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This chapter presents evidence supporting the use of ultrasound to take the epidural catheterization and spinal injections away from being blind techniques, therefore aiming to help reduce the incidence of the potentially serious complications resulting from Central neuraxial blockade (CNB). CNB remains the gold standard technique of providing both analgesia and anesthesia in the obstetric population, a fact which is unlikely to change in the near future. Creating an ultrasound image is done in three steps: producing a sound wave, receiving the echoes and interpreting those echoes. Most diagnostic ultrasound transducers use artificial polycrystalline ferroelectric materials such as lead zirconate titanate. There is very little published data regarding the use of ultrasound for real-time visualization of epidural puncture for neuraxial blockade. Overall, the use of ultrasound in all aspects of regional anesthesia allows continual development and improvement of current techniques.
Neuraxial analgesia techniques are commonly performed to relieve pain during labor and to provide analgesia during cesarean section. When combined spinal-epidural (CSE) is used for labor analgesia it provides a faster onset with minimal motor block. This chapter describes the history and use of CSE techniques in laboring patients and for cesarean section. It discusses the advantages and disadvantages of these techniques compared to traditional spinal and epidural techniques. The chapter outlines the use of continuous spinal anesthesia (CSA) in obstetric patients. The catheter appears to be at least as effective as with the epidural technique; however, CSE has a higher rate of complications (e.g. nerve damage, infection) and side effects (e.g. pruritus, fetal heart rate (FHR) abnormalities) compared to epidural analgesia. The theoretical advantages of hemodynamic stability and prolonged block can be easily achieved with other techniques such as CSE at much lower complication rates.
Neuraxial opioids are an essential component of the pharmacologic options available for use in present-day obstetrical anesthesia practice. By producing an analgesic action in the absence of associated motor block or reduction in sympathetic tone, neuraxial opiates are an ideal component of the list of analgesic medications available for use by the obstetrical anesthesiologist. Morphine is a hydrophilic opioid, among the first to be used for postsurgical analgesia when administered by epidural or intrathecal route. The lipid solubility of hydromorphone is between that of lipid soluble fentanyl and hydrophilic morphine. Fentanyl is a highly lipid soluble opioid with a resulting rapid onset and short duration of action. The beneficial effects of neuraxial opioid administration are associated with potential complications or side effects, both in the mother and in the fetus. Hydrophilic drugs are primarily used as part of a multimodal analgesia plan for postoperative pain management following cesarean section.
Remifentanil's safety profile in neonates combined with rapid onset and offset means that it offers potential not only as a labor analgesic, when administered as patient-controlled analgesia (PCA), but also as an adjunct to general anesthesia, particularly in high-risk obstetric patients. An ideal intravenous opiate should have an onset and offset that can match the time course of uterine contractions, while preserving uterine contractility and a reassuring cardiotocograph (CTG). The analgesia experienced should be considered worthwhile and there should be minimal maternal and neonatal effects, allowing administration up to and during delivery. Remifentanil can offer sedation and analgesia for the anxious patient without the risk of persistent opioid effects. Systemic opioids are the mainstay of managing discomfort during epidural anesthesia for cesarean section. High doses of remifentanil with general anesthesia have unpredictable neonatal effects, making attendance by a physician trained in neonatal resuscitation mandatory.
Hypotension following spinal anesthesia in obstetric patients is commonplace. Spinal anesthesia induces a sympathectomy, leading to vasodilation, increased venous capacitance, and decreased venous return. High levels of sympathetic blockade can decrease maternal cardiac output although with lesser height and degrees of sympathetic blockade a compensatory increase in cardiac output may be seen secondary to reductions in cardiac afterload. Risk factors associated with spinal-induced hypotension include: increasing age, pre-existing hypertension, higher infant birth weight and obesity. Many studies have been carried out to determine the role of ephedrine and phenylephrine during spinal anesthesia for cesarean section. Chronic hypotension, especially if accompanied by decreased cardiac output, may reduce placental perfusion and impair fetal oxygenation. Drawbacks to ephedrine include variable efficacy at prophylaxis of hypotension secondary to spinal anesthesia in low doses or in doses normally used in the clinical setting.