Optimising Cardiac Output to improve clinical outcomes of anaesthesia in high-risk paediatric patients

During the last decade, there has been an increase in paediatric anaesthesia mortality due to an increase in surgical procedures in high-risk groups. Registries and large single centre studies have consistently reported these high-risk groups are young children (< 2 years), children in poor physical condition at the time of surgery (ASA III and higher) and with significant comorbidities such as congenital heart disease (CHD). The anaesthesia morbidity has been attributed to airway and cardiovascular complications. The cardiovascular complications have numerous aetiologies but ultimately result in a low cardiac output (CO) state. CO is a primary determinant of oxygen transport to tissues. Circulating volume assessment and CO are integral to the practice of anaesthesia as both can change rapidly and unpredictably during anaesthesia. Most anaesthesia drugs are myocardial depressants, decreasing CO directly or by effects on the systemic vasculature. Actual or effective intravascular volume loss (haemorrhage and distributive shock respectively) can result in poor tissue perfusion due to low “effective” CO. Certain CHD conditions affect myocardial performance directly, reducing CO (such as pulmonary hypertension, single ventricle pathologies) or cause conditions where supranormal CO is required (such as intracardiac shunt lesions) to maintain adequate systemic tissue perfusion. This thesis is presented as a thesis by publication. The work presented in the first chapters (2-4) address some of the difficulties in assessing low CO states and identifying risk factors in two conditions with increased morbidity and mortality under anaesthesia. The next chapters (5-8) address manipulations of CO and efforts to optimise current treatment. Chapter 5 describes the development of an assay to measure milrinone drug levels to improve the precision of therapy. Chapter 6 describes the on-going RCT investigating if real time milrinone levels improve clinical outcomes in patients post cardiac surgery. The next two chapters address problems associated with manipulation of CO to supranormal levels. I present a study describing the complications associated with the current management of paediatric patients undergoing renal transplantation. Current paediatric anaesthesia transplantation protocols call for CVP values of 15 cmH20, based on evidence from adult studies. The distensibility of a paediatric patient’s vessels means achieving such values is difficult and can be associated with morbidity. I then present an alternative strategy to augmenting CO using intraoperative echocardiography to guide fluid management. The next four chapters address resuscitation- the final common pathway of inadequate CO. In these chapters I present research measuring the effectiveness of resuscitation. I begin with the current standards for resuscitation documentation, which guides clinical care, research, education and quality improvement initiatives and describe the current challenges in cardiac arrest documentation. I present a study describing a novel measurement of the technical aspects of resuscitation and then progress to analysing the non-technical skills of experienced resuscitation teams. With this knowledge, I describe a new role in resuscitation teams, which was implemented in local training and resuscitation management. This thesis concludes with an evaluation of resuscitation teaching for school aged children to improve bystander CPR rates and effectiveness, thus reducing morbidity and mortality of low CO states at a public health level. The impact of this body of research has been a change in our local resuscitation team structure for training and clinical care and informing public health programs in teaching CPR in programs such as “Kids Save Lives”