Preoperative use of incentive spirometry does not affect postoperative lung function in bariatric surgery

Preoperative use of incentive spirometry does not affect postoperative lung function in bariatric surgery

FEATURED NEW INVESTIGATOR Preoperative use of incentive spirometry does not affect postoperative lung function in bariatric surgery DAVIDE CATTANO*, A...

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FEATURED NEW INVESTIGATOR Preoperative use of incentive spirometry does not affect postoperative lung function in bariatric surgery DAVIDE CATTANO*, ALFONSO ALTAMIRANO, ANDREA VANNUCCI, VLADIMIR MELNIKOV, CHELSEA CONE, and CARIN A. HAGBERG HOUSTON, TEX AND ST. LOUIS, MO

Morbidly obese patients undergoing general anesthesia for laparoscopic bariatric surgery are considered at increased risk of a postoperative decrease in lung function. The purpose of this study was to determine whether a systematic use of incentive spirometry (IS) prior to surgery could help patients to preserve their respiratory function better in the postoperative period. Forty-one morbidly obese (body mass index [BMI] . 40 kg/m2) candidates for laparoscopic bariatric surgery were consented in the study. All patients were taught how to use an incentive spirometer but then were randomized blindly into 2 groups. The control group was instructed to use the incentive spirometer for 3 breaths, once per day. The treatment group was requested to use the incentive spirometer for 10 breaths, 5 times per day. Twenty experimental (mean BMI of 48.9 6 5.67 kg/m2) and 21 control patients (mean BMI of 48.3 6 6.96 kg/ m2) were studied. The initial mean inspiratory capacity (IC) was 2155 6 650.08 (SD) cc and 2171 6 762.98 cc in the experimental and control groups, respectively. On the day of surgery, the mean IC was 2275 6 777.56 cc versus 2254.76 6 808.84 cc, respectively. On postoperative day 1, both groups experienced a significant drop of their IC, with volumes of 1458 6 613.87 cc (t test P , 0.001) and 1557.89 6 814.67 cc (t test P , 0.010), respectively. Our results suggest that preoperative use of the IS does not lead to significant improvements of inspiratory capacity and that it is a not a useful resource to prevent postoperative decrease in lung function. (Translational Research 2010;156:265–272) Abbreviations: ABG ¼ arterial blood gases; BiPAP ¼ bilevel positive airway pressure; BMI ¼ body mass index; CPAP ¼ continuous positive airway pressure; FEV1 ¼ forced expiratory volume in 1 s; FiO2 ¼ fraction of inspired oxygen; FRC ¼ functional residual capacity; IC ¼ inspiratory capacity; IS ¼ incentive spirometry; OHS ¼ obesity hypoventilation syndrome; PACU ¼ postanesthesia care unit; PEEP ¼ positive end-expiratory pressure

*

Davide Cattano, MD, PhD, is an Assistant Professor in the Department of Anesthesiology, University of Texas Medical School at Houston – Home. His article is based on a presentation given at the Combined Annual Meeting of the Central Society for Clinical Research and Midwestern Section American Federation for Medical Research held in Chicago, Ill, April 2010. From the Department of Anesthesiology, The University of Texas Health Science Center Houston, School of Medicine, Houston, Tex; Department of Anesthesiology, Washington University School of Medicine, St. Louis, Mo.

Submitted for publication May 20, 2010; revision submitted August 9, 2010; accepted for publication August 12, 2010. Reprint requests: Davide Cattano, MD, PhD, Department of Anesthesiology, Medical Director Preoperative Anesthesia Clinic, School of Medicine, UTHSC-Houston, 6431 Fannin, MSB 5.020, Houston, TX 77030; e-mail: [email protected] 1931-5244/$ - see front matter Ó 2010 Mosby, Inc. All rights reserved. doi:10.1016/j.trsl.2010.08.004

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AT A GLANCE COMMENTARY Cattano D, et al. Background

Morbidly obese patients undergoing bariatric surgery are at higher risks for perioperative pulmonary atelectasis and impaired gas exchange. Muscle paralysis and intraoperative mechanical ventilation (often with high Fi02, insufficient levels of positive end-expiratory pressure, and erratically applied alveolar recruiting maneuvers) can aggravate preexisting deficiencies in respiratory mechanics. Translational Significance

