The Open Anesthesia Journal


Formerly: The Open Anesthesiology Journal

ISSN: 2589-6458 ― Volume 13, 2019
CLINICAL TRIAL STUDY

Dexmedetomidine was Better at Lowering Intraocular Pressure than Magnesium when Combined with Local Anesthetics in Peribulbar Blocks for Posterior Segment Eye Surgery



Dalia Ahmed Ibrahim*, Dina Salah
Anesthesia Department, Ain Shams University Hospitals, Cairo, Egypt

Abstract

Background and Aim:

Many medications are combined with local anesthetics for peribulbar blocks to improve the quality of the block, however, few studies have compared the effect of dexmedetomidine and magnesium on intraocular pressure when combined with local anesthetics which was the primary endpoint of this double blinded study.

Materials and Methods:

A randomized controlled clinical trial was conducted on 60 ASA Physical Status (ASA PS) I-II patients scheduled for elective posterior segment eye surgeries under peribulbar anesthesia. Patients were randomly allocated to one of three groups of 20 each according to the medications they received. Local anesthetic solution was prepared using 8 ml of bupivacaine 0.5% and lidocaine 2% in a 1: 1 ratio plus 1ml of hyaluronidase (150 units) making a total volume of 9 ml: Group D received: local anesthetic + 20 µg dexmedetomidine diluted with 1 mL of normal saline. Group M received: local anesthetic + magnesium sulphate 50 mg in 1 ml normal saline. Group C received local anesthetic + 1 ml normal saline. Intraocular pressure was measured with the Perkins applanation tonometer immediately before injection and at 1, 5, 10, 15 minutes (min) after injection and then at the end of the procedure, the onset and duration of lid and globe akinesia were assessed. Postoperative analgesia and the first dose of analgesic medication were also assessed.

Results:

Intraocular pressure measurements were statistically lower in group D than the other two groups at 10 and 15mins. The onset of globe and lid akinesia was the most rapid in Group D compared to the other two groups. The duration of globe and lid akinesia was the longest in group D. Time to first analgesic dose request was significantly longer in group D followed by group M then group C. Visual analogue score for pain was significantly less between group D and other two groups. There were no episodes of hypotension or bradycardia in the three groups. No side effects or complications as hemorrhage, globe perforation, brain stem anesthesia sedation were observed.

Conclusion:

In our study addition of dexmedetomidine to a peribulbar block was statistically better at reducing IOP, increasing the duration of optic anesthesia and delaying the need for postoperative analgesic dose request than magnesium.

Keywords: Peribulbar block, Dexmedetomidine, Magnesium sulphate, Intraocular pressure, Measurements, Local anesthetics, Postoperative analgesic dose.


Article Information


Identifiers and Pagination:

Year: 2018
Volume: 12
First Page: 42
Last Page: 48
Publisher Id: TOATJ-12-42
DOI: 10.2174/2589645801812010042

Article History:

Received Date: 15/5/2018
Revision Received Date: 18/6/2018
Acceptance Date: 17/7/2018
Electronic publication date: 30/08/2018
Collection year: 2018

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© 2018 Ibrahim and Salah.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: (https://creativecommons.org/licenses/by/4.0/legalcode). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


* Address correspondence this author at the Anesthesia Department Ain Shams University Hospitals, Cairo, Egypt, Tel: 01005307867; E-mails: Ahmeddrdalia66@gmail.com; drdaliaahmed1976@yahoo.com




