Effectiveness and Safety of Single Percutaneous Peribulbar Block Using Magnesium Sulphate as an Adjuvant to Local Anesthetics Versus the Standard Peribulbar Block for Strabismus Surgery in Adults
Norhan Aly Sherif1, *, Mayada Khairy Mohamad1, Sameh Galal Taher2, Ahmed Abdou Hannon2, Hesham Mohamed Salem1
Identifiers and Pagination:Year: 2019
First Page: 100
Last Page: 105
Publisher Id: TOATJ-13-100
Article History:Received Date: 12/07/2019
Revision Received Date: 14/09/2019
Acceptance Date: 24/09/2019
Electronic publication date: 24/10/2019
Collection year: 2019
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.
Peribulbar anesthesia in ophthalmic surgeries is limited by delayed and/or incomplete orbital akinesia and inadequate operative and postoperative analgesia.
The aim of this study was to assess the safety and effectiveness of a single percutaneous peribulbar block technique with 100 mg magnesium sulphate added to the local anesthetics used compared with the standard peribulbar block technique in adult strabismus surgery.
A total of 54 consecutive patients undergoing strabismus surgery were included in the study. They were divided into two equal groups (27 patients each). In group I, 1 ml (100 mg/ml) magnesium sulphate added to a mixture of 2 ml lidocaine 2%, 2 ml bupivacaine 0.5% and 1 ml hyaluronidase (150 units/ml) was administered through a single percutaneous peribulbar injection with a short (1 inch) needle, while in group II, a mixture of 1 ml saline added to 2 ml lidocaine 2%, 2 ml bupivacaine 0.5% and 1 ml hyaluronidase (150 units/ml) was administered using the standard peribulbar block technique. The collected data included patient's baseline characteristics, perioperative and early postoperative outcomes and follow-up data.
The elapsed time before the onset of anesthesia and akinesia of the globe was significantly shorter in group I compared with group II (1.9 ± 0.7 vs. 3.9 ± 1.0 min, p < 0.001; 2.3 ± 0.7 vs. 4.4 ± 1.2 min, p < 0.001 respectively), and the duration of anesthesia was significantly longer in group I compared with group II (180.0 ± 0.0 vs. 43.0 ± 8.5 min, p < 0.001). The median VAS pain score was significantly lower in group I compared with group II (1.0 vs. 4.0, p < 0.001), and the patient's satisfaction was significantly higher in group I compared with group II (100.0% vs. 25.9%, p < 0.001).
Co-administration of 100 mg magnesium sulphate with the local anesthetics was effective and safe. It achieved suitable conditions to start surgery rapidly. Further, it improved the quality of operative conditions and patient satisfaction.
Regional anesthesia has been considered the standard method of anesthesia in ophthalmic surgery. It has shown high success rate and safety in different ocular procedures including difficult and extended time surgeries . Compared with general anesthesia, the use of regional anesthesia has the advantages of quick patient recovery and shorter hospital stay .
Retrobulbar and peribulbar blocks are considered the two main approaches of regional anesthesia in eye surgery. They can achieve suitable conditions for intraocular surgeries, including analgesia and profound akinesia of the globe . However, retrobulbar block technique has many complications such as brainstem anesthesia, globe perforation and retrobulbar hemorrhage . Hence, the Peribulbar Block Anesthesia (PBA) has gained wide acceptance in ophthalmic anesthetic practice .
The peribulbar block is a needle-based technique that varies from the retrobulbar block in terms of the depth and angulation of needle placement within the orbit . The rate of major complications under peribulbar anesthesia was reported to be 0.006%. However, its main disadvantage is the need for a larger volume of local anesthetic agent .
Rizzo et al.  evaluated the efficacy and safety of a single medial percutaneous injection technique using a small volume of anesthetic for ocular peribulbar anesthesia, and they reported that it was simple and effective in producing an adequate motor block and surgical anesthesia.
To address the drawbacks of PBA, many additive drugs to local anesthesia have been investigated. These include hyalu-ronidase, adrenaline and sodium bicarbonate , clonidine , corticosteroids  and neuromuscular blocking agents [11, 12]. However, these agents are also associated with some side-effects such as allergic reactions, bradycardia, sedation, dryness of mouth and systemic neuromuscular blockade .
Magnesium has been used with a local anesthetic solution in different regional anesthesia techniques to decrease the onset time of block and to increase the quality and duration of anesthesia [14-16]. Few studies evaluated magnesium sul-phate as an adjuvant with the local anesthetic for a peribulbar block in different eye surgeries [17-19], but no previous studies evaluated it specifically in strabismus surgery.
Currently, no ideal adjuvant for the peribulbar block has been reported. Therefore, the aim of this study was to assess the safety and effectiveness of a single percutaneous peribulbar block technique with 100 mg magnesium sulphate added to the local anesthetics used compared with the standard peribulbar block technique in adult strabismus surgery.
2. PATIENTS AND METHODS
2.1. Study Type and Setting
This single center, prospective cohort study was carried out at the Anesthesia Department, Research Institute of Ophthalmology, Cairo, Egypt during the period from January 2018 to January 2019.
