Anaesthesia, 1991, Volume 46, pages 922-924
Intra-ocular pressure changes using the laryngeal mask airway and tracheal tube
R. HOLDEN, C. D. G. MORSMAN, J. BUTLER, G. S. CLARK, D. S. HUGHES
AND
P. J. BACON
Summary Intra-ocular pressure was measured before and throughout airway establishment with either the laryngeal mask airway or tracheal tube. Similar measurements were made on removal of either airway and the amount of coughing noted in thejrst minute after removal. There was a significantly smaller increase in intra-ocular pressure ( p < 0.001) using the laryngeal mask airway, both on placement and removal, than with the tracheal tube. Postoperative coughing was significantly reduced using the laryngeal mask airway ( p < 0.001). There was a significantly greater rise in heart rate using the tracheal tube ( p < 0.01) probably related to an increased cardiovascular response. The laryngeal mask airway is recommended as an alternative to tracheal intubation in routine and emergency intra-ocular surgery.
Key words Eye; intra-ocular pressure. Equipment; laryngeal mask airway, tracheal tube. The stress response to tracheal intubation and extubation is associated with a rise in intra-ocular pressure (IOP),'-3 mainly due to increased ocular blood flow.4 In perforating eye injuries a transient rise in IOP during intubation can be deleterious and increased IOP during extubation places a stress on wound closure, which is exacerbated by coughing. The Brain laryngeal mask airway is an alternative to the tracheal tube for artificial ventilation of the lungs in the paralysed ~ a t i e n t The . ~ mask is placed directly over the posterior larynx, avoiding tracheal stimulation and so theoretically the systemic and ocular stress response associated with tracheal intubation and extubation is avoided. This prospective study compares the changes in IOP throughout tracheal intubation with that due to placement of the laryngeal mask airway. Intra-ocular pressure changes and coughing on removal of either airway were also compared. Method Ethics committee approval was obtained. Fifty-two patients scheduled to undergo elective general anaesthesia for cataract surgery were randomly allocated, by coin toss, into two groups of 26. All were ASA grade 1 or 2,6 without a history of diabetes mellitus, hypertension, carotid artery
disease or glaucoma. Patients were to receive intermittent positive pressure ventilation in one group using a laryngeal mask airway and in the other group using a tracheal tube. The anaesthetists in the study (J.B. and G.C.) regularly use both techniques in their normal practice. A standardised anaesthetic routine was used in all cases. Premedication with temazepam 10 mg, atropine 0.6 mg and ranitidine 150 mg orally was followed by induction with a sleep dose of etomidate 0.2-0.25 mg/kg and alfentanil 0.012 mg/kg. Neuromuscular blockade with vecuronium 0.1 mg/kg was monitored using a peripheral nerve stimulator. The patient's lungs were ventilated with 1S% isoflurane in 100% oxygen for 3 minutes before intubation. At this point the anaesthetist was informed of the method for management of the airway. The laryngeal mask airway was placed without using an introducer in one group of patients. In the other group, the larynx was sprayed with lignocaine 4% under direct vision and the trachea intubated using a RAE preformed tube. Anaesthesia was maintained with 66% nitrous oxide and 1.5% isoflurane in oxygen. The lungs were ventilated using a Penlon co-axial circuit and a Penlon Nuffield ventilator to maintain normal end-tidal carbon dioxide concentrations. Neuromuscular blockade was maintained with incremental doses of vecuronium, and reversed with neostigmine and
R. Holden*, FRCS, FCOphth, Registrar, C.D.G. Morsman, FRCS(Ed), FCOphth, Senior Registrar, J. Butler, FFARCS, Consultant, G.S. Clark, FFARCS, Consultant, D.S. Hughes, FRCS, FCOphth, Registrar, P.J. Bacon, MRCP, FCOphth, Senior Registrar, Departments of Ophthalmology and Anaesthesia, St Woolos Hospital, Stow Hill, Newport, Gwent NP9
4sz.
*Present address: Clinical Cataract Research Unit, Nuffield Laboratory of Ophthalmology, Oxford OX2 6AW. Accepted 18 April 1991. 0003-2409/91/110922 i-03 $03.00/0
@ 1991 The Association of Anaesthetists of Gt Britain and Ireland
922
Intra-ocular pressure changes using the LMA and tracheal tube Table 1. Baseline data for each group. Values are expressed as mean (SD).
