Parabulbar Anesthesia for Primary Vitreoretinal Surgery

Parabulbar Anesthesia for Primary Vitreoretinal Surgery Tarun Sharma, MD, Lingam Gopal, MD, Sunil Parikh, MD, Mahesh P. Shanmugam, MD, Sengamedu S. Badrinath, FRCS(C), Bickol N. Mukesh, MSc, MPhil Purpose: The efficacy and safety of parabulbar anesthesia was investigated prospectively in 100 patients undergoing primary vitreoretinal surgery. Methods: The technique involved three steps: (1) orbicularis oculi injection, (2) subconjunctival injection, and (3) sub-Tenon irrigation. The effect of anesthesia was graded 0 to 5 depending on inadequate anesthesia-akinesia with or without local supplementation. Ninety-three patients underwent vitrectomy without buckfing and 4 with an encircling band; 3 had scleral buckling. Mean duration of surgery was 89.38 minutes. Results: In 69% of patients (grades 4 and 5), no supplementation was required and in 31% (grades 1-3}, local supplementation was needed for inadequate anesthesia or akinesia or both. No ocular or systemic complication occurred. Early onset of anesthesia correlated with adequate anesthesia throughout the procedure (P < 0.04}. Conclusions: Parabulbar anesthesia is a safe and effective technique of local anesthesia in patients undergoing primary vitreoretinal surgery. Ophthalmology 1997; 104:425-428

Conventional retrobulbar anesthesia, used to administer local anesthesia in patients undergoing vitreoretinal surgery, has been associated with complications such as grand mal seizures, ocular perforation, cardiopulmonary arrest, injection into the subarachnoid space, retrobulbar hemorrhage, and optic nerve injury. 1- 6 Peribulbar anesthesia avoids some of these complications. Unfortunately, globe perforation has also been reported with this technique.7-10 Critics of peribulbar anesthesia cite a lower rate of adequate block, a delayed and inconsistent onset of anesthesia, the possible need for multiple injections, and a large dose of anesthetic resulting in tight orbit. 11 - 16 There also is a waiting period of 15 minutes for the super pinkie to obtain adequate anesthesia and akinesia. 16 - 18 Parabulbar anesthesia (sub-Tenon), which provides rapid anesthesia and eliminates the risks associated with Originally received: December 21, 1995. Revision accepted: October 2, 1996. From the Vitreoretina1 Service, Sankara Nethralaya, Madras, India. Presented at the American Academy of Ophthalmology Annual Meeting, Atlanta, November 1995. Supported by Vision Research Foundation, 18 College Road, Madras 6, India. Reprint requests to Tarun Sharma, MD, Vision Research Foundation, 18 College Road, Madras 600 006, India.

blind placement of a needle behind the eye, 19 - 21 has not been evaluated regarding onset of anesthesia, volume of anesthetic mixture, need for local or systemic supplementation, and grading of its efficacy. Therefore, the current prospective study was designed to evaluate the efficacy and safety of parabulbar anesthesia in patients undergoing primary vitreoretinal surgery.

Materials and Methods One hundred consecutive patients underwent primary vitreoretinal surgery while receiving parabulbar anesthesia between July and November 1994. The exclusion criteria included age younger than 18 years, previous retinal surgery, active ocular infection, known allergy to xylocaine or bupivacaine, mental retardation, or patient's opting for general anesthesia. No preoperative sedation was administered. The parabulbar anesthesia was administered in three stages: (1) orbicularis oculi injection; (2) subconjunctival injection; and (3) sub-Tenon irrigation. The patient was positioned on the operating table and topical 4% lignocaine was instilled into the conjunctival sac. The anesthetic mixture consisted of a 50:50 mixture of 2.0% lignocaine and 0.5% bupivacaine with hyaluronidase (25 U/

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Figure 1. Subconjunctival injection at the commencement of the surgical procedure.

