Early postoperative 6-minute walk test in cardiac surgery patients: an observational study assessing safety, feasibility, and predictors of completion in India

Prasanth Jayaraman; Puvaneswari Kanagaraj; Shrinivas Hittalamani

doi:10.4266/acc.000050

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Original Article Nursing Early postoperative 6-minute walk test in cardiac surgery patients: an observational study assessing safety, feasibility, and predictors of completion in India: Acute and Critical Care 2025;40(4):614-626.
DOI: https://doi.org/10.4266/acc.000050
Published online: November 28, 2025

Prasanth Jayaraman¹

, Puvaneswari Kanagaraj²

, Shrinivas Hittalamani³

¹Narayana Hrudayalaya Institute of Cardiac Sciences, Bangalore, India

²Department of Nursing, College of Applied Medical Sciences, University of Bisha, Bisha, Saudi Arabia

³Department of Intensive Care, Dr. Sulaiman Al Habib Hospital, Dubai, United Arab Emirates

Corresponding Author: Puvaneswari Kanagaraj Department of Nursing, College of Applied Medical Sciences, University of Bisha, P.O. Box 551, Bisha, Saudi Arabia Tel: +966-50-977-8016, Email: puvaneswariramesh@gmail.com

• Received: June 25, 2024 • Revised: August 13, 2025 • Accepted: August 15, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Abstract
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
KEY MESSAGES
NOTES
SUPPLEMENTARY MATERIALS
REFERENCES

Abstract

Background
Early mobilization after cardiac surgery is crucial for enhancing recovery, minimizing complications, and promoting timely discharge. The 6-minute walk test (6MWT) is a validated measure of functional capacity; however, its use during the early postoperative period—particularly in intensive care unit (ICU) settings in India—remains underexplored. This study assesses the safety, feasibility, and functional performance outcomes of the 6MWT administered on postoperative days (PODs) 2 to 4 and identifies factors associated with test completion.
Methods
A cohort-based observational study was conducted in a tertiary care ICU between June and September 2021. In total, 150 cardiac surgery patients aged 30–70 years were enrolled. Inclusion required hemodynamic stability, no vasopressor/inotropic support, and ambulation from POD 2. The 6MWT was administered per the American Thoracic Society guidelines. Clinical, demographic, and physiological parameters were recorded and analyzed using descriptive statistics, paired t-tests, and regression analyses.
Results
Of the 150 patients, 140 completed the test. The mean age was 52±14 years, and 75% of participants were male. Mean walking distances improved from 78.14 m (21.7% of predicted) on POD 2 to 193.51 m (53.75%) on POD 4. Completion rates increased from 40.0% to 99.2%. Physiological responses remained within safe limits, and no serious adverse events occurred. The regression analyses identified education, diet, and oxygen saturation as positive predictors and comorbidities, being female, oxygen use, and physical occupation as negative predictors.
Conclusions
The 6MWT is a safe, feasible, and informative tool for assessing early functional recovery in stable post-cardiac surgery ICU patients to aid individualized rehabilitation and discharge planning.
Key Words: cardiac rehabilitation; cardiac surgical procedures; exercise tolerance; postoperative period; walk test

INTRODUCTION

Cardiovascular disease (CVD) remains the leading cause of mortality worldwide, accounting for approximately 19.8 million deaths in 2022—nearly one-third of all human deaths globally [1]. This growing burden is driven by demographic shifts such as population aging, increasing urbanization, sedentary lifestyles, and metabolic risk factors, including diabetes mellitus (DM) and hypertension (HTN) [2]. Low- and middle-income countries are disproportionately affected, with India alone contributing nearly 20% of global CVD-related deaths, often in a relatively young population [3]. In India, CVD accounts for 28.1% of total mortality [4]. Consequently, there has been a substantial rise in cardiac surgical procedures—particularly coronary artery bypass grafting (CABG) and valve replacement surgeries—with current estimates indicating that approximately 300,000 such procedures are performed annually [5].

These surgical interventions significantly improve survival, alleviate symptoms, and enhance quality of life [6]. However, the early postoperative period presents challenges, including diminished functional capacity, reduced skeletal muscle strength, and a heightened risk of pulmonary complications such as pneumonia, pleural effusion, and atelectasis [7]. Optimizing functional recovery during this phase is essential for improving patient outcomes, minimizing complications, shortening hospital stays, and reducing readmission rates [8].

Functional capacity is a key prognostic indicator following cardiac surgery that reflects both physiological recovery and surgical success [9]. Among the available assessment tools, the 6-minute walk test (6MWT) is a simple, submaximal, and objective measure that correlates well with peak oxygen uptake and is feasible in clinical settings [10,11]. A walking distance of 300–360 m generally corresponds to a functional capacity of approximately 3.5 metabolic equivalents, which is adequate for performing basic daily activities [11]. Traditionally, the 6MWT is performed close to hospital discharge, typically between postoperative days (PODs) 5 and 7 [12]. However, recent advances in perioperative care and a growing emphasis on early mobilization have increased interest in administering the test earlier during recovery.