1. INTRODUCTION

Davis and Mandel [1Davis DB II, Mandel MR. Posterior peribulbar anesthesia: An alternative to retrobulbar anesthesia. J Cataract Refract Surg 1986; 12(2): 182-4.[http://dx.doi.org/10.1016/S0886-3350(86)80040-2] [PMID: 3701637] ] in 1986 described the peribulbar block, which has delayed onset and needs a higher volume of Local Anesthetic (LA) than a retrobulbar block but believed it was safer with a lower incidences of complications [2Davis DB II, Mandel MR. Efficacy and complication rate of 16,224 consecutive peribulbar blocks. A prospective multicenter study. J Cataract Refract Surg 1994; 20(3): 327-37.[http://dx.doi.org/10.1016/S0886-3350(13)80586-X] [PMID: 8064611] , 3Riad W, Akbar F. Ophthalmic regional blockade complication rate: A single center audit of 33,363 ophthalmic operations. J Clin Anesth 2012; 24(3): 193-5.[http://dx.doi.org/10.1016/j.jclinane.2011.07.012] [PMID: 22459339] ]. However, peribulbar block can cause a transient increase in Intraocular Pressure (IOP), due to the increase in the orbital pressure caused by the injection of LA [4Johnson RW, Forrest FC. Anaesthesia of ophthalmic surgery.1996; 110: 1-29.]. Many medications have been added to local anesthetics, such as clonidine, hyaluronidase, sodium bicarbonate, muscle relaxants, and opioids for ocular blocks to hasten the onset of the block and increase anesthetic duration [5Eldeen HM, Faheem MR, Sameer D, Shouman A. Use of clonidine in peribulbar block in patients undergoing cataract surgery. Aust J Basic Appl Sci 2011; 5: 247-50.-8Abdellatif AA, El Shahawy MA, Ahmed AI, Almarakbi WA, Alhashemi JA. Effects of local low-dose rocuronium on the quality of peribulbar anesthesia for cataract surgery. Saudi J Anaesth 2011; 5(4): 360-4.[http://dx.doi.org/10.4103/1658-354X.87263] [PMID: 22144920] ].

Dexmedetomidine is a selective alpha two adrenoreceptor agonist. It provides dose-dependent sedation, analgesia, sympatholysis, and anxiolysis without relevant respiratory depression [9Paris A, Tonner PH. Dexmedetomidine in anaesthesia. Curr Opin Anaesthesiol 2005; 18(4): 412-8.[http://dx.doi.org/10.1097/01.aco.0000174958.05383.d5] [PMID: 16534267] ]. Recently, dexmedetomidine has been combined with local anesthetics in peripheral nerve block, brachial plexus block and intrathecal anesthesia and has been shown to improve the quality of both neuraxial and peripheral nerve blocks [10Gandhi RR, Shah AA, Patel I. Use of dexmedetomidine along with bupivacaine for brachial plexus block. Natl J Med Res 2012; 2: 67-9.]. In addition, dexmedetomidine, as well as other alpha 2 agonist compounds have been shown to lower IOP in animals and humans since 1966 [11Makabe R. Ophthalmologische Untersuchungen mit Dichlorophenyl aminoimidazolin. Dtsch Med Wochenschr 1966; 91: 1686.[http://dx.doi.org/10.1055/s-0028-1111575] [PMID: 5917871] ], hence making using dexmedetomidine use in posterior eye surgeries possibly beneficial.

Magnesium is a physiological calcium channel blocker and non-competitive antagonist of N-Methyl-D-Aspartate (NMDA) receptors [12Do SH. Magnesium: A versatile drug for anesthesiologists. Korean J Anesthesiol 2013; 65(1): 4-8.[http://dx.doi.org/10.4097/kjae.2013.65.1.4] [PMID: 23904932] ]. It was used successfully with a local anesthetic solution in variable regional anesthesia techniques to reduce the onset time of block and to enhance the quality and duration of anesthesia [13Malleeswaran S, Panda N, Mathew P, Bagga R. A randomised study of magnesium sulphate as an adjuvant to intrathecal bupivacaine in patients with mild preeclampsia undergoing caesarean section. Int J Obstet Anesth 2010; 19(2): 161-6.[http://dx.doi.org/10.1016/j.ijoa.2009.08.007] [PMID: 20171080] -15Gunduz A, Bilir A, Gulec S. Magnesium added to prilocaine prolongs the duration of axillary plexus block. Reg Anesth Pain Med 2006; 31(3): 233-6.[http://dx.doi.org/10.1097/00115550-200605000-00010] [PMID: 16701189] ].

This study was done to evaluate the efficacy of adding magnesium sulfate versus adding dexmedetomidine to local anesthetic mixture on the onset, duration of globe and lid akinesia, effect on intraocular pressure, and first analgesic request with peribulbar block in posterior segment eye surgeries.

2. PATIENTS AND METHODS

After obtaining institutional ethical committee approval and written informed consent, between April 2015 till December 2016, 60 ASA PS I and II patients, undergoing posterior segment surgeries aged 18 to 60 years with axial eye length ranged from 22 to 28 mm were enrolled in this prospective randomized double blinded study. Patient refusal to participate, reduced mental capacity, history of bleeding disorder, allergy to drugs used and severe cardiac/respiratory disease were excluded from the study. Non-invasive blood pressure, heart rate and oxygen saturation (SpO2) were monitored throughout the operation and for the first two postoperative hours. After obtaining intravenous access, a combination of midazolam (1 mg) and fentanyl (30 µg) were given for sedation and (possible) intra-procedural amnesia for the placement of the blocks. Supplemental oxygen was given through nasal cannula at 4 L/minute (min). Topical anesthesia to the conjunctiva was done by applying 0.4% oxybuprocaine drops directly before performing the block.

