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Controlled Hypotension During Endoscopic Sinus Surgery: A Comparison of Propofol and Magnesium Sulfate

Objective: Controlled hypotension is considered as an effective technique for reducing blood loss and optimizing the surgical field. This study was designed to compare intravenous infusion of propofol and magnesium sulfate for achieving controlled hypotension during elective endoscopic sinus surgery. Methods: This randomized, double blinded, comparative study was conducted on fifty patients of either sex, aged between 18 and 45 years old underwent elective endoscopic sinus surgery. Patients were randomly categorized into two equal groups (25 patients each). Propofol group: patients were received intravenous infusion 75 mcg/kg/min of propofol for the first 15 minutes post induction and then a maintenance infusion of propofol (50 mcg/kg/min). Magnesium group: before induction of anesthesia, magnesium sulfate intravenous infusion was started at 40 mg/ kg in 100 ml saline over 10 minutes as a loading dose then magnesium sulfate infusion of 167 mcg/kg/min during surgery. Perioperative mean arterial blood pressure and heart rate were recorded. The intra-operative surgical field assessment and surgeon satisfaction score were assessed. The recovery profile was assessed by Ramsay sedation score and modified Aldrete score. Postoperative complications in the terms of postoperative nausea and vomiting and shivering were also recorded. significantly decreased in propofol group at 15, 30, 45, 60 and 75 minutes after induction when compared to magnesium group. However, perioperative heart rate showed no significant changes between both studied groups. No statistical changes between the two studied groups as regard surgeon satisfaction and bleeding scores. Nitroglycerine doses were significantly higher in magnesium group than propofol group (P value<0.001). Postoperative Ramsay sedation scores were statistically significant higher, and the recovery time was significantly longer in magnesium group compared to propofol group (P value <0.001). Postoperatively shivering was significantly higher in propofol group compared to magnesium group while nausea and vomiting showed no significant changes between both groups. Conclusion: This study concluded that intravenous infusion of propofol provided easily controlled hypotension, while intravenous infusion of magnesium sulfate was associated with a better recovery profile and reducing the incidence of postoperative shivering.


Introduction
Endoscopic Sinus Surgery (ESS) in which primary objective is the removal of pathology in the ostiomeatal complex has gained widespread acceptance in treatment of chronic sinus disease [1]. Endoscopic Sinus surgery usually associated with bleeding, despite using of local vasopressor injection [2], head up position [3], and tight control of the end-tidal carbon dioxide tension [4], using different pharmacological agents have been used to induce controlled hypotension [5].
Propofol is a good agent for controlled hypotension by decreasing systemic vascular resistance due to arterial and venous vasodilation and a decrease in myocardial contractility with a dosedependent property [1]. Magnesium Sulfate also has been reported as an agent of hypotensive anesthesia by inhibition of the release of norepinephrine by blocking N-type calcium channel at the nerve ending beside acting as a vasodilator [6].
The pharmacodynamic effects of the intravenous infusion of propofol or magnesium sulfate may prove the advantage of this drugs in controlling intraoperative blood pressure and decrease the bleeding from surgical field. To the best of our knowledge, there have been no studies comparing controlled hypotension by propofol versus magnesium sulfate for endoscopic sinus surgery. So, the current study was designed to compare the efficacy of propofol and magnesium sulfate to control blood pressure during endoscopic sinus surgery and the resultant effects on the quality of the surgical field including bleeding and visibility. The primary outcome was the mean arterial blood pressure (MAP) after 15 minutes from the initiation of the intravenous infusion of the study drug. The secondary outcomes were the intraoperative heart rate (HR), total amount of intraoperative blood loss, need for blood transfusion and the consumed intraoperative amount of nitroglycerine, and ephedrine. Postoperative sedation scores, nausea, and vomiting (PONV), recovery time and surgical field assessment were also included. Eligible patients were randomly allocated to one of two equal groups, each included 25 patients, by a computer-generated randomization table and concealed closed envelope method. The propofol group: patients were received intravenous infusion (IVI) of propofol, while the magnesium sulfate group: patients were received intravenous infusion of magnesium sulfate. The studied drug was prepared by wrapping its container and the line with opaque cover by the anesthetist who was not involved in the data collection. Over 10 minutes before induction, first 100 ml of normal saline was infused in propofol group, while in magnesium group 40mg/kg magnesium sulfate in 100 ml normal saline solution was administrated.

