Ventilation-Perfusion Abnormalities in the Premature Infant: Triple Gradient

Abstract

Extract: Serial studies of arterial and alveolar oxygen, carbon dioxide, and nitrogen tensions, arterial pH, and ratios of dead space: tidal volume were made in 24 nondistressed premature infants. By determining arterial-alveolar gradients, the sequence of development of ventilation/perfusion relations in the non-distressed premature infant can be determined. The presence of an arterial-alveolar carbon dioxide gradient and elevated V_D/V_T ratio indicate the presence of overventilated/underperfused areas. Alveolar-arterial oxygen gradients may be due to shunting, underventilation (low ventilation/perfusion ratio), or diffusion block. Although underventilation exists, as evidenced by the presence of a urinary-alveolar gradient for N₂, it is not a major cause of arterial unsaturation. This evidence suggests that shunting of blood, either through intracardiac shunts or atelectatic lung, is a major cause of arterial unsaturation in the premature infant.

Speculation: Further extension of this work should make possible the construction of V_A/Q curves for the individual patient and thus show in even greater detail the maturation of pulmonary ventilation and perfusion.

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