The selection of PODs 2 to 4 as a window for functional assessment is based on evidence that most stable patients recover from anesthesia and surgical stress within 48–72 hours, allowing safe initiation of low-intensity mobilization such as the 6MWT [12-14]. Early assessment during this period might help mitigate the effects of physical deconditioning, promote cardiopulmonary recovery, and facilitate the design of individualized rehabilitation protocols [15]. Additionally, functional performance during PODs 2 to 4 could have predictive value for important clinical outcomes, including readiness for discharge, hospital stay duration, and the risk of postoperative complications [16]. This timing also aligns with emerging clinical practice guidelines that recommend the initiation of mobilization by POD 2 in hemodynamically stable cardiac surgery patients [17,18], which reinforces the clinical applicability and relevance of this timing.

Despite those advances, little evidence supports the feasibility, safety, and clinical utility of the 6MWT during this early postoperative window, especially in the Indian healthcare context. A lack of standardized reference data for early 6MWT performance impedes its integration into routine postoperative rehabilitation. The goal of this observational study was to evaluate the safety, feasibility, and functional outcomes (distance walked) of administering the 6MWT to post–cardiac surgery intensive care unit (ICU) patients on PODs 2 to 4 and identify clinical and physiological factors associated with 6MWT completion and performance, thereby informing early rehabilitation strategies and enhancing recovery outcomes.

MATERIALS AND METHODS

Ethical approval was obtained from the Narayana Health Academic Ethics Committee and Institutional Review Board (No. NHH/AEC-CL2020-536). Formal permission was also obtained from the Head of the Cardiac Surgery Department. All participants were fully informed about the study objectives and provided written informed consent. Participation was voluntary, and participants had the right to withdraw at any time without penalty. Confidentiality was maintained, and no identifiable data were collected.

Study Design

This cohort-based observational study was conducted to evaluate early postoperative mobilization using the 6MWT in cardiac surgery patients admitted to the ICU. The study focused on assessing patients’ functional performance and the safety and feasibility of administering the 6MWT on PODs 2 to 4. It was carried out in a single tertiary care center during a 3-month period. The following hypotheses were tested. H1: the 6MWT is safe and feasible for most cardiac surgery patients during the early postoperative period and will not cause significant adverse events. H2: clinical factors (e.g., age, sex, type of surgery, comorbidities) and physiological parameters (e.g., heart rate, oxygen saturation, pain score) are significantly associated with the ability to complete the 6MWT during this period. In this study, the early postoperative period was defined as PODs 2, 3, and 4. A significance level of 0.05 was adopted for hypothesis testing. The study is reported in accordance with the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines (see Supplementary Material 1 for the completed checklist). This study was registered with the Clinical Trial Registry of India (CTRI/2020/12/029843).

Setting

This study was conducted at Narayana Hrudayalaya Institute of Cardiac Sciences, a tertiary care center in India with a total bed capacity of 750. The institution contains three adult ICUs and one pediatric cardiac ICU that offer specialized services for critically ill cardiac patients.

Sampling and Sample Size

Post-cardiac surgical patients formed the accessible population. A consecutive sampling technique was used to reduce selection bias. The sample size was determined based on an earlier observational study conducted at the University of York, UK [19]. In a power analysis conducted with an expected proportion of 0.254, a 7% precision level, and a 95% CI, the calculated sample size was 149. Accordingly, 150 patients were enrolled to ensure adequate representation for data analysis.

Inclusion and Exclusion Criteria

All participants were adults aged 30 to 70 years who were hemodynamically stable by POD 2, did not require inotropic or vasopressor support, and were able to ambulate independently. Patients were excluded if they had been on mechanical ventilation for more than 24 hours, had undergone re-exploration for bleeding or other complications, had a history or risk of arrhythmias or angina, presented with neurological or neuromuscular disorders, or showed signs of disorientation or cognitive impairment.

Study Instruments

A structured tool was used, comprising three components. Part I: demographic and Clinical Variables collected age, sex, occupation, education, dietary pattern, habit of smoking, medical diagnosis, name of the surgery, comorbidities, ejection fraction (EF), and body mass index. Part II: Borg Rating of Perceived Exertion (RPE) scale collected perceived exertion using a 0–10 scale that is categorized as follows: 1 (very light), 2–3 (light), 4–6 (moderate), 7–8 (vigorous), 9 (very hard), and 10 (maximum effort). Part III: 6MWT assessment form captured pre- and post-test physiological parameters: heart rate, blood pressure, respiratory rate, oxygen saturation (SpO₂), pain score, number of laps, and total distance walked in meters.

Validity and Reliability of the Tool

The content validity of the study tool was established through expert evaluation by professionals in anesthesiology, intensive care, and medical-surgical nursing. The Content Validity Index was 0.96 for demographic variables and 0.85 for clinical variables, indicating a high level of agreement. The 6MWT demonstrates excellent test–retest reliability, with an intraclass correlation coefficient of 0.97 [20]. Similarly, the RPE scale showed strong psychometric properties, with reported test–retest reliability ranging from 0.80 to 0.95 and validity coefficients between 0.70 and 0.90 [21,22].

Exposure: 6-Minute Walk Test

The 6MWT was administered according to the American Thoracic Society (ATS) guidelines. It was conducted as a self-paced, submaximal exercise test in a straight, enclosed corridor within the adult ICU. The test formed part of the exercise-based cardiac rehabilitation program initiated on POD 2. A certified physiotherapist, trained in basic life support and advanced cardiovascular life support, conducted the test. The procedure was halted if patients experienced symptoms such as discomfort, dizziness, chest pain, unsteadiness, muscle cramps, or excessive sweating. Emergency equipment, including a crash cart, automated external defibrillator, and a chair, was available on-site as per the ATS protocols.