ml). The orbicularis oculi injection was similar to superficial injection of peribulbar anesthesia as described by Davis and Mandel. 16 A small skin wheel was raised by injecting 0.5 ml of anesthetic inferomedial to the lateral canthus. The needle was then advanced more deeply and 0.5 to 1.00 ml was infiltrated in the plane of the orbicularis oculi. The procedure was then repeated in the upper lid superomedial to the lateral canthus. Because the branches of the seventh nerve enter the lids from the lateral side, the injection in the upper lid can also be given temporally just above and medial to the lateral canthus. Subconjunctival injection was given after the routine sterile preparation and draping. With the patient looking down, the superior bulbar conjunctiva was tented up with a toothed forceps. A 30-gauge needle was used to inject approximately 1.0 to 1.5 ml of anesthetic mixture beneath the conjunctiva to form a bleb around the circumference of the limbus (Fig 1). The anesthetized conjunctiva was incised to bare sclera with a curved tenotomy scissors. A standard peritomy was performed. If pars plana vitrectomy without scleral buckling was contemplated, a blunt dissection was done posterior to the muscle ring, as performed routinely in scleral buckling surgery, to make tunnels along the inferior border of the lateral rectus and superior border of the medial rectus. Thereafter, subTenon irrigation was done using a blunt-tipped, 19-gauge irrigating cannula, by keeping the tip either at or just posterior to the equator of the eyeball. (Fig 2). Approximately 1.5 to 2.0 ml of anesthetic mixture per quadrant (lower temporal and upper nasal) was then placed in the tunnels between the Tenon's capsule and the globe. Adequate anesthesia and its onset were determined immediately after sub-Tenon infiltration by holding bulbar conjunctiva and lateral rectus muscle insertion. Motor akinesia was ascertained by intraoperative ocular movements in all directions. Patients were encouraged to inform the surgeon about pain during the surgery. Whenever required, the supplement anesthetic mixture was irrigated into the sub-Tenon space. The efficacy of anesthesia was graded by the surgeon as follows: grade 0, inadequate

426

anesthesia or akinesia or any other complication necessitating termination of the operative procedure, despite supplementation; grade 1, inadequate akinesia and anesthesia, supplementation required; grade 2, inadequate akinesia, adequate anesthesia, supplementation required; grade 3, inadequate anesthesia, adequate akinesia, supplementation required; grade 4, adequate anesthesia, inadequate akinesia, no supplementation required; and grade 5, adequate anesthesia and akinesia throughout surgery without , any supplementation. Other variables noted were preoperative diagnosis, type of surgery, onset of anesthetic effect, volume of anesthetic mixture, onset of pain during surgery, type of supplementation, and duration of surgery. All vital signs were monitored throughout the surgery. Postoperative pain- vomiting and the need for analgesics or antiemetics or both were also recorded. The chi-square test and a Fisher's exact test were used, and differences were considered significant at P = 0.05.

Results Of the 100 patients who underwent parabulbar anesthesia, 75 were men and 25 were women, at the mean age of 47 years (range, 19-84 years). Preoperative diagnosis was proliferative vascular retinopathy in 90 patients, retinal detachment in 9 patients, and inflammatory vitreous membrane in 1 patient. Surgical procedures are listed in Table 1. Most patients underwent pars plana vitrectomy with associated procedures such as endolaser or fluid-gas exchange or both. Mean duration of surgery was 89.4 minutes (range, 30-210 minutes). An adequate anesthetic effect was obtained within 1 to 2 minutes in 94% of patients and within 3 to 5 minutes in the remaining 6% of patients. The volume of the anesthetic mixture was less than 10 ml in 92% of the patients (Table 2). Parabulbar anesthesia was graded as grade 5 in 56 patients, grade 4 in 13, grade 3 in 19, grade 2 in 5, and grade 1 in 7 patients. No patient was graded at 0. Thirty-four patients experienced some amount of pain during the surgery at a mean interval of 69.8 minutes after the start of surgery. Thirty patients needed local supplementation (i.e., reinfiltration of anesthetic mixture

Figure 2. A, opening up of the sub· Tenon space. B, sub-Tenon irrigation.

Sharma et al · Parabulbar Anesthesia Table 1. Vitreoretinal Surgical Procedures (n = 100) Procedures Vitrectomy and associated procedures Lensectomy + vitrectomy + gas/silicone oil, endolaser Scleral buckling Vitrectomy + encircling and associated procedures Lensectomy + vitrectomy + endolaser Lensectomy + vitrectomy + encircling + silicone oil injection + IOFB removal + endolaser Lensectomy + vitrectomy + encircling + gas + endolaser

No. of Patients

87 4 4 2 2

IOFB = intraocular foreign body.

in the sub-Tenon space), and only 1 patient needed both local and systemic supplementation by intravenous 5-mg injection of diazepam. The need for local supplementation was 57.1% in those who required scleral buckling or encircling or both, compared to 28% in those who did not (P = 0.02). Likewise, patients undergoing surgery for a longer duration needed more intraoperative supplementation and, thereby, a larger volume of anesthetic mixture. Parabulbar anesthesia was found to be more effective in patients in whom the onset of anesthesia was rapid, after the infiltration (P < 0.04) (Fig 3). No correlation was found with respect to patient's age and sex. Postoperative pain (within 24 hours) occurred in 67 patients with 60 patients requiring analgesics. Postoperative vomiting occurred in eight patients. In three patients, subconjunctival hemorrhage was noted after the subconjunctival injection, and in two patients the orbit became tight after the sub-Tenon infiltration. One patient was apprehensive about surgery until sub-Tenon irrigation was given, and in another patient increased blood pressure during surgery was attributed to intraoperative pain, causing intraocular bleeding during diabetic vitrectomy. No other significant systemic complication occurred during or after the surgery.

