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MODIFICATION BY FENTANYL AND ALFENTANIL OF THE INTRAOCULAR PRESSURE RESPONSE TO SUXAMETHONIUM AND TRACHEAL INTUBATION
Br. J. Anaesth. (1989), 63, 688-691
MODIFICATION BY FENTANYL AND ALFENTANIL OF THE INTRAOCULAR PRESSURE RESPONSE TO SUXAMETHONIUM AND TRACHEAL INTUBATION J. SWEENEY, S. UNDERHILL, T. DOWD AND S. M. MOSTAFA
PATIENTS AND METHODS
The study was approved by the District Medical Ethics Committee. A pilot study was conducted in seven patients to demonstrate the effects of suxamethonium and tracheal intubation on IOP. This showed an increase in IOP from 12 to 21 mm Hg (mean 9.0, range 5-15 mm Hg) similar to that described in previous reports [1-3, 7, 8]. The increase in IOP lasted for approximately 8 min. An increase in mean arterial pressure (mean 30, range 28-34 mm Hg) and heart rate (mean 21, range 14-30 beat min"1) was noted also. Therefore we studied 40 consecutive adult patients who gave written informed consent: 16 males and 24 J. SWEENEY*, F.F.A.R.C.S. (ENG.); S. UNDERHILL, F.F.A.R.C.S. (ENG.); S. M. MOSTAFA, F.F.A.R.C.S. (ENG.), Anaesthetic Office,
12th Floor, Royal Liverpool Hospital, Prescot Street, Liverpool L7 8XP. T. DOWD, B.SC, D.O., F.R.C.S.(GLAS.).,
Department of Ophthalmology, St Paul's Eye Hospital, Old Hall Street, Liverpool 3. Accepted for Publication: June 6, 1989. * Present address: Department of Anaesthesia, Arrowe Park Hospital, Upton, Wirral L49 5LN. Correspondence to S.M.M.
SUMMARY We have measured in a double-blind study the changes in intraocular pressure (IOP) in 40 consecutive patients (pretreated with fentanyl or alfentanil) who received suxamethonium and tracheal intubation. Although IOP increased significantly following administration of suxamethonium, mean IOP in both groups remained significantly less than control values (P < 0.002). Tracheal intubation caused a further significant increase in IOP in the fentanyl, but not the alfentanil group. There were no significant differences in mean IOP between the fentanyl and alfentanil groups. Both opioids reduced, but did not abolish the haemodynamic responses to tracheal intubation.
females of ASA class I and II undergoing routine ophthalmic operations under general anaesthesia. Immediately before induction of anaesthesia, patients were allocated randomly to one of two groups to receive fentanyl or alfentanil. All IOP measurements were performed by the same investigator (T.D.) using a hand held Perkins applanation tonometer [9] following application of one or two drops of 0.4% benoxinate solution. With the patient in the supine position, intraocular pressure was measured on the unoperated normal eye (denned as an eye with preoperative IOP of 22 mm Hg or less [10]). Control IOP, heart rate and systemic arterial pressure measurements were made immediately before administration of the trial drugs. The patient was then given 0.1 ml kg"1 of the study drug (equivalent to 2.5 or 10 jig kg"1 of fentanyl or alfentanil, respectively). Further measurements of IOP, mean arterial pressure and heart rate were
Downloaded from http://bja.oxfordjournals.org/ at Harvard University on July 17, 2015
Suxamethonium and tracheal intubation increase intraocular pressure (IOP) [1-3], but are essential components of anaesthesia for much eye surgery. Fentanyl and alfentanil decrease IOP and attenuate haemodynamic responses to laryngoscopy and tracheal intubation [4,5]. Anaesthetic techniques which reduce IOP or prevent an increase may minimize vascular congestion of the eye and its contents [6]. This study was undertaken to assess and compare the efficacy of alfentanil and fentanyl in the prevention of increases of IOP following the administration of suxamethonium and tracheal intubation.