Anesthetic management
All patients were premedicated with intravenous midazolam

Collecting Data
The MAP and HR were recorded before induction of anesthesia, intraoperatively immediately after induction, after Adrenaline local infiltration, then 5,15,30,45,60,75 and 90 minutes after general anesthesia induction, then immediately after anesthetics discontinuation and at the surgery end, and 15 minutes postoperatively.
EBV equals weight in kg x average 65 in adult female and 75 in adult male [7]. Hb start in gm/dl was the initial preoperative hemoglobin and Hb target was 8 gm/dl. Blood transfusion in the form of packed red blood cells (RBCs) was considered when the intraoperative blood loss exceeded the calculated MABL.
The intra-operative surgical field assessment was assessed by the same surgical team in terms of bleeding and visibility using a 6 point scale: 0 = no bleeding; 1 = minor bleeding, but no aspiration required; 2 = minor bleeding, aspiration required; 3 = minor bleeding, frequent aspiration required; 4 = moderate bleeding, visible only with aspiration; 5 = severe bleeding, continuous aspiration required [8]. Surgeon's satisfaction with the operative field was rated using a 4-point scale at the end of surgery: 1= bad, 2 = moderate, 3 = good, and 4 =excellent.
The mathematical calculation of the intraoperative blood loss was calculated according to the formula stating: Estimated blood loss (ml) =expected blood volume (ml) x In (Hct1 / Hct2) Where: In is a calculator abbreviation refers to the natural logarithm of the current entry. Hct 1(%) is the initial preoperative hematocrit, Hct 2 (%) is the 1-hour postoperative hematocrit [9]. Hct was estimated one hour postoperatively. Ramsay sedation score was evaluated at 15, 30, 45 and 60 minutes post-extubation: 1=Anxious, agitated, restless, 2=Cooperative, oriented, tranquil. 3=Responsive to commands only, 4=brisk response to stimulus, 5-sluggish response to stimulus, 6-no response to stimulus [10]. Postoperative shivering was recorded while nausea and vomiting were assessed for the first postoperative 24 hours at 0-6, 6-12, 12-24 hour on scoring system; Absence of nausea or vomiting was = 0, nausea without vomiting = 1, vomiting one or two times-=2, and vomiting more than 2 times = grade 3 [11]. Time needed to reach a modified Aldrete score ≥ 9 was defined as the recovery time. The patients were discharged from the recovery room when they reached a modified Aldrete score of 10 (when they were able to move all extremities on response to a request, able to breathe deeply and cough freely, fully awake and had oxygen saturation >94% while breathing room air) [12]. The surgical duration in minutes and the total doses of intraoperative nitroglycerine, atropine and ephedrine were also calculated.

Sample size Calculation
Using a previous study [13], the mean ± standard deviation of the MAP at 15 minutes after induction of magnesium group was (76±6.9) assuming Þ error of 0.05; ß error of 10% (power 90%),

Statistical analysis
Statistical analyses were performed using SPSS version 24 (IBM, SPSS Inc., Chicago, IL, USA). The normality of data was tested using the Kolmogorov-Smirnov test. Continuous data of normal distribution are presented as mean ± standard deviation (SD) and were analyzed with the unpaired student's t-test. Non-normally

Results
As shown in Figure 1, a total of fifty patients were included in this prospective, randomized, double blind, comparative study.
25 patients were analyzed in each group. The demographic characteristics and surgical duration of were summarized in Table   1. There were no significant differences as regard to patient age, sex, BMI, ASA class and surgical duration between the two studied groups.
Concerning the primary outcome measure, the intraoperative  Table 2. Surgeon satisfaction and bleeding scores revealed insignificant statistical changes between the two studied groups (Table 3). Postoperative Ramsay sedation scores were significantly higher in magnesium group compared to propofol group at 15 and 30 minutes, while there was no significant change at 45 and 60 minutes in both groups ( Table 4). The recovery time in magnesium group was significantly longer than in propofol group (P value <0.001) ( Table 5). During the first postoperative hour, shivering was significantly lower in magnesium group than propofol group (Table 5). Post-operative 24 hours nausea and vomiting (PONV) score showed no significant changes between the both groups (

