Respiratory events in patients undergoing laparoscopic gastric bypass surgery [v1; ref status: approved 1, approved with reservations 1, not approved 1, http://f1000r.es/YYXoAZ]
Coastal Anesthesiology, 100 Whetstone Place, St. Augustine, FL 32086, USA
University of Illinois at Chicago, 1740 West Taylor Street, Suite 3200W, MC515, Chicago, IL 60612, USA
Flagler Life Institute, 30 San Bartola Drive, St. Augustine, FL 32095, USA
U.S. Bariatrics, 300 Health Park Boulevard, Suite 5200, St. Augustine, FL 32086, USA
Grant information: The author(s) declared that no grants were involved in supporting this work.
The incidence of morbid obesity is increasing and has led to an increase in bariatric procedures1. The incidence of obstructive sleep apnea (OSA) amongst patients undergoing bariatric surgery has been shown previously to be 71%2. The prevalence of moderate OSA (apnea hypopnea index – AHI≥15) in obese patients with a body mass index (BMI) of >40kg/m2 is 42–55% in men and 16–24% in women3. Patients with OSA have a higher rate of postoperative complications4,5.
We investigated if patients with OSA undergoing laparoscopic gastric bypass surgery have an increased risk of postoperative respiratory events and desaturations in the first postoperative night. In this observational study we examined the data of n=89 consecutive patients undergoing gastric bypass surgery.
Patients and methods
After Institutional Review Board (IRB) approval was obtained, data on all patients undergoing gastric bypass surgery in a community hospital was collected between 7/2010 and 2/2011. All patients schedule for gastric bypass surgery were enrolled and managed according to our routine clinical protocol. The need for consent was waived by our IRB due to the entirely observational nature of our study.
The clinical protocol includes a simplified Berlin questionnaire to detect sleep disordered breathing preoperatively. If patients were determined to be at risk for OSA they were evaluated by a pulmonologist to determine if a sleep study is indicated and continuous positive airway pressure CPAP therapy necessary.
Patients with known OSA were encouraged to bring their CPAP equipment for perioperative use. Patients that used their CPAP device preoperatively were considered to be compliant (OSAc). Patients that were not using their CPAP device preoperatively were considered noncompliant (OSAn). All patients received oxygen via nasal cannula (2–4 l/min) and were monitored with continuous pulse oximetry and EKG after PACU discharge. Desaturations were defined as a pulse oximetry reading <90%. Time spent with an oxygen saturation below 90% during the monitoring period was defined as T90%. If patients showed frequent desaturations the oxygen flow was increased. If this was insufficient to resolve hypoxemia a mask or CPAP with oxygen was applied to increase the inspired fraction of oxygen and resolve possible obstruction.
The monitoring time started on the day of operation between 21:00–22:00 and ended between 07:00–07:30 the following morning. Pain was managed with intravenous hydromorphone PCA with standard settings (hydromorphone 0.2mg q 6min, 4h lockout 6mg, no basal rate). Hydromorphone consumption was recorded intraoperatively and during the monitoring period. Narcotics given after PACU discharge and before the monitoring time were not recorded.
All respiratory events were counted during the immediate postoperative period starting in PACU until the following morning. A respiratory event was defined as a deviation from the standard management protocol as described above. Application of an oral airway, oxygen mask or CPAP, prolonged postoperative ventilation and unplanned admission to the intensive care unit were considered respiratory events. CPAP is not routinely started in PACU in our institution. The administration of naloxone was considered a respiratory event as it is administered in patients that are considered to be hypoventilating. For all details please see Table 7.
The initial data was entered in an EXCEL spreadsheet and later transferred to a SAS data set for analysis. The categorical data was analyzed with the chi square test for independence. For small subsets for which there was insufficient data for the chi square test to be valid, data analysis was done with the two-tailed Fisher’s Exact Test.
89 patients, 63 (70.8%) female and 26 (29.2%) male, underwent gastric bypass surgery. Patients were grouped according to the diagnosis OSA (OSA/n=48) and no diagnosis of OSA (NOSA/n=41). In the OSA group 29 (60.4%) patients were female and 19 (39.6%) male. In the NOSA group 34 (82.9%) patients were female and 7 (17.1%) male. The gender distribution is significantly different in both groups (p=0.02).
