Documenta Ophthalmologica 82: 201-210, 1992. 9 1992 Kluwer Academic Publishers. Printed in the Netherlands.
A l f e n t a n i l / p r o m a z i n e versus Meperidine/promazine as a sedative regimens during local analgesia for cataract operation
OSAMA EL-BASSIOUNY, 1 EZZAT MOHAMED EL-TAHER 2 & MOHAMED EMAD EL-DIN ABD EL-GHAFFAR 2
1Department of Ophthalmology and 2Department of Anaesthesiology, Faculty of Medicine, Suez Canal University, Ismailia, Egypt Accepted 9 September 1992
Key words: Alfentanil, Anaesthesic technique, Cataract operation, IOP, Local analgesia, Meperidine, Promazine, Sedative
Abstract. The influence of two intravenous (IV) sedative regimens on intra-ocular pressure (IOP) was investigated in conjunction with retrobulbar local analgesia. Forty patients of either sex, and similar age with body weight within 40-90 kg were allocated equally and randomly to two groups: Group A (alfentanil/promazine) and group M (meperidine/promazine). Measurement of IOP, systolic pressure, pulse rate, respiratory rate, PaCO2, PaO2 and O2 saturation were made before operation, after premedication, after IV sedation and post-operatively. In the Alfentanil group there was significantly stronger decrease of IOP (p < 0.001). In group A the IOP dropped from 18.1 -+ 3.2mm Hg to 10.3 -+ 2.7ram Hg, i.e. 43%, while in group M the reduction IOP was from 17.6 -+ 3.5 mm Hg to 12.6 -+ 1.9 mm Hg, i.e. 28.4%. Meperidine caused a significant increase in PaCO 2 (4.2 -+ 0.3 mm Hg), however this increase was not sufficient to cause the IOP alterations. The oxygen saturation was lower in group M (decreased by 1.5 -+ 1% in group M versus decrease by 1.0 -+ 1.2% in group A). Cardiovascular parameters were more stable in group A. In conclusion the alfentanil regimen produced a better reduction of the IOP with excellent sedation, operative condition and least anaesthetic side effects.
Introduction T h e c o n t r o l of i n t r a o c u l a r p r e s s u r e ( I O P ) d u r i n g o p h t h a l m i c s u r g e r y is of p r i m e i m p o r t a n c e a n d t h e factors which influence I O P h a v e b e e n d e s c r i b e d [1], i.e. a r t e r i a l p r e s s u r e [2], c e n t r a l v e n o u s p r e s s u r e [3, 4], a n d a r t e r i a l c a r b o n d i o x i d e t e n s i o n [4, 5]. M u c h p u b l i s h e d w o r k has i n v o l v e d t h e use o f g e n e r a l a n a e s t h e s i a [6, 7], b u t an i n c r e a s i n g a m o u n t o f c a t a r a c t s u r g e r y is p e r f o r m e d u n d e r local a n a e s t h e s i a with s e d a t i o n [8] since c a t a r a c t s u r g e r y is p e r f o r m e d c o m m o n l y o n an e l d e r l y p o p u l a t i o n . D u r i n g s u r g e r y I O P is i n f l u e n c e d b y the e x t r a - o c u l a r m u s c l e t o n e , scleral r i g i d i t y a n d v a s c u l a r i t y of t h e orbit. A m a r k e d i n c r e a s e in c e n t r a l v e n o u s p r e s s u r e , for e x a m p l e b y t h e v a l s a l v a m a n o e u v r e o r b y v e n o u s e n g o r g e m e n t d u e to h y p e r c a p n i a , will i n c r e a s e I O R M o s t c e n t r a l n e r v o u s s y s t e m d e p r e s sants, i n c l u d i n g n a r c o t i c analgesics t h a t a r e u s e d to p r o d u c e s e d a t i o n d u r i n g c a t a r a c t s u r g e r y u n d e r local a n a l g e s i a cause a r e d u c t i o n in l O P [9]. B u t t h e
202 possibility exists that other effects of sedation such as hypercapnia or hypoxia may affect the lOP adversely. Meperidine/promazine is often used as a sedative regimen during cataract surgery performed under local analgesia; Alfentanil is a recently introduced short acting opioid analgesic [10-12]. It has a more rapid onset of action, shorter duration and a more rapid recovery than meperidine [10]. The aim of this study was to compare the influence of two intravenous regimens, i.e. meperidine/promazine and alfentanil/promazine on the intraocular pressure in patients who have cataract surgery performed under local anaesthesia.