The local anesthetic solution was a combination of 8 ml of bupivacaine 0.5% and lidocaine 2% in a 1: 1 ratio plus 1ml of hyaluronidase (150 units) was added to speed tissue penetration making a total volume of 9 ml. The patients were then divided randomly using a computer generated randomization table and opaque sealed envelopes into three groups (20 patients in each group). All patients had peribulbar anesthetic block according to the medications they received: Group D (Dexmedetomidine group) received: local anesthetic 9 ml + 20 µg dexmedetomidine (Precedex, 200 µg per 2 mL; Hospira, Lake Forest, IL) diluted with 1 mL of normal saline. Group M received: local anesthetic + magnesium sulphate 50 mg in 1 ml normal saline. Group C received local anesthetic + 1ml of normal saline. The study solution for peribulbar block was prepared by the anesthesiologist who was not involved in the study. All the blocks were performed by anesthesiologist who did not participate in the remainder of the study and were blinded to the drugs given in the block.

Light orbital compression was applied for 1 min then evaluation of the onset and duration of lid and globe akinesia were assessed at 1min., 3min., 5min., 10min., 15 min. until maximum blockade and then every 15 min after surgery until complete recovery of the block. Motor block evaluation includes lid akinesia (lid closure by orbicularis and lid opening by the levator muscles). For assessment of lid akinesia, the patients were asked to open their eyelids and then squeeze them together maximally. Globe akinesia was assessed using 3-point scale for each muscle. These were scored using the movements of the extra ocular muscles in all 4 main directions on a scale of 0 to 2 [16Sarvela PJ. Comparison of regional ophthalmic anesthesia produced by pH-adjusted 0.75% and 0.5% bupivacaine and 1% and 1.5% etidocaine, all with hyaluronidase. Anesth Analg 1993; 77(1): 131-4.[http://dx.doi.org/10.1213/00000539-199307000-00026] [PMID: 8317720] ] as shown in Table 1. The block was considered satisfactory with loss of at least two movements of the 4 cardinal directions. If the patient complained of pain during the surgery, subtenon's block was administered, and the patient was excluded from the study and replaced by another one. IOP was measured with the Perkins applanation tonometer, immediately before injection (0 min), and at 1, 5, 10, 15 min after injection and then at the end of the procedure.

Table 1
Scoring system of global akinesia [16Sarvela PJ. Comparison of regional ophthalmic anesthesia produced by pH-adjusted 0.75% and 0.5% bupivacaine and 1% and 1.5% etidocaine, all with hyaluronidase. Anesth Analg 1993; 77(1): 131-4.[http://dx.doi.org/10.1213/00000539-199307000-00026] [PMID: 8317720] ].


Significant changes in heart rate and blood pressure were defined as a 20% reduction in blood pressure and heart rate respectively in relation to pre-block values. Postoperative analgesia was assessed by using the first analgesic dose request together with Visual Analogue Score (VAS) every hour for 6 hours postoperatively as 0 (no pain) to 10 cm (maximum pain imaginable). If the VAS was > 3, diclofenac 75mg was injected intramuscular. Any side effect or complication (globe perforation, hemorrhage, brain stem anesthesia or sedation) of the block were recorded, and appropriate management was done according to standard protocol.

2.1. Statistical Analysis

Data were analyzed using Statistical Program for Social Science (SPSS) version 20.0.Quantitative data were expressed as mean ± Standard Deviation (SD) or median and Interquartile Range (IQR) as appropriate. Qualitative data were expressed as frequency and percentage. Data were tested for normality.

The following tests were done

  • A one-way Analysis of Variance (ANOVA) when comparing between more than two means of parametric data.
  • Kruskall Wallis test: for multiple-group comparisons in non-parametric data.
  • If a significant difference was found, post Hoc test: Least Significant Difference (LSD) was used for multiple comparisons between different variables.
  • Chi-square (X2) test or Fisher's exact test was used in order to compare proportions between qualitative parameters.
  • Probability (P-value)
  • P-value < 0.05 was considered significant.
  • P-value > 0.05 was considered insignificant.

