• exercise;
  • exercise tolerance;
  • post-operative complications;
  • risk factors;
  • surgery


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Background and objective:  Field exercise tests have been increasingly used for pulmonary risk assessment. The six-min walking distance (6MWD) is a field test commonly employed in clinical practice; however, there is limited evidence supporting its use as a risk assessment method in abdominal surgery. The aim was to assess if the 6MWD can predict the development of post-operative pulmonary complications (PPCs) in patients having upper abdominal surgery (UAS).

Methods:  This prospective cohort study included 137 consecutive subjects undergoing elective UAS. Subjects performed the 6MWD on the day prior to surgery, and their performance were compared with predicted values of 6MWD (p6MWD) using a previously validated formula. PPCs (including pneumonia, tracheobronchitis, atelectasis with clinical repercussions, bronchospasm and acute respiratory failure) were assessed daily by a pulmonologist blinded to the 6MWD results. 6MWD and p6MWD were compared between subjects who developed PPC (PPC group) and those who did not (no PPC group) using Student's t-test.

Results:  Ten subjects experienced PPC (7.2%) and no significant difference was observed between the 6MWD obtained in the PPC group and no PPC group (466.0 ± 97.0 m vs 485.3 ± 107.1 m; P = 0.57, respectively). There was also no significant difference observed between groups for the p6MWD (100.7 ± 29.1% vs 90.6 ± 20.9%; P > 0.05).

Conclusions:  The results of the present study suggest that the six-min walking test is not a useful tool to identify subjects with increased risk of developing PPC following UAS.


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Pulmonary complications are associated with substantial morbidity and mortality following upper abdominal surgery (UAS).1 For this reason, several studies have focused on strategies to identify patients with an increased risk of developing post-operative pulmonary complications (PPCs).2–7 Assessment of pulmonary risk may provide a means of allocating increased care and resources to high-risk patients and thus improve post-operative outcome.3,5–7 Several studies reported that spirometry has limited clinical value as a screening test and most pulmonary risk indexes, in spite of having a high predictive value, have not been specifically validated for patients undergoing UAS.6 Therefore, there is still no consensus regarding the best method of predicting the development of PPC.8,9

Exercise testing has been increasingly used as a risk assessment method, and there is evidence suggesting that patients with poor exercise tolerance have an increased risk of developing post-operative complications after cardiothoracic10,11 and non-cardiothoracic surgeries.12,13 The causal mechanism that links exercise testing and risk of complications is unclear. One possible explanation is that patients with a lower exercise capacity are less likely to cope with the metabolic demands created by the trauma of surgery.12 In pulmonary risk assessment, the use of exercise testing may be particularly useful to detect deficits in oxygen transport (e.g. pulmonary diseases), which may be part of the pathophysiologic basis of PPC.

Cardiopulmonary exercise testing is considered the gold standard method to assess exercise capacity;14 however, it requires expensive laboratory equipment not available in many centres. For this reason, recent studies have proposed the use of field tests of exercise capacity for pulmonary risk assessment. For instance, field exercise tests such as the shuttle walk test and stair climbing test may predict post-operative outcome following thoracic and non-thoracic surgeries.15–17 The six-min walk is the field test most commonly employed in clinical practice18 because it is simple, inexpensive, reproducible and supported by guidelines,19 which possibly accounts for its popularity. However, to our knowledge, there is no evidence supporting the use of the six-min walk test as a risk assessment in UAS.

The aim of the present study is to assess if the six-min walk distance (6MWD) can predict PPC following open UAS. We hypothesized that patients with shorter 6MWD prior to surgery will be more likely to develop PPC.


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This prospective cohort study recruited consecutive adult subjects (≥18 years) admitted for elective UAS in a tertiary university hospital from May 2006 to May 2009. UAS was defined as any surgical procedure performed through ‘an incision above or extending above the umbilicus’20 and included 42 (30%) gastrectomy/oesophagectomy, 36 (26%) rectosigmoidectomy/colectomy, 22 (16%) gastroduodenopancreatectomy/pancreatectomy, 14 (10%) exploratory laparotomy, 13 (9.4%) hepatectomy, five (3.6%) splenectomy, three (2.1%) incisional hernia repair and two (1.4%) cholecystectomy procedures. Subjects were excluded if they refused to perform the six-min walking test or had neurologic, vascular or musculoskeletal diseases or co-morbidities that limited their ability to walk. The subjects were withdrawn from the study in cases of surgery cancellation, laparoscopic surgery, surgery through thoracic approach, intra-operative death or re-operation. The study was approved by the hospital ethics committee and written informed consent was obtained from each subject before surgery.


