|Ahead of print publication
Perioperative complications and Intensive Care Unit utilization in super-superobese patients undergoing laparoscopic bariatric surgery
Chia-Li Kao1, Cheuk-Kwan Sun2, Hsiu-Jung Lin1, Kuo-Chuan Hung3
1 Department of Anesthesiology, E-Da Hospital, Kaohsiung, Taiwan
2 Department of Emergency Medicine, E-Da Hospital and School of Medicine for International Students, I-Shou University, Kaohsiung, Taiwan
3 Department of Anesthesiology, Chi Mei Medical Center, Tainan, Taiwan
|Date of Submission||16-Apr-2018|
|Date of Decision||19-Jun-2018|
|Date of Acceptance||18-Jul-2018|
|Date of Web Publication||02-Apr-2019|
Department of Anesthesiology, Chi-Mei Medical Center, 901, Chung-Hwa Road, Yung-Kung District, Tainan
Source of Support: None, Conflict of Interest: None
Objective: Anesthetic management for super-superobese (SSO) patients (body mass index [BMI] ≥60 kg/m2) presents a challenge for anesthesiologists. This study aimed at characterizing the early complications and Intensive Care Unit (ICU) utilization in SSO patients receiving laparoscopic bariatric surgery. Materials and Methods: Totally, 25 SSO patients receiving laparoscopic bariatric surgery between June 2006 and December 2011 were reviewed. The data collected included patient demographics, preoperative comorbidities, anesthetic techniques, airway management, perioperative adverse events, ICU utilization, and early complications occurring within 30 days of index surgery. Early complications were defined as the adverse events that led to permanent detrimental effects or required significant additional intervention. Results: A retrospective analysis was performed on data from 25 consecutive SSO patients (age: 31.2 ± 11.1 years; BMI: 64.9 ± 4.7 kg/m2). Tracheal intubation was attempted successfully in all patients but was difficult in two cases when using laryngoscopy. Bronchospasm was observed in five cases (20%) after tracheal intubation. Postoperative ICU utilization was required in five cases (20%). Early complications occurred in two cases during their stay in postanesthesia care unit (including one case of respiratory failure and one case of hyperkalemia) and in two cases during their stay in ICU (both with respiratory failure). The incidence of early complications was 16%. All patients were discharged from the hospital without sequelae. Conclusions: It is imperative to anticipate the potential for developing perioperative adverse events and postoperative complications in SSO patients after bariatric surgery. Appropriate utilization of ICU resources may enhance patient safety.
Keywords: Anesthesia, Early complications, Intensive Care Unit utilization, Super-superbase
|How to cite this URL:|
Kao CL, Sun CK, Lin HJ, Hung KC. Perioperative complications and Intensive Care Unit utilization in super-superobese patients undergoing laparoscopic bariatric surgery. Tzu Chi Med J [Epub ahead of print] [cited 2019 May 22]. Available from: http://www.tcmjmed.com/preprintarticle.asp?id=255353
Chia-Li Kao and Cheuk-Kwan Sun contributed equally to this work.
| Introduction|| |
Bariatric surgery has become an increasingly utilized therapeutic option for patients with morbid (body mass index [BMI] >40 kg/m2) or complicated (BMI of 35–40 kg/m2 with comorbidities) obesity to obtain sustainable weight loss. However, morbidly obese (MO) patients often have a high prevalence of cardiopulmonary diseases and multiple comorbidities, which often predispose these patients to an increased risk of postoperative morbidity and mortality. In addition, because of anatomic and physiologic changes in obese patients, a high BMI was reported to positively correlate with the risks of intraoperative atelectasis, difficult mask ventilation, difficult airway management, and reduced cardiorespiratory fitness. A previous study demonstrated no differences in outcome between MO patients (BMI 40–49.9 kg/m2) and superobese (SO) patients (BMI ≥50 kg/m2), including super-SO (SSO) (BMI ≥60 kg/m2), undergoing bariatric operations under similar anesthetic management. However, because of small number of SSO patients (i.e., n = 5) in that study, the present investigation was designed to further address the bariatric surgery-associated perioperative complications in this particular patient population. Here, we report the anesthetic management of the initial 25 SSO patients undergoing laparoscopic bariatric surgery in a tertiary referral center. We summarized the perioperative adverse events and early perioperative complications encountered in SSO patients. The incidence, indications, and outcomes of patients requiring Intensive Care Unit (ICU) utilization after laparoscopic bariatric surgery were also analyzed.
