- Email: [email protected]
The Effect of Laryngeal Mask Airway Insertion on Intraocular Pressure Measurement in Children Receiving General Anesthesia
The Effect of Laryngeal Mask Airway Insertion on Intraocular Pressure Measurement in Children Receiving General Anesthesia PATRICK WATTS, MAY KIM LIM, RAVIKIRAN GANDHEWAR, AYCHUT MUKHERJEE, RICHARD WINTLE, TREVOR ARMSTRONG, TAHSIN ZATMAN, RHYS JONES, AND HASAN AL MADFAI ● PURPOSE: To study changes in intraocular pressure (IOP) in children while under general anesthesia before and after laryngeal mask airway (LMA) insertion. ● DESIGN: Prospective, comparative study. ● METHOD: IOP was measured in children after induction and one minute after LMA insertion. Children younger than 16 years who were scheduled to undergo elective ophthalmic surgery while receiving a general anesthetic were included. Children with a history of glaucoma or previous intraocular surgery were excluded. Data were collected on the age of the child, IOP, heart rate (HR), end tidal CO2, and blood pressure (BP) before and after LMA insertion. ● RESULTS: Sixty-six children with a mean age of 5.5 ⴞ 3.6 years (range, four months to 16 years) were included in the study. The mean IOP was 13.6 ⴞ 3.9 mm Hg and 13.6 ⴞ 3.6 mm Hg in right and left eyes, respectively, before LMA insertion and 15.5 ⴞ 3.8 mm Hg and 15.2 ⴞ 3.8 mm Hg in right and left eyes, respectively, after LMA insertion (P ⴝ .001). A decrease in BP was significantly associated with an increase in IOP (P ⴝ .008), and the interaction between the change in the BP, HR, and CO2 affected the change in IOP measured after insertion of the LMA (P ⴝ .04). There was no correlation between the age of the child and the change in IOP measured after insertion of the LMA. ● CONCLUSIONS: In our study, a small but significantly higher IOP was found after LMA insertion than before. It is recommended that the measurement of IOP in children receiving a general anesthetic is carried out before the insertion of the LMA. (Am J Ophthalmol 2007;144:507–510. © 2007 by Elsevier Inc. All rights reserved.)
Accepted for publication Jun 4, 2007. From the Departments of Ophthalmology (P.W., M.K.L., R.G., A.M., R.W.) and Anesthesia (T.A., T.Z., R.J.), University Hospital of Wales, Cardiff, Wales, United Kingdom; and the Department of Statistics, University of Glamorgan, Glamorgan, Wales, United Kingdom (H.A.M.). Inquiries to Patrick Watts, Department of Ophthalmology, University Hospital of Wales, Cardiff CF14 4XW, United Kingdom; e-mail: [email protected] 0002-9394/07/$32.00 doi:10.1016/j.ajo.2007.06.010
©
2007 BY
T
HE MEASUREMENT OF INTRAOCULAR PRESSURE (IOP)
in children is often carried out while they are under general anesthesia as part of the ocular examination. In current practice, the IOP in children is measured during the administration of the inhalational anesthetic agent via a face mask. Measurement of the IOP at this stage often is inconvenienced by limited access while the anesthesiologist attempts to maintain an adequate airway. It is also possible that the inadvertent pressure on the globe by the face mask affects the IOP. Performing the IOP measurement after the airway is secured allows easy access both for ocular examination and the estimation of the IOP. Tracheal intubation with an endotracheal tube (ETT) is associated with an increase in IOP,1–5 and recommendations exist on the optimal timing of performing IOP measurements in children after tracheal intubation to minimize this error.4 An alternative device, the laryngeal mask airway (LMA),6 has been reported to have negligible influence on the IOP measurement compared with the ETT.5,7,8 In this study, we aimed to determine the change in IOP after insertion of the LMA in children receiving general anesthesia using sevoflurane and the influence of the hemodynamic responses on its measurement in children.