The BMI of patients in both groups was statistically not significantly different. Both groups had a similar number of smokers and patients on pain medication. In the OSA group significantly more patients were using antidepressants and anxiolytics. Patients who had OSA also had a significantly higher number of comorbidities (Table 1).
Table 1. Clinical characteristics of patients with and without obstructive sleep apnea (OSA/NOSA).
|Gender f/m (%)||29/19|
|Age||53.25 (11.1)||50.9 (12.9)||0.36 (NS)|
|Height (cm)||165.48 (10.10)||163.34 (9.49)||0.32 (NS)|
|Weight (kg)||128.6 (30.4)||127.3 (24.7)||0.09 (NS)|
|BMI||45.84 (9.29)||43.70 (6.57)||0.14 (NS)|
|Smoker||7 (14.6%)||4 (9.8%)||0.49 (NS)|
|Pain Medication||15 (31.3%)||11 (28.8%)||0.65 (NS)|
|29 (60.4%)||16 (39.0%)||0.04|
|Comorbidities||4.83 (2.0)||3.65 (2.48)||0.01|
Both groups (OSA vs. NOSA) received similar amounts of midazolam (2.25mg vs. 2.20mg; p=0.802), fentanyl (198μg vs. 207μg; p=0.59) and hydromorphone (1.07mg vs. 0.85mg; p=0.344) intraoperatively (mean doses; p value). One patient in the OSA group and 2 patients in the NOSA group received ketamine intraoperatively. Two patients in the OSA group and one the NOSA group received morphine intraoperatively.
Patients were monitored during the first postoperative night with continuous pulse oximetry and EKG. Data was collected at a central monitoring unit. The monitoring time did not differ significantly between groups (Table 2). Patients were monitored for an average of 9.67 hours (9.71 hours in the OSA group/9.62 hours in the NOSA group).
Table 2. Total monitoring time during the first postoperative night between patients with and without obstructive sleep apnea (OSA/NOSA).
|9.7 (0.56)||9.6 (0.53)||9.67 (0.55)||0.40 (NS)|
Data was unavailable for 5 patients: 3 patients in the OSA group and two patients in the NOSA group.
The hydromorphone consumption during the monitoring time did not differ significantly between the two groups (Table 3). Patients undergoing gastric bypass surgery required on average 2.13mg hydromorphone during the first night.
Table 3. Hydromorphone consumption during first postoperative night between patients with and without obstructive sleep apnea (OSA/NOSA).
|2.09 (1.40)||2.16 (1.49)||2.13 (1.59)||0.84|
Data was unavailable for 6 patients: one patient in the OSA group and 5 patients in the NOSA group.
Two patients in the OSA group received extra analgesic medication. One received 30mg ketorolac intravenous and the other received his home dose of gabapentin (300mg) at night.
The total number of desaturations were compared in all groups. A desaturation was defined as oxygen saturation <90%. Patients noncompliant with CPAP showed significantly more desaturations than patients without OSA (NOSA). The other comparisons did not show statistical significance (see Table 4).
Table 4. Comparison of overnight oxygen desaturation <90% between patients with obstructive sleep apnea in general (OSA), patients compliant or non-compliant with CPAP therapy (OSAc/OSAn) and patients without sleep apnea (NOSA).
* chi-square test.
Patients who presented with an oxygen desaturation below 90% during the monitoring time did not use more hydromorphone (2.2mg vs 2.0mg; p=0.66).
T90% is defined as the time an oxygen saturation below 90% was measured during the monitoring time. The T90% was not significantly different in patients with OSA compared to patients that didn’t have a diagnosis of OSA. Patients that were compliant with using CPAP (OSAc) had a similar T90% compared to patients that didn’t have OSA (NOSA). Patients that were noncompliant with using CPAP (OSAn) showed a higher T90% than patients that were compliant with CPAP (OSAc) (p=0.19), but this finding was not statistically significant. This indicates that patients in all groups had similar T90%s (Table 5).
Table 5. Time of oxygen concentration <90% during monitoring time in percent (T90%) between patients with and without obstructive sleep apnea (OSA/NOSA).
* Significance between OSA and NOSA (Chi-square Analysis).
Data was unavailable for 3 patients: one patient in the OSA group and two patients in the NOSA group.