3. RESULTS

There were no statistically significant differences between the three groups regarding demographic data and duration of surgery (Table 2).

Table 2
Comparison among the three groups as regard the patients' characteristics and duration of surgery.


Table 3 shows that IOP measurements were comparable between the three groups at 0, 1, 5 min and at the end of operation, whereas IOP measurements were statistically lower in group D than the other two groups (M and C) at 10 and 15 mins.

Table 3
Comparison between IOP (mmHg) among the 3 groups at different times.


The onset of lid akinesia at 1 min was statistically the fastest in D group (12 patients) compared to C and M groups (2 and 4 patients respectively) and was statistically comparable between group C and group M at 1 min. Onset of lid akinesia was comparable between group D and M at 3 min and they were both faster than group C. Onset of lid akinesia was comparable between the three groups at 5, 10 and 15 min. The duration of lid akinesia was significantly shorter in group C compared to group M and D, whereas it was significantly longer in group D compared to group M (Table 4).

Table 4
Comparison between groups regarding onset and duration of lid akinesia.


The onset of globe akinesia was comparable in the three groups at 1 min. At 3 and 5 min, the onset of globe akinesia was the most rapid in Group D with significantly higher number of patients (16 patients at 3 min, 20 patients at 5 min) compared to group C (4 patients at 3 min, 16 patients at 5 min) and group M (5 patients at 3 min, 16 patients at 5 min). Onset of globe akinesia was comparable between group M and group C at 3 and 5 min. Onset of group akinesia was comparable between the three groups at 10 and 15 min. The duration of globe akinesia was significantly longer in group D compared to the other two groups and it was shorter in group C when compared to group M (Table 5). None of the cases required performance of subtenon's block.

Table 5
Comparison between groups according to onset and duration of globe akinesia.


Time to first analgesic dose request was significantly longer in group D compared to group M and C while it was significantly longer in group M compared to group C (Table 6).

Table 6
Comparison among the three groups as regard the time to first analgesic dose request.


VAS of pain was significantly less in group D compared with the other two groups at 1 and 2 hour with no significant difference between group M and C at 1 hour, while VAS at 2 hour was significantly lower in group M compared to group C. VAS was insignificantly different between the three groups at time 3, 4, 5 and 6 hours (Table 7).

There were no episodes of hypotension and bradycardia in the three groups. No side effects or complications such as (hemorrhage, globe perforation, brain stem anesthesia, sedation) were recorded.

Table 7
Comparison among the three groups as regard the VAS of pain.


4. DISCUSSION

This study demonstrated that the addition of dexmedetomidine to local anesthetics in posterior segment eye surgeries decreases the IOP when compared with both magnesium and control groups. The onset of lid and globe akinesia was the most rapid in dexmedetomidine group compared to the other two groups. The duration of lid and globe akinesia was the longest in the dexmedetomidine group. The first analgesic dose request was delayed and VAS was less for 2 hours postoperatively in the dexmedetomidine group compared to the other two groups.

Due to the importance of regional anesthesia in ophthalmic surgery when compared to general anesthesia, multiple studies have attempted to optimize and improve the quality of local anesthesia to offer more patient comfort and hemodynamic stability. However, these studies gave little attention to the acute increase in the IOP after local anesthesia injection in peribulber block as it may reach up to 25 mmHg in some patients with glaucoma [8Abdellatif AA, El Shahawy MA, Ahmed AI, Almarakbi WA, Alhashemi JA. Effects of local low-dose rocuronium on the quality of peribulbar anesthesia for cataract surgery. Saudi J Anaesth 2011; 5(4): 360-4.[http://dx.doi.org/10.4103/1658-354X.87263] [PMID: 22144920] ]. This is due to the fact that the orbit is a rigid non-compliant cavity with a volume of about 30 ml whereas the injection volume is about 10 ml so a definite rise in IOP occurs and it differs from one patient due to variation in eye size (volume) in relation to the size of the orbit and especially with glaucoma. This acute rise in IOP should be lowered even less than the baseline measures for more comfortable operative field for both the patient and the surgeon satisfaction.

Throughout our literature research, no study was found that compared dexmedetomidine with magnesium as adjuvants to local anesthesia in ophthalmic blocks.

