Melissa Aromin Anesthesia Clerkship. Adult Circulation Fetal Circulation -RA LA -RA PA Aorta

Melissa Aromin

Anesthesia Clerkship

Neonatal vs Adult Cardiac Physiology

AdultCirculation

Fetal Circulation

- RA LA- RA PA Aorta

First breath decrease pulm vascular resistance increase pulm blood flow functional FO closure

Increase arterial oxygen functional DA closure

Anatomic Closure• FO: months• DA: 2-3 weeks

Reversal of closures:- hypoxia, hypercarbia,

acidosis- Increase pulm

vascular resistance open DA

- Increase right heart pressure open FO

Fetal Hemoglobin- Fetal Adult hemoglobin

at 2-3 months physiological anemia

- Fetal hemoglobin left shift decrease oxygen delivery to tissues

- Increase oxygen delivery by:- Higher hemoglobin

concentration- Increase CO

Cardiac Output

Neonatal myocardium: immature contractile elements and less compliant

Affect on Cardiac Output- CO = SV x HR- Fluids little change in SV- Must increase HR to increase CO

Neonatal sympathetic NS and baroreceptor reflexes: immature •Hypovolemia with decreased vasoconstriction -> hypovolemia without tachycardia• Reduced concentration of neurotransmitter, but mature adrenergic receptors respond better to direct-acting inotropes

10% reduction in blood volume will cause a 15-30% decrease in MAP

Neonate Adult

Cardiac Output HR dependent SV and HR dependent

Contractility Decreased Normal

Starling Response Limited Normal

Compliance Decreased Normal

Afterload Compensation

Limited Effective

Physiological differences between neonatal and adult myocardium

ReferencesSwamy et al. Applied aspects of anatomy and physiology of relevance to pediatric anesthesia. Indian J. Anaesth. 2004;48(5):333-339.

Brasoveanu E. Neonatal physiology and anesthesia. www.bu.edu/.../05sprgmedanesthesiology/.../Neonatal%20Physiology/Neonatal%20Physiology%20and%20Anesthesia.doc

Burd et al. Neonatal and childhood perioperative considerations. Surg Clin North Am. 2006;86(2):227-247.