METHODS THE STUDY WAS CARRIED OUT AT A UNIVERSITY HOSPITAL
with written informed consent obtained from the parent or legal guardian. All children (age, ⬍16 years) scheduled for elective ophthalmic surgery in a 12-month period were recruited into this study. Children with glaucoma or previous intraocular surgery were excluded from the study. General anesthesia was induced with either intravenous propofol or inhaled sevoflurane in oxygen and then maintained with 2% to 4% sevoflurane in oxygen and air. Additionally remifentanil was used in some patients. After induction of anesthesia, the IOP was measured when the end-tidal CO2 could be maintained at least 4 kPa (kilopascals) with positive pressure ventilation using the face mask. The IOP was measured using a Tono-Pen (Mentor O&O, Inc, Norwell, Massachusetts, USA), with
ELSEVIER INC. ALL
RIGHTS RESERVED.
507
a concerted effort to avoid pressure on the eyes while holding the face mask. The first IOP measurement was performed after induction of anesthesia, with the face mask in situ, before insertion of the LMA by one examiner (P.W.). Three readings were taken, and an average of the two closest readings were used in the analyses (all readings within 1 mm Hg of each other within 5% probability of accuracy). The IOP measurement was repeated similarly after secure insertion of the LMA by a second examiner (K.L.) masked to the results of the first. The IOP measurement was made on every occasion only when the patient’s end-tidal CO2 was stable. The second measurement thus was performed two minutes after insertion of the LMA. In addition to the IOP, the blood pressure (BP) and heart rate (HR) also were recorded. The differences in IOP in both eyes before and after insertion of the LMA were analyzed simultaneously using a multivariate repeated measures analysis of variance (ANOVA), with the age of the children younger and older than three years and gender as fixed factors. The effects of the BP, HR, and end-tidal CO2 on the IOP were studied using multivariate regression analysis (MANOVA) with Bonferroni corrections for multiple comparisons. In addition, the Pearson correlation coefficient was used to investigate further the relationships between age and postinsertion changes in IOP.
FIGURE. Scatterplot showing intraocular pressure (IOP) before (pre) and after (post) laryngeal mask airway (LMA) insertion.
TABLE. Changes in Intraocular Pressure, Heart Rate, Blood Pressure, and End-Tidal CO2 before and after Insertion of the Laryngeal Mask Airway
IOP (mm Hg) HR (bpm) BP (mm Hg) CO2 (kpa)
RESULTS study, 66 were included in the data analysis. The excluded children were those with missing data (n ⫽ 9) and those in whom atracurium, a muscle relaxant, was used during anesthetic induction. The mean age was 5.5 ⫾ 3.6 years (range, four months to 16 years). There were 40 male children. Among the 66 children, 83.9% were American Society of Anesthesiologists9 (ASA) grade 1, 14.3 % were ASA grade 2, and 1.8% were ASA grade 3. There was no influence of ASA grading in the changes in IOP (P ⫽ .3 and P ⫽ .1 for the right eye and left eyes, respectively). The mean IOP was 13.6 ⫾ 3.9 mm Hg and 13.6 ⫾ 3.6 mm Hg in right and left eyes, respectively, before LMA insertion and 15.5 ⫾ 3.8 mm Hg and 15.2 ⫾ 3.8 mm Hg in right and left eyes, respectively, after LMA insertion (Figure). The IOP remained stable in nine eyes, decreased in 86 eyes, and increased in 36 eyes. The mean difference between right and left eyes was ⫺0.01 mm Hg and 0.3 mm Hg before and after LMA insertion, respectively. There was a concordance between right and left eye measurements, with 60% of eyes showing an increase, 25% showing a decrease, and 15% showing stable IOP before and after LMA insertion. The mean change in IOP in the right eye was ⫺1.8 ⫾ 4.3 mm Hg (range, ⫺15.5 to 8.5 mm Hg) and ⫺1.5 ⫾ 4.1 AMERICAN JOURNAL
After LMA Insertion
P value
13.6 ⫾ 3.7 100.9 ⫾ 22.4 67.6 ⫾ 15.1 4.7 ⫾ 0.9
15.3 ⫾ 3.8 108.1 ⫾ 22.8 62.3 ⫾ 7.1 6.2 ⫾ 1.2
.0005 .0003 .01 .01
BP ⫽ blood pressure; bpm ⫽ beats per minute; HR ⫽ heart rate; IOP ⫽ intraocular pressure; kpa ⫽ kilopascals; LMA ⫽ laryngeal mask airway.
