THE ROLE OF NEURAXIAL ANESTHESIA IN ANESTHETIC PRACTICE
Almost all operations at or below the neck have been performed under neuraxial anesthesia. Indeed, car-diac and thoracic surgeries have been performed in this manner. However, because intrathoracic, upper abdominal, and laparoscopic operations can signifi-cantly impair ventilation, general anesthesia with endotracheal intubation is usually necessary. So why perform a regional anesthetic for these cases, or for any other?
Some studies suggest that postoperative morbidity—and possibly mortality—may be reduced when neuraxial blockade is used either alone or in combination with general anesthesia. Neuraxial blocks may reduce the incidence of venous thrombosis and pulmonary embolism, cardiac com-plications in high-risk patients, bleeding and trans-fusion requirements, vascular graft occlusion, and pneumonia and respiratory depression following upper abdominal or thoracic surgery in patients with chronic lung disease. Neuraxial blocks may also allow earlier return of gastrointestinal function following surgery. Proposed mechanisms (in addi-tion to avoidance of larger doses of anesthetics and opioids) include amelioration of the hypercoagu-lable state associated with surgery, sympathectomy-mediated increases in tissue blood flow, improved oxygenation from decreased splinting, enhanced peristalsis, and suppression of the neuroendocrine stress response to surgery. In patients with coronary artery disease, a decreased stress response may result in less perioperative ischemia and reduced morbid-ity and mortality. Reduction of parenteral opioid requirements may decrease the incidence of atelecta-sis, hypoventilation, and aspiration pneumonia and reduce the duration of ileus. Postoperative epidural analgesia may also significantly reduce both the time until extubation and the need for mechanical ven-tilation after major abdominal or thoracic surgery. Regional anesthesia may also preserve immunity perioperatively, reducing the risk of cancer spread according to some studies.
Anesthesiologists are all too familiar with situa-tions in which a consultant “clears” a sick elderly patient with significant cardiac disease for surgery “under spinal anesthesia.” But, is a spinal anes-thetic really safer than general anesthesia in such a patient? A spinal anesthetic with no intravenous sedation may reduce the likelihood of postopera-tive delirium or cognitive dysfunction, which is sometimes seen in the elderly. Unfortunately, some, if not most, patients require some sedation during the course of the procedure, either for comfort or to facilitate cooperation. Is spinal anesthesia always safer in a patient with severe coronary artery dis-ease or a decreased ejection fraction? Ideally, an anesthetic technique in such a patient should not produce either hypotension (which decreases myo-cardial perfusion pressure) or hypertension and tachycardia (which increase myocardial oxygen consumption), and, also, should not require large fluid infusions (which can precipitate congestive heart failure). Spinal anesthesia can produce both hypotension and bradycardia, which may be rapid in onset and are sometimes profound. Moreover, treatment that includes rapid administration of intravenous fluid can cause fluid overload (when the vasodilatation wears off ). The slower onset of hemodynamic responses to epidural anesthesia may give the anesthesiologist more time to correct these changes. General anesthesia, on the other hand, also poses potential problems for patients with cardiac compromise. Most general anesthetics are cardiac depressants, and many cause vasodila-tation. Deep anesthesia can readily cause hypoten-sion, whereas light anesthesia relative to the level of stimulation causes hypertension and tachycar-dia. Insertion of a laryngeal mask airway causes less of a stress response than does endotracheal intubation, but deeper levels of general anesthesia are still required to blunt the response to surgical stimulation.
Th us, arguments can be made for and against neuraxial and regional anesthesia in this setting. Perhaps then it is not the technique, per se, that is critical as much as the careful execution with appro-priate monitoring and management of whatever anesthetic technique is planned.
Neuraxial anesthesia has had a great impact in obstetrics. Currently, epidural anesthesia is widely used for analgesia in women in labor and during vaginal delivery. Cesarean section is most com-monly performed under epidural or spinal anes-thesia. Both blocks allow a mother to remain awake and experience the birth of her child. Large popula-tion studies in Great Britain and the United States have shown that regional anesthesia for caesarean section is associated with less maternal morbidity and mortality than is general anesthesia. This may be largely due to a reduction in the incidence of pulmonary aspiration and failed intubation when neuraxial anesthesia is employed. Fortunately, the increased availability of video laryngoscopes may also reduce the incidence of adverse outcomes related to airway difficulties associated with general anesthesia for cesarean section.
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