Surgical risk tests related to cardiopulmonary postoperative complications . Comparison between upper abdominal and thoracic surgery

PURPOSE: To investigate if tests used in the preoperative period of upper abdominal or thoracic surgeries are able to differentiate the patients that presented cardiopulmonary postoperative complications. METhODS: Seventy eight patients, 30 submitted to upper abdominal surgery and 48 to thoracic surgery were evaluated. Spirometry, respirometry, manovacuometry, six-minute walk test and stair-climbing test were performed. Complications from immediate postoperative to discharge from hospital were registered. RESULTS: The postoperative complications rate was 17% in upper abdominal surgery and 10% in thoracic surgery. In the univariate regression, the only variable that kept the correlation with postoperative complications in the upper abdominal surgery was maximal expiratory pressure. In thoracic surgery, the maximal voluntary ventilation, six-minute walk test and time in stair-climbing test presented correlation with postoperative complications. After multiple regression only stair-climbing test continued as an important risk predictor in thoracic surgery. CONCLUSION: The respiratory pressure could differentiate patients with complications in upper abdominal surgery, whereas in thoracic surgery, only spirometric values and exercise tests could differentiate them.


Introduction
The upper abdominal and thoracic surgeries are routinely performed for treatment of many diseases, and sometimes for diagnosis.Such surgeries can present cardiopulmonary postoperative complications (POC) more frequently than the lower abdominal surgeries, as due to the surgical incision interfering in the respiratory muscles as by the own changes caused by the surgery and anesthesia.
POC after upper abdominal surgery and thoracic surgery increase the morbidity and mortality rates, mainly in those ones presenting cardiopulmonary disturbs, and these two type of surgery present a high incidence of complications among major surgery 1,2 .POC result from the interaction of factors related to the general health of the patient and the surgical procedure to which it is subjected 3 .Such POC cause damages to the patients due to the long postoperative hospital stay as well as the high costs for health system.
Due to the high incidence of POC in major surgeries, the preoperative cardiopulmonary evaluation has to be performed in the preparation of such patients in order to predetermine those that would have higher risks to develop POC 4 .Consequently, it is possible to intensify the pre-operative care in order to minimize the POC.
However, in spite of being well determined in thoracic surgery, there has not been a standardization in which tests to determine the most susceptible patients to develop postoperative complications should be used in the preoperative period of upper abdominal surgery.Surgical risk scales are routinely used to predict surgical risks, but relating to cardiopulmonary tests, little has been investigated yet 17,18 .
Therefore the purpose of study was determining if tests performed in order to evaluate heart and lung function in the preoperative period of upper abdominal and thoracic surgery can differentiate the patients who have higher chances to develop postoperative complications and also which tests are more important concerning to each one intervention.Weight was measured in kilograms, and height in meters in order to calculate the body mass index (BMI).During preoperative period, in the maximum 30 days before the surgery, an interview and the following tests were performed: spirometry, peak expiratory flow, respirometry, manovacuometry, 6MWT and SCT.