| Materials and Methods|| |
After approval from the institutional review board of E-Da Hospital (EMRP-107-008), we retrospectively reviewed the data of 25 SSO patients between June 2006 and December 2011 from the anesthesia database of our institution. The study population comprised SSO patients who underwent bariatric surgeries and received tracheal intubation under general anesthesia. Patients were excluded if they had a history of abdominal surgery before the index surgery or the surgery was not performed electively. The study was conducted in accordance with the Declaration of Helsinki and was approved by the local ethics committee of the institute. Informed written consent was waived because the study was a retrospective data analysis.
All patients were evaluated for potential difficulty in airway management before surgery (between 2 and 4 weeks) in an anesthetic assessment clinic. Data including laboratory tests as well as results of electrocardiography (ECG), chest radiography, pulmonary spirometry, abdominal echography, and gastroscopy were also reviewed. Pulmonary function tests were selectively performed on patients with a notable history and/or findings on preoperative physical examination, including those with pulmonary disease, dyspnea on exertion, or limited functional capacity. Pulmonary function test abnormalities were classified as minor, moderate, or severe. In our hospital, since polysomnography is not routinely performed before bariatric surgery, the diagnosis of obstructive sleep apnea was made based on the patients' medical histories.
Anesthesia and airway management
Routine monitoring included ECG, noninvasive blood pressure, pulse oximetry, end-tidal CO2(EtCO2), and body temperature measurements. Invasive arterial blood pressure and central venous pressure were monitored in patients with severe cardiovascular comorbidities. All patients were preoxygenated in a 30° reverse Trendelenburg position. After anesthetic induction with propofol or thiopental sodium, nondepolarizing muscle relaxant (rocuronium or cisatracurium) was used to facilitate tracheal intubation with a Macintosh laryngoscope and Flexislip stylet (Willy Rüsch AG, Kernen, Germany) which is a common practice at our institution for airway establishment. For SSO patients, a fiberoptic bronchoscope, McCoy laryngoscope (Truphatek International Ltd., Netanya, Israel), Trachway® intubating stylet (Biotronic Instrument Enterprise Ltd., Taichung, Taiwan), and other airway instruments (e.g., an intubating laryngeal mask airway) were available in the operating room for airway rescue. After tracheal intubation, inhalation agents were used to maintain the anesthetic depth. A calibrating orogastric tube (36 F gauge; Obtech Medical Sàrl, Le Locle, Switzerland) was inserted through the esophagus into the stomach for gastric decompression and pouch formation. The calf-length pneumatic compression device was used for venous thromboembolism (VTE) prophylaxis.
Volume-controlled or pressure-controlled mechanical ventilation was initially set at a respiratory rate of 12 breaths/min and a tidal volume of 12–15 mL/kg based on ideal body weight. Afterward, mechanical ventilation was modified to maintain an EtCO2 of 35–40 mmHg and peak airway pressure of <35 cmH2O. During laparoscopic bariatric surgeries, intra-abdominal insufflation pressure was constantly maintained at between 12 and 15 cmH2O. At the end of surgery, neuromuscular blockade was reversed with reverse agents. Before tracheal extubation, the patient must be able to squeeze his/her hand and lift head off the bed and hold it up for 5 s. Tracheal extubation was performed on fully awake patients in 30° reverse Trendelenburg position.
After tracheal extubation was completed in the operating room or in the postanesthesia care unit (PACU), oxygen supplement via face mask was provided to maintain oxygen saturation >95% and bolus dose of morphine (5–10 mg) was given if required in the PACU. Bedside monitoring of the patient's respiratory status was performed intensively. Coughing and deep breathing were encouraged while in the PACU. After discharge to the ward, SSO patients were encouraged to ambulate early and bolus dose of nalbuphine was used as the analgesics for postoperative pain.
