Postoperative analgesia is the oldest direction of long-term epidural anesthesia. Indeed, if a catheter has already been inserted into the epidural space, through which maintenance doses of a local anesthetic have been introduced during the operation — why not to use this catheter for postoperative anesthesia? Moreover, epidural analgesia has the following advantages over standard systemic (intramuscular or intravenous) administration of opioids after surgery.
1. The absence of nausea and vomiting – side effects of opioids, which also have a sedative effect, is not always desirable. After surgeries outside the abdominal cavity, regional analgesia allows early oral nutrition.
2. Early restoration of function of the gastrointestinal tract, seriously oppressed by opioids.
3. Reliable protection from operational stress (but for this, analgesia must be continuous).
4. Prevention of deep vein thrombosis of the lower extremities and in general improvement of blood circulation in them (if sympathetic blockade covers these extremities).
But even where for many years all operations were performed under epidural anesthesia with a catheter, postoperative epidural analgesia was not used due to a number of shortcomings:
5. For narrow (low-segment) anesthesia, small maintenance doses of a local anesthetic are needed , the effect of which will be short.
For these reasons, the blockage zone should be narrow and as close as possible to the operated area (it depends on the placement of the tip of the epidural catheter): at the hip joint — in the lumbar, after the lower abdominal operations — at the level of T11-T12, after the top non-abdominal operations — at the level of T8-T9,after thoracic operations — also at the appropriate level. A local anesthetic should have an analgesic effect as long as possible, with a minimum of the motor block, so bupivacaine at low concentrations are optimal , either frequent and small repeated doses (4-6 ml 0.5 % every hour), or by infusion (0.125% —15 ml / hour or 0.1% —20 ml / hour) or, better still, ropivacaine (Naropin). If it is necessary to eliminate visceral pain, opioids and other adjuvants are also added to local anesthetics for epidural administration (see below).
Monitoring (at least every hour) breathing, hemodynamics, and blocked segments, and when infusing into the epidural space — also of the injected solution — makes epidural analgesia not such a simple task, even in conditions of an intensive care ward.
Anesthesia after injury. Epidural analgesia is most often used for multiple rib fractures on both sides (one or two broken ribs can be easier and safer to anesthetize the blockade of the intercostal nerves, and a larger number of rib fractures on the one hand — a paravertebral or subpleural blockade). The tip of the catheter should stand in the middle of the corresponding segments. The most popular local anesthetics are bupivacaine (a bolus of 4-6 ml 0.5%, and then an infusion of 0.125 % –
10 ml / hour, adjusting as needed) and ropivacaine.
Stimulation of peristalsis is an important advantage of epidural analgesia after operations on the abdominal organs. This effect of epidural administration of local anesthetics is sometimes also used in the treatment of dynamic intestinal obstruction, the sympathetic innervation of which is carried out by the T9 and TIOh T11segments .
Acute pancreatitis, especially after laparotomy, which confirmed the diagnosis, can be treated with epidural blockade of segments 77, T8 and T9, eliminating pancreatitis pain, improving breathing and splanchnic blood flow and even relaxing the sphincter of Oddi. Local anesthetics are used predominantly (and not opioids, the exception is buprenorphine), since a sympathetic blockade is needed first of all, and many opioids, especially morphine, cause Ophane sphincter spasm.
Stone in the ureter, if conservative treatment is chosen, and pain is not eliminated even by opioids, it is possible to treat the lumbar truncus sympathicus at the level of L1 and L2 or epidural block (better long-term, with a catheter) at the same level. Local anesthetics (not opioids) are also used, because they are needed sympathetic blockade.
The expansion of the vessels, due to the blocking of epidurally administered local anesthetics of sympathetic fibers, is also a positive effect. The expansion of the splanchnic vessels improves blood circulation in the intestine and promotes the healing of the anastomoses. During postoperative epidural analgesia of the lower extremities, the blood flow in them also increases, although not in the muscles, but in the skin. However, it improves the healing of the skin wound, and also enhances the movement of blood in the arteries and in the veins, reducing the risk of thrombosis.
OPIOIDS
Since the early 1980s, after the discovery of opioid receptors in the back horns of the spinal cord, narcotic analgesics (opioids) have become widely used for epidural anesthesia.
MECHANISM OF ACTION
A comparison of the mechanisms of action of epidurally administered opioids and local anesthetics is given in Table. 24. Local anesthetics block the conduction of pulses (including pain) along the fibers. Opioids modulate the response of nerve cells in the posterior horns of the spinal cord, reducing (unfortunately, not by 100%) their excitation under the influence of pain signals.