مقایسه اثرات پروپوفول و ایسفلوران بر روی فشار اکسیژن شریانی، فشار شریانی متوسط و تغییرات ضربان قلب پس از تهویه یک ریه ای در جراحی های قفسه سینه A Comparison of Effects of Propofol and Isoflurane on Arterial Oxygenation Pressure, Mean Arterial Pressure and Heart Rate Variations Following One-Lung Ventilation in Thoracic Surgeries

۱٫ Background Hypoxemia during the one-lung ventilation (OLV) is a major concern in the management of anesthesia for thoracic surgery. Significant drop in arterial oxygen saturation (SPO2<90 %) during one-lung ventilation occurs in one to ten percent of population undergoing thoracic surgery in the presence of FIO2 = 100 % (fraction = 1.0). The pulmonary arteriovenous shunt of unsaturated blood is the main cause of hypoxemia during one-lung ventilation which is not ventilated. Hypoxic pulmonary vasoconstriction (HPV) is the most important defense mechanism against shunting (1). According to the different effects of anesthetics on the inhibition of HPV, it is crucial to use drugs with the minimal inhibitory effects on this vital mechanism (2). Therefore, it may be necessary to evaluate the effects of the two major anesthetic maintenance agents on HPV and their subsequent pressure of arterial oxygen using propofol (intravenous anesthetic) and isoflurane (inhaled anesthetic). It is obvious that the impact of this mechanism will emerge as SPO2 changes (2). Despite the extensive use of these drugs, their car- diovascular effects have not been thoroughly evaluated during OLV for thoracic surgery. Thus, it seems necessary that the effects of these drugs (propofol and isoflurane) should be examined on systemic hemodynamics (mean arterial blood pressure and heart rate). ۲٫ Objectives The present study aimed to evaluate the effects of propofol and isoflurane on patients’ arterial oxygen pressure following one-lung ventilation during thoracic surgeries. 3. Materials and Methods In this randomized clinical trial 60 patients with ASA class I and II who were the candidates for right elective thoracotomy were recruited for lung resection in two groups of intervention and control. The calculation of sample size of the study, with two-tailed α error of 5 % and β error of 20 %, was done based on PaO2 measured during OLV under propofol anaesthesia in a published study [123.7 (54.7) mmHg] (3). Based on this measurement, thirty patients per group were required to detect a difference of 39.7 mmHg in the lowest PaO2 between two groups. The method of sampling was convenience and non-probability. ۳٫۱٫ Eligibility The studied population consisted of the patients referred to our subspecialty teaching Hospital, Mashhad, Iran to undergo elective thoracic surgery and OLV. Field data collection using checklist and direct observation by an operating room technician unaware of the study protocol and its objectives Inclusion criteria included age between 18 and 75 years, ASA class I and II, satisfaction of thoracic surgery with OLV complied with the conditions of the study. Exclusion criteria included liver dysfunction (AST > 40 and ALT > 40), ischemic or valvular heart disease (heart disease was examined by medical history, physical condition, ECG and echocardiography), end-stage obstructive or restrictive pulmonary disease, patients with OLV less than 30 minutes, patients who showed a ETCO2 > 45 with respiratory rate of 12 breaths/minutes and patients who had a pathological lesion in left lung (dependent lung) in preoperative assessment including HRCT and PFT. ۳٫۲٫ Randomization Randomization was simple and accomplished by using random assignment tables. ۳٫۳٫ Endpoints The arterial oxygen pressure were evaluated as primary endpoints: 10 minutes after initiation of two-lung ventilation and 5 and 10 minutes after the start of one-lung ventilation. Hemodynamic parameters were evaluated as secondary endpoints: average of mean arterial blood pressure and heart rate assessing 10 minutes after initiation of two-lung ventilation and 5 and 10 minutes after the start of one-lung ventilation. ۳٫۴٫ Intervention After taking a history, the required description of the research was given to