Dynamic Tests and Parameters to Predict Fluid Responsiveness After OPCAB

Overview

Objective: To assess the predictive value of dynamic tests and parameters for evaluation of fluid responsiveness after off-pump coronary artery bypass grafting (OPCAB). After arrival to ICU, all patients received positive end-expiratory pressure test (PEEP-test), mini-fluid challenge test (mFCT) and standard fluid challenge test (sFCT) to assess fluid responsiveness. In addition, investigators measured pulse pressure variation using two monitoring systems (PPVPiCCO and PPVNK), stroke volume variation (SVV), heart-lung interaction index (HLI) and plethysmogram variability index (PVI) before and after sFCT.

All patients were intubated using the standard induction technique with sodium thiopental (4 mg/kg), fentanyl (2.5-3.0 mcg/kg) and pipecuronium bromide (0.1 mg/kg). Anaesthesia was maintained using sevoflurane (0.5-3.0 vol.% at the end of expiration) and fentanyl (2.0-4.0 mcg/kg/hr). Depth of anaesthesia was adjusted to maintain bispectral index (BIS) values between 40-60 (LifeScope, Nihon Kohden, Japan). In all cases, preoxygenation with 80% O2 was provided during 3-5 minutes before anesthesia. After tracheal intubation, patients were ventilated using a protective volume-controlled mode (Dräger Primus, Germany) with tidal volume of 6-8 mL/kg of predicted body weight, flow of 1 L/min and positive end-expiratory pressure (PEEP) of 5 cm H2O. The value of FiO2 was set to at least 50% or higher to achieve intraoperative SpO2 above 95%. The respiratory rate was adjusted to maintain end-tidal CO2 values within 30-35 mm Hg. All the patients were operated by the same team of surgeons using Acrobat SUV OM-9000S (Guidant, Santa Clara, USA) device for stabilization of the heart during revascularization. After surgery, all patients were transferred to the postoperative cardiac ICU and sedated during 60 min with continuous infusion of propofol (2-4 mcg/kg/hr) to maintain BIS values within 60-70. Respiratory support in ICU was continued by a G5 ventilator (Hamilton Medical, Switzerland) using pressure controlled ventilation mode with parameters same as for intraoperative period. Investigators provided invasive hemodynamic monitoring (PiCCO2, Pulsion Medical Systems, Germany; Nihon Kohden, MU-671RK, Japan) to all patients. After the initial stabilization of patient, investigators performed three dynamic tests in a consequent order. The positive end-expiratory pressure test (PEEP-test) consisted of a transient increase of PEEP from 5 to 20 cm H2O during 120 seconds. The PEEP-test was interrupted if mean arterial pressure (MAP) decreased below 55 mm Hg and/or pulse contour cardiac index (PCCI) decreased below 1.5 L/min/m2. Mini-fluid challenge test (mFCT) consisted of rapid infusion of crystalloids 1.5 mL/kg during 120 seconds. Thereafter, all patients received fluid challenge (standard fluid challenge test, sFCT). During the sFCT, patients received 7 mL/kg of crystalloids within 10 minutes. During PEEP-test and mFCT, investigators performed continuous monitoring of MAP, SVV, PPV and PCCI (PiCCO2). Investigators also measured SVV, PPVPiCCO, PVVNK (Nihon Kohden), HLI (Hamilton G-5, Switzerland) and PVI (Masimo, USA) before and after sFCT. In addition, investigators assessed cardiac index (CI), extravascular lung water index (EVLWI) and global end-diastolic volume index (GEDVI) using transpulmonary thermodilution (PiCCO2). During the study, investigators measured arterial blood gases and lactate concentration. The patients who demonstrated an increase in CI ≥ 15 % after sFCT were defined as fluid responders.10, 11 After the initial measurements, sedation was stopped, and the weaning from respiratory support was initiated. The weaning protocol included gradual decrease of inspiratory pressure and mandatory respiratory rate followed by spontaneous breathing trial after achieving pressure support of 8 cm H2O. After passing the 30-min spontaneous breathing trial, all the patients were extubated and received oxygen inhalation via facial mask. In addition to hemodynamic and respiratory parameters, recorded the preoperative EuroScore II, duration of postoperative mechanical ventilation, length of ICU stay and fluid balance after OPCAB and on postoperative Day 1.