All subjects underwent standardized preoperative assessment including complete clinical history, physical examination and spirometry. The subjects performed 6MWD 1 day prior to surgery. PPC was assessed daily by a pulmonologist who was blinded to the 6MWD results. The subjects received standard respiratory therapy sessions (breathing exercises and ambulation) daily until hospital discharge. Surgical outcome data were obtained from medical records.

The six-min walk test

The test was performed according to the recommendations of the American Thoracic Society.19 The subjects were asked to walk along a 30-m corridor to a maximum of 6 min. The subjects were allowed to rest during the test if required, and this time was included in the 6 min. The test was performed twice with a 1-h rest between tests. The best distance was recorded. Normal predicted values of 6MWD (p6MWD) were calculated using the equations proposed by Enright and Sherril.21


The subjects were considered to have developed PPC when they were diagnosed with one or more of the following:22

  • • 
    pneumonia: presence of radiological evidence of pulmonary infiltration associated with at least two of the following criterion––purulent sputum, elevated body temperature (>38.0°C) and leukocytosis (≥25% above baseline preoperative value).
  • • 
    tracheobronchitis: marked increase in sputum production or presence of purulent sputum in a patient with normal chest X-ray.
  • • 
    atelectasis with clinical repercussion: radiological evidence of lung atelectasis associated with dyspnoea.
  • • 
    acute respiratory failure: acute deficiency of gas exchange with necessity for invasive or non-invasive mechanical ventilation.
  • • 
    bronchoconstriction: presence of wheezing associated with dyspnoea, requiring bronchodilator prescription or change in previous dosage of bronchodilator prescription.

Statistical analysis

Sample size was calculated using preliminary data from a pilot study (n = 11) with the 6MWD as the main outcome measure. Calculations were based on a univariate comparison between the subjects who developed PPC (PPC group) and the subjects who did not (no PPC group) using a formula for unequal group sizes.23 To detect a difference higher than 100 m between groups, expecting an incidence of PPC of 9.1%, standard deviation of 100 m and assuming α > 0.05 (two-tailed) and power of 0.80, a sample of 10 subjects would be required in the PPC group and 60 subjects in the no PPC group.

Student's t-test (for continuous variables with normal distribution), Mann–Whitney test (for continuous variables with non-normal distribution) and χ2 test (for categorical variables) were used to compare demographic data between the PPC group and no PPC group. 6MWD and p6MWD were compared between the two groups using univariate analysis (Student's t-test). A P-value < 0.05 was considered to be statistically significant. Statistical analysis was performed using SPSS software package version 19.0 (Chicago, IL, USA).


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From 188 subjects screened over 3 years, 137 performed 6MWD and completed the study. None of the subjects had any adverse events during the exercise test. A flow diagram of subject recruitment is presented in Figure 1. Seventeen patients were unable to perform the six-min walking test and reasons included the following: 10 (58.8%) for claudication; five (29.4%) for limb amputation; and two (11.7%) for hemiplegia.


Figure 1. Study flow diagram.

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Ten subjects (7.2%) were diagnosed as having at least one PPC (Table 1). The patients' demographic and surgical outcome data in the PPC and no PPC groups are presented in Table 2. There were no differences between groups in terms of gender, body mass index, smoking habits and lung function. The subjects in the PPC group were older than the subjects in the no PPC group (67 ± 12 vs 57 ± 14 years; P = 0.03). Preoperative diagnosis of pulmonary disease (50% vs 16%; P = 0.01) and gastro-oesophageal procedures (80% vs 27%; P = 0.001) were more frequent in the PPC group. The subjects in the PPC group had longer surgery time (448.0 ± 117.4 vs 358.0 ± 121.7 min; P = 0.02) and longer post-operative hospitalization (19.1 ± 9.2 vs 11.4 ± 13.5 days; P = 0.001). Nine subjects died after surgery (6.6%). Post-operative mortality was higher in the PPC group (50% vs 3%; P = 0.0001).

Table 1.  Post-operative pulmonary complications (PPC) in patients having upper abdominal surgery
  1. Values are presented as the number of subjects and percentage, in parentheses.