The use of preoperative incentive spirometry (IS) was proposed in this clinical investigation with the speculation that encouraging morbidly obese patients to breathe to total lung capacity and, therefore, opening collapsed alveoli would minimize postoperative respiratory dysfunction. Because of the differences in previous studies, the therapeutic value of preoperative IS has not yet been fully understood. The prevalence of obesity is high in the United States, exceeding 30% in most age and sex groups.1 Morbid obesity affects millions of Americans that, in association with obesity, frequently carry several additional medical problems such as type 2 diabetes mellitus, gastroesophageal reflux disease, arthritis, heart disease, and importantly for anesthesiologists, pulmonary diseases such as obesity hypoventilation syndrome (OHS).2 OHS is a term used to describe the pulmonary state of patients with obesity, chronic hypercapnia, and sleepdisordered breathing.3 It is most common in patients with a body mass index (BMI) $40 kg/m2 (defined by the World Health Organization as morbidly obese4) and often involves pulmonary hypertension and restrictive lung disease.2 Morbidly obese patients undergoing bariatric surgery are at higher risks for perioperative pulmonary complications such as atelectasis and impaired gas exchange.5 Muscle paralysis and intraoperative mechanical ventilation (often with high Fi02, insufficient levels of positive end-expiratory pressure [PEEP], and erratically applied alveolar recruiting maneuvers) can aggravate preexisting deficiencies in respiratory mechanics.6 The insufflation of pneumoperitoneum and postural changes associated with bariatric procedures may impair respiratory function and gas exchange further both intraoperatively and postoperatively.7 In fact, hypoxemia is

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a common postoperative complication in these patients even in the absence of preoperative obstructive pulmonary symptoms, indicating a need for routine positive pressure treatment.8 Postoperative chest physiotherapy in the form of mechanical breathing devices such as continuous positive airway pressure (CPAP), bilevel positive airway pressure (BiPAP), and incentive spirometry (IS) have been introduced to prevent pulmonary complications after bariatric surgery. The use of CPAP immediately after extubation has been shown to reduce the loss of significant lung volumes after surgery, which may be an additional intervention in risk minimization.9 However, many surgeons caution the use of positive pressure airway ventilation as they are concerned about anastomosis tension and sutures breakage. IS uses a device that allows the patient to mimic natural yawning or sighing by having them take slow, deep breaths while sustaining maximal inspiration. Studies directed at combating pulmonary risk in the postoperative period demonstrate that lung volume expansion techniques, such as aggressive IS and early ambulation, are useful in preventing respiratory complications,10,11 obviating the need for positive pressure techniques such as BiPAP and CPAP that can be labor intensive and expensive to implement. Still, several studies suggest that IS is taught inconsistently (a brief explanation in the preoperative clinics; the brochure is provided. Instructions are given to bring in the spirometer the day of surgery, yet no education is provided regarding its use, and then it likely is used inadequately by patients) and the effects of IS may be measured inconsistently because of the different variables in each clinical trial.10,12-14 All of these studies looked at the effect of prophylactic respiratory physiotherapy on several measures of postoperative outcome, but none focused on the modalities of IS use. Our hypothesis was that a systematic use of IS for at least 3 days prior to surgery could increase the preoperative inspiratory capacity of our patients on the day of surgery and also could result in a smaller decrease in the postoperative inspiratory lung volume of bariatric patients. Therefore, our primary goal was to determine whether IS could lead to improved preoperative respiratory mechanics, as assessed by measuring inspiratory lung volumes postoperatively. The underlying assumption was that optimizing and preserving the respiratory function can result in better perioperative oxygenation and in a lower incidence of pulmonary complications in this high-risk population and that a formal preoperative program of IS utilization could help the patient to familiarize themselves with the device and possibly to appreciate the benefits, resulting in a better utilization

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and compliance in the postoperative period with minimal reliance on the hospital staff support. The secondary aims of our study were to assess postoperative respiratory complications’ rate, patients’ satisfaction with IS treatment, and patient compliance (indirect assessment). METHODS

