Accelerometer-Measured Inpatient Physical Activity and Associated Outcomes After Major Abdominal Surgery: Systematic Review

{"Background": "Early mobilization has been a cornerstone of postoperative care since the Enhanced Recovery After Surgery (ERAS) guidelines were first published in 2005, recommending that patients spend 2 hours out of bed on the day of surgery and 6 hours per day out of bed until discharge. Despite widespread acceptance, these recommendations are built on expert consensus with little supporting data, and early mobilization remains poorly defined. Accelerometers offer a quantitative method to measure physical behaviors, and their use in research has grown exponentially. This systematic review aimed to summarize the current literature on accelerometer-measured postoperative physical activity in the acute inpatient setting and its impact on clinical outcomes after major abdominal surgery.", "Methods": "The authors searched PubMed and Google Scholar in October 2021, supplemented by reference list reviews, identifying 2470 articles. After screening, 103 underwent full-text review and 15 met inclusion criteria. Studies were included if they used accelerometers to measure inpatient physical behaviors immediately after major abdominal surgery and evaluated effects on postoperative outcomes. Studies involving participants aged <18 years were excluded. Risk of bias was assessed using RoBANS for observational studies and RoB 2 for RCTs. Data were synthesized qualitatively due to heterogeneity.", "Key Results": "Fifteen studies were identified (9 observational, 6 RCTs), with 14 of 15 (93%) published between 2017 and 2021. Risk of bias was high in 14 of 15 studies (93%). Most studies (11/15, 73%) had sample sizes <100. Step count was the most commonly reported physical activity outcome (12/15, 80%). In observational studies, increased physical activity was consistently associated with better outcomes: every additional 100 steps on postoperative day 1 was associated with shorter length of stay (OR 0.63, 95% CI 0.45-0.84; P=.003); patients taking >1050 steps on postoperative day 2 had fewer complications (32% vs 71%; P<.05), shorter time to flatus (2.4 vs 3.3 days; P<.01), and shorter length of stay (5.4 vs 8.8 days; P<.01); each 10% increase in return to preoperative baseline steps was associated with a 40% decrease in 30-day readmission risk (OR 0.60, 95% CI 0.39-0.91; P=.02). However, only 1 of 6 RCTs (17%) demonstrated improved outcomes (shorter time to flatus: 2.3 vs 3.1 days, P=.04; shorter length of stay: 6.6 vs 7.7 days, P=.01) with a mobility-enhancing intervention. Notably, 4 of 6 RCTs (67%) failed to increase postoperative physical activity with their interventions. The well-conducted RCT by Fiore et al found that despite achieving 2-fold greater step counts in the intervention group, primary and secondary outcomes were similar between groups (return to baseline 6MWT at 4 weeks: 54% vs 51%, P=.58).", "Clinical Implications": "This review confirms that accelerometer-measured physical activity is a strong predictor of postoperative outcomes, but the failure of most RCTs to demonstrate benefit from mobility-enhancing interventions raises important questions. Postoperative physical activity may be more of a prognostic indicator than a modifiable risk factor, as factors associated with reduced mobilization and worse outcomes overlap (e.g., preoperative fitness, surgical approach, operative duration). The high risk of bias across studies, small sample sizes, and use of consumer-grade accelerometers with proprietary algorithms (80% of studies) limit the ability to synthesize specific mobilization recommendations. Most validation studies of accelerometers have been conducted in laboratory or free-living conditions, not in inpatient settings where patients walk significantly slower. Future research should focus on higher-risk populations (e.g., open surgery, frail patients), clearly define mobilization components (timing, type, duration, frequency, intensity), adequately control for confounders, and measure physical behaviors beyond step counts to capture the full spectrum of inpatient mobility."}