A comparative study between 25 × 0.70 mm and 20 × 0.55 mm needles for retrobulbar block with small volume of anesthetic for the treatment of cataracts by phacoemulsification

Abstracts

JUSTIFICATIVA E OBJETIVOS: Comparar a qualidade e a segurança da anestesia retrobulbar (ARB) para tratamento de catarata por facoemulsificação utilizando agulhas de dois diferentes tamanhos: 25 x 0,70 mm ou 20 x 0,55 mm. MÉTODOS: Seleção prospectiva de candidatos a bloqueio oftálmico para tratamento de catarata por facoemulsificação. Após sedação e monitorização padronizada, foi realizada anestesia retrobulbar (ARB) em punção única ínfero-lateral com 4 mL de ropivacaína 1%, contendo hialuronidase. No Grupo I (GI) a agulha utilizada foi de 25 x 0,70 mm e no Grupo II (GII), de 20 x 0,55 mm. Em um paciente de cada grupo foram realizadas tomografias computadorizadas no momento da realização do bloqueio oftálmico e após cinco minutos da administração da solução anestésica com contraste radiológico. A mobilidade ocular foi avaliada após três, cinco e dez minutos. Por meio de um questionário padronizado, foram comparadas a incidência de complicações entre os grupos, a satisfação dos pacientes e cirurgiões. RESULTADOS: Foram avaliados 54 pacientes adultos (27 por grupo). Nenhum paciente relatou dor ou percepção luminosa intra-operatória. O procedimento anestésico foi considerado muito bom (MB) ou excelente (E) em 96,30% dos casos nos dois grupos. A mesma avaliação foi feita por 100% dos pacientes. Não houve diferença na necessidade de repetição do bloqueio entre os grupos (p = 1,0). O GI apresentou menor mobilidade ocular aos 3 minutos (p = 0,03). Observou-se o posicionamento da agulha em posição retrobulbar intraconal em ambos os grupos. A dispersão anestésica foi similar entre os grupos aos 5 minutos. CONCLUSÃO: A ARB realizada com a agulha de 20 × 0,55 mm, em punção única ínfero-lateral, utilizando baixas doses de anestésicos, se apresenta como uma opção eficaz e segura para tratamento de catarata por facoemulsificação.

CIRURGIA, Oftálmica; CIRURGIA, Oftálmica; TÉCNICAS ANESTÉSICAS, Regional

SCIENTIFIC ARTICLE

A comparative study between 25 × 0.70 mm and 20 × 0.55 mm needles for retrobulbar block with small volume of anesthetic for the treatment of cataracts by phacoemulsification^*

Estudio comparativo entre agujas de 25 × 0,70 mm o de 20 × 0,55 mm para la anestesia retrobulbar con bajo volumen anestésico en tratamiento de catarata por facoemulsificación

Haroldo Maciel Carneiro, M.D.^I; Kim Irsen Santos Teixeira, M.D.^II; Marcos Pereira de Ávila, M.D.^III; Onofre Alves Neto, TSA, M.D.^IV; Rosanna Zacharias Hannouche, M.D.^V; Leopoldo Magacho, M.D.^VI

^IAnestesiologista; Mestrando em Ciências da Saúde (Oftalmologia); Membro dos CET HC/UFG e Humberto Bufaiçal; Coordenador do Serviço de Anestesiologia do CEROF/HC/UFG

^IIMédico Radiologista; Professor Doutor do Departamento de Radiologia e Diagnóstico por Imagem HC-UFG; Professor Doutor do Departamento de Radiologia e Diagnóstico por Imagem HC-UFG

^IIIProfessor Doutor do Departamento de Oftalmologia; Chefe do CEROF/HC/UFG

^IVProfessor Adjunto de Anestesia da UFG; Responsável pelo CET/SBA do HC-UFG

^VOftalmologista; Mestranda em Ciências da Saúde, UFG

^VIOftalmologista; Coordenador do Setor de Glaucoma do CEROF/HC/UFG; Professor da Pós-Graduação da UFG; Doutor em Ciências Médicas (Oftalmologia) pela UNICAMP

Correspondence to

SUMMARY

BACKGROUND AND OBJECTIVES: The objective of this study was to compare the quality and safety of retrobulbar block for the treatment of cataracts by phacoemulsification using needles of different sizes: 27 × 0.70 mm and 20 × 0.55 mm.

