Association between early mobilisation after abdominal cancer surgery and postoperative complications

and secondary outcome was severity of complications. Data were obtained from medical records. Logistic regression was used to investigate the association between exposure and outcomes. Results: Of 133 patients included in the study, 25 were readmitted to the hospital within 30 days after discharge. The analysis showed no association between early mobilisation and readmission or severity of complications. Conclusion: Early mobilisation does not seem to increase the odds of readmission, nor the severity of complications. This study contributes to the limited research on the association between early mobi-lisation and postoperative complications after abdominal cancer surgery. © 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:/


Introduction
Early mobilisation at hospital is thought to reduce postoperative complications after major abdominal cancer surgery [1].Readmission to hospital due to postoperative complications after discharge is common after abdominal cancer surgery with a high rate of cardiovascular, pulmonary, gastrointestinal, or infectious complications [2e6].To maintain physical function and optimise recovery, early mobilisation is one of several interventions in the protocol for enhanced recovery after surgery (ERAS) [1].ERAS is established within most abdominal surgical disciplines and has shown effects by reducing hospital stay and postoperative complications [7].For early mobilisation, the protocol recommends that patients be out of bed for at least 2 h on the day of surgery, and thereafter at least 6 h per day until discharge [8].Although included in the ERAS protocol, evidence for early mobilisation after abdominal cancer surgery is scarce [9,10].Incomplete descriptions of protocols for mobilisation and the absence of objectively measured mobilisation have resulted in recommendations not to use structured mobilisation protocols after abdominal surgery [9].Adherence to early mobilisation according to the ERAS protocol has also been shown to be low, although it is seldom measured [11,12].As a result of the lacking evidence, early mobilisation is mainly recommended based on evidence of prolonged immobilisation [13,14].
In a recent non-randomised controlled trial (nRCT), we evaluated the Activity Board (Tr€ aningstavlan® Phystec) as a method to enhance mobilisation and postoperative recovery after abdominal cancer surgery [15].All patients in the trial received individualised standard treatment, i.e., evidence-based physiotherapy including mainly mobilisation and breathing exercises, until discharge from hospital.Approximately seventy-five percent of the patients were treated according to ERAS protocols or Enhanced Recovery Programme (ERP) [8,16,17].One group of patients were allocated to also use the Activity Board.Level of mobilisation was measured with the activity monitor activPAL™.The results showed that the patients with the Activity Board had higher levels of mobilisation, particularly more steps per day.The patients allocated to the Activity Board also had a shorter time to first flatus and stool, as well as a shorter hospital stay.
Due to the limited evidence for early mobilisation after abdominal cancer surgery, knowledge on how early mobilisation may influence the development of postoperative complications is also scarce.In general, physical activity has a positive impact on the immune system, blood circulation and bowel peristalsis [18e20].Hence, in theory, early mobilisation might influence the development of postoperative complications, such as infections, thromboses and ileus.However, what level of early mobilisation is safe for the patients and optimises recovery is unknown.The aim of this study was therefore to evaluate the association between the level of early mobilisation after major abdominal cancer surgery and readmission to hospital due to postoperative complications.In addition, we investigate the association between level of early mobilisation and severity of postoperative complications, as well as different categories of complications.

Participants and setting
This observational study was based on a secondary analysis of an nRCT, and the reporting of the study follows the STROBE checklist [21].Patients who were planned for abdominal cancer surgery at any of three wards at Karolinska University Hospital between January 2017 and May 2018 were asked to participate in the study.The patients were diagnosed with urinary bladder cancer, colorectal or ovarian cancer, and planned for open or robotic surgery; a hospital stay of at least three days was expected.Only adults who could walk and understand Swedish were included in the study.Preoperative exclusion criteria were neurological disorder, impaired cognition, a pacemaker, and patients undergoing palliative surgery.After surgery, the exclusion criteria were restrictions on sitting, no activity monitor attached to the patient, an extended stay at the postoperative unit or a ward that was not part of the study, or a hospital stay longer than 14 days.Patients with urinary bladder cancer were treated according to an ERP protocol and patients with colorectal cancer were treated according to ERAS protocols [8,16,17].
This study was approved by the regional ethical review board in Stockholm (Dnr 2012/2214-31/4, Dnr 2016/484-32) and the Swedish Ethical Review Authority (2020e06249).Sample size was determined by the number of patients that were included in the analysis of the nRCT.Hence, for this study no power calculation was conducted.Data on demographic and clinical characteristics were obtained from the patients' medical records.The duration of anaesthesia was obtained from the patient data management system for documentation of the perioperative process.