FENTANYL, ALFENTANIL AND IOP
689
the end of the operation with neostigmine 50 ug kg"1 and glycopyrrolate 10 ug kg"1. Changes in IOP, mean arterial pressure and heart rate within groups were analysed by means of two-way analysis of variance. Comparisons between groups were analysed by means of an unpaired t test. RESULTS
There were no significant differences between the two groups in physical characteristics of the patients and mean dose of thiopentone (table I). The majority of operations comprised cataract extraction and dacryocystorhinostomy. There were no significant differences between mean control IOP, mean arterial pressure and heart rate in the two groups (tables II, III). Administration of fentanyl or alfentanil before anaesthesia produced a significant decrease iri IOP (P<0.03 and 0.002, respectively). Suxamethonium and tracheal intubation increased IOP in both groups. Although the increase was significant compared with the values obtained immediately before administration of suxamethonium (P < 0.001), mean IOP following suxamethonium was significantly lower than control values in both groups (P < 0.002). Furthermore, mean IOP values after intubation were not significantly different from control values. The increase in IOP following tracheal intubation was significant only in the fentanyl group (P < 0.01). Alfentanil produced a significant reduction (7.1 %) in mean arterial pressure before induction
TABLE I. Patient details mean (SD) Sex Group Fentanyl Alfentanil
Age (yr)
Weight (kg)
(M/F)
Thiopentone (mg kg"1)
66.1 (14.6) 65.8 (16)
60.8(11) 63 (10)
7/13 9/11
2.41 (0.65) 2.68 (0.7)
TABLE II. Mean (SD) intraocular pressures (mm Hg) in patients given fentanyl or alfentanil. Sux. = Suxamethonium; PI = post-intubation. *P < 0.05; **P < 0.01, compared with control Time after suxamethonium (min) Group
n
Fentanyl
20
Alfentanil
20
Control value 12 (2.9) 11.9 (4.3)
Before induction 9.9* (3.6) 9.8** (2.8)
Before sux. 6.8** (3.9) 5.9** (2.2)
1
2.5(PI)
5
7.5
10
12.5
9.1** (4.1) 9.2** (2.9)
11.8 (5.6) 10.8 (3.7)
6.4 (3.8) 7.3 (2.7)
5.1 (4.1) 6.1 (3.3)
4 (2.8) 4.1 (2.4)
3.3 (2.5) 3.5 (2.7)
Downloaded from http://bja.oxfordjournals.org/ at Harvard University on July 17, 2015
obtained simultaneously 3 min later (pre-induction), before administration of suxamethonium and 1, 2.5, 5, 7.5, 10 and 12.5 min thereafter. All patients were premedicated with diazepam 5-10 mg orally 2 h before operation. Anaesthesia was induced with thiopentone 2-4 mg kg"1 and followed by suxamethonium 1.5 mg i.v. Inflation of the lungs with 66 % nitrous oxide in oxygen, laryngoscopy and spraying of the vocal cords with lignocaine 1.5 mg kg"1 were performed after satisfactory neuromuscular block was achieved. None of the patients showed movement during intubation of the trachea with a size 8- or 9-mm cuffed Magill tracheal tube. Ventilation of the lungs was controlled using a mixture of 66 % nitrous oxide in oxygen fed into the delivery tube of a Bain type co-axial breathing circuit [11]. Fresh gas flow from the anaesthetic machine was adjusted to deliver total fresh gas flow as close as possible to 70 ml kg"1 min"1 to produce normocapnia during controlled ventilation [12]. In order to maintain the smallest mean intrathoracic pressure and optimal ventilation of the lungs, the tidal volume was adjusted to approximately 10-12 ml kg"1 with a ventilatory frequency of 12 b.p.m. Atracurium 0.6 mg kg"1 was given i.v. at the end of the study period or upon the earliest sign of recovery of neuromuscular function. Surgery commenced when the study period was completed and anaesthesia continued with 66% nitrous oxide and 0.8% enflurane in oxygen. Droperidol 5 mg i.v. was given as an antiemetic. Residual neuromuscular block was antagonized at
BRITISH JOURNAL OF ANAESTHESIA
690
TABLE III. Mean (SD) cardiovascular variables in patients given fentanyl or alfentanil. Sux. = Suxamethonium; PI = post-intubation. P < 0.05; *compared with control; -[compared with preintubation Time after suxamethonium (min) n
Mean arterial pressure (mm Hg) 20 Fentanyl 20
Alfentanil 1
Heart rate (beat min" ) Fentanyl Alfentanil
20 20
value
Before Before induction sux.
