Abstract
Objectives: To investigate the effects of low-flow anesthesia on hemodynamic parameters and recovery from anesthesia in obese individuals undergoing laparoscopic surgery.
Methods: This randomized-controlled and prospective study included 44 obese patients who underwent laparoscopic sleeve gastrectomy operation. The patients were randomly allocated into 2 groups as low-flow and high-flow anesthesia. Further, the groups compared in terms of hemodynamic parameters, anesthesia recovery times, operation times, and arterial blood gas parameters.
Results: The groups were similar with respect to demographic data. Heart rate, peripheral oxygen saturation, arterial blood pressure measurements, end-tidal, and CO2, lactate levels measurements were similar in both groups during the entire procedure. There was also no statistically significant difference in terms of arterial blood gas parameters or anesthesia recovery periods.
Conclusion: Low-flow anesthesia in laparoscopic obesity surgery seems to be safer compared to high-flow anesthesia in terms of the adequacy of tissue perfusion, depth of anesthesia, and postoperative recovery.
Low-flow anesthesia is a technique in which at least 50% of the exhaled gas is returned into the system by rebreathing. Although not preferred much in the past, this method has become widespread with the introduction of new generation anesthesia devices and monitors and volatile agents. Despite its prominent advantages such as reduction of environmental pollution, minimal loss of heat and moisture, and low cost due to the use of less anesthetic drugs, low-flow anesthesia needs a more advanced technical infrastructure due to the necessity to follow the patients more closely.1-3 Obesity surgery may lead to many complications, such as difficult intubation, increased risk of atelectasis, obesity hypoventilation syndrome, and so forth.4-6 In these patients, respiratory capacity, which is already constrained due to obesity, is further limited due to the presence of carbon dioxide (CO2) insufflation and the lithotomy position during laparoscopic surgery. These factors increase the risk of developing hypoxia. Therefore, the use of low current was limited in these patients. However, considering the publications on tissue oxygenation for obese individuals with normal heart pumping functions and sufficient blood volume and hemoglobin levels, it can be predicted that oxygen will be sufficient at the tissue level in low-flow anesthesia.7 Also, there are studies where low-flow anesthesia in laparoscopic surgery resulted in successful outcomes in addition to balanced oxygen delivery consumption.8,9 Although limited, there are studies reporting use of low-flow anesthesia in bariatric surgery.9-11
This paper aims to examine the effects of low-flow anesthesia on arterial blood gas, hemodynamic parameters, and anesthesia recovery in patients with morbid obesity who underwent laparoscopic sleeve gastrectomy.
Methods
Concern for hypoxia plays an important role in avoiding the use of low flow in morbidly obese individuals. For this reason, studies on this subject remain limited. Therefore, we think that this original clinical study could be a reference to studies of low flow use in morbidly obese patients. The study proceeded with the permission from the Ethics Committee of the Clinical Research, Kafkas University, Kafkas, Turkey (26.06.2016/132). The ethical standards of the Declaration of Helsinki were adhered to. For the sample size of the study, a similar study previously conducted was referenced. The minimum sample size calculated by taking 0.05 alpha error and 0.20 beta error was found as 15 patients in both groups. This prospective randomized controlled clinical trial, which is also an equivalent clinical trial was performed with 44 adult patients with American Society of Anesthesiologists scores of I-II, aged 18-75 years, and with a body mass index (BMI) of >35 kg/m2. Informed consent was obtained from all participants. Patients with cardiovascular disease, liver disease, pulmonary disease or cerebrovascular disease and those refusing to give an informed consent were excluded. The references for the research were created using PubMed and Google academic indexes.
Upon receiving their informed consent, patients were randomly allocated to 2 groups as a study and a control group. This randomized study was performed by the blind anesthesiologist, who did not participate in the study, using the coin flip method. The patients were examined preoperatively and were taken to the operating room without premedication after the appropriate fasting period.
