Effects of Low-Flow Anesthesia on Hemodynamic Parameters and Oxygenation in Morbidly Obese Patients Undergoing Bariatric Surgery: A Prospective, Randomized Clinical Trial
Phase: NA
Conditions: Morbid Obesity, Hemodynamic Instability, Bariatric Surgery Candidate
Sponsor: Inonu University

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Effects of Low-Flow Anesthesia on Hemodynamic Parameters and Oxygenation in Morbidly 
Obese Patients Undergoing Bariatric Surgery: A Prospective, Randomized Clinical Trial  
*Sedat Akbas, Asst. Prof. Department of Anesthesiology and Reanimation, Inonu University 
Medical Faculty, Malatya, Turkey 
Ahmet Selim Ozkan, Asst. Prof. Department of Anesthesiology and Reanimation, Inonu 
University Medical Faculty, Malatya, Turkey 
Mehmet Ridvan Yalin, Postgraduate student. Department of Anesthesiology and Reanimation, 
Inonu University Medical Faculty, Malatya, Turkey 
 
Address all correspondence to: 
Sedat Akbas, Asst. Prof. Department of Anesthesiology and Reanimation, Inonu University 
Medical Faculty, Malatya, Turkey 
Mail: drsedatakbas@gmail.com 
Phone Number: +905058263912  
Fax Number: +904223410728 
 
A short title: Effects of Low-Flow Anesthesia in Morbidly Obese Patients 
 
Conflict of Interest:  
The authors declare that they have no conflict of interest. 
Funding Information:  
None 
 

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Study Protocol 
Morbidly obese patients with American Society of Anesthesiology (ASA) scores of III-IV, who 
were aged 18–65 years old, and had a BMI>40 were included in our study. Patients were 
interviewed before surgery to obtain informed consent. Patients were excluded if they were 
pregnant or had uncontrolled diabetes mellitus, cardiovascular disease, pulmonary disease, 
cerebrovascular disease, or drug and alcohol addiction. Patients who refused informed consent 
were also excluded.  
Patients were taken to the operating room without premedication. Standard monitoring procedures 
were used, including heart rate (HR), noninvasive blood pressure (NIBP), electrocardiogram 
(ECG), peripheral oxygen saturation (SpO2), and body temperature. A general anesthesia protocol 
was administered in all patients by an experienced anesthesiologist. After preoxygenation (100% 
4 L/min O2 for 5 min), propofol (1–2 mg.kg-1), rocuronium (0.8–1  mg.kg-1) and fentanyl (0.1 μ 
g.kg-1) were administered during the induction of anesthesia via intravenous (IV) route at doses 
calculated according to ideal body weights. Randomization was performed with the MedCalc for 
Windows (medcalc.com.tr.), version 16 statistical software. Forty-eight patients were randomly 
allocated to two study groups: a low-flow group (Group L, n = 24) and a normal-flow group (Group 
N, n = 24). Patients in Group L received a fresh gas flow of 4 L/min for the first 10 minutes and 
were then maintained with a fresh gas flow of 0.75 L/min. Patients in Group N received the same 
initial fresh gas flow of 4 L/min for the first 10 minutes but were then maintained with a fresh gas 
flow of 1.5 L/min. All patients were mechanically ventilated with a tidal volume of 8 mL/kg based 
on ideal body weight and a frequency of 12–16 breaths/min using a Dräger Primus ventilator 
(Dräger AG, Lübeck, Germany). End-tidal carbon dioxide (EtCO2) was continuously monitored 
after intubation. Tidal volume and ventilation rate were adjusted to maintain EtCO2 partial pressure 

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of arterial blood at 35–45 mmHg. Rocuronium was intermittently injected according to need based 
on Train of Four (TOF; Dräger AG, Lübeck, Germany) values. TOF responses were assessed by 
ulnar nerve stimulation and adductor muscle response. Anesthesia was maintained in both groups 
at desflurane inhalation in a 0.5 O2 oxygen-air mixture. Desflurane was discontinued with the 
beginning of the skin sutures and the fresh gas flow was changed to 4 L/min of oxygen for both 
groups. In patients who did not experience complications during the surgery, sugammadex (IV, 2–
4 mg/kg, Bridion®, MSD, Greenville, USA) was then administrated to reverse residual muscle 
relaxation at the end of surgery.  All patients received the standard surgical procedures determined 
by the same team of surgeons with experience in gastroenterology surgery. Pneumoperitoneum 
pressure ranged between 10 – 12 mmHg. Surgical management of sleeve gastrectomy was not 
changed in any way. In all patients, postoperative analgesia was achieved IV analgesic medication 
using appropriate doses of tramadol (0.5-1 mg/kg, IV) and paracetamol (1 gr, IV) at the time of 
beginning skin sutures (16).  
Hemodynamic parameters such as HR, SpO2, EtCO2, MAP and values of arterial blood gas were 
recorded before anesthesia (T0), 5 min before insufflation of CO2 (T1) and 15 min after awakening 
from anesthesia (T2). In addition to anesthesia and surgery times, perioperative and postoperative 
complications were recorded. 
 
 
 
 
 

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Statistical Analysis Plan 
Using the power calculation method (OpenEpi, Version 3), assuming an alpha of 0.05 and a beta 
of 0.80, we calculated that 22 patients per group should be included in this study. Data were 
analyzed using the Statistical Package for the Social Sciences program (SPSS 22.0). As some pre 
and anesthetic characteristics of patients were distributed abnormally nonparametric statistics was 
used. Quantitative data are presented as mean or standard deviation and categorical data are shown 
as numbers or percentages. Continuous variables were compared between the groups using Mann-
Whitney U-test. Categorical variables were summarized using frequencies and percentages (%) 
and compared between the groups using Chi-Squared Test. The results were evaluated at a 95% 
confidence interval at a significance level of p<0.05.