1
2.5(PI)
5
7.5
10
12.5 74
105.7 (15.3) 107.2 (17.9)
102.9 (15.8) 99.6 (15.1)
96.3 (12.3) 94.6 (17.2)
96.8 118.2*f 101.6 (11.9) (22.7) (23.7) 98.6 127.4*t 109.3 (17.6) (26.8) (22.7)
85.6 (23.6) 95.5 (20.1)
76.8 (17.4) 87.2 (23.5)
(11.1) 85.5 (24.1)
74.4 (14.1) 76.1 (9.9)
73.4 (13.6) 74.6 (12.4)
73.8 (12.2) 73.1 (10.7)
76.4 (17.1) 77.5 (11.4)
65.8 (15.9) 66.2 (11.4)
62.9 (12.1) 64.9 (11.6)
62.1 (9.8) 64.3 (11.7)
DISCUSSION
Suxamethonium and tracheal intubation have been shown to increase IOP [1-3, 7, 8, 13, 14]. Many techniques have been advocated to prevent the increase in IOP caused by suxamethonium, but none has been shown to prevent the response consistently. Pretreatment with acetazolamide, lignocaine, non-depolarizing neuromuscular blocking drugs, diazepam and " self-taming " by suxamethonium 10 mg were advocated by some authors, only to be refuted by others [15]. Central venous pressure and arterial carbon dioxide tension may influence IOP [16]. In the present study all measurements were made with the patient in the horizontal position and ventilation was assisted or controlled via a Bain circuit to maintain normocapnia. Both groups would have been affected similarly. Our study confirms the results of previous
investigations that fentanyl, alfentanil and thiopentone significantly reduce IOP [4, 14]. A much greater reduction in IOP occurred following thiopentone than after fentanyl or alfentanil. The present study was designed to compare the efficacy of the two analgesics in attenuating the increase in IOP following administration of suxamethonium and tracheal intubation. The stimulus of tracheal intubation causes an increase in IOP which is greater than that produced by suxamethonium [3,8, 13]. In addition, tracheal intubation exaggerates the increase in IOP caused by suxamethonium [3,8]. The present study demonstrates that, while IOP increased following suxamethonium, mean IOP remained significantly lower than control values in both groups. Thus both fentanyl and alfentanil may attenuate or prevent the increase in IOP caused by suxamethonium. Furthermore, despite an increase following tracheal intubation in both groups which was significant only in the fentanyl group IOP did not differ significantly from control values. The mechanisms by which fentanyl and alfentanil reduce IOP are probably similar to those of other central nervous system depressants [14, 15]. These include relaxation of intra- or extraocular muscles, facilitation of outflow of aqueous humour or decrease in production of aqueous humour. Fentanyl 5 (ig kg"1 and alfentanil 30 ug kg"1 successfully attenuated the cardiovascular effects of tracheal intubation [5]. Similar doses may produce cardiovascular depression in elderly patients [Kirby IJ, personal communication]. Although the larynx and trachea were sprayed with topical lignocaine, its efficacy in prevention
Downloaded from http://bja.oxfordjournals.org/ at Harvard University on July 17, 2015
of anaesthesia (P < 0.01). In both groups tracheal intubation produced a significant increase in mean arterial pressure above control and preintubation values (P < 0.01). There were no significant differences between the two groups. There were no significant differences between the mean heart rate changes from control over the study period between the two groups. Tracheal intubation significantly increased mean heart rate above control by 11.7 % and 12.6% in the alfentanil and fentanyl groups, respectively (P < 0.01). Satisfactory operating conditions in both groups were reported by the surgeons. After operation, one patient in each group developed nausea and vomiting.
