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Summary

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References

The intra-ocular pressure immediately before glaucoma surgery can be raised. We wished to investigate if ocular compression for 20 min before a combined peri- and retrobulbar injection would result in a lower pressure after the block. Sixty consecutive patients scheduled for filtration surgery were randomly assigned to receive ocular compression using an external pressure device for 20 min before combined peri- and retrobulbar injection (intervention group, who also received compression after the block) or to a control group in whom pressure was applied only after the block was completed. The intra-ocular pressure was measured at baseline, after the 20-min pre-injection compression (intervention group), after injecting the block, and after the 10-min post-injection compression. The pressure did not differ between groups at baseline, after the block or after the post-injection compression. In the intervention group, the compression before the block reduced the median (IQR [range]) pressure from 21.0 (17.0–25.0 [12.0–40.0]) mmHg to 16.8 (12.5–22.5 [7.5–33.5]) mmHg (p < 0.001). We conclude that external ocular compression reduces the intra-ocular pressure, but applying an additional compression for 20 min before injecting the block is not beneficial.

Glaucoma causes progressive visual field loss in eyes in which the intra-ocular pressure (IOP), in spite of maximal-tolerated medication, is too high compared with the perfusion pressure of the optic nerve head [1]. Deep sclerectomy or trabeculectomy surgery may save the sight of patients with uncontrolled glaucoma by decreasing the IOP [1]. Sub-Tenon’s anaesthesia is not appropriate [2] and general anaesthesia is often avoided for ophthalmic anaesthesia because of the 20–30% risk of postoperative nausea and vomiting [3]. Uncontrolled glaucoma is often associated with systemic disease [4] or advanced age, which further increase the risks of general anaesthesia. A high IOP at the start of glaucoma surgery predisposes the eye to large and sudden drops in pressure during surgery, increasing the risk of bleeding-related complications such as hyphaema and intra-operative or delayed suprachoroidal haemorrhage [5, 6]. The IOP should be optimised before surgery and any increase related to peri- and retrobulbar injections should be avoided, as far as possible.

The aim of this study was to determine, in patients with glaucoma, whether external ocular compression with the Autopressor® IOP reducer (Storz, Heidelberg, Germany) before and after injection of local anaesthetic would result in a lower pre-operative IOP compared with external compression performed after injection of the block only.

Methods

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References

Approval of the Finnish National Agency for Medicines and the Institutional Review Board was obtained and all participants gave their written, informed consent for inclusion in the study. Sixty consecutive patients scheduled for filtration surgery (either trabeculectomy or deep sclerectomy) for uncontrolled glaucoma were included. Patients with previous penetrating eye injury or penetrating eye surgery during the previous 6 months were not studied. Patients were randomly assigned to an intervention or a control group using sealed envelopes. In the control group, local anaesthetic solution was injected followed by ocular compression (25 mmHg) for 10 min using the Autopressor. Patients in the intervention group underwent ocular compression (25 mmHg) with the Autopressor for 20 min before the block in addition to the 10 min of compression after the injection.

The IOP was measured four times in the intervention group: the first measurement was performed immediately before treating the patient (T1); the second measurement was immediately after 20 min of ocular compression (T2); the third was immediately after injecting the combined peri- and retrobulbar block (T3); and the fourth was immediately after 10 min of ocular compression after the injection (T4). In the control group the IOP was measured three times (T1, T3 and T4). The IOP was measured using the Goldmann applanation tonometer (Haag-Streit®, Bern, Switzerland) after topical application of a fluorescein 0.25 mg.ml−1 and oxybuprocaine hydrochloride 0.6 mg.ml−1 combination (Oftan-Flurekain®; Santen Oy, Tampere, Finland). The measurements were repeated once, and if there was a difference of > 2 mmHg between the two readings, the measurement was repeated again. From the three readings, the two closest ones were used to calculate the mean IOP.

