Neonatologist performed functional echocardiography in the neonatal intensive care: clinical and research applications

Echocardiography by the neonatologist is a discipline where the frontline neonatal care giver uses ultrasound as an adjunct to their clinical acumen (extension of clinical skills).The objective is to gain further insight into disease pathophysiology so as to provide physiology driven care. There is recent data where the skill was shown to be useful and life-saving in critically sick infants. This thesis aims to address the following clinical and research applications for this discipline: a. The spread of the discipline of echocardiography by the neonatologist, clinical benefits obtained, barriers towards learning, and the need for structured training. b. Patent ductus arteriosus (PDA): how to assign haemodynamic significance and the role of ductal disease staging. c. Surgical ligation of the patent ductus arteriosus: haemodynamic issues relevant to focussed peri-operative care. d. Haemodynamic effects of common neonatal interventions such as indomethacin and surfactant. e. The effects of intrauterine growth restriction on cardiovascular function. f. The usefulness of echocardiography by the neonatologist in critically ill infants. g. Bronchopulmonary dysplasia and its effects on cardiac and vascular function. h. Role of newer imaging modalities such as speckle tracking echocardiography. The foremost issue is that of a PDA and the lack of consensus regarding whether a PDA is pathological to the extent that it should be treated very early on. Equipoise persists as to the clinical and echocardiographic significance of a PDA. Studies where treatment was based on a single echocardiographic parameter or where no stratification for the ‘severity’ of ductal disease was considered did not show significant benefit in clinical outcomes. We proposed a scoring system based on echocardiography to stratify patient population. The thesis also depicts the benefits of this discipline in understanding peri-operative haemodynamics following surgical ligation of the PDA. Surgical duct ligation is followed by a significant elevation in systemic vascular resistance, which temporally coincides with a reduction in cardiac contractility. Amongst commonly used medications, indomethacin usage was associated with a significant though transient decrease in coronary blood flow (very similar to the effect seen on mesenteric, cerebral and renal perfusion). Surfactant replacement therapy on the other hand, led to acute changes in pulmonary to systemic blood flow ratio in small preterm infants. Cardiac and vasomotor function of infants with intrauterine growth restriction has been the focus of much recent work. Cardiac function (especially diastolic function) was impaired and the data on vasomotor function showed the systemic vessel (descending aorta) to be thicker and stiffer in the early postnatal period. Bronchopulmonary dysplasia is the commonest respiratory morbidity in surviving preterm infants. The systemic (left sided) haemodynamics are not particularly well studied. We noted systemic arterial thickness and reduced ventricular contractility in this cohort. Lastly, this thesis depicts the use of newer ultrasound technology in various clinical settings. Speckle tracking echocardiography is well established in adult cardiac literature with neonatal applications beginning to emerge. We used this modality to study infants with possible acute (severe birth asphyxia) and chronic involvements (intrauterine growth restriction) of the cardiovascular system. In conclusion, this thesis covers the logistical, training and clinically relevant issues of the discipline of the neonatologist performed echocardiography. Additionally, it’s clinical and research applications are outlined with the help of already published peer-reviewed work. The clinical scenarios outlined in this work are commonly encountered in neonatal intensive care units worldwide. Some of the concepts have tremendous clinical benefits while others elucidate novel imaging technologies with exciting prospects to improve understanding of different disease states.