|Year : 2015 | Volume
| Issue : 3 | Page : 79-84
Dexmedetomidine versus magnesium sulfate for oligemic field in middle ear surgery
Ahmed Z Mohamed1, Usama G Abd-Elnaby2
1 Department of Anesthesia and Intensive Care, Faculty of Medicine, Minia Univeristy, Minia, Egypt
2 Department of Otorhinolaryngeology, Faculty of Medicine, Minia Univeristy, Minia, Egypt
|Date of Submission||14-May-2015|
|Date of Acceptance||21-Sep-2015|
|Date of Web Publication||30-Dec-2015|
Ahmed Z Mohamed
MD, Department of Anesthesia, Faculty of Medicine, Minia University Hospital, Minia City 61511
Source of Support: None, Conflict of Interest: None
Aim of study
To compare between the effects of dexmedetomidine and magnesium sulphate on quality of surgical field visualization in middle ear surgery.
Patients and Methods
60 patients scheduled for middle ear surgery were included in the study. Patients were randomly divided into two equal groups, the 1st group received dexmedetomidine infusion (D group) while the 2nd received magnesium sulphate infusion (Mg group). Induction of anesthesia was done by propofol 2 mg/kg and atracurium 0.5 mg/kg. Anesthesia was maintained with sevoflurane which titrated to obtain 30% decrease in blood pressure. Infusion of dexmedetomidine 1 μg/kg over 10 minutes followed by 0.5 μg/kg/hr in D group while infusion of 50 mg/kg magnesium sulphate over 10 minutes followed by 15 mg/kg/hr magnesium sulphate in Mg group. Quality of surgical field visualization, Amount of blood loss, blood pressure, heart rate and postoperative side effects were recorded.
Quality of surgical field visualization was better and amount of blood loss was less in group D than group Mg without serious side effect.
Dexmedetomidine provided better quality of surgical field vision and less bleeding when compared to magnesium sulphate without any side effects in middle ear surgery.
Keywords: Dexmedetomidine, magnesium sulfate, middle ear surgery
|How to cite this article:|
Mohamed AZ, Abd-Elnaby UG. Dexmedetomidine versus magnesium sulfate for oligemic field in middle ear surgery. Res Opin Anesth Intensive Care 2015;2:79-84
|How to cite this URL:|
Mohamed AZ, Abd-Elnaby UG. Dexmedetomidine versus magnesium sulfate for oligemic field in middle ear surgery. Res Opin Anesth Intensive Care [serial online] 2015 [cited 2018 Dec 13];2:79-84. Available from: http://www.roaic.eg.net/text.asp?2015/2/3/79/172795
| Introduction|| |
Middle ear surgeries have made a significant progress with the usage of the operating microscope, which magnifies the surgical field many times; however, it also magnifies the blood droplets and thus a small amount of blood can obscure the surgical field . Multiple physical techniques are used to decrease blood loss and to provide an oligemic field, such as avoidance of venous obstruction of the neck and mild elevation of the head 15-30°, but these techniques are associated with increased incidence of air embolism .
Induction of controlled hypotension (reduction of 30% of baseline mean blood pressure) can decrease blood loss and provide a relatively bloodless operative field. Many pharmacological agents have been used for induction of controlled hypotension, such as inhalational anesthetics (isoflurane and sevoflurane) , vasodilators (e.g. sodium nitroprusside and nitroglycerine), β-adrenoceptor blocker (e.g. esmolol), opioids (e.g. remifentanil) , a-2 adrenergic agonists (clonidine and dexmedetomidine) , and recently magnesium sulfate .
Dexmedetomidine, which is an a-2 adrenergic agonist, can inhibit noradrenaline release and decreases sympathetic activity on blood vessels and regulates cardiovascular systems. This leads to decrease in the heart rate (HR) and the blood pressure, resulting in decreased bleeding and thus improving the quality of surgical field vision in a predictable and dose-dependent manner .
Magnesium sulfate, which is a noncompetitive N-methyl δ-aspartate receptor antagonist with antinociceptive effects, may be a good agent for controlled hypotension because it acts as a cell membrane stabilizer through the inhibition of Ca ATPase and Na-K ATPase involved in transmembrane ion exchange leading to membrane stabilization. Moreover, it acts as a vasodilator by increasing the synthesis of prostacyclin and inhibiting angiotensin-converting enzyme activity .