Exposure
Number of steps, as a measure of early mobilisation, during the first three postoperative days was measured with an activity monitor, activPAL3™ micro.The validated activity monitor was attached to the patient's thigh and was worn 24 h a day [22].When the patient mobilises, the activity monitor provides information regarding body posture and acceleration.With the PAL software Suite (PAL Technologies Ltd, version 7, Glasgow, UK), the activPAL data were downloaded, and by proprietary algorithms the number of steps was calculated.The monitor was attached to the thigh with a band-aid and did not give any feedback to the patient.The mean number of steps over the first three postoperative days was used in the analysis as a continuous variable.A three day interval was chosen as all patients stayed at the hospital for at least three days, and we were interested in the early mobilisation, i.e., the first days after surgery.

Outcome variables
Primary outcome was readmission to hospital within 30 days after discharge following abdominal cancer surgery.Some patients were readmitted more than once within 30 days but only the first occasion was used in the analysis [23].Data regarding readmission to hospital was obtained from medical records and was defined as readmission to any hospital in the Stockholm region.The variable readmission was analysed as binary (yes/no).Secondary outcomes were the severity of complications, registered according to the Clavien-Dindo classification, and different categories of complications [24,25].The first author retained data on readmission and complications from the patients' medical records and registered these according to Clavien-Dindo.The complications were then validated by a urologist, one of the co-authors.The most severe complication on each occasion was included in the analysis, and the severity of complications was dichotomised (Clavien 1 or 2/Clavien 3a or 3b).

Covariates
The covariates were first determined based on previous research and clinical relevance, and the final models also included variables related to the outcomes at p 0.2 in adjusted analyses [23].The covariates were sex (men/women), age (75/76 ), smoker (never smoked or quit 6 months before surgery/quit 6 months before surgery or smoker), body mass index (BMI) (24.9/25.0 ), allocated to Activity Board (yes/no), neoadjuvant chemotherapy (yes/ no), previous abdominal cancer surgery (yes/no), classification according to the American Society of Anaesthesiologists (ASA) (1 or 2/ 3 or 4), surgical technique (open/robotic assisted laparoscopic), duration of anaesthesia (time as continuous variable), and length of hospital stay, which was defined as from the day of surgery until the day of discharge (7 days/8 14 days).

Statistical methods
Demographic and clinical characteristics, and overall complications, were described with percentage and proportions for categorical variables.Continuous variables were presented with a mean (sd) if they were normally distributed or with a median (min e max) if the variable was non-normally distributed.Steps were described as the mean number over the first three postoperative days with the median (min e max) due to non-normally distributed data.To evaluate the association between daily steps and readmission, severity of complications, and different categories of postoperative complications, logistic regression was used.Clinically relevant variables and independent variables with p 0.2 were carried forward in the regression analyses for crude and adjusted analyses.The statistical analyses were performed using IBM SPSS statistics version 28.

Participants
In total, 133 patients from the nRCT were included in this study with a mean (sd) age of 68.3 (12.3) years.Most patients had abdominal surgery due to urinary bladder cancer, and the median (min e max) length of hospital stay was 6 [3e14] days.Demographic and clinical characteristics are presented in Table 1.

Readmission and complications
Of the 133 patients, 25 were readmitted to hospital within 30 days after discharge.One patient deceased within 30 days after discharge; this patient was not readmitted to hospital and is therefore not included in the analysis.Some patients were diagnosed with several complications.A description of the overall complications is presented in Table 2.The most common category of complications was infection, which was diagnosed in 60% of the readmitted patients.The mean number of steps taken during the first three postoperative days for the patients who were both not readmitted and readmitted, with respect to severity of complication and infection, are presented, respectively, in Table 3.For a few patients, steps for one, two or even three of the days were missing, and data on the mean number of steps over the three days was, therefore, also missing.The logistic regressions, crude and adjusted, showed no significant associations between early mobilisation and readmission, severity of complication, or infectious complication, see Table 4.