Sex ratio (M :F) Mean age; years Mean IOP before airway placement; mmHg Mean IOP before airway removal; mmHg ~
~~
~
LMA
Tube
P
1:l 72.7 (12) 17.9 (3.8)
1:1.6 71.5 (10.6) 18 (4.1)
NS NS
26.3 (5.9)
25.2 (5.4)
NS
~
~~
Coughing in the first minute after airway removal was classed as ‘negligible’ if there were less than five coughs or ‘present’ if there were more than five coughs. Cardiovascular parameters were recorded before and after induction of anaesthesia, and after airway establishment. The heart rate was continuously monitored and the blood pressure (BP) measured using a Dinamap 1846 automated sphygmomanometer set to record every 60 seconds during this period. Cardiovascular parameters were not recorded at airway removal on the first 10 patients who formed a feasibility study.
~~
IOP, Intra-ocular pressure; LMA, laryngeal mask airway; NS, not significant (Student’s t-test).
Results
glycopyrronium. The laryngeal mask airway or tracheal tube was removed once spontaneous ventilation was established. A Clarke’s lid speculum was used to expose the cornea of the non-operated eye which had previously been anaesthetised with benoxinate hydrochloride 4%. IOP was measured with the Alcon pneumotonometer which continuously records the IOP on a paper strip and digital meter. The accuracy of the pneumotonometer compares well with the Goldman tonometer.’ Measurements were taken before and after induction, continuously during airway placement and thereafter for 30 seconds. In all cases, the highest IOP was in the first 20 seconds of airway placement. The change in IOP was taken as the difference between postinduction IOP and the highest IOP recorded during airway establishment. The IOP was measured after reversal of neuromuscular blockade and then continuously during airway removal.
The sex ratio, mean age, and mean IOP before airway placement and airway removal in each group are shown in Table 1. The mean change in IOP during airway placement and removal is shown in Table 2. Tracings of typical pneumotonometer readings are shown in Figure 1. Ten patients in the tracheal tube group had negligible coughing in the first minute after extubation compared with 25 in the laryngeal mask airway group. This difference is statistically significant (Chi-squared test = 17.1, p < 0.001). J.B. anaesthetised 33 of the 52 patients and G.C. 19. There was no statistical difference between the anaesthetists with regard to IOP changes during airway placement and removal (Student’s t-test) or postoperative coughing (Chisquared test) in either group. The maximum IOP recorded during tracheal intubation was 44 mmHg compared with 28 mmHg during laryngeal mask airway placement (normal IOP 10-20 mmHg). The maximum pressure during
Table 2. Ocular changes. Values are expressed as mean (SD). LMA Mean change IOP during airway placement; mmHg Mean change IOP during airway removal; mmHg
Tube
P
CI
+1.8 (2.1)
f 6 . 8 (5.5) < 0.001* 2-7
+ 1.4 (1.4)
+5.0 (5.8) ~
i 0.001*
0-4
~
LMA, laryngeal mask airway; IOP, Intra-ocular pressure; ‘Mann-Whitney U-test; CI, 95% confidence interval.
Table 3. Cardiovascular changes. Values are expressed as mean (SD). Airway placement Mean change heart rate; beats/minute Mean change systoIic B P mmHg Mean change diastolic BP; mmHg Airway removal Mean change heart rate; beats/minute Mean change systolic BP; mmHg Mean change diastolic BP; mmHg
923
LMA (n = 26)
Tube (n = 26)
f 3 . 1 (10.2)
f
15.3 (14.3)
+2
f
I6
(21.5)
f 8 . 6 (6) LMA (n = 22)
(34.4)
p
< O.OI* NS
+7.8 (6)
NS
Tube (n = 20)
p
+0.9 (7.6)
f 3 . 9 (10.3)
NS
-0.1 (12.4)
+7.7 (13.4)
NS
-0.5 (10.2)
f 3 . 2 (10.8)
NS
LMA, laryngeal mask airway; NS, not significant (Student’s f-test); *Student’s t-test.
