The effect of two different surgical positions on pulmonary functions ın laparoscopic sleeve gastrectomies: reverse Trendelenburg vs beach chair
The study is a prospective randomized controlled study and started after ethics committee approval İstinye University Human Research Ethics Committee decision no: 2024/03–24-80 and patients signing a written informed consent form. ClinicalTrials.gov ID: NCT06402474 . Criteria for inclusion in the study: Patients who could tolerate general anesthesia and pneumoperitoneum, give informed consent for surgery, were over 18 years of age, had a body mass index (BMI) > 30 kg/m 2 , and had an American Society of Anesthesiologists (ASA) physical status I–III were included. Patients who have serious underlying cardiovascular disease (e.g., congestive heart failure, conduction disorders, and ischemic heart disease); with chronic kidney disease stage 3 or greater (creatinine clearance less than 60 mL/min); have a history of cerebrovascular disease such as intracranial hypertension, cerebral infarction, cerebral hemorrhage, carotid stenosis or cerebral ischemia; have a history of chronic lung diseases such as chronic obstructive pulmonary disease, asthma, pulmonary bullae, or respiratory failure; and patients who had previous abdominal surgery, including esophagus, stomach, liver and pancreas resection, surgeries lasting longer than 90 min, patients with ASA class IV, patients with psychiatric disorders, patients who were pregnant or breastfeeding, and patients with a history of seizures were not included in the study. Study protocol Randomization of the study was done by the envelope method and the patients were divided into two groups. Group RTP: 30° reverse Trendelenburg (control) (Image 1). Group BC: 30° reverse Trendelenburg with legs 30° hip flexion (beach chair position) (Image 2). The intraoperative process after positioning continued with the same protocol for both groups. Study parameters Preoperative: blood pressure, pulse, and peripheral oxygen saturation values of the patients were recorded before anesthesia induction. Intraoperative: After the patients were taken to the routine operating room and standard ASA monitoring was performed, they were intubated under standard general anesthesia. Anesthesia maintenance was continued with remifentanil infusion in addition to 1–1.5 MAC sevoflurane and air mixture. Respiratory parameters were adjusted in pressure control mode, with respiratory rate and tidal volume changes, so that the end-respiratory carbon dioxide level (EtCO2) was between 30 and 35 mmHg. After the patient was draped sterile after intubation, the patient was given a randomly drawn position from the randomization envelope by an experienced personnel; Group RTP (control): standard 30° reverse Trendelenburg with feet flat (image 1); and Group BC (beach chair): after 30° reverse Trendelenburg, the feet were flexed 30° at the hips (image 2). In both groups, while in the supine position after intubation but before the position (preop), starting from the 10th minute after the positioning and pneumoperitonium was performed (10th minute), at 10-min intervals until the end of the case, and at the 10th minute after the pneumoperitonium was terminated (70th minute); blood pressure (systolic and diastolic), pulse, peripheral oxygen saturation (SpO2), EtCO2, respiratory rate (RR), inspiratory pressure (Pins), positive end-expiratory pressure (PEEP), minute volume, tidal volume, peak airway pressure (Ppeak), and lung dynamic compliance was recorded. Pneumoperitoneum was created in all patients with carbon dioxide insufflation, keeping the maximum pressure limit up to 15 mm Hg. The general surgeon was asked about his satisfaction with the intra-abdominal operation site view (0: very dissatisfied—10: very satisfied) and whether he was uncomfortable with the position (yes/no). The study was conducted under the same general surgeon. No patient required position change during the operation. Postoperative: All patients were routinely extubated and taken to the postoperative recovery room, and blood pressure, pulse, and SpO2 were recorded at the 10th and 20th minutes postoperatively. The primary outcome of the study is to compare the effect of 30° RTP with BC position on respiratory parameters in laparoscopic gastrectomies with 30° RTP alone. Secondary outcomes: In addition to the effects of both positions on cardiac parameters, to investigate surgical field of view satisfaction and whether the surgeon is uncomfortable with the position. Statistical analysis The power analysis of the study was based on the study of Gao et al. . According to this study, arterial oxygen pressure increased in the 30° reverse Trendelenburg position compared to the supine position (262.5 ± 31.2 vs 243.1 ± 26.6). We predict that 30° RTP combined with the BC position will increase the improvement in respiratory parameters by 10%. Accordingly, in the power analysis, it was calculated that the required number of patients should be 50 in total, 25 in each group, for alpha to be 0.05 and power to be 85%. Continuous variables were shown as mean ± standard deviation values. Categorical variables are shown with numbers. The distributions of the groups were determined by Shapiro–Wilk and Kolmogorov–Smirnov tests. Independent t test or Mann–Whitney U test was used to determine the relationship between continuous variables. The relationship between categorical variables was evaluated with the chi-square test. SPSS® for Windows version 23.0 (IBM, Chicago, IL, United States) program was used in statistical analyses. Statistical significance level was accepted as p < 0.05. 

