In Reply:-Thank you for the opportunity to comment on the report by Ezri et al. and their very interesting observations. We are gratified with the concept “anesthesia management by evaluating autonomic reactivity,” because it may provide important information regarding the depth of anesthesia, as Dr. Anderson pointed out. 
Laser-Doppler (LD) flowmetry measures superficial cutaneous microcirculation under the probe, whereas plethysmography evaluates changes in the whole blood volume in the finger. The basic wave in LD skin blood flow wave is coincident with the simultaneously recorded baseline fluctuation in the plethysmographic wave. It has not been confirmed whether a linear, quantitative correlation exists between the amplitude of the skin vasomotor reflex measured by LD flowmetry and the pulse amplitude of the plethysmography. The report of Ezri et al. suggests that the changes in the pulse amplitude of plethysmography may also reflect sympathetically mediated vasomotion. Any progress toward an inexpensive and simpler autonomic monitor will prove to be beneficial to the spread of patient-by-patient-based anesthesia management.
Analyses of pulse waves (e.g., arterial blood flow, LD skin blood flow, and plethysmography wave) have a common weak point. For example, anesthesia induction with propofol and anaphylactoid reactions increases the pulse amplitude of the plethysmography and LD skin blood flow. This problem has limited the application of pulse wave analysis in assessing the depth of anesthesia. For reducing this problem, we prefer to evaluate autonomic reactivity using a known quantitative stimulus before anesthesia, surgical procedures, or both, rather than to evaluate the changes in autonomic indicators induced by the procedures.
Osamu Shimoda, M.D.
Department of Anesthesiology; Kumamoto University School of Medicine; Kumamoto, Japan;email@example.com
(Accepted for publication June 18, 1998.)