Knowledge
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Although there is some evidence of different efficacy among commonly used vasopressors, translating this to clinically-significant outcome differences is still uncertain.
Singh's 2020 Bayesian network meta-analysis is the most comprehensive study to date investigating this issue. The researchers concluded that norepinephrine, metaraminol, and mephentermine showed the lowest probability of adverse neonatal acid-base effects, and ephedrine showed the greatest.
Previously phenylephrine infusion has been the consensus recommendation.
Nonetheless, other than ephedrine which should not be a first-choice pressor during Caesarean section, there is not enough evidence to strongly recommend one pressor over another. Clinical familiarity and institutional availability are probably the most important factors when choosing a vasopressor.
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- Remifentanil infusions above 0.20-0.25 μg/kg/min are associated with hyperalgesia (OIH = Opioid Induced Hyperalgesia) and tolerance (AOT = Acute Opioid Tolerance) respectively.
- Some of these effects can be mitigated by multimodal analgesia (notably ketamine), and possibly by gradual weaning of a remifentanil infusion.
- The findings have been predominately identified in rats and volunteer human studies. The clinical and longterm significance is still uncertain.
- Although OIH and AOT arise from different physiological mechanisms, they are clinically difficult (if not impossible) to differentiate.
- The clinical priority for management is prevention.
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