Comparative evaluation of ventilatory function through pre and postoperative peak expiratory flow in patients submitted to elective upper abdominal surgery

Objective: to evaluate the ventilatory function by Peak Expiratory Flow (PEF) in the immediate pre and postoperative periods of patients undergoing elective surgical procedures in the upper abdomen. Methods: we conducted a prospective cohort study including 47 patients admitted to the Hospital Regional de Mato Grosso do Sul from July to December 2014, who underwent elective surgeries of the upper abdomen, and submiited to spirometric evaluation and measurement of PEF immediately before and after surgery. Results: of the 47 patients, 22 (46.8%) were male and 25 (53.20%) female. The mean preoperative PEF was 412.1±91.7, and postoperative, 331.0±87.8, indicating significant differences between the two variables. Men had higher PEF values than women, both in the pre and postoperative periods. There was a reasonable inverse correlation between age and decreased PEF. Both situations showed statistical significance (p<0.001). The group of smokers had lower PEF values both before and after surgery. The group of patients with comorbidities (hypertension and/or diabetes) showed lower PEF values both pre and postoperatively (p=0.005). In both groups, surgery resulted in a significant decrease in PEF (p<0.001). The type of surgery performed and the type of anesthesia did not show significant differences. Conclusion: the variables most involved in decreased lung function were: advanced age, smoking and presence of comorbidities. However, there is no consistent evidence to suggest conducting routine spirometry in such patients.

of 12/12/2012, the Conselho Nacional de Saúde (CNS), we held a prospective cohort study.We evaluated 47 patients from May to December 2014.
We measured the PEF with a portable device, the Mini-Wright® Peak Flow Meter 3103 (Airmed), ranging from 60 to 850 l/min, according to the Guidelines for Pulmonary Function Tests, 2002, with the patient sitting 4 .We instructed the patients to exert a maximal inspiration to total lung capacity followed by a maximal, short and explosive forced expiration through the measuring device, without extending the measure to residual volume.The expiratory effort needed last only a second or two.We repeated the test three times, considering the best result if the readings did not differ more than 20 l/ min from each other.
We provided an informed consent form, and evaluated the patients within 24 hours preoperatively and within the first 24 postoperative hours.We selec-

Pre and Post-operative Peak Expiratory Flow Analysis
The results of PEF analysis in the pre and postoperative periods of the 47 patients were mean ± stan- The "t" test for paired data (analysis of differences between groups) showed significant differences between the pre and postoperative PEFs (p<0.001).

Correlation between groups
The result of the Pearson test showed a correlation coefficient r=0.967 (p<0.001),indicating a strong and direct relationship between the two variables.

Gender
The two-way analysis of variance (two-way ANOVA) detected differences between the experimental groups.The post-hoc Bonferroni test showed that males has higher PEF values than females in both pre and postoperatively (p<0.001), as shown in Table 1.

Age Group
The two-way analysis of variance (two-way ANOVA) detected differences between the experimental groups.The post-hoc Bonferroni test showed that all age groups have higher PEF values preoperatively than postoperatively (p<0.001), as shown in Table 2.

Smoking
The two-way analysis of variance (two-way ANOVA) detected differences between the experimental groups.The post-hoc Bonferroni test showed that the group of smokers had lower PEF values both pre and postoperatively (p=0.008).In both groups, surgey determined a significant decrease in PEF (p<0.001), as brought by Table 3.

Comorbidities
The two-way analysis of variance (two-way ANOVA) detected differences between the experimental groups.The post-hoc Bonferroni test showed that the group of patients with comorbidities had lower PEF values both pre and postoperatively (p=0.005).In both groups, surgery determined a significant decrease in PEF (p<0.001), as shown in Table 4.

Postoperative PEF
Analysis of variance showed no significant differences between the types of surgery performed and PEF (p=0.055).Table 5 shows these values.

Anesthetic technique and PEF
The Mann-Whitney test showed no significant differences between the types of anesthesia used and postoperative PEF (p=0.178).Table 6 shows these values.

