intravenous Acetaminophen on Postoperative Hypoxemia After Abdominal Surgery: the FACTOR Randomized Clinical Trial (NCT02156154; Alparslan Turan; registered on June 5, 2014),34 which evaluated the effect of intravenous acetaminophen on postoperative opioid-related complications after colorectal surgery; and Transversus Abdominis Plane Block with Liposomal Bupivacaine versus Continuous Epidural Analgesia for Major Abdominal Surgery: the EXPLANE clinical trial (NCT02996227; Alparslan Turan; registered on December 19, 2016), which compared the effect of continuous epidural analgesia and transversus abdominis plane blocks on postoperative analgesia and opioid consumption after abdominal surgery. Both trials enrolled patients who had abdominal surgery and used a continuous vital sign recording system that also captures mobilization information, and were approved by the Cleveland Clinic Institutional Review Board (IRB; Cleveland, Ohio). The current analysis was approved by the IRB with waived individual consent and was designed before completing the trial enrollment (Cleveland Clinic IRB No. 19-341; approval date March 19, 2019).
Patients were managed according to Cleveland Clinic enhanced recovery after surgery protocols. Orogastric tubes were removed before endotracheal extubation. Patients were encouraged to walk on the evening of surgery and were offered noncarbonated liquids ad libitum. On the first postoperative day, patients were encouraged to walk at least one round of the nursing floor (approximately 60 m) up to five times, to sit out of bed between walks, and to perform regular incentive spirometry. Liquids were allowed and solid food offered if tolerated. Intraoperative analgesia was provided with short-acting opioids, and intravenous patient-controlled analgesia was used during the postoperative period. Oral analgesia was started, and the Foley catheter was removed on postoperative day 1.35–37
We included adult inpatients having elective open or laparoscopic abdominal surgery scheduled to last at least 2 h with general anesthesia at the Cleveland Clinic between February 2014 and September 2019 who participated in FACTOR or EXPLANE and had continuous postoperative activity monitoring. We excluded patients who had less than 12 h of continuous activity monitoring during the initial 48 postoperative hours, along with patients who had missing pain assessments or lacked important confounding variables.
Postoperative pain was recorded using the numerical rating scale, which is an 11-point Likert scale from 0 (no pain) to 10 (worst imaginable pain). Pain scores were recorded at least every 30 min while patients remained in the postanesthesia care unit, and at least every 4 h while hospitalized. All available pain scores during the monitoring period were collected from patients’ electronic medical records, and time-weighted average pain score was calculated for each patient. Opioid consumption during the initial 48 postoperative hours was also collected from patients’ electronic records and converted into milligram of intravenous morphine equivalents.38,39
Our primary outcome was duration of mobilization, defined as hours per monitoring day spent sitting or standing. Position and activity were continuously monitored and recorded at 15-s intervals from postanesthesia care unit admission until the earlier of 48 postoperative hours or hospital discharge using the ViSi Mobile monitoring system (Sotera Wireless, Inc., USA), which is cleared by the U.S. Food and Drug Administration (Silver Spring, Maryland) for noninvasive continuous vital sign monitoring.40
The ViSi Mobile monitoring system includes a three-axis accelerometer that characterizes patients’ orientation and activity.41 It captures posture status as upright 90 degrees, upright 45 degrees, supine, lying on the side, walking, and fallen. We defined mobilization as standing or sitting position, with standing defined “walking” posture and sitting as “upright 90 degrees” posture. When more than one posture was detected during a 15-s interval, a combined posture was recorded. For example, if a patient walked and sat upright 45° during a single 15-s interval, the posture would be recorded as upright 45 degrees and walking. Combined postures were considered as mobilization if one of the components was eligible. Neither patients nor clinicians had access to mobilization data.
The exploratory outcome was a composite of postoperative complications, including myocardial injury (defined as either a postoperative peak fourth-generation troponin T concentration 0.03 ng/ml or greater within the first 7 days after surgery, apparently of cardiac origin, or an International Classification of Diseases code for myocardial infarction)42 ; stroke or transient ischemic attack; venous thromboembolism; pulmonary complications; and all-cause in-hospital mortality (appendix, table A1). Data were extracted from patients’ electronic medical records, the anesthesia record-keeping system, and pharmacy records.