To the best of our knowledge, there have been no studies comparing dexmedetomidine and magnesium sulfate in providing an oligemic field in patients scheduled for microscopic middle ear surgery. We hypothesized that both dexmedetomidine and magnesium sulfate are effective in decreasing blood loss and improving the quality of surgical field vision under the microscope in middle ear surgery. The primary outcome objective of this prospective randomized blind study was to compare dexmedetomidine and magnesium sulfate in providing oligemic field during microscopic middle ear surgery. Blood pressure, sevoflurane concentration, and side effects of both drugs were also recorded and compared.
| Patients and methods|| |
Following approval of the research ethics committee in Faculty of Medicine in El-Minia University and informed written consent collected from all patients included in this study, which was conducted during the period from January 2012 to January 2013 in El-Minia University Hospital on 60 patients of ASA physical status I or II, aged between 18 and 60 years, and planned to undergo microscopic operation in the middle ear. Patients with liver or renal impairment, cardiac disease, hypertensive or on antihypertensive drugs, and those with known allergy to the study drugs were excluded from the study. Patients with coagulopathy or on anticoagulant therapy were also excluded from the study. Patients eligible for the study (60 patients) were randomly allocated into the two study groups of 30 patients each using the random allocation software (Windows software, version 1.0, May 2004) (M. Saghaei, MD., Isfahan University of Medical Sciences, Isfahan, Iran). The allocation ratio was 1 : 1, and the group identification paper was put in a sealed and opaque envelopes to hide allocation. The surgeon and the nursing staff who follow-up the patients in the postanesthesia care unit (PACU) were blinded with the type of the drug used. A 20-G cannula was inserted in the dorsum of the hand when they entered the operation room. Standard monitoring such as HR, blood pressure, and oxygen saturation (SpO 2 ) were applied to the patients. Advisor monitors (Smith Medical PM Inc., Waukesha, Wisconsin, USA) were used in this study. Preoxygenation with a face mask for 3 min, followed by induction of anesthesia with 2 mg/kg propofol 1% together with 50 mg lidocaine 2% in the same syringe, was carried out until loss of verbal communication. Thereafter, 0.5 mg/kg of atracurium, followed by positive pressure ventilation with the face mask delivering sevoflurane 4%, was administered until adequate relaxation and intubation was performed with a suitably sized endotracheal tube. Patients in the dexmedetomidine group (D) (n = 30) received a loading dose of 1 μg/kg of dexmedetomidine in 200 ml of normal saline 0.9% and subsequent doses of 0.5 μg/kg/h, whereas patients in the magnesium sulfate group (Mg) (n = 30) received a loading dose of 50 mg/kg of magnesium sulfate in 200 ml of normal saline 0.9 % and subsequent maintenance doses at 15 mg/kg/h during the operation. Anesthesia was maintained with sevoflurane and atracurium. Patients were under controlled ventilation at a respiratory rate of 12 cycles/min and a tidal volume (TV) of 6 ml per kg. Sevoflurane percentage was titrated to maintain mean blood pressure around 30% descents in the blood pressure. Sevoflurane percentage was recorded every 15 min until extubation. Blood pressure, oxygen saturation, and HR were recorded at the following times: before intubation (baseline), 1, 5, 15, 30, 60, 90, 120, and 180 min. A volume of 5 ml/kg/h of 0.9% saline was given during the operation. Bleeding at the surgical field and quality of vision under the operating microscope were evaluated by the same surgeon every 15 min in the first hour and then every 30 min according to the Intraoperative Surgical Field Evaluation (IOSFE) Boezart scale  [Table 1].
The amount of blood loss was calculated as follows: volume of bloody fluid in the suction container-volume of the irrigating fluid. After correct and secured placement of the tympanic membrane graft, the test drug was stopped and the blood pressure was allowed to return to the baseline value. At the end of the surgery, anesthesia was discontinued and muscle relaxation was reversed with intravenous 0.01 mg/kg atropine followed by 0.05 mg/kg neostigmine. After return of reflexes, extubation was performed and patients were transferred to the PACU, where they were followed up for HR, blood pressure, oxygen saturation, and pain through visual analogue scale. The duration of the surgery (the time from skin incision until end of the surgery) and awakening time (time from the reverse of muscle relaxant until sustained eye opening on command) were recorded.
In the PACU, patients were monitored for SpO 2 , HR, and BP on admission to the PACU, at 15 min, and at 30 min. Side effects of the study drugs, such as nausea, vomiting, respiratory depression, hypotension, bradycardia, excessive sedation, and loss of knee jerk, were recorded.