Randomization of the study was done by the envelope method and the patients were divided into two groups. Group RTP: 30° reverse Trendelenburg (control) (Image 1). Group BC: 30° reverse Trendelenburg with legs 30° hip flexion (beach chair position) (Image 2). The intraoperative process after positioning continued with the same protocol for both groups. 

Preoperative: blood pressure, pulse, and peripheral oxygen saturation values of the patients were recorded before anesthesia induction. Intraoperative: After the patients were taken to the routine operating room and standard ASA monitoring was performed, they were intubated under standard general anesthesia. Anesthesia maintenance was continued with remifentanil infusion in addition to 1–1.5 MAC sevoflurane and air mixture. Respiratory parameters were adjusted in pressure control mode, with respiratory rate and tidal volume changes, so that the end-respiratory carbon dioxide level (EtCO2) was between 30 and 35 mmHg. After the patient was draped sterile after intubation, the patient was given a randomly drawn position from the randomization envelope by an experienced personnel; Group RTP (control): standard 30° reverse Trendelenburg with feet flat (image 1); and Group BC (beach chair): after 30° reverse Trendelenburg, the feet were flexed 30° at the hips (image 2). In both groups, while in the supine position after intubation but before the position (preop), starting from the 10th minute after the positioning and pneumoperitonium was performed (10th minute), at 10-min intervals until the end of the case, and at the 10th minute after the pneumoperitonium was terminated (70th minute); blood pressure (systolic and diastolic), pulse, peripheral oxygen saturation (SpO2), EtCO2, respiratory rate (RR), inspiratory pressure (Pins), positive end-expiratory pressure (PEEP), minute volume, tidal volume, peak airway pressure (Ppeak), and lung dynamic compliance was recorded. Pneumoperitoneum was created in all patients with carbon dioxide insufflation, keeping the maximum pressure limit up to 15 mm Hg. The general surgeon was asked about his satisfaction with the intra-abdominal operation site view (0: very dissatisfied—10: very satisfied) and whether he was uncomfortable with the position (yes/no). The study was conducted under the same general surgeon. No patient required position change during the operation. Postoperative: All patients were routinely extubated and taken to the postoperative recovery room, and blood pressure, pulse, and SpO2 were recorded at the 10th and 20th minutes postoperatively. The primary outcome of the study is to compare the effect of 30° RTP with BC position on respiratory parameters in laparoscopic gastrectomies with 30° RTP alone. Secondary outcomes: In addition to the effects of both positions on cardiac parameters, to investigate surgical field of view satisfaction and whether the surgeon is uncomfortable with the position. 

The power analysis of the study was based on the study of Gao et al. . According to this study, arterial oxygen pressure increased in the 30° reverse Trendelenburg position compared to the supine position (262.5 ± 31.2 vs 243.1 ± 26.6). We predict that 30° RTP combined with the BC position will increase the improvement in respiratory parameters by 10%. Accordingly, in the power analysis, it was calculated that the required number of patients should be 50 in total, 25 in each group, for alpha to be 0.05 and power to be 85%. Continuous variables were shown as mean ± standard deviation values. Categorical variables are shown with numbers. The distributions of the groups were determined by Shapiro–Wilk and Kolmogorov–Smirnov tests. Independent t test or Mann–Whitney U test was used to determine the relationship between continuous variables. The relationship between categorical variables was evaluated with the chi-square test. SPSS® for Windows version 23.0 (IBM, Chicago, IL, United States) program was used in statistical analyses. Statistical significance level was accepted as p < 0.05. 