Subjects having at least one PPC10
Subjects having more than one PPC6 (4.3)
Pneumonia5 (50)
Acute respiratory failure5 (50)
Atelectasis with clinical repercussion4 (40)
Tracheobronchitis2 (20)
Bronchoconstriction1 (10)
Table 2.  Comparison of demographic and surgical outcomes between patients with (PPC) or without (no PPC) post-operative pulmonary complication
 PPC group (n = 10) (%)No PPC group (n = 127) (%)P value
  • Values are presented as mean ± standard deviation or number of subjects. In parentheses, data are presented as percentage.

  • *

    P < 0.05 evaluated by Student t-test; P < 0.05 evaluated by chi-square test.

  • BMI, body mass index; FEV1, forced expiratory volume in the first second; FVC, forced vital capacity.

 Age, year67.0 ± 12.057.0 ± 14.00.03*
 Male : female7 (70):3(30)60 (47):67 (53)0.20
 BMI, kg/m223.5 ± 5.424.6 ± 4.80.48
Lung function   
 FVC % predicted92.0 ± 30.391 ± 22.50.89
 FEV1 % predicted92.6 ± 34.089 ± 22.60.62
 FEV1/FVC1.0 ± 0.21.03 ± 0.20.82
 Diagnosis of pulmonary disease5 (50)20 (15)0.01
 Current smoker3 (30)62 (49)0.33
 Malignant surgical disease10 (100)103 (81)0.20
 Gastro-oesophageal surgical disease8 (80)34 (27)<0.01*
Peri- and post-surgical   
 Surgery time, min448 ± 117.4358 ± 121.70.02*
 Post-operative length of stay, days19.1 ± 9.211.4 ± 13.5<0.001*
 Post-operative death5 (50)4 (3)<0.001*

No difference was observed in the univariate analysis comparing the 6MWD between the subjects in the PPC group and the subjects in the no PPC group (466.0 ± 97.0 m vs 485.3 ± 107.1 m; P = 0.57) nor was there any difference between the groups for p6MWD (100.7 ± 29.1% vs 90.6 ± 20.9%; P = 0.15) (Table 3).

Table 3.  Comparison between groups of the 6MWD and p6MWD
 PPC Group (n = 10)No PPC group (n = 127)P value
  1. Values are presented as mean ± standard deviation.

  2. 6MWD, six-min walking distance; m, meters; no PPC group, patients without post-operative pulmonary complication; p6MWD, predicted values of 6MWD; PPC group, patients with post-operative pulmonary complication.

6MWD, m466.0 ± 97.0485.3 ± 107.10.57
p6MWD, %100.7 ± 29.090.6 ± 20.90.15


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The subjects who developed PPC did not have reduced 6MWD compared with those patients who did not develop PPC. The result of this study therefore suggests that 6MWD is not a useful tool to identify subjects at increased risk for PPC following UAS.

Exercise testing is considered an important tool to determine the physiological capacity of patients to cope with the metabolic demands created by the trauma of major surgery.12 Previous studies showed that results obtained from field tests of exercise capacity such as the shuttle walk and stair climbing tests can predict post-operative outcome.17,20,21 Thus, we hypothesized that similar results would be observed when using the six-min walk test. There are several possible explanations for these results. First, the present study included candidates for distinct upper abdominal surgeries (e.g. gastrectomy, oesophagectomy, etc.), while most studies showing that exercise capacity is predictive of post-operative complications involve subjects undergoing surgeries, such as lung resection,24–26 who are likely to have some degree of impairment in lung function prior to surgery. Therefore, field tests could be more sensitive to identify lower exercise capacity in subjects with higher risk due to their clinical condition. Maybe the 6MWD could be a more useful predictor of PPC in a specific patient subgroup such as those that have a confirmed diagnosis of pulmonary disease.

Second, differences in the cardiopulmonary response to the six-min walking test in comparison with other exercise field tests may be considered for the results of the present study. Shuttle walking and stair climb tests have better correlation with maximum oxygen uptake.16,27 Therefore, the six-min walking test may not require patients maximal effort of cardiopulmonary reserve. As a result, the test may not be able to uncover deficits in oxygen transport and thus identify patients at increased risk of complications.

Our study population demonstrated a wide variability in the observed 6MWD results, which may have possibly reduced the statistical power of the study. However, this variability is similar to other published studies and may be explained by individual characteristics such as gender, age, height and weight.19,28,29 To minimize this influence, a sample size calculation was performed using a formula proposed by Enright and Sherril,21 which estimates normal p6MWD. Although data variance was reduced, we still did not observe statistical difference between groups.

