In Reply:—

As noted in our article, the 82.6% incidence of venous air embolism (VAE) detected by precordial Doppler monitor during craniectomy is higher than previously reported. 1However, it is not dramatically different from the incidence of 66% reported by Harris et al. , 2who used a similarly sensitive monitor. One would expect the incidence of VAE to be higher when using a precordial Doppler monitor as compared with only end-tidal carbon dioxide (ETco2) monitoring. In the current article, 51.6% of VAE episodes were associated with decreases in ETco2(36% with ETco2decrease only, and 15.6% with hypotension and decreased ETco2). However, I do not believe that in the absence of Doppler monitoring, these decreases in ETco2would be diagnosed as episodes of VAE. I would expect that the majority of these episodes of decreased ETco2not associated with changes in hemodynamic status would not be diagnosed and that a portion of those episodes with hypotension would also not be attributed to VAE. Therefore, I do not agree with the observation of Meyer et al.  that extrapolation of our data would result in a 40% incidence of VAE if monitored with ETco2only.

Our data agree with the suggestion of Meyer et al.  that precordial Doppler monitoring detects transient episodes of small-volume VAE. Even without detection, many of these episodes are likely to be self-limited because the surgeons wax bone edges or proceed in other ways to obliterate sources of air entry as a routine part of the procedure. However, use of the Doppler monitor allows the surgeon and the anesthesiologist to evaluate the success of these maneuvers. It is not surprising that, in the study by Meyer et al. , 3the incidence of hypotension during VAE is greater. The monitor used to detect VAE is less sensitive than precordial Doppler monitor, which results in the undetected transient, small VAE episodes and causes other episodes of VAE to progress to larger volumes of air entrained than before the diagnosis. In the study by Cucchiara et al. , 4the incidence of hypotension with VAE was 69% in children, rather than 36%. It should be noted that these children were also in the sitting position. Precordial Doppler monitoring is a noninvasive monitoring tool that adds to the anesthesiologist’s understanding of intraoperative events. Children undergoing craniosynostosis repair are subject to significant hemodynamic changes, including VAE and significant blood loss. The major advantage of precordial Doppler monitoring is that it allows the diagnosis of potentially dangerous VAE before it becomes clinically significant.

Faberowski LW, Black S, Mickle JP: Incidence of venous air embolism during craniectomy for craniosynostosis repair. A nesthesiology 2000; 92; 20–3
Harris MM, Yemen TA, Davidson A, Strafford MA, Rowe RW, Sanders SP, Rockoff MA: Venous air embolism during craniectomy in supine infants. A nesthesiology 1987; 67; 816–9
Meyer P, Cuttaree H, Charron B, Jarreau MM, Perie AC, Sainte-Rose C: Prevention of venous air embolism in paediatric neurosurgical procedures performed in the sitting position by combined use of MAST-suit and PEEP. Br J Anaesth 1994; 73; 795–800
Cucchiara RF, Bowers B: Air embolism in children undergoing suboccipital craniotomy. A nesthesiology 1982; 57; 388–9