Subjects and methods Forty patients who were to undergo elective cataract surgery under local anaesthesia with sedation were recruited from January to July 1991 in University Medical Center after patients' consent. Adult patients of either sex, within the weight range 40-90 kg were included. Patients with severe system impairment, known sensitivity to opioid, parkinsonism, or who had drug therapy with known extrapyramidal side effects and patients showing markedly increased lOP were not included in the study. The patients were premedicated with 10 mg diazepam orally 2 hours before operation. An intravenous cannula was placed in the dorsum of the hands. The patients were allocated randomly in two equal groups. Group A (Alfentanil group) received 7 ~xg/kg alfentanil and 0.3 mg/kg promazine as an intravenous sedative regimen and group M (Meperidine group) received 0.7 mg/kg meperidine and 0.3 mg/kg promazine as an intravenous sedative regimen pre-operatively. Local anaesthetic nerve blocks (retrobulbar and facial nerve) were performed by the surgeon, two minutes after sedation, using 15 ml of 2:1 mixture of 2% lidocaine and 0.5% bupivacaine without adrenaline. The ophthalmic surgeon was unaware of the nature of the sedation. The patients were in supine position after instillation of benoxinate 0.5 (2 drops in each eye before lOP measurements using the standardized Schiotz indentation tonometer). In order to exclude the effect of scleral rigidity 2 weights (5.5 and 10) were used. Also, an average of three readings was taken at each time. lOP was measured one day before operation and again two hours after oral premedication by 10mg diazepam. The last measurements was taken as a baseline measurement for IOP. Further measurements were immediately after sedation and after retrobulbar and facial nerve block. At the end of the surgery the lOP was measured in the normal (non operated) eye. Arterial blood samples were taken from a radial arterial cannula during presedation (as baseline measurement) and at 5, 20, and 40 minutes post sedation and finally 6 hours post-operatively. Oxygen saturation, PaCO 2 and
203 PaO 2 were measured in these blood samples using a blood gas analyzer (ABL2-Radiometer). Vital signs were measured during presedation (as baseline measurements) at 5, 15, 45, 60 minutes post sedation then further every 2 hours during next 11 hours (12 hours monitoring), in addition to measurements, the perioperative conditions were assessed as follows: A- Surgeon's satisfaction for the operative condition as being complete, moderate or insufficient. B- Patient's satisfaction for the anaesthetic technique. Each patient was interviewed post operatively. C- Pain assessment during operation by the anaesthetist according to a 5 step scale as follows: 0. No pain. 1. Very slight pain. 2. Slight pain that can be temporarily forgotten. 3. Permanent and tolerable pain that cannot be forgotten. 4. Marked pain that leads the patient to request an analgesia. 5. Intolerable pain with screams and restlessness. This five-step scale was explained pre-operatively to the patients and pain was measured by asking the patient during surgery and post-operatively if he wanted any more analgesic. When the patient was asleep, pain was estimated at (0) level. Side effects as nausea, vomiting, increase narcotic dose, itching, urinary retention, respiratory depression and others were noted during surgery and post-operatively for 12 hours. Data were collected, tabulated and analyzed using paired and unpaired students t-test.