Using a chi square test, there was no statistically significant difference in the incidence of respiratory events in patients in the OSA group compared with in the NOSA group (p=0.29) (Table 6). Patients compliant with using CPAP (OSAc) had a similar incidence of respiratory events to patients without OSA (NOSA) (p=0.96). Patients noncompliant with using CPAP (OSAn) presented a statistically significant increased risk of suffering a respiratory event compared to patients compliant with CPAP (OSAc) (p=0.03).
Table 6. Respiratory events in patients after gastric bypass surgery between patients with obstructive sleep apnea in general (OSA), patients compliant or non-compliant with CPAP therapy (OSAc/OSAn) and patients without sleep apnea (NOSA).
* Significance between OSA and NOSA (Chi-square Analysis).
We considered assisted or prolonged ventilation, administration of naloxone and unplanned admission to the SICU as serious events. There were 5 serious respiratory events in the OSA group and 2 in the NOSA group (patients 70, 107, 149, 69, 97 and 96, 129). For all details please see Table 7.
Table 7. Narrative of patients having respiratory events.
|Description of respiratory event|
|OSA (n=48)||c||11||Preoperative nebulizer, intraoperative steroids, inhalers first night|
|c||70||Prolonged intubation: on T-piece in PACU after 0.3mg naloxone,|
hypoventilation, sedated with propofol and mechanically ventilated,
extubated 1.5h after the end of surgery
|c||50||OAW in PACU|
|c||75||CPAP in PACU|
|c||124||Wheezing and UAW obstruction, CPAP and nebulizer treatment in PACU|
|c||23||Oxygen mask overnight, no CPAP|
|c||22||Subjective “hot and suffocating”, normal clinical exam, normal vitals,|
improvement after nebulizer
|n||87||UAW obstruction, started CPAP first night|
|n||141||Requiring oxygen on PACU discharge|
|n||107||Intraoperative bronchospasm, facemask in PACU then weaned to 4l/min,|
apnea first night, naloxone 0.3mg given
|n||149||Bag-mask ventilation on PACU arrival, CPAP started in PACU, unable to|
wean from CPAP
|n||57||Mild wheezing in PACU, inhalers and CPAP first night|
|n||69||UAW obstruction in PACU, BiPAP started, unplanned admission to SICU|
|n||97||Severe UAW obstruction, BiPAP applied, unplanned admission to SICU|
|NOSA (n=41)||96||Apnea during first night, naloxone 0.3mg|
|29||OAW in PACU|
|58||UAW obstruction, started CPAP first night|
|102||UAW obstruction, started CPAP first night|
|109||UAW obstruction, started CPAP first night|
|62||UAW obstruction, started CPAP first night|
|65||UAW obstruction, started CPAP first night|
|129||Bag-mask ventilation in PACU, BiPAP started, prolonged PACU stay|
We prospectively collected data on 89 consecutive patients undergoing gastric bypass surgery between 7/28/2010 and 2/15/2011. 48 patients were previously diagnosed with OSA. Sleep apnea in the surgical population is an independent risk factor for pulmonary complications6. This study was not controlled for BMI. Morbidly obese patients seem to have an increased risk of postoperative mortality7. It is unclear in the literature if bariatric patients with OSA have a higher incidence of postoperative complications5.
Hwang et al. found that sleep-disordered breathing (SDB) is associated with an increased risk of postoperative complications. The authors screened patients preoperatively. If patients showed clinical features suggestive of OSA they were selected for home nocturnal oximetry testing. They measured the number of episodes per hour of oxygen desaturation (oxygen desaturation index – ODI) of ≥ 4% (ODI4%) and the percentage of the study time spent with an oxygen saturation of <90% (T90%). A total of 172 patients aged 27 to 85 years were enrolled. They could show that an ODI4% ≥ 5 and a T90% were associated with an increased risk of postoperative complications5,8,9.
These findings are consistent with Liao et al., who reported in their retrospective study, that patients with OSA have an increased incidence of postoperative complications compared to matched controls9.