924
R. Holden et al.
Fig. Pneumotonometer tracing throughout placement of laryngeal mask airway (top left) and removal (top rig..-), and throughout tracheal tube insertion (bottom left) and removal (bottom right). Arrow indicates start of each procedure. Intra-ocular pressure in mmHg. One abcissa square = one second.
removal of the tracheal tube was 48 mmHg compared with 33mmHg using the laryngeal mask airway. One patient monitored whilst coughing had a peak IOP of 54mmHg. The cardiovascular responses to placement and removal of the airway in each group are shown in Table 3. Discussion To our knowledge there are no studies in the literature in which the effect on IOP of placing a laryngeal mask airway is compared with that of tracheal intubation. In this study the change in IOP was significantly lower using the laryngeal mask airway. Previous studies of IOP changes during intubation have tended to take periodic measurements of the IOP, with a hand-held instrument, after a delay of about one This would miss the peak pressure, which we found to occur in the first 20 seconds. The mean changes in IOP during airway placement in either group are not clinically important. However, the maximum IOP recorded during tracheal intubation was greater than 40mmHg in some patients and this may be important, particularly in penetrating injuries. The tracheal tube group had a significantly greater change in heart rate. These readings were taken continuously during airway placement therefore they indicate a greater cardiovascular response in this group. The BP readings were not instantaneous and although there was not a significant difference between the two groups with regard to the BP, the trend was for the systolic BP to be higher in the tracheal tube group. This lack of significance may have been due to the fact that the BP monitoring was not continuous. Further studies with instantaneous measurement of BP would be required to clarify this. The standardisation of conditions for airway removal is more difficult than airway placement and at this stage the anaesthetist was aware of the type of airway. Both these factors have to be taken into account when the results of airway removal are interpreted. The change in IOP and amount of coughing was significantly lower in the laryngeal mask airway group. At this stage, coughing probably has a greater effect on the IOP than airway removal itself. The
mechanism is likely to be similar to that of the Valsalva manoeuvre, in which raised intra-thoracic pressure is transmitted to the ocular veins thus raising the IOP.' Although only one patient's IOP was monitored whilst actually coughing, the IOP of greater than 50mmHg probably reflects what usually occurs, therefore a reduction in coughing in the immediate postoperative period is evidently desirable. The laryngeal mask airway caused a smaller rise in IOP than the tracheal tube, both on placement and removal. This is likely to be due to a decreased cardiovascular response. Furthermore, postoperative coughing is reduced with the laryngeal mask airway. These findings should be taken into account when considering the type of airway maintenance for anaesthesia in routine and emergency intra-ocular surgery.
References 1. DRENGER B, PE'ER J. Attenuation of ocular and systemic
2.
3.
4. 5.
6. 7. 8.
responses to tracheal intubation by intravenous lignocaine. British Journal of Ophthalmology 1987; 71: 546-8. MIRAKHURRK, ELLIOTTP, SHEPHERDWFI, ARCHERDB. Intra-ocular pressure changes during induction of anaesthesia and tracheal intubation. A comparison of thiopentone and propofol followed by vecuronium. Anaesthesia 1988; 43 (Suppl.): 54-7. MOSTAFA SM, WILESJR, DOWD T, BATESR, BRICKERS. Effects of nebulized lignocaine on the intraocular pressure responses to tracheal intubation. British Journal of Anaesthesia 1990; 64: 515-7. ROBINSON R, WHITEM, MCCANNP, MAGNERJ, EUSTACE P. Effect of anaesthesia on intraocular blood flow. British Journal of Ophthalmology 1991; 7 5 92-4. BRAINAIJ, MCGHEETD, MCATEEREJ, THOMAS A, AW-SAAD MAW, BUSHMAN JA. The laryngeal mask airway. Development and preliminary trials of a new type of airway. Anaesthesia 1985; 40: 356-61. American Society of Anesthesiologists. New classification of physical status. Anesthesiology 1963; 24: 1 11. JAIN MR, MARMIONVJ. A clinical evaluation of the British Journal of applanation pneumatonograph. Ophthalmology 1976; 60: 107-10. MACRIFJ. Acetazolamide and the venous pressure of the eye. Archives of Ophthalmology 1960; 6 3 953-65.
