Spinal anesthesia heart rate

In 34 women undergoing cesarean section at full term under spinal anesthesia, heart rate and cardiac output increased significantly within 2 minutes of the rapid administration of either 5 or 10 units of oxytocin, with an associated 10 mmHg fall in mean arterial pressure in those who received 10 units (6). There were significant ST segment changes in 11 of 26 women undergoing cesarean section, with raised concentrations of troponin I in two however, the relationship to oxytocin administration was not clear in this report (7). 

Mephentermine (wyamine sulfate) acts both directly and indirectly. After an intramuscular injection, the onset of action is prompt (within 5—15 minutes), and ejfects may last for several hours. Since the drug releases NE, cardiac contraction is enhanced, and cardiac output and systolic and diastolic pressures usually are increased. The change in heart rate is variable, depending on the degree of vagal tone. Adverse ejfects are related to CNS stimulation, excessive rises in blood pressure, and arrhythmias. Mephentermine is used to prevent hypotension, which frequently accompanies spinal anesthesia. 

In 90 women who underwent cesarean deliveries under spinal anesthesia, phenylephrine, phenylephrine + ephedrine, and ephedrine were used to maintain the blood pressure near baseline by adjusting the infusion rates [40 f. Fetal heart rates increased significantly after infusion of phenylephrine - -ephedrine and ephedrine alone but did not change after phenylephrine alone. After ephedrine, umbilical arterial and venous pH and base excess were lower than after phenylephrine alone and phenylephrine + ephedrine. Umbilical arterial PCO2 and plasma concentrations of lactate and glucose after ephedrine were greater than after phenylephrine. The authors concluded that phenylephrine may be better than ephedrine for treating the hypotension of spinal anesthesia for cesarean delivery. 

In a prospective study in 32 elderly patients, ASA grades 1-3, who received spinal anesthesia with bupivacaine 10-17.5 mg, baseline blood pressure variabDity and near-infrared spectroscopy reduction predicted hypotension with high sensitivity (0.73 and 0.90 respectively) and specificity (0.78 and 0.64, respectively) [32. However, heart rate, systemic vascular resistance index, baroreceptor sensitivity, and heart rate variability were of limited predictive value. 

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