Visual analogue scale was recorded every 30 min in the PACU; if patients suffered from pain (visual analogue scale more than 4), they were given ketrolac 30 mg intravenously. If they suffered from vomiting they were treated with metoclopramide 10 mg intravenously.
Statistical analysis was carried out with a personal computer using Statistical Package for the Social science (SPSS), version 21 (SPSS Inc., Chicago, Illinois, USA). Numerical data were presented as mean and SD and numbers. Intergroup differences were analyzed using an unpaired t-test. Categorical data such as sex of patients and ASA classification were analyzed using the χ2 -test. A P value less than 0.05 was considered statistically significant.
Primary outcome variable was the score of the oligemic field assessed by the surgeon according to the ISOFE scale
The main measured variable was intraoperative surgical field evaluation (IOSFE) which should be 2 or 3 with SD close to 1.1, the sample size was determined to be 30 patients per group at an α error margin of 0.05, β value of 0.95, and 10% dropout rate.
| Results|| |
A total of 60 patients of ASA physical status I or II undergoing middle ear surgery were enrolled in the study and analyzed [Figure 1]. They were randomized into two groups of 30 each: the dexmedetomidine (D) group and the magnesium sulfate (Mg) group. There was no statistically significant difference between the two groups as regards demographic data such as age, weight, height, sex of patients, and type of surgery [Table 2].
As regards HR, there was no significant difference between the two groups in the following study times: baseline (before intubation), 1 min, and 5 min. HRs recorded were lower in the dexmedetomidine group when compared with the magnesium sulfate group in the other study times, and this difference became statistically significant at 15, 30, 60, 90,120, and 180 min [Figure 2].
|Figure 2: Heart rate (beats/min) changes in the study period. Data are expressed as mean. PACU, postanesthesia c are unit. There was a significant difference at 15, 30, 60, 90, 120, and 180 min. *P<0.05, significant.|
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As regards mean blood pressure, it was lower in the dexmedetomidine group when compared with the magnesium sulfate group, except for the baseline, 1 min, and 5 min readings, but this difference was not significant [Figure 3].
|Figure 3: Changes in mean blood pressure (mmHg) in the study period. Data are expressed as mean. Mean blood pressure (MBP) in the dexmedetomidine group was lower than MBP in the magnesium group, but without statistical significance.|
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The amount of blood loss was significantly lower in the dexmedetomidine group (60 ± 8 ml) than in the magnesium sulfate group (80 ± 15 ml) [Table 3]. Surgical time was 160 min in the dexmedetomidine group, which was significantly lower than that in the magnesium sulfate group, which was 190 min. Awakening time was 15.4 min in the dexmedetomidine group, which was comparable to 14.5 min in the magnesium sulfate group [Table 3].
|Table 3: Amount of intraoperative blood loss, surgical time, and awakening time|
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The main outcome in this study is the IOSFE scale [Table 4], which was statistically significantly lower (better quality of vision of the surgical field) in the dexmedetomidine group than in the magnesium sulfate group in all study times. There was no statistically significant difference between the two groups as regards sevoflurane concentration in all study times [Table 5].
There were no patients suffering from respiratory depression (SpO 2 <90%) or loss of knee jerk or excessive sedation in both groups during the postoperative period. Only three (10%) patients in the dexmedetomidine group and four (13.3%) patients in the magnesium sulfate group suffered from vomiting [Table 6].
|Table 6: Side effects occurred in postanesthesia care unit expressed as number|
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| Discussion|| |
In the current study we found that the quality of surgical field visualization during microscopic middle ear surgeries as investigated with the IOSFE scale was better in the dexmedetomidine group than in the magnesium sulfate group. This correlates with the study by Nasreen et al. . They conducted a controlled study on 42 patients scheduled for middle ear surgery who were divided into two groups: the first group received 1 μg/kg of dexmedetomidine infusion 10 min before induction of anesthesia, followed by infusion of 0.4 μg/kg/h, and the second group received the same volume of saline to provide hypotensive anesthesia in middle ear surgery. They found that dexmedetomidine provided better quality of the surgical field vision assessed by the surgeons when compared with the placebo. This is in agreement with the findings of Gupta et al. , who examined the effect of dexmedetomidine infusion of 0.5 μg/kg/h as adjuvant to the isoflurane as inhalational anesthetic in middle ear surgery, and they found that bleeding in the surgical field, quality of vision, and hemodynamic stability in the dexmedetomidine group was better than that in the placebo group without lengthening of the awakening time or delay recovery from anesthesia.