Data collection and analysis
The anesthetic records, operative notes, admission records, and discharge summaries of these patients were reviewed, and the following data were collected retrospectively: patient characteristics, preexisting comorbidities, preoperative examinations and laboratory data, surgical procedure, anesthetic techniques, characteristics of recovery, and length of hospital stay as well as the incidences of difficult tracheal intubation (attempt of tracheal intubation >2), intraoperative adverse events, early complications, and ICU utilization. Adverse events were defined as transient detrimental effects or needs for further intervention. Early complications (those occurring within 30 days of index surgery) were defined as the adverse events that led to permanent detrimental effects or required significant additional intervention. The data were summarized using descriptive statistics and presented as the mean (standard deviation) or number (proportion) as applicable. Paired t- tests were used to analyze the significance of differences in hemodynamic data at each time point. Data were analyzed using SPSS version 13 for Windows (SPSS Inc., Chicago, IL, USA). A P < 0.05 was considered statistically significant.
| Results|| |
The data from 25 consecutive SSO patients (age: 31.2 ± 11.1 years; BMI: 64.9 ± 4.7 kg/m2) undergoing laparoscopic bariatric surgery were retrospectively reviewed. All the surgical procedures were performed by a single surgeon. The demographic data, number of comorbidities per patient, type of operation, comorbidities, and abnormal laboratory examination are shown in [Table 1], [Table 2], [Table 3], respectively. The laparoscopic Roux-en-Y gastric bypass (LRYGB) was performed in 96% of patients (n = 24), and this surgical technique has been described in details previously. Due to technical difficulty, the LRYGB procedure was converted to a mini-gastric bypass for one patient with a BMI of 71.6 kg/m2. All of the procedures were performed laparoscopically with no conversions to laparotomy.
|Table 1: Demographic and clinical data of super-superobese patients and type of operation (n=25)|
Click here to view
|Table 3: Incidence of abnormal laboratory tests or examinations in super-superobese patients (n=25)|
Click here to view
Tracheal intubation was attempted successfully in 92% of patients (n = 23) using a short handle laryngoscope or a McCoy laryngoscope, and difficult tracheal intubation with laryngoscopy was documented in two patients. Awake fiberoptic endotracheal intubation was performed successfully in 8% of the patients (n = 2). Difficult mask ventilation or difficult tracheal intubation was not observed in patients with a history of obstructive sleep apnea (n = 5). Respiratory and hemodynamic adverse events are shown in [Table 4]. After tracheal intubation, occurrence of bronchospasm was documented in five patients (20%) and one patient developed transient hypoxemia (SaO2 =91%) intraoperatively. Despite intervention with bronchodilator, the patient suffered from a high peak airway pressure (ranged from 33 to 40 cmH2O) and hypercapnia (EtCO2 ranged from 61 to 75 mmHg) intraoperatively. The patient, who was sent to ICU for observation postoperatively, later received tracheal reintubation because of respiratory failure. The hemodynamic change after anesthetic induction and CO2 pneumoperitoneum is shown in [Figure 1]. Compared with the baseline mean blood pressure (MBP), there was a significant decrease in MBP after anesthetic induction (P < 0.001) and CO2 insufflation (P < 0.001). Compared with the MBP after anesthetic induction, the use of CO2 insufflation did not have a significant impact on MBP (P = 0.252).
|Figure 1: Changes in MBP before anesthesia (i.e. baseline), immediately after anesthetic induction, and after creation of CO2 pneumoperitoneum. *P < 0.001 compared to baseline; **P < 0.001 compared to baseline; no significant difference between MBP immediately after induction and that after CO2 insufflation (P = 0.252). CO2: Carbon dioxide, MBP: Mean blood pressure|
Click here to view
The recovery characteristics of these patients are shown in [Table 5]. Unplanned ICU admission was required in five patients (20%). The indications for ICU utilization and subsequent complications are shown in [Table 5]. The decision for ICU utilization was made in three patients during surgery and in two patients during their stay in PACU. Unexpected tracheal reintubation was performed in one patient because of acute respiratory failure and acute conscious change in the PACU (coma scale: E4VEM6–E1VEM1). Arterial blood gas analysis in this unconscious patient revealed pH, PaO2, PaCO2, potassium, HCO3, and base excesses of 7.19 mmHg, 96.8 mmHg, 46.2 mmHg, 7.02 mEq/L, 17.2 mEq/L, and −10.9 mEq/L, respectively. In these five patients, preoperative pulmonary function tests demonstrated only mild impairment in three patients, and this examination was not performed in the other two. All SSO patients (n = 25) were discharged from the hospital without sequelae or 30-day readmission.
