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

Abstract

Background:

Cardiovascular diseases have been increasing worldwide in recent decades due to the increased occurrence of triggering factors. In the postoperative period of cardiovascular surgery, patients experience a functional decline, which may be potentiated by the length of hospital stay. Therefore, it is important to evaluate these patients' functional capacity.

Objective:

To compare the length of hospital stay with the gait speed in patients undergoing cardiac surgery.

Method:

Prospective, cohort study carried out at the Instituto Nobre de Cardiologia (Incardio) at Santa Casa de Misericórdia (Feira de Santana, Bahia). Upon discharge, all patients were evaluated with the 6-minute walk test (6MWT). The length of hospital stay in the postoperative period was also recorded at the same time and correlate with the gait speed. We used the Kolmogorov-Smirnov test to evaluate the assumption of normality, and Spearman's correlation to correlate the gait velocity with age, length of hospital stay, and duration of cardiopulmonary bypass (CPB) and invasive mechanical ventilation (IMV). All conclusions were based on a significance level of 5%.

Results:

In all, 64 patients were included (33 males [51.5%], mean age 57.2 ± 14.06 years). The mean distance walked by the patients was 375.8 ± 197.6 meters, the mean gait speed was 0.98 ± 0.53 m/s, and the mean hospital stay was 8.2 ± 2.3 days. A weak correlation was observed between the length of hospital stay and gait speed (r = 0.27 and p = 0.02).

Conclusion:

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

Trial registration:

Registered at CAAE (41151214.5.0000.5654) on June 26, 2015.

Keywords:
Cardiovascular Diseases / surgery; Thoracic Surgery; Hospitalization; Walking; Physiotherapy; Velocity Measurement

Resumo

Fundamento:

As doenças cardiovasculares têm aumentado em todo o mundo nas últimas décadas devido ao aumento na ocorrência de fatores desencadeantes. No período pós-operatório de cirurgia cardiovascular, os pacientes experimentam um declínio funcional, que pode ser potencializado pelo tempo de internação hospitalar. Portanto, é importante avaliar a capacidade funcional destes pacientes.

Objetivo:

Comparar o tempo de internação hospitalar com a velocidade da marcha em pacientes submetidos à cirurgia cardíaca.

Método:

Estudo de coorte prospectivo, realizado no Instituto Nobre de Cardiologia (Incardio) da Santa Casa de Misericórdia (Feira de Santana, Bahia). Na alta hospitalar, todos os pacientes foram avaliados com o teste de caminhada de 6 minutos (TC6). O tempo de internação hospitalar no período pós-operatório foi também registrado no momento da avaliação e correlacionado com a velocidade da marcha. Utilizamos o teste de Kolmogorov-Smirnov para avaliar a suposição de normalidade e a correlação de Spearman para correlacionar a velocidade da marcha com a idade, tempo de hospitalização e com a duração da circulação extracorpórea (CEC) e da ventilação mecânica invasiva (VMI). Todas as conclusões foram baseadas em um nível de significância de 5%.

Resultados:

Ao todo, 64 pacientes foram incluídos (33 homens [51,5%], idade média 57,2 ± 14,06 anos). A distância média percorrida pelos pacientes foi de 375,8 ± 197,6 metros, a média da velocidade da marcha foi de 0,98 ± 0,53 m/s e a média de permanência hospitalar foi de 8,2 ± 2,3 dias. Foi observada uma fraca correlação entre o tempo de internação hospitalar e a velocidade da marcha (r = 0,27 e p = 0,02).

Conclusão:

A duração da hospitalização mostrou uma fraca correlação com a velocidade da marcha na alta hospitalar em uma amostra de pacientes submetidos à cirurgia cardíaca.

Registro do estudo:

Registrado no CAAE (41151214.5.0000.5654) em 26 de junho de 2015.

Palavras-chave:
Doenças Cardiovasculares / cirurgia; Cirurgia Torácica; Hospitalização; Caminhada; Fisioterapia; Medição de Velocidade

Introduction

Cardiovascular diseases have been increasing considerably worldwide, with genetic predisposition, poor diet, and sedentary lifestyle emerging as major triggering factors.¹ Thus, 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. Factors such as age, duration of extracorporeal circulation (ECC), and respiratory complications (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.^3,4 The 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.⁵

Therefore, 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.⁶

Considering 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.⁷ During 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.

Table 1
Characteristics of the sample of patients included in the study

Variable
Gender (n)
Male	33 (51.5%)
Female	31 (48.5%)
Age (years)	57.2 ± 14.06
Type of surgery (n)
CABG	44
Valvular	16
Correction of atrial septal defect	4
Duration of CPB (minutes)	71.3 ± 21.4
Duration of IMV (hours)	7.7 ± 2.9
Walk distance (meters)	375.8 ± 197.6
Walking speed (m/s)	0.98 ± 0.53
Duration of hospital stay (days)	8.2 ± 2.3

• CABG: coronary-artery bypass grafting; CPB: cardiopulmonary bypass; IMV: invasive mechanical ventilation; m/s: meters per second.

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.

Table 2
Correlation between gait speed and the study variables

Variables	Gait speed (m/s)
	ra	p value
Age (years)	-0.17	0.16
Length of hospital stay (days)	0.27	0.02
Duration of cardiopulmonary bypass (minutes)	-0.22	0.07
Duration of mechanical ventilation (hours)	-0.007	0.96

• ^a
  Spearman's correlation coefficient.

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).⁸

The 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.⁹ The 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.^10,11

A retrospective 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.^14-16 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.¹⁸ Age above 85 years is a risk that must be taken into account in patients undergoing CABG.^15,16,19 In 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 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.²⁰

One 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.