the patients and the informed consent was obtained. After preoxygenation in all patients, anesthesia was induced with sodium thiopental (4 mg/ kg), sufentanil (0.2 μg / kg) and atracurium (0.5 mg / kg). Initially left-sided double-lumen tube with MPI brands (Medicoplast GmbH factory) was placed for the patients, the proper placement was determined by auscultation and fiberoptic bronchoscopy. After a positional change to the lateral decubitus, the proper position was confirmed again by auscultation and fiberoptic bronchoscopy before the start of OLV. Ventilator settings were similar in all patients during a two – lung ventilation (TLV) and OLV and included: Tidal volume (TV): 6 cc/kg, respiratory rate (RR = 12) (to maintain ETCO2 between 35 and 45), inspiratory/expiratory ratio was 1:2 (I/E = 1/2), the fraction of inspired oxygen (FIO2) = 1. During surgery, patients randomly received propofol (100 μg /kg/min) or one Mac (1.1 %) isoflurane as a maintenance drug based on their group. For all patients, BIS was maintained between 40 and 60 and the maintenance dosage adjustment was made if necessary. Fluid deficit was compensated with normal saline or Ringer’s lactate using the “4-2-1” rule for every hour fasting before induction of anesthesia. Monitoring included electrocardiography (ECG), endtidal carbon dioxide tension (PETCO2), saturation of peripheral oxygen (SPO2), BIS and invasive arterial blood pressure (IBP) inserting radial artery catheter. In this step, ABG was performed twice: The first phase (during two-lung ventilation (TLV)): In this phase, 10 minutes after positioning in the left lateral decubitus during TLV. The second phase (during the first 10 minutes of OLV): in this phase, OLV is initiated and then ABG was performed at 5 and 10 minutes after the start of OLV. SpO2 was monitored continuously during this period, and the surgeon was allowed to open the chest. If the SPO2 was 90 % or less, ABG would be taken immediately and the two-lung ventilation (TLV) was restored. This arterial blood sample was considered as the lowest patient’s SPO2 and more blood samples were not taken for further study. ABG evaluation was done using GEM® Premier™ ۳۰۰۰ (Instrumentation Laboratory, The Netherlands) and SPO2 and BP were measured by operating room patient monitoring system (SAZGAN model VECTRA, Tehran, Iran) ۳٫۵٫ Statistical Analysis Data description was done using percentage, frequency and relevant descriptive graphs and we used Chi-square test and t-test for data analysis when assessment of normality by Kolmogrov-Smirnov test showed normal distribution of the selected variable. SPSS software, version 16, was used for statistical analysis and in all statistical measurements P value less than 0.05 was considered significant. ۳٫۶٫ Ethical Consideration The current study protocol was approved by ethical committee of mashhad university of medical sciences (No. 910182, 2013/2/2 ) and All the patients gave their written informed consent to the procedure and they were ensured that their confidentiality will be kept on their personal information, in any circumstance, will not disclosed or given to any third party. ۴٫ Results Sixty patients, mean age 41.24 ± ۱۸٫۶۳ years, were enrolled in this study. There was no statistical differences (P = 0.782) in mean age between two groups (propofol group = 40.52 ± ۱۹٫۲۰ years and isoflurane group = 41.93 ± ۱۸٫۳۸ years). There were 23 females (38.3 %) and 37 males (61.7 %). The results showed no statistically significant difference (P = 0.426) in terms of gender distribution between two groups (in propofol group, 66.67 % males and isoflurane group, 43.33 % males). We found no differences between two groups concerning the pressure of arterial oxygen during TLV and 5 and 10 minutes after the start of OLV (Table 1 and Figure 1). There were no significant differences in mean arterial pressure and heart rate during TLV and also 5 and 10 minutes after the start of OLV in both groups (Tables 2 and 3). The diagrams of Po2 in various measured time interval is shown in Figure 2. And there was no significant difference between them in two groups of the study