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Department of Anesthesiology Yonsei University College of Medicine Seoul, South Korea
To the Editor:
I read with interest the report of Allison et al. (1) concerning how sevoflurane was associated with a lower incidence of the oculocardiac reflex (OCR), airway irritability, and fewer ventilatory interventions compared with halothane in children undergoing outpatient strabismus surgery with spontaneous breathing via laryngeal mask airway. In their result, the baseline PETCO2 was higher in halothane group, and the values are included in the range of hypercapnia despite statistical significance. According to the studies of Blanc et al. (2,3), hypercapnia was an important adjuvant factor of OCR during strabismus surgery. Moreover, because it is clear that the OCR may be evoked by traction on the extrinsic muscles of the eyes, may produce hypercapnia and hypoxemia, and may aggravate the consequences of the OCR, controlled ventilation is recommended for patients undergoing strabismus surgery at least immediately before and during the muscular traction.
References
Department of Anesthesiology Academic Hospital Vrije Universitalt 1018 HV Amsterdam, The Netherlands
In Response:
We would like to thank Dr. Kil for his interest in our article.
His first comment is that hypercapnia is an adjuvant factor for triggering of the oculocardiac reflex (OCR). This has been a point of discussion in the past. He quotes two articles by Blanc et al. (1,2). The first study showed a higher incidence of the OCR in the group with PETCO2 40–55 mm Hg as compared with the group with PETCO2 of 26–39 mm Hg (1). In the second quoted study by Blanc et al. (2), only two of the patients had PETCO2 monitoring, and little conclusion over the OCR can be drawn from this. However, Mirakhur et al. (3) showed that controlled ventilation did not reduce the incidence of the OCR compared with spontaneous ventilation. In their study, the mean PETCO2 in the spontaneous ventilation group was 48 mm Hg and the controlled ventilation group 35 mm Hg. In our study, the mean PETCO2 values were 40 and 45 mm Hg in the sevoflurane and halothane groups, respectively, a small difference.
Dr. Kil’s second comment is to recommend that ventilation be controlled during strabismus surgery. As it is not clear whether hypercapnia increases the risk of the OCR, there will be anesthesiologists who will choose to let their patients breathe spontaneously.
References
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