Preoperative Pulmonary Function Testing Predicts Cough Effectiveness Early After Laparoscopic Bariatric Surgery

Abstract

Background:

Cough is a protective mechanism providing bronchial drainage and helps to protect secretion retention in postoperative patients. Although laparoscopic bariatric surgery significantly decreases postoperative respiratory complications, there is an increase in patients with abnormal pulmonary function test results. The aim of the study was to investigate the relationship between preoperative pulmonary function testing (PFT) variables and cough effectiveness early after laparoscopic bariatric surgery.

Methods:

Twenty-seven patients (8 male and 19 female, median age 39 years) who had undergone laparoscopic sleeve gastrectomy were enrolled in the study. Preoperative PFT was recorded from patient files. Cough effectiveness was assessed using a portable flow meter to measure peak cough flow (PCF) on the first postoperative day.

Results:

None of the patients showed an obstructive (median forced expiratory volume in 1 s/forced vital capacity [FEV₁/FVC] ratio was 83%), restrictive (median FVC was 92%), or mixed pattern before surgery. Postoperative median PCF value was 300 L/min that was 68.2% predicted according to normative values. Postoperative PCF showed moderate positive correlations with peak expiratory flow (PEF) and forced expiratory flow at 25–75% (FEF_25–75: rho = 0.500, p = 0.008; rho = 0.440, p = 0.022, respectively).

Conclusion:

Preoperative PFT, specifically PEF and FEF_25–75, predicts cough effectiveness early after laparoscopic bariatric surgery even in patients with normal test results. The patients, especially with abnormal PEF and FEF_25–75, could be encouraged for an effective cough with directed cough maneuvers both in preoperative and postoperative periods.

Introduction

Obesity is a growing epidemic leading to serious systemic diseases and premature mortality.¹ Although prevention is a long-term solution for obesity, more definite treatment approaches are needed after it occurs, one of which is surgical interventions. Laparoscopic sleeve gastrectomy (LSG) is the most preferred procedure for morbid obesity with fewer surgical complications, satisfactory weight loss, and improvement of metabolic diseases.² LSG allows early mobilization after surgery with less postoperative pain and analgesic usage, leading to less respiratory complications compared with open techniques.³ However, bariatric surgery candidates are at high risk for postoperative respiratory complications because of obesity itself.⁴ Despite the conflict about the necessity of preoperative pulmonary function testing (PFT), subjects with abnormal test results had a threefold risk of complications even after laparoscopic bariatric surgery.⁵ Preoperative PFT was also suggested for bariatric surgery candidates in case of a presence of a risk factor for respiratory complications such as obstructive sleep apnea syndrome (OSAS).⁴

Cough is a major defense mechanism of the airways to clear excessive secretions.⁶ A normal cough includes taking a deep breath, closing the glottis, and compressing abdominal and thoracic muscles to generate pressure followed by an explosive release of gas as the glottis opens.⁷ Suppression of cough after abdominal surgery is one of the main reasons for postoperative respiratory complications as effective cough requires active contraction of abdominal muscles. Impaired cough effectiveness is associated with mucus retention that independently increases the risk for postoperative atelectasis and pneumonia.⁸

We hypothesize that preoperative PFT may help to predict cough effectiveness in the early postoperative period among patients who had undergone laparoscopic bariatric surgery. Therefore, our study aimed to measure cough effectiveness at the first postoperative day in patients after LSG whose preoperative pulmonary function variables were taken from the medical records.

Materials and Methods

Subjects

Twenty-seven morbidly obese patients (body mass index of 40 kg/m² or more) aged between 18 and 60 years who underwent laparascopic bariatric surgery at Dokuz Eylul University Faculty of Medicine, Deparment of General Surgery, were included in the study. LSG was applied by the same surgery team and patients underwent the same general anesthesia procedures. Patients were excluded if they had postoperative neuromuscular or cognitive impairment and hemodynamic instability before cough measurements (mean arterial blood pressure <70 mmHg and/or heart rate >120 beats/min). Subjects were withdrawn from the measurements if they became hemodynamically unstable (mean arterial blood pressure <70 mmHg and/or heart rate >120 beats/min) and had signs of dyspnea (respiratory rate >35 breaths/min and use of respiratory accessory muscles).

The study was conducted in accordance with the ethical standards of Helsinki Declaration and was approved by the research ethics committee of Dokuz Eylul University. All the subjects gave written consent to participate in the study after receiving appropriate verbal and written information.

Pulmonary function testing

Results of preoperative PFT that was a routine respiratory evaluation before surgery for candidates of LSG in our institution were recorded from the medical records of the patients. Spirometry was performed by an expert using a Sensormedics Vmax 22 machine (SensorMedics, Inc., Anaheim, CA) with subjects in a sitting position and nose clips in place according to the American Thoracic Society/European Respiratory Society statement.⁹ All values obtained were related to height, age, and gender and were expressed as percentage of their predicted value. The predicted values for forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), FEV₁/FVC ratio, peak expiratory flow (PEF), and forced expiratory flow at 25–75% (FEF_25–75) were used for analysis.

