Continuous infusion epidurals for obstetric analgesia.

Continuous infusion of local anaesthetic for epidural analgesia in obstetrics was first described in 1963. t However, this method of providing pain relief in labour did not become popular, probably because of the limitation of the mechanical pumps available at that time and also the tachyphylaxis associated with the use of lidocaine or mepivacaine. 2 Recently, continuous infusions have been described using modern infusion devices and low concentrations of bupivacaine (0.125-0.375 per cent). 3-1~ The claimed advantages for this technique over intermittent bolus injections include: (1) A more stable level of analgesia, because of the elimination of the return of painful contractions, which is the usual indication for a repeat injection of local anaesthetic in the intermittent injection technique. (2) Lower blood concentrations of local anaesthetic which result from decreased absorption from the epidural space during continuous infusion. (3) Lower blood concentrations of local anaesthetic if the epidural catheter is inadvertently placed in a vein and a direct intravenous injection is made. (4) A reduced risk of total spinal block if the epidural catheter is inadvertently positioned in the subarachnoid space. (5) A reduced incidence of hypotensive episodes due to decreased sympathetic blockade. In the studies so far reported the rate of acceptable analgesia varied from 70 per cent (infusion rate 6 ml/hour of 0.25 per cent bupivacaine) 6'7 to 90 per cent (6 ml/hour of 0.3 per cent or 10 ml/hour of 0.25 per cent bupivacaine). 7'8 This compares favourably