After approval from the local institutional board, this study was registered at www.clinicaltrials.gov. (NCT01004146), and 41 ASA 1–3 bariatric patients were enrolled and consented in this study. All patients enrolled presented to the preoperative anesthesia clinic for evaluation at least 3 days prior to their procedure date. Morbid obesity with a BMI $40 kg/m2 was a prerequisite for inclusion in the study. Patients were excluded if they had both current symptoms of obstructive sleep apnea and actively were being treated with CPAP during their sleep. After written informed consent, patients received an incentive spirometer (Cardinal Health Inc., Dublin, Ohio) and were randomized to the experimental group or the control group. Patients assigned to the experimental group were instructed to use the spirometer by inhaling as slowly and deeply as possible in a set of 10 times and to repeat the process at least 5 times every day until the day of surgery. Patients assigned to the control group were educated on the proper technique of using the incentive spirometer and were instructed to use it for 3 breaths once per day to become able to use the device properly and consistently. During the preoperative visit, all patients were instructed on how to use the spirometer effectively. The principal investigator made sure that they all could use it properly after instruction. The IS volume (best out of 2 attempts) achieved was documented, as well as the relevant pulmonary history, planned date of surgery, type of the bariatric surgical procedure, and their demographic information such as age, sex, height, and weight; and the BMIIS volume always was measured first in the sitting position and then in the supine position. All patients were given a log sheet (included in the manufacturer’s packaging) to record their IS volumes while at home. They were requested to record the volume inspired on the third attempt in each cycle of using the spirometer. For example, patients in the experimental group recorded at least 5 attempts per day as they were instructed to repeat 5 cycles of 10 attempts per day. These log sheets were collected on their arrival to the day surgery unit on the day of the operation, and each patient was interviewed as to their use of the spirometer. Room air SpO2, baseline heart rate, respiratory rate, and IS volume (best out of 2 attempts) achieved all

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were documented. The level of compliance with the assigned protocol was measured objectively by reviewing the lung volumes recorded on the patient log sheet and by reviewing the patient questionnaire regarding improvement in breathing. A standard intravenous induction of general anesthesia was achieved with full muscle relaxation. Intraoperatively, SpO2, tidal volume, peak airway pressures, ventilation modality, PEEP applied via ventilator, and any intraoperative events (bucking, coughing, desaturation, and evidence of aspiration) all were documented. All patients in our study were reversed fully prior to extubation. Invasive blood pressure monitoring was established after the induction of general anesthesia and endotracheal intubation. The ventilatory support during the bariatric procedures is standardized to 10 mL/kg to 12 mL/kg (ideal body weight), 7 cmH2O to 10 cmH2O of PEEP is used for patients with a BMI below or equal and above 50, respectively, and fraction of inspired oxygen (FiO2) is maintained at 60%. Typically, no recruiting maneuvers are performed after endotracheal intubation unless peripheral oxygen saturations levels are unexpectedly below 97%. Extubation is perfomed with patient in a 30-degree semirecumbent position and with 100% FiO2. After the operation, the patients to be discharged on the same day were approached in the postanesthesia care unit (PACU) and requested to use the spirometer again. The volume (best out of 2 attempts) was recorded together with the same vital signs recorded preoperatively. Patients who were admitted to the hospital were requested to use the spirometer again on postoperative day 1. The largest IS volume (out of 2 attempts) was recorded in addition to their vital signs. Additionally, any postoperative complications were noted (fever, atelectasis on chest x-ray, postoperative pneumonia, desaturation episodes, shortness of breath, and cough), and any interventions undertaken to improve respiratory status also were documented (nebulizer/inhaled medication use, CPAP, BiPAP, intubation, and respiratory physiotherapy). These items were assessed daily during the first 3 postoperative days. Patients also were given a questionnaire to report notes on the subjective improvement with their breathing in the preoperative period, as well as convenience of use of the device, level of pain, ease of breathing on day 1 postoperatively, and, finally, their overall evaluation regarding their prescribed usage of IS. Measurements. An IS calibration was performed randomly before the start of this study on 3 incentive spirometers and compared with spirometry. A difference of ,5% was noted for volumes greater than 3 L, 10% for volumes of 1 L to 3 L, and between 10% and 15% for volumes ,1 L.