|Table 5: Anesthetic time, recovery characteristics, and complications in super-superobese patients with or without Intensive Care Unit utilization|
Click here to view
| Discussion|| |
This study represents the first investigation focusing on anesthesia-related adverse events, complications, and the need for ICU utilization in SSO patients. The findings of our study bear several striking clinical implications. First, tracheal intubation, either with laryngoscope or fiberscope, can be first attempted with backups of airway rescue devices as reflected in the 100% success rate of tracheal intubation in our SSO patients. Second, our results showed that respiratory adverse events such as bronchospasm, gaseous and airway pressure anomalies, as well as hemodynamic adverse events are not uncommon in SSO patients. Third, the high incidences of ICU utilization and early complications (i.e., 25% and 16%, respectively) and the most frequent early complication of respiratory failure in our SSO patients highlight the necessity of intensive postoperative monitoring and management for this patient population.
Difficult tracheal intubation and difficult mask ventilation are common among obese patients,,. Precautions at our institute during induction in general anesthesia for SSO patients included preoxygenation in a 30° reverse Trendelenburg position and preparation of rescue airway devices required for securing the airway. In spite of the two cases of failed intubations in our series, the airway was established successfully in all patients. Although there is insufficient evidence to support increased BMI alone as an independent predictor of difficult laryngoscopy or difficult intubation,, obese patients are prone to suffer from desaturation during induction of anesthesia and obesity is a predisposing risk factor for difficult mask ventilation. Therefore, careful selection of the suitable method, equipment, and rescue devices required for securing the airway of SSO patients is mandatory.
Because of obesity-associated physiologic changes and comorbidities, respiratory adverse events are not uncommon in SSO patients. Pneumoperitoneum during laparoscopic bariatric surgery also worsens respiratory mechanics and predisposes SSO patients to perioperative atelectasis. We found that the occurrence of bronchospasm may have a significant impact on subsequent early respiratory complications. One of our patients, who developed intraoperative bronchospasm after tracheal intubation, suffered from intraoperative desaturation and postoperative respiratory failure. The high prevalence of bronchospasm (20%, n = 5) after tracheal intubation in our series is consistent with the previous finding that increasing obesity is associated with a significant increase in airway responsiveness, and that bronchospasm is more common in obese than lean children undergoing general anesthesia. Additional strategies should be developed to mitigate this pulmonary adverse event in SSO patients during airway management.
The incidence of pulmonary complications after bariatric surgery has been reported to range from 4% to 7%. A greater BMI is found to correlate with a high incidence of pulmonary embolism and respiratory failure after bariatric surgery,. In our series, postoperative respiratory failure occurred in three male patients (12%) with concurrent mild obstructive lung disease, for whom prolonged surgical time, intraoperative pulmonary adverse events, and concurrent surgical complications may be potential contributors. On the other hand, VTE, which includes pulmonary embolism and deep vein thrombosis, is one of the potentially life-threatening complications that may occur within 6 months following bariatric surgery. In our series, the absence of this complication may be attributed to the use of calf-length pneumatic compression devices before anesthesia induction and mandatory ambulation beginning on the day of operation, which are routine practice at our institute.
In our series, hyperkalemia (i.e., plasma potassium >5.3 mEq/L) occurred postoperatively in a diabetic patient with uneventful anesthesia. This patient presented with an altered mental status during his/her PACU stay without further complications after medical intervention. Postoperative rhabdomyolysis, which is a possible cause of hyperkalemia, has been reported in postoperative obese patients. The reported incidence of rhabdomyolysis in obese patients following laparoscopic bariatric surgery varies widely, ranging from 1.4% to 22.7%,. There is an increased risk of postoperative rhabdomyolysis for patients with massive obesity (BMI >60 kg/m2) and for those undergoing long operations (>4 h). The presence of diabetes is also identified as a factor associated with an increased risk of rhabdomyolysis. Mognol et al. suggested that rhabdomyolysis after bariatric surgery is the result of unrelieved muscle pressure while on the operating table, which leads to the development of compartment syndrome. Our diabetic patient had a BMI of 60.4 kg/m2 and the anesthetic time of 285 min. Therefore, we suggest that the levels of creatine phosphokinase and potassium should be monitored in SSO patients undergoing bariatric surgery, especially when the surgical time is prolonged.
