A similar alternative is time-weighted average blood pressure under a threshold, which is area divided by duration, thus having units of mmHg. Even better ones consider both duration and severity of exposure such as area under a threshold, which has units of mmHg times minute. More sophisticated definitions consider exposure time, such as cumulative minutes of mean arterial pressure less than 65 mmHg. However, dichotomous definitions (such as hypotensive or not) discard much information and therefore poorly characterize continuous measures. Perioperative hypotension can be defined as a binary event based on a single blood pressure value ( e.g., mean arterial pressure less than 65 mmHg at least once) or by cumulative or consecutive time with blood pressure under a certain threshold ( e.g., mean arterial pressure less than 65 mmHg for at least 5 consecutive or cumulative minutes). Consequently, measures that characterize hypotensive excursions are generally more helpful than case averages. ![]() Harm from hypotension appears to mostly accrue from brief periods at low pressures rather than from prolonged exposure to moderate pressures. 21 Applying an absolute mean arterial pressure threshold of 65 mmHg yielded an incidence of 65% for a greater than or equal to 1-min exposure, 49% for a greater than or equal to 5-min exposure, and 31% for a greater than or equal to 10-min exposure. 21 For example, considering a 20% reduction in systolic blood pressure resulted in an incidence of intraoperative hypotension of 93% for a greater than or equal to 1-min exposure, 88% for a greater than or equal to 5-min exposure, and 78% for a greater than or equal to 10-min exposure. 21 Applying these definitions to a retrospective cohort of more than 15,000 adults who had noncardiac surgery showed that the incidence of intraoperative hypotension varies substantially depending on the selected definition. 21 The most common definition was a 20% reduction in systolic blood pressure from baseline. Definitions were based on either systolic blood pressure or mean arterial pressure or a combination of both, considering either absolute thresholds or thresholds relative to a baseline. ![]() 21 identified 140 definitions for intraoperative hypotension in 130 articles. Hypotension is generally defined using absolute or relative thresholds for various blood pressure components, and may specify a duration of exposure. ![]() There are no clear or widely accepted definitions of intraoperative or postoperative hypotension.
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