Results
The two groups (A & M) were well matched in terms of the age, sex, weight (Table 1), in the base line measurement of IOP, vital sign (systolic pressure, pulse rate, respiratory rate), blood gases (PaO 2, PaCO 2 and 0 2 saturation), Table 2. Few patients in both groups were suffering from concomitant physical conditions such as hypertension, diabetes, asthma and angina pectoris. Their condition was stable and they were receiving a variety of
Table 1. Demographic data of study population
Age (years) Sex (male:female) Weight (kg)
Alfentanil group
Meperidine group
71 -+ 6.5 5:15 68 -+ 9.7
72 -+ 7.1 6:14 69 -+ 10.5
204 drugs including antihypertensive agents, bronchodilator, antiarrhythmic and oral hypoglycemic agents (Table 3). The mean operating time was similar in each group (35.5 +-5.1 rain in group A and 37.6 +- 6.0 rain in group M) with similar overall time from start IV sedation to end of surgery (sedation time) (45 +- 3 min in group A and 46 +- 5 min in group M). In each group there was a small but statistically significant decrease in lOP, after premedication with oral diazepam. In group A lOP decreased from a mean of 19.5 mm Hg to 18.1 mm Hg (p 0.5). Before 02 administration by face mask there was a decrease in 0 2 saturation from 9 5 -+ / . 5 % to 94-+0.3% in group A and from 95.9-+2.1% to 94.4-+ 1.1% in groups M. The difference between two groups was statistically insignificant. The increase in 0 2 saturation after administration of 0 2 by face mask was similar in both groups A and M. PaO 2 measurements increased significantly from baseline in both groups (p < 0.001) due to 0 2 supplementation by face mask, but there were no significant differences between the groups A and M (Table 5). The peri-operative conditions, the surgeon- and patient-satisfaction for operative and anaesthetic technique, the side effects and complications, and the post-operative, analgesic requests are shown in Table 6. In the AllenTable 5. 02 saturation, PaO 2 and PaC02 in both group (pre-sedation, post-sedation, and post-operatively) Time
Pre-sed. Post-sed. 5min 20rain 40rain Post-op (6 hours)
0 2 Saturation
PaO:
Alfentanil
Meperidine
96.5-+1.5
95.9-+2.1
95-+0.3 98.5-+0.7 98.5+0.2 96.3-+0.9
PaCO 2
Alfentanil
Meperidine
Alfentanil
Meperidine
96.2-+5.1
95.4-+2.3
39.9+1.8
40.1+0.5
94.4-+1.1 97.9-+0.3 98.3-+0.4
93.4+-7.9 119.5-+4.6 150.3_+3.1
94.5-+8.1 120.6-+7.3 152.2-+3.1
42.9-+3.5 42.8-+2.7 41.5-+2.1
44.3+0.8 43.7-+1.5 42.3-+0.7
95.4-+1.0
98.1-+4.3
97.5-+3.7
40.1-+0.7
40.7-+0.3
Table 6. Peri-operative condition: surgeon's satisfaction, patient's satisfaction, side effect and post-operative analgesic request in both groups Alfentanil g r o u p
*Surgeon satisfaction complete satisfaction - moderate satisfactory - unsatisfactory *Patient satisfaction - satisfactory - unsatisfactory *Peri-operative side e f f e c t s and complications - Vomiting - f e e l i n g pain > 3* - resp. depression *Post-operative analgesic requirement -
*According to the 5 steps scale.
Meperidine
group
No. of patient
%
No. of patient
%
18 1 1
90 5 5
12 3 5
60 15 25
19 1
95 5
12 8
60 40
-
-
3 2
15 10
1 .
5 .
3
. 15
. -
-
208 tanil group, there was more surgeon- (90%) and patient- (95%) satisfaction; in the meperidine group these numbers were 60% respectively. The least side effects were seen in the Alfentanil group, only 15% requested for analgesic 6 hours post-operatively.