Data Collection

Data collection was conducted from June 6 to September 2, 2021. Eligible participants were recruited consecutively based on the predefined inclusion and exclusion criteria. The 6MWT was initiated by the physiotherapy team on POD 2. The primary investigator, a nurse practitioner, observed all test sessions across the three days for each patient without interfering with the physiotherapy team. The data collected included reasons for test termination.

Data Analysis

In alignment with the study objectives, data were analyzed using both descriptive and inferential statistics in IBM SPSS statistics version 22 (IBM Corp.). The descriptive statistics for the demographic and clinical variables, completion rates, and adverse events are presented as frequencies and percentages (Tables 1 and 2). Means and standard deviations were calculated for continuous variables, including the 6-minute walk distance (6MWD) and physiological parameters. Paired t-tests were used to assess changes in physiological parameters—SpO₂, heart rate, respiratory rate, pain score, and blood pressure—before and after the 6MWT on PODs 2 to 4 (Table 3). Regression analyses were used to identify predictors of 6MWT performance and non-completion. Two multiple linear regression models were developed separately for sociodemographic/nutritional and physiological/clinical variables. Independent variables were selected based on their clinical relevance, univariate significance (P<0.10), and absence of multicollinearity, assessed using the variance inflation factor. Stepwise regression was applied to derive the most parsimonious models, and changes in R² are reported. Additionally, stepwise regression was used to identify predictors of 6MWT non-completion on PODs 2 and 3. Complete data were available for all 140 participants; hence, no imputation was necessary.

RESULTS

Of the 150 patients initially recruited, 10 were excluded from the 6MWT due to predefined safety concerns—five with hypotension, four with tachycardia, and one who voluntarily withdrew. The remaining 140 clinically stable patients commenced testing from POD 2, and all completed 6MWT assessments on PODs 2, 3, and 4 except one patient on POD 4 (Figure 1).

Demographic and Clinical Characteristics

Most of the post-cardiac surgery patients were older than 50 years, with 33.6% older than 60 and 31.4% between 51 and 60 years. Males comprised 75% of the sample. Most patients were employed (61.4%) and had attained at least a graduate-level education (37.9%). A predominant proportion (91.4%) followed a non-vegetarian diet, and 12.1% reported a history of smoking. Coronary artery disease (52.9%) and valvular heart disease (45%) were the most common diagnoses, consistent with the surgeries performed: CABG in 52.9% and valve replacement in 47.1% of patients. Nearly 39% of participants had no comorbidities, and 20% had both HTN and DM. EF was mainly between 46%–50% (37.9%) and 36%–45% (27.9%). Regarding body mass index, 42.1% of the participants were overweight, 37.9% had normal weight, and 12.9% were obese (Table 1).

Functional Performance and Perceived Exertion

Patients demonstrated progressive improvement in functional performance and reduced perceived exertion from POD 2 to POD 4 (Figure 2). On POD 2, most patients (95%) completed only 1–10 laps, with the majority (62.2%) walking between 201 and 300 steps. By POD 4, a substantial shift had occurred, with 72.9% completing 11–20 laps and 21.4% achieving 21–30 laps. Correspondingly, 59.3% walked between 401 and 500 steps, indicating notable gains in endurance. Perceived exertion decreased over time, with “light” exertion reports rising from 9.3% on POD 2 to 79.3% on POD 4, while “moderate” exertion dropped from 90% to 20.7%. No participants reported vigorous exertion after POD 2.

Distance Walked and Safety Outcomes

The average 6MWD increased significantly across the early PODs. The mean 6MWD on POD 2 was 78.14±29.24 m, representing 21.7% of the predicted distance (360 m), and the test completion rate was 40%. The reference value of 360 m was adopted as a standardized benchmark based on established norms for minimal predicted 6MWD in older adults recovering from cardiac surgery, as supported by prior studies and clinical guidelines [11,23]. Although predictive equations can vary depending on population characteristics, the use of a consistent reference point (360 m) allows for meaningful comparisons of functional capacity across PODs and facilitates monitoring of early recovery progress within the ICU setting. Completion rates improved significantly over time, rising to 79.2% on POD 3 and 99.2% on POD 4. Correspondingly, the mean 6MWD increased to 136.71±34.9 m (37.8%) on POD 3 and 193.51±43.71 m (53.75%) on POD 4. Adverse events were minimal. On POD 2, 11 participants discontinued the test due to sternal pain (n=7), fatigue (n = 3), or drowsiness (n=1), with an average early termination time of 20.45 seconds. On POD 3, only one participant discontinued early (12 seconds). By POD 4, nearly all patients (99.2%) successfully completed the 6MWT without interruption, highlighting both the safety and increasing tolerance of the test during the early postoperative period (Table 2).