In contrast to the above findings there was no statistical difference in our study in respiratory events in the OSA compared to the NOSA group (p=0.29). In our study 29.2% (14/48) of patients with OSA had a respiratory event compared to 19.5% (8/41) in the group of patients without OSA (NOSA). Patients in both studies had a lower BMI than in our study and patients underwent a variety of different surgical procedures5,9. Interestingly the two patients with an ODI4% <5 in one study that suffered a complication were morbidly obese5. In the other study complications included mild and severe desaturations9. OSA is defined as a reduction or cessation of airflow with respiratory effort during sleep leading to oxygen desaturations10. It would be therefore anticipated to find a higher incidence of desaturations in the OSA group as compared to the control group. It is difficult to determine if mild desaturations with an oxygen saturation greater than 90% but less than 95% pose a significant immediate health risk and can therefore be counted as a complication, and it is unclear if the number of total respiratory “complications” in this study would have reached clinical significance9.
Jensen et al. reported that CPAP and bilevel positive airway pressure (BiPAP) use can be safely omitted after laparoscopic gastric bypass operation. The authors reported data on 1095 patients undergoing gastric bypass surgery. Out of 284 patients with a diagnosis of OSA, 144 used CPAP/BiPAP and 140 did not use CPAP/BiPAP. Patients received supplemental oxygen 2–4 l/min using a nasal cannula postoperatively. CPAP/BiPAP was not used after surgery and patients were instructed not to use it after discharge. The authors defined a respiratory complication as respiratory distress, pneumonia or reintubation within 30 days after gastric bypass operation. Data on overnight oxygen saturations were not published8. None of our patients required reintubation, developed pneumonia or respiratory distress postoperatively during the first 24h. CPAP treatment is primarily indicated to treat upper airway obstruction in patients with OSA during deep stages of sleep to prevent hypoxemia11. It can also be used to prevent reintubation in patients developing hypoxemia after surgery. In a randomized controlled trial the use of CPAP with oxygen to treat postoperative hypoxemia after abdominal surgery compared to oxygen alone decreased the need for reintubation and mechanical ventilation and appeared to be safe. As secondary endpoints, CPAP helped to prevent pneumonia, infection and sepsis but in this study, patients with sleep disorders or BMI>40 kg/m2 were excluded12.
In the literature only 25.8–50% of patients with OSA undergoing bariatric surgery are compliant with CPAP13. Patients with OSA who are noncompliant with CPAP seem to have a higher rate of complications compared to patients with OSA who are using CPAP9. OSA was shown to be a risk factor in adverse outcome in bariatric surgery14. In the present study 35 patients (72.9%) were using their CPAP and only 13 patients (27.1%) were noncompliant. 53% of patients with OSA that were noncompliant with CPAP therapy (OSAn) had a respiratory event in the direct postoperative period. This is statistically significant in comparison to patients diagnosed with OSA that are compliant with CPAP (OSAc) (p=0.03).
In the present study patients compliant with CPAP (OSAc) have a similar complication rate compared to patients that don’t have OSA (NOSA) (p=0.96). In the study by Liao et al. patients with OSA that were compliant with CPAP had a higher rate of complication than the control group. Patients in the OSA group had a higher BMI9 and this may have influenced the results. Morbidly obese patients are at greater risk of desaturations15. Obesity is an independent risk factor for sleep-disordered breathing (SDB) and the development of OSA16. In our study both groups had a similar BMI and were using similar amounts of opioids during the monitoring time. The mean BMI in two large multicenter studies was 46.9–47.0 kg/m214,17. The average BMI in our study was 47.1 kg/m2.
Opioid consumption has a profound effect on SDB and affects sleep architecture.
Anesthetic and analgesic agents used during the perioperative period can decrease pharyngeal tone, and depress ventilatory response to hypoxia and hypercapnia18. Midazolam and narcotic consumption during surgery and the monitoring period were similar in the OSA group and in the NOSA group. Narcotic consumption may lead to hypoventilation, hypercarbia and hypoxemia. By increasing the inspired concentration of oxygen hypercarbia induced hypoxemia can be prevented. All but one patient received oxygen via a nasal cannula with a flow to up to 4l/min. Incentive spirometry was also encouraged. 3 patients had to be treated with naloxone due to opioid induced hypoventilation (two patients in the OSA group and one in the NOSA group).
