This randomized clinical trial (Trial registration number CTRI/2015/ 11/006336) was approved by the Scientific Committee and the Institutional Ethics Committee of Kasturba Medical College Mangalore, Manipal University. The purpose of the study was explained and the informed consent was taken from the willing participants. Study was carried out in a Kasturba medical college Hospital, Mangalore, Southern India, was conducted between March 2014 and March 2015. The sample size was calculated based on the values obtained from pulmonary function test in a pilot study (10 subjects; 5 in flow incentive spirometry group and 5 in volume incentive spirometry group). The following formula was used for calculating the same.

A total of 50 patients were included in the study (37 males and 13 females). Allocation of members of the group was carried out by block randomization as follows: 25 subjects would perform flow incentive spirometry and the other 25 would perform volume incentive spirometry. In the flow incentive spirometry group 23 subjects were included preoperatively and postoperatively. In the volume incentive spirometry group 24 subjects were included preoperatively and postoperatively. Two subjects in the flow incentive spirometry group and 1 subject in the volume incentive spirometry group refused to walk pre and postoperatively. All subjects underwent evaluations of pulmonary function with measurement of Forced Vital Capacity (FVC), Forced Expiratory Volume in the first second (FEV1), Peak Expiratory Flow (PEF). The measurements were taken in the preoperative period and were repeated on the 1^st, 2^nd, 3^rd, 4^th and 5^th postoperative day, for both groups. Exercise tolerance was measured by a Six-Minute Walk Test (6MWT) during the preoperative period and measured again at the time of discharge for both groups [Table/Fig-1].

[Table/Fig-1]:

Consort Flow Chart.

Incentive spirometry was administered to the patient who has made to lie at 45°to the horizontal position i.e., half-lying. A pillow was placed beneath the patients knees. The patient then exhaled slowly and passively and avoided any forceful expiration. The process was first demonstrated to the patient just to ensure that he/she had understood the technique before performing it. Initially the spirometer was held in front of the patient by the therapist. The therapist gave the patient an explanation of inspiratory flow. Following the patient held the spirometer him/herself and practiced the manoeuver. The patient was instructed to perform 3 sets of 5 repeated deep breaths and do this exercise every waking hour. The treatment was administered to the patient four times a day and the patient was instructed to perform the same exercises on the rest of the day. A log book record was maintained of the same.

The 6MWT was performed according to the standardized procedure which was supervised by a physiotherapist. The patients were asked to walk at their own maximal pace along a 30m long, flat, and straight hospital corridor. The patient was not given any encouragement and the test was limited by the symptoms. Therefore, if any signs of significant distress such as dyspnea, dizziness, angina or skeletal muscle pain, the patient was asked to stop. However, the patient was instructed to resume walking as soon as possible. The distance covered by the patient was recorded in meters.

Data was analysed using SPSS package version 17.0. The primary outcome measure pulmonary function was analysed by post-hoc analysis and was carried out using Bonferroni’s t-test. The secondary outcome measure exercise tolerance was analysed by Paired ‘T’-test.

A total of 50 patients were included in the study; 25 patients were allocated to the Flow Incentive Spirometry group and 25 patients to the Volume Incentive Spirometry group.

Baseline demographic characteristics of the participant’s age, gender, height, weight, duration of surgery and anaesthesia and co-morbidities are presented in [Table/Fig-2]. There was no statistical difference seen between the Flow Incentive Spirometry and Volume Incentive Spirometry groups. The different types of abdominal surgeries and incisions in the Flow Incentive Spirometry and Volume Incentive Spirometry groups are summarized in [Table/Fig-3].

For both the flow and volume–oriented incentive spirometry groups, a statistically significant decrease was seen in Forced Vital capacity (FVC) on the 1^st, 2^nd and 3^rd postoperative day as compared with FVC during the preoperative period. However, on 4^th and 5^th postoperative day statistically significant difference was not seen in both flow - and volume - incentive spirometry groups as patients had reached normal baseline values [Table/Fig-4].