2.2. Inclusion Criteria
- Age more than 16 years old.
- ASA I and II (Physical status, American Society of Anesthesiologists).
- Concomitant strabismus.
- Patients with previous complications and those refusing general anesthesia.
2.3. Exclusion Criteria
- Age less than 16 years old.
- ASA III and IV.
- Uncooperative patients.
- Previous extraocular or strabismus surgery.
- Allergy to local anesthesia.
- Patient refusal of local anesthesia.
2.4. Data Collection
A total of 54 consecutive patients undergoing strabismus surgery were included in the study. They were divided into two equal groups (27 patients each). In group I, 1 ml (100 mg/ml) magnesium sulphate added to a mixture of 2 ml lidocaine 2%, 2 ml bupivacaine 0.5% and 1 ml hyaluronidase (150 units/ml) was administered using single percutaneous peribulbar injection with a short (1 inch) needle as described by Rizzo et al. . While in group II, a mixture of 1 ml saline added to 2 ml lidocaine 2%, 2 ml bupivacaine 0.5% and 1 ml hyaluronidase (150 units/ml) was administered using the standard peribulbar block technique. The collected data included patients’ baseline characteristics, perioperative and early postoperative outcomes and follow-up data.
2.5. Outcome Parameters
- Ocular anesthesia, akinesia (onset & duration)
- Forced duction test
- Muscle stretch
- Pain score: The intensity of pain was recorded using a numeric pain rating Visual Analog Scale (VAS).
- Postoperative alignment
- Need for intraoperative sedation or local anesthesia supplement
2.6. Statistical Analysis
Data analysis was carried out using SPSS version 22. All numerical variables were checked for normality by Shapiro Wilk test. Normally distributed numerical variables were presented as mean ± Standard Deviation (SD), and differences between the two groups were tested using Independent T-test. Abnormally distributed numerical variables were expressed as the median and interquartile range (25th - 75th percentile) and differences between the two groups were tested using Mann-Whitney test. Categorical variables were summarized as frequencies and percentages, and the association between the variables was tested using X2 tests (Pearson's Chi square for independence or Fisher Exact Tests as appropriate). A p-value of < 0.05 was considered statistically significant.
Age and ASA physical status of the studied patients were comparable between the two groups (p > 0.05) as shown in Table 1.
The mean elapsed time before the onset of anesthesia and akinesia of the globe was significantly shorter in group I compared with group II (anesthesia: 1.9 ± .7 min and 3.9 ± 1.0 min, akinesia: 2.3 ± 0.7 min and 4.4 ± 1.2 min, respectively). Additionally, the mean duration of anesthesia was significantly higher in group I (180.0 ± 0.0 min) than in group II (43.0 ± 8.5 min) (Table 2).
During surgery, a positive forced duction test was significantly lower in group I (p = 0.046). Muscle stretch was normal in 24 (88.9%) patients in group I compared to only 5 (18.5%) patients in group II with a statistically significant difference (p < 0.001). There was no need for sedation in group I compared to 17 (63.0%) patients in group II with a statistically significant difference (p < 0.001). Concerning oculo-cardiac reflex, it did not occur in group I (0.0%) but occurred in 9 (33.3%) patients in group II with a statistically significant difference (p = 0.002). The operation was performed successfully in all patients with no significant difference regarding postoperative alignment between both the groups (p = 1.0). During postoperative follow-up, the median VAS pain score was significantly lower in group I compared with group II (<0.001). The need for postoperative analgesia was significantly lower in group I (0.0%) than group II (48.1%). Patient's satisfaction was significantly higher in group I compared to group II (100.0% vs. 25.9% respectively) (Table 3).
|Groups||Tests of Significance|
N = 27
N =2 7
|Mean ± SD||40.6 ± 13.4||40.6 ± 13.3|
|Groups||Tests of Significance|
N = 27
N = 27
|Anesthesia Onset (Min)||Minimum- Maximum||1.0-3.0||2.0-6.0||< 0.001*|
|Mean±SD||1.9 ±0.7||3.9 ±1.0|
|Anesthesia Duration (Min)||Minimum- Maximum||180.0-180.0||30.0-60.0||< 0.001*|
|Mean±SD||180.0 ±0.0||43.0 ±8.5|
|Akinesia Onset (Min)||Minimum- Maximum||1.0-4.0||3.0-7.0||< 0.001*|
|Mean±SD||2.3 ±0.7||4.4 ±1.2|
|Groups||Tests of Significance|
|Forced Duction Test||Negative palsy||13||48.1%||6||22.2%||0.046*|
Mechanical restriction: resistance
|Need for Sedation||No||27||100.0%||10||37.0%||<0.001*|
This study demonstrated favorable effects of 100 mg magnesium sulphate as an adjuvant to a mixture composed of 2 ml lidocaine 2%, 2 ml bupivacaine 0.5% and 1 ml hyaluronidase (150 units/ml) in peribulbar anesthesia for strabismus surgery in adults. It accelerated the onset of sensory block and globe akinesia and prolonged the duration of globe anesthesia. Thus, time for suitable conditions to start surgery was enhanced. Moreover, magnesium sulphate addition enhanced the quality of operative conditions. It was associated with more normal muscle stretch, with no need for intraoperative sedation and complete prevention of the life-threatening oculocardiac reflex. Also, it increased the patient's satisfaction with no need for postoperative analgesia, besides the absence of any marked side effects.