METHODS: Candidates for ophthalmic block for the treatment of cataracts by phacoemulsification were selected prospectively. After sedation and standardized monitoring, a retrobulbar block with 4 mL of 1% ropivacaine containing hyaluronidase was performed with a single inferolateral puncture. In Group I (GI), the 25 × 0.70 mm needle was used, while in Group II (GII) a 20 × 0.55 mm needle was used. All patients had a CT scan at the time of the blockade and five minutes after the administration of the anesthetic solution with radiologic contrast. Ocular mobility was assessed after three, five, and ten minutes. The incidence of complications in both groups and the satisfaction of patients and surgeons were compared by applying a standardized questionnaire.

RESULTS: Fifty-four adult patients were evaluated (27 per group). Patients did not complain of intraoperative pain or perception of light. The anesthetic procedure was considered very good (VG) or excellent (E) in 96.3% of the cases in both groups. All patients were subjected to the same assessment. The need of block repetition between both groups did not differ (p = 1.0). Patients in GI showed decreased ocular mobility at 3 minutes (p = 0.03). The intraconal retrobulbar placement of the needle was observed on both groups. Anesthetic dispersion at 5 minutes was similar in the two groups.

CONCLUSIONS: Retrobulbar block with a single inferolateral puncture with a 20 × 0.55 mm needle, using low doses of anesthetics, is an effective and safe option for the treatment of cataracts by phacoemulsification.

Key Words: SURGERY, Ophthalmologic: cataracts, phacoemulsification; TECHNIQUE, Regional: retrobulbar block

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: Comparar la calidad y la seguridad de la anestesia retrobulbar (ARB) para tratamiento de catarata por facoemulsificación, utilizando agujas de dos diferentes tamaños: 25 x 0,70 mm o de 20 x 0,55 mm.

MÉTODOS: Selección prospectiva de candidatos a bloqueo oftálmico para tratamiento de catarata por facoemulsificación. Después de la sedación y monitoreo estandarizado, se realizó anestesia retrobulbar (ARB) en punción única ínfero-lateral con 4 mL de ropivacaina 1%, con hialuronidasa. En el Grupo I (GI), la aguja utilizada fue de 25 x 0,70 mm y en el Grupo II (GII), de 20 x 0,55 mm. En un paciente de cada grupo fueron realizadas tomografías computadorizadas al momento de la realización del bloqueo oftálmico y después de cinco minutos de la administración de la solución anestésica con contraste radiológico. La movilidad ocular se evaluó después de tres, cinco y diez minutos. A través de un cuestionario estandarizado, se compararon la incidencia de complicaciones entre los grupos, y la satisfacción de los pacientes y de los cirujanos.

RESULTADOS: Fueron evaluados 54 pacientes adultos (27 por grupo). Ningún paciente relató dolor o percepción luminosa intraoperatoria. El procedimiento anestésico fue considerado muy bueno (MB) o excelente (E) en un 96,30% de los casos en los dos grupos. La misma evaluación se hizo en un 100% de los pacientes. No hubo diferencia en la necesidad de repetición del bloqueo entre los grupos (p = 1,0). El GI presentó menor movilidad ocular a los 3 minutos (p = 0,03). Se observó el posicionamiento de la aguja en posición retrobulbar intraconal en los dos grupos. La dispersión anestésica fue similar entre los grupos a los 5 minutos.