FROM A TOTAL OF 80 CHILDREN WHO TOOK PART IN THE
508
Before LMA Insertion
mm Hg (range, ⫺18 to 9 mm Hg) in the left eye (Wilks lambda, 0.855; F(2,56) ⫽ 4.7; P ⫽ .01). Age group, gender, and their interactions had no significant effect on the changes in IOP (P ⫽ .5, P ⫽ .1, and P ⫽ .2, respectively). Further analysis using the Pearson correlation coefficient revealed no significant association between the ages of children and the change in IOP (right eye, r ⫽ 0.2, P ⫽ .2; left eye, r ⫽ 0.09, P ⫽ .5). Anesthesia was induced with sevoflurane in 25 patients and with a combination of sevoflurane and remifentanil in five patients; 36 patients were induced with propofol. Anesthesia was maintained with sevoflurane in all children. There was no correlation between the type of the anesthetic used and the change in the IOP (P ⫽ .2 for both eyes). The HR (P ⫽ .005) and end-tidal CO2 (P ⬍ .000) increased during the IOP measurements, whereas the mean BP dropped (P ⫽ .007; Table). A multivariate ANOVA revealed a significant effect of the change in BP and change in HR on the measured IOP variable (P ⫽ .008 and P ⫽ .004). The interaction of mean HR change and mean BP change with changes in CO2 OF
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OCTOBER 2007
levels had a significant effect on the measured change in IOP (P ⫽ .04; Wilks lambda, 0.82; observed power, 0.87; and P ⫽ .009; Wilks lambda, 0.87; observed power, 0.8). The sample size was significant to detect a change in 10%, giving a power of 80%.
DISCUSSION THIS STUDY DEMONSTRATES THAT, ON AVERAGE, THE IN-
sertion of an LMA is associated with a significant increase in IOP in children receiving general anesthesia. Although the mean change in the IOP was small, the standard deviation of the change was 4.2 mm Hg, with a range of a decrease in IOP of 9 mm Hg to an increase in IOP of 18 mm Hg. This increase in IOP occurs with a concomitant decrease in BP and an increase in HR and end-tidal CO2. It is possible that the observed hemodynamic changes in HR are related causally to the increase in IOP. Alternatively, the stimulus induced by the insertion of the LMA evokes an increased HR and IOP, and with increasing depth of anesthesia, a decreased BP results; as a previous report suggests, lidocaine attenuates the elevation of IOP in children who are intubated.10 However, the decrease in the mean BP observed cannot be reconciled physiologically with the observed change in IOP. The possible explanation for this phenomenon was that the BP reading did not coincide exactly with the IOP measurement, whereas the HR did, because this was monitored continuously. An increased end-tidal CO2 is known to cause an increased IOP; statistical analysis using a MANOVA showed that this factor significantly affected the IOP change only by its interaction with the change in BP and HR. It is well known that the insertion of an ETT is associated with an elevation in IOP5,7,8; however, no significant change in IOP has been reported with the insertion of the LMA.5,8 The explanation for the difference in the results observed between a previous report5 (where the primary aim was a comparison of IOP change after ETT intubation and LMA insertion) and this study was the smaller sample size (n ⫽ 20 randomized to LMA insertion), the use of nitrous oxide, halothane, and atracurium, a muscle relaxant that may have altered any change induced by insertion of the LMA in the previous study. One of the studies8 was conducted in adults, with the IOP being measured with a different device. Clinically, it is our experience that single IOP values with the Tono-Pen may be highly variable; hence in this study, three consistent readings for each eye were obtained before
