Effects of sevoflurane versus propofol on cerebral autoregulation during anaesthesia for robot-assisted laparoscopic prostatectomy.

Robot-assisted laparoscopic prostatectomy requires a pneumoperitoneum combined with steep Trendelenburg positioning, and these conditions can be associated with impairment of cerebral autoregulation. The objective of this study was to determine if choice of anaesthetic agent affects the preservation of cerebral autoregulation during robot-assisted laparoscopic prostatectomy. We randomly assigned 30 patients to maintenance of general anaesthesia with either propofol or sevoflurane. Cerebral autoregulation was tested by administration of intravenous phenylephrine to increase mean arterial pressure from approximately 80 mmHg to 100 mmHg while assessing cerebral blood flow using transcranial Doppler ultrasonography. Autoregulation was first tested in the supine position and then approximately once every hour after Trendelenburg positioning. The main outcome measure was the result of the final autoregulation test prior to completion of surgery. At that time, we found cerebral autoregulation to be significantly impaired in six of the 15 patients receiving sevoflurane and none of the 15 patients receiving propofol (P = 0.02). However, it should be noted that some patients in the propofol group had impaired autoregulation on earlier tests. In conclusion, we found that autoregulation during robot-assisted laparoscopic prostatectomy is less likely to be impaired with propofol compared to sevoflurane anaesthesia, particularly towards the end of the surgery.

Adding low concentrations of clonidine to ropivacaine for transversus abdominis plane blocks does not reduce plasma ropivacaine levels, suggesting a lack of vasoconstrictor effect.

Clonidine has been used successfully to prolong the duration of action of local anaesthetics in peripheral nerve blocks, but its mechanism of action in this setting remains unclear. Some studies suggest that clonidine exerts a vasoconstrictor effect, limiting the washout of local anaesthetic from its site of deposition. We investigated this potential vasoconstrictor effect, using plasma ropivacaine concentrations as a surrogate measure of vasoconstriction, in patients who received transversus abdominis plane (TAP) blocks with and without clonidine. Eighty women undergoing laparoscopic gynaecological surgery were randomly assigned to receive one of four TAP block solutions: 0.2% ropivacaine (control), ropivacaine with clonidine 2 µg/kg (clonidine), ropivacaine with 1:400,000 adrenaline (adrenaline) or ropivacaine and a subcutaneous injection of clonidine 2 µg/kg (SC clonidine). The primary outcome was total venous plasma ropivacaine concentrations up to 6 h after the block. There were no significant differences in plasma ropivacaine concentrations between the control group and the clonidine group at any timepoint in the study, nor were there differences in either the mean maximum ropivacaine concentration ( Cmax) (1.99 µg/mL versus 2.05 µg/mL, P = 0.712) or the time to maximum concentration ( Tmax) (51.0 min versus 56.0 min, P = 0.537). The SC clonidine group also did not differ significantly from the controls ( Cmax 2.13 µg/mL versus 1.99 µg/mL, P = 0.424; Tmax 43.5 min versus 51.0 min, P = 0.201). Plasma ropivacaine concentrations in the adrenaline group were significantly lower than the controls from 10 to 90 min ( P < 0.003 for each comparison), and the Cmax was less than that of the control group (1.36 µg/mL versus 1.99 µg/mL, P < 0.001) with a longer Tmax (103.5 min versus 51.0 min, P = 0.001). These findings indicate that clonidine at a concentration of 1.35 µg/mL added to ropivacaine for TAP blocks did not produce a reduction in plasma ropivacaine concentrations. This suggests a lack of vasoconstrictor effect during TAP blocks. Further studies should evaluate whether vasoconstriction occurs when clonidine is used at higher concentrations or for other blocks.