The leak test of the anesthesia device was performed for each patient before anesthesia. The soda lime used as the CO2 absorbent was changed when the color changed. Standard monitoring procedures were used for electrocardiogram, and peripheral oxygen saturation (SpO2). Besides, a 20G cannula was inserted into the radial artery, and intraarterial pressure was continuously monitored. The patients underwent 5 minutes of preoxygenation (100% 4 L/min O2) followed by propofol 2 mg kg-1 (Propofol 1%, Fresenius® Fresenius Kabi Medicine, Istanbul, Turkey), fentanyl 1 mcg kg-1 (Fentanyl 0.05 mg/ml, Johnson and Johnson Medicine, Istanbul, Turkey) and rocuronium bromide 0.6 mg kg-1 (Curon® 50 mg/5 ml Mustafa Nevzat, Istanbul, Turkey) administered intravenously during the induction of anesthesia.
Following intubation with an appropriate endotracheal tube, patients were connected to the anesthesia device. End-tidal carbon dioxide (EtCO2), amount of sevoflurane, nitrous oxide, and oxygen flow were continuously monitored after intubation.
In order to provide faster depth of anesthesia at the beginning of anesthesia in the low-flow (study) group, the combination of 2 L min-1 nitrous oxide (N2O), 2 L min-1 oxygen (O2), and 2-3% sevoflurane (Sevorane®, Liquid 100%, Queenborough, UK) was administered with a minimum alveolar concentration (MAC) of 1 for 5 minutes. Later, 50% O2 + 50% N2O and 2-3% sevoflurane was given by setting the fresh gas flow to 1 L min-1. In the high-flow (control) group, a combination of 2 L min-1 N2O, 2 L min-1 O2, and 2-3% sevoflurane was given at the same concentration throughout the procedure. At the end of the operation, fresh gas flow was removed at 6-8 L min-1 and inhalation of the anesthetic agent was closed for all patients. Ventilation was continued manually with 100% O2. For the reversal of the neuromuscular block, neostigmine 0.04 mg/kg-1 (Neostigmine, Adeka Samsun, Turkey) and atropine 0.02 mg/kg-1 (Atropine Sulphate, Galen Medical, Istanbul, Turkey, 0.02 mg kg-1 intravenously) were administered. For the treatment of postoperative pain, tramadol (1 mg/kg-1) and dexketoprofen (50 mg) were administered.
Patients’ demographic data, vital signs at 30 min intervals (heart rate [HR], peripheral oxygen saturation [SpO2], and arterial pressure), and preoperative, intraoperative (30, 60, 90 and 120 min), and postoperative arterial blood gas values, operation times, and postoperative complications were recorded. In this clinical trial, we do not analyze the variability of the vital signs according to the time in their own. We analyzed all vital signs between groups for each minutes as aforementioned.
Statistical analysis were performed using the Statistical Package for Social Sciences (IBM Corp., Armonk, NY, USA) version 22. Continuous and categorical variables are expressed as mean ± standard deviation and percentages. Differences in subject characteristics between low-flow and high-flow anesthesia were analyzed using the t-test and the Mann-Whitney U test for continuous variables and the Chi-squared test/Fisher’s exact test for categorical variables. The dependent t-test and repeated measurement analysis of variance (ANOVA) and the Friedman test were used to compare laboratory parameters between the beginning and the end of the study period.
Results
The study population consisted of 44 patients (mean age 36±9 years; 31.8% male) who underwent sleeve gastrectomy operation. The low-flow anesthesia technique was performed in 27 (61.4%) patients and the high-flow anesthesia technique was performed in 17 (38.6%).
The 2 groups were statistically similar in terms of demographic data. Patients’ demographic, clinical, and operation feature are listed in Table 1. Ten-minute HR values were statistically higher in the high-flow anesthesia group (p=0.035). Heart rate values at other times were similar in both groups (p>0.05). Systolic, diastolic, mean arterial pressures, end tidal CO2 levels, and O2 saturation were similar in both groups (p>0.05 for all) (Table 2). Arterial blood gas values were evaluated throughout the operation. Patients with low-flow and high-flow anesthesia had similar pressure of oxygen (pO2), partial pressure of carbon dioxide (pCO2), arterial oxygen saturation (SatO2), bicarbonate (HCO3), base excess (BE), and lactate levels (p>0.05 for all) (Table 3). During the entire procedure, including the onset, the 30th, 60th, and 90th minutes, and the extubation period, the patients with low-flow anesthesia showed similar values to those with high-flow anesthesia (p>0.05 for all). Although, the duration of exubation and recovery was shorter in the low-flow anesthesia, albeit not statistically significant.
- Demographic data.
- Analysis of vital signs.