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For all patients enrolled in the study, IS volumes achieved were recorded for the best out of 2 attempts in both the sitting and the supine positions during the anesthesia clinic visit, preoperatively in the day surgery unit, postoperatively in the PACU, and on postoperative day 1. Intraoperative data collected included length of surgery, intraoperative SpO2, ventilatory modality, application of PEEP, intraoperative tidal volume, intraoperative peak airway pressures, and any adverse intraoperative events. Postoperative data collected included vital signs in PACU and postoperative day 1, any postoperative pulmonary complications (as outlined previously), and any pulmonary interventions undertaken (as outlined previousy) in the first 3 postoperative days. The patient questionnaire included several questions that the patient had to rate on a Liekert scale (eg, 1 5 highly improved to 5 5 no improvement on their breathing progression preoperatively using IS, and 1 5 no pain to 5 5 severe on level of pain postoperatively). Statistical analysis. A power analysis (a 5 0.05; b 5 0.20) to estimate the sample size was conducted considering a clinically significant difference of 15% in inspiratory volumes, based on mean and standard deviation values reported in a previous study.15,16 A minimum of 21 patients per group was deemed necessary. Data were compared between the groups using the t test for unpaired data, analysis of correlation, Pearson’s c2 test, or Fisher exact test when appropriate with the analysis of association. Results were presented as means with standard deviations and confidence intervals; P , 0.05 was considered statistically significant. RESULTS

Forty-one ASA 1–3 patients consented to participate in the study. These patients were randomized into 2 groups—the control (21) and the experimental (20). Four of these patients were discharged home on the same day of surgery. As a result, postoperative day 1 data and analysis was performed on 37 patients (control n 5 19; experimental n 5 18) only. The physical and clinical characteristics of the patients in the 2 groups were similar, as indicated in Table I. Most patients in both groups were middle-aged women. Patients received 1 of 3 procedures, including laparoscopic small pouch gastric bypass, laparoscopic gastric sleeve, or laparoscopic gastric banding. No significant differences were present in BMI, age, or length of preoperative IS use between the 2 groups. None of the patients experienced intraoperative desaturation or required arterial blood gas monitoring for abnormal peripheral oxygen saturation.

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The use of preoperative IS before the scheduled surgery was similar in both groups—control (7.2 6 4.91 days) and experimental (6.4 6 3.30 days) (P , 0.330). The inspiratory capacity (IC) volumes were comparable in the preoperative anesthesia clinic for both groups (control 5 2171.43 6 762.98; experimental 5 2155 6 650.08) (P , 0.941). Figure 1 illustrates that a significant decrease occurred in IC in both groups when comparing the day of surgery volume (control 5 2254.76 6 808.84, experimental 5 2275 6 777.56) with the postoperative day 1 volume within each group (control 5 1557.90 6 814.67, experimental 5 1458.33 6 613.87), (P , 0.010 and P , 0.001, respectively). In addition, the 2 groups were compared with each other, and no significant difference (P , 0.935) was found in the day of surgery IC volumes (as noted previously). The postoperative day 1 IC volumes (as mentioned earlier) also were compared between the control and experimental groups, and again, no significant difference (P , 0.676) was found between the 2 groups. Clinical evaluation on postoperative day 1 revealed no pulmonary complications for either group. Univariate analysis of different variables did not detect any difference between the 2 groups or any correlation with postoperative IC lung loss in a particular gender, length of IS use, length of surgery, type of surgery, or pain score. However, the BMI and the preoperative ratio between the actual volume and the ideal volume showed a trend toward an inverse relationship, but the P level was not statistically significant. All patients were considered together regardless of their study assignment and were subdivided into 2 categories based on their BMI (BMI ,40 mg/kg2 to 49.9 mg/kg2 and BMI $50 mg/kg2). The preoperative day of surgery IC was compared with the postoperative day 1 IC. When evaluating the group with a BMI ,40 mg/kg2 to 49.9 mg/kg2, the IC on the day of surgery was 2214 6 775 cc, which decreased to 1532.61 6 688 cc displaying a 31% (P , 0.002) reduction, whereas the group with a BMI $50 mg/kg2 exhibited a decrease of 36% (P , 0.008) when their IC decreased 2312.50 6 819 cc on the day of surgery to 1471.43 6 784 cc on postoperative day 1. Figure 2 exhibits the IC separately in both the control and the experimental groups when each is subdivided into the following categories: BMI ,40 mg/kg2 to 49.9 mg/kg2 (23 patients) and BMI $50 mg/kg2 (14 patients). When separately evaluating the preoperative day of surgery IC and the postoperative day 1 IC in both groups with a BMI ,40 mg/kg2 to 49.9 mg/kg2, the IC in the control group (12/23 patients) was reduced from 2488.46 6 815 cc to 1854.17 6 822 cc, respectively, decreasing by 25% (P , 0.070). The IC in the