Forced expiratory volume in one second (FEV₁) was compared with in the flow and volume incentive spirometry groups before and after open abdominal surgery. There was a statistically significant decrease seen in the Forced Expiratory Volume in one second (FEV₁) on the 1^st, 2^nd, 3^rd and 4^th postoperative day for both flow- and volume- incentive spirometry groups, when compared to the preoperative period. There was no statistically significant difference found on the 4^th and 5^th postoperative day in volume incentive spirometry groups when compared with preoperative day. But in Flow incentive spirometry group on 5^th postoperative day there was no statistical significant difference found when compared with preoperative day. (Given in [Table/Fig-5])

Peak expiratory flow rate (PEFR) were compared with the flow and volume incentive spirometry groups before and after open abdominal surgery. When compared with the preoperative period there was a statistically significant decrease seen in the Peak Expiratory Flow Rate (PEFR) on the 1^st, 2^nd, 4^th and 5^th day for the flow- incentive spirometry group. However, on the 3^rd postoperative day, a statistically significant difference in PEFR compared to the preoperative period was not seen for the flow- incentive spirometry group.

In volume incentive spirometry group there was a statistical significance decrease seen in PEFR in 1^st postoperative day compared to the preoperative period. On 2^nd, 3^rd, 4^th and 5^th postoperative day as patients are reaching normal to baseline period [Table/Fig-6]. Both flow- and volume- incentive spirometry groups showed a statistically significant difference in the preoperative and postoperative distance covered in the 6MWT. Of the groups, the volume- incentive spirometry group showed values which were found highly significant. Mean of preoperative and discharge distance covered in both flow- and volume- incentive spirometry groups is [Table/Fig-7].

The study was conducted to determine the efficacy of flow and volume incentive spirometry on pulmonary function and exercise tolerance in patients undergoing open abdominal surgery. In our study we included 25 patients who had undergone open abdominal surgery. They varied from 18 to 90 years of age. The patients were equally and randomly assigned to 2 groups: a) the flow incentive spirometry group; b) the volume incentive spirometry group. Our research hypothesis is accepted as flow and volume incentive spirometry on pulmonary function and exercise tolerance showed a significant difference.

Based on our study results, the pulmonary function {FVC, FEV1, and PEFR} on 1^st postoperative day when compared to the preoperative period had a significant decrease in both flow- and volume- incentive spirometry groups. This is possibly owing to the fact that in the postoperative period there is shallow, monotonous breathing without periodic sighs and prolonged restraint in bed due to postoperative pain, incision site, analgesics, duration of anaesthesia and surgery, all of which decrease the ventilation to dependent lung regions [11].

In the immediate postoperative, the patient may present hypoventilation owing to the administration of anaesthesia which leads to ventilation-perfusion mismatch, hypoxaemia and shunt. Anaesthetic agents and narcotic analgesics depress the hypoxic ventilatory drive and suppress the normal periodic “sighing” respiration which is necessary for maintenance of normal lung inflation [17]. A reduction of the effectiveness of the cough reflex and increased risks associated with the retention of sputum are caused by impaired mucociliary clearance [8]. Direct trauma to the abdominal wall and the incision affect diaphragmatic function [5]. This is due to reflex inhibition of the phrenic nerve after the manipulation of abdominal viscera [18]. All these factors impair the function of respiratory muscles which lead to decrease in functional residual and vital capacity [17]. In a study it has been suggested that chest physiotherapy helps in improving the distribution of ventilation and increasing clearance of secretions in surgical patients [19].

Our results are in accordance with Ford et al., showed that reduction in diaphragmatic performance was the main determinant of impaired lung function [20]. Scholes et al., found that respiratory co-morbidity and the duration of anaesthetic were significantly associated with the increased risk of postoperative pulmonary complications after abdominal surgery [21]. Martinez et al., in their study found that anaesthesia and pain are responsible for respiratory muscle dysfunction [22]. Karine et al., found that the supine position, incision near respiratory muscles and the use of painkillers are responsible for the postoperative physiological changes in abdominal surgery [17].