Before injecting the local anaesthetic, patients received fentanyl 50 μg and topical anaesthesia with oxybuprocaine hydrochloride (Oftan-Obukain®; Santen Oy). The local anaesthetic mixture for the combined peri- and retrobulbar block contained lidocaine 1%, l-bupivacaine 0.375%, and hyaluronidase 3.75 IU.ml−1 [7]. It was prepared at the bedside shortly before injection using a 1:1 mixture of lidocaine 20 mg.ml−1 and l-bupivacaine 7.5 mg.ml−1 (Chirocaine®; Abbott Scandinavia AB, Solna, Sweden). One millilitre of hyaluronidase 150 IU.ml−1 (Hylase® Dessau; RIEMSER Arzneimittel AG, Greifswald, Germany) was added to 40 ml of the local anaesthetic mixture. The standard approach of our institute was used for the combined peri- and retrobulbar block. First, a peribulbar injection was performed on the nasal side of the caruncle and medial rectus muscle [8] using a 30-G, 13-mm sharp needle. A second, retrobulbar, injection was performed using an inferotemporal approach [8] with a 27-G, 31-mm sharp needle. Both injections contained 3 ml of the local anaesthetic mixture. Lid and ocular movements were tested immediately after the last IOP measurements (T4). If ocular movements persisted, a rescue retrobulbar block was injected. All blocks were performed by one senior anaesthetist (HK) before the start of surgery. Any supplemental blocks and the need for rescue fentanyl during surgery were recorded. After completing the surgery, the surgeon recorded complications of anaesthesia, satisfaction with the anaesthetic (0 = surgery not difficult, 1 = slightly difficult, 2 = difficult and 3 = very difficult), and the co-operation of the patient during surgery (0 = excellent, 1 = good, 2 = compromised and 3 = absent). An ophthalmologist recorded the pre-operative ophthalmic history, examination, surgical complications and the need for postoperative surgical procedures in the first month.

A power analysis was performed using the results obtained by Ling and co-workers [9]. We determined that a 25% decrease in IOP (from 16 to 12 mmHg) at the start of surgery (T4) would be clinically relevant. We used the mean value of the standard deviation (4.25) in the previous study [9] in our calculation. A sample size of 30 patients in each arm gave a power 95% (β = 0.95) at a significance level (α) of 0.05. Non-normally distributed data were compared using the Mann–Whitney rank sum test (between groups). Sequential IOP data were analysed using Friedman’s repeated measures ANOVA on ranks and Wilcoxon’s signed rank test was used post-hoc for within-group comparisons. For continuous, normally distributed data Student’s t-test was used. Binominal data were tested with the chi-squared test. A p value of < 0.05 was considered significant. Statistical analyses were performed using SigmaStat®, version 3.5 and graphs prepared using SigmaPlot®, version 10 (Systat Software Inc., Point Richmond, CA, USA).

Results

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References

There were no differences in patients' characteristics, pre-operative ophthalmic data, success of the blocks, complications related to the combined peri- and retrobulbar injections or complications of surgery (Table 1). Ten patients (16.7%) required treatment for wound leakage. No patients had subconjunctival haemorrhage, retrobulbar haemorrhage or globe perforation. The median (IQR [range]) duration of surgery did not differ between groups (56.5 (45.0–65.0 [35.0–104.0]) min and 61.5 (53.0–66.0 [45.0–113.0]) min for intervention and control groups, respectively).

Table 1.   Results of combined peri- and retrobulbar block with (intervention group) and without (control group) pre-injection ocular compression. Values are number (proportion) or median (IQR [range]). See text for definitions of surgical satisfaction and patient co-operation.
 Intervention (n = 30)Control (n = 30)p value
Supplemental block02 (6.7%)NS
Squeezing of eyelids1 (3.3%)2 (6.7%)NS
Eye movements2 (6.7%)1 (3.3%)NS
Rescue fentanyl3 (10.0%)1 (3.3%)NS
Eyelid haemorrhage2 (6.7%)3 (10.0%)NS
Chemosis01 (3.3%)NS
Surgical satisfaction0 (0–0 [0–1])0 (0–0 [0–1])NS
Co-operation of the patient0 (0–0 [0–1])0 (0–0 [0–1])NS