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Table I. Patient demographics, length of preoperative, IS use, surgical procedures, and inspiratory vital capacity in both groups. No significant differences were found in any the data on this table Data

Control group (n 5 21)

Experimental group (n 5 20)

Gender Age (year) Weight (kg) Height (m) BMI (kg/m2) Length of preoperative IS (d) Gastric bypass (n) Gastric sleeve (n) Gastric lap band (n) Clinic lung volume (sitting) (cc) DOS lung volume (sitting) (cc) POD lung volume (sitting) (cc)

81% female 45.0 6 12.4 136.15 6 19.38 1.68 6 0.09 48.3 6 6.9 7.2 6 4.91 16 3 2 2171.43 6 762.98 2254.76 6 808.84 1557.90 6 814.67

90% female 45.2 6 12.3 134.95 6 22.53 1.65 6 0.07 48.9 6 5.7 6.4 6 3.30 14 2 4 2155.00 6 650.08 2275.00 6 777.56 1458.33 6 613.87

NS NS NS NS NS NS NS NS NS NS NS NS

Abbreviations: NS, not significant; DOS, day of surgery; POD, postoperative day 1.

experimental group (11/23 patients) decreased from 1958.33 6 656 cc on the day of surgery to 1181.82 6 197 cc on postoperative day 1, showing a 40% reduction (P , 0.002). The groups with a BMI $50 mg/kg2 had the opposite effect in which the IC in the control group (7/14 patients) decreased from 1875 6 681 cc on the day of surgery to 1050 6 525 cc on postoperative day 1, a 44% reduction (P , 0.020). The IC in the experimental group (7/14 patients) decreased by 31% (P , 0.052), starting from 2750 6 732 cc on the day of surgery and decreasing to 1892.86 6 802 cc on postoperative day 1. A multivariate analysis was performed in which 10 patients exhibiting $3000 cc IC volume in the initial

Fig 1. IC volumes measured preoperatively (day of surgery) and postoperatively in patients separated by their assigned group. Both the experimental and the control groups showed a significant difference in IC lung volume as shown by the (*). The percentage loss for the control group was 31%, and for the experimental group, it was 36%. No significant differences were found between the control and the experimental groups when comparing day of surgery and postoperative day 1 IC volumes as shown by the 2 solid connecting bars. (Color version of figure is available online.)

preoperative anesthesia clinic assessment were removed, and the 31 patients left were organized within their respective groups according to an actual/ideal volume ratio of 0.70. The actual/ideal volume ratio $0.70 decreased (from the preoperative anesthesia clinic to postoperative day 1) by 29% (P , 0.009) and 37% (P , 0.001) in the control (9 patients) and experimental (10 patients) groups, respectively. In addition, both groups with a ratio ,0.70 also exhibited a similar outcome, with the control group (6 patients) decreasing

Fig 2. Preoperative and postoperative IC volumes. The groups were divided further by their BMI. The experimental group with BMI .50 showed an improvement (31% vs 44%) of IC lung loss. (Color version of figure is available online.)

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by 35% (P , 0.039) and the experimental group (6 patients) decreasing by 21% (P , 0.017). Patient questionnaires regarding IS use and breathing improvement, as illustrated in Table II, revealed that 48% (10/21) of patients in the control group (3 breaths once per day) described moderate-to-high improvement in breathing after their preoperative use of IS. In the experimental group (10 breaths 5 times per day), 45% (9/20) of patients exhibited a moderate-to-high improvement in breathing. We also investigated the level of pain through the questionnaire, and only 11% of patients in both groups stated they were experiencing moderate pain postoperatively the day after surgery (no patients were in severe or intolerable pain at the time of the visit), whereas the remaining patients were comfortable or slightly in pain. Univariate analysis was performed on both groups based on the patient’s subjective feeling of improvement in breathing after IS usage. No absolute or relative change was noted in lung volume in both groups when comparing the IC from the clinic with the day of surgery or when comparing the day of surgery with postoperative day 1. None of the patients in both groups had a SpO2 lower than 95% on postoperative day 1 at the time of IS assessment (no significant difference between experimental vs control group). DISCUSSION