Physiological Responses to the 6MWT

Physiological measurements taken before and after the 6MWT from POD 2 to POD 4 revealed a significant decrease in SpO₂ on POD 2 (t=2.078, P<0.05) and POD 3 (t=3.194, P<0.01), though the values remained within safe limits. The respiratory rate increased significantly after the test on all days, most notably on POD 2 (t=11.489), reflecting the normal exertional response. The oxygen requirement remained unchanged, indicating adequate cardiopulmonary reserve. The heart rate rose significantly post-test across all days, with the highest increase on POD 4 (t=10.454). Pain scores showed minor, but significant, increases on POD 2 and 3, but not on POD 4. Blood pressure remained stable, except for a slight decrease in diastolic pressure on POD 4 (t=3.150, P<0.001), which was not clinically significant. These results confirm the expected physiological changes with minimal adverse effects, supporting the safety and feasibility of performing the 6MWT in the early postoperative period (Table 3).

Predictors of 6MWT Performance

Multiple linear regression analyses identified significant predictors of 6MWT performance. In the sociodemographic model, three variables were significant: Occupation was negatively associated with performance (B=–22.498, β=–0.252, P=0.008), suggesting reduced test completion among those engaged in physically demanding work; education level positively predicted 6MWD (B=6.539, β=0.182, P=0.043), as did adherence to a non-vegetarian diet (B=28.722, β=0.185, P=0.034). This model explained 14.6% of the variance in walking performance (R²=0.146). In the physiological/clinical model, baseline SpO₂ positively predicted performance (B=50.917, β=0.195, P=0.020), and higher oxygen requirement was a negative predictor (B=–21.630, β=–0.250, P=0.002); better spirometry scores were also associated with improved walking distance (B=20.562, β=0.179, P=0.034). This model accounted for 19.6% of the variance (R²=0.196) (Table 4).

Predictors of 6MWT Non-completion

A stepwise multiple regression analysis identified key predictors of 6MWT non-completion on PODs 2 and 3. On POD 2 (n=84), two variables were significantly associated with 6MWT non-completion. The presence of comorbidities (B=–10.46, β=–0.352, P=0.012; 95% CI, –18.54 to –2.38) explained 12.4% of the variance. This suggests that patients with underlying chronic conditions were more likely than others to be unable to complete the test. Sex also emerged as a significant predictor (B=20.16, β=0.233, P=0.025; 95% CI, 2.54 to 37.78), with male patients showing a greater likelihood than female patients of completing the 6MWT. The inclusion of sex increased the explained variance to 15.3%. On POD 3 (n=35), sex remained a significant factor (B=10.117, β=0.453, P=0.014; 95% CI, 2.24 to 17.99), accounting for 20.5% of the variance, further reinforcing that female sex could be associated with reduced early postoperative mobility (Table 5).

DISCUSSION

This study demonstrates that the 6MWT is a safe, feasible, and clinically valuable tool for assessing early functional recovery from PODs 2 to 4 in hemodynamically stable cardiac surgery patients in the ICU. Progressive improvement in walking distance, completion rates, and perceived exertion was observed across the three days, with no serious adverse events. Regression analyses identified education, diet, and SpO₂ as positive predictors of 6MWD, and comorbidities, occupation, oxygen use, and female sex were associated with lower performance and test non-completion.

The demographic profile revealed a predominantly older adult cohort, with a large proportion older than 50 years, consistent with global trends of increased cardiac surgeries among aging populations due to cumulative cardiovascular risk [24]. The marked male predominance reflects well-documented sex disparities in cardiac disease incidence [25]. Socioeconomic indicators such as employment status and educational attainment indicated a relatively health-literate population. Most patients were employed and had completed at least secondary or graduate-level education, both of which have been associated with good adherence to rehabilitation and clinical guidance [26,27]. Dietary patterns showed a strong preference for non-vegetarian diets. Although such diets can support recovery through higher protein intake, they also carry potential cardiovascular risks, depending on their composition [28]. Smoking prevalence was low, potentially reflecting the effectiveness of public health policies or possibly underreporting.

Comorbidities, particularly HTN and DM, were common and are known to impede postoperative recovery [29]. The surgical case mix included nearly equal proportions of CABG and valve replacement procedures, suggesting a dual burden of ischemic and valvular heart diseases. Notably, a significant portion of the cohort had preserved or mildly reduced EF, and more than half were overweight or obese, which are established risk factors that influence postoperative recovery trajectories [30,31].

Functional recovery demonstrated progressive improvement during the early postoperative period, as reflected in increasing 6MWT completion rates and the reduction of adverse events. Early ambulation, beginning on POD 2, was feasible and well tolerated in these hemodynamically stable patients. Although a few patients required early termination on POD 2 due to mild symptoms such as sternal pain and fatigue, no major complications were recorded. These findings align with previous research demonstrating the safety and efficacy of early mobilization in cardiac surgery patients [17,32,33].

Improvement in functional capacity over time, as evidenced by enhanced walking performance and reduced exertion levels, supports the 6MWT as both a safe and sensitive tool for monitoring early postoperative progress, consistent with reports of rapid gains in submaximal exercise capacity during the first postoperative week [13]. Additionally, the progressive decline in perceived exertion and absence of adverse events by POD 4 reinforce the tolerability and clinical utility of the test [23].

Although some studies recommend delaying such assessments until after discharge [34], the current findings demonstrate that the 6MWT can be safely performed during ICU recovery. The use of a standardized reference value (360 m) facilitated day-to-day comparison and functional trend analysis, even though population-specific prediction equations were not applied—an approach that enhances applicability in acute care environments where complex assessments might not be feasible.