The baseline (T1) IOP did not differ between groups (Fig. 1; 21.0 (17.0–25.0 [12.0–40.0]) mmHg and 20.8 (18.0–25.0 [15.0–50.0]) mmHg in the intervention and control groups, respectively). In the intervention group, the 20 min compression before block injection reduced the IOP significantly (T2) to 16.8 (12.5–22.5 [7.5–33.5]) mmHg. Block injection increased the IOP in both groups (T3) to 24.0 (21.0–28.5 [8.5–35.0]) mmHg and 24.5 (20.0–28.0 [14.0–80.0]) mmHg, for intervention and control groups, respectively. Compression after the injection reduced the IOP in both groups to 19.0 (15.5–20.0 [10.5–33.0]) mmHg and 18.8 mmHg (14.0–24.0 [8.5–45.0]) mmHg, for intervention and control groups, respectively.

image

Figure 1.  Intra-ocular pressure in the pre-injection compression group (intervention group; grey boxes and circles) and no pre-injection compression group (control group; open boxes and circles). The horizontal line indicates median, the box indicates IQR, the whiskers indicates the 10–90th centiles and the circles indicate outliers. The IOP was measured at baseline (T1), after external ocular compression for 20 min with the Autopressor® device (T2), after injecting combined peri- and retrobulbar block (T3) and after external ocular compression for 10 min with Autopressor device (T4) in the intervention group and at T1, T3 and T4 in the control group. For within-group differences over time, p < 0.001 is indicated with *(T1 vs T2 intervention group), †(T2 vs T3 intervention group),‡ (T3 vs T4 intervention group), §(T3 vs T4, control group), and ¶(T1 vs T4 control group), p = 0.002 with **(T1 vs T4 intervention group), and p = 0.03 with ††(T1 vs T3 control group). There was no difference between the groups at T1, T3 or T4.

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Discussion

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References

External ocular compression for 20 min before injecting a combined peri- and retrobulbar reduced the IOP. Despite this, the post-injection IOP (T3) was comparable with that in control group without pre-injection ocular compression. Furthermore, compression after the injections resulted in a similar IOP in both groups at the start of surgery.

Minimising the volume of local anaesthetic solution used in retrobulbar [10, 11] and peribulbar [11–13] injections can prevent an immediate increase in IOP. However, in patients with glaucoma the increase in IOP after peri- or retrobulbar anaesthesia is greater and persists longer than in non-glaucomatous eyes [14]. In patients without glaucoma, increases in IOP after a retrobulbar block can be normalised by use of an ocular compression device for 10–20 min [9, 15, 16]. The IOP decreases most during the first 10–20 min of ocular compression and the effect lasts 35 min [17, 18]. In patients with glaucoma, external ocular compression (at a pressure of 30 mmHg) immediately after a retrobulbar block reduces the IOP more than in non-glaucomatous eyes [19]. Furthermore, in non-glaucomatous eyes external ocular compression before a retrobulbar block can reduce the IOP to a similar degree compared with compression after the injection of the block [20].

In previous studies, the IOP has been shown to increase after injection of local anaesthetic solution [11], and various compression devices have decreased it. These findings were confirmed in the present study. However, there are no studies identical to our study. In the closest, a Superpinkie® rubber ball (no longer marketed) was applied to the eye for 35 min to reduce the IOP in patients without glaucoma before a retrobulbar block, compared with patients in whom compression with the Superpinkie was performed after the block [20]. After the block, the mean increase in IOP was 2.95 mmHg vs 5.50 mmHg in the compression-before and compression-after injection groups, respectively.

In the present study, the mean increase in IOP after injection (T3) was 1.88 mmHg vs 2.92 mmHg in our intervention and control groups, respectively. We found that additional compression before local anaesthetic injection did not reduce the magnitude of the increase in IOP caused by the injection. In the Superpinkie study there was a significantly reduced magnitude of increase in the group receiving compression before the injection [20]. One explanation could be that in this study we used a shorter duration of the compression (20 min vs 35 min). We chose a 20-min compression because the IOP decreases more after 20 min than after 10 mins use of the Autopressor [16]. The present protocol was not planned to test the effect of duration of the compression.

In summary, we found that ocular compression treatment (with the Autopressor) for 10 min after a combined peri- and retrobulbar block is an effective method to reduce IOP before surgery. Although a 20-min ocular compression before the block injection also reduces the IOP, this has no additional benefits when compared with post-injection compression alone.

Competing interests

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References

No external funding or competing interests declared.

References

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References