The incidence of PPC following UAS observed in the present study was 7.2% and it is considered lower than previous studies, showing an incidence ranging from 9% to 40%.1,3,5 In the present study, we used criteria for PPC with clinical relevance, and this may explain the discrepancy of our results. The wide range in the literature is due to the use of different diagnostic criteria for PPC that is recognized to account for most of this variation.1 Interestingly, previous studies from our group using the same diagnostic criteria reported higher incidence of PPC following UAS (14%22 and 24%30), and this discrepancy may be explained by an improvement in perioperative care advances in recent years. In addition, our results are not applicable for laparoscopic surgery since this type of procedure is less invasive and the incidence of PPC is lower compared with laparotomy.

In the present study, patients from the PPC group were older, had longer surgery duration and presented higher diagnosis of pulmonary disease, outcomes that are recognized in the literature as important risk factors for the development of PPC.1,3,5,6 We also observed that patients submitted to gastro-oesophageal surgeries presented a higher prevalence of PPC and this fact has been explained by the closer proximity of the diaphragm1 or because these patients have a poorer preoperative clinical condition in comparison with patients submitted to other upper abdominal procedures.31 Lastly, we observed that hospitalization period was longer and mortality was higher in the subjects who have PPC, which is a common finding in the literature.32,33

In addition to the factors noted earlier, our study has other limitations. Initially, there is no consensus to define PPC; therefore, our results may be comparable only with studies using similar definitions. In addition, 17 patients with co-morbidities were excluded. Since low functional status has been shown as an important risk factor for the development of PPC,1,5 the exclusion of these patients may have influenced the study's results. It is important to highlight that this study is not applicable to patients who are laparoscopic surgery since they were not evaluated. Finally, normal p6MWD used in our study were calculated for the American population.21

In conclusion, our results suggest that 6MWD is not useful in detecting increased risk of developing PPC following UAS. Further studies should be considered to evaluate other exercise field tests such as shuttle walk and stair climbing testing.


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We are grateful for Dr Ilka Santoro Lopes contribution, the fellow physiotherapists from the Respiratory Department for their assistance and Ms Sze-Ee Soh from The University of Melbourne for revision comments.

Denise M Paisani was supported by a doctorate scholarship from CAPES, Brazil.