Physiological responses to the 6MWT were consistent with expected exertional patterns. A transient, statistically significant but clinically negligible drop in SpO₂ on POD 2 aligned with earlier observations of mild desaturation during early mobilization [12]. The respiratory rate increased significantly post-test across all days, reflecting normal exertional physiology, as reported in previous studies [35], but the oxygen requirement remained stable, indicating adequate cardiopulmonary adaptation during early mobilization [32]. Heart rate elevations post-6MWT on all PODs confirmed cardiovascular responsiveness [13], and minor increases in pain on PODs 2 and 3 did not impair test feasibility, consistent with prior observations of manageable discomfort during early ambulation [36]. Blood pressure remained stable, suggesting hemodynamic safety [33].

Multivariate regressions revealed several significant predictors of 6MWT performance. Occupational status was negatively associated with completion, possibly due to physical demands or return-to-work anxiety. Educational attainment, in contrast, positively influenced test performance highlighting the role of health literacy in postoperative recovery [27]. Interestingly, a non-vegetarian dietary pattern also predicted better performance, which might be attributable to higher protein intake facilitating muscular recovery, although that remains a nuanced and debated topic, given dietary risks [28]. Among the physiological predictors, higher baseline SpO₂ and spirometry values supported successful test completion, consistent with a previous prospective cohort study [10].

The stepwise regression analysis identified comorbidities and sex as key predictors of 6MWT non-completion, particularly on POD 2. Patients with DM, HTN, or both demonstrated delayed functional recovery, in line with prior research [9,29].Female sex was also associated with reduced test completion, consistent with reports of lower exercise capacity in females during early recovery [37]. However, such disparities might diminish with equitable access to rehabilitation in later stages, highlighting the need for targeted support for female patients during the early postoperative period.

In summary, this study confirms that the 6MWT is a safe, feasible, and valuable tool for evaluating early functional recovery in hemodynamically stable patients following cardiac surgery. When guided by clinical stability, its use from POD 2 onward can support individualized mobilization plans, track progress effectively, and identify patients at risk for delayed recovery. Early integration of structured ambulation protocols, with attention to comorbidities and sex-specific needs, could enhance outcomes and accelerate rehabilitation in the critical early phase of postoperative care.

Despite its strengths, this study has certain limitations that warrant consideration. First, it was conducted at a single center with a specific patient population, which might limit the generalizability of the findings to broader or more diverse cardiac surgical populations. Second, although the 6MWT was initiated early, patients who developed hemodynamic instability (e.g., hypotension, tachycardia) prior to test initiation or required prolonged ventilation or inotropic support were excluded based on predefined safety criteria. This selective inclusion could limit the applicability of these findings to more critically ill cardiac surgery patients. Third, although the use of a standardized reference value (360 m) allowed for simplified comparisons, population-specific predictive equations might have provided more individualized benchmarks. Additionally, factors such as pain management protocols, psychological readiness, and environmental influences were not explicitly analyzed, though they might have influenced mobility outcomes. Lastly, follow-up beyond POD 4 was not conducted, limiting insight into longer-term recovery trajectories.

This study confirms that the 6MWT is a safe, feasible, and effective tool for assessing early functional recovery in stable patients after cardiac surgery. Progressive improvements in performance and minimal adverse events support its use from POD 2 onward in hemodynamically stable patients. The test also helped identify key predictors of recovery, enabling more targeted postoperative care. Broader studies with extended follow-up are recommended to further validate these findings.

KEY MESSAGES

• This study establishes the safety and feasibility of initiating the 6-minute walk test (6MWT) as early as postoperative day (POD) 2 in stable post-cardiac surgery patients, with minimal adverse events.

• The findings highlight significant functional gains and reduced exertion from PODs 2 to 4, validating 6MWT as a reliable tool for monitoring early intensive care unit recovery.

• This study identifies comorbidities, oxygen requirement, education level, and sex as key predictors of early mobility, underscoring the need for tailored rehabilitation approaches adaptable to diverse clinical and healthcare settings.

NOTES

CONFLICT OF INTEREST

No potential conflict of interest relevant to this article was reported.

FUNDING

None.

ACKNOWLEDGMENTS

The authors are thankful to the Deanship of Scientific Research at University of Bisha for supporting this work through the Fast-Track Research Support Program. We appreciate and thank the post-operative cardiac patients who participated in the study. Special thanks to the administrators and team members of the adult intensive care unit for their motivation and support during data collection.

AUTHOR CONTRIBUTIONS

Conceptualization: PJ, PK, SH. Methodology: PJ, PK, SH. Formal analysis: PJ, SH. Data curation: PJ, PK. Writing - original draft: PJ, PK. Writing - review & editing: PJ, PK, SH. All authors read and agreed to the published version of the manuscript.

SUPPLEMENTARY MATERIALS

Supplementary materials can be found via https://doi.org/10.4266/acc.000050.

Supplementary Material 1.

STROBE statement—checklist of items that should be included in reports of cohort studies

acc-000050-Supplementary-Material-1.pdf

Figure 1.

Flow diagram. 6MWT: 6-minute walk test; POD: postoperative day.

Figure 2.