Magnesium is an important cation, which is necessary for enzymatic reactions in the human body . The anesthetic and analgesic effects of magnesium observed in this study could be explained by its function as a physiological calcium channel blocker and noncompetitive antagonist of N-methyl-D-aspartate receptors . Also, magnesium sulphate has a high therapeutic index and cost-effectiveness . Accordingly, appropriate use of magnesium sulphate would improve surgical outcome and patients' satisfaction in strabismus surgery.
In agreement with our findings, Sinha et al.  concluded that the addition of 50 mg magnesium sulphate to the lidocaine-bupivacaine mixture for peribulbar block in adult patients scheduled for elective ophthalmic surgery accelerates the onset of akinesia without any obvious side effect. Likewise, effective and safe use of 50 mg magnesium sulphate in patients who underwent elective posterior segment surgery was reported. Impact of magnesium addition was evidenced by fast onset of globe block, long duration of akinesia and analgesia with excellent patient and surgeon satisfaction, besides the absence of systemic or local complication . Similarly, Abd El-hamid  reported that the administration of magnesium as a co-factor to the local anesthetic in peribulbar anesthesia for posterior segment eye surgeries accelerated the onset of sensory and motor block without any side effects.
A recent study assessed the efficacy and safety of addition of dexmedetomidine versus magnesium sulphate to the local anesthetic mixture for peribulbar block in cataract surgery. Both the drugs enhanced the onset of globe anesthesia and akinesia with no significant changes in the hemodynamic measurements .
On the other hand, the addition of 50 mg magnesium sulphate to local anesthesia in older (40-80 years-old) patients who underwent cataract surgery did not show any benefit regarding the onset of block or akinesia score . AbdAlali et al.  reported better analgesic and anesthetic effects of rocuronium as an additive to local anesthetic drugs in the peribulbar block than magnesium sulphate. Additionally, Abu Elyazed and Mostafa compared 50 mg of magnesium sulphate and 20 µg fentanyl as additives to a mixture of lidocaine 2% and bupivacaine 0.5% plus 150 IU of hyaluronidase. They found that magnesium could accelerate the onset of globe anesthesia, akinesia and lid akinesia in comparison to the control group, but still can significantly slower than the fentanyl group .
Mogahed et al.  compared 50 mg versus 100 mg of magnesium sulphate in peribulbar block in cataract surgery. They observed more rapid onset and prolonged duration of akinesia and reduction of the postoperative analgesic requirements with a higher dose of magnesium sulphate. This supports our findings, and together they provide an evidence for using 100 mg regimen of magnesium sulphate to achieve better outcomes. Fortunately, the use of 100 mg magnesium sulphate in the present study was safe with no noticed adverse effects.
Supporting evidence of anesthetic effects of magnesium sulphate was previously recorded. Gunduz et al.  found prolonged sensory and motor block of the axillary nerve when 150 mg magnesium was added to prilocaine without any side effects. When added to bupivacaine, magnesium sulphate improved the onset and the level of the epidural block as well .
Strabismus surgery is frequently associated with OCR, and unfavorable consequences of the reflex such as cardiac arrest and sudden death might occur. So, it is essential to accurately control the heart rate during ophthalmic surgeries . Different modalities of treatments have been investigated to prevent or alleviate OCR with conflicting findings . This was considered in our study, and it was observed that magnesium sulphate addition completely inhibited the occurrence of OCR reflex. It is known that OCR reflex is triggered by pressure on the globe, conjunctiva and orbital structures and traction on the extraocular muscles, and its complete inhibition with magnesium sulfate addition to the local anesthetic might be attributed to the deep globe anesthesia and analgesia .
Co-administration of 100 units magnesium sulphate with the local anesthetic was effective and safe. It achieved suitable conditions to start surgery rapidly and improved the quality of operative conditions and patient satisfaction.
LIST OF ABBREVIATIONS
|PBA||= Peribulbar Block Anesthesia|
|ASA||= American Society of Anesthesiologists|
|VAS||= Visual Analog Scale|
|OCR||= Oculo-Cardiac Reflex|
|SD||= Standard Deviation|
ETHICS APPROVAL AND CONSENT TO PARTICIPATE
The protocol of this study was approved by the Research Ethics Committee of the Research Institute of Ophthalmology, Cairo, Egypt. All patients’ data were kept confidential after assigning a code number to each patient, known only by the researchers.
HUMAN AND ANIMAL RIGHTS
No animals were used in the study. All humans 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 2008.
CONSENT FOR PUBLICATION
Informed consent was obtained from each patient.
AVAILABILITY OF DATA AND MATERIALS
CONFLICT OF INTEREST
The authors declare no conflict of interest, financial or otherwise.