and after LMA insertion with a 5% probability. The Tono-Pen compares well with the Goldmann applanation tonometer, the gold standard for measuring IOP.11 Inhalational anesthetics reduce the IOP11; however, this study was conducted to measure the IOP soon after induction and soon after LMA insertion. This was timed to be two minutes after the insertion of the LMA. Sevoflurane recently was reported to lower IOP in children.12 This study compared the IOP measured after induction with sevoflurane and ketamine. An LMA was used only in three of the 15 patients who received sevoflurane, where the change in IOP after LMA insertion was not reported. All our patients had sevoflurane with additional agents that did not influence the IOP at the time of its measurement. Although our study was carried out in children without a diagnosis of glaucoma, the change noted cautions against measurements of IOP after LMA insertion in children with glaucoma. Although the mean change noted was small, the standard deviation and the range of change was high. Although it is acknowledged that any change in treatment for glaucoma in children also is governed by the change in the corneal diameter, the axial length, and optic cup size in children younger than 3 years of age and by consistently high IOP readings with changes in the optic cup in older children, IOP does play an important part in management decisions for glaucoma therapy. This study failed to show a correlation between the change in IOP measured after insertion of the LMA and the age of the child. An erroneous low measurement of IOP could miss pathologically raised IOP, and similarly, an erroneous high IOP reading may lead to overtreatment.13 However, caution should be exercised when extrapolating our findings to a population of children with glaucoma where a wider range of IOP may influence the results. We conclude that IOP measurement in children receiving general anesthesia currently should be measured with the face mask in situ before the insertion of the LMA, because this is associated with statistically significant changes in IOP. The change in IOP measured correlates with a decrease in BP and the interaction of the changes in BP, HR, and end-tidal CO2. These measured changes may influence changes in the treatment of a child with glaucoma. The magnitude of change of IOP reported in this study after the insertion of the LMA were within the normal range and hence may not seem clinically significant; however, when dealing with children with glaucoma, the measured change may dictate change in therapy. This study hence forms the basis for a similar study in children with glaucoma to validate the above findings in a sample of children with glaucoma.
THE AUTHORS INDICATE NO FINANCIAL SUPPORT OR FINANCIAL CONFLICT OF INTEREST. INVOLVED IN DESIGN AND conduct of study (P.W., H.A.); data collection and management (T.Z., T.A., R.J., R.W., A.M., K.L., R.G., P.W.); analysis and interpretation of data; and preparation (P.W., H.A., K.L., R.G.) and review or approval (T.Z., T.A., R.J.) of the manuscript. Ethical approval was obtained from the Local Research Ethics Committee of Wales and the Research and Development Department of Cardiff and Vale NHS Trust, Wales, United Kingdom.
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7. Holden R, Morsman CDG, Butler J, Clark GS, Hughes DS, Bacon PJ. Intraocular pressure changes using the laryngeal mask airway and tracheal tube. Anaesthesia 1991:46:922–924. 8. Whitford AM, Hone SW, O’Hare B, Magner J, Eustace P. Intraocular pressure changes following laryngeal mask airway insertion: a comparative study. Anaesthesia 1997:52:794 –796. 9. American Society of Anesthesiologists. New classification of physical status. Anesthesiology 1963;24:111. 10. Lerman J, Kiskis AA. Lidocaine attenuates the intraocular pressure response to rapid intubation in children. Can Anaesth Soc J 1985;32:339 –345. 11. Li J, Herndon LW, Asrani SG, Stinnett S, Allingham RR. Clinical comparison of the Proview eye pressure monitor with the Goldmann applanation tonometer and the TonoPen. Arch Ophthalmol 2004:122:1117–1121. 12. Blumberg D, Congdon N, Jampel H, Gilbert G, Elliot R, Rivers R, et al. The effects of sevoflurane and ketamine on intraocular pressure in children during examination under anesthesia. Am J Ophthalmol 2007;143:494 – 499. 13. Shields MB. The intraocular pressure. In: Textbook of Glaucoma. 2nd ed. Baltimore, Maryland: Williams & Wilkins, 1982:47– 49.