Functional performance and perceived exertion during the 6-minute walk test (6MWT) across postoperative days (PODs) 2 to 4 in cardiac surgery patients. (A) Number of laps completed during the 6MWT (stacked percentage). (B) Total steps covered during the 6MWT (grouped percentage). (C) Perceived exertion during the 6MWT (grouped percentage). 1 Lap=1.3 m.

Table 1.

Frequency and percentage distribution of postoperative cardiac surgery patients by demographic and clinical variables (n=140)

Variable	f	%
Age (yr)
<40	19	13.6
41–50	30	21.4
51–60	44	31.4
>60	47	33.6
Sex
Male	105	75.0
Female	35	25.0
Occupation
Employed	86	61.4
Unemployed	54	38.6
Education
Graduation	53	37.9
Higher secondary school	33	23.6
High school	27	19.3
Primary school	22	15.7
Illiterate	5	3.5
Dietary pattern
Vegetarian	12	8.6
Non-vegetarian	128	91.4
Habit of smoking
Yes	17	12.1
No	123	87.9
Medical diagnosis
Coronary artery disease	74	52.9
Valvular heart disease	63	45.0
Rheumatic heart disease	3	2.1
Name of the surgery
CABG	74	52.9
Valve replacement	66	47.1
Comorbidity
HTN	27	19.3
DM	17	12.1
HTN and DM	28	20
Hypothyroidism	5	3.5
Hypothyroidism, HTN and DM	4	2.9
Others	5	3.6
No comorbidities	54	38.6
Ejection fraction (%)
≤35	8	5.7
36–45	39	27.9
46–50	53	37.9
51–55	33	23.5
≥56	7	5.0
BMI
Underweight	10	7.1
Normal	53	37.9
Overweight	59	42.1
Obese	18	12.9

CABG: coronary artery bypass grafting; HTN: hypertension; DM: diabetes mellitus; BMI: body mass index.

Table 2.

6MWD, percentage of predicted value, completion rates, and adverse events across postoperative days 2 to 4 in cardiac surgery patients (n=140)

POD	6MWD (m, mean±SD)	% Predicted 6MWD (360 m)	Range (m)	Attempted- 6MWT	Completed 6MWT (n, %)	Stopped early adverse events	Average time taken to stop (sec)
2	78.14±29.24	21.7	30–170	140	56 (40.0)	11 (7%): sternal pain (n=7), fatigue (n=3), drowsiness (n=1)	20.45
3	136.71±34.9	37.8	56–256	140	111 (79.2)	1 (0.7%): sternal pain	12
4	193.51±43.71	53.8	86–296	140	139 (99.2)	0	0

6MWD: 6-minute walk distance; POD: postoperative day; SD: standard deviation; 6MWT: 6-minute walk test

Table 3.

Mean and SD of SPO₂, respiratory rate, oxygen requirement, heart rate, pain and blood pressure with baseline and post-observation with 6MWT on PODs 2, 3, and 4 (n=140)

	Observation	POD 2		POD 3		POD 4
	Observation	Mean±SD	t (P-value)	Mean±SD	t (P-value)	Mean±SD	t (P-value)
SPO₂ (%)	Baseline	98.79±1.130	2.078 (0.040)	99.55±0.68	3.194 (0.0017)	99.98±0.12	0.816 (0.416)
SPO₂ (%)	Post-observation	97.87±1.67	2.078 (0.040)	99.34±0.71	3.194 (0.0017)	99.97±0.17	0.816 (0.416)
Respiratory rate (breath/min)	Baseline	19.64±3.26	11.489 (<0.001)	17.76±8.54	2.411 (0.017)	14.67±1.93	2.411 (0.017)
Respiratory rate (breath/min)	Post-observation	22.7±4.04	11.489 (<0.001)	19.5±2.69	2.411 (0.017)	17.53±1.89	2.411 (0.017)
Oxygen requirement (L/min)	Baseline	3.9±0.99	1.643 (0.103)	2.57±0.91	0.419 (0.676)	2.15±0.52	0.377 (0.707)
Oxygen requirement (L/min)	Post-observation	3.96±0.97	1.643 (0.103)	2.59±0.91	0.419 (0.676)	2.14±0.50	0.377 (0.707)
Heart rate (beats/min)	Baseline	88.11±13.14	6.081 (<0.001)	86.45±10.86	2.214 (0.028)	82.36±9.17	10.454 (<0.001)
Heart rate (beats/min)	Post-observation	92.42±14.05	6.081 (<0.001)	88.46±13.81	2.214 (0.028)	87.27±10.15	10.454 (<0.001)
Pain score	Baseline	4.22±0.68	5.705 (<0.001)	3.58±0.55	3.235 (0.002)	3.21±0.41	1.745 (0.083)
Pain score	Post-observation	4.46±0.64	5.705 (<0.001)	3.68±0.61	3.235 (0.002)	3.25±0.43	1.745 (0.083)
Systolic BP (mm Hg)	Baseline	122.84±15.58	0.697 (0.487)	126.02±14.02	0.294 (0.769)	126.3±8.46	0.394 (0.694)
Systolic BP (mm Hg)	Post-observation	122.19±15.87	0.697 (0.487)	126.31±9.89	0.294 (0.769)	126.53±8.76	0.394 (0.694)
Diastolic BP (mm Hg)	Baseline	68.01±11.09	1.148 (0.253)	68.19±9.78	1.835 (0.069)	68.74±8.27	3.150 (0.002)
Diastolic BP (mm Hg)	Post-observation	67.11±11.48	1.148 (0.253)	66.83±11.1	1.835 (0.069)	66.74±10.22	3.150 (0.002)

SD: standard deviation; SPO₂: peripheral capillary oxygen saturation; 6MWT: 6-minute walk test; POD: postoperative day; BP: blood pressure.

