In any patient, there is an interaction between respiratory parameters set by the ventilator and the interaction with cardiovascular function. In neonates, this response is more dramatic due to their small size.
The following are several ways in which Respiratory parameters affect the cardiovascular system:
- Mean Airway Pressure: As MAP is increased, there is a decrease in preload (as blood is trapped in the pulmonary vasculature) and decrease in afterload too.
- Inspiratory time: In general, as you increase this you also decrease preload.
- Mode of ventilation
- Pressure mode will give you higher MAP (bp) for lower PIP
- Volume mode will lead to lower MAP (bp) for higher PIP
- Oxygenation – neonates have reduced free radical system, so key to reduce amount of iO2 if possible. O2>90% permissable. However, higher oxygenation will lead to increased… PAP?
- CO2: Permissive hypercapnia acceptable(paCO2<50), unless there is pulmonary HTN.
Inspiratory time compared to expiration:
- 1st beat: augmented filling of LV
- 2nd beat: decreased filling slightly below expiration level
- 3rd beat: significantly decreased preload, resulting decreased CO
PVR also is altered by CO2 of course, but the response in neonates is more dependent on pH. As pH goes from 7.4 to 8.0, alkalinization, the PVR subsequently decreases, while the PVR only gradually increases from pCO2 increases.
PEEP titration is another consideration. PEEP improves oxygenation, but also alters CO. As you increase PEEP, you trap more blood in the pulmonary vasculature, therefore decreasing preload and CO.
Finally, Hemoglobin also