Regardless of the group, the average age of the cases was 36.7 ± 12.1 years. The groups were similar in terms of age, gender, BMI, and operation time (Table ). There was no statistically significant difference between systolic, diastolic blood pressures and heart rates between the groups ( p > 0.05), but a significant decrease in blood pressure and a non-significant slight increase in heart rate were observed in the first 10 min after RTP in both groups (Fig. ). In comparing the groups in terms of respiratory parameters, there was no difference between EtCO2, respiratory rate, PEEP, minute volume, tidal volume, and postoperative oxygen saturation ( p > 0.05, Table ). However, when we looked at the changes over time, it was determined that EtCO2 decreased at the 10th minute in both groups compared to preoperative values. Tidal volume increased significantly at the 10th minute compared to preoperative values only in the BC position. Additionally, postoperative oxygen saturations in both groups were lower than preoperative values, but after the abdomen was deflated (70th minute), oxygen saturation increased significantly in both groups ( p < 0.05, Table ). In comparing pressures from respiratory parameters, a statistically significant difference was detected between the groups in terms of inspiratory pressure (Pins), peak pressure (PPeak) and dynamic compliance throughout the operation period. According to our findings, pressures such as Pins and Ppeak were lower in the BC position, and dynamic compliance was significantly higher ( p < 0.05, Table ). Similarly, when we evaluated these parameters according to time within the group, the 10th minute after positioning was the time interval in which Pins and Ppeak decreased the most and dynamic compliance increased the most, according to preoperative values in both groups ( p < 0.05, Table ). There was no difference in these parameters between the 70th minute when pneumoperitoneum was terminated and the previous 60th minute. When the situations related to this statistical significance in pressures were investigated, it was found that it was only related to BMI. We grouped BMI to understand how BMI affects these pressures. When we grouped it as 30–35, 35.1–40, and 40.1 and above and looked at its effect on intergroup pressures, it was seen that the BC position decreased the inspiratory and peak pressures and increased the dynamic complication in patients with BMI: 35.1—40 ( p < 0.05, Table ). However, when the effect of BMI differences within the groups on pressures was examined, no significant difference was detected. There was no significant difference in surgeon satisfaction with field of view and discomfort with the position. Surgical satisfaction was high for both positions (Table ). 

