A prospective observational trial was conducted in Cairo University hospital after Institutional Research Ethics approval (N-91-2018) including a cohort of 36 adult critically ill patients with acute kidney injury (AKI). Written informed consent was obtained from patients or their surrogates before inclusion in the study. We included patients who were scheduled for first session intermittent hemodialysis according to Kidney Disease Improving Global Outcomes (KDIGO) guidelines (pulmonary oedema, uremic complications, hyperkalemia not responding to other measures and intractable acidosis). 9 All enrolled patients were classified as KDIGO stage III 9.
We excluded patients with pre-existing end-stage renal disease, patients with severe vascular disease compromising measurements of PPI, and patients with major burns which precluded the application of electrical cardiometry electrodes.
Acute kidney injury was diagnosed if the patient showed any of the following criteria: 1- Increase in serum creatinine by at least 0.3 mg/dL within 48 hours. 2- Increase in serum creatinine to 1.5 times baseline. 3- Urine volume of less than 0.5 mL/kg per hour for 6 hours. Hemodialysis was decided by the attending nephrologist for volume overload, severe electrolyte disturbance (Acidosis, hyperkalemia) or severe uremia. 9
Parameters of dialysis session were determined by the attending nephrologist with pump rate of 200-250 ml/min, session time not exceeding 3 hours, and maximum ultrafiltration rate of 1L/hour, Hemodialysis sessions were performed using hemodialysis machine (Gambro AK96), and 1.7 m2 biocompatible filters.
Standard monitors were applied for all patients during the session of hemodialysis. Non-invasive arterial blood pressure (systolic, diastolic and mean) monitor was measured every 5 minutes. Electrocardiogram (ECG) and pulse oximetry were applied continuously. Central venous pressure (CVP) was measured via a right internal jugular central venous catheter.
PPI was measured using Masimo SET Radical- 7 device (Masimo Corp., Irvine, Calif., USA). The adhesive sensor was attached onto the index finger (Masimo SET ® LNCS Adtx, adult sensor).
Electrical cardiometry ICON device (Osyka Medical, Berlin Germany) was used to measure advanced hemodynamic variables (cardiac output, systemic vascular resistance, and HRV). HRV analysis by the electrical cardiometry was determined using time-domain analysis, specifically standard deviation of the normal-to-normal R-R interval. 8
Hypotensive episode was diagnosed as 20% reduction of mean blood pressure from the baseline value which required either initiation or increased rate of norepinephrine infusion. Patients were categorized into 2 groups. Hypotensive group and stable group. Hypotensive group included any patient who had one or more hypotensive episodes.
Our primary outcome is to detect the predictive ability of PPI for intradialytic hypotension. Secondary outcomes included non-invasive blood pressure, heart rate, cardiac output, systemic vascular resistance, CVP, and HRV. All hemodynamic values were recorded at the following time points: 30 minutes before the hemodialysis session, 15 minutes before the start of hemodialysis session, every 5 minutes during the session, and 15 minutes after the conclusion of the session.
Our primary outcome was the area under receiver operating characteristic (AUROC) curve for PPI in prediction of intradialytic hypotension. In a previous study, the AUROC for PPI for prediction of hypotension during continuous hemodialysis was 0.8 5. Thus, we calculated our sample size using MedCalc version 220.127.116.11 (MedCalc Software bvba, Mariakerke, Belgium) to detect AUROC of 0.8 with null hypothesis of 0.5. The calculated minimum number of patients to have a study power of 80% and alpha error of 0.05 was 26 patients with at least 13 positive and 13 negative cases.
Statistical analysis was performed using SPSS 15 (Chicago, IL). Categorical data were presented as frequency (%); continuous data were checked for normal distribution by Kolmogorov-Smirnov test. Normally distributed continuous data were presented as mean±SD, and skewed data were presented as median (quartiles). Patients were classified into hypotensive patients and stable patients; Chi-square test was used to compare frequencies between the two groups. Unpaired t-test and Mann-Whitney test were used to compare the means for continuous data as appropriate.
To compare the performance of different variables in predicting intradialytic hypotension, receiver operating characteristic (ROC) curves were constructed and the AUROC curve was calculated for each variable. MedCalc software generated values with the highest sensitivity and speciﬁcity (Youden index). The AUROC curves were compared using a Hanley-McNeil test. The level of significance was set at P < 0.05 for two-tailed tests.