Infants with right to left intracardiac shunts may be at increased risk for which of the following?
A. Local anesthetic toxicity
B. Pulmonary overcirculation resulting in pulmonary hypertension
C. Hyperoxia
D. Slowed inhalational induction with halothane
The answer is A. Ok, so who knew this one? But I promise you its a good one. Right to left shunts will cause HYPOXIA and relative pulmonary UNDERCIRCULATION. Also, a right to left shunt will only cause a (clinical significant) slowed induction with the insoluble agents (desflurane, sevoflurane), not with the soluble agents (isoflurane, halothane).
Local anesthetics (especially amides) are influenced by the lungs. Normally, the lungs will alter the pharmacokinetics of LA by slowing the rate of rise and influence the peak plasma concentration. The lung extraction ratio for amide local anesthetic agents is high (approximately 0.8), resulting in a difference between mixed venous and arterial concentrations. Infants with right- to-left cardiac shunts may therefore be at greater risk of toxicity. Tricky, huh?