There has been some observational evidence that a greater depth of anesthesia, as measured by BIS, may be associated with an increase in post-operative mortality. In particular the association of the "triple low state" (low BIS, low volatile-ET, low MAP) with post-operative mortality is worrying.
Completion of the Balanced Anaesthesia Study Group’s large RCT looking at this issue however brings us as close to a final word as we may expect. Short et al. (2019) showed no difference in 1-year mortality for older patients undergoing major surgery, whether they received a deep (BIS target 35) or light (BIS target 50) general anaesthetic.
It is likely that earlier observational studies were showing the consequences of intraoperative hypotension resulting from anaesthetic depth, rather than anaesthetic depth itself.summary
Why the excitement?
Since the landmark 2017 WOMAN trial (collected below) showed that tranexamic acid (TXA) may reduce mortality in post-partum haemorrhage, TXA has increasingly been found in close proximity to where obstetric spinal anaesthetics are commonly performed.
TXA's operating theatre ubiquity has also been enhanced by it's replacement of aprotonin in cardiac surgery (Myles 2017, Koster 2015), after the former's associated mortality bump, along with the increasingly routine use of TXA in major joint surgery to reduce bleeding and transfusion (Ho 2003, Poeran 2014).
Recent reviews have identified 21 case reports of mistaken intrathecal administration of TXA over 60 years of anaesthetic publications – although it is likely many cases have been unreported.
Seems rare - why should I be concerned?
- Intrathecal TXA has a 50% mortality, and frequently leaves survivors with permanent neurological injury.
- Once recognised, immediate, aggressive management may improve outcome (particularly, CSF lavage).
- Although rarely published, the increased use of intra-operative TXA may bring it into close proximity with common intrathecal drug ampoules, increasing the risk of this devastating error. Case report publication dates support the increasing incidence.
- Knowing the potential for this error is the first step to avoiding it both personally and systemically.
- Almost all cases involve drug swap errors with major human factor contributions.
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