Knowledge
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Is the conventional assumption that left-lateral tilt and uterine displacement avoids aortocaval compression during Caesarean section actually valid?
50 years of assumed orthodoxy is challenged by studies showing that:
- True aortal compression is relatively uncommon (Higuchi 2015, Lee 2012).
- Caval compression is probably near-universal, but also usually not improved by a mere 15 degree tilt. (An impractical 30 degrees is more likely required for meaningful impact!) (Palmer 2015).
- Caval compression probably has limited haemodynamic or fetal consequences in the fit, well, term parturient (Higuchi 2015; Lee 2012).
- Judicious use of vasopressor infusions may obviate the need for traditional uterine displacement (Lee 2017; Farber 2017).
Time to change practice then?
Not quite yet...
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Hydroxyethyl starches, such as Hespan, Voluven, Volulyte, Tetrahes and Hestar, have been shown in several large trials to increase the risk of acute kidney injury (AKI) and/or the need for renal replacement therapies among critically ill patients, particulalry those suffering sepsis.
Evidence demonstrating harm among fit & healthy surgical patients is however lacking, notably Giles et al could find no increased risk of adverse event among surgical patients in their 2014 meta-analysis. Nonetheless, given the similar lack of demonstrable benefit of HES fluids for this group, avoidance of use in both the ICU and surgical population is prudent.
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...and 1 more note
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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.
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Also see Carbon Footprint from Anaesthetic gas use [pdf] from the UK’s Sustainable Development Unit.
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