Cardiovascular effects of low dose calcium chloride infusions during halothane anaesthesia in dorsally recumbent ventilated ponies.

The research studies the impact of administering low doses of calcium chloride on cardiovascular depression and blood calcium balance in ponies during halothane anaesthesia. The results show that the administration leads to increased blood pressure and decreased heart rate, possibly due to increased vagal activity, without influencing other cardiac parameters.

Study Design and Participants

• The study was conducted on ventilated ponies laying in dorsal recumbency, under halothane anaesthesia.
• After the initial anaesthetic stabilization period of 30 minutes, the ponies exhibited a significant decrease in all cardiac parameters and mean arterial blood pressure, indicating pronounced cardiopulmonary depression.
• A marked drop was also observed in the total calcium plasma concentration, whereas the fraction of ionized and complexed calcium remained constant.

Calcium Chloride Infusion and Effects

• Calcium chloride was administered at different infusion rates (0.1, 0.2, and 0.3 mg/kg/min), inducing an increase in mean systemic blood pressure in a dose-dependent manner.
• This increase was attributed to an observed rise in total peripheral resistance due to vasoconstriction caused by the exogenous calcium.
• Simultaneously, a dose-dependent decrease in heart rate was noted, which the researchers suggest may have been due to increased vagal activity stimulated by the calcium infusions.

Other Observations

• The stroke volume of the heart also exhibited a dose-dependent increase but cardiac output, arterial blood gases, or packed cell volume remained unaffected by the exogenous calcium infusions.
• While notable increases were documented in mean pulmonary artery pressure and total pulmonary resistance, these were deemed time-related responses, likely not directly caused by the calcium infusions.

Additional Inferences

• While the study did not measure LV dP/dt max (a parameter used to assess heart contractility), the researchers suggest that minor positive inotropic effects might still be possible. This is because the observed increase in stroke volume could indicate an enhancement in ventricular contractility function.
• The total and ionized complexed calcium in plasma increased during infusions, however, their respective proportions remained consistent.