Study approved by the
Patients were submitted to spirometry according to the American Thoracic Society (ATS) 19 using Koko spirometer 606055 ® .At least three reproductive studies of Forced Vital Capacity (FVC) and Forced Expiratory Volume in the first second (FEV 1 ) in liters and percentage of predict, the ratio between two values FEV 1 /FVC in percentage and maximal voluntary ventilation (MVV) in liters/minute and percentage of predict.In order to obtain the peak flow values, a maximal inspiration until total lung capacity was carried out and after an inspiratory pause of two seconds in the maximum a forced expiration was carried out through a nozzle of the device Mini-Wright ® Peak Flow Med (Airmed), without the prolonged maneuvers to the residual volume, so a short explosive exhalation was carried out.Expired minute volume (MV) was obtained with the patient sitting, wearing a nose clip, breathing quietly for one minute in a spirometer Wright ® .The tidal volume (TV) was determined by the formula: TV = MV/RR, where RR corresponds to respiratory rate.
Maximal inspiratory and expiratory pressures (MIP and MEP), were obtained according to the norms of ATS 19 in a manovacuometer (Salcas ® MD 00983/08), with variation capacity of -200 to +200 cmH 2 O. Six-minute walking test was carried out in a 120 meters long corridor, divided in marks of 0.75 m and in the shade and was performed according to ATS 19 .Previously and at the end of the test, the heart rate (HR), respiratory rates (RR), oxygen saturation (SpO 2 ) and Borg Scale 20 were evaluated.The calculation of the predicted distance in the 6MWT was carried out with the equation proposed by Soares and Pereira 21 .
SCT was carried out in a six flights staircase in the shade, 12 steps each flight in a total of 12.16 m height, as standardized by Cataneo and Cataneo 11 .The time in seconds was taken in the end of the staircase ascent and was named time of stair climbing test (tSCT) and the power (P) in watts (w) was calculated using the classic formula 11 .
The patients were followed up during the postoperative period (PO) and the cardiopulmonary complications, if present, were registered: acute myocardial infarction, unstable angina pectoris, congestive heart failure, arrhythmias requiring therapy, reintubation, prolonged intubation for more than 24-hours, pneumonia, atelectasis that required bronchoscopy, pulmonary thromboembolism, PaCO 2 higher or equal to 50 mmHg and death.
Length of stay in Intensive Care Unit and in hospital stay were also registered.
The data was analysed initially evaluating if the variables had a normal distribution by Shapiro-Wilki test in order to differentiate groups that presented complications and the ones that did not present complications, as well as to compare the two kinds of surgery studied.Student's test was used when such variables presented normal distribution and Mann-Whitney test when they had not normal distribution.Univariate logistic regression was used in order to verify which variables were associated with the POC, where the variables that were significant in this model, were analyzed in a multiple logistic regression.The significance level considered was p<0.05 and the program used was SAS (Statistical Analysis System), version 9.2.

Results
Initially, 208 patients were selected to upper abdominal surgery (UAS Group) and thoracic surgery (TS Group), 92 in UAS Group and 116 in TS Group.From the patients selected in UAS Group, there was a loss of five patients (three due to the cancellation of surgery; one due to alteration of procedure in the intraoperative and one due to the need of interrupting the tests to be submitted to other interventions).There was a loss of 57 patients in TS Group, but all of them related to alterations on surgical procedures and suspended surgery.Fifty seven patients were excluded in UAS Group and eleven in TS Group according exclusion criteria.
Seventy eight patients were evaluated; 30 in UAS Group and 48 in TS Group.The patients were divided into two subgroups according to POC absence (A) or presence (P).Five patients (17%) from UAS Group presented POC (subgroup UAP) and five (10%) from TS Group (subgroup TP).The complications that occurred in the upper abdominal surgery for each patient were: prolonged intubation and death; prolonged intubation, reintubation and death; pneumonia; reintubation, pneumonia and death; arrhythmias requiring intervention.Four complications had pulmonary origin and one cardiac origin and three deaths occurred in this subgroup.The complications in the thoracic surgery were: prolonged intubation in two cases; pneumonia and death; pulmonary thromboembolism; prolonged intubation and reitubation.All the complications in the thoracic surgery had pulmonary origin and one death occurred in this subgroup.
Demographics according to the groups and p values are presented on Table 1.When the muscle strength and spirometry were analyzed, it was noticed that the thoracic group achieved better respiratory pressures, but the spirometry was better in the upper abdominal surgery group.However, related to exercise tests there were not great differences between the groups (Table 1).

Demographics according subgroups and p values are
presented on Table 2.The subgroup TP is significantly older than TA.The length of stay in the intensive care unit (ICU) was significantly higher in the subgroups presenting complications (UAP and TP) (Table 2).The mean length of stay and surgery were significantly higher only in the subgroup TP (Table 2).

Surgical risk tests related to cardiopulmonary postoperative complications.
Comparison between upper abdominal and thoracic surgery Acta Cirúrgica Brasileira -Vol.28 (6) 2013 -461   Spirometric variables FVC, FEV 1 and MVV were significantly lower only for the patients that presented complications in TS Group and the same occurred regarding to MIP and MEP for the patients that presented complications in UAS Group (Table 3).
The exercise tests only had significant differences in TS, not significantly different UAS group relative to patients with or without complications (Table 4).Patients submitted to procedures that involve the chest wall had high rates of POC at the same way, even without a lung parenchyma resection.Surgical incision affects the integrity of the respiratory muscles and its function and general anesthesia effects interferes in respiratory muscle contraction 23 .Pathophysiological changes of thoracic surgery involves gas exchange, ventilatory patterns, pulmonary volumes and defense mechanisms of respiratory system, but mostly surgical aggression brings important morbidity and mortality in borderline patients 24 .

