Acta Anaesthesiol Scand 1990: 34: 202-205
Comparison of the effects of isoflurane and halothane on intraocular pressure R. K. MIRAKHUR, P. ELLIOTT,W. F. I. SHEPHERD and J. N. MCGALLIARD Departments of Anaesthesia and Ophthalmology, Royal Victoria Hospital, Belfast, Northern Ireland, UK
Intraocular pressure (IOP) was measured in four groups of patients receiving isoflurane or halothane in consecutively increasing or decreasing concentrations (1.0, 2.0 and 3.0 MAC in 70% nitrous oxide). IOP decreased significantly in all groups irrespective of whether the higher or the lower concentration of the volatile agent was used first. There were no further significant changes in IOP whether the concentrations were increased or decreased, suggesting no dose-relation. Maximum reductions in IOP were slightly greater in those receiving the higher concentrations of the volatile agents first (64 and 66% with isoflurane and halothane, respectively) in comparison to those receiving the lower concentrations first (54 and 46%, respectively). Receiued 2 May, accepted for publication 7 November 1989
Key words: Ophthalmic anesthesia: intraocular pressure; volatile anesthetics: isoflurane, halothane.
Good control of intraocular pressure (IOP) is an important determinant of the success of intraocular surgery (1). A variety of measures are employed during general anaesthesia for maintaining a low IOP. Volatile anaesthetics often constitute a part of the overall general anaesthetic technique employed in ophthalmic anaesthesia for intraocular surgery. Halothane has been a popular agent, but there are differing opinions about its effectiveness in controlling I O P (2, 3 ) . Isoflurane is perhaps one of the most commonly used volatile agents now and, although there are some reports about its effects on IOP, the results from these appear to be contradictory (4-6). Whereas Earnshaw (5) and Craig & Cook (6) showed a reduction in adults, Ausinch et al. (4) were unable to show any change in I O P in children. Moreover, there is no information about the effects of isoflurane on I O P with increasing or decreasing concentrations. I n the present study, we have investigated the effects of sequentially increasing or decreasing concentrations of isoflurane on I O P and compared the results with halothane administered in a similar way.
tion. Ventilation was carried out with 70% nitrous oxide in oxygen (as determined by an in-line oxygen analyser) and was adjusted to maintain an end-tidal carbon dioxide concentration of 4.5-5.0%. Following intubation, patients were randomly allocated to one of the four groups of six each. Groups I and I11 were administered isoflurane or halothane, respectively, at concentrations of 1.O, 2.0 and 3.0 MAC (end-tidal in 70% nitrous oxide) sequentially for periods of 10 rnin each. Groups I1 and IV received isoflurane or halothane in decreasing concentrations, i.e., 3.0, 2.0 and 1.0 MAC sequentially, again for periods of 10 min each. The actual concentrations of the volatile agents were 0.5, 1.0 and 1.5% for isoflurane and 0.3,0.6and 0.9% for halothane, equivalent to 1.0,2.0and 3.0 MAC, respectively, of the two volatile agents (7). IOP, heart rate and arterial blood pressure were measured in each patient prior to induction of anaesthesia, immediately following intubation and at the end of each 10min period. End-tidal concentrations of carbon dioxide and the volatile agent were monitored continuously. IOP was measured with a hand-held Perkins’applanation tonometer (8) in the eye not to be operated upon. Heart rate was measured from ECG, arterial pressure using an oscillotonometer (Dinamap) and the end-tidal concentrations of carbon dioxide and the volatile agent using infra-red analysers (Engstrom Eliza capnograph; Datex Normac vapour monitor). The measurement of IOP prior to induction of anaesthesia was carried out following the instillation of 0.4% benoxinate. All patients stayed horizontal throughout the study. Surgery was started after completion of all measurements. The results were subjected to repeated measures analysis of variance and t-tests to determine their statistical significance. A P-value of < 0.05 represented a statistically significant result.