Discussion
The specific anaesthetic requirements for cataract surgery include also maintenance of low lOP, the absence of vascular congestion and ocular immobility, as an operating microscope is invariably used. The dangers of oculo-cardiac reflex which can be evoked while applying traction on ocular structures must be avoided. A smooth recovery with no restlessness, coughing or vomiting is necessary to avoid a rise in IOP and possible intra-ocular haemorrhage [13]. The major factors which can rapidly influence IOP include: Central venous pressure, systolic blood pressure and PaCO 2. The effects of these variable is largely mediated through variations in choroidal blood flow [14]. In the evaluation of the effect of any anaesthetic technique on IOP, the necessity of standardization of the condition is now well established [15]. In the present study an alfentanil/promazine regimen was compared with meperidine/promazine as IV sedative regimens in patients during cataract operation under local anaesthesia. After oral diazepam premedication there was decrease in IOP in both groups (1.4 mm Hg in group A and 1.3 mm Hg in group M). As IOP can vary by up to 3 mm Hg under normal condition and this small drop correlates with previous studies on the effect of premedication on IOP [16, 17], but may also be due to diurnal IOP variation. This study demonstrates that IV sedation provokes significant decrease in lOP in both groups after IV sedation, but the decrease was much greater in the Alfentanil group than in the Meperidine group. In the Alfentanil group the maximum drop in IOP was 43% (from 18.1 +- 3.2 mm Hg to 10.3 _+2.7 mm Hg) while in the Meperidine group the maximum drop was 28.4% (from 17.6 +- 3.5 to 12.6 +_ 1.9 mm Hg. This drop in lOP was maintained until the end of the measurements. Retrobulbar and facial nerve blocks were performed by an experienced surgeon and in no case there was any concern about the adequacy of the block. A retrobulbar block with local anaesthetic should cause some relaxation of extra-ocular muscles and thus may lead to a slight decrease in IOP [18]. So, any relaxation of extra-ocular muscles due to local nerve block is unlikely to account for the significant decrease in IOP which was noted in this study after sedation. Retrobulbar block carries a small risk of respiratory depression, probably due to intradural injection [19]. It is important under these circumstances, to choose a sedative technique which does not compound the tendency to respiratory depression.
209 The increase in P a C O 2 within each group and between groups was statistically insignificant but somewhat greater in the Meperidine group. It is known that the increased PaCO 2 leads to a rise in IOP and a close linear relationship exists between the two [3]. In this study, the increase in PaCO 2 observed in both groups after sedation PaCO 2 increased by 7.5% in the Alfentanil group and by 10.47% in the Meperidine group. It was not sufficient to exert any significant effect on IOP. In both groups we did not observe signs of respiratory depression either from retrobulbar block or due to the sedative technique as there was no significant decrease in P a O 2 in between group or groups when compared with the base line measurement before O 2 supplementation by face mask. In the same time respiratory rate never reached the depression level at any time (
A l f e n t a n i l / p r o m a z i n e versus Meperidine/promazine as a sedative regimens during local analgesia for cataract operation
OSAMA EL-BASSIOUNY, 1 EZZAT MOHAMED EL-TAHER 2 & MOHAMED EMAD EL-DIN ABD EL-GHAFFAR 2
1Department of Ophthalmology and 2Department of Anaesthesiology, Faculty of Medicine, Suez Canal University, Ismailia, Egypt Accepted 9 September 1992
Key words: Alfentanil, Anaesthesic technique, Cataract operation, IOP, Local analgesia, Meperidine, Promazine, Sedative
Abstract. The influence of two intravenous (IV) sedative regimens on intra-ocular pressure (IOP) was investigated in conjunction with retrobulbar local analgesia. Forty patients of either sex, and similar age with body weight within 40-90 kg were allocated equally and randomly to two groups: Group A (alfentanil/promazine) and group M (meperidine/promazine). Measurement of IOP, systolic pressure, pulse rate, respiratory rate, PaCO2, PaO2 and O2 saturation were made before operation, after premedication, after IV sedation and post-operatively. In the Alfentanil group there was significantly stronger decrease of IOP (p < 0.001). In group A the IOP dropped from 18.1 -+ 3.2mm Hg to 10.3 -+ 2.7ram Hg, i.e. 43%, while in group M the reduction IOP was from 17.6 -+ 3.5 mm Hg to 12.6 -+ 1.9 mm Hg, i.e. 28.4%. Meperidine caused a significant increase in PaCO 2 (4.2 -+ 0.3 mm Hg), however this increase was not sufficient to cause the IOP alterations. The oxygen saturation was lower in group M (decreased by 1.5 -+ 1% in group M versus decrease by 1.0 -+ 1.2% in group A). Cardiovascular parameters were more stable in group A. In conclusion the alfentanil regimen produced a better reduction of the IOP with excellent sedation, operative condition and least anaesthetic side effects.
