1. Background/Introduction: The surgical management of congenital heart diseases (CHD) in children has seen rapid advances in the recent years. This has enabled more number of children safely undergoing congenital heart surgery. The increase in number as well as complexity of cases has increased the duration and cost of perioperative care. Fast-tracking is a multidisciplinary approach conceptualized to reduce the length of post-operative hospitalization. The rate limiting step in fast tracking is early post-operative extubation and they are almost synonymous in the goal to achieve shorter hospital stay and improved outcomes.^1,2 The definition of fast-tracking has been variable but the goal of every protocol is safe early extubation either in the operating room or within a few hours of admission in ICU. Fast tracking has been practiced in surgical management of CHD. ^3-6 with neuraxial analgesia being an integral part of the process. ^7-10 Neuraxial analgesic technique with opioids provide effective and prolonged analgesia and blunts stress response to surgery. ^11-13 There are concerns over its safety especially with the use of continuous thoracic epidural catheters in heparinized patients. The incorporation of dexmedetomidine, propofol and shorter acting opioids has given it a new dimension. Our center is a high volume pediatric cardiac surgical unit. We intend to share our experience of fast-tracking with continuous epidural analgesia in CHD surgery.
2. Details of procedure and methodology proposed to be used in investigations (300 words)

This is a retrospective cohort study. The data of children below 18 years of age, who underwent cardiac surgery over the past 24 months will be analyzed. Children will be excluded if they have evidence of preoperative sepsis, on mechanical ventilation before surgery, on extra-corporeal membrane oxygenation (ECMO) perioperatively and patients who were never extubated and died in post-operative period. Patients extubated in the operating room or within 6 hours of arrival to the pediatric cardiac ICU (PCICU) will be defined as early extubation. Anesthetic technique was as per standard institutional protocol, i.e. balanced general anesthesia (GA) with thoracic epidural analgesia (TEA). All patients were taken into the operating room premedicated with intranasal ketamine 7 mg/kg and nasal midazolam 0.3-0.5 mg/kg. Induction was done with 2 mg/kg IV ketamine supplemented with 2 µg/kg IV fentanyl and IV rocuronium 1 mg/kg was administered to assist oral endotracheal intubation. Anesthesia was maintained with sevoflurane 2% and vecuronium injection adapted to the patient’s physiological reaction to surgical stimuli. After intubation epidural catheter was placed in T4 to T8 space with the patient in left lateral position. 1 mL/kg bolus of 0.25% bupivacaine and 50 µg/kg morphine administered in two divided doses 30 minutes apart, in the epidural catheter followed by infusion of 0.125% bupivacaine at the rate 0.1 mL/kg, throughout the intraoperative period and in the ICU. Ventilation was maintained with 50% fraction of inspired oxygen (FiO₂) and sevoflurane. Dexmedetomidine was started intraoperatively at the rate of 0.25 µg/kg/hour and continued throughout the postoperative period. 

Cardiopulmonary bypass (CPB) with ultrafiltration was performed according to our institutional protocol (see supplementary material). Milrinone was started with the loading dose 100 µg/kg at the release of aortic cross clamp (ACC) and infusion of milrinone at the dose of 0.75 µg/kg/minute was maintained thereafter if pulmonary arterial hypertension (PHT) or ventricular dysfunction was present.

Perioperative goal-oriented hemodynamic support (i.e. heart rate and mean arterial pressure at 95 percentile for age, central venous pressure as per the CHD taking into account mechanical ventilation at positive end-expiratory pressure of 4 to 5 cm H₂O, mixed venous oxygen saturation >65%) was established according to institutional standards. Hematocrit was maintained to > 35% in all patients and >40% in cyanotics. Extubation was decided by the anesthesiologist as per the institutional protocol. Post-operative analgesia in PCICU was maintained with continuous epidural infusion of 0.125% bupivacaine at the rate of 0.1 mL/kg/hour and rescue analgesia as fentanyl boluses of 1 µg/kg. 

Oxygen through high flow nasal cannula (HFNC) device (AIRVO2® with Optiflow Junior nasal prong ® ,Fisher & Paykel Healthcare limited, Auckland, New Zealand) was applied to the patient after extubation with disposables wide-bore snug-fitting nasal cannula of different sizes for children of different ages (Optiflow Junior Cannula). 

Echocardiography and cardiac catheterization reports, operative notes, anesthesia notes, perfusion charts and PCICU nursing charts will be reviewed along with case notes for the data collection. The inotropic requirement will be assessed in terms of vasopressor inotropic score (VIS). 

Statistical analysis: The distribution of the continuous data will be tested with the Kolmogorov-Smirnov 1-sample test. Continuous data will be reported as the mean + standard deviation and dichotomous data will be expressed as numbers and percentages. Comparison between the groups will be carried out using unpaired Student’s t-test or chi-square contingency tables. Univariate analysis will be performed using the Kruskal Wallis test and multiple regression analysis will be performed to predict failure in fast-tracking. Statistical analysis will be performed using SPSS software (IBM SPSS Statistics version 21, Chicago IL, USA) with p-value <0.05 being considered statistically significant.