A thorough understanding of the nature of the parturient’s pain is the first aspect in providing optimal obstetric anesthetic care. Once the biology and pathophysiology of this special acute pain is discussed, the benefits of analgesia for this pain will appropriately follow. Pharmacology of local anesthetics and related drugs will be reviewed, with special emphasis on complications associated with their administration. A variety of techniques including epidural, subarachnoid, and other regional and analgesia techniques will be discussed with benefits and complications reviewed. General anesthesia (GA) for cesarean section delivery will be outlined. A variety of special consideration patients will be addressed, including: (1) the preeclamptic patient, (2) preterm birth patient on tocolytics, (3) human immunodeficiency virus (HIV)–positive mothers, (4) coagulopathies, (5) cardiac disease, and (6) pulmonary disease. Highlights from the updated report by the American Society of Anesthesiologists task force on Obstetric Anesthesia and Society for Obstetric Anesthesia Perinatology will be reviewed.
NATURE OF THE PATIENT’S PAIN
The current concept of pain focuses on the peripheral nervous system relaying a stimulus to the central nervous system (CNS) for interpretive evaluation—the somatosensory system (Fig. 20-1). The peripheral system consists of afferent neurons that are embedded in body tissues awaiting nociceptive (painful) stimuli. These afferent neurons are termed Ad (A-delta) and C-fibers. These fibers transverse into the spinal segments and synapse at the dorsal spinal ganglion. Here, substance-P is released causing the painful effect to be initiated. From each spinal segment stimulated, these messages ascend through one of two pathways to the thalamus for further modulation: the lateral spinothalamic tract or the medial lemniscus tract. Once at the thalamus, adjustment and regulation from inherent emotional and psychological factors occur. The data support the emphasis on the importance of perceptual factors that influence a patient’s total pain experience (Table 20-1). The psychodynamics of prior experience, motivation, anxiety, anticipation of pain, attention, personality, and ethnic and cultural factors all influence the modulation of substance-P release, affecting the pain experience. From the thalamus, this information is synthesized in the sensory cortex for relay to the many effector sites that contribute to the pain response. Once pain has been perceived, there is an initiation of the pain response that has neuroendocrine, behavioral, and psychological implications.
Schematic of the somatosensory system.
TABLE 20-1Pain Perception ||Download (.pdf) TABLE 20-1 Pain Perception
|Psychological ||Anxiety, fear, emotional arousal |
|Behavioral ||Verbalization, motor activity |
|Neuroendocrine ||Hyperventilation—maternal respiratory |
| ||Endocrine (stress) response |
| || ↑ adrenocorticotropic hormone (ACTH), ↑ cortisol |
| || ↑ epinephrine, norepinephrine |
| || ↑ lipolytic metabolism—metabolic acidosis |
| ||Cardiovascular Response |
| || ↑ systemic vascular resistance |
| || ↑ cardiac output |
| || ↑ blood pressure |
| || ↑ oxygen consumption |
| || ↑ left ventricular stroke work |
| ||Gastrointestinal function |
| || ↓ gastric motility |
| || ↑ risk for gastroesophageal reflux/aspiration |