Discussion
This study is one of few that has evaluated the association between early mobilisation during inpatient recovery after abdominal cancer surgery and readmission to hospital.No association was found between the number of steps, as a measure of early mobilisation, and readmission, severity of complications, or infectious complications, respectively.Previous studies have shown that a higher level of early mobilisation after abdominal cancer surgery could be correlated to a shorter hospital stay [10,26].In addition, this study showed that a higher level of early mobilisation was not associated with more complications after discharge.Consequently, a higher level of early mobilisation and a shorter hospital stay seem to be safe for patients concerning the development of postoperative complications at home.
Except for the important aspect of safety, recent studies with patients undergoing major abdominal surgery have shown that more steps early after surgery are associated with a a reduced risk of readmission after discharge [27e29].A high proportion of patients' preoperative steps on the day before discharge was associated with a lower risk of readmission to hospital [27].Another study showed that a low number of steps on the first and second postoperative day was associated with a higher incidence of readmission [28].Moreover, a high number of steps during inpatient recovery up to 34 days could also predict a lower risk for readmission [29].These results are interesting to compare with this study, where the mean number of steps over the first three postoperative days was used as exposure.Defining when during inpatient recovery it is most crucial for patients to achieve a high number of steps that is safe and also reduces the risk of readmission calls for more research.
To reduce the risk of readmission due to postoperative complications, knowledge of when different complications develop is important.The intervention of early mobilisation could thereby theoretically target different complications.The most common postoperative complication and reason for readmission in this study was infectious complications, which confirms previous knowledge on complications after discharge [30,31].Early complications are often defined as complications within 30 days after surgery.Of these early complications, cardiovascular and pulmonary complications seem to primarily occur during the first days or week after surgery [32e34].Depending on the length of hospital stay, they potentially affect patients most often during the hospital stay.Infectious complications, on the other hand, have been suggested to debut approximately at postoperative day three or four, and continue to be common during the first 30 days [32e34].To reduce the frequency of infections after discharge from hospital would have a significant impact on patients' postoperative outcomes.During recent decades, evidence of an association between higher levels of physical activity and less infection has increased [35,36].Therefore, facilitating for higher levels of mobilisation at the hospital and after discharge would possibly hinder the development of infectious complications.
In this study, no association between early mobilisation and readmission due to postoperative complications was shown.However, neither physical activity levels before surgery nor after discharge from hospital were measured, although both could be possible confounders to the association between early mobilisation and readmission.To also measure physical activity after discharge could add important knowledge of when during the postoperative recovery period physical activity has the best possibility to predict readmission.One study with patients who underwent abdominal surgery showed that patients, who at postoperative day 28 took less than 50% of their preoperative number of steps, had an increased risk of readmission to hospital [37].However, it could also be difficult to know if changes in the levels of physical activity after discharge could predict the postoperative complications, or if the changes are results of the postoperative event [38].
Number of steps, as a measure of early mobilisation, was in this study evaluated by activity monitoring, which has been shown to be a valid and feasible method to objectively measure steps in patients who undergo abdominal cancer surgery [39e41].The activity monitoring was chosen since self-reported activity has shown to have low validity [42].Studies that have objectively measured mobilisation after major abdominal surgery have been lacking but have fortunately increased over time [12,43].If the usage of the objective measurement of mobilisation and physical activity after abdominal cancer surgery continues, it will be possible to establish the dose that could lead to fewer complications and readmission.Knowing the optimal timing and dose of early mobilisation and physical activity that is safe and reduces the readmission rate could motivate both patients and the medical team to enhance more mobilisation at the hospital and physical activity at home.
The readmission rate in this study was 19%, much lower than among patients undergoing abdominal surgery for urinary bladder cancer, but it is slightly higher than among patients with colorectal or gynaecological cancer [2,4,44].The patients that were included in this study comprise a heterogenous group with regard to age, preoperative physical status, diagnosis, and severity of diagnosis.The diversity within the studied group could be a strength since the results could be generalised to many patients with ovarian, colorectal, or urinary bladder cancer.However, the absence of information about the patients who were not included in the study could affect generalisability as well.Heterogeneity of included patients can also affect the power of the study, resulting in difficulties in achieving significant results.Another limitation is the unknown levels of physical activity before surgery and after discharge from the hospital.

Conclusion
This study showed no association between early mobilisation after abdominal cancer surgery and readmission or the severity of postoperative complications.The study contributes to the limited research on the association between early mobilisation and postoperative complications after abdominal cancer surgery.That a higher number of steps was not associated with more postoperative complications for this patient group is clinically important for postoperative care.Future larger studies on the association between objectively measured mobilisation and postoperative complications are needed to increase the evidence.Steps for a 100 patients, b 24 patients, c 3 patients, d 14 patients.

Table 4
Associations between mean number of steps over the first three postoperative days and readmission within 30 days after discharge, severity of complications and infectious complication, respectively.

Declarations of interest
None.

Table 1
Demographic and clinical characteristics of study population (n ¼ 133).

Table 3
Steps as mean number over the first three postoperative days, median (min e max), per readmission within 30 days after discharge, severity of complications and infectious complication.
. Porserud, M. Aly, M. Nygren-Bonnier et al.European Journal of Surgical Oncology 49 (2023) 106943 a Adjusted for age, sex, allocation to Activity Board, body mass index, surgical technique, and duration of anaesthesia.bAdjusted for age, sex, and allocation to Activity Board.A