To delay tracheal extubation in obese patients was reported to increase the pulmonary clearance of residual inhaled anesthetics and enhance postoperative recovery. In our study, only 40% of patients (n = 10) were extubated in the operating room at the end of surgery, which reflected the anesthesiologist's concern that increased BMI might increase the body's capacity to retain potent inhaled anesthetics that may delay airway reflex recovery. MO patients often experience postoperative oxygen desaturation. Furthermore, Memtsoudis et al. demonstrated that surgical patients with sleep apnea were at a higher risk of having perioperative pulmonary complications. Although sleep apnea syndrome is a commonly encountered comorbidity in SSO patients, we found that this comorbidity does not seem to increase the frequency of oxygen supplement required when patients were discharged to the ward, corroborating the findings of a previous study. In the current study, one out of the five patients with obstructive sleep apnea experienced major complication (20%) compared with 16% in all patients (4/25). Therefore, it appeared that obstructive sleep apnea was not a particularly important contributor to bariatric surgery-related complications in this study.
In our SSO patients (BMI ≥60 kg/m2), we found that MBP did not increase significantly after abdominal insufflation compared with that during anesthetic induction [Figure 1]. The finding is different from that of a previous study that demonstrated an abdominal insufflation-induced increase in MBP in MO patients (BMI 40–60 kg/m2) attributable to elevated systemic vascular resistance. Whether a higher BMI in our patients contributed to the discrepancy in results remains to be elucidated.
This study had several limitations in addition to those inherent to all retrospective studies. First, the small size of the patient population in this study (n = 25) precluded adequate performance of statistical analysis on the possible association between perioperative complications (or outcomes) and abnormal data (or examinations) due to the presence of various confounders (e.g., depth of anesthesia, BMI, and smoking history). Second, we did not have data on pulmonary function tests and apnea–hypopnea index in all patients so that the prevalence of obstructive sleep apnea may be underestimated. Third, the incidence and type of postoperative complications may vary with patient selection, experience of the anesthesiologists, and operating surgeons as well as the laparoscopic bariatric surgical approaches being chosen. Finally, we did not have a long-term (>30 days) follow-up of outcomes after bariatric surgery.
| Conclusions|| |
When dealing with SSO patients undergoing laparoscopic bariatric surgery, it is imperative to anticipate the potential for their development of perioperative adverse events and postoperative complications. Taking into account the relatively high incidence of early postoperative complications, loosening of the criteria for postoperative intensive care may be considered in this patient population.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Mitka M. Surgery for obesity: Demand soars amid scientific, ethical questions. JAMA 2003;289:1761-2.
Murphy C, Wong DT. Airway management and oxygenation in obese patients. Can J Anaesth 2013;60:929-45.
Strandberg A, Tokics L, Brismar B, Lundquist H, Hedenstierna G. Constitutional factors promoting development of atelectasis during anaesthesia. Acta Anaesthesiol Scand 1987;31:21-4.
Kheterpal S, Han R, Tremper KK, Shanks A, Tait AR, O'Reilly M, et al.
Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology 2006;105:885-91.
Juvin P, Lavaut E, Dupont H, Lefevre P, Demetriou M, Dumoulin JL, et al.
Difficult tracheal intubation is more common in obese than in lean patients. Anesth Analg 2003;97:595-600.
McCullough PA, Gallagher MJ, Dejong AT, Sandberg KR, Trivax JE, Alexander D, et al.
Cardiorespiratory fitness and short-term complications after bariatric surgery. Chest 2006;130:517-25.
Leykin Y, Pellis T, Del Mestro E, Marzano B, Fanti G, Brodsky JB. Anesthetic management of morbidly obese and super-morbidly obese patients undergoing bariatric operations: Hospital course and outcomes. Obes Surg 2006;16:1563-9.
Huang CK, Lee YC, Hung CM, Chen YS, Tai CM. Laparoscopic roux-en-Y gastric bypass for morbidly obese Chinese patients: Learning curve, advocacy and complications. Obes Surg 2008;18:776-81.
Lundstrøm LH, Møller AM, Rosenstock C, Astrup G, Wetterslev J. High body mass index is a weak predictor for difficult and failed tracheal intubation: A cohort study of 91,332 consecutive patients scheduled for direct laryngoscopy registered in the Danish Anesthesia Database. Anesthesiology 2009;110:266-74.