In a study by Ahmad et al., 40 patients underwent bariatric surgery. There was no difference in hypoxemic episodes in the group of patients diagnosed with OSA versus patients without OSA. 29 patients underwent gastric bypass surgery and 11 gastric banding. Surgical time for gastric bypass surgery compared to gastric band was longer (150–180min versus 116–125min), more invasive and more painful. Patients required higher doses of narcotic medication intra- and postoperatively (remifentanil 1060–1520μg vs 525–737μg; morphine 22–25.5mg vs 2–5.4mg). Patients undergoing gastric bypass surgery had a longer hospital stay than patients having gastric banding (60–73h versus 28–29h, respectively). The authors state in their discussion “the lack of a uniform surgical procedure could have affected the results”1. In other words the differences in surgical stress and narcotic consumption could have affected sleep architecture19. In our study, all patients underwent gastric bypass surgery by one of the two coauthors, (either J. Koppman or R. Marema).
In the study by Ahmad et al. oxygen saturation was measured for the first 24h following PACU discharge1. OSA is a sleep related disorder and may not influence daytime, awake oxygen saturation. Therefore differences that may be found at night may become insignificant when calculating long periods of wakefulness into a data set. This reduced the percent of time spent <90% saturation to 0.2–0.6%. The total monitoring time in our study was exclusively at night when one would expect the most desaturations. The patients in the present study showed the percentage time spent <90% saturation (T90%) of 6.05% in the OSA group and 5.14% in the NOSA group.
Ahmad et al. defined an ODI4% as a “hypoxemic” episode. The ODI showed a correlation to apnea-hypopnea-index (AHI) in the polysomnogram (PSG) which helped to determine the severity of OSA20. We defined clinically relevant hypoxemia as oxygen saturation <90%. The T90% was greater in patients who experienced complications compared to those without a complication (20.8% vs 9.9%). Patients in the ODI4% ≥5 group had significantly higher BMI, more comorbidities and underwent a variety of surgical procedures5. These factors may have influenced the results.
The small difference in desaturation (T90%) in the present study may be explained by the fact that we failed to identify patients with OSA in the NOSA group. Frey et al. found that the incidence of OSA is present in 71% of patients that have been evaluated for bariatric surgery2. In a multicenter study the incidence of OSA in patients undergoing gastric bypass surgery was 47%17. Application of CPAP or BiPAP was considered a respiratory event. 13 patients required CPAP/BiPAP postoperatively [7 (14.6%) patients in the OSA group and 6 (14.6%) patients in the NOSA group]. The STOP-BANG assessment has a high sensitivity (>90%) in detecting patients at risk for obstructive sleep apnea21. We did not screen the patients in this study with the STOP-BANG index. We collected only four of the 8 variables available (history of hypertension (HTN), BMI, gender and age). In the group of patients without OSA (NOSA, n=41) 27 (65.9%) patients had at least 3 positive answers. The number of patients with at least three positive answers would most likely be greater if we would have screened for all parameters of the STOP-BANG index. This may make it not very useful in identifying patients at risk for OSA in the bariatric population.
Also the application of oxygen may have prevented more desaturations in the first postoperative night. In the OSA group an average oxygen flow of 3.33l/min was administered. In the NOSA group an average oxygen flow of 2.75l/min was administered. We did not measure inspired oxygen concentration or oxygen flow provided overnight. Patients in one group could have been treated with higher oxygen concentration during the monitoring time influencing the results in this study.
Also the unequal gender distribution may have affected our results. In our study 70.8% of patients were female and 29.2% male. In the literature 77.5–83% of patients that undergo bariatric surgery are female1,2,14,17 whereas more male patients have OSA than female2 and we did indeed observe a higher percentage of male patients in the OSA group as compared to the NOSA (39.6% vs. 17.1%) group.
In the study by Ahmad et al. 74.2% in the OSA group were female and 25.8% male patients. In the NOSA group; all patients were female1.
The results in the present study suggest that morbidly obese patients with OSA have a similar rate of respiratory complications and desaturations compared to patients without OSA (NOSA) undergoing laparoscopic gastric bypass surgery. Patients with OSA that are noncompliant with CPAP (OSAn) have a statistically significant increase in respiratory complications compared to patients with OSA that are compliant in the use of CPAP (OSAc). The significant increase in desaturations and T90% in the OSAn group simply confirms the diagnosis of OSA. Our study suggest that it may be beneficial to educate and encourage patients with OSA in the use of CPAP to reduce postoperative respiratory events and that adequately treated OSA is not an independent risk factor for respiratory events22,23.