Gaps in activity/posture monitoring were removed and subtracted from total monitoring time, so that each patient’s mobilization was calculated as hours of mobility per day by multiplying average mobilization minutes per monitoring hour by 24 h/day. Around 4% of all postures were recorded as unknown and were treated as missing and removed. Demographic and clinical characteristics of patients were summarized and presented by time-weighted average pain score category in table 1, only for presentation purposes.
For the primary analysis, a quantile regression model was used to assess the association between time-weighted average pain score and mobilization time, in hours per day. A similar model was used to secondarily assess the association between opioid consumption during the first 48 postoperative hours and mobilization time. The associations were adjusted for all demographics and surgical variables in table 1.
We conducted four sensitivity analyses. The first evaluated associations between time-weighted average pain scores and opioid consumption and postoperative mobilization, restricted to patients older than 65 yr. Second, we restricted the definition of mobilization to include only standing position. Third, we restricted the analysis to daytime, defined as 7 am to 10 pm. For our final sensitivity analysis, we restricted the analysis to the first 24 postoperative hours.
For our exploratory analysis, the incidence of a composite of myocardial injury, stroke or transient ischemic attack, venous thromboembolism, pulmonary complications, and all-cause in-hospital mortality was summarized by quartiles of mobilization time.
We did two post hoc analyses. First, we fitted a quantile regression model with interaction between surgical approach (open or laparoscopic) and both exposures (pain and opioid consumption) with mobilization time as the outcome; and second, we explored the relationship between the mobilization time in hours per day and the composite of postoperative complications through a logistic regression model adjusting for age, sex, race, and surgery duration.
We performed a complete case analysis, as participants with missing data were excluded. Data were assumed to be missing at random. The significance level was 0.025 for each association (pain and mobilization/opioid consumption and mobilization) after Bonferroni correction for the primary and secondary analyses. All analyses were conducted using the Statistical Analysis System (SAS) statistical software package, version 9.04.01 (SAS Institute Inc., USA).
We did a simulation using quantile regression to calculate the effect size we could detect. With the current sample size, we had more than 90% power for detecting a 0.2-h reduction in mobilization per day for each unit increase in pain score, or to detect a 0.13-h reduction in mobilization per day for each doubling of morphine consumption at a significance level of 0.025.
A total of 984 patients who had elective open or laparoscopic abdominal surgery were enrolled in the underlying trials, 570 from FACTOR and 414 from EXPLANE. Our analysis was restricted to 673 patients among the 914 who had ViSi Mobile monitoring (fig. 1). Baseline medical, demographic, anesthetic, and surgical data are presented in table 1, divided by time-weighted average pain scores.
The median [interquartile range] monitoring duration (after removal of gaps) was 32 [23 to 40] h during the first 48 postoperative hours. Overall, patients spent a median [interquartile range] of 7% [3 to 13%] of the total monitoring time sitting or standing, corresponding to 1.7 [0.7 to 3.1] h/day.
In patients with time-weighted average pain scores 3 or less, mobilization time was 8% [4 to 15%], corresponding to 1.9 [1.0 to 3.6] h/day. In patients with time-weighted average pain scores between 3 and 6, mobilization time was 7% [3 to 13%], corresponding to 1.7 [0.7 to 3.1] h/day. In patients with time-weighted average pain scores 6 or greater, mobilization time was 5% [2 to 11%], corresponding to 1.2 [0.5 to 2.6] h/day (fig. 2). Each unit increase in time-weighted average pain score was associated with an adjusted median decrease of 0.12 (97.5% CI, 0.02 to 0.24) h/day (P = 0.009; table 2).