CONCLUSIÓN: La ARB realizada con la aguja de 20 x 0,55mm, en punción única ínfero-lateral, utilizando bajas dosis de anestésicos, se presenta como una opción eficaz y segura para el tratamiento de catarata por facoemulsificación.

INTRODUCTION

Cataracts are the main cause of reversible blindness in the world ¹. Its treatment consists of the surgical removal of the opaque lens, which is substituted by an intraocular lens. A successful surgery requires anesthetic procedure with adequate analgesia, providing comfort and safety. Despite the development of new techniques such topical, intracameral, and sub-Tenon's block ², ophthalmic blocks are still widely used ³. A variable terminology is used for ophthalmic blocks. In the present study we use the expression retrobulbar block because the authors consider that in the techniques described below the tip of the needle is always placed behind the eye globe.

A consensus on the ideal needle length for those blocks does not exist. To improve safety without the loss of quality it has been suggested that the needle should not be introduced more than 30 mm inside the eye chamber. Van den Berg (2004) considers the 25 mm long needle more adequate ⁵ despite the complications described in the literature ^6,7. Smaller needles are considered less traumatic; however, there are reports of a greater incidence of failed blocks with those needles, which does not stimulate their routine use ⁵.

The primary objective of this study was to compare the quality and safety of the retrobulbar block with a small volume of anesthetic using 25 × 0.7 mm or 20 × 0.55 mm needles for the treatment of cataracts by phacoemulsification. Secondary objectives included: 1 - to evaluate the final position of the needle in the eye chamber, therefore contributing for a more adequate terminology; and 2 - to observe the dispersion of the anesthetic in the eye chamber.

METHODS

This is a prospective, comparative, randomized, double-blind study.

After approval by the Ethics Committee of the Hospital das Clínicas da Universidade Federal de Goiás and signing of the informed consent, patients with surgical indication of phacectomy by phacoemulsification with implantation of intraocular lens at the Centro de Referência em Oftalmologia of the Universidade Federal de Goiás (CEROF-UFG) were enrolled in this study. Only one eye of each patient was included in the study. Patients with monocular vision, any changes in eye mobility (e.g., strabismus, paralysis), history of past ophthalmologic surgery, with contraindications for ophthalmologic block under sedation, and history of allergy to iodine-containing contrast were excluded from the study. The same professional, one of the authors of this report (HMC), performed all blockades.

All study patients underwent echobiometry with an Ocusan I (Alcon Labs, Fort Worth, TX, USA) echobiometer to determine the intraocular lens to be implanted and to measure the axial length of the eye.

The anesthetic technique consisted of standard monitoring, including pulse oximetry (SpO₂), continuous cardioscopy, and non-invasive blood pressure (NIBP). After peripheral venipuncture (22G catheter), D5W solution was administered, followed by the administration of oxygen, 2 L.min^-1 via nasal catheter. Patients were sedated with fixed doses of diazepam (2.5 mg) and fentanyl (25 µg), and fractionated doses of propofol until the loss of response to verbal commands. After antisepsis with topical povidine and removal of excess anti-septic solution, retrobulbar block was performed with a single puncture, modified inferolateral ⁸. In this technique, the needle is introduced with mild pressure on the inferior border of the bony orbit at the level of the inferior eyelid (Figure 1), perpendicular to the skin for the first 10 mm and, after a slight superomedial inclination, the rest of the needle was introduced until its hub touched the skin.