Table 4.

Multiple regression analysis of association of factors affecting the ability to complete the 6MWT among post cardiac surgical patients (n=140)

Factor	Unstandardized coefficients		Standardized coefficients			95% CI for B
Factor	B	SE	β	t	P-value	95% CI for B
Occupation	–22.498	8.294	–0.252	2.713	0.008	–38.907 to–6.089
Education	6.539	3.196	0.182	2.046	0.043	0.216 to 12.862
Diet pattern	28.722	13.401	0.185	2.143	0.034	2.212 to 55.233
R² change (%)	14.6
SPO₂	50.917	21.546	0.195	2.363	0.020	8.295 to 93.541
Oxygen	–21.631	6.941	–0.250	–3.116	0.002	–35.363 to –7.921
Spirometry	20.562	9.571	0.179	2.148	0.034	1.629 to 39.495
R² change (%)	19.6

6MWT: 6-minute walk test; SE: standard error; SpO₂: peripheral capillary oxygen saturation.

Table 5.

Regression analysis (stepwise) of factors with 6MWT (not completed) among post-cardiac surgical patients on POD 2 (n=84) and POD 3 (n=29)

Factor	Unstandardized coefficients		Standardized coefficients		P-value	95% CI for B	R² change (%)
Factor	B	SE	β	t	P-value		R² change (%)
POD 2
Comorbidity	–10.461	4.021	–0.352	–2.602	0.012	–18.542 to –2.378	12.4
R² change (%)	12.4
Sex	20.162	8.856	233	2.277	0.025	2.542 to 37.784	15.30
R² change (%)	15.3
POD 3
Sex	10.117	3.837	0.453	2.637	14	2.244 to 17.989	20.50
R² change (%)	20.5

6MWT: 6-minute walk test; POD: postoperative day; SE: standard error.

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Early postoperative 6-minute walk test in cardiac surgery patients: an observational study assessing safety, feasibility, and predictors of completion in India

Acute Crit Care. 2025;40(4):614-626. Published online November 28, 2025

DOI: https://doi.org/10.4266/acc.000050

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Figure

Early postoperative 6-minute walk test in cardiac surgery patients: an observational study assessing safety, feasibility, and predictors of completion in India

Figure 1. Flow diagram. 6MWT: 6-minute walk test; POD: postoperative day.

Figure 2. Functional performance and perceived exertion during the 6-minute walk test (6MWT) across postoperative days (PODs) 2 to 4 in cardiac surgery patients. (A) Number of laps completed during the 6MWT (stacked percentage). (B) Total steps covered during the 6MWT (grouped percentage). (C) Perceived exertion during the 6MWT (grouped percentage). 1 Lap=1.3 m.

Figure 1.

Figure 2.

Early postoperative 6-minute walk test in cardiac surgery patients: an observational study assessing safety, feasibility, and predictors of completion in India

Variable	f	%
Age (yr)
<40	19	13.6
41–50	30	21.4
51–60	44	31.4
>60	47	33.6
Sex
Male	105	75.0
Female	35	25.0
Occupation
Employed	86	61.4
Unemployed	54	38.6
Education
Graduation	53	37.9
Higher secondary school	33	23.6
High school	27	19.3
Primary school	22	15.7
Illiterate	5	3.5
Dietary pattern
Vegetarian	12	8.6
Non-vegetarian	128	91.4
Habit of smoking
Yes	17	12.1
No	123	87.9
Medical diagnosis
Coronary artery disease	74	52.9
Valvular heart disease	63	45.0
Rheumatic heart disease	3	2.1
Name of the surgery
CABG	74	52.9
Valve replacement	66	47.1
Comorbidity
HTN	27	19.3
DM	17	12.1
HTN and DM	28	20
Hypothyroidism	5	3.5
Hypothyroidism, HTN and DM	4	2.9
Others	5	3.6
No comorbidities	54	38.6
Ejection fraction (%)
≤35	8	5.7
36–45	39	27.9
46–50	53	37.9
51–55	33	23.5
≥56	7	5.0
BMI
Underweight	10	7.1
Normal	53	37.9
Overweight	59	42.1
Obese	18	12.9

POD	6MWD (m, mean±SD)	% Predicted 6MWD (360 m)	Range (m)	Attempted- 6MWT	Completed 6MWT (n, %)	Stopped early adverse events	Average time taken to stop (sec)
2	78.14±29.24	21.7	30–170	140	56 (40.0)	11 (7%): sternal pain (n=7), fatigue (n=3), drowsiness (n=1)	20.45
3	136.71±34.9	37.8	56–256	140	111 (79.2)	1 (0.7%): sternal pain	12
4	193.51±43.71	53.8	86–296	140	139 (99.2)	0	0