REFERENCES 1. Mirakhur RK, Elliot P, Shepherd WFI, Archer DB. Intraocular pressure changes during induction of anesthesia and tracheal intubation. A comparison of thiopentone and propofol followed by vecuronium. Anaesthesia 1988;43:S54 – S57. 2. Robinson R, White M, McCann P, Magner J, Eustace P. Effect of anesthesia on intraocular blood flow. Br J Ophthalmol 1991;75:92–93. 3. Murphy DF. Anesthesia and intraocular pressure. Anesth Analg 1985;64:520 –530. 4. Watcha MF, Chu FC, Stevens JL, White PF. Intraocular pressure and hemodynamic changes following tracheal intubation in children. J Clin Anaesth 1991;3:310 –313. 5. Watcha, MF, White PF, Tychsen L, Stevens JL. Comparative effects of laryngeal mask airway and endotracheal tube insertion on intraocular pressure in children. Anesth Analg 1992;75:355–360. 6. Brain AIJ. The laryngeal mask—a new concept in airway management. Br J Anaesth 1983;55:801– 805.
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Biosketch Patrick Watts obtained his undergraduate degree in medicine and a postgraduate degree in Ophthalmology in India. He was awarded a Fellowship of the Royal College of Surgery in Edinburgh and Fellow of the Royal College of Ophthalmologists after passing the required examinations. After a fellowship at the Hospital for Sick Children in Toronto Canada in Paediatric Ophthalmology he took up a Consultant Paediatric Ophthalmology post in Cardiff, UK in 2002.
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Accepted for publication Jun 4, 2007. From the Departments of Ophthalmology (P.W., M.K.L., R.G., A.M., R.W.) and Anesthesia (T.A., T.Z., R.J.), University Hospital of Wales, Cardiff, Wales, United Kingdom; and the Department of Statistics, University of Glamorgan, Glamorgan, Wales, United Kingdom (H.A.M.). Inquiries to Patrick Watts, Department of Ophthalmology, University Hospital of Wales, Cardiff CF14 4XW, United Kingdom; e-mail: [email protected] 0002-9394/07/$32.00 doi:10.1016/j.ajo.2007.06.010
©
2007 BY
T
HE MEASUREMENT OF INTRAOCULAR PRESSURE (IOP)
in children is often carried out while they are under general anesthesia as part of the ocular examination. In current practice, the IOP in children is measured during the administration of the inhalational anesthetic agent via a face mask. Measurement of the IOP at this stage often is inconvenienced by limited access while the anesthesiologist attempts to maintain an adequate airway. It is also possible that the inadvertent pressure on the globe by the face mask affects the IOP. Performing the IOP measurement after the airway is secured allows easy access both for ocular examination and the estimation of the IOP. Tracheal intubation with an endotracheal tube (ETT) is associated with an increase in IOP,1–5 and recommendations exist on the optimal timing of performing IOP measurements in children after tracheal intubation to minimize this error.4 An alternative device, the laryngeal mask airway (LMA),6 has been reported to have negligible influence on the IOP measurement compared with the ETT.5,7,8 In this study, we aimed to determine the change in IOP after insertion of the LMA in children receiving general anesthesia using sevoflurane and the influence of the hemodynamic responses on its measurement in children.
METHODS THE STUDY WAS CARRIED OUT AT A UNIVERSITY HOSPITAL
with written informed consent obtained from the parent or legal guardian. All children (age, ⬍16 years) scheduled for elective ophthalmic surgery in a 12-month period were recruited into this study. Children with glaucoma or previous intraocular surgery were excluded from the study. General anesthesia was induced with either intravenous propofol or inhaled sevoflurane in oxygen and then maintained with 2% to 4% sevoflurane in oxygen and air. Additionally remifentanil was used in some patients. After induction of anesthesia, the IOP was measured when the end-tidal CO2 could be maintained at least 4 kPa (kilopascals) with positive pressure ventilation using the face mask. The IOP was measured using a Tono-Pen (Mentor O&O, Inc, Norwell, Massachusetts, USA), with
ELSEVIER INC. ALL
RIGHTS RESERVED.
