We performed this prospective interventional study on adult patients undergoing hepatobiliary pancreatic surgeries after obtaining approval from the Ethical and Scientific Committee of Fayoum University Hospital (D154) and the National Liver Institute (0146/2018). We received written informed consent from the patients or their surrogates to participate in this study. We registered this study at ClinicalTrials.gov (NCT03546179).
We conducted the study at the National Liver Institute Hospital, Menoufia, Egypt. We studied patients aged > 18 years undergoing hepatic, pancreatic, or biliary tumor resection. Patients with preoperative cardiac arrhythmias, peripheral vascular disease, low left ventricular function (ejection fraction < 40%), significant valvular heart disease, or fulminant hepatic failure were excluded from this study.
On the day of surgery, intravenous access was obtained. Demographic and anthropometric data including age, sex, height, actual body weight, PBW, body mass index, body surface area, smoking history, and comorbid diseases were recorded. All patients were monitored using 5-lead electrocardiography, non-invasive blood pressure monitoring, and pulse oximetry. General anaesthesia was induced with propofol (2 mg.kg− 1 IV), fentanyl (3 µg.kg− 1 IV) and rocuronium (0.6 mg.kg− 1 IV). Anesthesia was maintained with sevoflurane (1.5–3%).
Mechanical ventilation was given to all patients to keep end-tidal CO2 between 35 and 40 mmHg. A 7 F triple-lumen central venous catheter was inserted in the right internal jugular vein with ultrasound guidance. The left radial artery was cannulated, a pressure transducer was placed on the midaxillary line, fixed to the operating table to keep the sensor at the atrial level, and zeroed to atmospheric pressure for measuring invasive arterial blood pressure. An indwelling urinary bladder catheter was inserted to monitor urinary output. Head and extremity wraps and warmer systems in the form of forced warming system were applied to maintain body temperature. A trans-oesophageal Doppler probe (Cardio QP EDM™; Deltex Medical, Chichester, UK, Fig. 1) was greased with a lubricating gel and passed nasally into the mid-esophagus until the aortic blood flow signals were best identified. Four skin electrodes (iSense electrical cardiometry skin sensors; Osypka Medical) were placed on the neck and thorax of patients as per the manufacturer’s recommendations and an electrical cardiometry monitor (ICON Cardiotronics, Inc., La Jolla, CA USA; Osypka Medical GmbH, Berlin, Germany, Fig. 2) was connected to the sensor cable. The Masimo Pulse Co-Oximeter probe (Masimo SET Rainbow R2-25r and R225a; Masimo Corp., Irvine, CA, USA, see Fig. 3) was placed on the index finger of patients.
Throughout surgery, packed red blood cells (300 ml) were transfused when the hematocrit level was < 25%. Fresh frozen plasma (200 ml) was administrated when the fibrinogen level was < 2 g.dl− 1 or the international normalized ratio was > 2. Patients were extubated either in the operating room or postoperatively in the ICU.
Intervention protocol (Fig. 4)
After the tumor resection phase, baseline hemodynamic variables including heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), stroke volume index (SVI), PVI, perfusion index (PI), stroke volume variation (SVV), index of contractility (ICON) and corrected flow time (FTc) with a 6 ml/kg VT ventilation were recorded. After baseline measurement, VT was increased to 8 ml/kg PBW for 1 min, and the above-mentioned hemodynamic variables were recorded. The VT has then decreased to 6 ml/kg PBW and after 1 min, measurements were recorded.
After these hemodynamic measurements, volume expansion was performed for 10 minutes using an infusion of a balanced crystalloid solution (6 ml/kg actual body weight). The same hemodynamic parameters were measured under ventilation with a VT of 6 ml/kg 5 min after volume loading. Then, the absolute change (ΔPVI6 − 8) (PVI after − PVI before VT challenge) and percentage change (%ΔPVI6 − 8) (PVI after − PVI before VT challenge / PVI before VT challenge) between the PVI at 6 ml/kg of PBW (PVI6) and that at 8 ml kg− 1 of PBW (PVI8) (i.e., after performing a VT challenge) were calculated. The change in PVI after giving the fluid bolus (ΔPVIfb) (PVI after − PVI before fluid bolus) was also calculated. The percentage change in SVI, according to volume loading, was used as the principal indicator of fluid responsiveness. Responders or non-responders were determined when the increase in SVI was ≥ 10% or < 10% after volume loading, respectively [12].
No more than two VT challenges can be performed in any patient. Doses of vasoactive medications, if used, and positive end-expiratory pressure were kept constant.
We defined the primary outcome as the best cut-off value of ΔPVI6 − 8 in hepato–pancreatico–biliary surgeries using a VT challenge. The secondary outcomes were the evaluation of hemodynamic variables in fluid responders and non-responders and the detection of sensitivity and specificity of PVI6, PVI8, ΔPVI6 − 8, and other measured dynamic variables of fluid responsiveness.
The Statstodo online computer program (www.statstodo.com) was used to calculate the sample size requirement for comparing two receiver operating characteristics (ROC) curves with expected areas under the curves (AUC) of 0.65 (PVI6) and 0.90 (ΔPVI6 − 8), assuming an α error of 0.05 and a power of 90%. A minimum of 40 patients were needed to detect an AUC difference of 0.25 when supposing that the number of responders was similar to that of non-responders [13]. Since our expected data loss was 20%, 48 patients had to be enrolled in this study.
The SPSS software Version 21.0 (IBM, Armonk, NY, USA) was used to perform statistical analysis. Data were presented as mean (standard deviation), median [interquartile range (range)], or percentage (%). Distribution normality was assessed using the Shapiro–Wilk test. Changes in continuous variables from 6 to 8 ml/kg PBW were compared using the paired t-test or Wilcoxon signed rank-sum test. Group comparisons between responders and non-responders were performed using the independent t-test or Mann–Whitney U test. Categorical variables were analyzed using the chi-square test or Fisher exact test. To test the abilities of the dynamic preload indices to predict fluid responsiveness, the AUCs of responders were calculated and compared using the Hanley–McNeil test (AUC = 0.5, a useless test with no prediction possible; AUC = 0.6–0.69, a test with poor predictability; AUC = 0.7–0.79, a fair test; AUC = 0.8–0.89, a test with good predictability; AUC = 0.9–0.99, an excellent test; AUC = 1.0, a perfect test with the best possible prediction) [14]. An optimal threshold value was determined for each variable to maximize the Youden index [sensitivity + (specificity − 1)] [15].