Hypobaric type oxygenators - physics and physiology

Brain injury is still a serious complication after cardiac surgery. Gaseous microemboli (GME) are known to contribute to both short and longer-term brain injury after cardiac surgery. Hypobaric and novel dual-chamber oxygenators use the physical behaviors and properties of gases to reduce GME. The aim of this review was to present the basic physics of the gases, the mechanism in which the hypobaric and dual-chamber oxygenators reduce GME, their technical performance, the preclinical studies, and future directions. The gas laws are reviewed as an aid to understanding the mechanisms of action of oxygenators. Hypobaric-type oxygenators employ a high oxygen, no nitrogen environment creating a steep concentration gradient of nitrogen out of the blood and into the oxygenator, reducing the risk of GMEs forming. Adequately powered clinical studies have never been carried out with a hypobaric or dual-chamber oxygenator. These are required before such technology can be recommended for widespread clinical use.

Warm versus cold blood cardioplegia in paediatric congenital heart surgery: a randomized trial

OBJECTIVES

Intermittent cold blood cardioplegia is commonly used in children, whereas intermittent warm blood cardioplegia is widely used in adults. We aimed to compare clinical and biochemical outcomes with these 2 methods.

METHODS

A single-centre, randomized controlled trial was conducted to compare the effectiveness of warm (≥34°C) versus cold (4-6°C) antegrade cardioplegia in children. The primary outcome was cardiac troponin T over the 1st 48 postoperative hours. Intensive care teams were blinded to group allocation. Outcomes were compared by intention-to-treat using linear mixed-effects, logistic or Cox regression.

RESULTS

97 participants with median age of 1.2 years were randomized (49 to warm, 48 to cold cardioplegia); 59 participants (61%) had a risk-adjusted congenital heart surgery score of 3 or above. There were no deaths and 92 participants were followed to 3-months. Troponin release was similar in both groups [geometric mean ratio 1.07; 95% confidence interval (CI) 0.79-1.44; P = 0.66], as were other cardiac function measures (echocardiography, arterial and venous blood gases, vasoactive-inotrope score, arrhythmias). Intensive care stay was on average 14.6 h longer in the warm group (hazard ratio 0.52; 95% CI 0.34-0.79; P = 0.003), with a trend towards longer overall hospital stays (hazard ratio 0.66; 95% CI 0.43-1.02; P = 0.060) compared with the cold group. This could be related to more unplanned reoperations on bypass in the warm group compared to cold group (3 vs 1).

CONCLUSIONS

Warm blood cardioplegia is a safe and reproducible technique but does not provide superior myocardial protection in paediatric heart surgery.

Intermittent antegrade warm-blood versus cold-blood cardioplegia in children undergoing open heart surgery: a protocol for a randomised controlled study (Thermic-3)

INTRODUCTION

Surgical repair of congenital heart defects often requires the use of cardiopulmonary bypass (CPB) and cardioplegic arrest. Cardioplegia is used during cardiac surgery requiring CPB to keep the heart still and to reduce myocardial damage as a result of ischaemia-reperfusion injury. Cold cardioplegia is the prevalent method of myocardial protection in paediatric patients; however, warm cardioplegia is used as part of usual care throughout the UK in adults. We aim to provide evidence to support the use of warm versus cold blood cardioplegia on clinical and biochemical outcomes during and after paediatric congenital heart surgery.

METHODS AND ANALYSIS

We are conducting a single-centre randomised controlled trial in paediatric patients undergoing operations requiring CPB and cardioplegic arrest at the Bristol Royal Hospital for Children. We will randomise participants in a 1:1 ratio to receive either 'cold-blood cardioplegia' or 'warm-blood cardioplegia'. The primary outcome will be the difference between groups with respect to Troponin T levels over the first 48 postoperative hours. Secondary outcomes will include measures of cardiac function; renal function; cerebral function; arrythmias during and postoperative hours; postoperative blood loss in the first 12 hours; vasoactive-inotrope score in the first 48 hours; intubation time; chest and wound infections; time from return from theatre until fit for discharge; length of postoperative hospital stay; all-cause mortality to 3 months postoperative; myocardial injury at the molecular and cellular level.

ETHICS AND DISSEMINATION

This trial has been approved by the London - Central Research Ethics Committee. Findings will be disseminated to the academic community through peer-reviewed publications and presentation at national and international meetings. Patients will be informed of the results through patient organisations and newsletters to participants.

TRIAL REGISTRATION NUMBER

ISRCTN13467772; Pre-results.

Direct Arterial Cannulation Allows Easy and Safe Continuous Selective Cerebral Perfusion During Repair of Interrupted Aortic Arch Even for Low Birth Weight Neonates

OBJECTIVES

To review the outcomes of direct innominate artery cannulation for continuous cerebral perfusion used for repair of interrupted aortic arch (IAA) in a consecutive cohort of neonates regardless of weight.

METHODS

Between September 1999 and April 2016, forty-four children with IAA (18 type A and 26 type B) underwent repair using continuous, hypothermic (18°C) low-flow cerebral perfusion via direct innominate artery cannulation. Associated cardiac lesions were truncus arteriosus (TA; 5), ventricular septal defect (VSD; 30), transposition of the great arteries (TGA; 1), unbalanced atrioventricular septal defect (1), double-inlet left ventricle (1), double-outlet right ventricle (3), and aortopulmonary window (APW; 5). Truncus arteriosus, single VSD, TGA, and APW were corrected while the other patients were palliated.

RESULTS

Age at the time of surgery was 7 days (4-120 days) and weight 3.1 kg (2.1-5.8 kg). Selective cerebral perfusion was maintained in all patients. During the selective cerebral perfusion, perfusion flow rate was maintained at 30 mL/kg/min. Aortic cross-clamp time, low-flow, and total cardiopulmonary bypass time were 63 (40-116), 28 (17-41), and 108 (80-217) minutes, respectively. There were no deaths nor clinical evidence of neurological injury. Postoperative ventilation time, length of intensive care unit, and hospital stay were 3 (2-14), 5 (3-21), and 13 (6-27) days, respectively. Follow-up, complete at 84 months (24-221), revealed no late clinically evident neurologic sequelae nor innominate artery complications.

CONCLUSIONS

Direct innominate arterial cannulation with continuous selective cerebral perfusion can be safely applied for repair of IAA even in low birth weight neonates. It is technically simple and associated with excellent clinical outcomes.

Development of the orpheus perfusion simulator for use in high-fidelity extracorporeal membrane oxygenation simulation

Despite its life-sustaining potential, extracorporeal membrane oxygenation (ECMO) remains a complex treatment modality for which close teamwork is imperative with a high risk of adverse events leading to significant morbidity and mortality. The provision of adequate training and continuing education is key in mitigating these risks. Traditional training for ECMO has relied predominantly on didactic education and hands-on water drills. These methods may overemphasize cognitive skills while underemphasizing technical skills and completely ignoring team and human factor skills. These water drills are often static, lacking the time pressure, typical alarms, and a sense of urgency inherent to actual critical ECMO scenarios. Simulation-based training provides an opportunity for staff to develop and maintain technical proficiency in high-risk, infrequent events without fear of harming patients. In addition, it provides opportunities for interdisciplinary training and improved communication and teamwork among team members (1). Although simulation has become widely accepted for training of practitioners from many disciplines, there are currently, to our knowledge, no commercially available dedicated high-fidelity ECMO simulators. Our article describes the modification of the Orpheus Perfusion Simulator and its incorporation into a fully immersive, high-fidelity, point-of-care ECMO simulation model.