Ethics and patients
This study protocol was approved by the Ethics committee of Kashan University of Medical Sciences (Ghotb-e-Ravandi Blvd, 5th Km, Kashan Road, 8715988141, Kashan, I. R. Iran- Postal code: 8715988141). All methods were carried out in accordance with relevant guidelines and regulations and with CONSORT recommendations. The study was registered in Kashan University of Medical Sciences ( The link for the study registry: https://irct.ir/user/trial/24834/view, Trial Id: 24834, IRCT Id: IRCT2016122731611N1, Registration date: 18/03/2017).
In this prospective, randomized, parallel and one-way blinded clinical trial, 78 patients with ASA class 1 and 2, aged between 18 and 75 years old, who were candidates for posterior spinal fixation surgery, were included and then randomly divided into two groups of 39 subjects after obtaining the written informed consent.
This study was prospective, randomized, and parallel (allocation ratio = 1:1).
For the participants’ allocation, the permuted block randomization was used by applying a computer-generated list of random numbers and using sealed envelopes. Although surgeons and nurses who were involved in patient care, were aware of the study they were blinded to the details of the study’s protocol. The surgical procedure was performed by one surgeon and a single surgical team using the same method.
The permuted block randomization was used for the participants’ allocation (allocation ratio=1:1). in this regard used random numbers that extracted from computer-generated list and sealed envelopes.
Anesthesia was induced and then maintained by the attending anesthesiologist, who managed anesthesia using a standard regimen in the study protocol; however, he was blinded to the details of the study protocol. After establishing routine patient monitoring (Heart rate, noninvasive blood pressure, pulse oximetry, and end tidal CO2), anesthesia was induced with an intravenous premedication of 2µg/kg fentanyl, 0.03 mg/kg midazolame, 5 mg/kg sodium thiopental, and 0.5 mg/kg atracurium. Endotracheal tube with a suitable size, a high-volume, and a low-pressure cuff was inserted for the patients.
Anesthesia was maintained with infusion of propofol 100-200Mic/Kg/min as well as 30/70% of O2/N2O mixture to maintain 70 mmHg of MAP, if any additional drug was necessary to maintain 70 mmHg of MAP labetalol infused. In the PCV group, mechanical ventilation begun with PIP=15 mmHg, RR=12/min, I/E= ½, and PEEP=0 and then the PIP was adjusted to achieve a tidal volume that was calculated as the ideal body weight (50 [female: 45.5] + 0.91 [height − 152.4]) × 7 ml. In addition, the respiratory rate was controlled. Using the end-tidal carbon dioxide pressure (ETco2) ranged from 35 to 40 mmHg. In the VCV group, TV=7ml/IBW and RR, I/E, and PEEP were chosen as one group. Afterward, anesthesia was reversed with 0.04 mg/Kg neostigmine and 0.02 mg /Kg atropine.
Measurements hemodynamic changes BP, HR, MAP, amount of blood loss, and transfusion were recorded intera and post-operative duration of surgery was recorded as well.
In this study, the amount of bleeding was calculated based on the volume of blood lost in the suction, the number of completely impregnated gases (4 x 4 cm, 15 cc each), large amount of completely impregnated blood (30 x 30 cm per 50 cc), and the amount of blood in the hemovac drain of the patients and then registered until the end of the operation.
Additionally, the amount of blood and blood products injected during the operation along with blood pressure and heart rate were recorded before the induction, immediately after the intubation, after being in the prone position, during the operation every 15 minutes, at the end of the operation, after being in the supine position, and after endotracheal tube exit and recovery time.
Afterward, postoperative hemoglobin levels were checked after the arrival to general ward.
Surgeon’s satisfaction from the field of surgery was also questioned and recorded as good, moderate, and weak, which were stated based on the volume of bleeding, the bleeding conditions of the operation field, and the surgeon's personal opinion.
All the obtained data were measured and recorded by one trained observer who was not aware of each group. All the patients operated by one surgeon who was not informed of the method of ventilation.