70 83.8* (15.4) (14.2) 84.7*t 70.7 (13.4) (9.7)
FENTANYL, ALFENTANIL AND IOP
691
of the pressor response to laryngoscopy and tracheal intubation is no greater than that of saline [17]. Although mean arterial pressure increased significantly, IOP did not increase above control values. This would support the view that changes in arterial pressure appear to be relatively unimportant in control of IOP [3, 14]. Our results also support the view that depth of anaesthesia has a profound effect on the increase in IOP following suxamethonium. The lighter the anaesthetic, the more likely is an increase in IOP [18-20].
2. 3. 4. 5. 6. 7.
8.
Downloaded from http://bja.oxfordjournals.org/ at Harvard University on July 17, 2015
1.
intraocular hypertension produced by suxamethonium. British Journal of Anaesthesia 1972; 44: 191. 9. Perkins ES. Hand-held applanation tonometer. British Journal of Ophthalmology 1965; 49: 591-593. 10. Utting JE. Anaesthesia for ophthalmic surgery. In: Gray TC, Nunn JF, Utting JE, eds. General Anaesthesia, 4th Edn, Vol. 2. London: Butterworths, 1980; 1205. 11. Bain J, Sporrel WE. Flow requirements for modified Mapleson D system during controlled ventilation. Canadian Anaesthetists Society Journal 1973; 20: 629636. 12. Henville JD, Adams AP. The Bain anaesthetic system. An assessment during controlled ventilation. Anaesthesia 1976; 31: 247-256. 13. Joshi C, Bruce DL. Thiopental and succinylcholine: action on intraocular pressure. Anesthesia and Analgesia 1975; 54: 471. REFERENCES 14. Duncalf D, Fouldes FF. Effect of anesthetic drugs and muscle relaxants on intraocular pressure. International Cook JH. The effects of suxamethonium on intraocular Ophthalmology Clinics 1973; 13: 21. pressure. Anaesthesia 1981; 36: 354-365. Adams AK, Barnett KC. Anaesthesia and intraocular 15. Cunningham AJ, Barry P. Intraocular pressure— physiology and implications for anaesthetic management. pressure. Anaesthesia 1966; 21: 202-210. Canadian Anaesthetists Society Journal 1986; 33: 195. Bowen DJ, McGrand JC, Hamilton AG. Intraocular pressures after suxamethonium and endotracheal intu- 16. Hvidberg A, Kessing SV, Fernandes A. Effect of changes in Pco2 and body positions on intraocular pressure during bation. Anaesthesia 1978; 33: 518-522. general anaesthesia. Acta Ophthalmologica 1981; 59: 465. Mostafa SM, Lockhart A, Kumar D, Bayoumi M. Comparison of effects of fentanyl and alfentanil on 17. Derbyshire DR, Smith G, Achola KJ. Effect of topical lignocaine on the sympathoadrenal responses to tracheal intraocular pressure. Anaesthesia 1986; 41: 493-498. intubation. British Journal of Anaesthesia 1987; 59: 300. Black TE, Kay B, Healy TEJ. Reducing the haemodynamic responses to laryngoscopy and intubation. 18. Libonati MD, Margaret M, Leahy JJ, Ellison N. The use of succinylcholine in open eye surgery. Anesthesiology Anaesthesia 1984; 39: 883-887. 1985; 62: 637-640. Duncalf D, Rhodes DH jr. Anesthesia in Clinical Ophthalmology. Baltimore: Williams and Wilkins, 1963; 11. 19. Lincoff HA, Breinin GM, Devoe AG. The effect of succinylcholine on extraocular muscles. American Journal Wynends JE, Romwell DE. Intraocular tension in asof Ophthalmology 1957; 43: 440-444. sociation with succinylcholine and endotracheal intubation: a preliminary report. Canadian Anaesthetists 20. Lewallen WM jr, Hicks BL. The use of succinylcholine in Society Journal 1960; 7: 39. ocular surgery. American Journal of Ophthalmology 1963; 49: 773-780. Pandey K, Badola RP, Kumar S. Time course of
