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Forty patients admitted with acute retention of urine were treated by transurethral resection of the prostate by either the continuous or intermittent flow resectoscope. No significant differences or trends were demonstrated between the 2 techniques in respect of speed of resection, blood loss and amount of glycine absorbed. There was a marked degree of haemodilution during surgery in some patients.

modifications, the system could prove to be the first practical design step to preventing accidental crossconnection of neuraxial and intravenous lines, thereby improving patient safety. There is a good correlation between the calculated effect site concentration and the depth of anaesthesia. Propofol is known to depress the cardiovascular system but the relationship between the effect site concentration and cardiovascular depression has not been extensively studied. A previous study by Kazama et al. showed that the maximal cardiovascular depression (using systolic blood pressure only) would happen some 8 min after peak plasma propofol concentrations [1]. We wished to investigate this further while using effect site concentration target-controlled infusions (TCI) of total intravenous anaesthesia (TIVA). MethodsLocal Research Ethics Committee approval was given and informed consent obtained from 20 patients of ASA physical status 1-2 due to undergo elective day surgery. They were then anaesthetised using a standard effect site concentration TIVA technique. From the time of attaining a steady state effect site concentration of both propofol and remifentanil ([ES] ss ) we measured Bispectral Index, heart rate, blood pressure and cardiac index every minute for 25 min. Any alterations were then mathematically modelled in a nonlinear regression model to calculate when they reached a steady plateau with 95% certainty. ResultsThese are shown in Table 1. DiscussionWe have shown that the time to maximal cardiovascular depression occurs well after that previously claimed [1]. The depression of cardiovascular parameters is most profound in the vasodilatation that is well known with propofol, reflected in the drop in mean arterial pressure. The reduction in heart rate is also significant but reflex mechanisms of increasing the stroke volume ensures that the measured cardiac index changes less. These results show that after achieving steady state concentrations of anaesthetic agents the cardiovascular system depresses further with a maximal time of depression 78 min after achieving calculated steady state anaesthesia. Papers using patients at 'steady state' anaesthesia must either have a comparable control arm to the experiment or wait for 78 min until the cardiovascular systems achieve a steady plateau.