Mallampati grade and laryngeal mask placement.

We thank Dr. Settergren for his interest in our work (1) and for pointing out a relevant paper, published long ago as a supplement to Acta Anestkesiologicu Scandinavica, of which we were not aware (2). Dr. Settergren is right in that para-aminohippurate clearance may not accurately measure renal plasma flow during hypothermic cardiopulmonary bypass, and the results we reported at that time therefore become questionable. Nevertheless, our renal plasma flow measurements during normothermic bypass, when hippuran clearance is an appropriate technique, were not significantly different from those during hypothermia. Dr. Settergren also questions as wrong the values we reported, because he arrived at different arterial pressure values by recalculating backwards from the renal resistance and flow reported by us. We rechecked our calculations, and they were in fact correct. What was wrong was, first, that Dr. Settergren assumed hematocrit values higher than the real ones. Secondly, he committed a frequent mathematical mistake: You cannot calculate the average of renal vascular resistances from the averages of pressure and flow. You must calculate each resistance individually, before averaging.