Intraoperative variables
The time of surgery was higher in the POC subgroups, with significant difference in TS Group and had no significant but tending to be higher in UAS Group.Surgical time and POC correlation does not have so much value alone because many other factors may have interfered in the occurrences of POC, but such fact should warn not to extend the surgical time.Other studies have already demonstrated that the extended surgical time is related to pulmonary complications 17 .
In order to perform these surgeries, the patients were submitted to general anesthesia, which can alter the form and the pattern of chest wall movements what can lead to changes in the elastic properties of the lungs and in the gas distribution 25 .Additionally general anesthesia affects diaphragmatic function due to the relaxing of muscular fibers and also decrease mucociliary clearance predisposing POC mostly if it is prolonged 26 .In the present study, the time of anesthesia was higher in the subgroups that presented complications and can have contributed for the occurrence of POC.The more extended surgeries in the UAS Group may be contributed for a higher rate of POC leading to a significant increase in the hospital length of stay.

Lung volumes and capacity
The upper abdominal surgery demonstrably affects the function of respiratory muscles mainly involving diaphragmatic function.Sometimes it is caused by direct trauma due to the surgical incision and most of them due to reflex inhibition of phrenic nerve after manipulation of abdominal viscera leading to changes in breathing patterns predisposing to respiratory complications 4,23 .
The significantly lower spirometric values found in TS Group compared to UAS Group, demonstrate that respiratory disease is responsible for lung function deterioration.Pulmonary function, once reduced and allied to a higher decrease in the postoperative period from thoracic surgery 25 lead to a shortness of breathing and favors to pulmonary complications.
The spirometric variables were able to differentiate the subgroup that presented complications in TS Group, which were significantly lower in POC group.That fact demonstrated the importance of the exam in the preoperative preparation of patients that had spirometric values below predicted, mainly for MVV% that also had a protective correlation in the univariate regression.
Such variables did not present a significant difference between the subgroups in UAS Group, leading us to question if these exams are necessary.Some studies demonstrated correlations with lower spirometric values and higher rates of POC 27,28 however, other believe that spirometry is not necessary in elective upper abdominal surgery in the absence of medical history, respiratory symptoms, history of smoking and chronic lung disease 29,30 .
Nevertheless, it is important to highlight that spirometry should not be totally discarted in elective upper abdominal surgery, but should be performed according to a higher indication criteria to provide data about risk of POC 30 .In the other hand, pulmonary function tests have been considered a good predictor of surgical risk in thoracic surgery 31 .

Respiratory muscle strength
Previous studies in thoracic surgery found out that patients who had unresponsive respiratory muscle strength to training have higher probability to develop POC 32,33 .Hulzebos et al. 34 found out that MEP values higher than 75% had POC protective effect in cardiac surgery.Bellinetti et al. 35 concluded more recently that the abnormal respiratory muscle strength during preoperative period of thoracic surgery and elective upper abdominal surgery was associated to a higher incidence of POC or death and when abnormal can be considered a risk factor.However, an association between the respiratory pressures and POC was not found in TS Group from the present study.
In fact all these studies considered just pulmonary POC while the present study considered also the cardiac POC.
Another difference concerning the study methodology is that some authors 32,33 used fixed reference values, regardless age and gender, while Bellinetti's 35 and the present study used the predict values in percentage.
Manovacuometry was the only test proposed that determined a significant difference in the subgroups of upper abdominal surgery but only MEP% had POC protective correlation.
Respiratory pressures in the present study were significantly lower in the UAS Group, probably due to the own interference of abdominal disease that can cause a discomfort during tests.These pressures were able to differentiate the POC subgroup and made it more important than spirometry in this group.For that group, in order to minimize POC, patients with reduced respiratory pressures should be submitted to preoperative preparation 36 .