The use of preoperative IS was proposed in this clinical investigation with the speculation that encouraging morbidly obese patients to breathe to total lung capacity and therefore opening collapsed alveoli would minimize postoperative respiratory dysfunction. Because of the many differences in previous studies’ design and the etherogeneity of investigated popula-

tions, the therapeutic value of preoperative IS has not yet been fully understood.11,17 Studies have been done comparing the use of IS, CPAP, and a combination of cough and deep breathing to prevent postoperative pulmonary complications in patients undergoing upper abdominal surgery. Investigators comparing CPAP, IS, and the combination of cough and deep breathing have suggested that using IS or CPAP may be beneficial; however, CPAP may increase mean functional residual capacity (FRC) more rapidly in patients receiving the combination of IS or cough and deep breathing. Nonetheless, no statistically significant differences were found between the groups, as was reported by Pasquina et al18 and in a recent review from the Cochrane review.14 Our results demonstrate that patients undergoing a bariatric procedure do not benefit from the preoperative use of IS, as assessed with IS exercises performed within the first 24 h after surgery, and in fact, a decrease was noted postoperative lung volume. We investigated whether this volume decline was related to preoperative inspiratory volume. To increase the sensitivity of our post hoc analysis, we pooled together both groups, stratifying them by BMI (,50 or $50). The preoperative IC volumes were not significantly different between the 2 BMI groups nor were the postoperative volumes. This result is consistent with the hypothesis, that both preoperative and postoperative IC not only are determined by patients’ BMI but may be affected by other preoperative factors that we did not consider in the present analysis. Even if preoperative IS was not sufficient in our study to prevent a decrease in IC postoperatively, it did not lead to any complication, was not too consuming or expensive, and was well received by patients overall. We

Table II. Patient questionnaire responses for level of pain, feeling of breathing improvement, and patient satisfaction with prescribed IS usage.* Questionnaire patient response Questions

Control (n) (%)

Experimental (n) (%)

How would you rate your level of improvement in regard to breathing after IS usage? (1–5) What level of pain are you experiencing? (POD) (1–5)†

10 (48%) Moderate/high improvement 5 (24%) Undecided 6 (28%) Little to no improvement 2 (11%) Moderate/severe pain 1 (,1%) Undecided 16 (84%) Little to no pain 1 (4%) Too much 15 (71%) Just right 3 (14%) Not enough 2 (10%) Undecided

9 (45%) Moderate/high improvement 5 (25%) Undecided 6 (30%) Little to no improvement 2 (11%) Moderate/severe pain 3 (1%) Undecided 13 (73%) Little to no pain 1 (5%) Too much 17 (85%) Just right 1 (5%) Not enough 1 (5%) Undecided

How would you rate the prescribed usage of IS? (1–4)

*The responses were graded as follows: (1 5 no pain to 5 5 severe pain; 1 5 highly improved to 5 5 no improvement; 1 5 too much to 3 5 not enough and 4 undecided). † Two fewer patients were included in this question per group because 4 patients (2 control and 2 experimental) were discharged the same day of surgery.