MODIFICATION BY FENTANYL AND ALFENTANIL OF THE INTRAOCULAR PRESSURE RESPONSE TO SUXAMETHONIUM AND TRACHEAL INTUBATION J. SWEENEY, S. UNDERHILL, T. DOWD AND S. M. MOSTAFA
PATIENTS AND METHODS
The study was approved by the District Medical Ethics Committee. A pilot study was conducted in seven patients to demonstrate the effects of suxamethonium and tracheal intubation on IOP. This showed an increase in IOP from 12 to 21 mm Hg (mean 9.0, range 5-15 mm Hg) similar to that described in previous reports [1-3, 7, 8]. The increase in IOP lasted for approximately 8 min. An increase in mean arterial pressure (mean 30, range 28-34 mm Hg) and heart rate (mean 21, range 14-30 beat min"1) was noted also. Therefore we studied 40 consecutive adult patients who gave written informed consent: 16 males and 24 J. SWEENEY*, F.F.A.R.C.S. (ENG.); S. UNDERHILL, F.F.A.R.C.S. (ENG.); S. M. MOSTAFA, F.F.A.R.C.S. (ENG.), Anaesthetic Office,
12th Floor, Royal Liverpool Hospital, Prescot Street, Liverpool L7 8XP. T. DOWD, B.SC, D.O., F.R.C.S.(GLAS.).,
Department of Ophthalmology, St Paul's Eye Hospital, Old Hall Street, Liverpool 3. Accepted for Publication: June 6, 1989. * Present address: Department of Anaesthesia, Arrowe Park Hospital, Upton, Wirral L49 5LN. Correspondence to S.M.M.
SUMMARY We have measured in a double-blind study the changes in intraocular pressure (IOP) in 40 consecutive patients (pretreated with fentanyl or alfentanil) who received suxamethonium and tracheal intubation. Although IOP increased significantly following administration of suxamethonium, mean IOP in both groups remained significantly less than control values (P < 0.002). Tracheal intubation caused a further significant increase in IOP in the fentanyl, but not the alfentanil group. There were no significant differences in mean IOP between the fentanyl and alfentanil groups. Both opioids reduced, but did not abolish the haemodynamic responses to tracheal intubation.
females of ASA class I and II undergoing routine ophthalmic operations under general anaesthesia. Immediately before induction of anaesthesia, patients were allocated randomly to one of two groups to receive fentanyl or alfentanil. All IOP measurements were performed by the same investigator (T.D.) using a hand held Perkins applanation tonometer [9] following application of one or two drops of 0.4% benoxinate solution. With the patient in the supine position, intraocular pressure was measured on the unoperated normal eye (denned as an eye with preoperative IOP of 22 mm Hg or less [10]). Control IOP, heart rate and systemic arterial pressure measurements were made immediately before administration of the trial drugs. The patient was then given 0.1 ml kg"1 of the study drug (equivalent to 2.5 or 10 jig kg"1 of fentanyl or alfentanil, respectively). Further measurements of IOP, mean arterial pressure and heart rate were
Downloaded from http://bja.oxfordjournals.org/ at Harvard University on July 17, 2015
Suxamethonium and tracheal intubation increase intraocular pressure (IOP) [1-3], but are essential components of anaesthesia for much eye surgery. Fentanyl and alfentanil decrease IOP and attenuate haemodynamic responses to laryngoscopy and tracheal intubation [4,5]. Anaesthetic techniques which reduce IOP or prevent an increase may minimize vascular congestion of the eye and its contents [6]. This study was undertaken to assess and compare the efficacy of alfentanil and fentanyl in the prevention of increases of IOP following the administration of suxamethonium and tracheal intubation.
