The effect of pneumoperitoneum on haemodynamic parameters in morbidly obese patients
Department of Anaesthesiology and Intensive Therapy, Medical University of Łódź
Background. The type of anaesthetic used affects the cardiovascular function in morbidly obese patients during pneumoperitoneum. In this prospective randomized study, we evaluated the influence of inhalation anaesthesia with sevoflurane or intravenous anaesthesia with propofol on haemodynamic performance in obese patients during laparoscopy.
Methods. Patients scheduled for laparoscopic bariatric procedures were randomly divided into two groups: sevoflurane (group S) or propofol (group P). Haemodynamic function was measured using the transoesophageal Doppler method after induction of anaesthesia (T1), insuflation of CO2 (T2) and in the anti-Trendelenburg position with pneumoperitoneum (T3).
Results. One hundred patients were enrolled in the study. The demographic data did not differ between the groups. At T2, the blood flow parameters and ventricle ejection parameters decreased in both groups whereas the systemic vascular resistance and mean arterial pressure increased. The heart rate was stable. At T3, afterload parameters and heart rate increased in both groups yet blood flow parameters decreased in group P. The changes observed were not accompanied by any serious clinical signs of cardiovascular deterioration.
Conclusions. Pneumoperitoneum has an important negative impact on haemodynamic function in morbidly obese patients but those changes are not accompanied by severe cardiovascular disturbances. Volatile anaesthesia provides better haemodynamic stability during laparoscopic bariatric surgery in such patients.
Obesity is met when the body mass index (BMI) is over 30 kg m-2; morbid obesity is characterized by BMI>40 kg m-2, and superobesity by BMI>50 kg m-2. In addition to problems with venous access, patient positioning and airway control, obesity is associated with many cardiovascular conditions that have important implications for the administration of anaesthesia. Although there are many papers available on the haemodynamic effect of pneumoperitoneum (PP) in obese patients, they do not compare the influence of different types of anaesthesia and anaesthetics on the cardiovascular function during laparoscopy. From the anaesthetist’s point of view, optimization of transoperative management represents a real challenge that may determine the success of surgery, the development of complications, and the final outcome. The type of anaesthesia may reduce the negative impact of PP on cardiovascular function.
The aim of the study was to compare the influence of two types of anaesthesia, inhalation (sevoflurane) and intravenous (propofol), on the hemodynamic function in morbidly obese patients at two important moments of the laparoscopic procedure: after creating PP and after positioning the patient with PP in the anti-Trendelenburg position.
After obtaining the approval of the Local Ethical Committee (Protocol no. RNN/257/03/KE) and written informed consent from all subjects, patients scheduled for elective laparoscopic adjustable gastric banding were randomly chosen for prospective, randomized study. The inclusion criteria were morbid obesity (BMI>40 kg m2), ASA ≤ II, NYHA ≤ II, and the exclusion criteria were coexisting cardiovascular diseases, except for well-controlled hypertension. The patients were divided into two groups: half of them were anaesthetized with sevoflurane/O2/air (group S) and half with propofol TIVA (group P). In both groups, anaesthesia was induced with propofol 1.5-2.0 mg kg-1 of the corrected body weight, fentanyl 100 mg, midazolam 3 mg and atracurium 0.6 mg kg-1 of ideal body weight.
In group S, the lungs were ventilated with a mixture of oxygen, air and sevoflurane in the doses depending on age and clinical parameters. In group P, anaesthesia was maintained with the continuous intravenous infusion of propofol according to the Robert`s method (beginning the infusion with 10 mg kg-1min-1 for 10 min, maintaining anaesthesia with 6-8 mg kg-1min-1, ending anaesthesia with 4-6 mg kg-1min-1) In both groups, repeated doses of fentanyl 0.005 mg kg-1 of corrected body weight and atracurium 0.2 kg-1 of ideal body weight were administrated intravenously. Haemodynamic function was measured by the transoesophageal Doppler method using a HemoSonic 100 device (Arrow, USA). Measurements were performed at the following time points: T1 - after induction of anaesthesia, T2 - insufflation of the abdomen (creating PP), T3 – in the anti-Trendelenburg position and PP. The PP pressure was set at 15 mm Hg (2 kPa).
The following parameters were recorded:
1. real time, adjusted every 5 sec: heart rate (HR), acceleration (Acc), peak velocity (PV), left ventricular ejection time (LVET), mean aortic diameter DI;
2. estimated: cardiac output (CO) and index (CI), stroke volume (SV) and index (SVI); and systemic vascular resistance – SVR (dyn sec-1cm-5).
The measurements were taken continuously and adjusted automatically by the device every 5 sec. At each time point, 2-4 measurements were recorded and means calculated. The values of parameters at the individual time points and the inter-point differences were analysed.
Statistical significance was set at 5%. The distribution of data was tested with the Shapiro-Wilk test. Statistical analysis was performed between the subgroups using Friedman ANOVA; differences between groups were analysed with the Tukey`s post hoc test; the t-test and non-parametric Wilcoxon test were used for dependent samples; finally, changes in parameters between the groups were compared using the t-test and the Mann-Whitney test was applied for non-parametric data.
