Relationship between intraoperative drop in pulse pressure and minimum mean arterial pressure with postoperative length of stay according to main patients’ characteristics: A retrospective monocentric study

Intraoperative hypotension (IOH) is associated with organ failure. There is no consensus on the IOH definition, but the recommendations agree on a threshold of mean arterial pressure (MAP) between 60-70 mmHg. Prolonged postoperative length of stay (pLOS) is a surrogate for organ injuries. Our study focuses on the relationship between IOH and pLOS risk considering the main patient characteristics (sex and age) using a retrospective single-centre cohort study of adult patients having received general anesthesia for a scheduled non-cardiac surgical procedure. pLOS was defined as a LOS higher than the median value (main outcome). Relationships between the IOH variables selected from a previous study (difference between the larger and smaller pulse pressure values (DropPP), minimal MAP (MinMAP), and cumulative time pulse pressure spent above 61mmHg (CumTimePP>61mmHg) and the risk of pLOS are represented by knotted linear splines. Our study examined 9,516 patients. The relationship between DropPP and pLOS risk was pseudolinear with no activation threshold (slope 0.29-0.52%/mmHg). For MinMAP, this relationship describes an activation threshold at 73 mmHg below which the association is linear (slope -0.64%/mmHg). For CumTimePP>61, the risk of pLOS rapidly rises (initial slope 8.39%/min) up to a saturation threshold at two minutes. Women had a lower pLOS risk and IOH threshold. Older patients had a higher pLOS risk and did not exhibit an IOH threshold. The IOH threshold (MAP<73 mmHg) is consistent with the existing literature. The variability of PP as well as age and sex are key parameters in pLOS risk.

Methods
This retrospective single-centre study was managed in a tertiary academic private non-profit hospital. Patients were collectively informed (by means of posters) that their data could be used for research purposes, on condition that the data were anonymized. This information included the necessary information to enable them to refuse their participation. As a result of this procedure, the need for consent was waived by the local Ethics Committee which approved this retrospective study. Authors had no access to information that could identify individual participants during or after data collection.

Patient characteristics and preoperative medications were collected from Cesare™, a computerized software for preoperative anesthetic evaluation (Bow Médical, 80440 Boves, France). Centricity Anesthesia software was used to collect intraoperative variables (GE Healthcare, 78 530 Buc, France). The length of stay and in-hospital mortality were obtained by questioning the health data warehouse.