The opioid consumption ranged from 8 [0 to 50] mg of morphine equivalents in patients with low pain scores to 67 [34 to 171] mg of morphine equivalents in patients with the highest pain scores (table 1). The main opioids used and their morphine equivalents are shown in table A2. There was no significant association between postoperative opioid consumption and mobilization time, with an estimated adjusted median change of –0.04 (97.5% CI, –0.12 to 0.08) h/day for a twofold increase in morphine equivalent opioid consumption (P = 0.508; fig. 2; table 2).
There was no significant association between time-weighted average pain score or opioid consumption and postoperative mobilization among patients more than 65 yr old (table 2). We did not find significant associations between time-weighted average pain score and standing position; opioid consumption was inversely associated with standing, although not by a clinically meaningful amount (estimated adjusted median change of –0.01 [97.5% CI, 0.01 to –0.004] hours per day with each twofold increase in opioid consumption). Daytime (from 7 am to 10 pm) mobilization was inversely associated with both time-weighted average pain score and opioid consumption. The estimated adjusted median change was –0.40 (97.5% CI, –0.72 to –0.08) hours per daytime day for each unit increase of time-weighted average pain score and –0.32 (97.5% CI, –0.56 to –0.08) hours per daytime day for each doubling of opioid consumption. Mobilization during the first 24 postoperative hours was not associated with time-weighted average pain score or with opioid consumption.
We found a significant interaction between pain score and surgical approach (P = 0.033; table 2). For patients who had open procedures, each unit increase in pain score was associated with 0.17 (97.5% CI, 0.06 to 0.28; P <0.001) fewer hours of mobilization per day; this association was no longer significant for patients who had laparoscopic surgery, where each unit increase in pain score was associated with 0.05 more hours per day (97.5% CI, –0.15 to 0.25; P = 0.628). We did not find an interaction between morphine use and the surgical approach (P = 0.586). After additional adjustment for surgical approach in our primary outcome analysis, the results were similar to our primary analysis, where a doubling of morphine use was associated with 0.04 (97.5% CI, –0.14 to 0.05) fewer hours of mobilization per day (table 2).
The composite of postoperative complications was observed in 17 patients, 9 of whom had pulmonary complications; 3 had myocardial injury; 1 had a stroke/transitional intravascular accident, and 4 had venous thromboembolism (table 3). Considering quartiles of mobilization time, the incidence of the composite outcome was 6.0% (10 of 168 patients) among patients who spent 0 to 0.7 h in mobilization per day, 4.2% (7 of 168) among patients who spent 0.7 to 1.6 h in mobilization per day, and none among the remaining 337 patients in the highest two quartiles, who had more than 1.6 h/day. There was thus a significant association between mobilization time and postoperative complications with an estimated adjusted odds ratio of 0.34 (95% CI, 0.16 to 0.72) for each hour increase of mobilization per day, adjusting for age, sex, race, and surgery duration; P = 0.005. Preoperative American Society of Anesthesiologists Physical Status, intensive care unit admission, length of hospital stay, surgical approach, and surgery duration were also summarized by mobilization time.
Postoperative mobilization was inversely associated with pain scores, suggesting that inadequate postoperative analgesia impairs mobilization. Unsurprisingly, the association was threefold stronger when analysis was restricted to daytime, which is reasonable since few patients mobilize at night, irrespective of pain management. The association was also 1.5-fold stronger when patients had open surgery. In contrast, there was little association between opioid consumption and overall mobilization. To the extent that the relationship is causal, our results suggest that improving postoperative analgesia by about 3 points on an 11-point Likert scale might increase mobilization time by as much as 25%—even if opioids are used to improve analgesia.
Remarkably, all postoperative complications occurred in patients who were in the lowest two mobilization quartiles, those who spent less than 7% (1.7 h/day) of their time sitting or standing during the initial 48 postoperative hours. Importantly, potential confounders as American Society of Anesthesiologists Physical Status as well as surgery approach and duration did not differ much among postoperative pain levels, suggesting similar surgical severity and baseline comorbidities. A difference of 0.7 h of mobilization per day between patients with low or high level of pain might seem marginal. Nonetheless, this small difference corresponded to a substantial difference in the incidence of complications. Even 1.6 h of mobilization per day are therefore associated with reduced complications.