DISCUSSION
Postoperative Lung Complications (POLC) include atelectasis, pneumonia, bronchitis, bronchospasm, hypoxemia, respiratory failure and prolonged mechanical ventilation 5 .The incidence of POLC varies around 20% between studies 6 , but they are at least as common as cardiac complications as regards the abdominal surgeries 7 .
The most important predictor for the development of POLC is the surgical site.The complication rate when the surgical incision is in the upper abdomen or chest varies between 10% and 40% of all cases, while staying between 0.3% and 0.4% in laparoscopic cholecystectomy 8 .In the present study, we excluded from the analysis patients  Both mentioned studies considered the presence of advanced age, smoking and comorbid conditions as some of the main factors related to changes in ventilatory function both pre and postoperatively, and such results agree with those obtained in this study.
In older studies (1984 and 1989), on the other hand, Warner et al. found that patients who still smoked or stopped smoking less than two months before surgery had complication rates about four times higher than patients who had stopped smoking more than two months before surgery, and all had greater impairment of ventilatory function regardless of which examination was held 13 .These data corroborate our study, which showed that smoking is inversely correlated to pre and postoperative PEF. 165-170 ted the patients according to the following criteria: a) all patients over 13 years old, admitted electively in HRMS to undergo upper abdominal surgery, and accepted, or the legal guardian authorized, to participate in the study.The Exclusion criteria were: a) patients younger than 13 years; b) patient who refused to participate in the study; c) patients admitted on an emergency basis; d) patients who failed to properly perform the lung function test in pre or postoperative periods; e) patients whose surgical procedure was changed for some reason; f) patients with some type of postoperative complication, such as the need for hospitalization in Intensive Care Unit (ICU) or need for prolonged intubation.We compared the data using descriptive and analytical parametric statistics, ANOVA package.The programs used were GraphPad Prism version 6.01 and SPSS version 22.0.
dard deviation -PEF pre = 412.1 ± 91.7; PEF post = 331.0± 87.8.The D'Agostino and Pearson Test (analysis of the distribution type) showed that the sample distribution was Gaussian, which authorized the use of a parametric test for statistical analysis.
who had some postoperative complications, not recording data about such conditions.In addition to the surgical site, other factors also stand out, such as advanced age, presence of pulmonary disease or other medical illnesses, smoking and its intensity, obesity, malnutrition, type of anesthesia, duration of surgery and surgical technique, abnormal spirometry values, decreased ability to exercise and prolonged time of preoperative hospitalization1,2 .Anesthesia, bed rest, phrenic nerve dysfunction, surgical trauma and pain affect respiratory muscle function after surgery, inducing a shallow, monotonous breathing pattern, without periodic physiological sighs.With the reduction of breathing efficiency, there is a decrease in vital capacity, functional residual capacity, tidal volume and forced expiratory volume in one second, factors that may facilitate the onset of pulmonary complications9 .Thus, prior knowledge of these values in the preoperative period may allow the diagnosis and quantification of ongoing ventilatory disorders, preventing possible respiratory complications in the postoperative period10 .The primary goal of preoperative pulmonary assessment is precisely to identify, quantify and reduce the risk of such complications9 .The peak of postoperative diaphragm dysfunction occurs in the period between two to eight hours after surgery, returning to preoperative values in seven to ten days, interfering in most spirometric values, including PEF 10 .Silva et al. evaluated pre and postoperative PEF values in patients undergoing upper abdominal floor surgery and found a significant decrease of this variable, as well as smaller PEF values in females, data similar to those obtained in our study 11 .According to Filardo et al., in the patient preoperative evaluation, some important variables have been associated with increased risk for POLC: advanced age, presence of pulmonary disease or other comorbidities, smoking and its intensity, obesity and malnutrition 1 .Pereira et al. studied the incidence of pulmonary complications in the postoperative period of 408 patients undergoing upper abdominal surgery and identified several risk factors that associated with these complications.From there, they formulated a prognostic index, which included the presence of comorbidities (hypertension and/or diabetes) as one of the elements favorable to the emergence of POLC and decrease in spirometric values 12 .

Table 1 .
Peak expiratory flow values before and after surgery, for both genders.Different letters indicate statistically distinct groups.

Table 2 .
Peak expiratory flow values before and after surgery, for the different age groups.Different letters indicate statistically distinct groups.
ScheerenComparative evaluation of ventilatory function through pre and postoperative peak expiratory flow in patients submitted to elective upper abdominal surgery 165-170

Table 3 .
Peak expiratory flow values before and after surgery, regarding smoking.Different letters indicate statistically distinct groups.

Table 4 .
Peak expiratory flow values before and after surgery according to comorbidities.Different letters indicate statistically distinct groups.

Table 5 .
Peak expiratory flow values after surgery according to the different types of surgery.Different letters indicate statistically distinct groups.

Table 6 .
Peak expiratory flow values after surgery according to anesthetic technique.Different letters indicate statistically distinct groups.We conclude from our survey that the most involved variables in the decrease in ventilatory function were the same found in the literature, such as advanced age, smoking status and presence of comorbidities.However, there are still no significant evidence to suggest routinely conducting preoperative breath tests for such patients and each case should be individualized and evaluated by a specialist when necessary, a conduct adopted in the HRMS.The study reinforces the importance of greater attention to the ventilatory function in this patients group, which can determine interventions that reduce the morbidity and mortality rates related to POLC 165-170