Introduction T h e c o n t r o l of i n t r a o c u l a r p r e s s u r e ( I O P ) d u r i n g o p h t h a l m i c s u r g e r y is of p r i m e i m p o r t a n c e a n d t h e factors which influence I O P h a v e b e e n d e s c r i b e d [1], i.e. a r t e r i a l p r e s s u r e [2], c e n t r a l v e n o u s p r e s s u r e [3, 4], a n d a r t e r i a l c a r b o n d i o x i d e t e n s i o n [4, 5]. M u c h p u b l i s h e d w o r k has i n v o l v e d t h e use o f g e n e r a l a n a e s t h e s i a [6, 7], b u t an i n c r e a s i n g a m o u n t o f c a t a r a c t s u r g e r y is p e r f o r m e d u n d e r local a n a e s t h e s i a with s e d a t i o n [8] since c a t a r a c t s u r g e r y is p e r f o r m e d c o m m o n l y o n an e l d e r l y p o p u l a t i o n . D u r i n g s u r g e r y I O P is i n f l u e n c e d b y the e x t r a - o c u l a r m u s c l e t o n e , scleral r i g i d i t y a n d v a s c u l a r i t y of t h e orbit. A m a r k e d i n c r e a s e in c e n t r a l v e n o u s p r e s s u r e , for e x a m p l e b y t h e v a l s a l v a m a n o e u v r e o r b y v e n o u s e n g o r g e m e n t d u e to h y p e r c a p n i a , will i n c r e a s e I O R M o s t c e n t r a l n e r v o u s s y s t e m d e p r e s sants, i n c l u d i n g n a r c o t i c analgesics t h a t a r e u s e d to p r o d u c e s e d a t i o n d u r i n g c a t a r a c t s u r g e r y u n d e r local a n a l g e s i a cause a r e d u c t i o n in l O P [9]. B u t t h e
202 possibility exists that other effects of sedation such as hypercapnia or hypoxia may affect the lOP adversely. Meperidine/promazine is often used as a sedative regimen during cataract surgery performed under local analgesia; Alfentanil is a recently introduced short acting opioid analgesic [10-12]. It has a more rapid onset of action, shorter duration and a more rapid recovery than meperidine [10]. The aim of this study was to compare the influence of two intravenous regimens, i.e. meperidine/promazine and alfentanil/promazine on the intraocular pressure in patients who have cataract surgery performed under local anaesthesia.
Subjects and methods Forty patients who were to undergo elective cataract surgery under local anaesthesia with sedation were recruited from January to July 1991 in University Medical Center after patients' consent. Adult patients of either sex, within the weight range 40-90 kg were included. Patients with severe system impairment, known sensitivity to opioid, parkinsonism, or who had drug therapy with known extrapyramidal side effects and patients showing markedly increased lOP were not included in the study. The patients were premedicated with 10 mg diazepam orally 2 hours before operation. An intravenous cannula was placed in the dorsum of the hands. The patients were allocated randomly in two equal groups. Group A (Alfentanil group) received 7 ~xg/kg alfentanil and 0.3 mg/kg promazine as an intravenous sedative regimen and group M (Meperidine group) received 0.7 mg/kg meperidine and 0.3 mg/kg promazine as an intravenous sedative regimen pre-operatively. Local anaesthetic nerve blocks (retrobulbar and facial nerve) were performed by the surgeon, two minutes after sedation, using 15 ml of 2:1 mixture of 2% lidocaine and 0.5% bupivacaine without adrenaline. The ophthalmic surgeon was unaware of the nature of the sedation. The patients were in supine position after instillation of benoxinate 0.5 (2 drops in each eye before lOP measurements using the standardized Schiotz indentation tonometer). In order to exclude the effect of scleral rigidity 2 weights (5.5 and 10) were used. Also, an average of three readings was taken at each time. lOP was measured one day before operation and again two hours after oral premedication by 10mg diazepam. The last measurements was taken as a baseline measurement for IOP. Further measurements were immediately after sedation and after retrobulbar and facial nerve block. At the end of the surgery the lOP was measured in the normal (non operated) eye. Arterial blood samples were taken from a radial arterial cannula during presedation (as baseline measurement) and at 5, 20, and 40 minutes post sedation and finally 6 hours post-operatively. Oxygen saturation, PaCO 2 and
