Hypotension may contribute to perioperative stroke risk
MedWire News: Patients who develop hypotension during surgery may be at an increased risk for perioperative stroke, show findings from a case-control study.
"Although case-control studies generally are considered to be hypothesis generating, these hypotheses are of valuable clinical importance because perioperative blood pressures are controllable, potentially providing an opportunity to alter the postoperative stroke risk, especially in high-risk patients," say the researchers.
The results also add to those of the Perioperative Ischemic Evaluation Study (POISE) study, which found a higher risk for perioperative stroke in patients given metoprolol than in those given placebo, suggesting that hypotension could aggravate perioperative stroke risk.
Perioperative stroke is a rare event; in the current study it occurred in just 42 (0.09%) of 48,241 patients undergoing noncardiac and nonneurosurgical procedures. The researchers, led by Jilles Bijker (University Medical Center Utrecht, the Netherlands) matched the stroke patients by age and type of surgery to 252 control patients.
Bijker et al defined perioperative stroke as that occurring within 10 days of surgery, rather than the more usual 30 days. "We chose a period of 10 postoperative days to find a compromise between finding too few cases with a very short period and a questionable association with postoperative events when using a very long period," they comment in Anesthesiology.
The team assessed a range of absolute blood pressure thresholds and changes from baseline. No absolute blood pressure threshold, whether for systolic or mean blood pressure, was significantly associated with perioperative stroke risk.
Several thresholds for blood pressure reduction from baseline were associated with perioperative stroke risk; however, just one threshold was significantly associated with stroke at the researchers' chosen statistical threshold of p=0.001. This was a 30% reduction in mean blood pressure, and each minute below this threshold was associated with a 1.3% increase in stroke risk.
Notably, the 99.9% confidence intervals were much smaller for all blood pressure measures that were relative to baseline than they were for absolute blood pressure thresholds - in other words, defining hypotension as a change from baseline provided a much more precise estimate of stroke risk than defining it according to an absolute threshold.
"In this context, hypotension is best defined as a decrease in mean blood pressure relative to a preoperative baseline, rather than an absolute low blood pressure value," says the team.
Bijker and team note that the overall increase is smaller than that seen in POISE, but say that the trial used one high dose of a beta blocker, whereas patients in the current study received a wide variety of drugs and doses.
Just 17% of patients in the current study had strokes in watershed areas (areas vulnerable to low perfusion in the event of hypotension), but the researchers argue that hypotension could also exacerbate embolic stroke by reducing blood flow to the ischemic penumbra.
"The current study suggests that [intraoperative hypotension] may indeed play a role, albeit limited, in the occurrence of a postoperative stroke," the team concludes.
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By Eleanor McDermid