Effects of peribulbar bupivacaine as an adjunct to general anaesthesia on peri-operative outcome following retinal detachment surgery

Authors


Dr D. Shende

Abstract

Sixty premedicated, ASA physical status I or II patients weighing > 25 kg scheduled for elective retinal detachment repair were randomly assigned to receive either peribulbar block with 10 ml of 0.25% bupivacaine (block group) or intravenous morphine 150 µg.kg−1 (morphine group), prior to the induction of general anaesthesia (n = 30 in each group). Patients were evaluated for intra-operative oculocardiac reflex , peri-operative pain relief, recovery from anaesthesia and postoperative nausea and vomiting. Apart from significantly reducing the incidence of oculocardiac reflex (30% vs. 70%, p = 0.0019), peribulbar bupivacaine also attenuated the severity of the reflex. Postoperative pain relief was superior in the block group. More block group patients had the maximum recovery score in the immediate postoperative period (80% vs. 27%, p < 0.0001) and they achieved complete recovery significantly faster than the morphine group (17.3 (14.7) min vs. 66.7 (29.7) min, p < 0.0001). The incidence (40% vs. 77%, p = 0.004) and severity of postoperative nausea and vomiting were significantly less in the block group. In summary, peribulbar bupivacaine, when administered together with general anaesthesia, attenuated oculocardiac reflex, provided comparable intra-operative and superior postoperative analgesia, resulted in significantly earlier and better recovery from anaesthesia, and significantly reduced the incidence and severity of postoperative nausea and vomiting.

Retinal detachment surgery is associated with a high incidence of postoperative nausea and vomiting and peri-operative pain, requiring extended inpatient care [1]. General anaesthesia, or regional anaesthesia either with retrobulbar or peribulbar blocks, are the usual methods of providing anaesthesia for retinal detachment surgery. Regional anaesthesia may minimise the likelihood of postoperative nausea and vomiting, thereby reducing the risk of intra-ocular bleeding and rise in the intra-ocular tension in eyes undergoing vitreoretinal surgery [2]. Retrobulbar blocks [3] and retrobulbar irrigation [4] with bupivacaine for retinal detachment surgery under general anaesthesia have been reported to be superior to general anaesthesia alone in terms of postoperative pain relief, recovery and safety. Traditionally, retrobulbar block was the local anaesthetic method for ocular surgery. Because of the complications of retrobulbar block [5–10] and the safety and effectiveness of peribulbar block [11–14], the latter has gained wide acceptance in ophthalmic anaesthetic practice in recent times. Recent comparison of peribulbar and retrobulbar anaesthesia has documented that peribulbar anaesthesia can be expeditiously and efficiently used for a full range of vitreoretinal surgical procedure [15].

The beneficial effects of regional anaesthesia [2–4], especially the safer peribulbar block, have not been studied when it is used as the sole means of providing intra-operative analgesia during a balanced anaesthetic technique for patients undergoing retinal detachment surgery. This clinical trial was designed to evaluate the feasibility of ‘peribulbar analgesia’ as a part of a balanced anaesthetic technique. We determined to evaluate the effects of 0.25% peribulbar bupivacaine as an adjunct to general anaesthesia on peri-operative pain, oculocardiac reflex, recovery from anaesthesia and postoperative nausea and vomiting, and to compare it with intravenous morphine analgesia combined with general anaesthesia for retinal detachment surgery.

Methods

After Institutional Ethics Committee approval and informed consent, we studied 60 consecutive ASA physical status I and II patients scheduled for retinal detachment surgery. Patients weighing < 25 kg, age less than 12 years, or who had been taking analgesics, anti-emetics or drugs that might affect haemodynamics were not studied. All patients were examined and reassured by one of the investigators pre-operatively and were premedicated with oral diazepam 0.2 mg.kg−1 given 90 min before surgery. A computer-generated random number table was used to assign patients randomly to receive either general anaesthesia plus peribulbar block (block group) or general anaesthesia with morphine as analgesia intra-operatively (morphine group).

