The data used in this study comes from a prospective cohort study published previously by our team . We screened 576 consecutive patients who underwent abdominal surgery between 1 October 2018 and 15 July 2019 in a university hospital. Procedures of organ procurement (n = 11), reoperations (n = 24), procedures performed in local anaesthesia or monitored anaesthetic supervision (n = 33), and those classified as immediate according to the NCEPOD Classification of Intervention  (n = 14) were excluded (Fig. 1). Demographic and medical data were recorded, including sex, age, weigh, height, comorbidities and its pharmacological treatment, according to the ICD 10 criteria. Body mass index (BMI) and Charlson Comorbidity Index (CCI) were subsequently calculated. Type and duration of anaesthesia, and type, duration and urgency of surgery were recorded. Perioperative risk was assessed based on individual patient’s risk, according to the American Society of Anaesthesiology (ASA) physical status (PS) classification , and procedural risk, according to the European Society of Cardiology and European Society of Anaesthesiology recommendations . Primary arterial hypertension was diagnosed based on medical records.
Figure 1. Flow diagram for the patient selection process
Systolic (SBP) and diastolic blood pressure (DBP) were measured on a non-dominant arm with an automated oscillometric non-invasive BP monitoring device (Dräger Infinity Gamma XL) with a cuff of appropriate size depending on patient’s arm circumference and recorded in five-minute intervals during anaesthesia, from the first pre-induction measurement until the last measurement during recovery from anaesthesia in the operating theatre. Mean (MAP) blood pressure values were automatically calculated. Pulse pressure was calculated as the difference between SBP and DBP. A need for norepinephrine (NE) use, its doses and duration of infusion, together with intraoperative fluid balance were analysed.
As PP revolves usually around values of 40 mmHg and that, based on other studies on clinical consequences of abnormal PP, we distinguished the following absolute PP thresholds: >50 mmHg, > 55 mmHg, > 60 mmHg, > 65 mmHg, > 70 mmHg, > 75 mmHg, > 80 mmHg, > 85 mmHg and > 90 mmHg [5, 12–14]. Additionally, by analysing the maximal PP during a procedure, the best cut-off point associated with the occurrence of outcomes was estimated. Moreover, we analysed the occurrence of high systolic (defined as SBP > 160 mmHg ), low diastolic (defined as DBP < 50 mmHg ) and low mean arterial pressure (defined as MAP < 60 mmHg . We excluded pre-induction measurements in order to assess only those blood pressure values that occurred during anaesthesia.
In the postoperative period, the incidents of hypoperfusion of vital organs were recorded, and included the occurrence of AKI, stroke and MI according to their international definitions [18–20]. This composite endpoint was considered as the outcome.
STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) statement was applied for appropriate reporting .
Statistical analysis was performed using MedCalc Statistical Software version 18.1 (MedCalc Software Ltd., Ostend, Belgium). Continuous variables were expressed as median and interquartile range (IQR). Qualitative variables were expressed as absolute values and/or percent. Between-group differences for quantitative variables were assessed using Mann-Whitney U-test. Their distribution was verified with Shapiro-Wilk test. Chi-square test were applied for qualitative variables. The correlation was assessed using Spearman’s rank correlation coefficient. ROC curve analysis was implemented to assess the relationship between composite outcome and maximal PP values and pre-induction PP values. In order to control for potential confounding factors, we used multivariable logistic regression with all variables that achieved p-value of less than 0.1 in univariable analysis. If applicable, odds ratios (OR) and Area Under the Receiver Operating Characteristics (AUROC) with their 95% confidence intervals (CI) were calculated. All tests were two-tailed. A ‘p’ value < 0.05 was considered statistically significant.