Correlation between Length of Hospital Stay and Gait Speed in Patients Submitted to Cardiac Surgery

Mailing Address: André Luiz Lisboa Cordeiro Rua Japão, 94. Postal Code: 44052-022, Caseb, Feira de Santana, BA – Brazil E-mail: andrelisboacordeiro@gmail.com Correlation between Length of Hospital Stay and Gait Speed in Patients Submitted to Cardiac Surgery André Luiz Lisboa Cordeiro, Daniel Lago Borges, Max Paulo Peruna, André Raimundo Guimarães, Lucas de Assis Cacau Escola Bahiana de Medicina e Saúde Pública, Salvador, BA, Brasil; Hospital Universitário da Universidade Federal do Maranhão, São Luís, MA; Faculdade Nobre; Instituto Nobre de Cardiologia, Feira de Santana, BA; Hospital Primavera, Aracaju, SE – Brazil


Introduction
Cardiovascular diseases have been increasing considerably worldwide, with genetic predisposition, poor diet, and sedentary lifestyle emerging as major triggering factors.¹Thus, an increasing number of highly complex procedures such as cardiac surgery has emerged, and the presence of complications arising from these procedures may increase the length of hospital stay.¹ ,² Despite technological advances, postoperative complications are common and may affect a patient's lung function and peripheral muscle strength.(including atelectasis, pleural effusion, and respiratory failure) may increase the length of hospital stay in patients undergoing invasive mechanical ventilation (IMV) 3 which, in turn, is associated with prolonged hospital stay. 3,4The main complications affecting the musculoskeletal system are respiratory and peripheral muscle weakness and decreased functional capacity, 4 whereas the pulmonary changes include atelectasis, respiratory infection, and hypoxemia. 5erefore, it becomes necessary to evaluate the functional capacity of these patients during the postoperative period because of the potential decline in their activities after surgery.The 6-minute walk test (6MWT) is a practical and inexpensive method that has been used to evaluate treatment responses and functional capacity, in addition to being used as a morbidity and mortality predictor in patients with cardiovascular and respiratory diseases. 6nsidering that increased hospital stay may worsen an individual's ability to perform exercises, as assessed with the 6MWT, the aim of this study was to evaluate the correlation between the duration of hospital stay and walking speed in patients undergoing cardiac surgery.

Methods
This was a prospective cohort study conducted at the Instituto Nobre de Cardiologia (Incardio) at Santa Casa de Misericórdia (Feira de Santana, Bahia) from July to October 2015.The inclusion criteria were patients aged over 18 years, of both genders, and undergoing cardiac surgery (coronary-artery bypass grafting [CABG], aortic and/or mitral valve procedures, or correction of atrial septal defect) via sternotomy and cardiopulmonary bypass (CPB).
We excluded patients who were unable to understand the techniques proposed in the study or who had uncontrolled arrhythmia, hemodynamic instability before or during the 6MWT (systolic blood pressure above 150 mmHg or below 90 mmHg), history of pulmonary disease, neurological and/or motor deficits, and musculoskeletal limitations that prevented the completion of the protocol, in addition to those who were readmitted to the intensive care unit (ICU), had died, or refused to sign the consent form.The study was approved by the Research Ethics Committee of the [omitted] under the protocol number 796,580.
The information collected included the age of the participants and duration of CPB and IVM.
Upon discharge, all patients underwent the 6MWT following recommendations by the American Thoracic Society. 7During the test, the patients were instructed to walk 30 meters as fast as they could without running.The path was marked every 3 meters, with the turnaround point marked with a cone, and the total distance covered by the patient was measured.
To determine the patient's gait speed, we divided the distance walked during the test by 360, which corresponds to the number of seconds in 6 minutes.
At the same time of the 6MWT, we recorded the length of hospital stay in the postoperative period to correlate this variable with the gait speed.

Statistical analysis
We used the Kolmogorov-Smirnov test to analyze the normality of the sample.As the distribution of the sample was deemed normal, we expressed continuous and categorical variables as mean and standard deviation.
In order to correlate the gait velocity with the variables age, length of hospital stay, and duration of CPB and IMV, we used Spearman's correlation.An alpha < 5% was adopted as statistically significant.