In the block group, 0.25% bupivacaine 10 ml with 50 µg of epinephrine and 150 IU of hyaluronidase was injected into the peribulbar space through the inferotemporal single-point approach using a 26-gauge needle. The peribulbar block was performed in the operating room prior to the induction of general anaesthesia with lead II electrocardiography (ECG), oxygen saturation (Spo2) and noninvasive blood pressure (NIBP) monitoring. Immediate complications while performing the block, including oculocardiac reflex, were noted. After the block, gentle digital ocular massage was given. The onset of conjunctival and corneal anaesthesia (tested by abolition of conjunctival and corneal reflex), analgesia of upper and lower eyelids, and hypokinesia of lids (levator palpebrae and orbicularis) and recti were noted. The block was considered successful when the conjunctival and corneal reflexes were abolished and analgesia of the lids was achieved. In the morphine group, 150 µg.kg−1 of morphine was given intravenously 5–10 min before the induction of anaesthesia. The observing anaesthetist was not involved in patient care in the operating room until after morphine was administered intravenously or the peribulbar block had been performed and the eye scheduled for surgery had been covered with a pad, thus effectively blinding the observer. All patients were anaesthetised with thiopental 5 mg.kg−1 and underwent tracheal intubation after vecuronium 100 µg.kg−1. Anaesthesia was maintained with 0.5–1.0% halothane and 66% nitrous oxide in oxygen. Intra-operatively, heart rate, ECG, Spo2, NIBP and end-tidal CO2 were monitored using the Datex Cardiocap II (Datex Instruments Inc., Finland) monitoring system. If analgesia was considered inadequate (> 20% rise in heart rate and blood pressure from basal values after surgical incision), a bolus of 50 µg.kg−1 of morphine was given intravenously as an analgesic supplement. Intra-operatively, end-tidal CO2 was maintained in the normocapnoeic range (4.7–6 kPa). The oculocardiac reflex was defined as a rapid reduction in heart rate by 10 beat.min−1 or more or arrhythmia that occurred during ocular manipulation [16]. The severity and duration of oculocardiac reflex including occurrence of arrhythmia and treatment required were noted. At the end of surgery, residual neuromuscular blockade was reversed with 50 µg.kg−1 of neostigmine and 20 µg.kg−1 of atropine. Halothane was discontinued 5 min before the end of surgery.

Recovery was evaluated in all the patients immediately on the operating table after extubation as well as in the recovery unit by using Aldrete's postanaesthesia recovery scoring system ( Table 1) [17]. The time taken for patients to reach the maximum score of 10 was also noted.

Table 1.  Aldrete's postanaesthesia recovery scoring system
 Scores
  1. SBP = systolic blood pressure.

1. Activity
 Able to move all four limbs2
 Able to move only two limbs1
 Not able to move any limb0
2. Respiration
 Able to breathe deeply, and cough2
 Respiratory effort was limited or dyspnoea apparent1
 No spontaneous respiratory activity0
3. Circulation
 SBP ± 20% of the pre-anaesthetic level2
 SBP between 20 and 50% of the pre-anaesthetic level1
 SBP alteration ± 50% or more0
4. Consciousness
 Fully alert, evidenced by the ability to answer questions2
 Aroused only by calling their name1
 Auditory stimulation fails to elicit a response0
5. Colour
 Obviously normal or pink colour2
 Pale, dusky, or blotchy discoloration, as well as jaundice1
 Frank cyanosis0
Total score10

Postoperatively, patients were followed up for 24 h. A 10-point verbal numerical scale (VNS) (0-no pain at all, 10-the worst pain imaginable) was used to assess postoperative pain at 2, 6, 12, 18 and 24 h after the procedure. If the patient had pain (VNS > 4), diclofenac sodium 1.5 mg.kg−1 was given intramuscularly. We used VNS for pain rather than a visual analogue scale (VAS) because of its simplicity and its correlation with VAS for pain and because patients with bilateral retinal detachment and partial or total blindness might find it difficult to complete a VAS [18]. The time to first analgesic supplement in the postoperative period was defined as the end of the surgical procedure until the time at which the pain score was > 4.

The incidence and severity of postoperative nausea and vomiting at 0–2, 2–6 and 6–24 h were evaluated by a categorical scoring system (0, no nausea or vomiting; 1, nausea once; 2, vomited once; 3, vomited twice or more). If patients vomited twice or more (score 3) it was defined as severe postoperative nausea and vomiting and treated with metoclopramide 150 µg.kg−1 intravenously.

A global assessment of the entire postoperative comfort and experience of the patients was made using an 11-point verbal numeric scoring system (0, not at all satisfied; 10, fully satisfied).