203 PaO 2 were measured in these blood samples using a blood gas analyzer (ABL2-Radiometer). Vital signs were measured during presedation (as baseline measurements) at 5, 15, 45, 60 minutes post sedation then further every 2 hours during next 11 hours (12 hours monitoring), in addition to measurements, the perioperative conditions were assessed as follows: A- Surgeon's satisfaction for the operative condition as being complete, moderate or insufficient. B- Patient's satisfaction for the anaesthetic technique. Each patient was interviewed post operatively. C- Pain assessment during operation by the anaesthetist according to a 5 step scale as follows: 0. No pain. 1. Very slight pain. 2. Slight pain that can be temporarily forgotten. 3. Permanent and tolerable pain that cannot be forgotten. 4. Marked pain that leads the patient to request an analgesia. 5. Intolerable pain with screams and restlessness. This five-step scale was explained pre-operatively to the patients and pain was measured by asking the patient during surgery and post-operatively if he wanted any more analgesic. When the patient was asleep, pain was estimated at (0) level. Side effects as nausea, vomiting, increase narcotic dose, itching, urinary retention, respiratory depression and others were noted during surgery and post-operatively for 12 hours. Data were collected, tabulated and analyzed using paired and unpaired students t-test.
Results
The two groups (A & M) were well matched in terms of the age, sex, weight (Table 1), in the base line measurement of IOP, vital sign (systolic pressure, pulse rate, respiratory rate), blood gases (PaO 2, PaCO 2 and 0 2 saturation), Table 2. Few patients in both groups were suffering from concomitant physical conditions such as hypertension, diabetes, asthma and angina pectoris. Their condition was stable and they were receiving a variety of
Table 1. Demographic data of study population
Age (years) Sex (male:female) Weight (kg)
Alfentanil group
Meperidine group
71 -+ 6.5 5:15 68 -+ 9.7
72 -+ 7.1 6:14 69 -+ 10.5
204 drugs including antihypertensive agents, bronchodilator, antiarrhythmic and oral hypoglycemic agents (Table 3). The mean operating time was similar in each group (35.5 +-5.1 rain in group A and 37.6 +- 6.0 rain in group M) with similar overall time from start IV sedation to end of surgery (sedation time) (45 +- 3 min in group A and 46 +- 5 min in group M). In each group there was a small but statistically significant decrease in lOP, after premedication with oral diazepam. In group A lOP decreased from a mean of 19.5 mm Hg to 18.1 mm Hg (p 0.5). Before 02 administration by face mask there was a decrease in 0 2 saturation from 9 5 -+ / . 5 % to 94-+0.3% in group A and from 95.9-+2.1% to 94.4-+ 1.1% in groups M. The difference between two groups was statistically insignificant. The increase in 0 2 saturation after administration of 0 2 by face mask was similar in both groups A and M. PaO 2 measurements increased significantly from baseline in both groups (p < 0.001) due to 0 2 supplementation by face mask, but there were no significant differences between the groups A and M (Table 5). The peri-operative conditions, the surgeon- and patient-satisfaction for operative and anaesthetic technique, the side effects and complications, and the post-operative, analgesic requests are shown in Table 6. In the AllenTable 5. 02 saturation, PaO 2 and PaC02 in both group (pre-sedation, post-sedation, and post-operatively) Time
Pre-sed. Post-sed. 5min 20rain 40rain Post-op (6 hours)
0 2 Saturation
PaO:
Alfentanil
Meperidine
96.5-+1.5
95.9-+2.1
95-+0.3 98.5-+0.7 98.5+0.2 96.3-+0.9
PaCO 2
Alfentanil
Meperidine
Alfentanil
Meperidine
96.2-+5.1
95.4-+2.3
39.9+1.8
40.1+0.5
94.4-+1.1 97.9-+0.3 98.3-+0.4
93.4+-7.9 119.5-+4.6 150.3_+3.1
94.5-+8.1 120.6-+7.3 152.2-+3.1
42.9-+3.5 42.8-+2.7 41.5-+2.1
44.3+0.8 43.7-+1.5 42.3-+0.7
95.4-+1.0
98.1-+4.3
97.5-+3.7
40.1-+0.7
40.7-+0.3
Table 6. Peri-operative condition: surgeon's satisfaction, patient's satisfaction, side effect and post-operative analgesic request in both groups Alfentanil g r o u p
*Surgeon satisfaction complete satisfaction - moderate satisfactory - unsatisfactory *Patient satisfaction - satisfactory - unsatisfactory *Peri-operative side e f f e c t s and complications - Vomiting - f e e l i n g pain > 3* - resp. depression *Post-operative analgesic requirement -
*According to the 5 steps scale.
