Effect of mydriatics on blood pressure in premature infants

Systolic blood pressure (SBP) was measured by doppler methods at 5, 15, 30, 45, and 60 minutes in 52 premature infants after triple instillation of aqueous phenylephrine 2.5% and tropicamide 1.0%. Systolic blood pressures were insignificantly increased 3.9 +/- 2.0 mm Hg (mean +/- S.E.) at 15 minutes when compared with controls matched for initial blood pressure, birth weights and age at examination. Though a 964 gm, 28-week Caucasian male with retinopathy of prematurity had been uneventfully dilated, pupillary dilatation one week later with triple instillations of phenylephrine 2.5% and tropicamide 1.07% was accompanied by an acute increase in systolic blood pressure to 108 mm Hg at 15 minutes, which remained elevated for 150 minutes. A new lower dose, single instillation mydriatic became available whose final concentration was phenylephrine 2.5%, tropicamide 0.5% and cyclogyl 0.5%. A single drop was found to produce mydriasis equal to the triple instillation regime. The single administration produced no significant effect on systolic blood pressure in 30 low birth weight infants (birth weight less than 1750 gm) when compared with balanced salt solution (placebo) in a randomized, double--masked study. Mechanisms of acute hypertension after topical mydriasis are discussed.