Orbital compression was used to solve the problem of increased IOP after local anesthetic injection in ophthalmic blocks in several studies [17Constable PH, Porter EJB. Extraocular compression prior to cataract surgery: Time course of reduction and subsequent recovery of intraocular pressure. Eye (Lond) 1993; 7(Pt 6): 731-4.[http://dx.doi.org/10.1038/eye.1993.170] [PMID: 8119420] , 18Kallio H, Harju MP, Ihanamäki T, Vesti ET, Kivelä T. Reduction of intra-ocular pressure by ocular compression before combined peri- and retrobulbar block. Anaesthesia 2011; 66(4): 278-82.[http://dx.doi.org/10.1111/j.1365-2044.2011.06627.x] [PMID: 21401541] ]. In the current study, the addition of dexmedetomidine to local anesthetic in peribulbar block for posterior segment surgery attenuated the rise in IOP significantly when compared to M group and control group as dexmedetomidine, an α-2 agonist lowers the production of aqueous humor by direct vasoconstriction of afferent vessels in the ciliary body and facilitating the drainage of aqueous humor by decreasing the sympathetically mediated vasomotor tone in the ocular drainage system [19Macri FJ, Cevario SJ. Effects on aqueous humor formation and intraocular pressure. Arch Ophthalmol 1978; 96(11): 2111-3.[http://dx.doi.org/10.1001/archopht.1978.03910060491022] [PMID: 718505] , 20Vartiainen J, MacDonald E, Urtti A, Rouhiainen H, Virtanen R. Dexmedetomidine-induced ocular hypotension in rabbits with normal or elevated intraocular pressures. Invest Ophthalmol Vis Sci 1992; 33(6): 2019-23.[PMID: 1349879] ]. This finding was consistent with Jaakola et al. [21Jaakola ML, Ali-Melkkilä T, Kanto J, Kallio A, Scheinin H, Scheinin M. Dexmedetomidine reduces intraocular pressure, intubation responses and anaesthetic requirements in patients undergoing ophthalmic surgery. Br J Anaesth 1992; 68(6): 570-5.[http://dx.doi.org/10.1093/bja/68.6.570] [PMID: 1351736] ] who found that using IV and topical dexmedetomidine reduced both normal and high IOP.

This effect on IOP, however, was not observed in both the control and M groups. Magnesium sulphate which is a competitive NMDA antagonist has no effect on IOP reduction because it does not cross the blood brain barrier. Bianco et al. [22Bianco F, Candela L, Laveneziana D, Riva A. Magnesium sulfate does not inhibit the increase in ocular tonus induced by succinylcholine. Minerva Anestesiol 1987; 53(6): 369-72.[PMID: 3444542] ] found that magnesium sulphate failed to decrease IOP after succinylcholine injection.

In the present study, it was found that using dexmedetomidine locally shortened the onset of the block, prolonged its duration, and delayed the first post-operative analgesic dose. This is supported by Channabasappa et al. [23Channabasappa SM, Shetty VR, Dharmappa SK, Sarma J. Efficacy and safety of dexmedetomidine as an additive to local anesthetics in peribulbar block for cataract surgery. Anesth Essays Res 2013; 7(1): 39-43.[http://dx.doi.org/10.4103/0259-1162.113987] [PMID: 25885718] ] as they reported that the addition of dexmedetomidine to local anesthetic mixture in peribulber block shortened the onset of the block, prolonged the duration and helped significantly in decreasing IOP. Many studies have identical results that the dexmedetomidine delays the first post-operative analgesic dose request as Ge et al. [24Ge DJ, Qi B, Tang G, Li JY. Intraoperative dexmedetomidine promotes postoperative analgesia and recovery in patients after abdominal hysterectomy: A double-blind, randomized clinical trial. Sci Rep 2016; 6: 21514.[http://dx.doi.org/10.1038/srep21514] [PMID: 26903197] ] and Olutoye et al. [25Olutoye OA, Glover CD, Diefenderfer JW, et al. The effect of intraoperative dexmedetomidine on postoperative analgesia and sedation in pediatric patients undergoing tonsillectomy and adenoidectomy. Anesth Analg 2010; 111(2): 490-5.[http://dx.doi.org/10.1213/ANE.0b013e3181e33429] [PMID: 20610555] ].

