Contradictory effects of dopamine at 32°C in pigs anesthetized with ketamine

Abstract

Dopamine increased CO and MAP in normothermia but not at 32 degrees C, where there was even a significant reduction of MAP in this porcine model.

Effects of dopamine on porcine myocardial action potentials and contractions at 37 °C and 32 °C

“…The physiologic effects of pharmacological vasodilatation might also be more pronounced in hypothermia, since the possibility for a compensatory tachycardia is reduced. We think these aspects might explain the earlier reported paradoxic decrease in cardiac output after dopamine at 32 °C (2).…”

“…A study in sheep (4) showed a decrease in dP/dt, MAP and CO with low doses of dopamine in hypothermia, whereas higher doses in hypothermia and all doses in normothermia increased these parameters. In a study using small pigs, we also found that administration of dopamine at 32 °C caused a substantial decrease in blood pressure and no increase in cardiac output, although the heart rate increased (2). However, it seems likely that a relatively high baseline heart rate after cooling in this study may have led to a tachycardia during dopamine infusion that influenced ventricular filling in hypothermia (16).…”

“…Furthermore, it is important to bear in mind that cooling increases the duration of systole and also lowers the myocardial relaxation rate, thus reducing the time available for ventricular filling (16). Thus, a drug with positive chronotropic properties, such as dopamine, can possibly induce a tachycardia, which may interfere with ventricular filling in the hypothermic state (2, 16). The physiologic effects of pharmacological vasodilatation might also be more pronounced in hypothermia, since the possibility for a compensatory tachycardia is reduced.…”

“…P HARMACOLOGIC support of the cardiovascular system may be required in hypothermic patients (1), but knowledge about the effects of drugs with cardiovascular action in hypothermia is limited. Whereas some studies on pigs (2) and sheep (3, 4) have indicated a paradoxic decrease in cardiac output after dopamine in hypothermia, others have reported increases in cardiac output and to some extent also in arterial pressure in hypothermic dogs (5) and pigs (6, 7). Furthermore, a study in dogs showed that infusion of dopamine or noradrenaline led to a reduced incidence of ventricular fibrillation during cooling and to a dramatic lowering of the lethal hypothermic temperature from 19 °C to 12 °C (8).…”

Altered pharmacological effects of adrenergic agonists during hypothermia

“…Likewise, positive inotropic effects of dopamine were found in pigs core cooled to 30 °C [57]. However, in pigs surface cooled to 32 °C [62] and 25 °C [63] dopamine did not elevate CO. In the latter study, which was conducted in our lab [63], dopamine infusion at 25 °C gave a four-fold increase in plasma concentration compared to normothermia.…”