Noninvasive monitoring of blood gases in the neonatal period

Abstract

Sick neonates benefit from continuous monitoring of transcutaneous blood gases, since a blood sample only represents a single point on a variable curve. The tcpO₂ value alone, does not predict the oxygen saturation or the critical point on the hemoglobin-oxygen dissociation curve above which hypoxia is avoided. There are several conditions in which the tcpO₂ may not be reliable. The most important factors are those of hypovolemia/hypotension and a right to left shunt through a patent ductus arteriosus. The introduction of pulse oximetry, which estimates oxygen saturation, is thus a helpful supplement in neonatology, but will not on its own predict toxic levels of pO₂. The pulse oximeter does not need calibration nor time for stabilization. It is easy to place on a hand or a foot, and is therefore of great value during resuscitation and during transport. This technique does also give rise to misinterpretations. These are, however, minimized if the device shows a reliable pulse wave curve on its display. Both tcpO₂/tcpCO₂ and pulse oximetry are important tools, supplementing each other as they all yield valuable information.

Although both are noninvasive, blood samples are still needed. Now and then a correlation with an arterial sample has to be performed, and a noninvasive pH electrode does not exist.

Key-words:

• transcutaneous pO₂
• transcutaneous pCO₂
• pulse oximetry
• hemoglobin-oxygen dissociation curve