Complete sets of data were collected from 41 patients in group S and from 40 in group P. No complications were observed. There was no statistical difference in demographic characteristics between the groups (Table 1).
The initial haemodynamic parameters (T1) were similar in both groups. At T2, the blood flow parameters and ventricle ejection parameters significantly decreased in both groups (CO, SV, Acc, PV, CI and SVI) whereas SVR and MAP significantly increased. Both groups showed a reduction in LVET, however this decrease was only significant in group P. HR was stable. In group S, no significant changes in the majority of parameters (CO, LVET, Acc, PV and CI) were observed at T3. However, SV and SVI decreased significantly whereas SVR, MAP and HR increased significantly. In group P, CO, SV, PV and SVI also decreased significantly. The other parameters (LVET, Acc, CI, HR, MAP) changed as in group S. Although the observed changes were significant, there was no significant difference between the groups for most parameters at individual time points, except for SV at T3, Acc at T2, PV at T2, MAP at T2, and HR at T3 (Table 2).
The analysis of differences between the values at T2 and T3 revealed a significantly higher decrease in CO, SV, CI, and SVI in group P compared to group S (Table 3). In group S, CO increased at T3 while in group P at T2. At T2, a higher MAP increase was found in group S than in group P; at T3, a higher HR increase was observed in group P compared to group S. At T3, there were no significant differences between the groups for most parameters. However, more parameters changed significantly in group P than in group S.
Laparoscopy represents a modern method of bariatric surgery, generally associated with lower morbidity and mortality, compared with the traditional surgical approach. However, in patients with impaired cardiovascular function, the laparoscopic approach is limited by the potential adverse haemodynamic impact. There are many available studies showing the impact of PP on the cardiovascular system in morbidly obese patients [1, 2]. Some of them, with findings similar to ours, report significant haemodynamic and respiratory changes, mostly unfavourable, that occurred in obese patients when creating PP for laparoscopy . According to some other studies, parameters like CO increased , which is contrary to our results, or remained unchanged after PP  (in our study CO decreased significantly after PP). Most authors conclude that PP does not significantly impair cardiac function during laparoscopy and is well tolerated by patients. In our opinion, the drop by 20% of the initial CO value after creating PP in morbidly obese patients is significant and the anaesthesiologist should be aware of this problem.
In our study, the differences between volatile and intravenous anaesthesia were evaluated with particular attention focused on their pharmacologic effects on the force-velocity relations of the ventricular myocardium and on the global effect on ventricular performance.
Sevoflurane, like other volatile anaesthetics, has a depressive effect on the cardiovascular system . It decreases the myocardial contractility in a dose-dependent way and reduces the mean arterial pressure, cardiac index and cardiac output [7, 8]. Moreover, sevoflurane has been found to induce a decrease in the ejection fraction . A decrease in cardiac output results from a decrease in systemic vascular resistance . Sevoflurane leads to a dose-dependent decrease in end-diastolic and end-systolic pressure in the left ventricle , yet its influence on the coronary arteries is not so pronounced. Sevoflurane has been shown to have a cardioprotective effect . Although it does not cause significant arrhythmias, an important common side effect of high sevoflurane concentrations is dose–dependent bradycardia and hypotension. The recovery of cardiovascular function after sevoflurane is rapid .
Propofol causes a significant dose-dependent decrease in blood pressure of up to 40% . This is due to a decrease in cardiac output, cardiac index and systemic vascular resistance (15-25%). The decrease in cardiac output is caused by the direct depressive effect of the drug on the myocardium , while the decrease in systemic vascular resistance results from both the decreased activity of the sympathetic nervous system and the direct vasodilatation effect on veins and arteries . Propofol causes a decrease in end-diastolic volume in the right ventricle. The heart rate usually remains unchanged because propofol has a depressive effect on the baroreceptors reacting to decreased blood pressure in the aorta . Moreover, propofol exerts depressive effects on the sinoatrial node  and the cardiovascular system, which may last long after the infusion has been discontinued .
Our study confirms that PP has an important negative impact on haemodynamic function during general anaesthesia in morbidly obese patinets. After insufflation of the abdomen, blood flow parameters decreased significantly and afterload parameters increased. However, these changes were not clinically regarded as serious cardiovascular disturbances. There was no significant difference between the two types of anaesthesia as for their influence on haemodynamic function during laparoscopy. Positioning the patient in the anti-Trendelenburg’s position during PP had varying effects on haemodynamic stability depending on the type of anaesthesia used. In patients anaesthetized with propofol, haemodynamic changes were more expressed than in those anaesthetized with sevoflurane. In group S, the majority of parameters remained unchanged compared to the neutral supine position during PP. In patients anaesthetized with propofol, positioning the patient in the anti-Trendelenburg’s position caused a significant decrease in bl
ood flow parameters; however, no other significant differences were found between the groups.