Intra-ocular pressure changes using the laryngeal mask airway and tracheal tube
R. HOLDEN, C. D. G. MORSMAN, J. BUTLER, G. S. CLARK, D. S. HUGHES
AND
P. J. BACON
Summary Intra-ocular pressure was measured before and throughout airway establishment with either the laryngeal mask airway or tracheal tube. Similar measurements were made on removal of either airway and the amount of coughing noted in thejrst minute after removal. There was a significantly smaller increase in intra-ocular pressure ( p < 0.001) using the laryngeal mask airway, both on placement and removal, than with the tracheal tube. Postoperative coughing was significantly reduced using the laryngeal mask airway ( p < 0.001). There was a significantly greater rise in heart rate using the tracheal tube ( p < 0.01) probably related to an increased cardiovascular response. The laryngeal mask airway is recommended as an alternative to tracheal intubation in routine and emergency intra-ocular surgery.
Key words Eye; intra-ocular pressure. Equipment; laryngeal mask airway, tracheal tube. The stress response to tracheal intubation and extubation is associated with a rise in intra-ocular pressure (IOP),'-3 mainly due to increased ocular blood flow.4 In perforating eye injuries a transient rise in IOP during intubation can be deleterious and increased IOP during extubation places a stress on wound closure, which is exacerbated by coughing. The Brain laryngeal mask airway is an alternative to the tracheal tube for artificial ventilation of the lungs in the paralysed ~ a t i e n t The . ~ mask is placed directly over the posterior larynx, avoiding tracheal stimulation and so theoretically the systemic and ocular stress response associated with tracheal intubation and extubation is avoided. This prospective study compares the changes in IOP throughout tracheal intubation with that due to placement of the laryngeal mask airway. Intra-ocular pressure changes and coughing on removal of either airway were also compared. Method Ethics committee approval was obtained. Fifty-two patients scheduled to undergo elective general anaesthesia for cataract surgery were randomly allocated, by coin toss, into two groups of 26. All were ASA grade 1 or 2,6 without a history of diabetes mellitus, hypertension, carotid artery
disease or glaucoma. Patients were to receive intermittent positive pressure ventilation in one group using a laryngeal mask airway and in the other group using a tracheal tube. The anaesthetists in the study (J.B. and G.C.) regularly use both techniques in their normal practice. A standardised anaesthetic routine was used in all cases. Premedication with temazepam 10 mg, atropine 0.6 mg and ranitidine 150 mg orally was followed by induction with a sleep dose of etomidate 0.2-0.25 mg/kg and alfentanil 0.012 mg/kg. Neuromuscular blockade with vecuronium 0.1 mg/kg was monitored using a peripheral nerve stimulator. The patient's lungs were ventilated with 1S% isoflurane in 100% oxygen for 3 minutes before intubation. At this point the anaesthetist was informed of the method for management of the airway. The laryngeal mask airway was placed without using an introducer in one group of patients. In the other group, the larynx was sprayed with lignocaine 4% under direct vision and the trachea intubated using a RAE preformed tube. Anaesthesia was maintained with 66% nitrous oxide and 1.5% isoflurane in oxygen. The lungs were ventilated using a Penlon co-axial circuit and a Penlon Nuffield ventilator to maintain normal end-tidal carbon dioxide concentrations. Neuromuscular blockade was maintained with incremental doses of vecuronium, and reversed with neostigmine and
R. Holden*, FRCS, FCOphth, Registrar, C.D.G. Morsman, FRCS(Ed), FCOphth, Senior Registrar, J. Butler, FFARCS, Consultant, G.S. Clark, FFARCS, Consultant, D.S. Hughes, FRCS, FCOphth, Registrar, P.J. Bacon, MRCP, FCOphth, Senior Registrar, Departments of Ophthalmology and Anaesthesia, St Woolos Hospital, Stow Hill, Newport, Gwent NP9
4sz.
*Present address: Clinical Cataract Research Unit, Nuffield Laboratory of Ophthalmology, Oxford OX2 6AW. Accepted 18 April 1991. 0003-2409/91/110922 i-03 $03.00/0
@ 1991 The Association of Anaesthetists of Gt Britain and Ireland
922
Intra-ocular pressure changes using the LMA and tracheal tube Table 1. Baseline data for each group. Values are expressed as mean (SD).