PATIENTS AND METHODS Twenty-four adult patients conforming to ASA Grade I scheduled to undergo elective ophthalmic surgery were included in the study with their informed consent and the approval of the Regional Ethical Committee. Premedication was with diazepam 10 mg orally 60 min preoperatively, and anaesthesia was induced with thiopentone 4-5 mg/kg, preceded by fentanyl 100 pg. Pancuronium in a dose of 0.07 mg/kg was administered to provide muscle relaxation. Tracheal intubation was carried out about 4 min after the relaxant administra-
RESULTS The patients in the four groups were comparable with regard to age, weight and baseline (awake) and postintubation IOP (Table 1). I O P increased, although not significantly, in three out of four groups following tracheal intubation.
283
ISOFLURANE, HALOTHANE AND IOP Table 1 Age, weight and intraocular pressure (IOP). Halothane
Isoflurane Group I Age (yr+s.d) Weight (kg + s.d) Baseline IOP (mmHg s.d) (kPa f s.d) Post-induction IOP (mmHg f s.d.) (kPa+s.d)
36 f 14.8 74 f 16.6 14.8 f 0.98 (2.0f0.13) 16.8 f 2.79 (2.2 f 0.37)
Group I1
Group I11
Group IV
47 f 14.7 68 f 10.9 14.0 f 2.83 (1.9 f0.38) 14.8 f 5.08 (2.0 f 0.68)
31 f 13.2 65 f 16.0 13.5 f 2.81 (1.8f0.37) 14.3 3.50 (1.9f 0.47)
38k 17.6 64 f 15.0 16.0f 3.90 (2.1+ 0.52) 14.7 f 3.01 (2.05 0.40)
Groups I and 111 received the volatile agents in sequentially increasing concentrations, i.e. 1 MAC followed by 2 and 3 MAC; Groups I1 and IV received the volatile agents in sequentially decreasing concentrations.
The I O P values in patients administered isoflurane (Groups I and 11) are shown in Fig. 1. I O P decreased significantly ( P < 0.01) from mean baseline values of 14.8 and 14.0 mmHg (2.0 and 1.9 kPa) respectively to 7.5 and 6.0 mmHg (1.O and 0.8 kPa) after administration of 1.0 and 3.0 MAC isoflurane. Any further changes in I O P were insignificant in both groups. I O P changes in patients administered halothane (Groups I11 and IV) are shown in Fig. 2. IOP decreased once again in these groups in a manner similar to that observed in the isoflurane groups. It decreased significantly (P
Comparison of the effects of isoflurane and halothane on intraocular pressure R. K. MIRAKHUR, P. ELLIOTT,W. F. I. SHEPHERD and J. N. MCGALLIARD Departments of Anaesthesia and Ophthalmology, Royal Victoria Hospital, Belfast, Northern Ireland, UK
Intraocular pressure (IOP) was measured in four groups of patients receiving isoflurane or halothane in consecutively increasing or decreasing concentrations (1.0, 2.0 and 3.0 MAC in 70% nitrous oxide). IOP decreased significantly in all groups irrespective of whether the higher or the lower concentration of the volatile agent was used first. There were no further significant changes in IOP whether the concentrations were increased or decreased, suggesting no dose-relation. Maximum reductions in IOP were slightly greater in those receiving the higher concentrations of the volatile agents first (64 and 66% with isoflurane and halothane, respectively) in comparison to those receiving the lower concentrations first (54 and 46%, respectively). Receiued 2 May, accepted for publication 7 November 1989
Key words: Ophthalmic anesthesia: intraocular pressure; volatile anesthetics: isoflurane, halothane.
Good control of intraocular pressure (IOP) is an important determinant of the success of intraocular surgery (1). A variety of measures are employed during general anaesthesia for maintaining a low IOP. Volatile anaesthetics often constitute a part of the overall general anaesthetic technique employed in ophthalmic anaesthesia for intraocular surgery. Halothane has been a popular agent, but there are differing opinions about its effectiveness in controlling I O P (2, 3 ) . Isoflurane is perhaps one of the most commonly used volatile agents now and, although there are some reports about its effects on IOP, the results from these appear to be contradictory (4-6). Whereas Earnshaw (5) and Craig & Cook (6) showed a reduction in adults, Ausinch et al. (4) were unable to show any change in I O P in children. Moreover, there is no information about the effects of isoflurane on I O P with increasing or decreasing concentrations. I n the present study, we have investigated the effects of sequentially increasing or decreasing concentrations of isoflurane on I O P and compared the results with halothane administered in a similar way.
