- •Hypotension has heterogenous underlying pathophysiological causes and organ-specific effects on tissue perfusion.
- •Hypotension does not always lead to organ hypoperfusion; in fact, it may not affect or may even increase organ perfusion.
- •The overall evidence from RCTs does not support the notion that a higher blood pressure target always leads to improved patient outcomes.
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Hypotension and outcomes based on cohort studies
Hypotension and outcomes based on randomised controlled trials
|Year (Authors)||Surgery||Patients (n)||Higher BP target||Lower BP target||Outcomes||Conclusion|
|1999 (Williams-Russo and colleagues)|
|Hip surgery under epidural anaesthesia||235||MAP=55–70 mm Hg||MAP=45–55 mm Hg||Cognitive, cardiac and renal complications||No difference|
|2016 (Carrick and colleagues)|
|Laparotomy or thoracotomy for trauma||168||MAP=65 mm Hg||MAP=50 mm Hg||30 day mortality||No difference|
|2017 (Futier and colleagues)|
|Major abdominal surgery||292||SBP=90–110% of resting value||SBP >80 mm Hg or 60% of resting value||A composite of systemic inflammatory response syndrome and organ dysfunction by day 7 after surgery||A higher BP target is beneficial|
|1995 (Gold and colleagues)|
|CABG with CPB||248||MAP=80–100 mm Hg during CPB||MAP=50–60 mm Hg during CPB||Mortality, cardiac, neurologic, and cognitive complications, and changes in quality of life||A higher MAP during CPB is beneficial|
|2007 (Charlson and colleagues)|
|CABG with CPB||412||MAP target=80 mm Hg during CPB||MAP target=pre-bypass level during CPB||Mortality, major neurologic or cardiac complications, cognitive complications or deterioration in functional status||No difference|
|2011 (Siepe and colleagues)|
|CABG with CPB||92||MAP=80–90 mm Hg during CPB||MAP=60–70 mm Hg during CPB||Early postoperative cognitive dysfunction and delirium||A higher MAP during CPB is beneficial|
|2014 (Azau and colleagues)|
|Cardiac surgery with CPB||300||MAP=75–85 mm Hg during CPB||MAP=50–60 mm Hg during CPB||Acute kidney injury||No difference|
|2018 (Vedel and colleagues)|
|Cardiac surgery with CPB||197||MAP=70–80 mm Hg during CPB||MAP=40–50 mm Hg during CPB||Cerebral infarcts detected by DWI||No difference|
Nature of blood pressure
Hypotension has different underlying pathophysiological mechanisms
- •SVR decreases whereas CO remains stable (Fig. 2b).
- •SVR decreases whereas CO increases, but the effect of the SVR decrease exceeds the effect of the CO increase (Fig. 2c).
- •CO decreases whereas SVR remains stable (Fig. 2d).
- •CO decreases whereas SVR increases, but the effect of the CO decrease surpasses the effect of the SVR increase (Fig. 2e).
- •Both CO and SVR decrease (Fig. 2f).
Organ-specific impact of hypotension on perfusion
- •Organ perfusion remains stable if the effects of the decreases in perfusion pressure and RVR are comparable, a scenario in which the underlying pathophysiology of hypotension is an SVR decrease without changes in CO (Fig. 2b). This impact is consistent with the conventional concept of pressure autoregulation, as discussed in the following section.
- •Organ perfusion increases if the effect of the perfusion pressure decrease is less than that of the RVR decrease, a scenario in which hypotension is secondary to an SVR decrease accompanied by a lesser degree of CO increase (Fig. 2c), as exemplified by the use of certain calcium channel blockers.82
- •Organ perfusion decreases if perfusion pressure decreases in the face of one of the following changes in RVR: (1) an unchanged RVR – that is a scenario in which the underlying pathophysiology of hypotension is a CO decrease without changes in SVR (Fig. 2d); (2) an increased RVR – that is a scenario in which hypotension is secondary to a CO decrease accompanied by a lesser degree of SVR increase (Fig. 2e); or (3) a decreased RVR, with the degree of the RVR decrease less than that of the perfusion pressure decrease – a scenario in which hypotension is secondary to a decrease in both CO and SVR (Fig. 2f).
Organ blood flow regulation
Importance of cardiac output to organ perfusion
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Proposed definition and classification of hypotension
Organ perfusion assessment
Clinical scenarios involving hypotension
Beta blocker-related hypotension
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Hypotension related to angiotensin converting enzyme inhibitors or angiotensin II receptor blockers
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Neuraxial block-related hypotension
Acute anaemia-related hypotension
Septic shock-related hypotension
Appendix A. Supplementary data
- Multimedia component 1
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