Sex ratio (M :F) Mean age; years Mean IOP before airway placement; mmHg Mean IOP before airway removal; mmHg ~
~~
~
LMA
Tube
P
1:l 72.7 (12) 17.9 (3.8)
1:1.6 71.5 (10.6) 18 (4.1)
NS NS
26.3 (5.9)
25.2 (5.4)
NS
~
~~
Coughing in the first minute after airway removal was classed as ‘negligible’ if there were less than five coughs or ‘present’ if there were more than five coughs. Cardiovascular parameters were recorded before and after induction of anaesthesia, and after airway establishment. The heart rate was continuously monitored and the blood pressure (BP) measured using a Dinamap 1846 automated sphygmomanometer set to record every 60 seconds during this period. Cardiovascular parameters were not recorded at airway removal on the first 10 patients who formed a feasibility study.
~~
IOP, Intra-ocular pressure; LMA, laryngeal mask airway; NS, not significant (Student’s t-test).
Results
glycopyrronium. The laryngeal mask airway or tracheal tube was removed once spontaneous ventilation was established. A Clarke’s lid speculum was used to expose the cornea of the non-operated eye which had previously been anaesthetised with benoxinate hydrochloride 4%. IOP was measured with the Alcon pneumotonometer which continuously records the IOP on a paper strip and digital meter. The accuracy of the pneumotonometer compares well with the Goldman tonometer.’ Measurements were taken before and after induction, continuously during airway placement and thereafter for 30 seconds. In all cases, the highest IOP was in the first 20 seconds of airway placement. The change in IOP was taken as the difference between postinduction IOP and the highest IOP recorded during airway establishment. The IOP was measured after reversal of neuromuscular blockade and then continuously during airway removal.
The sex ratio, mean age, and mean IOP before airway placement and airway removal in each group are shown in Table 1. The mean change in IOP during airway placement and removal is shown in Table 2. Tracings of typical pneumotonometer readings are shown in Figure 1. Ten patients in the tracheal tube group had negligible coughing in the first minute after extubation compared with 25 in the laryngeal mask airway group. This difference is statistically significant (Chi-squared test = 17.1, p < 0.001). J.B. anaesthetised 33 of the 52 patients and G.C. 19. There was no statistical difference between the anaesthetists with regard to IOP changes during airway placement and removal (Student’s t-test) or postoperative coughing (Chisquared test) in either group. The maximum IOP recorded during tracheal intubation was 44 mmHg compared with 28 mmHg during laryngeal mask airway placement (normal IOP 10-20 mmHg). The maximum pressure during
Table 2. Ocular changes. Values are expressed as mean (SD). LMA Mean change IOP during airway placement; mmHg Mean change IOP during airway removal; mmHg
Tube
P
CI
+1.8 (2.1)
f 6 . 8 (5.5) < 0.001* 2-7
+ 1.4 (1.4)
+5.0 (5.8) ~
i 0.001*
0-4
~
LMA, laryngeal mask airway; IOP, Intra-ocular pressure; ‘Mann-Whitney U-test; CI, 95% confidence interval.
Table 3. Cardiovascular changes. Values are expressed as mean (SD). Airway placement Mean change heart rate; beats/minute Mean change systoIic B P mmHg Mean change diastolic BP; mmHg Airway removal Mean change heart rate; beats/minute Mean change systolic BP; mmHg Mean change diastolic BP; mmHg
923
LMA (n = 26)
Tube (n = 26)
f 3 . 1 (10.2)
f
15.3 (14.3)
+2
f
I6
(21.5)
f 8 . 6 (6) LMA (n = 22)
(34.4)
p
< O.OI* NS
+7.8 (6)
NS
Tube (n = 20)
p
+0.9 (7.6)
f 3 . 9 (10.3)
NS
-0.1 (12.4)
+7.7 (13.4)
NS
-0.5 (10.2)
f 3 . 2 (10.8)
NS
LMA, laryngeal mask airway; NS, not significant (Student’s f-test); *Student’s t-test.
