Authors (including presenting author) :
Tam OY (1), Lam KM (2), Cheng CP (2), Lau CW (2), Yip PL (2), Leung WC (1), Li KW (1), Kwan WS (1), Mak MY (1)
Affiliation :
(1) Department of Physiotherapy, Tuen Mun Hospital, New Territories West Cluster, Hospital Authority, Hong Kong
(2) Department of Anaesthesia and Operation Theatre Services, Tuen Mun Hospital, New Territories West Cluster, Hospital Authority, Hong Kong
Introduction :
Cardiopulmonary exercise testing (CPEX) is a golden standard assessment on prediction of perioperative risk for major abdominal and pulmonary surgeries. Systematic review concluded that anaerobic threshold (AT) less then11ml/kg/min (1) and peak oxygen consumption (VO2 peak) less than 15ml/kg/min predicts high perioperative risk for patients undergo pulmonary surgery (2). However, service cost of CPEX is high and CPEX is not easily available in Hong Kong. Hence, a simple objective measurement of exercise capacity is needed for risk stratification. 6-minute walk test (6MWT) is a simple and repeatable assessment for functional capacity. Previous studies demonstrated a positive correlation between CPEX variables and distance walked in 6MWT in patients who would undergo non-cardiac surgery. However, there is no literature in Hong Kong to show the correlation between 6MWT and CPEX parameters and cutoff point to predict perioperative risk.
Objectives :
To determine the correlation between the distance walked in 6MWT and CPEX parameters.
To evaluate the cutoff of the distance walked in 6MWT in predicting CPEX parameters of high perioperative risk.
Methodology :
A retrospective study was undertaken for patients who would undergo non-cardiac surgery in Tuen Mun Hospital from October 2019 to December 2020. Patients who had undergone both CPEX and 6MWT were recruited in this study. Data on total distance covered in 6MWT, VO2 peak and oxygen consumption at AT in CPEX were captured. Pearson’s correlation analysis was used to determine the correlation between distance covered in 6MWT and different parameters in CPEX. Receiver operating characteristics (ROC) curve analysis was used to determine the cutoff of 6MWT distance in predicting an AT < 11ml/kg/min and VO2 peak < 15ml/kg/min. (3) The optimal cutoff point was determined as the value with the minimal distance from the left-upper corner of the unit square and the point where the Youden’s index is maximum. The weighting for sensitivity: specificity was 1:1. (4)
Result & Outcome :
There were 115 patients had undergone CPEX and 6MWT between October 2019 and November 2020. 8 patients were excluded due to fail to reach AT and undergo CPEX with arm ergometer. 107 patients (76 males and 31 females), with a mean age of 70.59, were included. The 6MWT distance correlated positively with VO2 peak (r = 0.562, p = < 0.05) and AT (r = 0.465, p = 0.05). The cutoff of 6MWT distance to predict high perioperative risk was 368.5m (Sensitive 71.7%, Specificity 85.2%). The area under curve of ROC curve was 0.819.
Discussion
The 6MWT is a useful assessment for functional capacity to provide risk stratification for patients undergoing non-cardiac surgery, when CPEX is not available. Patients with 6MWT distance < 368.5m should be referred for further evaluation before surgery.
Reference
1. Moran J, Wilson F, Guinan E, et al. Role of cardiopulmonary exercise testing as a risk assessment method in patients undergoing intra-abdominal surgery: a systematic review. British Journal of Anaesthesia. 2016; 116(2): 177-91.
2. Armstrong P, Congleton J, Fountain SW, et al. BTS guidelines: guidelines on the selection of patients with lung cancer for surgery. Thorax. 2001; 56: 89-108.
3. Sinclair RCF, Batterham AM, Davies S, et al. Validity of the 6 min walk test in prediction of the anaerobic threshold before major non-cardiac surgery. British Journal of Anaesthesia. 2012; 108(1): 30-5
4. Habibzadeh F, Habibzadeh P, Yadollahie M. On determining the most appropriate test cut-off value: the case of tests with continuous results. Biochemia Media. 2016; 26(3): 297-307