In this study, the effect of RTP and BC position on intraoperative pulmonary functions in LGS, which is encountered in increasing numbers in the treatment of obesity. While there was no difference between the two positions in terms of hemodynamic (blood pressure and heart rate) and respiratory (EtCO2, PEEP, minute volume, tidal volume, SpO2) parameters, inspiratory and peak pressures were significantly lower in the BC position and dynamic compliance was higher in the BC position. It was observed that these three parameters were only related to BMI and that the BC position was more ameliorative in terms of intraoperative pressures and dynamic compliance, especially in patients with a BMI between 35.1 and 40. In addition, the surgeon’s field of view satisfaction was the same in both positions and there was no discomfort in either position. Laparoscopic bariatric procedures in obese patients; it requires creating pneumoperitoneum and maintaining patients in RTP, which is known to cause changes in cardiac output and peripheral tissue perfusion. RTP under general anesthesia may cause hypotension due to decreased preload caused by venous pooling in the lower extremities and pelvis . As intra-abdominal pressure increases, systemic vascular resistance increases as a result of mechanical compression of the abdominal aorta, release of neurohumoral hormones, such as vasopressin, and activation of the renin–angiotensin–aldosterone axis. Narrowing of the inferior vena cava reduces preload, which may result in decreased cardiac output and therefore decreased arterial pressure. In our study, a significant decrease in blood pressure and a slight increase in heart rate were observed in both groups after positioning and creating pneumoperitoneum. Our findings were consistent with the literature [ – ], but there was no difference between blood pressure and heart rates in comparisons in terms of two different positions. Although obesity places greater demands on the respiratory system to maintain normal PaCO2, most patients with severe obesity are eucapnic . In simple obesity, tidal volume is normal both at rest and during maximum exercise. In our study, the patients were eucapnic in the preoperative period. During laparoscopic operations, pneumoperitoneum is created by CO2 insufflation. During pneumoperitoneum, factors such as intraperitoneal CO2 absorption, increased intra-abdominal pressure, patient position, artificial ventilation, as well as anesthesia can affect respiratory mechanics and blood gases . In this study, there was no significant difference between two different positions in terms of respiratory rate, PEEP, minute volume, EtCO2, and tidal volume, among the parameters that can be adjusted to maintain eucapnia under anesthesia and pneumoperitoneum and to provide adequate tidal volume according to ideal body weight. Although many obesity studies in the literature are aimed at finding ideal PEEP [ – ], in our study, we aimed to investigate the effect of BC position alone on respiratory mechanics by keeping PEEP as constant as possible and observed that BC position has no effect on the parameters mentioned. Obese patients are more likely to develop intraoperative atelectasis because they exhibit a decrease in functional residual capacity (FRC) during general anesthesia . Atelectasis is one of the main causes of postoperative hypoxemia (PH) and may predispose to adverse postoperative outcomes, such as respiratory failure, pneumonia, and mortality . In our study, in line with the literature , postoperative oxygen saturations were significantly lower than preoperative values ​​in both groups, but there was no difference between the two groups. They approached their initial values ​​with nasal oxygen support. As we mentioned before, we attributed this situation to both general anesthesia, the inability to breathe strongly due to postoperative pain, and atelectasis caused by the increase in intra-abdominal and intrathoracic pressure due to the pneumoperitoneum created by CO2 insufflation . Our data supporting this finding was that when pneumoperitoneum was terminated, oxygen saturations increased significantly in both groups, being more in the BC group. Despite relative intraoperative hypoxemia, no serious clinical respiratory complications were reported in the postoperative period. It is generally accepted that respiratory system compliance is low in obesity due to the effect of obesity on the chest wall. Lung compliance decreases by approximately 25% in simple obesity. Part of the decrease is probably due to deterioration of lung elasticity due to increased pulmonary blood volume and part of it is due to the decrease in FRC. In addition, these patients are characterized by an increase in respiratory resistance. The most important reason for increased lung and respiratory resistance is the decrease in lung volume . Based on all these data, it is an undeniable fact that the apparent irregularity in the FRC, elastic (decrease in lung and chest wall compliance), and resistive (increase in lung resistance) components of the respiratory system may be responsible for the significant respiratory dysfunction and arterial hypoxemia that occur in the postoperative period. Therefore, methods to improve respiratory mechanics in such patients are needed. In our present study, we found that the BC position reduced inspiratory and peak pressures significantly more than RTP alone and improved dynamic compliance by 33.9% versus 11.8%. Although there is no study in the literature similar to our study comparing two positions, we come across data to support our findings in individual position studies. In the study conducted by Gao et al. , they suggested that 30 degrees reverse Trendelenburg can increase static lung compliance, reduce pulmonary shunt, and increase arterial oxygen pressure and oxygenation compared to the supine position. Valenza et al.  claimed that lung volumes almost doubled in the beach chair position, airway pressures decreased, oxygenation and respiratory mechanics improved, and when applied with PEEP, they managed to eliminate the harmful effects of pneumoperitoneum. Another finding that attracted our attention in our study was that the effects of pneumoperitoneum continued to be seen in the measurements 10 min after the intra-abdominal pressure was relieved. We believe that this is a subject open to research. It is known that lung resistance and changes in respiratory mechanics are related to BMI . As BMI increases, lung resistance also increases and a decrease in the compliance of the respiratory system is observed . In our study, similar to the literature, we found that as BMI increased, inspiratory and peak pressures, in other words resistances, increased and dynamic compliance decreased, regardless of the group. The finding that caught our attention was that the BC position improved respiratory mechanics more in patients with BMI 35.1–40 than in other BMI groups. In light of this finding, we believe that the BC position may be beneficial in certain patient groups. However, this finding should be supported by other studies. It is important for the surgeon to have sufficient intra-abdominal working area during laparoscopic surgery in obese patients. Most surgeons use an inflation pressure of 15 mmHg. Müljer et al.  calculated the minimum intra-abdominal volume required for laparoscopic upper abdominal surgery as 3 L and stated that the field of view is restricted in smaller volumes. In the same study, they found that there was sufficient working space in 50% of patients in the reverse Trendelenburg position and in 80% of patients in the beach chair position, that the BC position helped improve the surgical working area in cases where the body position was not sufficient, and that it was the most effective method in improving the working area by 770 mL after complete muscle relaxation. Additionally, they stated that the beach chair position did not disturb the surgeon, who remained between open and raised legs while performing laparoscopic upper abdominal surgery. Although surgical field of view measurement was not performed in our study, the surgeon’s field of view satisfaction was 8 or above in both positions and they stated that they were not disturbed by the position. There are some limitations in our study. First of all, our sample size is not sufficient to generalize the application of BC position. Since our study is the first comparison study in the literature, more randomized controlled studies with a larger number of cases are needed. Especially, a larger sample size and more advanced parameters (such as blood gas analysis) are needed to make a general conclusion about why respiratory parameters did not change in the 30–35 BMI and 40.1 and above BMI groups. Another limitation of ours is that we were not able to measure lung volumes and blood gases due to financial concerns. Another limitation is that we did not monitor respiratory mechanics in the early postoperative period, only the first 20 min of the postoperative period. There is a need for studies that consider the intraoperative and postoperative pulmonary effects of the BC position together. Since it was not among our primary objectives, 30-day complications were not investigated. However, future studies may be in this direction. Additionally, the study was conducted by the same surgeon. Therefore, it cannot be concluded from this article that other surgeons may also use the split-leg position. 

In this study, the effect of RTP and BC positions in LSGs on intraoperative pulmonary functions was investigated. There was no difference between the two positions in terms of hemodynamic and respiratory parameters. It was observed that inspiratory and peak pressures (resistance) were lower and dynamic compliance was higher in the BC position. It was observed that these parameters were related to BMI and that the BC position was more ameliorative in terms of intraoperative pressures and dynamic compliance, especially in patients with a BMI between 35.1 and 40. In light of our findings, we believe that the BC position may be preferred in terms of lung-protective ventilation strategies. 

Below is the link to the electronic supplementary material. Supplementary file1 (DOC 52 KB) Image 1: Group RTP (control): standard 30° reverse Trendelenburg with feet flat Supplementary file2 (JPG 3199 KB) Image 2: Group BC (beach chair): After 30° reverse Trendelenburg, the feet were flexed 30° at the hips Supplementary file3 (JPG 2562 KB) 

