Fig. 30.4. Venous and arterial pressure tracings may be used to facilitate placement and detect misplacement. A: The catheter has been pulled back through the ductus venosus, and the tip lies in the portal

system. The portal venous pressure is higher than the central venous pressure, there are no venous pressure waves, and there is a small positive deflection during inspiration. B: Tip of catheter in the superior

vena cava near the right atrium shows a deflection of more than 4 mm Hg during spontaneous inspiration

(I) and a large negative deflection of more than 15 mm Hg during a sigh (S). Atrial tracing shows an AC

and a V wave. AC wave occurs with atrial contraction and closure of atrioventricular valve after P wave of

ECG. V wave occurs with ventricular contraction near T wave of electrocardiogram. (Based on data from

Kitterman JA, Phibbs RH, Tooley WH. Catheterization of umbilical vessels in newborn infants. Pediatr

Clin North Am. 1970;17:895, with permission.) C: Pressure tracing from right ventricle and pulmonary

artery. Right ventricular pressure tracing shows a single large rise and fall, beginning just after onset of

QRS complex. Pulmonary artery tracing usually shows a dicrotic notch at end of T wave. Diastolic pressure is higher than that in right ventricle. Pulmonary capillary wedge tracing should resemble atrial tracing, inasmuch as it reflects left atrial pressure transmitted to the catheter tip when anterograde pulmonary

arterial flow is occluded. Note: The marked negative deflection in the right atrial tracing would be more

typically seen in infants who are receiving mechanical ventilation and, thus, have a positive airway pressure that exceeds ventricular filling pressures during each inspiration. In a spontaneously breathing

neonate, positive airway pressure occurs only during expiration and never exceeds ventricular filling pressures. There are extremely small changes in cardiac pressures (i.e., on inspiration: right atrial [RA] mean

pressure ↑, 1 mm Hg; left atrial [LA] mean pressure ↓ 1 mm Hg; on expiration: RA pressure ↓ 1 mm Hg;

LA pressure ↑ 1 mm Hg) during the respiratory cycle as a result of changes in venous filling or preload.

Right and left atrial pressures remain approximately equal in both inspiration and expiration (36).