Investigation should be undertaken in an environment free from stress and with the infant or child in as near a stable haemodynamic state as feasible for the entire duration of the procedure. In practice, this is best achieved with general anaesthesia and controlled (mechanical) ventilation. The FiO2 should be kept to the minimum necessary to maintain a normal pulmonary vein oxygen saturation and tension. A trans-cutaneous oxygen-monitoring system is useful in confirming stability. Ventilation is adjusted to maintain normal arterial pCO2 levels. Figure 6.1 shows the lowering effect on the pulmonary arterial pressure of correcting the arterial blood gas status by changes in ventilation.
Measures should be undertaken to ensure that the body temperature is maintained, particularly during an extended procedure, and the oesophageal or rectal temperature is monitored. Fluid balance should be maintained intravenously, and arterial blood gas and blood sugar measurements made at regular intervals. The ECG and arterial blood pressure will need to be monitored from both an anaesthetic and a cardiological viewpoint. Excessive blood loss is unlikely to be encountered during diagnostic procedures, although it may be necessary to replace losses during interventional procedures involving the use of large-diameter catheters, especially if unexpected and sudden.
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