Cardiopulmonary exercise test
Exercise determines an increase in lung ventilation and perfusion, accelerating the gas exchange as well as in the postoperative of major surgeries 12 .At that way, cardiopulmonary exercise tests evaluate patient fitness and are able to identify defects in oxygen transport system.VO 2 obtained during ergospirometry is considered the gold standard to determine the capacity of exercise 37 , but due to the fact it is an expensive equipment not available in most of hospitals, field tests can be used for it (6MWT, SCT).
Six-minute walking test is widely used to determine the physical capacity in several diseases as well as post-treatment assessment, nevertheless in pre-operative evaluations it has not been so wide explored.Holden et al. 9 identified that a shorter distance in walking tests can help to determine morbidity, mortality and also the need for prolonged mechanical ventilation.Szekely et al. 16 used 6MWT for COPD patients in the pre-operative of bullectomy and the distance had a significant correlation with hospital length of stay.According to these authors patients that walk less than 200 meters have a higher risk of postoperative death 16 .
Exercise tests, either 6MWT or SCT, are able to differentiate the subgroups with or without complications in the TS Group but it is not the same in UAS Group probably because such tests are dependent on spirometry rather than respiratory muscle strength.

Surgical risk tests related to cardiopulmonary postoperative complications. Comparison between upper abdominal and thoracic surgery
Acta Cirúrgica Brasileira -Vol.28 (6) 2013 -465 The degree of limitation becomes proportional to the degree of lung function impairment in patients that have difficult to climb stairs 38 .Previous studies found a strong correlation between SCT and complications after pulmonary resection.Olsen et al. 8 correlated the number of flights climbed in SCT to POC and concluded the higher number of flights climbed the lower the incidence of POC as well as lesser hospital length of stay.Girish et al. 10 ; BMI -body mass index; ICU -intensive care unit.*p<0.05 It was already demonstrated that patients submitted to upper abdominal surgery have an increased chance to develop postoperative complications.Although there are a lot of tests used in pre-operative evaluations and an attempt to identify those which predict the susceptibility to POC, the efficacy of each one in order to predict complications is still limited in such kind of surgery.The supine position during upper abdominal surgery, the incision near the respiratory muscles and the use of painkillers are responsible for peri and postoperative physiological changes.Lung volumes alterations and functional respiratory muscle deficiency occurs leading to mucociliary defense mechanisms disability and to microatelectasis22 .

TABLE 1 -
The comparison of variables between two groups: upper abdominal surgery (UAS Group) and thoracic surgery (TS Group).Mean ± standard deviation or median (1º and 3º quartile) and p.

TABLE 2 -
Age, weight, height, body mass index and time of surgery, anesthesia, stay in hospital and in intensive care unit, in the subgroup upper abdominal surgery absence (UAA) and presence of complications (UAP), and subgroup thoracic surgery absence (TA) and presence of complications (TP).Mean ± standard deviation or median (1º and 3º quartile) and p values.

TABLE 4 -
Stress test variables in the subgroup upper abdominal surgery absence (UAA) and presence of complications (UAP), and subgroup thoracic surgery absence (TA) and presence of complications (TP).Mean ± standard deviation or median (1º, 3º quartile) and p values.
40ve determined in their study that patients who climb around 13.4 meters don't have POC and recently Brunelli et al.12demonstrated that patients who climb less than 12 meters have more POC.All patients included in the present study climbed the whole stair (12.16 meters) but despite limited height, the speed of ascent can vary, so our option to use the time of SCT as other authors14.Epstein et al.39observed those who are not able to perform SCT had 79% POC compared to 35% of those ones who are able to perform the test.Brunelli et al.40also verified that patients unable to perform maximal exercise tests have a higher risk of mortality.There is not a standardization to perform SCT and evaluating physical capacity using different variables makes the comparison between the results difficult and also impossible to determine a cut-off point.Despite there is a lot of SCT studies, nothing has been done in upper abdominal surgery that demonstrate its importance isolated.This fact motivated us to study this test also in upper abdominal surgery to determine the risk of POC but the time in SCT demonstrated to be the single risk predictor only in thoracic surgery.The search for ideal tests to predict the risk of postoperative complications is important to minimize it and even if it is not possible to modify it, it is important to be aware of POC.Since the attention and care should be intensified for high risk patients, the present research lead us to believe that the best preoperative preparation for upper abdominal surgery is to improve the respiratory muscle strength, while for thoracic surgery is to improve spirometric values as well as exercise capacity.