Is research reporting intraoperative hypotension apt enough?

Intraoperative hypotension (IOH) needs urgent attention as it significantly affects organ perfusion and patient outcomes.1 Depending on its severity and duration, it might result in major organ dysfunction, ischaemia, and failure, even leading to case fatality.2-5 Despite being so crucial, there is no uniform definition or universally accepted threshold to define IOH.2 A systematic review by Bijker JB et al.6 identified 140 definitions of IOH provided in over 100 studies from January 2000 to April 2006. Frequently used definitions include systolic blood pressure (SBP) 20% below baseline, and a combination of definitions consisting of an absolute SBP of 30% drop from baseline)'. Therefore, either can be used to define hypotension and initiate management.22,23 Nevertheless, the duration of hypotension is also crucial. In non-cardiac surgery, Sun et al.24 found that acute kidney injury is linked to intraoperative MBP <55–60 mmHg for ≥11–20 min. Salmasi et al.25 found that postoperative heart and kidney injury risk in non-cardiac surgery increases with a reduction in intraoperative MBP <50–60 mmHg for 1–30 min or 20%–50% of the preoperative value for ≥5 min. In a recent retrospective multi-centre cohort study including 316,717 non-cardiac surgical patients, an MBP of <55 mmHg was associated with an increased rate of postoperative delirium.26 Applying personalised SBP targets, as opposed to standard blood pressure (BP) management, dramatically reduced the incidence of postoperative organ dysfunction as found in multi-centre INPRESS trials.27 The baseline reading timing is also crucial as it can impact the definition of hypotension, especially when the percentage fall from the baseline is considered while defining IOH. In clinical practice, BP measurements taken just before induction of general anaesthesia are often used as a surrogate for the patient's baseline. However, a prospective observational study comparing ambulatory and perioperative BP in 370 patients showed that pre-induction MBP values do not reflect mean daytime MBP values.28 Thus, pre-induction MBP values should not serve as a surrogate for the individual normal daytime MBP.3 Blood pressure and heart rate in the preoperative area and operation theatre are significantly affected by preoperative anxiety.29 Anxiety is frequently noted in the preoperative period, even after pre-anaesthesia evaluation and counselling.30 Such anxieties can be because of multiple factors such as fear of needles, waking up and pain during surgery, and inadequate information about surgery and anaesthesia, leading to preoperative anxiety.31 Our analysis found that the timing for the baseline value for BP was also variable. The first reading of the operating table was the most common, that is, 6 (46.15%). The researcher also took the ward and preoperative area values; one study did not report it. To conclude, the practice and research reporting have remained diverse in defining IOH. Although it might be difficult to put one BP above another, MAP can be chosen to define hypotension in most cases. A personalised approach might be the best approach. However, it might not always be feasible. Nonetheless, a fall of 20% from the baseline might be the nearest resemble of a personalised approach rather than an absolute value, especially in chronic hypertensive patients. The first reading on the operating table or preoperative area might be affected by anxiety or pre-medication; thus, taking the average ward BP reading as a baseline might be better in admitted patients.