Discussion Both retrobulbar and peribulbar anesthesia involve the insertion of a needle in the retrobulbar and peribulbar spaces, respectively. Consequently, both techniques have the potential for causing vision-threatening complications.8·10·22 Parabulbar anesthesia (sub-Tenon), an alternative technique of local anesthesia, has the advantage of being performed under direct observation and thereby helps avoid the risk of globe perforation. This technique allows the surgeon to place the anesthetic mixture of lesser volume in the correct anatomic space, resulting in rapid anesthesia in the majority of patients. The second main advantage of parabulbar anesthesia is the faster onset of action. The anesthetic mixture is placed in the

inferior temporal quadrant, where the intermuscular septa are absent and intraconal fat is arranged in large fusiform lobule, held in loose alignment, making the diffusion of anesthetic mixture faster. 23 Likewise, placement of anesthetic mixture along the upper border of the medial rectus is advantageous, because, of all the rectus muscles, only the medial is separated significantly from the adjacent bony orbital wall by an adipose tissue compartment, communicating superiorly and inferiorly.Z4 Thus, bulk spread of local anesthetic injected into this medial compartment extends into these compartments and into the orbital apex posteriorly. No intraoperative supplementation was required in 69% of the patients in this study. Conversely, when peribulbar anesthesia was used for vitreoretinal surgery, intraoperative supplementation was needed in 36.8% to 83.0% of patients. 16•25 •26 Recently, the need for a separate seventh cranial nerve block has been questioned. When higher volumes of local anesthetics admixed with hyaluronidase are injected into the orbit, effective spread from the orbit through the orbital septum occurs to achieve akinesia of the orbicularis oculi musculature. 27 '28 The periconal block is particularly effective in obtunding the tone in the central orbicularis muscle. 29 However, in parabulbar anesthesia, a low volume (1.5-2 ml) is infiltrated in the subTenon space. Adequate anesthesia and akinesia by separate orbicularis oculi block may be necessary to place a lid suture. Lid sutures may provide improved exposure of the operative field when the surgeon decides to remove the lid speculum intraoperatively to facilitate passing of either a #240 band or a scleral buckle. If the eye speculum is not removed, the corneal epithelium may be damaged by contact with the speculum as the eyeball is rotated. We preferred a separate orbicularis oculi block to supplement parabulbar anesthesia. In the current study, a long-acting but slow-onset agent, bupivacaine, was admixed with a fast onset, shorter-acting agent, lidocaine, to produce the combined advantages of faster onset and longer action. 30 Despite inadequate akinesia, no intraoperative supplementation was attempted in 19 patients in this study. Probably, minimal ocular movements are controlled by the bimanual instrumentation during pars plana surgery. However, while performing complex maneuvers, even minimal movement can increase the risks of iatrogenic complications. Therefore, it is prudent to supplement the block if the operating surgeon judges that inadequate akinesia may compromise the surgical goals. This study also highlighted the important fact that there was excellent block

Table 2. Volume of Anesthetic Mixture (n = 100) Volume (ml)

<5

5-7

8-10 11-13 13-15

No. of patients

20

43

29

5

3

427

J5 JO

p

25

a l

i

~

11

l

lO

-

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lmmHiiatr

D D D

10.


11.

J-5 \lin

15

12.

10

13. flica c~·

Figure 3. Comparison of onset of anesthesia vs. efficacy of block.

14. 15. 16.

throughout the procedure in patients in whom the onset of anesthesia was rapid. If the tip of the irrigating cannula is not placed at or just posterior to the equator, the anesthetic mixture may not reach the posterior ciliary nerves. Because the intraoperative pain usually begins at 70 minutes after the start of the surgery, the surgeon may supplement the block late in the procedure by irrigating the anesthetic mixture into sub-Tenon space. Parabulbar anesthesia is effective and safe for patients undergoing primary vitreoretinal surgery.

17. 18. 19. 20. 21.

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