There was a highly statistically significant improvement seen in pulmonary function groups of the flow- and volume- incentive spirometry groups, from the 2^nd to 5^th postoperative day, when compared to the preoperative period.

The possible reason for the improvement in pulmonary function in abdominal surgeries could be the use of incentive spirometry, which is a mechanical device used to encourage patients to take long, slow, sustained deep inspirations which leads to achieving maximal inflating pressure in the alveoli and maximal inhaled volume, and also helps to maintain the patency of the smaller airways. Postoperative hypoxaemia is reduced by using incentive spirometry which provides low-level resistance training to the diaphragm and minimizes fatigue thereby improving inspiratory muscle strength and enhancing lung inflation [9,23].

Our results are in accordance with Stephen et al., found that incentive spirometry is more effective than deep breathing exercise in restoring vital capacity to preoperative levels [24]. Westwood et al., concluded that incentive spirometry plays a significant role in preventing atelectasis and its complications in major abdominal surgeries [25]. It was found that abdominal surgery patients with surgical incisions close to the diaphragm were placed at a high risk of pulmonary complications. The researchers also stressed that incentive spirometry was effective as a pulmonary risk-reduction method [25]. Hall et al., showed that incentive spirometry was the most efficient prophylaxis against pulmonary complications in high risk patients after abdominal surgery [19]. Celli et al., compared intermittent positive-pressure breathing, incentive spirometry and deep breathing exercises in patients who had undergone abdominal surgery and concluded that incentive spirometry showed significantly lower incidence of postoperative pulmonary complications [23].

The next objective in our study was Six-Minute Walk Test (6MWT) which has been validated for use in preoperative and postoperative periods as a measure of recovery and physical capacity in flow- and volume- incentive spirometry groups [26]. There was a statistically significant improvement seen in the distance covered postoperatively when compared with preoperatively. Mobilization of postoperative patients with low intensity exercise aims at eliciting cardiopulmonary responses which enhances oxygen transport and assists in reduction of postoperative pulmonary complications [27].

An important recommendation, made to patients undergoing abdominal surgery is early mobilization. Early mobilization is shown to increase lung volume, prevent atelectasis and improve gas exchange. Our results are similar to the findings of Brasher et al., who have suggested that early mobilization seems more effective than deep breathing exercises in the prevention of postoperative pulmonary complications [3]. Breiger et al., reported early mobilization was observed to hasten recovery and reduce the incidence of postoperative pulmonary complications. A study carried out by Neilsen et al., concluded that mobilization involving an upright position is most beneficial in the early postoperative period and produces evidence of improvement in pulmonary function. Mackey et al., suggests that early mobilization may reduce the incidence of postoperative pulmonary complications [15].

The limitation of the study was there was no control group and a smaller sample size; this limits the generalizability of the results. The same investigator recorded the Pulmonary Function Test and Six Minute Walk Test values. There was no blinding in the study procedure and postoperative pain and the type of analgesics used were not assessed by the investigator. This can affect the study findings. The patients’ adherence to incentive spirometry was not assessed, as a result of which we are not sure that the patients have strictly followed the instructions. Further research can be done on a larger sample size with a control group. Similar, type of study can be done on cardiac and thoracic surgeries along with other techniques such as diaphragmatic breathing exercises and inspiratory muscle training can be focused in future researches.

Based on results from our study, flow and volume incentive spirometry can be safely recommended to patients undergoing open abdominal surgery as there are no adverse events recorded on the one hand and on other hand, these have shown demonstrable improvement in pulmonary function and exercise tolerance.

From our study we concluded that there is a significant decrease in pulmonary function in the flow- and volume- incentive spirometry groups on the 1^st postoperative day when compared with the preoperative day. There is a significant improvement seen in the flow- and volume-incentive spirometry groups on the 2^nd, 3^rd, 4^th and 5^th postoperative day when compared with the preoperative day. From our study we also found that there was a significant increase in the Six-Minute Walk Test distance covered postoperatively when compared with the preoperative day in both flow- and volume- incentive spirometry groups.