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now consider that it may be advantageous to institute a form of aggressive IS (as reported by Jensen et al11) associated with early ambulation and preoperative patient education. Such an approach was accompanied, in fact, by a low incidence of postoperative pulmonary complications and early patient discharge. However, no patient enrolled in our study required a hospital stay longer than 3 days. We used a BMI stratification to identify any difference between the 2 groups as related to weight. IS did not impact the postoperative day 1 lung volumes in patients with BMI $50 mg/kg2. The control groups actually fared better and experienced a smaller percentage decrease than the experimental group. However, when evaluating patients of both groups with a BMI $50 mg/kg2, IS was beneficial in the experimental group whose patients had a less important decrease in lung volume than those in the control group. Although this result may suggest that preoperative IS might benefit patients with a BMI $50 mg/kg2 undergoing bariatric surgery, we cannot rule out a b error because of the small number of enrolled patients, and any hypothetical effect is deferred to further investigation. This study has several limitations. First, patients undergoing 3 specific procedures were included in this study, so we have combined different surgical procedures that possibly could have a different impact on respiratory mechanics. Another limitation of the study was the underpowered sample size. A prestudy power analysis described the need for 21 patients per group (25 considering the patient drop-out for 50 patients) for a 15% improvement in total IC. However, based on our results, to achieve a relative 50% improvement, 60 patients would have been required. Perioperative respiratory function usually is assessed with a combination of parameters obtained with pletismography, arterial blood gases (ABG), and spirometry, such as FRC, forced expiratory volume in 1 s (FEV1), and vital capacity. However, our study focus was limited to the incentive spirometer, which is not a sophisticated tool and only provided measurements of IC. Another limitation of our study is that enrolled patients used IS for nonuniform periods of time, as the study protocol requested at least 3 preoperative treatment days but could not assure the same interval to all patients between the preoperative assessment and the day of surgery followed by the postoperative evaluation. As several patients only used IS for 3 days before surgery, they may not have had sufficient time to receive the full benefits. Adequate tidal volume and the use of PEEP intraoperativley are important factors in preventing the formation of intraoperative atelectasis that may persist after extubation. In our study, mechanical ventilation settings were not consistent. Furthermore, it has been shown

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Fig 3. Preliminary results of lung spirometry from a cohort of bariatric patients. (Color version of figure is available online.)

that keeping a FiO2 at 70% at extubation is effective in preventing the formation of atelectasis that otherwise could last up to 24 h after surgery.19,20 Our results could have been influenced by our institution’s standard practice of administrating 100% oxygenation immediately before extubation, causing atelectasis formation that may mask a possible beneficial effect of the preoperative spirometry on lung volumes. Because ABG monitoring was not included in the research protocol, the correlation between arterial blood oxygen tension and lung volumes was not calculated. Besides, in general, female patients populate studies on bariatric surgery, and we cannot exclude an influence determined by gender discrepancies in the study population. Neither postoperative pain therapy nor pain scores were standardized to rule out an interference from pain on IS performance; however, based on our questionnaires, no patients were affected by inappropriate pain control. The postoperative evaluation of IS was scheduled at postoperative day 1 after surgery. Therefore, we cannot comment on the possibility that continuing postoperative IS and repeating lung volume measurements during the next 2 days postoperatively could provide better data on lung volume. Indeed, a previous preliminary study on 21 patients (76% female) at an outside institution (unpublished data graciously provided by A.V.) demonstrated that spirometry of patients undergoing bariatric surgery demonstrated a significant decrease in all 3 major values (FRC, FEV1, and FEF 75% to 25%) that persisted up to the day of discharge (Fig 3). The patients in this study were 38 6 11 years of age with a BMI of 40 6 2.8 kg/m2.

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CONCLUSION

Patients undergoing bariatric surgery seem to not benefit, in terms of postoperative inspiratory lung volumes, from preoperative use of IS as applied in our study. Of interest, none of the patients experienced any pulmonary complications. However, our analysis was limited to measuring lung volumes up until postoperative day 1. Overall, both groups of patients were satisfied with their designated use of IS and the study itself, but some concern was present of poor compliance with the treatment as reflected by the questionnaires. Extending this study a few days postoperatively likely would allow us to achieve a better understanding of the course of respiratory function recovery, and it might allow us to detect a possible longer term benefit from preoperative IS use. Additionally, based on our results, any treatment that results in at least a relative 50% improvement of IC would require a sample population of 30 patients per group. Future studies are necessary to identify the predictors or risk factors of postoperative volume loss more accurately in individual patients and to identify therapeutic strategies better. A larger study consisting of patients with a BMI .50 kg/m2 undergoing a single lengthy bariatric procedure, such as gastric bypass, stratified by gender, that would include a sensitive marker of blood oxygenation (ABG) and lung function (spirometry) to be correlated with IS possibly might provide better data regarding the perioperative respiratory physiology derangements in this population. We thank Vineela Maddukuri, MD, for her assistance in the statistical analysis and research organization, Russell Graham, RT, and Joey Wilson, RT, for support by providing patient education on incentive spirometry use and data on the incentive spirometer, the Bariatric Surgery Team at the Memorial Hermann Hospital for their collaboration, and Memorial Hermann Hospital—Texas Medical Center for their support.

REFERENCES

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