Severe preeclampsia is another comorbid condition in which markedly decreased blood pressure can be predicted when neuraxial analgesia is used. Wallace and associates (1995) randomly assigned 80 women with severe preeclampsia undergoing cesarean delivery at Parkland Hospital to receive general anesthesia or either epidural or combined spinal-epidural analgesia. Maternal and neonatal outcomes did not difer. Still, 30 percent of women given epidural analgesia and 22 percent of those given spinal-epidural blockade developed hypotension. he average reduction in mean arterial pressure ranges between 15 and 25 percent.
Relief of labor and childbirth pain, including cesarean delivery, can be accomplished by injection of a local anesthetic agent into the epidural or peridural space 25-3). his potential space contains areolar tissue, fat, lymphatics, and the internal vertebral venous plexus. This plexus becomes engorged during pregnancy such that the volume of the epidural space is appreciably reduced. Entry for obstetrical analgesia is usually through a lumbar intervertebral space. Although only
Spinal needle punctures the dura mater for injection 1 I:
FIGURE 25-3 Neuraxial analgesia: A. Combined spinal-epidural analgesia. B. Epidural analgesia.
one injection may be elected, usually an indwelling catheter is placed for subsequent agent boluses or infusion via a volumetric pump. he American College of Obstetricians and Gynecologists (2017 a) concludes that under appropriate physician supervision, labor and delivery nursing personnel who have been specifically trained in the management of epidural infusions should be able to adjust dosage and also discontinue infusions.
Complete analgesia for the pain of labor and vaginal delivery necessitates a block from the TIO to the S5 dermatomes (see Fig. 25-1). For cesarean delivery, a block extending from the T4 to the S1 derma tomes is desired. The efective spread of anesthetic depends on the catheter tip location; the dose, concentration, and volume of anesthetic agent used; and whether the mother is head-down, horizontal, or head-up (Setayesh, 2001). Individual variations in anatomy or presence of synechiae may preclude a completely satisfactory block.
Finally, the catheter tip may migrate from its original location during labor.
One example of the sequential steps and techniques for performance of epidural analgesia is detailed in Table 25-7. Before injection of the local anesthetic therapeutic dose, a test dose is given. The woman is observed for features of toxicity from intravascular injection and for signs of high or total blockade from subdural or subarachnoid injection. If these are absent, only then is a full dose given. Analgesia is maintained by intermittent boluses of similar volume or by small volumes delivered continuously by infusion pump (Halpern, 2009). Current pumps used for epidural analgesia ofer a programmed intermittent epidural bolus (PIEB) mode, which reduces the required concentration of local anesthetics, the degree of lower extremity motor blockade, and rates of operative vaginal delivery (Capogna, 2011). he addition of small doses of a short-acting narcotic-fentanyl or sufentanil-has been shown to improve analgesic eicacy while avoiding motor blockade (Chestnut,
TABLE 25-7. Technique for Labor Epidural Analgesia
Informed consent is obtained, and the obstetrician consulted Monitoring includes the following:
Blood pressure every 1 to 2 minutes for 15 minutes ater giving a bolus of local anesthetic Continuous matenal heart rate monitoring during analgesia induction
Hydration with 500 to 1000 mL of lactated solution The woman assumes a lateral decubitus or sitting position