924
R. Holden et al.
Fig. Pneumotonometer tracing throughout placement of laryngeal mask airway (top left) and removal (top rig..-), and throughout tracheal tube insertion (bottom left) and removal (bottom right). Arrow indicates start of each procedure. Intra-ocular pressure in mmHg. One abcissa square = one second.
removal of the tracheal tube was 48 mmHg compared with 33mmHg using the laryngeal mask airway. One patient monitored whilst coughing had a peak IOP of 54mmHg. The cardiovascular responses to placement and removal of the airway in each group are shown in Table 3. Discussion To our knowledge there are no studies in the literature in which the effect on IOP of placing a laryngeal mask airway is compared with that of tracheal intubation. In this study the change in IOP was significantly lower using the laryngeal mask airway. Previous studies of IOP changes during intubation have tended to take periodic measurements of the IOP, with a hand-held instrument, after a delay of about one This would miss the peak pressure, which we found to occur in the first 20 seconds. The mean changes in IOP during airway placement in either group are not clinically important. However, the maximum IOP recorded during tracheal intubation was greater than 40mmHg in some patients and this may be important, particularly in penetrating injuries. The tracheal tube group had a significantly greater change in heart rate. These readings were taken continuously during airway placement therefore they indicate a greater cardiovascular response in this group. The BP readings were not instantaneous and although there was not a significant difference between the two groups with regard to the BP, the trend was for the systolic BP to be higher in the tracheal tube group. This lack of significance may have been due to the fact that the BP monitoring was not continuous. Further studies with instantaneous measurement of BP would be required to clarify this. The standardisation of conditions for airway removal is more difficult than airway placement and at this stage the anaesthetist was aware of the type of airway. Both these factors have to be taken into account when the results of airway removal are interpreted. The change in IOP and amount of coughing was significantly lower in the laryngeal mask airway group. At this stage, coughing probably has a greater effect on the IOP than airway removal itself. The
mechanism is likely to be similar to that of the Valsalva manoeuvre, in which raised intra-thoracic pressure is transmitted to the ocular veins thus raising the IOP.' Although only one patient's IOP was monitored whilst actually coughing, the IOP of greater than 50mmHg probably reflects what usually occurs, therefore a reduction in coughing in the immediate postoperative period is evidently desirable. The laryngeal mask airway caused a smaller rise in IOP than the tracheal tube, both on placement and removal. This is likely to be due to a decreased cardiovascular response. Furthermore, postoperative coughing is reduced with the laryngeal mask airway. These findings should be taken into account when considering the type of airway maintenance for anaesthesia in routine and emergency intra-ocular surgery.
References 1. DRENGER B, PE'ER J. Attenuation of ocular and systemic
2.
3.
4. 5.
6. 7. 8.
responses to tracheal intubation by intravenous lignocaine. British Journal of Ophthalmology 1987; 71: 546-8. MIRAKHURRK, ELLIOTTP, SHEPHERDWFI, ARCHERDB. Intra-ocular pressure changes during induction of anaesthesia and tracheal intubation. A comparison of thiopentone and propofol followed by vecuronium. Anaesthesia 1988; 43 (Suppl.): 54-7. MOSTAFA SM, WILESJR, DOWD T, BATESR, BRICKERS. Effects of nebulized lignocaine on the intraocular pressure responses to tracheal intubation. British Journal of Anaesthesia 1990; 64: 515-7. ROBINSON R, WHITEM, MCCANNP, MAGNERJ, EUSTACE P. Effect of anaesthesia on intraocular blood flow. British Journal of Ophthalmology 1991; 7 5 92-4. BRAINAIJ, MCGHEETD, MCATEEREJ, THOMAS A, AW-SAAD MAW, BUSHMAN JA. The laryngeal mask airway. Development and preliminary trials of a new type of airway. Anaesthesia 1985; 40: 356-61. American Society of Anesthesiologists. New classification of physical status. Anesthesiology 1963; 24: 1 11. JAIN MR, MARMIONVJ. A clinical evaluation of the British Journal of applanation pneumatonograph. Ophthalmology 1976; 60: 107-10. MACRIFJ. Acetazolamide and the venous pressure of the eye. Archives of Ophthalmology 1960; 6 3 953-65.
