Proteomic signatures for perioperative oxygen delivery in skin after major elective surgery: mechanistic sub-study of a randomised controlled trial

Hypotension as a marker or mediator of perioperative organ injury: a narrative review

Perioperative hypotension has been repeatedly associated with organ injury and worse outcome, yet many interventions to reduce morbidity by attempting to avoid or reverse hypotension have floundered. In part, this reflects uncertainty as to what threshold of hypotension is relevant in the perioperative setting. Shifting population-based definitions for hypertension, plus uncertainty regarding individualised norms before surgery, both present major challenges in constructing useful clinical guidelines that may help improve clinical outcomes. Aside from these major pragmatic challenges, a wealth of biological mechanisms that underpin the development of higher blood pressure, particularly with increasing age, suggest that hypotension (however defined) or lower blood pressure per se does not account solely for developing organ injury after major surgery. The mosaic theory of hypertension, first proposed more than 60 yr ago, incorporates multiple, complementary mechanistic pathways through which clinical (macrovascular) attempts to minimise perioperative organ injury may unintentionally subvert protective or adaptive pathways that are fundamental in shaping the integrative host response to injury and inflammation. Consideration of the mosaic framework is critical for a more complete understanding of the perioperative response to acute sterile and infectious inflammation. The largely arbitrary treatment of perioperative blood pressure remains rudimentary in the context of multiple complex adaptive hypertensive endotypes, defined by distinct functional or pathobiological mechanisms, including the regulation of reactive oxygen species, autonomic dysfunction, and inflammation. Developing coherent strategies for the management of perioperative hypotension requires smarter, mechanistically solid interventions delivered by RCTs where observer bias is minimised.

Lifting the lid on perioperative goal-directed therapy

The complex cellular interactions that underlie pathologies related to reduced oxygen delivery after surgery are poorly defined and difficult to measure. Heywood and colleagues explored the patterns of protein expression in skin biopsies taken from a subgroup of patients enrolled in a randomised trial designed to evaluate perioperative goal-directed therapy. One of their key findings was that a failure of participants to maintain preoperative systemic oxygen delivery was associated with an upregulation of intracellular proteins involved in counteracting oxidative stress. Their study highlights the importance of oxidative stress in the perioperative setting and suggests that maintenance of baseline oxygen delivery might be an important regulator of redox balance.