	Observation	POD 2		POD 3		POD 4
	Observation	Mean±SD	t (P-value)	Mean±SD	t (P-value)	Mean±SD	t (P-value)
SPO₂ (%)	Baseline	98.79±1.130	2.078 (0.040)	99.55±0.68	3.194 (0.0017)	99.98±0.12	0.816 (0.416)
SPO₂ (%)	Post-observation	97.87±1.67	2.078 (0.040)	99.34±0.71	3.194 (0.0017)	99.97±0.17	0.816 (0.416)
Respiratory rate (breath/min)	Baseline	19.64±3.26	11.489 (<0.001)	17.76±8.54	2.411 (0.017)	14.67±1.93	2.411 (0.017)
Respiratory rate (breath/min)	Post-observation	22.7±4.04	11.489 (<0.001)	19.5±2.69	2.411 (0.017)	17.53±1.89	2.411 (0.017)
Oxygen requirement (L/min)	Baseline	3.9±0.99	1.643 (0.103)	2.57±0.91	0.419 (0.676)	2.15±0.52	0.377 (0.707)
Oxygen requirement (L/min)	Post-observation	3.96±0.97	1.643 (0.103)	2.59±0.91	0.419 (0.676)	2.14±0.50	0.377 (0.707)
Heart rate (beats/min)	Baseline	88.11±13.14	6.081 (<0.001)	86.45±10.86	2.214 (0.028)	82.36±9.17	10.454 (<0.001)
Heart rate (beats/min)	Post-observation	92.42±14.05	6.081 (<0.001)	88.46±13.81	2.214 (0.028)	87.27±10.15	10.454 (<0.001)
Pain score	Baseline	4.22±0.68	5.705 (<0.001)	3.58±0.55	3.235 (0.002)	3.21±0.41	1.745 (0.083)
Pain score	Post-observation	4.46±0.64	5.705 (<0.001)	3.68±0.61	3.235 (0.002)	3.25±0.43	1.745 (0.083)
Systolic BP (mm Hg)	Baseline	122.84±15.58	0.697 (0.487)	126.02±14.02	0.294 (0.769)	126.3±8.46	0.394 (0.694)
Systolic BP (mm Hg)	Post-observation	122.19±15.87	0.697 (0.487)	126.31±9.89	0.294 (0.769)	126.53±8.76	0.394 (0.694)
Diastolic BP (mm Hg)	Baseline	68.01±11.09	1.148 (0.253)	68.19±9.78	1.835 (0.069)	68.74±8.27	3.150 (0.002)
Diastolic BP (mm Hg)	Post-observation	67.11±11.48	1.148 (0.253)	66.83±11.1	1.835 (0.069)	66.74±10.22	3.150 (0.002)

Factor	Unstandardized coefficients		Standardized coefficients			95% CI for B
Factor	B	SE	β	t	P-value	95% CI for B
Occupation	–22.498	8.294	–0.252	2.713	0.008	–38.907 to–6.089
Education	6.539	3.196	0.182	2.046	0.043	0.216 to 12.862
Diet pattern	28.722	13.401	0.185	2.143	0.034	2.212 to 55.233
R² change (%)	14.6
SPO₂	50.917	21.546	0.195	2.363	0.020	8.295 to 93.541
Oxygen	–21.631	6.941	–0.250	–3.116	0.002	–35.363 to –7.921
Spirometry	20.562	9.571	0.179	2.148	0.034	1.629 to 39.495
R² change (%)	19.6

Factor	Unstandardized coefficients		Standardized coefficients		P-value	95% CI for B	R² change (%)
Factor	B	SE	β	t	P-value		R² change (%)
POD 2
Comorbidity	–10.461	4.021	–0.352	–2.602	0.012	–18.542 to –2.378	12.4
R² change (%)	12.4
Sex	20.162	8.856	233	2.277	0.025	2.542 to 37.784	15.30
R² change (%)	15.3
POD 3
Sex	10.117	3.837	0.453	2.637	14	2.244 to 17.989	20.50
R² change (%)	20.5

Table 1. Frequency and percentage distribution of postoperative cardiac surgery patients by demographic and clinical variables (n=140)

CABG: coronary artery bypass grafting; HTN: hypertension; DM: diabetes mellitus; BMI: body mass index.

Table 2. 6MWD, percentage of predicted value, completion rates, and adverse events across postoperative days 2 to 4 in cardiac surgery patients (n=140)

6MWD: 6-minute walk distance; POD: postoperative day; SD: standard deviation; 6MWT: 6-minute walk test

Table 3. Mean and SD of SPO2, respiratory rate, oxygen requirement, heart rate, pain and blood pressure with baseline and post-observation with 6MWT on PODs 2, 3, and 4 (n=140)

SD: standard deviation; SPO₂: peripheral capillary oxygen saturation; 6MWT: 6-minute walk test; POD: postoperative day; BP: blood pressure.

Table 4. Multiple regression analysis of association of factors affecting the ability to complete the 6MWT among post cardiac surgical patients (n=140)

6MWT: 6-minute walk test; SE: standard error; SpO₂: peripheral capillary oxygen saturation.

Table 5. Regression analysis (stepwise) of factors with 6MWT (not completed) among post-cardiac surgical patients on POD 2 (n=84) and POD 3 (n=29)