PREOPERATIVE PERIOD

Figure 1A summarises the situation in the preoperative period. The systemic and pulmonary circulations are both supplied by the right ventricle. The balance between flow to the lungs and flow to the body via the patent arterial duct is critical: too much pulmonary blood flow will result in systemic underperfusion and too little in hypoxaemia. A satisfactory balance between adequate oxygenation and perfusion is often achieved in the early newborn period without specific intervention, other than intravenous prostaglandin to maintain ductal patency. However, if signs of a low systemic cardiac output develop (low urine output and progressive acidosis) it will be necessary to increase the pulmonary vascular resistance by active respiratory management: it may seem counterintuitive to reduce inspired oxygen in a sick, shocked neonate but this is frequently necessary to achieve stability. Furthermore, the oxygen levels in inspired air may prove …