The influence of baricity on the haemodynamic effects of intrathecal bupivacaine 0.5%

This study compared the haemodynamic effects of subarachnoid block with pla in bupivacaine 0.5% (dextrose-free), heavy bupivacaine 0.5% (in dextrose 8% ) and a mixture of these two solutions, i.e. bupivacaine 0.5% in dextrose 4 %. Thirty-six male patients, aged 55-89 years, undergoing transurethral sur gery were recruited. Invasive systolic arterial and central venous pressure s were recorded at 5-s intervals after the block was initiated using a comp uterised data-collection system. The height of sensory blockade was recorde d at 5-min intervals. No preload was given and episodes of hypotension were treated with colloid (8 ml.kg(-1)) and, if this was ineffective, a metaram inol infusion. Systolic arterial and central venous pressures decreased in all three groups following block (p < 0.05). These decreases were more rapi d in onset in the heavy bupivacaine group compared with plain bupivacaine g roup (p < 0.005). Patients in the heavy bupivacaine group also had a greate r requirement for early treatment of hypotension (< 10 min) and treatment w ith metaraminol (p < 0.05). The onset of sensory blockade was more rapid in the heavy group compared with the mixed group, although final sensory leve ls were similar. The onset of haemodynamic and sensory changes are more rap id when using heavy bupivacaine intrathecally. This leads to a higher and e arlier incidence of hypotension and requirement for treatment.