FENTANYL, ALFENTANIL AND IOP
689
the end of the operation with neostigmine 50 ug kg"1 and glycopyrrolate 10 ug kg"1. Changes in IOP, mean arterial pressure and heart rate within groups were analysed by means of two-way analysis of variance. Comparisons between groups were analysed by means of an unpaired t test. RESULTS
There were no significant differences between the two groups in physical characteristics of the patients and mean dose of thiopentone (table I). The majority of operations comprised cataract extraction and dacryocystorhinostomy. There were no significant differences between mean control IOP, mean arterial pressure and heart rate in the two groups (tables II, III). Administration of fentanyl or alfentanil before anaesthesia produced a significant decrease iri IOP (P<0.03 and 0.002, respectively). Suxamethonium and tracheal intubation increased IOP in both groups. Although the increase was significant compared with the values obtained immediately before administration of suxamethonium (P < 0.001), mean IOP following suxamethonium was significantly lower than control values in both groups (P < 0.002). Furthermore, mean IOP values after intubation were not significantly different from control values. The increase in IOP following tracheal intubation was significant only in the fentanyl group (P < 0.01). Alfentanil produced a significant reduction (7.1 %) in mean arterial pressure before induction
TABLE I. Patient details mean (SD) Sex Group Fentanyl Alfentanil
Age (yr)
Weight (kg)
(M/F)
Thiopentone (mg kg"1)
66.1 (14.6) 65.8 (16)
60.8(11) 63 (10)
7/13 9/11
2.41 (0.65) 2.68 (0.7)
TABLE II. Mean (SD) intraocular pressures (mm Hg) in patients given fentanyl or alfentanil. Sux. = Suxamethonium; PI = post-intubation. *P < 0.05; **P < 0.01, compared with control Time after suxamethonium (min) Group
n
Fentanyl
20
Alfentanil
20
Control value 12 (2.9) 11.9 (4.3)
Before induction 9.9* (3.6) 9.8** (2.8)
Before sux. 6.8** (3.9) 5.9** (2.2)
1
2.5(PI)
5
7.5
10
12.5
9.1** (4.1) 9.2** (2.9)
11.8 (5.6) 10.8 (3.7)
6.4 (3.8) 7.3 (2.7)
5.1 (4.1) 6.1 (3.3)
4 (2.8) 4.1 (2.4)
3.3 (2.5) 3.5 (2.7)
Downloaded from http://bja.oxfordjournals.org/ at Harvard University on July 17, 2015
obtained simultaneously 3 min later (pre-induction), before administration of suxamethonium and 1, 2.5, 5, 7.5, 10 and 12.5 min thereafter. All patients were premedicated with diazepam 5-10 mg orally 2 h before operation. Anaesthesia was induced with thiopentone 2-4 mg kg"1 and followed by suxamethonium 1.5 mg i.v. Inflation of the lungs with 66 % nitrous oxide in oxygen, laryngoscopy and spraying of the vocal cords with lignocaine 1.5 mg kg"1 were performed after satisfactory neuromuscular block was achieved. None of the patients showed movement during intubation of the trachea with a size 8- or 9-mm cuffed Magill tracheal tube. Ventilation of the lungs was controlled using a mixture of 66 % nitrous oxide in oxygen fed into the delivery tube of a Bain type co-axial breathing circuit [11]. Fresh gas flow from the anaesthetic machine was adjusted to deliver total fresh gas flow as close as possible to 70 ml kg"1 min"1 to produce normocapnia during controlled ventilation [12]. In order to maintain the smallest mean intrathoracic pressure and optimal ventilation of the lungs, the tidal volume was adjusted to approximately 10-12 ml kg"1 with a ventilatory frequency of 12 b.p.m. Atracurium 0.6 mg kg"1 was given i.v. at the end of the study period or upon the earliest sign of recovery of neuromuscular function. Surgery commenced when the study period was completed and anaesthesia continued with 66% nitrous oxide and 0.8% enflurane in oxygen. Droperidol 5 mg i.v. was given as an antiemetic. Residual neuromuscular block was antagonized at
BRITISH JOURNAL OF ANAESTHESIA
690
TABLE III. Mean (SD) cardiovascular variables in patients given fentanyl or alfentanil. Sux. = Suxamethonium; PI = post-intubation. P < 0.05; *compared with control; -[compared with preintubation Time after suxamethonium (min) n
Mean arterial pressure (mm Hg) 20 Fentanyl 20
Alfentanil 1
Heart rate (beat min" ) Fentanyl Alfentanil
20 20
value
Before Before induction sux.