Prestudy power analysis from a pilot study of morphine analgesia determined that 25 patients would be required in each group to have a 90% chance (β = 0.1) of detecting a 50% relative reduction in the number of patients requiring analgesic supplement with peribulbar bupivacaine in the first 24 postoperative hours with 95% confidence interval limits and α = 0.05 (Version 6.0, Epi Info., Center for Disease Control, USA, and World Health Organisation, Switzerland, 1997). The duration of surgery, recovery time, time to first analgesic supplement in the postoperative period, the duration and severity of oculocardiac reflex, and patient satisfaction scores were compared using Mann–Whitney U-tests and two-sample t-tests where appropriate. The incidence of oculocardiac reflex, recovery scores, requirement for postoperative analgesic supplements, and the incidence and severity of postoperative nausea and vomiting were compared by Chi-squared tests and Fisher's exact tests with a Yates' continuity correction, where appropriate. Results were expressed as mean (SD) or median (range) and p-values < 0.05 were considered statistically significant.

Results

Patient data were comparable in both groups with respect to age, sex, weight, ASA physical status and the duration of surgery ( Table 2).

Table 2.  Patient data. Values are given as mean (SD).
 Morphine group
(n = 30)
Block group
(n = 30)
Age; years 17.7 (9.3) 19.4 (12.1)
Weight; kg 43.6 (10.5) 44.6 (13.7)
Sex; M/F 24/6 26/4
ASA Physical Status; I/II 28/2 27/3
Duration of surgery; min154.8 (59.3)159.5 (51.8)

Oculocardiac reflex (Table 3)

While performing the peribulbar block, none of the patients manifested an oculocardiac reflex. All blocks were successful. Patients in the block group had a significantly lower incidence and severity of oculocardiac reflex intra-operatively, as compared with the morphine group. The incidence of arrhythmia was significantly lower in the block group.

Peri-operative pain and analgesics (Table 4)

Intra-operative requirements for analgesic supplements and time to first postoperative analgesia were similar. Fewer patients had VNS for pain > 4 and required analgesic supplement at 2, 6 and 12 h after surgery in the block group (p < 0.05), but this was not reflected at 18 and 24 h. Mean VNS at 12–18 h was significantly lower in the block group while, at other time intervals, VNS was similar.

Recovery from anaesthesia (Table 5)

Patients who received peribulbar block recovered significantly earlier than patients in the morphine group. A significantly greater number of patients achieved 10/10 Aldrete's score in the immediate postoperative period in the block group than in the morphine group (29/30 vs. 8/30, p < 0.0001).

Postoperative nausea and vomiting (Table 5)

The incidence of postoperative nausea and vomiting in the first 24 postoperative hours was significantly lower in the block group (12/30 vs. 23/30; p < 0.004). Need for anti-emetic therapy was also significantly less in the block group (p = 0.0219) during the first 24 h.

Patients in the block group had higher satisfaction scores than those in the morphine group (p < 0.001). Satisfaction of the patients with respect to the anaesthetic procedure and comfort in the first 24 postoperative hours was significantly better in the block group ( Table 5).

Table 5.  Post-anaesthesia recovery, postoperative nausea and vomiting and patient satisfaction. Values are given as mean (SD) or median (range).
 Morphine group
(n = 30)
Block group
(n = 30)

p
Number of patients with Aldrete 8/3024/30< 0.0001
score 10 in the immediate postoperative period
Time to achieve score of 10; min66.7 (29.7)17.3(14.7)< 0.0001
PONV incidence
 0–2 h16/30 8/300.0350
 2–6 h15/3010/300.1904
 6–24 h12/30 2/300.0060
 0–24 h23/3012/300.0040
Anti-emetic requirements
 0–24 h13/30 4/300.0219
Patient satisfaction scores 7 (5–10) 9 (8–10)< 0.001

None of the patients who received peribulbar block had any significant immediate or delayed complications associated with the block, such as oculocardiac reflex, globe penetration, perforation or haemorrhage.

