TYK25
All of the following are true concerning neonatal physiology EXCEPT:
A. Tidal volume is about the same in neonates as in children and adults on a volume per kilogram basis
B. Increases in afterload are poorly tolerated by the neonatal myocardium
C. The influence of the sympathetic nervous system on the heart is more mature than the influence of the parasympathetic system
D. Myocardial function is different in neonates because the cardiac myocytes have less organized contractile elements than in children and adults.
Answer
The answer is C. The TIDAL volume of the neonate is about the same as children and adults (when a ml/kg basis is used). Neonates are particularly sensitive to increases in afterload. This is one reason why phenylephrine or norepinephrine is usually poorly tolerated in this age group. Dramatic increases in afterload may cause decreased cardiac function and output. The parasympathetic system dominates in the neonatal period. Neonatal myocardium is poorly organized (when compared to the older counterparts). This decreased organization is particularly important in the T-tubule system and the subsequent calcium availability.
Notes
Anaesthesia UK:Pharmacology of Opioids II