The analysis of differences recorded at T2 and T3 revealed that haemodynamic disturbances were more dynamic and persistent in the propofol group than in the sevoflurane group. Sevoflurane-based anaesthesia provided better haemodynamic stability than propofol–based anaesthesia during laparoscopic procedures in the morbidly obese. In the sevoflurane group, the recovery of cardiovascular function was more rapid. The organism’s natural defensive mechanisms against drops in CO, such as an increase in sympathetic system activity during PP , are suppressed in the case of propofol . The vasoactive peripheral arterial circulation, its effect on the great venous capacitance and on peripheral venous tone is severely altered when propofol is used . The depressive effect of propofol on vascular tone lasts longer than the blood propofol concentration can account for .
In cases of agents such as propofol or sevoflurane, which have some vasoactive effect, the measurement of left ventricle function may be altered by their influence on pre- and afterload . According to Prior and co-workers , who used transoesophageal echocardiography, the left ventricular end-systolic wall stress (LVESWS) was high during PP. Since LVESWS is a determinant of myocardial oxygen demand, more aggressive control of blood pressure (ventricular afterload) in morbidly obese patients may be warranted to optimise the myocardial oxygen requirements. Fried and colleagues  concluded that neither systolic nor diastolic performance was significantly affected by the introduction of capnoperitoneum and positioning of the patient for surgery. Contrary to our results, they observed an increase in CO after creating PP.
Blood pressure measured by standard means does not provide precise information on cardiovascular haemodynamic function during laparoscopic procedures in obese patients. Changes in haemodynamic parameters can only be estimated by advanced haemodynamic monitoring.
We are aware that the transoesophageal echo-Doppler velocimetry has significant limitations. Bajorat and co-workers  compared measurements taken using the HemoSonic 100 with PiCCO, NICO and Swan-Ganz catheters. The results were similar; however, the HemoSonic 100 was likely to show slightly lower values than thermodilution. (correlation - 0.84)., which, according to the authors, could be associated with the method of predicting cardiac output by the HemoSonic 100.
CO is a sum of the blood flow in the descending aorta (ABF) and in the arteries emerging from the aortic arch, which cannot be measured by a transoesophageal probe. CO is calculated using the formula: CO=0.69+1.22xABF, which was created during cardiac surgery. The blood flow in the upper part of the body, especially through the carotid arteries, changes depending on several factors, e.g. changes in ABF caused by cardiac surgery and the PaCO2 influence on cerebral blood flow (CBF) . While CBF is usually 15% of CO and depends strongly on PaCO2, ABF does not depend on PaCO2 . Sawai and co-workers  indicate that ABF measured using the HemoSonic 100 method can change together with the changes in PaCO2 occurring during capnoperitoneum.
Another important disadvantage of the HemoSonic 100 method is its sensitivity to the patient’s movements [22, 25]. The axis between the echographic beam and aorta diameter should not exceed 20 degrees. The recommended transducer level is Th6 but in some patients, e.g. morbidly obese, it may be difficult to estimate. In our study, the measurements were found to be ineffective in 19 out of 100 patients included. Similar observations were made by Bernardin and colleagues . Despite its limitations, the HemoSonic 100 transoesophegeal Doppler measurement is a non-invasive, easy-to-perform method that causes very few possible complications when compared with more reliable methods such as thermodilution.
Perilli and co-workers  used the HemoSonic 100 device to estimate haemodynamic function during positive end-expiratory pressure (PEEP) and in the anti-Trendelenburg position in order to improve oxygenation in 20 morbidly obese patients undergoing bariatric surgery . Cardiac output significantly decreased with both PEEP and anti-Trendelenburg position, which is similar to our results. They concluded that such a position has an important effect on CO that can deteriorate the benefits of PEEP.
The weaknesses of our study are not only associated with the measurement method. Obesity itself is connected with changes in the cardiovascular system, e.g. increased blood volume affecting CO and SV in those patients. PV and Acc are exquisitely sensitive to loading conditions. We tried to standardise them by transfusing crystalloids 10 mL kg-1 of ideal body weight at the beginning of anaesthesia. Further studies using more advanced monitoring may be required.
1. Pneumopositoneum has a significant negative impact on haemodynamic function during general anaesthesia in morbidly obese patients. Those changes, however, are not clinically considered as serious cardiovascular disturbances.
2. Positioning the obese patient in the anti-Trendelenburg markedly decreases the flow parameters in patients anaesthetized with propofol, which is not so pronounced in the sevoflurane group.
3. Volatile anaesthesia has more stable haemodynamic performance during pneumoperitoneum in morbidly obese patients.
Funding: the work was supported by the government grant [N N403 3755 33].
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*Tomasz M. Gaszynski
Department of Anaesthesiology and Intensive Therapy,
Medical University of Lodz, Barlicki University Hospital,
ul. Kopcińskiego 22, 90-153 Łódź, Poland
tel. +48 42 6783748, email: email@example.com