An anesthetic solution containing 1% ropivacaine and hyaluronidase (50 IU.mL^-1) with a total fixed volume of 4 mL was injected at 0.5 mL.sec^-1. Intermittent compression of the ocular angle and inferior orbital border was applied for three minutes without direct compression of the globe (Figure 2) to facilitate the dispersion of the anesthetic solution and prevent it from depositing in the anterior portion of orbit. Patients were randomly divided into two groups: in Group I (GI), a 25 × 0.75 mm needle was used, and in Group II (GII) a 20 x 0.55 mm needle was used. One patient in each group was randomly selected for the administration of 0.5 mL of the water soluble iodine-containing contrast media (Iohexol - 300 mg.mL^-1) mixed with the anesthetic solution. Those patients had a computed tomography (MDCT) at the time of the anesthetic procedure when the needle was fully inserted to determine the position of the tip. A second MDCT was done five minutes after the injection of the contrast-containing anesthetic solution to observe its dispersion. The exam was done by a 6 channels Multiple Detector - Somaton Emotion (Siemens) CT scanner. Images were reconstructed by an specific software (Viewer Sinet Siemens) on axial, coronal, and oblique sagittal with continuous acquisitions of 0.6 mm. Images were analyzed by one of the authors of this report, a radiologist (KIST).

Three minutes after the administration of the anesthetic solution, a drop of antiseptic solution, 1% povidone iodine, was applied to the eye to be operated and the patient was questioned whether he/she felt pain or not, in order to evaluate the sensitivity to pain of the anesthetized eye.

Ocular mobility was evaluated on moments zero (before the anesthetic procedure), 3, 5, and 10 minutes. The four recti muscles of the eye and levator palpebrae superioris muscle were evaluated individually, establishing scores according to the ocular mobility of each muscle: 2 for normal mobility, 1 for decreased mobility, and 0 (zero) for muscular akinesia (total score varied from 0-10). The surgery was performed when the patient presented a score of 0 (zero). If at 3 minutes the patient presented a score other than 0 (zero), he/she was evaluated again at 5 minutes, when the surgery was performed if the total score < 3, or a supplementary block was done with the same needle used for the first puncture, in the supero-medial position, with 2 mL of the anesthetic solution if the score were > 3. In those cases, ocular mobility was evaluated again at 10 minutes, at which time the surgery was performed.

Surgeries were performed by physicians of the Ophthalmology Department of the CEROF-UFG who were not aware of the anesthetic technique used. Patients were followed by the outpatient clinic of the same institution until their discharge.

The incidence of ocular and systemic complications in both groups was compared. The level of patient and surgeon satisfaction was evaluated by a standardized questionnaire. All evaluations of this study were done by a single evaluator who was not aware of the group distribution.

The software SPSS 11.5 (SPSS Inc., Chicago, IL, USA) was used for the statistical analysis. The Chi-square test was used to compare categorical data. The independent Student t test was used to analyze parametric data and the Mann-Whitney U test was used for non-parametric data. A level of 5% (p < 0.05) was considered statistically significant.

RESULTS

Fifty-four adult patients, 27 in each group, with a mean age of 65.41 ± 11.41 years, in Group I (GI), and 67.55 ± 9.87 years, in Group II (GII) (p = 0.4), were enrolled in this study. Both groups did not show statistically significant differences regarding gender, age, weight, physical status according to the American Society of Anesthesiologists (ASA), axial length of the eye, and the side to be operated (Table I). The mean dose of propofol administered in GI was 27.4 ± 5.0 mg and in GII was 26.4 ± 4.1 mg (p = 0.4). At the end of the surgery patients did not complain of intraoperative pain or light perception. All patients in this study would undergo the same anesthetic procedure if they needed another ophthalmologic surgery (Table II). Surgeon satisfaction with the anesthetic technique was deemed very good (VG) or excellent (E) in 26 patients in GI (96.29%) and in 26 patients in GII (96.29%; p = 1.0). The procedure was considered VG or E by 100% of the patients. Surgeries were done with a single puncture, without supplementation with a second puncture, in 26 patients in GI (96.29%) and in 25 patients in GII (92.59%; p = 1.0). Ocular or systemic complications were not observed in this study. Patients in both groups did not complain of pain after the instillation of 1% povidone iodine at 3 minutes. Ocular mobility (Table III) was similar in both groups at all times, and only at three minutes a difference for the median was observed. Patients in GI showed the lower ocular mobility at three minutes (0.6 ± 1.1 vs. 1.3 ± 1.4, p = 0.03). Ocular mobility in both groups at 5 and 10 minutes was not statistically significant. Considering an alpha error of 0.05 and the differences to be detected between both groups equal to one, the statistical tests done in the present study achieved a power of 95%.