Comparing dexmedetomidine to magnesium sulphate in the current study showed that dexmedetomidine use decreases the onset time of the block, prolongs its duration and delays the first analgesic dose request more than magnesium sulphate. This is consistent with other studies comparing these two drugs as adjuvants in intrathecal and epidural blocks as Shukla et al. [26Shukla D, Verma A, Agarwal A, Pandey HD, Tyagi C. Comparative study of intrathecal dexmedetomidine with intrathecal magnesium sulfate used as adjuvants to bupivacaine. J Anaesthesiol Clin Pharmacol 2011; 27(4): 495-9.[http://dx.doi.org/10.4103/0970-9185.86594] [PMID: 22096283] ] and Shahi et al. [27Shahi V, Verma AK, Agarwal A, Singh CS. A comparative study of magnesium sulfate vs dexmedetomidine as an adjunct to epidural bupivacaine. J Anaesthesiol Clin Pharmacol 2014; 30(4): 538-42.[http://dx.doi.org/10.4103/0970-9185.142852] [PMID: 25425781] ]. In the present study, magnesium sulphate use shortened the onset time of the block and increased its duration more than the control group which is in accordance with other studies as El-Hamid [28El-Hamid AM. Evaluation of the effect of magnesium sulphate vs clonidine as adjuvant to local anesthetic during peribulbar block. Ain Shams J Anesthesiol 2011; 4: 21-6.] and Gunduz et al. [29Gunduz A, Bilir A, Gulec S. Magnesium added to prilocaine prolongs the duration of axillary plexus block. Reg Anesth Pain Med 2006; 31(3): 233-6.[http://dx.doi.org/10.1097/00115550-200605000-00010] [PMID: 16701189] ].

No side effects were observed in this study which is consistent with other studies that did not report any complications [23Channabasappa SM, Shetty VR, Dharmappa SK, Sarma J. Efficacy and safety of dexmedetomidine as an additive to local anesthetics in peribulbar block for cataract surgery. Anesth Essays Res 2013; 7(1): 39-43.[http://dx.doi.org/10.4103/0259-1162.113987] [PMID: 25885718] , 28El-Hamid AM. Evaluation of the effect of magnesium sulphate vs clonidine as adjuvant to local anesthetic during peribulbar block. Ain Shams J Anesthesiol 2011; 4: 21-6.]. Further studies are needed to investigate the effect of dexmedetomidine on IOP in glocumatous eye.

CONCLUSION

In conclusion, although dexmedetomidine and magnesium sulphate are both useful adjuvants to local anesthetics used in peribulbar blocks, the advantage of dexmedetomidine effect in decreasing the IOP makes it more attractive and suitable alternative in posterior segment eye surgeries.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

This study was done after obtaining institutional ethical committee approval from Ain Shams Ethics Committee and written informed consent was taken from all the patients.

HUMAN AND ANIMAL RIGHTS

No Animals were used in this research. All human research procedures followed were in accordance with the ethical standards of the committee responsible for human experimentation (institutional and national), and with the Helsinki Declaration of 1975, as revised in 2013.

CONSENT FOR PUBLICATION

Written informed consent was taken from all the patients.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or otherwise.

ACKNOWLEDGEMENTS

Declared none.

