Respiratory and cardiovascular effects of doxapram and theophylline for the treatment of asphyxia in neonatal calves

Respiratory stimulants are widely used in asphyxic neonatal calves despite a lack of data about their effectiveness and indications of possible side effects. The effect of doxapram and theophylline on respiratory, cardiovascular, and acid-base variables was investigated in 10 healthy neonatal calves (Bos Taurus). A venous, a peripheral arterial, and a pulmonary arterial catheter were placed, and central venous, pulmonary, and systemic blood pressures and cardiac output were measured using thermodilution technique. Doxapram, but not theophylline, led to an immediate increase in respiratory rate (P ≤ 0.01). The arterial pCO2 decreased to 27.1 ± 4.7 mm Hg within 30 sec after doxapram administration and to 46.3 ± 5.8 mm Hg within 120 min after theophylline administration (P < 0.0001). The systolic pulmonary pressure increased from 70 ± 8 mm Hg (mean ± SD) to 93 ± 19 mm Hg within 30 sec after doxapram, but decreased after theophylline. The pulmonary vascular resistance also increased after doxapram and decreased after theophylline (P < 0.01). Doxapram had a more pronounced and faster effect on respiratory rate and elimination of CO2 than theophylline. Doxapram, but not theophylline, is indicated for treatment of postnatal asphyxia in calves, but there are potential cardiovascular side effects.