Hemodynamic and respiratory effects of segmental subarachnoid analgesia in adult Holstein cows.

Hemodynamic measurements, arterial and mixed venous blood gas tensions, and pH were determined in 13 adult, nonpregnant Holstein cows (511.3 +/- 77.3 kg) after subarachnoid injection of a 5% procaine hydrochloride solution (av dosage level of 0.162 +/- 0.026 mg/kg) at the thoracolumbar (T13-L1) intervertebral space. Segmental analgesia occurred within 8 to 12 minutes after completing the procaine HCl injection and extended between spinal cord segments T7 and L3 on both sides of the spinal column. The average duration of analgesia, as determined by the cows' responses to superficial and deep muscular pinpricks, was 35.8 +/- 8.5 minutes (25 to 60 minutes, min-max). Subarachnoid injection of procaine HCl caused a significant (P less than 0.05) increase in heart rate and significant (P less than 0.05) decreases in pulse pressure and rectal temperature. Cardiac output, stroke volume, left ventricular stroke work, left ventricular minute work, total peripheral resistance, arterial blood pressure, arterial and mixed venous blood gas tensions, pH, oxygen transport, oxygen uptake, PCV, and total solids did not change significantly (P greater than 0.05) from base-line values. Similarly, no significant changes (P greater than 0.05) were observed in a group of 5 control cows after subarachnoid injection of sodium chloride solution (1.5 ml, 0.9%) at the T13-L1 intervertebral space. Segmental subarachnoid analgesia caused minimal circulatory disturbance and was well tolerated by adult, conscious, unsedated cows.