Meperidine
group
No. of patient
%
No. of patient
%
18 1 1
90 5 5
12 3 5
60 15 25
19 1
95 5
12 8
60 40
-
-
3 2
15 10
1 .
5 .
3
. 15
. -
-
208 tanil group, there was more surgeon- (90%) and patient- (95%) satisfaction; in the meperidine group these numbers were 60% respectively. The least side effects were seen in the Alfentanil group, only 15% requested for analgesic 6 hours post-operatively.
Discussion
The specific anaesthetic requirements for cataract surgery include also maintenance of low lOP, the absence of vascular congestion and ocular immobility, as an operating microscope is invariably used. The dangers of oculo-cardiac reflex which can be evoked while applying traction on ocular structures must be avoided. A smooth recovery with no restlessness, coughing or vomiting is necessary to avoid a rise in IOP and possible intra-ocular haemorrhage [13]. The major factors which can rapidly influence IOP include: Central venous pressure, systolic blood pressure and PaCO 2. The effects of these variable is largely mediated through variations in choroidal blood flow [14]. In the evaluation of the effect of any anaesthetic technique on IOP, the necessity of standardization of the condition is now well established [15]. In the present study an alfentanil/promazine regimen was compared with meperidine/promazine as IV sedative regimens in patients during cataract operation under local anaesthesia. After oral diazepam premedication there was decrease in IOP in both groups (1.4 mm Hg in group A and 1.3 mm Hg in group M). As IOP can vary by up to 3 mm Hg under normal condition and this small drop correlates with previous studies on the effect of premedication on IOP [16, 17], but may also be due to diurnal IOP variation. This study demonstrates that IV sedation provokes significant decrease in lOP in both groups after IV sedation, but the decrease was much greater in the Alfentanil group than in the Meperidine group. In the Alfentanil group the maximum drop in IOP was 43% (from 18.1 +- 3.2 mm Hg to 10.3 _+2.7 mm Hg) while in the Meperidine group the maximum drop was 28.4% (from 17.6 +- 3.5 to 12.6 +_ 1.9 mm Hg. This drop in lOP was maintained until the end of the measurements. Retrobulbar and facial nerve blocks were performed by an experienced surgeon and in no case there was any concern about the adequacy of the block. A retrobulbar block with local anaesthetic should cause some relaxation of extra-ocular muscles and thus may lead to a slight decrease in IOP [18]. So, any relaxation of extra-ocular muscles due to local nerve block is unlikely to account for the significant decrease in IOP which was noted in this study after sedation. Retrobulbar block carries a small risk of respiratory depression, probably due to intradural injection [19]. It is important under these circumstances, to choose a sedative technique which does not compound the tendency to respiratory depression.
209 The increase in P a C O 2 within each group and between groups was statistically insignificant but somewhat greater in the Meperidine group. It is known that the increased PaCO 2 leads to a rise in IOP and a close linear relationship exists between the two [3]. In this study, the increase in PaCO 2 observed in both groups after sedation PaCO 2 increased by 7.5% in the Alfentanil group and by 10.47% in the Meperidine group. It was not sufficient to exert any significant effect on IOP. In both groups we did not observe signs of respiratory depression either from retrobulbar block or due to the sedative technique as there was no significant decrease in P a O 2 in between group or groups when compared with the base line measurement before O 2 supplementation by face mask. In the same time respiratory rate never reached the depression level at any time (
