There may still be an increased risk of total spinal block up to 90 minutes after the last epidural bolus.

  Daniel Jolley

A case study describing a total spinal occurring in a 26 year old having an emergency caesarean section for failure to progress.

On arrival in theatre a block to pin prick was noted to T12, with the last epidural top-up having been 90 minutes earlier with only 5 mL of 0.25% bupivacaine. Total volume of epidural LA is not reported.

The epidural had partially dislodged, so anaesthesia was with 10.5 mg of spinal bupivacaine (equivalent to 2.1mL of 0.5%) resulting in a block to T6. 10 minutes later the patient became distressed, followed by respiratory arrest and unconsciousness.

Baby was delivered uneventfully and the mother made a full recovery. The authors ascribed the case to a total spinal resulting from cephalad spread of intrathecal bupivacaine.

  Daniel Jolley

Far from earth-shattering, though what I find (possibly) interesting is the long delay between the last epidural dose and the (apparent) total spinal.

90 min seems like it should be well and truly long enough for any epidural bupivacaine to be absorbed – in fact, this is probably only a little shorter than the duration of said dose. It's possible that the total spinal was totally unrelated to the epidural, but that's probably wishful thinking.

Previous studies (Dadarkar, IJOA 2014) have suggested that waiting 30 min between last epidural dose and spinal is safe (audit of 115 patients in Dallas).

The take-away for me is that there's probably more patient variability than we'd like to admit.

  Daniel Jolley