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the targeted intraoperative MAP in magnesium group were significantly higher than propofol group (P value<0.001). However, ephedrine doses needed treat the intraoperative hypotension were significantly higher in propofol group when compared to magnesium group (P value=0.019). Also, the percentage of patients required intraoperative nitroglycerine/ ephedrine were 4 (16%) /10(40%) in propofol group versus 13(52%) /3(12%) in magnesium group, respectively. No significant difference in atropine doses needed in both studied groups.   Surgeon satisfaction score: 1= bad, 2 = moderate, 3 = good and 4= excellent. Bleeding score: 0 = no bleeding; 1 = minor bleeding, but no aspiration required; 2 = minor bleeding, aspiration required; 3 = minor bleeding, frequent aspiration required; 4 = moderate bleeding, visible only with aspiration; 5 = severe bleeding, continuous aspiration required. Data are expressed as number (percentage). Ramsay sedation score: 1=Anxious, agitated, restless, 2=Cooperative, oriented, tranquil. 3=Responsive to commands only 4=brisk response to stimulus. 5-sluggish response to stimulus 6-no response to stimulus. Data are expressed as median (inter-quartile range). * Significant difference compared to propofol group. PONV score =postoperative nausea and vomiting score; absence of nausea or vomiting = 0, nausea without vomiting = 1, vomiting one or two times-=2, and vomiting more than 2 times = 3. Data are expressed as number (percentage). *significant difference compared to propofol group

Controlled hypotension has a definitive role in ESS as it reduces
bleeding during surgery and improves visibility of the surgical field; hence, it decreases the duration of surgery [7]. To best of our knowledge, this is one of the first randomized controlled trials comparing IVI of propofol and magnesium sulfate for controlled hypotension in ESS. In this study Propofol provided easily controlled hypotension. However, magnesium sulfate was found to be associated with a better recovery profile and reducing the incidence of postoperative shivering.
According to this study, MAP reduced significantly in propofol group than in magnesium group 15 minutes after induction suggesting more hypotensive effect of propofol in comparison to magnesium sulfate. The total number (percentage) of patients required intraoperative nitroglycerine/ ephedrine were 4 (16%) /10(40%) in propofol group versus 13(52%) /3(12%) in magnesium group which strongly confirm the more hypotensive effect of propofol. These results were consistent with Bayram A, et al. [14] who concluded that magnesium sulfate provided less controlled hypotension than dexmedetomidine in patients underwent ESS where ten patients in magnesium sulfate group needed intraoperative nitroglycerine versus only two patients in dexmedetomidine group.
In the current study, both groups showed a statistically significant decrease of all intraoperative MAP readings compared to their basal value. This greatest reduction explained by the combined effect of vasodilatation and myocardial depression of propofol [1,15] and calcium channel antagonism of magnesium sulfate with the production of vasodilator prostacyclin and nitric oxide [6,16].
This study demonstrated no statistically significant changes of all reading of the HR in both groups either between the two groups or in relation to the basal value in the same group which may be due to the balanced use of isoflurane inhalational anesthesia which has an additional vasodilatory effect associated with reflex tachycardia counteracting the possibility of propofol induce bradycardia [17].
While there was no associated tachycardia in magnesium group probably because of the association of magnesium sulfate infusion with angiotensin converting enzyme inhibition and slowing of sinoatrial node conduction [18]. On the contrary of our results, Despite of the high incidence of PONV after endoscopic sinus surgeries, both studied groups showed no significant changes in PONV score without the use of antiemetic drugs. These results may be due to the adjuvant effect of magnesium sulfate to produce periooperative analgesia by NMDA receptor antagonism [24], while the antiemetic effect of propofol may be due to the interaction with dopaminergic receptors in the chemoreceptor trigger zone thus limbic system inhibition affecting the cortical reflexes reaching the vomiting center [25].
In the current study, patients in magnesium group developed lower incidence of postoperative shivering (3 patients) than propofol group (10 patients) that explained by reducing the shivering threshold with subsequent smooth muscle relaxation in magnesium group [26]. These results are consistent with Ryu et al. [27] who concluded that both magnesium sulfate and remifentanil can induce adequate hypotensive anesthesia in patients undergoing middle ear surgery with reducing the incidence of shivering and PONV in magnesium group.

Study Limitations
limitations in this study was neither using of nerve stimulator nor bispectral index for neuromuscular block or anesthesia depth monitoring. Instead we depended on the recovery time and modified Aldrete score recording. Another limitation was postoperative non measurement of serum magnesium sulfate levels.

Conclusion: This study concluded that intravenous infusion of
propofol provided easily controlled hypotension, while intravenous infusion of magnesium sulfate was associated with a better recovery profile and reducing the incidence of postoperative shivering.