507
a concerted effort to avoid pressure on the eyes while holding the face mask. The first IOP measurement was performed after induction of anesthesia, with the face mask in situ, before insertion of the LMA by one examiner (P.W.). Three readings were taken, and an average of the two closest readings were used in the analyses (all readings within 1 mm Hg of each other within 5% probability of accuracy). The IOP measurement was repeated similarly after secure insertion of the LMA by a second examiner (K.L.) masked to the results of the first. The IOP measurement was made on every occasion only when the patient’s end-tidal CO2 was stable. The second measurement thus was performed two minutes after insertion of the LMA. In addition to the IOP, the blood pressure (BP) and heart rate (HR) also were recorded. The differences in IOP in both eyes before and after insertion of the LMA were analyzed simultaneously using a multivariate repeated measures analysis of variance (ANOVA), with the age of the children younger and older than three years and gender as fixed factors. The effects of the BP, HR, and end-tidal CO2 on the IOP were studied using multivariate regression analysis (MANOVA) with Bonferroni corrections for multiple comparisons. In addition, the Pearson correlation coefficient was used to investigate further the relationships between age and postinsertion changes in IOP.
FIGURE. Scatterplot showing intraocular pressure (IOP) before (pre) and after (post) laryngeal mask airway (LMA) insertion.
TABLE. Changes in Intraocular Pressure, Heart Rate, Blood Pressure, and End-Tidal CO2 before and after Insertion of the Laryngeal Mask Airway
IOP (mm Hg) HR (bpm) BP (mm Hg) CO2 (kpa)
RESULTS study, 66 were included in the data analysis. The excluded children were those with missing data (n ⫽ 9) and those in whom atracurium, a muscle relaxant, was used during anesthetic induction. The mean age was 5.5 ⫾ 3.6 years (range, four months to 16 years). There were 40 male children. Among the 66 children, 83.9% were American Society of Anesthesiologists9 (ASA) grade 1, 14.3 % were ASA grade 2, and 1.8% were ASA grade 3. There was no influence of ASA grading in the changes in IOP (P ⫽ .3 and P ⫽ .1 for the right eye and left eyes, respectively). The mean IOP was 13.6 ⫾ 3.9 mm Hg and 13.6 ⫾ 3.6 mm Hg in right and left eyes, respectively, before LMA insertion and 15.5 ⫾ 3.8 mm Hg and 15.2 ⫾ 3.8 mm Hg in right and left eyes, respectively, after LMA insertion (Figure). The IOP remained stable in nine eyes, decreased in 86 eyes, and increased in 36 eyes. The mean difference between right and left eyes was ⫺0.01 mm Hg and 0.3 mm Hg before and after LMA insertion, respectively. There was a concordance between right and left eye measurements, with 60% of eyes showing an increase, 25% showing a decrease, and 15% showing stable IOP before and after LMA insertion. The mean change in IOP in the right eye was ⫺1.8 ⫾ 4.3 mm Hg (range, ⫺15.5 to 8.5 mm Hg) and ⫺1.5 ⫾ 4.1 AMERICAN JOURNAL
After LMA Insertion
P value
13.6 ⫾ 3.7 100.9 ⫾ 22.4 67.6 ⫾ 15.1 4.7 ⫾ 0.9
15.3 ⫾ 3.8 108.1 ⫾ 22.8 62.3 ⫾ 7.1 6.2 ⫾ 1.2
.0005 .0003 .01 .01
BP ⫽ blood pressure; bpm ⫽ beats per minute; HR ⫽ heart rate; IOP ⫽ intraocular pressure; kpa ⫽ kilopascals; LMA ⫽ laryngeal mask airway.