1
2.5(PI)
5
7.5
10
12.5 74
105.7 (15.3) 107.2 (17.9)
102.9 (15.8) 99.6 (15.1)
96.3 (12.3) 94.6 (17.2)
96.8 118.2*f 101.6 (11.9) (22.7) (23.7) 98.6 127.4*t 109.3 (17.6) (26.8) (22.7)
85.6 (23.6) 95.5 (20.1)
76.8 (17.4) 87.2 (23.5)
(11.1) 85.5 (24.1)
74.4 (14.1) 76.1 (9.9)
73.4 (13.6) 74.6 (12.4)
73.8 (12.2) 73.1 (10.7)
76.4 (17.1) 77.5 (11.4)
65.8 (15.9) 66.2 (11.4)
62.9 (12.1) 64.9 (11.6)
62.1 (9.8) 64.3 (11.7)
DISCUSSION
Suxamethonium and tracheal intubation have been shown to increase IOP [1-3, 7, 8, 13, 14]. Many techniques have been advocated to prevent the increase in IOP caused by suxamethonium, but none has been shown to prevent the response consistently. Pretreatment with acetazolamide, lignocaine, non-depolarizing neuromuscular blocking drugs, diazepam and " self-taming " by suxamethonium 10 mg were advocated by some authors, only to be refuted by others [15]. Central venous pressure and arterial carbon dioxide tension may influence IOP [16]. In the present study all measurements were made with the patient in the horizontal position and ventilation was assisted or controlled via a Bain circuit to maintain normocapnia. Both groups would have been affected similarly. Our study confirms the results of previous
investigations that fentanyl, alfentanil and thiopentone significantly reduce IOP [4, 14]. A much greater reduction in IOP occurred following thiopentone than after fentanyl or alfentanil. The present study was designed to compare the efficacy of the two analgesics in attenuating the increase in IOP following administration of suxamethonium and tracheal intubation. The stimulus of tracheal intubation causes an increase in IOP which is greater than that produced by suxamethonium [3,8, 13]. In addition, tracheal intubation exaggerates the increase in IOP caused by suxamethonium [3,8]. The present study demonstrates that, while IOP increased following suxamethonium, mean IOP remained significantly lower than control values in both groups. Thus both fentanyl and alfentanil may attenuate or prevent the increase in IOP caused by suxamethonium. Furthermore, despite an increase following tracheal intubation in both groups which was significant only in the fentanyl group IOP did not differ significantly from control values. The mechanisms by which fentanyl and alfentanil reduce IOP are probably similar to those of other central nervous system depressants [14, 15]. These include relaxation of intra- or extraocular muscles, facilitation of outflow of aqueous humour or decrease in production of aqueous humour. Fentanyl 5 (ig kg"1 and alfentanil 30 ug kg"1 successfully attenuated the cardiovascular effects of tracheal intubation [5]. Similar doses may produce cardiovascular depression in elderly patients [Kirby IJ, personal communication]. Although the larynx and trachea were sprayed with topical lignocaine, its efficacy in prevention
Downloaded from http://bja.oxfordjournals.org/ at Harvard University on July 17, 2015
of anaesthesia (P < 0.01). In both groups tracheal intubation produced a significant increase in mean arterial pressure above control and preintubation values (P < 0.01). There were no significant differences between the two groups. There were no significant differences between the mean heart rate changes from control over the study period between the two groups. Tracheal intubation significantly increased mean heart rate above control by 11.7 % and 12.6% in the alfentanil and fentanyl groups, respectively (P < 0.01). Satisfactory operating conditions in both groups were reported by the surgeons. After operation, one patient in each group developed nausea and vomiting.
70 83.8* (15.4) (14.2) 84.7*t 70.7 (13.4) (9.7)
FENTANYL, ALFENTANIL AND IOP
691
of the pressor response to laryngoscopy and tracheal intubation is no greater than that of saline [17]. Although mean arterial pressure increased significantly, IOP did not increase above control values. This would support the view that changes in arterial pressure appear to be relatively unimportant in control of IOP [3, 14]. Our results also support the view that depth of anaesthesia has a profound effect on the increase in IOP following suxamethonium. The lighter the anaesthetic, the more likely is an increase in IOP [18-20].
2. 3. 4. 5. 6. 7.
8.
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