Images obtained by the MDCT in GI showed the tip of the needle in the retrobulbar intraconal space and the dispersion of contrast-containing anesthetic solution was preferentially periocular and intraconal (Figures 3, 4, 5, and ⁷). The tip of the needle in GI (25 × 0.7 mm) reached a 32-cm depth in the orbital cavity.

Multiple detector CT images in GII also showed clearly the retrobulbar intraconal placement of the 20 x 0.55 mm needle, at a 22 mm depth in the orbital cavity. Dispersion of the anesthetic solution in this group was also predominantly periocular and intraconal (^{Figures 7}, 8, 9, and ¹⁰).

DISCUSSION

The progressive increase in the number of ocular surgeries makes the ophthalmic block the most common anesthetic technique performed nowadays. Patients undergoing cataract treatment are usually elderly and frequently have associated systemic diseases and, for this reason, benefit from locoregional blocks associated or not with sedation ⁹. In this technique, besides the sensitive blockade, adequate control of ocular mobility provided by paralysis of extrinsic eye muscles through blockade of the oculomotor, trochlear, and abducens nerves, located behind the globe, is also desirable.

In retrobulbar intraconal block the local anesthetic is injected inside the muscular cone (space where the optic nerve, most motor and sensitive ocular nerves, and adnexa are located ¹⁰), by the percutaneous or transconjunctival approach. It has the advantage of providing fast onset of analgesia and akinesia using a small volume of anesthetic. However, complications caused by inserting the needle in the intraconal space, such as retrobulbar hemorrhage, trauma of the optic nerve, perforation of the sclera, stimulation of the oculocardiac reflex, spread of the anesthetic agent to the central nervous system through the sheath of the optic nerve, meningeal irritation, and optic atrophy have been described ^11-13.

Peribulbar block (PB) initially described by Davis and Mandel ¹⁴ consists of injecting the anesthetic in the extraconal space. It guarantees ocular stability and anesthesia during surgery, and it is considered by many a safer option than the retrobulbar intraconal block (RBIB). Most common, although rare, complications include periocular and retrobulbar hemorrhage, increase in intraocular pressure, depression of the central nervous system, perforation of the globe, and incomplete anesthesia and akinesia ^15,16. It also has a late onset of action and needs larger volumes of anesthetic ⁹.

Van Den Berg (2004) ⁵ classified this anesthesia according to the place the anesthetic solution was deposited: circumocular (sub-Tenon's or episcleral), periocular (anterior, superficial), periconal (posterior, deep), and apical (ultra-deep). The author concluded that the efficacy of this anesthetic technique depends on depositing the anesthetic close to the orbital apex. Since ophthalmic blocks are done without direct visualization of the tip of the needle, there are doubts on whether, occasionally, the retrobulbar intraconal block is achieved instead of the desired extraconal block ^4,17,18, justifying the good quality of the anesthesia with small volumes even when using the extraconal technique.

A consensus on the ideal needle length for ophthalmic block has not been achieved. Some authors ^5,19 consider the 25 mm long needle more adequate, stating that smaller needles would increase the need to repeat the blockade while longer needles would be associated with an increase in the rate of complications, without improving the quality of anesthesia ⁵. Others consider needles with less than 25 mm satisfactory and associated with reduced risk, but they consider to be performing a peribulbar block ^20,21.

