We have designed an automatic detector system for noninvasive monitori
ng of irrigating fluid absorption during transurethral resection of th
e prostate. Ethanol, which is used as a tracer for the fluid, is measu
red in the expired breath of the patient. The breath ethanol monitor c
an be used both in the awake patient and during general anaesthesia. A
lap-top computer controls the monitor and calculates the fluid absorp
tion 1-3 times per min and uses the pattern of ethanol changes to indi
cate whether the fluid is being taken by the intra- and/or extravascul
ar route. The monitor has been used in routine operations for one year
. The interpretation of absorption routes was checked by control metho
ds or by evaluation of the postoperative breath-ethanol curve. We foun
d the indicated absorption to be correct in all resections with absorp
tion large enough for the monitor to present an interpretation.