In the last decade, technology to monitor stroke volume and cardiac
output without a PAC has been implemented clinically. Utilizing a peripheral
arterial line and a central venous line minimally invasive hemodynamic
monitoring (Edwards Life Sciences Vigileo and LiDCO systems cardiac monitor)
is possible. These monitors operate on the assumption that end systolic volume
is fixed and that variability in stroke volume is due to variability in end diastolic
volume. Using low-dose lithium ion infusion, the LiDCO monitor continuously
measures cardiac output. These monitors are useful in measuring stroke
volume, cardiac output, SVR, and indirectly calculating volume status. Studies
in children at this point are lacking.
G. Further Notes on Umbilical Catheters
Critically ill neonates often require invasive monitoring. While peripheral
arterial access or central venous access is possible, it can be challenging in
small neonates. Umbilical vessel cannulation is common in these patients but,
again, is not without risk. Umbilical artery catheter (UAC) placement is
associated with mesenteric and renal arterial thrombosis. To decrease this risk,
the catheter tip should always be in the chest between T6 and T10. Patients
should be kept NPO while a UAC is in place. Umbilical venous catheterization is
associated with portal vein thrombosis and hepatic hematoma formation. The tip
of the catheter should be in the suprahepatic IVC. If the catheter falls back into
the hepatic veins it should be removed. Catheters are never advanced after the
initial placement due to the high risk of line infection. Most neonatologists advise