Cardiac Effects of Anesthetic Agents That May Be Used in Labor and Delivery

Medications for Neuraxial Anesthesia

Local anesthetics are the predominate agents used for neuraxial analgesia and anesthesia in parturients. The most common agents in use are lidocaine, bupivacaine, ropivacaine, and 3-chloroprocaine. These agents exert their effects by binding to sodium channels, decreasing the influx of sodium and preventing action potential initiation. This leads to a decreased rate of depolarization of excitable membranes. Local anesthetics exhibit a “state-dependent blockade,” preferentially binding to the activated form of sodium channels. As such, neurons with high-frequency firing rates, such as cardiac myocytes, will be more sensitive to blockade by local anesthetics. This property contributes to the use of these medications in tachyarrhythmias as class I antiarrhythmics and explains the bradycardia occasionally encountered after administration. Of note, bupivacaine is known to bind more strongly to and dissociate more slowly from cardiac sodium channels, making cardiac resuscitation more difficult in bupivacaine-induced local anesthetic toxicity.

Other than their antiarrhythmic properties, the hemodynamic effects of local anesthetics are indirect and result from the blockade of sympathetic output to blood vessels. The magnitude of the effect varies with epidural versus intrathecal administration, with more significant hemodynamic effects occurring with the latter because of its more rapid onset. Neuraxial local anesthetics block sensory, motor, and sympathetic nerves. The sympathectomy induced by these agents leads to a significant decrease in systemic vascular resistance, resulting in a decrease in both preload and afterload. A subsequent decrease in cardiac output is seen from reduced preload. The end effects of these changes in parturients with cardiac disease will depend on the patient’s specific cardiac physiology; however, they will be particularly problematic for patients with lesions that are preload dependent and those relying on optimal coronary perfusion.

During epidural placement, a test dose with lidocaine and epinephrine is given to assess for an inadvertent intrathecal or intravascular catheter placement. If the catheter is intravascular, the epinephrine commonly causes hypertension and tachycardia, which can have detrimental effects in patients with coronary artery disease or those prone to tachyarrhythmias.

Medications for General Anesthesia