Cough effectiveness

Cough effectiveness was assessed on the first postoperative day with the measurement of peak cough flow (PCF), which has been considered as a relevant measure of cough efficacy, as mucus clearance is largely dependent on the magnitude of expiratory flow during cough.¹⁰ PCF was measured with a portable flow meter (Mini Wright PEF meter) consisting of a mouth piece. All measures were taken by the same trained physiotherapist using the technique described by Fiore et al. while the patients were sitting in a semirecumbent position (60°) supporting their abdomen with a pillow.¹¹ Patients did not receive any orientation or training on assessment procedure preoperatively or any time before the measurement. They were instructed to “take a deep breath and cough as forcefully as possible.” Three measures were performed with intervals of 30 s between each. The highest PCF values were considered for analysis. Predicted PCF values were derived from the Nunn and Gregg regression equations.¹² Not to affect the outcomes of the PCF values, we did not deliver any physiotherapy intervention or education before the cough effectiveness assessment. After the data collection, all the patients received a routine postoperative physiotherapy program including deep breathing and coughing exercises and early ambulation.

Pain intensity during the cough measurement was evaluated using a visual numeric scale graduated from 0 (minimum) to 10 (maximum). Patients scored the pain intensity they felt before PCF measurement (at rest), and after the three attempts. The same postoperative analgesia procedure was administered to all patients.

Statistical analysis

SPSS software version 15 (SPSS, Inc., Chicago, IL) was used for data analysis. Descriptive statistics and frequencies were used for demographic and clinical features. Normality of the data distribution was tested by the Shapiro–Wilk test. Most of the variables were not normally distributed. Therefore, nonparametric tests were deemed more adequate for statistical analysis. Medians and interquartile ranges (25th–75th percentile) were used for descriptive analyses. Spearman's rank correlation coefficient rho (ρ) was used to identify the relationships between PCF with pain intensity and each preoperative pulmonary function variable. The strength of correlations was classified as very weak (rho = 0–0.19), weak (rho = 0.2–0.39), moderate (rho = 0.40–0.59), strong (rho = 0.6–0.79), and very strong (rho = 0.8–1). p values <0.05 were considered statistically significant.

Results

Twenty-seven patients who had undergone LSG (8 male and 19 female, median age 39 years) were able to complete PCF measurements without any withdrawal. Postoperative median PCF value was 300 L/min (68.2% predicted). Table 1 shows the demographic and clinical features of the patients.

Table 1.

Demographic and Clinical Features of Patients

Age, years	39 (32–49)
Weight, kg	128 (112–145)
BMI, kg/m²	46.21 (41.82–48.42)
Gender, n (%)
Male	8 (29.6)
Female	19 (70.4)
Smoking status, n (%)
Nonsmoker	7 (25.9)
Ex-smoker	7 (25.9)
Current smoker	13 (48.1)
ASA status, n (%)
ASA 1	2 (7.4)
ASA 2	23 (85.2)
ASA 3	2 (7.4)
Duration of surgery, min	225 (140–265)
Duration of hospital stay, day	7 (5–8)
Postoperative PCF, L/min	300 (250–390)
PCF, % predicted	68.02 (47.46–74.81)
Pain severity at rest, 0–10	3 (2–5)
Pain severity after measurements, 0–10	2 (4–5)

Data are expressed as median (interquartile range) or number of patients (%).

ASA, American Society of Anesthesiologists; BMI, body mass index; PCF, peak cough flow.

None of the patients showed an obstructive (FEV₁/FVC ratio <70%), restrictive (FVC <70%), or mixed pattern (combination of the two) before surgery. Four (15%) patients had OSAS. Preoperative PFT variables are shown in Table 2.

Table 2.

Preoperative Pulmonary Function Testing Variables

PFT variable	% predicted
FVC	92 (80–96)
FEV₁	87 (82–93)
FEV₁/FVC	83 (79–87)
PEF	86 (81–103)
FEF_25–75	74 (67–86)

Data are expressed as median (interquartile range).

FEV₁, forced expiratory volume in 1 s; FVC, forced vital capacity; PEF, peak expiratory flow; PFT, pulmonary function testing.

Postoperative PCF showed moderate positive correlations with PEF and FEF_25–75 (rho = 0.500, p = 0.008; rho = 0.440, p = 0.022, respectively). Table 3 is the correlation table between PCF, pain, and preoperative PFT variables.

Table 3.

Correlations Between Peak Cough Flow, Pain, and Preoperative Pulmonary Function Testing Variables

	PFT variables (% predicted) and pain severity at rest
	FVC	FEV₁	FEV₁/FVC	PEF	FEF_25–75	Pain
PCF, L/min	rho = −0.059	rho = 0.054	rho = 0.109	rho = 0.500	rho = 0.440	rho = 0.014
	p = 0.769	p = 0.788	p = 0.590	p = 0.008^a	p = 0.022^b	p = 0.947

Statistically significant p < 0.01.

Statistically significant p < 0.05.

