Intraoperative systolic BP variability predicts 30-day mortality
MedWire News: High blood pressure variability during cardiac surgery is associated with an increased risk for 30-day mortality, study findings show.
Solomon Aronson and colleagues, from Duke University Medical Center in Durham, North Carolina, studied blood pressure recordings from more than 7500 cardiac surgery patients and found that the absolute risk for 30-day mortality increased by 3% when systolic blood pressure (SBP) levels strayed outside the range 105 to 130 mmHg.
They report in the journal Anesthesiology that "although the absolute increased risk was small, intra-operative systolic blood pressure variability may represent an important modifiable risk factor for 30-day mortality."
The researchers electronically captured blood pressure data from 7504 patients aged an average of 65 years, who underwent coronary bypass surgery between 1996 and 2005. A total of 3.1 million intra-operative blood pressure evaluations were analyzed.
SBP variability was derived in 5038 of the patients and validated in 2466 patients. The 30-day mortality rates for these patient groups were 2.1% (n=99) and 2.6% (n=62), respectively.
The nine possible combinations associated with upper SBP thresholds of 130, 135, and 140 mmHg and lower SBP thresholds of 95, 100, and 105 mmHg were evaluated for their association with 30-day mortality.
All range combinations were highly associated with 30-day mortality, with the strongest odds ratios of 1.028 for an upper threshold of 130-140 mmHg and for a lower threshold of 100-105 mmHg.
Also, when blood pressure excursions outside the range of 130 to 95 mmHg were tested in separate multivariable logistic regression models accounting for length of surgery and Parsonnet score, these were associated with 30-day mortality, at a increase of 3% per mmHg/min.
Blood pressure excursions above 130 mmHg lasted an average of 5.12 minutes, and those below 105 mmHg lasted 11.06 minutes. Excursions outside of the range of 130 to 105 mmHg lasted an average of 8.03 minutes.
The researchers calculated that the probability of 30-day mortality was 1.9% for a mean duration of excursion outside this range of 8 minutes, increasing to 2.1% for a mean duration of 10 minutes, and 3.5% for a mean duration of 20 minutes.
Therefore, although an odds ratio of 1.03 represents a modest effect, "it is important to realize that this effect is per-minute effect, such that for every minute outside the 105 to 130 mmHg range, the odds ratio for 30-day mortality increases by 0.03," say Aronson and team.
They conclude that further investigation is needed to investigate whether a target systolic blood pressure band width or "sweet spot" exists.
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By Lucy Piper