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  • 1
    Smetana GW. Postoperative pulmonary complications: an update on risk assessment and reduction. Cleve. Clin. J. Med. 2009; 76: S605.
  • 2
    Serejo L, Silva-Junior F, Bastos JP et al. Risk factors for pulmonary complications after emergency abdominal surgery. Respir. Med. 2007; 101: 80813.
  • 3
    Arozullah AM, Daley J, Henderson WG et al. Multifactorial risk index for predicting postoperative respiratory failure in men after major noncardiac surgery. The National Veterans Administration Surgical Quality Improvement Program. Ann. Surg. 2000; 232: 24253.
  • 4
    Bapoje SR, Whitaker JF, Schulz T et al. Preoperative evaluation of the patient with pulmonary disease. Chest 2007; 132: 163745.
  • 5
    Arozullah AM, Conde MV, Lawrence VA. Preoperative evaluation for postoperative pulmonary complications. Med. Clin. North Am. 2003; 87: 15373.
  • 6
    Arozullah AM, Khuri SF, Henderson WG et al. Development and validation of a multifactorial risk index for predicting postoperative pneumonia after major noncardiac surgery. Ann. Intern. Med. 2001; 135: 84757.
  • 7
    McAlister FA, Bertsch K, Man J et al. Incidence of and risk factors for pulmonary complications after nonthoracic surgery. Am. J. Respir. Crit. Care Med. 2005; 171: 5147.
  • 8
    Fisher BW, Majumdar SR, McAlister FA. Predicting pulmonary complications after nonthoracic surgery: a systematic review of blinded studies. Am. J. Med. 2002; 112: 21925.
  • 9
    Brunelli A, Rocco G. Spirometry: predicting risk and outcome. Thorac. Surg. Clin. 2008; 18: 18.
  • 10
    Bayram A, Candam T, Gebitekin C. Preoperative maximal exercise oxygen consumption test predicts postoperative pulmonary morbidity following major lung resection. Respirology 2007; 12: 50510.
  • 11
    Matsuoka H, Nishio W, Sakamoto T. Prediction of morbidity after lung resection with risks factors using treadmill exercise test. Eur. J. Cardiothorac. Surg. 2004; 26: 4802.
  • 12
    Smith TB, Stonelli C, Purkayastha S et al. Cardiopulmonary exercise testing as a risk assessment method in non cardiopulmonary surgery: a systematic review. Anaesthesia 2009; 64: 88393.
  • 13
    Hightower CE, Riedel BJ, Morris GS et al. A pilot study evaluating predictors of postoperative outcomes after major abdominal surgery: physiological capacity compared with the ASA physical status classification system. Br. J. Anaesth. 2010; 104: 46571.
  • 14
    Palange P, Ward SA, Carlsen KH et al. Recommendations on the use of exercise testing in clinical practice. Eur. Respir. J. 2007; 29: 185209.
  • 15
    Biccard BM. Relationship between the inability to climb two flights of stairs and outcome after major non-cardiac surgery: implications for the pre-operative assessment of functional capacity. Anaesthesia 2005; 60: 58893.
  • 16
    Murray P, Whiting P, Hutchinson SP et al. Preoperative shuttle walking testing and outcome after esophagogastrectomy. Br. J. Anaesth. 2007; 99: 80911.
  • 17
    Girish M, Trayner E, Dammann O et al. Symptom-limited stair climbing as a predictor of postoperative cardiopulmonary complications after high-risk surgery. Chest 2001; 120: 114751.
  • 18
    Salzman SH. The 6-min walk test: clinical and research role, technique, coding, and reimbursement. Chest 2009; 135: 134552.
  • 19
    American Thoracic Society. Statement: guidelines for the six-minute walk test. Am. J. Respir. Crit. Care Med. 2002; 166: 11117.
  • 20
    Celli BR, Rodriguez KS, Snider GL. A controlled trial of intermittent positive pressure breathing, incentive spirometry, and deep breathing exercises in preventing pulmonary complications after abdominal surgery. Am. Rev. Respir. Dis. 1984; 130: 1215.
  • 21
    Enright PL, Sherril DL. Reference equations for the six-minute walk test in healthy adults. Am. J. Respir. Crit. Care Med. 1998; 158: 13847.
  • 22
    Pereira EDB, Faresin SM, Juliano Y et al. Risk factors of postoperative pulmonary complications after upper abdominal surgery. J. Bras. Pneumol. 1996; 22: 1926.
  • 23
    Hulley SB, Cummings SR, Browner WS et al. Designing Clinical Research: An Epidemiologic Approach, 2nd edn. Lippincott Williams & Wilkins. Philadelphia, PA, 2001.
  • 24
    Brunelli A, Refai M, Xiume F et al. Performance at symptom-limited stair climbing test is associated with increase cardiopulmonary complications, mortality and costs after major lung resection. Ann. Thorac. Surg. 2008; 86: 2407.
  • 25
    Colice GL, Shafazand S, Griffin JP et al. Physiologic evaluation of the patient with lung cancer being considered for resectional surgery. Chest 2007; 132: S16177.
  • 26
    Bolliger CT. Evaluation of operability before lung resection. Curr. Opin. Pulm. Med. 2003; 9: 3216.
  • 27
    Delahaye N, Cohen-Solal A, Faraggi M et al. Comparison of left ventricular responses to the six-minute walk test, stair climbing, and maximal upright bicycle exercise in patients with congestive heart failure due to idiopathic dilated cardiomyopathy. Am. J. Cardiol. 1997; 80: 6570.
  • 28
    Frankestein L, Remppis A, Graham J et al. Gender and age related predictive value of walk test in heart failure: do anthropometrics matter in clinical practice? Int. J. Cardiol. 2008; 127: 3316.
  • 29
    Troosters T, Gosselink R, Decramer M. Six minute walking distance in healthy elderly subjects. Eur. Respir. J. 1999; 14: 2704.
  • 30
    Filardo FA, Faresin SM, Fernandes ALG. Index for a pulmonary postoperative complication after upper abdominal surgery: a validation study. Rev. Assoc. Med. Bras. 2002; 48: 20916.
  • 31
    Grotenhuis BA, Wijnhoven BPL, Grune F et al. Preoperative risk assessment and prevention of complications in patients with esophageal cancer. J. Surg. Oncol. 2010; 101: 2708.
  • 32
    Dimick JB, Chen SL, Taheri PA et al. Hospital costs associated with surgical complications; a report from the private-sector National Surgical Quality Improvement program. J. Am. Coll. Surg. 2007; 204: 118898.
  • 33
    Abunasra H, Lewis S, Beggs L et al. Predictors of operative death after oesophagectomy for carcinoma. Br. J. Surg. 2005; 92: 102933.