tion. Ventilation was carried out with 70% nitrous oxide in oxygen (as determined by an in-line oxygen analyser) and was adjusted to maintain an end-tidal carbon dioxide concentration of 4.5-5.0%. Following intubation, patients were randomly allocated to one of the four groups of six each. Groups I and I11 were administered isoflurane or halothane, respectively, at concentrations of 1.O, 2.0 and 3.0 MAC (end-tidal in 70% nitrous oxide) sequentially for periods of 10 rnin each. Groups I1 and IV received isoflurane or halothane in decreasing concentrations, i.e., 3.0, 2.0 and 1.0 MAC sequentially, again for periods of 10 min each. The actual concentrations of the volatile agents were 0.5, 1.0 and 1.5% for isoflurane and 0.3,0.6and 0.9% for halothane, equivalent to 1.0,2.0and 3.0 MAC, respectively, of the two volatile agents (7). IOP, heart rate and arterial blood pressure were measured in each patient prior to induction of anaesthesia, immediately following intubation and at the end of each 10min period. End-tidal concentrations of carbon dioxide and the volatile agent were monitored continuously. IOP was measured with a hand-held Perkins’applanation tonometer (8) in the eye not to be operated upon. Heart rate was measured from ECG, arterial pressure using an oscillotonometer (Dinamap) and the end-tidal concentrations of carbon dioxide and the volatile agent using infra-red analysers (Engstrom Eliza capnograph; Datex Normac vapour monitor). The measurement of IOP prior to induction of anaesthesia was carried out following the instillation of 0.4% benoxinate. All patients stayed horizontal throughout the study. Surgery was started after completion of all measurements. The results were subjected to repeated measures analysis of variance and t-tests to determine their statistical significance. A P-value of < 0.05 represented a statistically significant result.
PATIENTS AND METHODS Twenty-four adult patients conforming to ASA Grade I scheduled to undergo elective ophthalmic surgery were included in the study with their informed consent and the approval of the Regional Ethical Committee. Premedication was with diazepam 10 mg orally 60 min preoperatively, and anaesthesia was induced with thiopentone 4-5 mg/kg, preceded by fentanyl 100 pg. Pancuronium in a dose of 0.07 mg/kg was administered to provide muscle relaxation. Tracheal intubation was carried out about 4 min after the relaxant administra-
RESULTS The patients in the four groups were comparable with regard to age, weight and baseline (awake) and postintubation IOP (Table 1). I O P increased, although not significantly, in three out of four groups following tracheal intubation.
283
ISOFLURANE, HALOTHANE AND IOP Table 1 Age, weight and intraocular pressure (IOP). Halothane
Isoflurane Group I Age (yr+s.d) Weight (kg + s.d) Baseline IOP (mmHg s.d) (kPa f s.d) Post-induction IOP (mmHg f s.d.) (kPa+s.d)
36 f 14.8 74 f 16.6 14.8 f 0.98 (2.0f0.13) 16.8 f 2.79 (2.2 f 0.37)
Group I1
Group I11
Group IV
47 f 14.7 68 f 10.9 14.0 f 2.83 (1.9 f0.38) 14.8 f 5.08 (2.0 f 0.68)
31 f 13.2 65 f 16.0 13.5 f 2.81 (1.8f0.37) 14.3 3.50 (1.9f 0.47)
38k 17.6 64 f 15.0 16.0f 3.90 (2.1+ 0.52) 14.7 f 3.01 (2.05 0.40)
Groups I and 111 received the volatile agents in sequentially increasing concentrations, i.e. 1 MAC followed by 2 and 3 MAC; Groups I1 and IV received the volatile agents in sequentially decreasing concentrations.
The I O P values in patients administered isoflurane (Groups I and 11) are shown in Fig. 1. I O P decreased significantly ( P < 0.01) from mean baseline values of 14.8 and 14.0 mmHg (2.0 and 1.9 kPa) respectively to 7.5 and 6.0 mmHg (1.O and 0.8 kPa) after administration of 1.0 and 3.0 MAC isoflurane. Any further changes in I O P were insignificant in both groups. I O P changes in patients administered halothane (Groups I11 and IV) are shown in Fig. 2. IOP decreased once again in these groups in a manner similar to that observed in the isoflurane groups. It decreased significantly (P