The present study does not support the notion that the use of 25 mm or longer needles are necessary for a RBIB of good quality. The incidence of repetition of the blockade in ophthalmic blocks using the 20 × 0.55 mm needles was not increased when compared with the 25 × 0.7 mm needles (3.7% vs. 7.4%, p = 1.0), and it was lower than reported in the literature (10% to 33%) ⁵. Currently, the success of anesthesia provided by ophthalmic blocks has been proportional to the experience of the anesthesiologist and adequate knowledge of the local anatomy, regardless of the name chosen, peribulbar block or retrobulbar block ^4,9. Despite the controversy regarding the terminology of ophthalmic blocks, MDCT images demonstrated clearly that an intraconal retrobulbar block was performed using the technique described with 25 × 0.7 mm or 20 × 0.55 mm needles.

Approximately 96% of the surgeons and 100% of the patients in both groups considered the technique very good (VG) or excellent (E). Patients did not complain of intraoperative pain or uncomfortable visual sensation. Subjective evaluation, both by surgeons and patients, was adequate and similar in both groups. This was reflected on the fact that all patients would undergo the same anesthetic technique in the future if they needed an ophthalmologic surgery.

The results of the present study demonstrated similar latency of the sensitive blockade in both groups (p = 1.0). However, at three minutes the motor blockade was greater when the 20 x 0.55 mm needle was used than the 25 × 0.7 mm needle, but it was the same at 5 minutes (p = 0.08). One can hypothesize that a small volume of the local anesthetic was deposited in the anterior portion of the retrobulbar intraconal space when using the 20 × 0.55 mm needle. The periocular placement of the local anesthetic would provide adequate pain control since the innervation of the eye globe penetrates in its posterior pole. To reach the motor innervation of the eye the anesthetic solution would have to disperse to the posterior portion of the intraconal space where the nerves are close together. But at 5 minutes both groups have similar results for all the parameters analyzed, demonstrating equivalence in the objective assessment of the blockade.

Although patients were not monitored with direct tests (e.g., retinal mapping, ultrasound) to detect possible complications, such as ocular perforation, careful clinical evaluation, including complaints of the patients (e.g., scintillating scotomas, blurred vision) did not suggest the development of complications.

Multiple detector CT images reinforced the clinical observations. It was demonstrated that the needle was advanced beyond the equatorial axis of the globe, characterizing a RBB, as predicted by the authors. In GI, the needle penetrated deeper in the orbital cavity than in GII, resting closer to the orbital apex, where the motor nerves of the eye are grouped together. It was also observed, in both groups, that the needle was placed inside the muscular cone, with similar dispersion of the anesthetic solution, which could justify the similarity in the quality of anesthesia in GI and GII.

Retrobulbar block with the 20 × 0.55 mm needle can be considered a safer option without losing quality when compared to the 25 × 0.70 mm, using the inferolateral approach for the treatment of cataracts by phacoemulsification. Assuming that the rate and severity of complications is proportional to the length of the needle, one can suggest the routine use of the 20 × 0.55 mm needles for ophthalmologic blockades in those procedures.

Multiple detector CT images demonstrated that in the anesthetic technique described here the tip of the needle can be placed beyond the equatorial axis of the globe, and that it can even be intraconal, using both the 25 × 0.7 mm and 20 × 0.55 mm needles, justifying the terminology of retrobulbar block (RB).

The contrast-containing anesthetic solution showed periocular and intraconal dispersion in both groups, as demonstrated by the MD-CT.

Further studies are necessary to evaluate the efficacy of anesthesia with the technique described here, with the 20 × 0.55 mm needle, for other types of ophthalmologic surgeries. This study, using MD-CT images during ophthalmologic blocks for treatment of cataracts, is part of a research line that includes the evaluation of relationship between needles used for blockades and orbital structures, contributing for more detailed knowledge of this anesthetic technique and less aggressive and more effective blocks, without the loss of efficacy.

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Publication Dates

• Publication in this collection
  14 Nov 2008
• Date of issue
  Dec 2008

History

• Received
  06 Mar 2008
• Accepted
  26 Aug 2008