Results
A total of 64 patients with a mean age of 57.2 ± 14.06 years were included in the study, of whom 33 were males (51.5%).All participants had been admitted to the Instituto Nobre de Cardiologia, Santa Casa de Misericórdia (Feira de Santana, Bahia -Brazil).
Table 1 shows the characteristics of the patients included in the study.
The mean length of hospital stay was 8.2 ± 2.3 days, and the mean gait speed was 0.98 ± 0.53 m/s.The length of hospital stay correlated significantly with the gait speed (p = 0.02), but this correlation was weak (r = 0.27).The duration of IMV (7.7 ± 2.9 hours) also showed no correlation with the gait speed (r = -0.007,p = 0.96).Other correlations are shown in Table 2.

Discussion
This study demonstrated that the length of hospital stay correlated weakly with the gait speed upon hospital discharge in a sample of patients undergoing cardiac surgery.
These findings are supported by the results of another prospective cohort with a smaller sample size that aimed to evaluate the influence of the pulmonary function, assessed by spirometry before and after surgery, on the walking ability of patients undergoing CABG and/ or valvular replacement.The authors demonstrated a significant correlation between the duration of hospital stay and the distance in the 6MWT, forced vital capacity (FVC), and forced expiratory volume in 1 second (FEV1). 8e mean distance walked after surgery in the present study was 375.8 ± 197.6 meters, which is similar (albeit with a higher standard deviation) to that found by Oliveira et al. 8 of 375.78 ± 50.66 meters.Our findings are also similar to those of another cohort study with a 2-year follow-up that included 215 patients undergoing CABG, in which the sedentary participants walked 375.53 ± 210.92 meters after 2 years. 9The 6MWT is a test well tolerated by adults and elderly patients after cardiac surgery without complications, 10 and the findings of this study suggest that early mobilization and ambulation have an important role in reducing the length of hospitalization.Therefore, the implementation of early mobilization as soon as possible is of paramount importance, and the physiotherapist has a major role in this approach after cardiac surgery. 10,11retrospective survey of women undergoing CABG found a lower complication rate in those operated on without CPB compared with those who underwent the procedure with CPB. 12 Although the study has a larger sample of women and the fact that women have a higher operative mortality, the gender factor had no independent prognostic impact.13 Another study has suggested that an ECC duration longer than 75 minutes increased the mortality rate by 3.2 times in patients over the age of 70 years.[14][15][16] In the study by Nogueira et al., 17 the results suggested that on-pump (versus off-pump) CABG was negatively associated with the patients' functional capacity.
Age above 60 years was an important predictor of death in this study, resulting in two score points.The EuroSCORE determines that there is an increased risk of death above the age of 60 years, with an additional point for each 5 years after this age. 18Age above 85 years is a risk that must be taken into account in patients undergoing CABG. 15,16,19In our study, age showed no significant correlation with gait speed.
On statistical analysis, the duration of IMV showed a poor correlation with the gait speed, which may be justified by a short time on the mechanical ventilator.A prospective study has reported that patients requiring IMV had a mean duration of ventilatory support of 7 days

Original Article
and mean length of ICU stay of 13 days.This study found that half of the patients who were not extubated within 24 hours remained in the ICU for more than one week. 20e of the hypotheses to explain the weak correlation between the variables in the present study is the fact that often, clinical factors such as international normalized ratio (INR) value and echocardiographic alterations may increase the length of hospital stay, but these variables do not correlate with the patient's functional capacity.Therefore, a longer length of hospitalization may be sufficient to help the patients return to their preoperative functionality and perform well during the tests.
The limitations of this study include the small sample size and the lack of information regarding the patients' pulmonary function and body mass index, which can have an impact on the completion of the 6MWT.
Moreover, the study did not include a preoperative evaluation to demonstrate the progression of the gait speed during hospital stay.

Conclusion
We conclude that the length of hospital stay correlated weakly with the gait speed upon hospital discharge in a sample of patients undergoing cardiac surgery.

Table 1 -Characteristics of the sample of patients included in the study
CABG: coronary-artery bypass grafting; CPB: cardiopulmonary bypass; IMV: invasive mechanical ventilation; m/s: meters per second.

Table 2 -Correlation between gait speed and the study variables
a Spearman's correlation coefficient.