REFERENCES

[1] Davis DB II, Mandel MR. Posterior peribulbar anesthesia: An alternative to retrobulbar anesthesia. J Cataract Refract Surg 1986; 12(2): 182-4.[http://dx.doi.org/10.1016/S0886-3350(86)80040-2] [PMID: 3701637]
[2] Davis DB II, Mandel MR. Efficacy and complication rate of 16,224 consecutive peribulbar blocks. A prospective multicenter study. J Cataract Refract Surg 1994; 20(3): 327-37.[http://dx.doi.org/10.1016/S0886-3350(13)80586-X] [PMID: 8064611]
[3] Riad W, Akbar F. Ophthalmic regional blockade complication rate: A single center audit of 33,363 ophthalmic operations. J Clin Anesth 2012; 24(3): 193-5.[http://dx.doi.org/10.1016/j.jclinane.2011.07.012] [PMID: 22459339]
[4] Johnson RW, Forrest FC. Anaesthesia of ophthalmic surgery.1996; 110: 1-29.
[5] Eldeen HM, Faheem MR, Sameer D, Shouman A. Use of clonidine in peribulbar block in patients undergoing cataract surgery. Aust J Basic Appl Sci 2011; 5: 247-50.
[6] Sarvela PJ. Comparison of regional ophthalmic anesthesia produced by pH-adjusted 0.75% and 0.5% bupivacaine and 1% and 1.5% etidocaine, all with hyaluronidase. Anesth Analg 1993; 77(1): 131-4.[http://dx.doi.org/10.1213/00000539-199307000-00026] [PMID: 8317720]
[7] Zahl K, Jordan A, McGroarty J, Gotta AW, Gotta AW. pH-adjusted bupivacaine and hyaluronidase for peribulbar block. Anesthesiology 1990; 72(2): 230-2.[http://dx.doi.org/10.1097/00000542-199002000-00003] [PMID: 2405735]
[8] Abdellatif AA, El Shahawy MA, Ahmed AI, Almarakbi WA, Alhashemi JA. Effects of local low-dose rocuronium on the quality of peribulbar anesthesia for cataract surgery. Saudi J Anaesth 2011; 5(4): 360-4.[http://dx.doi.org/10.4103/1658-354X.87263] [PMID: 22144920]
[9] Paris A, Tonner PH. Dexmedetomidine in anaesthesia. Curr Opin Anaesthesiol 2005; 18(4): 412-8.[http://dx.doi.org/10.1097/01.aco.0000174958.05383.d5] [PMID: 16534267]
[10] Gandhi RR, Shah AA, Patel I. Use of dexmedetomidine along with bupivacaine for brachial plexus block. Natl J Med Res 2012; 2: 67-9.
[11] Makabe R. Ophthalmologische Untersuchungen mit Dichlorophenyl aminoimidazolin. Dtsch Med Wochenschr 1966; 91: 1686.[http://dx.doi.org/10.1055/s-0028-1111575] [PMID: 5917871]
[12] Do SH. Magnesium: A versatile drug for anesthesiologists. Korean J Anesthesiol 2013; 65(1): 4-8.[http://dx.doi.org/10.4097/kjae.2013.65.1.4] [PMID: 23904932]
[13] Malleeswaran S, Panda N, Mathew P, Bagga R. A randomised study of magnesium sulphate as an adjuvant to intrathecal bupivacaine in patients with mild preeclampsia undergoing caesarean section. Int J Obstet Anesth 2010; 19(2): 161-6.[http://dx.doi.org/10.1016/j.ijoa.2009.08.007] [PMID: 20171080]
[14] Farouk S. Pre-incisional epidural magnesium provides pre-emptive and preventive analgesia in patients undergoing abdominal hysterectomy. Br J Anaesth 2008; 101(5): 694-9.[http://dx.doi.org/10.1093/bja/aen274] [PMID: 18820247]
[15] Gunduz A, Bilir A, Gulec S. Magnesium added to prilocaine prolongs the duration of axillary plexus block. Reg Anesth Pain Med 2006; 31(3): 233-6.[http://dx.doi.org/10.1097/00115550-200605000-00010] [PMID: 16701189]
[16] Sarvela PJ. Comparison of regional ophthalmic anesthesia produced by pH-adjusted 0.75% and 0.5% bupivacaine and 1% and 1.5% etidocaine, all with hyaluronidase. Anesth Analg 1993; 77(1): 131-4.[http://dx.doi.org/10.1213/00000539-199307000-00026] [PMID: 8317720]
[17] Constable PH, Porter EJB. Extraocular compression prior to cataract surgery: Time course of reduction and subsequent recovery of intraocular pressure. Eye (Lond) 1993; 7(Pt 6): 731-4.[http://dx.doi.org/10.1038/eye.1993.170] [PMID: 8119420]
[18] Kallio H, Harju MP, Ihanamäki T, Vesti ET, Kivelä T. Reduction of intra-ocular pressure by ocular compression before combined peri- and retrobulbar block. Anaesthesia 2011; 66(4): 278-82.[http://dx.doi.org/10.1111/j.1365-2044.2011.06627.x] [PMID: 21401541]
[19] Macri FJ, Cevario SJ. Effects on aqueous humor formation and intraocular pressure. Arch Ophthalmol 1978; 96(11): 2111-3.[http://dx.doi.org/10.1001/archopht.1978.03910060491022] [PMID: 718505]
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[21] Jaakola ML, Ali-Melkkilä T, Kanto J, Kallio A, Scheinin H, Scheinin M. Dexmedetomidine reduces intraocular pressure, intubation responses and anaesthetic requirements in patients undergoing ophthalmic surgery. Br J Anaesth 1992; 68(6): 570-5.[http://dx.doi.org/10.1093/bja/68.6.570] [PMID: 1351736]
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Endorsements



"Open access will revolutionize 21st century knowledge work and accelerate the diffusion of ideas and evidence that support just in time learning and the evolution of thinking in a number of disciplines."


Daniel Pesut
(Indiana University School of Nursing, USA)

"It is important that students and researchers from all over the world can have easy access to relevant, high-standard and timely scientific information. This is exactly what Open Access Journals provide and this is the reason why I support this endeavor."