- Arterial blood gas analysis.
Discussion
Low-flow anesthesia is becoming increasingly common with the provision of technical infrastructure and the development of continuous and detailed monitoring systems. However, low-flow anesthesia has not been preferred in morbid obese individuals because of the expectation of hypoxia and tissue hypoxia due to the weight of morbidly obese patients. Basic elements of tissue hypoxia include the amount of oxygen presented (fiO2), which is the amount of blood volume together with cardiac output, and the hemoglobin level.7 When tissue oxygenation is calculated in low-flow anesthesia, tissue hypoxia is not expected in healthy obese individuals whose surgical bleeding is replaced. Lactate level is an important indicator that reacts later than SatO2 and PO2 to tissue hypoxia. Here, we found no statistically significant difference in terms of lactate levels. These findings show that adequate tissue oxygenation can be provided at low-flow in obese individuals. However, close monitoring of oxygenation is still required. Low-flow anesthesia has been used in many different patient groups and has been found to be similar to or better than high-flow anesthesia in many ways.12,13
Obesity surgery has the potential to increase the risks of hypoperfusion, bleeding, hypovolemia, and prolonged surgical procedures. Moreover, pulmonary function is limited in morbid obesity.14,15 In laparoscopic surgery, a perioperative significant increase of intra-abdominal pressure with CO2 infusion is associated with further decrease of lung volumes and decreased diaphragm movements, which is clinically reflected in terms of hypoxia and increased EtCO2 levels.16-18 These patients benefit from intraoperative positive end-expiratory pressure (PEEP) and postoperative breathing exercises.18,19 We applied 10 cmH2O PEEP to prevent atelectasis during the operation. Also, all patients had respiratory exercises during the postoperative period. In the current study, PCO2, EtCO2, and SatO2 parameters were not different between obese patients receiving high-flow and low-flow anesthesia. We found that the risk for low-flow peripheral perfusion impairment was similar between groups. However, it should be kept in mind that close follow-up is required.
The depth of anesthesia is one of the main concerns of the anesthesiologist during operations. To evaluate the depth of anesthesia, many hemodynamic parameters, such as electroencephalography (EEG), pupil diameter, hemodynamic parameters have been used. Electroencephalography could not be performed because there was no EEG device in our hospital. Also, it was excluded from the evaluation as the pupil diameter may vary due to the narcotics used. Another factor affecting the depth of anesthesia is the use of different agents.20-22 In our study, the use of sevoflurane, rocuronium, and fentanyl in all patients neutralized this effect. Also, systolic blood pressure, diastolic blood pressure, mean arterial pressure, and HR were evaluated to assess the depth of anesthesia. These hemodynamic parameters did not differ between the low-flow and high-flow anesthesia groups.
As an important postoperative parameter, recovery time may depend on many variables, including the pharmacodynamics and pharmacokinetics of the anesthetic agent used, the anesthesia technique, operation time, and operation type.23,24 Many studies have shown that low-flow anesthesia is similar to or better than high-flow anesthesia in terms of recovery times.10,25 In the present study, rescue times were similar in both groups, consistent with the findings of other studies.
Study limitations
Kars is one of the smaller cities in Turkey with a population of approximately 250,000 people. Therefore, the number of patients included in the sample could not be increased during the research process due to such small population and the sociocultural structure; most of our patients came from other cities. Also, since there is no EEG or bispectral index device in our hospital, evaluation of depth of anesthesia was limited.
In conclusion, effects of low-flow anesthesia on arterial blood gas, hemodynamic parameters, and anesthesia recovery times were similar to high-flow anesthesia in laparoscopic obesity surgery. The use of low-flow anesthesia in laparoscopic obesity surgery seems to be safer than high-flow anesthesia in terms of the adequacy of tissue perfusion, depth of anesthesia, and postoperative recovery. We think that with careful monitoring, low-flow anesthesia can be used in obese individuals. However, further research on the matter is still needed.
Acknowledgment
We would like to thank protranslate and for English language editing. https://www.protranslate.net/tr/
Footnotes
Disclosure. Authors have no conflict of interests, and the work was not supported or funded by any drug company.
- Received October 7, 2020.
- Accepted January 24, 2021.
- Copyright: © Saudi Medical Journal
This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial License (CC BY-NC), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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