FROM A TOTAL OF 80 CHILDREN WHO TOOK PART IN THE
508
Before LMA Insertion
mm Hg (range, ⫺18 to 9 mm Hg) in the left eye (Wilks lambda, 0.855; F(2,56) ⫽ 4.7; P ⫽ .01). Age group, gender, and their interactions had no significant effect on the changes in IOP (P ⫽ .5, P ⫽ .1, and P ⫽ .2, respectively). Further analysis using the Pearson correlation coefficient revealed no significant association between the ages of children and the change in IOP (right eye, r ⫽ 0.2, P ⫽ .2; left eye, r ⫽ 0.09, P ⫽ .5). Anesthesia was induced with sevoflurane in 25 patients and with a combination of sevoflurane and remifentanil in five patients; 36 patients were induced with propofol. Anesthesia was maintained with sevoflurane in all children. There was no correlation between the type of the anesthetic used and the change in the IOP (P ⫽ .2 for both eyes). The HR (P ⫽ .005) and end-tidal CO2 (P ⬍ .000) increased during the IOP measurements, whereas the mean BP dropped (P ⫽ .007; Table). A multivariate ANOVA revealed a significant effect of the change in BP and change in HR on the measured IOP variable (P ⫽ .008 and P ⫽ .004). The interaction of mean HR change and mean BP change with changes in CO2 OF
OPHTHALMOLOGY
OCTOBER 2007
levels had a significant effect on the measured change in IOP (P ⫽ .04; Wilks lambda, 0.82; observed power, 0.87; and P ⫽ .009; Wilks lambda, 0.87; observed power, 0.8). The sample size was significant to detect a change in 10%, giving a power of 80%.
DISCUSSION THIS STUDY DEMONSTRATES THAT, ON AVERAGE, THE IN-
sertion of an LMA is associated with a significant increase in IOP in children receiving general anesthesia. Although the mean change in the IOP was small, the standard deviation of the change was 4.2 mm Hg, with a range of a decrease in IOP of 9 mm Hg to an increase in IOP of 18 mm Hg. This increase in IOP occurs with a concomitant decrease in BP and an increase in HR and end-tidal CO2. It is possible that the observed hemodynamic changes in HR are related causally to the increase in IOP. Alternatively, the stimulus induced by the insertion of the LMA evokes an increased HR and IOP, and with increasing depth of anesthesia, a decreased BP results; as a previous report suggests, lidocaine attenuates the elevation of IOP in children who are intubated.10 However, the decrease in the mean BP observed cannot be reconciled physiologically with the observed change in IOP. The possible explanation for this phenomenon was that the BP reading did not coincide exactly with the IOP measurement, whereas the HR did, because this was monitored continuously. An increased end-tidal CO2 is known to cause an increased IOP; statistical analysis using a MANOVA showed that this factor significantly affected the IOP change only by its interaction with the change in BP and HR. It is well known that the insertion of an ETT is associated with an elevation in IOP5,7,8; however, no significant change in IOP has been reported with the insertion of the LMA.5,8 The explanation for the difference in the results observed between a previous report5 (where the primary aim was a comparison of IOP change after ETT intubation and LMA insertion) and this study was the smaller sample size (n ⫽ 20 randomized to LMA insertion), the use of nitrous oxide, halothane, and atracurium, a muscle relaxant that may have altered any change induced by insertion of the LMA in the previous study. One of the studies8 was conducted in adults, with the IOP being measured with a different device. Clinically, it is our experience that single IOP values with the Tono-Pen may be highly variable; hence in this study, three consistent readings for each eye were obtained before
and after LMA insertion with a 5% probability. The Tono-Pen compares well with the Goldmann applanation tonometer, the gold standard for measuring IOP.11 Inhalational anesthetics reduce the IOP11; however, this study was conducted to measure the IOP soon after induction and soon after LMA insertion. This was timed to be two minutes after the insertion of the LMA. Sevoflurane recently was reported to lower IOP in children.12 This study compared the IOP measured after induction with sevoflurane and ketamine. An LMA was used only in three of the 15 patients who received sevoflurane, where the change in IOP after LMA insertion was not reported. All our patients had sevoflurane