Jacques Descotes
(Centre Antipoison-Centre de Pharmacovigilance, France)

"Publishing research articles is the key for future scientific progress. Open Access publishing is therefore of utmost importance for wider dissemination of information, and will help serving the best interest of the scientific community."


Patrice Talaga
(UCB S.A., Belgium)

"Open access journals are a novel concept in the medical literature. They offer accessible information to a wide variety of individuals, including physicians, medical students, clinical investigators, and the general public. They are an outstanding source of medical and scientific information."


Jeffrey M. Weinberg
(St. Luke's-Roosevelt Hospital Center, USA)

"Open access journals are extremely useful for graduate students, investigators and all other interested persons to read important scientific articles and subscribe scientific journals. Indeed, the research articles span a wide range of area and of high quality. This is specially a must for researchers belonging to institutions with limited library facility and funding to subscribe scientific journals."


Debomoy K. Lahiri
(Indiana University School of Medicine, USA)

"Open access journals represent a major break-through in publishing. They provide easy access to the latest research on a wide variety of issues. Relevant and timely articles are made available in a fraction of the time taken by more conventional publishers. Articles are of uniformly high quality and written by the world's leading authorities."


Robert Looney
(Naval Postgraduate School, USA)

"Open access journals have transformed the way scientific data is published and disseminated: particularly, whilst ensuring a high quality standard and transparency in the editorial process, they have increased the access to the scientific literature by those researchers that have limited library support or that are working on small budgets."


Richard Reithinger
(Westat, USA)

"Not only do open access journals greatly improve the access to high quality information for scientists in the developing world, it also provides extra exposure for our papers."


J. Ferwerda
(University of Oxford, UK)

"Open Access 'Chemistry' Journals allow the dissemination of knowledge at your finger tips without paying for the scientific content."


Sean L. Kitson
(Almac Sciences, Northern Ireland)

"In principle, all scientific journals should have open access, as should be science itself. Open access journals are very helpful for students, researchers and the general public including people from institutions which do not have library or cannot afford to subscribe scientific journals. The articles are high standard and cover a wide area."


Hubert Wolterbeek
(Delft University of Technology, The Netherlands)

"The widest possible diffusion of information is critical for the advancement of science. In this perspective, open access journals are instrumental in fostering researches and achievements."


Alessandro Laviano
(Sapienza - University of Rome, Italy)

"Open access journals are very useful for all scientists as they can have quick information in the different fields of science."


Philippe Hernigou
(Paris University, France)

"There are many scientists who can not afford the rather expensive subscriptions to scientific journals. Open access journals offer a good alternative for free access to good quality scientific information."


Fidel Toldrá
(Instituto de Agroquimica y Tecnologia de Alimentos, Spain)

"Open access journals have become a fundamental tool for students, researchers, patients and the general public. Many people from institutions which do not have library or cannot afford to subscribe scientific journals benefit of them on a daily basis. The articles are among the best and cover most scientific areas."


M. Bendandi
(University Clinic of Navarre, Spain)

"These journals provide researchers with a platform for rapid, open access scientific communication. The articles are of high quality and broad scope."


Peter Chiba
(University of Vienna, Austria)

"Open access journals are probably one of the most important contributions to promote and diffuse science worldwide."


Jaime Sampaio
(University of Trás-os-Montes e Alto Douro, Portugal)

"Open access journals make up a new and rather revolutionary way to scientific publication. This option opens several quite interesting possibilities to disseminate openly and freely new knowledge and even to facilitate interpersonal communication among scientists."


Eduardo A. Castro
(INIFTA, Argentina)

"Open access journals are freely available online throughout the world, for you to read, download, copy, distribute, and use. The articles published in the open access journals are high quality and cover a wide range of fields."


Kenji Hashimoto
(Chiba University, Japan)

"Open Access journals offer an innovative and efficient way of publication for academics and professionals in a wide range of disciplines. The papers published are of high quality after rigorous peer review and they are Indexed in: major international databases. I read Open Access journals to keep abreast of the recent development in my field of study."


Daniel Shek
(Chinese University of Hong Kong, Hong Kong)

"It is a modern trend for publishers to establish open access journals. Researchers, faculty members, and students will be greatly benefited by the new journals of Bentham Science Publishers Ltd. in this category."


Jih Ru Hwu
(National Central University, Taiwan)


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