FEF_25–75, forced expiratory flow at 25–75%; ρ, Spearman's rho.

Discussion

The results of our study show that preoperative PFT, specifically PEF and FEF_25–75, predicts cough effectiveness early after laparoscopic bariatric surgery.

Although preoperative PFT is a routine assessment before bariatric surgery, there is still a contradiction about its necessity before laparoscopic procedures. It is used to predict perioperative and postoperative respiratory complication risk in major surgeries. Preoperative PFT is suggested to identify the patients at risk for respiratory complications who will undergo abdominal surgeries.¹³ Nevertheless, it is not recommended for patients without any pulmonary symptoms before laparoscopic interventions as it significantly reduces the incidence of severe respiratory complications in comparison with open procedures.¹⁴ Similarly, Clavellina-Gaytán et al. suggested that abnormal preoperative spirometry predicted postoperative pulmonary complication risk after bariatric surgery only in patients with OSAS.⁴ Laparoscopic bariatric procedure was used for most patients in that study, whereas a few patients underwent either an open procedure or were converted from laparoscopic to open surgery. Therefore, it is not possible to generalize their results only for laparoscopic bariatric surgery. In contrast to Clavellina-Gaytán et al., Van Huisstede et al. recommended preoperative PFT before laparoscopic bariatric procedures as they found a threefold risk of postoperative complications in patients with abnormal spirometry results, specifically FEV₁ and FEV₁/FVC ratio.⁵

Cough is the main airway defense mechanism by protecting the inhalation of foreign particles and clearing the excessive secretions. Postoperative pain and restrictive lung function are believed to decrease cough effectiveness, which is often described as an independent factor for postoperative respiratory complications.¹⁰ However, both the mechanical composition and neurological control of cough are impaired after surgery.⁸ For an effective cough, development of a high intrathoracic pressure and a rapid expiratory flow of air are required in terms of mechanical composition of cough. In addition, which impairs the patient's ability to cough independently without encouragement is the increased reflex cough threshold in terms of neurological control. The threshold for triggering a reflex cough by chemical irritation was found to be significantly increased on the first day after upper abdominal surgery.¹⁵ Cough sensitivity was also decreased in obese patients with OSAS, which may further increase the pulmonary complication risk particularly after bariatric surgery, in addition to depressant effect of anesthesia and morphine analgesia on the cough reflex.¹⁶ This effect should not be underestimated as up to 70% of obese patients undergoing bariatric surgery have OSAS.¹⁷ In our study, only 15% of patients were diagnosed with OSAS. Unfortunately, we could not investigate the possible relationship between OSAS and cough effectiveness because of the scarcity of patients diagnosed with OSAS.

Effective cough that depends on the capacity to produce adequate PCF¹⁸ is necessary in postoperative period for obese patients even after laparoscopic bariatric surgery. Therefore, we measured PCF to determine cough effectiveness in our obese patients who had undergone LSG. Colucci et al. found significant impairments in cough effectiveness using the same method for measurement early after upper abdominal surgery, which was strongly correlated with FVC, indicating postoperative restrictive lung dysfunction.¹⁰ According to their findings, lower PCF on postoperative day 1 tended to increase the risk of postoperative respiratory complications.¹⁰ Owing to the lack of preoperative PCF measurement in our study population, which is one of our limitations, we were unable to interpret our data if a postoperative decrease in cough effectiveness occurred or not in comparison with preoperative values. However, median value for PCF, indicator of cough effectiveness, was found 68.2% predicted compared with normative values described in a previous study.¹² The lack of patients with abnormal spirometry results before surgery could be considered as another limitation of our study not allowing us to compare the results. However, we did not exclude any patients according to neither preoperative pulmonary assessment nor any kind of criteria that would be a bias. Therefore, we included all the patients who had undergone the surgery over a limited period of data collection who incidentally had normal spirometry values. Moreover, as our institution is fairly new for bariatric surgery and the number of patients is not quite high, waiting for a comparison group with suboptimal spirometry results could take some time, which would totally be a newly planned future study. From another point of view, we believe that our results are valuable as indicating the moderate correlation between postoperative cough effectiveness and preoperative PEF and FEF_25–75 even in patients without any restrictive or obstructive pattern. We also did not investigate the incidence of postoperative pulmonary complications in our patient group prospectively as it was not the aim of our study design. This would also be pointed out in future studies.

Conclusion

In our study, in which we aimed to investigate the relationship between preoperative PFT variables and cough effectiveness early after laparoscopic bariatric surgery, postoperative cough effectiveness showed a moderate correlation with preoperative PEF and FEF_25–75. This was not an unpredicted finding as PEF represents the maximum flow generated during expiration performed with maximal force and started after a full inspiration, which is a mainly necessary maneuver for an effective cough. After bariatric surgery, even in laparoscopic conditions, patients should be encouraged to cough effectively with directed cough maneuvers especially the maneuvers with impaired preoperative PEF and FEF_25–75 results. Cough training should be an integral part of preoperative and postoperative rehabilitation programs for bariatric surgery patients.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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