Noninvasive breathing analysis: repetitive chloral hydrate in neonatal guinea pigs

A noninvasive method was used to record neonatal breathing, heart rate (HR), and the electroencephalogram (EEG) in guinea pig pups. Neonates were randomly assigned at birth to chloral hydrate (CH) or placebo (PLA) treatment. Treatments were administered 30 min before each study on days 1, 3, 5, 7, 14, and 21 after birth. Animals were studied while they breathed room air followed by air with 5% CO2 and 30% O2. CH decreased breathing frequency (f) and inspiratory minute volume (VI), but not tidal volume (VT) during the first week (P less than 0.05), and reduced the rate of growth throughout the study (P less than 0.01), whereas breathing of CO2 increased f, VT, VI, HR, and the relative power in the delta frequency band of the EEG. The percent change in VI induced by CO2, however, was not affected by drug treatment. There was a significant day of life effect on all breathing parameters and HR. CH has cumulative effects on breathing and growth that should be considered when it is used as a sedative for repeated neonatal studies in guinea pigs.