The average mobilization time in our cohort was about 2 h/day, which is the recommended out-of-bed time for the day of surgery, but considerably shorter than the times recommended thereafter by many enhanced recovery pathways.5–7 Low adherence to mobilization recommendations is consistent with many qualitative reports.6,18,43,44 We note, though, that enhanced recovery after surgery mobilization recommendations are largely based on expert opinion rather than on strong evidence. Our results suggest that 2 h/day may suffice.2,5,6
Although postoperative mobilization is included in most enhanced recovery pathways,16,45–47 supportive evidence remains sparse.6 On one hand, Daskivich et al.18 report in a 100-patient study that 1,000 steps/day on the first postoperative day after major abdominal surgery was associated with lower probability of a prolonged length of stay. On the other hand, in patients recovering from colorectal surgery, staff-directed out-of-bed activities did not reduce the duration of hospitalization.12–17,19–23 Moreover, a systematic review of 500 patients concluded that current evidence is insufficient to draw strong conclusions regarding the benefits of early mobilization on postoperative outcomes.11 Some discrepancies might be partly explained by large variability in mobilization quantification, with some reports relying on nursing or patients’ subjective reports6,47 while others used walking distance19 or daily steps.16–18 An important consideration for all observational analyses—including ours—is that failure to mobilize early may be a reflection of poor recovery, rather than being the cause.
Mobility data were missing for 9% [3% to 20%] of the initial postoperative 48 h, in part because continuous monitoring was purely observational. Clinicians were therefore blinded to results, and to disconnections or technical failures. Missing data are always a concern in clinical research, but more so if data are missing nonrandomly. In our case, it is plausible that disconnections were most common in mobile patients, thus diminishing the apparent difference in mobility time for the highest and lowest quartiles. We adjusted for many potential confounding factors including duration of surgery, but it remains likely that larger and open procedures that cause much tissue injury simultaneously provoke pain and impair mobilization. Although few of our patients experienced complications, after adjusting for as many important confounders as we could, there was still a strong relationship between complications and mobilization, even over a small range of sitting and standing times. However, the association between postoperative complications and low levels of mobilization cannot exclude reverse causality since patients with postoperative complications surely move less. The extent to which the association between pain and mobilization is causal, and thus amenable to intervention, remains unclear. A future trial of analgesic approaches with differing efficacies could better evaluate causality.
In patients recovering from abdominal surgery on an enhanced recovery pathway, lower pain scores are associated with increased mobility, even when opioid consumption is increased. Patients spent only about 2 h/day mobilized, which is considerably less than the recommended time. There appears to be little beyond expert opinion to support the recommended daily mobilization goal, and our results suggest that 2 h/day may suffice.
The underlying Effect of Intravenous Acetaminophen on Postoperative Hypoxemia After Abdominal Surgery: the FACTOR Randomized Clinical Trial was supported by an investigator-initiated research grant from Mallinckrodt Pharmaceuticals (Hampton, New Jersey); and the underlying Transversus Abdominis Plane Block with Liposomal Bupivacaine versus Continuous Epidural Analgesia for Major Abdominal Surgery: the EXPLANE clinical trial was funded by PACIRA Pharmaceuticals (Parsippany, New Jersey). Sotera Wireless, Inc. (San Diego, California) and Respiratory Motion, Inc. (Watertown, Massachusetts) provided devices and disposables. However, this analysis was supported by internal funds only, and the sponsors had no role whatsoever in data analysis, manuscript preparation, or the decision to submit for publication. The sponsors have not reviewed this manuscript. Dr. Rivas received a grant from Instituto Salud Carlos III, Madrid, Spain (BA18/00048).
Dr. Sessler is a consultant for PACIRA Pharmaceuticals (Parsippany, New Jersey). Dr. Maheshwari is a consultant for Edwards Lifesciences (Irvine, California). The other authors declare no competing interests.