• Sources of Funding
  There were no external funding sources for this study.
• Study Association
  This article is part of the thesis of master submitted by André Luiz Lisboa Cordeiro, from Escola Bahiana de Medicina e Saúde Pública.

References

• ¹
  Leguisamo CP, Kalil RA, Furlani AP. Effetiveness of a preoperative physiotherapeutic approach in myocardial revascularization. Braz J Cardiovasc Surg. 2005;20(2):134-41.
• ²
  Shakouri SK, Salekzamani Y, Taghizadieh A, Sabbagh-Jadid H, Soleymani J, Sahebi L, et al. Effect of respiratory rehabilitation before open cardiac surgery on respiratory function: a randomized clinical trial. J Cardiovasc Thorac Res. 2015;7(1):13-7.
• ³
  Pinheiro AR, Christofoletti G. Fisioterapia motora em pacientes internados na unidade de terapia intensiva: uma revisão sistemática. Rev Bras Ter Intensiva. 2012;24(2):188-96.
• ⁴
  Fonseca L, Vieira FN, Azzolin KO. Fatores associados ao tempo de ventilação mecânica no pós-operatório de cirurgia cardíaca. Rev Gaúcha Enf. 2014;35(2):67-72.
• ⁵
  Preisig A, Lagni VB, Almeida VL, Vieira FN, Lucio EA, Santos LJ, et al. Ventilação não invasiva após cirurgia cardiovascular: um ensaio clínico randomizado. Rev Bras Cardiol. 2014;27(1):539-48.
• ⁶
  Laizo A, Delgado FE, Rocha GM. Complicações que aumentam o tempo de permanência na unidade de terapia intensiva na cirurgia cardíaca. Rev Bras Cir Cardiovasc. 2010;25(2):166-71.
• ⁷
  ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories. ATS statement guidelines for the six-minute walk test. Am J Respir Crit Care Med. 2002;166(1):111-7.
• ⁸
  Oliveira EK, Silva VZ, Turquetto AL. Relationship on walk test and pulmonary function tests with the length of hospitalization in cardiac surgery patients. Rev Bras Cir Cardiovasc. 2009;24(4):478-84.
• ⁹
  Nery RM, Martini MR, Vidor CD, Mahmud MI, Zanini M, Loureiro A, et al. Alterações na capacidade funcional de pacientes após dois anos da cirurgia de revascularização do miocárdio. Rev Bras Cir Cardiovasc. 2010;25(2):224-8.
• ¹⁰
  Fiorina C, Vizzardi E, Lorusso R, Maggio M, De Cicco G, Nodari S, et al. The 6-min walking test early after cardiac surgery. Reference values and the effects of rehabilitation programme. Eur J Cardiothorac Surg. 2007;32(5):724-9.
• ¹¹
  Cordeiro AL, Silva AA, Santana MI. Impacto hemodinâmico da deambulação nos pacientes submetidos a cirurgia cardíaca. Rev DERC. 2015;21(2):54-7.
• ¹²
  Escobar RD. Estudo comparativo entre cirurgia de revascularização miocárdica com e sem circulação extracorpórea em mulheres. Rev Bras Cir Cardiovasc. 2010;25(2):238-44.
• ¹³
  Amato VL, Timerman A, Paes ÂT, Baltar VT, Farsky PS, Farran JA, et al. Immediate results of myocardial revascularization: comparison between men and women. Arq Bras Cardiol. 2004;83 Spec No:14-20.
• ¹⁴
  Anderson AJ, Barros Neto FX, Costa MD, Dantas LD, Hueb AC, Prata MF. Preditores de mortalidade em pacientes acima de 70 anos na revascularização miocárdica ou troca valvar com circulação extracorpórea. Rev Bras Cir Cardiovasc. 2011;26(1):69-75.
• ¹⁵
  Alves Junior L, Rodrigues AJ, Evora PR, Basseto S, Scorzoni Filho A, Luciano PM, et al. Fatores de risco em septuagenários ou mais idosos submetidos a revascularização do miocárdio e ou operações valvares. Rev Bras Cir Cardiovasc. 2008;23(4):550-5.
• ¹⁶
  Silva AM, Campagnucci VP, Pereira WL, Rosa RF, Franken RA, Gandra SM, et al. Revascularização do miocárdio sem circulação extracorpórea em idosos: análise da morbidade e mortalidade. Rev Bras Cir Cardiovasc. 2008;23(1):40-5.
• ¹⁷
  Nogueira CR, Hueb W, Takiuti ME, Girardi PB, Nakano T, Fernandes F, et al. Quality of life after on-pump and off-pump coronary artery bypass grafting surgery. Arq Bras Cardiol. 2008;91(4):238-44.
• ¹⁸
  Cadore MP, Guaragna JC, Anacker JF, Albuquerque LC, Bodanese LC, Piccoli JD, et al. Score proposal to evaluate surgical risk in patients submitted to myocardial revascularization surgery. Rev Bras Cir Cardiovasc. 2010;25(4):447-56.
• ¹⁹
  De Bacco MW, Sartori AP, Sant'Anna JR, Santos MF, Prates PR, Kalil RA, et al. Risk factors for hospital mortality in valve replacement with mechanical prosthesis. Rev Bras Cir Cardiovasc. 2009; 24(3):334-40.
• ²⁰
  Esteban A, Anzueto A, Frutos F, Alía I, Brochard L, Stewart TE, et al; Mechanical Ventilation International Study Group. Characteristics and outcomes in adult patients receiving mechanical ventilation: a 28-day international study. JAMA. 2002;287(3):345-55.

Publication Dates

• Publication in this collection
  Mar-Apr 2017

History

• Received
  22 Oct 2016
• Reviewed
  28 Jan 2017
• Accepted
  01 Feb 2017