Discussion

The most common problems during the first 24 h after retinal detachment surgery are moderate to severe pain, nausea and vomiting [1]. Although vitreoretinal surgery can sometimes be done on an ambulatory basis, most cases require hospitalisation for optimum care [1]. Inpatient care immediately after vitreoretinal surgery is intended to treat pain and nausea and to minimise ocular complications [1]. At the present time, the vast majority of vitreoretinal procedures are performed using either retrobulbar or peribulbar anaesthesia because of the advantages of the regional anaesthesia such as better pain relief and recovery as well as less postoperative nausea and vomiting [3–19]. Peribulbar anaesthesia has been used successfully for vitreoretinal surgery as a sole anaesthetic technique [15] and has been shown to be safer than retrobulbar anaesthesia [12–14]. However, patients who undergo scleral-buckling techniques and procedures that will require longer than 2 h to complete will require general anaesthesia [2]. In this study, we compared two anaesthetic techniques for retinal detachment surgery, general anaesthesia plus peribulbar bupivacaine 0.25% and general anaesthesia with morphine as analgesic.

Bupivacaine has been shown to be a safe and effective anaesthetic for scleral-buckling surgery and its duration of action makes it an ideal anaesthetic agent for retinal detachment surgery [20], following which the maximum discomfort occurs in the first 24 h. In contrast to previous studies [3, 4], which used higher concentrations of bupivacaine, we performed peribulbar blocks with 10 ml bupivacaine 0.25% with the intention to provide peri-operative analgesia rather than anaesthesia and akinesia. In our study, during the intra-operative period, peribulbar bupivacaine provided analgesia as effectively as morphine 150 µg.kg−1. There have been conflicting opinions with regard to the effectiveness of retrobulbar anaesthesia on oculocardiac reflex [21, 22]. Moreover, retrobulbar block itself can stimulate oculocardiac reflex [23]. There have been no clinical trials to evaluate the efficacy of peribulbar anaesthesia on oculocardiac reflex. In our study, there were no complications due to peribulbar block, including oculocardiac reflex while performing the block. Rather, it significantly decreased the incidence of arrhythmia and the severity of the intra-operative oculocardiac reflex, probably by blocking the afferent limb of the reflex arc.

Patients in the block group had superior recovery from general anaesthesia, with significantly earlier recovery and better recovery scores than the patients in the morphine group. This is probably due to the morphine-sparing effect of the peribulbar block.

Even though there was no difference in the time to the first dose of analgesic, the number of patients who required analgesic supplement in the first 12 h (VNS for pain > 4) was statistically significantly lower in the block group. In the late postoperative period (12–18 h), pain relief in terms of VNS was superior in the block group. Retrobulbar block with bupivacaine 0.5% [3] and retrobulbar irrigation with bupivacaine 0.75% [4] have been shown to provide significantly better analgesia for a longer duration in the postoperative period, especially in the first few hours. The difference between our results and the previous reports [3, 4, 19] can be attributed to the higher concentration of bupivacaine [4], administration of the regional anaesthesia at the end of the surgery [4], and the additional narcotic analgesics used intra-operatively along with retrobulbar anaesthesia [3–19].

In our study, we found that peribulbar bupivacaine significantly reduced the incidence and attenuated the severity of postoperative nausea and vomiting. This reduction in nausea and vomiting in the block group can be explained partly by the narcotic-sparing effect, and partly by the probable effect of the block on the oculo-emetic reflex which shares its afferent limb of the reflex arc with the oculocardiac reflex [24]. Our findings are in accord with a study by Allen et al. [25], which reported a significant association between the occurrence of an intra-operative oculocardiac reflex and postoperative nausea and vomiting.

Children weighing less than 25 kg or less than 12 years of age were excluded from the study as they would have not co-operated with peribulbar block. Hence older children (12–17 years) formed the major bulk of our study population. Trauma was the most common aetiological factor for retinal detachment followed by myopia.

Peribulbar bupivacaine, by providing superior postoperative pain relief and by reducing postoperative nausea and vomiting, increased patient satisfaction. Comparison of the duration of the hospital stay would have been an another important peri-operative outcome measure, especially in a day-care set-up. We did not analyse these data as all our patients were in-patients, and the duration of the hospital stay was predominantly determined by the surgical outcome in our centre.

In conclusion, general anaesthesia plus peribulbar block with 10 ml bupivacaine 0.25% is an optimal anaesthetic technique for vitreoretinal surgery as this technique provided effective intra-operative analgesia and significantly contributed to postoperative analgesia, provided superior postanaesthesia recovery and effectively reduced the incidence and severity of intra-operative oculocardiac reflex (oculocardiac reflex) and postoperative nausea and vomiting. These effects may thereby result in reduced postoperative ocular morbidity.

Acknowledgments

We thank Mr V. K. Chhabra and Mrs V. Pandey for their statistical assistance.

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