Ezri T, Medalion B, Weisenberg M, Szmuk P, Warters RD, Charuzi I. Increased body mass index per se
is not a predictor of difficult laryngoscopy. Can J Anaesth 2003;50:179-83.
Jense HG, Dubin SA, Silverstein PI, O'Leary-Escolas U. Effect of obesity on safe duration of apnea in anesthetized humans. Anesth Analg 1991;72:89-93.
Reinius H, Jonsson L, Gustafsson S, Sundbom M, Duvernoy O, Pelosi P, et al.
Prevention of atelectasis in morbidly obese patients during general anesthesia and paralysis: A computerized tomography study. Anesthesiology 2009;111:979-87.
Torchio R, Gobbi A, Gulotta C, Dellacà R, Tinivella M, Hyatt RE, et al.
Mechanical effects of obesity on airway responsiveness in otherwise healthy humans. J Appl Physiol (1985) 2009;107:408-16.
Wang LY, Cerny FJ, Kufel TJ, Grant BJ. Simulated obesity-related changes in lung volume increases airway responsiveness in lean, nonasthmatic subjects. Chest 2006;130:834-40.
El-Metainy S, Ghoneim T, Aridae E, Abdel Wahab M. Incidence of perioperative adverse events in obese children undergoing elective general surgery. Br J Anaesth 2011;106:359-63.
Santry HP, Gillen DL, Lauderdale DS. Trends in bariatric surgical procedures. JAMA 2005;294:1909-17.
Gupta PK, Gupta H, Kaushik M, Fang X, Miller WJ, Morrow LE, et al.
Predictors of pulmonary complications after bariatric surgery. Surg Obes Relat Dis 2012;8:574-81.
Carmody BJ, Sugerman HJ, Kellum JM, Jamal MK, Johnson JM, Carbonell AM, et al.
Pulmonary embolism complicating bariatric surgery: Detailed analysis of a single institution's 24-year experience. J Am Coll Surg 2006;203:831-7.
Steele KE, Schweitzer MA, Prokopowicz G, Shore AD, Eaton LC, Lidor AO, et al.
The long-term risk of venous thromboembolism following bariatric surgery. Obes Surg 2011;21:1371-6.
Ettinger JE, de Souza CA, Santos-Filho PV, Azaro E, Mello CA, Fahel E, et al.
Rhabdomyolysis: Diagnosis and treatment in bariatric surgery. Obes Surg 2007;17:525-32.
Khurana RN, Baudendistel TE, Morgan EF, Rabkin RA, Elkin RB, Aalami OO. Postoperative rhabdomyolysis following laparoscopic gastric bypass in the morbidly obese. Arch Surg 2004;139:73-6.
Mognol P, Vignes S, Chosidow D, Marmuse JP. Rhabdomyolysis after laparoscopic bariatric surgery. Obes Surg 2004;14:91-4.
Lagandré S, Arnalsteen L, Vallet B, Robin E, Jany T, Onraed B, et al.
Predictive factors for rhabdomyolysis after bariatric surgery. Obes Surg 2006;16:1365-70.
Katznelson R, Naughton F, Friedman Z, Lei D, Duffin J, Fedorko L, et al.
Increased lung clearance of isoflurane shortens emergence in obesity: A prospective randomized-controlled trial. Acta Anaesthesiol Scand 2011;55:995-1001.
McKay RE, Malhotra A, Cakmakkaya OS, Hall KT, McKay WR, Apfel CC. Effect of increased body mass index and anaesthetic duration on recovery of protective airway reflexes after sevoflurane vs. desflurane. Br J Anaesth 2010;104:175-82.
Ahmad S, Nagle A, McCarthy RJ, Fitzgerald PC, Sullivan JT, Prystowsky J. Postoperative hypoxemia in morbidly obese patients with and without obstructive sleep apnea undergoing laparoscopic bariatric surgery. Anesth Analg 2008;107:138-43.
Memtsoudis S, Liu SS, Ma Y, Chiu YL, Walz JM, Gaber-Baylis LK, et al.
Perioperative pulmonary outcomes in patients with sleep apnea after noncardiac surgery. Anesth Analg 2011;112:113-21.
Nguyen NT, Ho HS, Fleming NW, Moore P, Lee SJ, Goldman CD, et al.
Cardiac function during laparoscopic vs. open gastric bypass. Surg Endosc 2002;16:78-83.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]