Comparison of the effects of caffeine and doxapram on respiratory and cardiovascular function in foals with induced respiratory acidosis.
OBJECTIVE
To determine and compare the effects of caffeine and doxapram on cardiorespiratory variables in foals during isoflurane-induced respiratory acidosis.


METHODS
6 clinically normal foals (1 to 3 days old).


METHODS
At intervals of > or = 24 hours, foals received each of 3 IV treatments while in a steady state of hypercapnia induced by isoflurane anesthesia (mean +/- SD, 1.4 +/- 0.3% endtidal isoflurane concentration). After assessment of baseline cardiorespiratory variables, a low dose of the treatment was administered and variables were reassessed; a high dose was then administered, and variables were again assessed. Sequential low- and high-dose treatments included doxapram (loading dose of 0.5 mg/kg, followed by a 20-minute infusion at 0.03 mg/kg/min and then 0.08 mg/kg/min), caffeine (5 mg/kg and 10 mg/kg), and saline (0.9% NaCl) solution (equivalent volumes).


RESULTS
Administration of doxapram at both infusion rates resulted in a significant increase in respiratory rate, minute ventilation, arterial blood pH, PaO(2), and arterial blood pressure. These variables were also significantly higher during doxapram administration than during caffeine or saline solution administration. There was a significant dose-dependent decrease in PaCO(2) and arterial bicarbonate concentration during doxapram treatment. In contrast, PaCO(2) increased from baseline values after administration of saline solution or caffeine. The PaCO(2) value was significantly lower during doxapram treatment than it was during caffeine or saline solution treatment.


CONCLUSIONS
Results indicated that doxapram restored ventilation in a dose-dependent manner in neonatal foals with isoflurane-induced hypercapnia. The effects of caffeine on respiratory function were indistinguishable from those of saline solution.
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0136, USA.
Steeve
S
Giguère
L Chris
LC
Sanchez
Andre
A
Shih
Nancy J
NJ
Szabo
Ariel Y
AY
Womble
Sheilah A
SA
Robertson
D000142:Acidosis, Respiratory / Q000139:chemically induced / Q000188:drug therapy / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000009:adverse effects; D000818:Animals; D002110:Caffeine / Q000627:therapeutic use*; D000697:Central Nervous System Stimulants / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D004315:Doxapram / Q000627:therapeutic use*; D006736:Horses; D007530:Isoflurane / Q000009:adverse effects
D018685:Anesthetics, Inhalation; D000697:Central Nervous System Stimulants; D002110:Caffeine; D004315:Doxapram; D007530:Isoflurane