with additional agents that did not influence the IOP at the time of its measurement. Although our study was carried out in children without a diagnosis of glaucoma, the change noted cautions against measurements of IOP after LMA insertion in children with glaucoma. Although the mean change noted was small, the standard deviation and the range of change was high. Although it is acknowledged that any change in treatment for glaucoma in children also is governed by the change in the corneal diameter, the axial length, and optic cup size in children younger than 3 years of age and by consistently high IOP readings with changes in the optic cup in older children, IOP does play an important part in management decisions for glaucoma therapy. This study failed to show a correlation between the change in IOP measured after insertion of the LMA and the age of the child. An erroneous low measurement of IOP could miss pathologically raised IOP, and similarly, an erroneous high IOP reading may lead to overtreatment.13 However, caution should be exercised when extrapolating our findings to a population of children with glaucoma where a wider range of IOP may influence the results. We conclude that IOP measurement in children receiving general anesthesia currently should be measured with the face mask in situ before the insertion of the LMA, because this is associated with statistically significant changes in IOP. The change in IOP measured correlates with a decrease in BP and the interaction of the changes in BP, HR, and end-tidal CO2. These measured changes may influence changes in the treatment of a child with glaucoma. The magnitude of change of IOP reported in this study after the insertion of the LMA were within the normal range and hence may not seem clinically significant; however, when dealing with children with glaucoma, the measured change may dictate change in therapy. This study hence forms the basis for a similar study in children with glaucoma to validate the above findings in a sample of children with glaucoma.
THE AUTHORS INDICATE NO FINANCIAL SUPPORT OR FINANCIAL CONFLICT OF INTEREST. INVOLVED IN DESIGN AND conduct of study (P.W., H.A.); data collection and management (T.Z., T.A., R.J., R.W., A.M., K.L., R.G., P.W.); analysis and interpretation of data; and preparation (P.W., H.A., K.L., R.G.) and review or approval (T.Z., T.A., R.J.) of the manuscript. Ethical approval was obtained from the Local Research Ethics Committee of Wales and the Research and Development Department of Cardiff and Vale NHS Trust, Wales, United Kingdom.
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7. Holden R, Morsman CDG, Butler J, Clark GS, Hughes DS, Bacon PJ. Intraocular pressure changes using the laryngeal mask airway and tracheal tube. Anaesthesia 1991:46:922–924. 8. Whitford AM, Hone SW, O’Hare B, Magner J, Eustace P. Intraocular pressure changes following laryngeal mask airway insertion: a comparative study. Anaesthesia 1997:52:794 –796. 9. American Society of Anesthesiologists. New classification of physical status. Anesthesiology 1963;24:111. 10. Lerman J, Kiskis AA. Lidocaine attenuates the intraocular pressure response to rapid intubation in children. Can Anaesth Soc J 1985;32:339 –345. 11. Li J, Herndon LW, Asrani SG, Stinnett S, Allingham RR. Clinical comparison of the Proview eye pressure monitor with the Goldmann applanation tonometer and the TonoPen. Arch Ophthalmol 2004:122:1117–1121. 12. Blumberg D, Congdon N, Jampel H, Gilbert G, Elliot R, Rivers R, et al. The effects of sevoflurane and ketamine on intraocular pressure in children during examination under anesthesia. Am J Ophthalmol 2007;143:494 – 499. 13. Shields MB. The intraocular pressure. In: Textbook of Glaucoma. 2nd ed. Baltimore, Maryland: Williams & Wilkins, 1982:47– 49.
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Biosketch Patrick Watts obtained his undergraduate degree in medicine and a postgraduate degree in Ophthalmology in India. He was awarded a Fellowship of the Royal College of Surgery in Edinburgh and Fellow of the Royal College of Ophthalmologists after passing the required examinations. After a fellowship at the Hospital for Sick Children in Toronto Canada in Paediatric Ophthalmology he took up a Consultant Paediatric Ophthalmology post in Cardiff, UK in 2002.
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