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Correspondence  |   March 2007
Use of Continuous Positive Airway Pressure in Anesthetized Infants
Author Affiliations & Notes
  • Mark W. Crawford, M.B.B.S., F.R.C.P.C.
    *
  • *The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
Article Information
Correspondence
Correspondence   |   March 2007
Use of Continuous Positive Airway Pressure in Anesthetized Infants
Anesthesiology 3 2007, Vol.106, 633-634. doi:
Anesthesiology 3 2007, Vol.106, 633-634. doi:
In Reply:—
We thank Dr. Rothstein for his interesting comments regarding our article.1 As he correctly points out, the effect of added elastic and/or resistive load on respiratory drive may differ in the awake and anesthetized states. In the awake state, an increase in elastic and/or resistive load is compensated by an increase in neuronal inspiratory drive. This compensatory neuronal drive may be absent or diminished during general anesthesia,2 and this may be particularly so in infants who are highly susceptible to anesthesia-induced attenuation of neuronal input. Continuous positive airway pressure (CPAP) may itself reduce inspiratory drive through the Herring-Breuer inflation reflex.3 The resulting hypercapnia will depend on the reduction in minute alveolar ventilation. In previous studies in anesthetized children, the impact of CPAP on minute ventilation has been clinically insignificant.4 Keidan et al.  studied the effect of CPAP (6 cm H2O) on work of breathing and respiratory indices in healthy spontaneously breathing children (median age, 1.0 yr) during halothane–nitrous oxide anesthesia.4 Application of CPAP via  a facemask significantly decreased the work of breathing but had no significant effect on inspiratory tidal volume, inspiratory minute volume, or end-tidal carbon dioxide tension. To the extent that CPAP relieves existing upper airway narrowing, CPAP can also improve gas exchange, resulting in a reduction of hypercapnia and improved oxygenation. It was the purpose of our study to determine the interaction of propofol anesthesia and CPAP on upper airway caliber and configuration in infants. We considered it neither relevant to the study hypothesis nor ethically justifiable to perform arterial puncture for blood gas analysis in our infant subjects. Given the relatively brief duration of CPAP application, any increase in arterial carbon dioxide tension was likely small; indeed, after removal of CPAP, we observed no outpouring of carbon dioxide as determined by end-tidal measurement.
*The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
References
Crawford MW, Rohan D, Macgowan CK, Yoo SJ, Macpherson BA: Effect of propofol anesthesia and continuous positive airway pressure on upper airway size and configuration in infants. Anesthesiology 2006; 105:45–50Crawford, MW Rohan, D Macgowan, CK Yoo, SJ Macpherson, BA
Friedman S, Campbell EJM: The ability of normal subjects to tolerate added loads. Resp Physiol 1970; 10:213–35Friedman, S Campbell, EJM
Motoyama EK: Respiratory physiology in infants and children, Smith's Anesthesia for Infants and Children, 6th edition. Edited by Motoyama EK, Davis PJ. St. Louis, Mosby, 1996, pp 11–67Motoyama, EK Motoyama EK, Davis PJ. St. Louis Mosby
Keidan I, Fine GF, Kagawa T, Schneck FX, Motoyama EK: Work of breathing during spontaneous ventilation in anesthetized children: A comparative study among the face mask, laryngeal mask airway and endotracheal tube. Anesth Analg 2000; 91:381–8Keidan, I Fine, GF Kagawa, T Schneck, FX Motoyama, EK