Guven et al.  conducted a prospective controlled study to examine a dexmedetomidine infusion of 1 μg/kg on 40 patients during conscious sedation in functional endoscopic surgery on hemodynamic parameters and surgeon satisfaction and they reported a significant improvement in the quality of surgical field visualization and less bleeding with better hemodynamic stability in patients who received dexmedetomidine infusion when compared with the control group.
Elsharnouby and Elsharnouby  in their randomized placebo-controlled study compared the infusion of magnesium sulfate at a loading dose of 40 mg/kg 10 min before induction of anesthesia, followed by infusion of 15 mg/kg, against the control group for endoscopic sinus surgery. They found that, in the magnesium sulfate group, there was a significant lowering of HR and mean blood pressure and better visual field quality with a significant decrease in surgical time, but there was prolongation of recovery time when compared with the placebo group. Akkaya et al. , in 2014, conducted a randomized clinical study on 60 patients scheduled for functional endoscopic sinus surgery to evaluate the role of dexmedetomidine (1 μg/kg loading dose 10 min before induction of anesthesia followed by 0.6 μg/kg/h infusion) and magnesium sulfate (50 mg/kg loading dose 10 min before induction of anesthesia followed by 15 mg/kg/h infusion) in the amount of bleeding and quality of vision of the surgical field during the operation, and they found that dexmedetomidine provided better visual quality of surgical field and reduced bleeding in surgical field compared with magnesium sulfate, with little or no side effects.
Ryu et al. , in their prospective controlled study on 40 patients, compared the effect of remifentanil 3-4 ng/kg infusion against magnesium sulfate infusion (50 mg/kg loading dose followed by 15 mg/kg/h) with sevoflurane to induce mean blood pressure between 60 and 70 mmHg for middle ear surgery. They found that the intraoperative conditions were good and comparable in the magnesium sulfate group and the remifentenil group, and they also reported that magnesium sulfate could induce deliberate hypotension as remifentanil, but magnesium had better emergence profile compared with remifentanil, because magnesium sulfate reduced anesthetic requirements.
As regards HR, this study found that HR in the dexmedetomidine group was lower than that in the magnesium sulfate group, which resulted in decreased bleeding at the surgical site and improved quality of vision in the former group, leading to decrease in the surgical time in the dexmedetomidine group than in the magnesium sulfate group. This is in agreement with the findings of Akkaya et al. , who found that the HR was slower in the dexmedetomidine group than in the magnesium sulfate group during functional endoscopic sinus surgery (FESS); they did not notice bradycardia less than 50 beats/min, which needed intervention with atropine. This coincided with the meta-analysis of previous studies, which showed that the incidence of bradycardia requiring intervention with atropine injection was increased when the maintenance dose of dexmedetomidine infusion was more than 0.7 μg/kg/h , whereas in our study and in the study by Akkaya the maintenance dose of dexmedetomidine was 0.5 μg/kg/h.
Awakening time in dexmedtomidine group was not prolonged in spite of the sedative effects of dexmedetomidine which could be explained by the fact that dexmedetomidine reduces the requirements of inhalational anesthetic used , beside that sedation of dexmedetomidine is easily to be aroused . This is in agreement with the findings of Gupta et al. , who examined dexmedetomidine for oligemic field in the middle ear surgery; they found that dexmedetomidine did not affect awakening time or delayed recovery from anesthesia.
Moreover, in the magnesium sulfate group, there was no prolongation of the awakening time. This is in agreement with the study by Koining et al. , who attributed this finding to the decrease in the anesthetic requirements caused by magnesium sulfate.
Limitations of this study
One of the limitations of this study was the different types of operations and different amounts of blood loss according to the causes of drum perforation either traumatic or cholesteatoma. Another limitation was the lack of a control group without hypotensive agent, because it was unethical to put an added difficulty to the surgeons by not limiting the bleeding, making the operative field to be obscured by blood and wasting time in suctioning. The third limitation was monitoring of quality of the surgical field visualization with a subjective scoring system, and we did not use laser Doppler flowmetry to evaluate blood supply to the middle ear.
| Conclusion|| |
This study concluded that dexmedetomidine provided better quality of surgical field vision and less bleeding when compared with magnesium sulfate, without any side effects in the microscopic middle ear surgery.
| Acknowledgements|| |
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]