epidural and high block

High block

Unexpectedly high block is a rare but potentially life threatening complication. In rare cases it can lead to significant drop in blood pressure and respiratory arrest. As the result of the use of low concentrations of local anesthetics for labor epidural and introduction of ropivacaine in recent years this complication is rare.

High block is a potentially life-threatening complication. In clinical practice however it seldom causes serious problems because of low concentration of local anesthetics used for epidurals and the introduction of Ropivacaine, sensory selective local anesthetic. High block is discussed in the chapter on fatal complications of epidural and will be addressed here briefly.

To reiterate, in order to produce adequate analgesia in labor the nerves from lower thoracic segments and lower need to be blocked. The epidural catheter is inserted at the lumbar level, and after the administration on the average of eight to ten milliliters of local anesthetic mixture sufficient pain relief is usually achieved. Out of the total amount of drugs given into the epidural space less than third diffuses through the Dura into the cerebro-spinal fluid and acts on the neural structures there. The rest is absorbed and taken away by the blood flow. If the whole dose however is administered straight into the subarachnoid space, the resulting block will extend too high up and may cause problems.

The most dangerous result of high block is the paralysis of the phrenic nerve that controls the most important respiratory muscle, the diaphragm. Phrenic nerve originates in the cervical segments, three to five (the mnemonic medical students use to remember: “C three, four, five keeps the diaphragm alive”). If local anesthetic spreads high enough to reach cervical segments and its concentration is sufficient to block this nerve the patient will not be able to take a breath. Another problem with high block is the profound drop in blood pressure, due to blocking sympathetic nerve fibers that govern vascular tone.

There are several ways for the high block to take place. Sometimes epidural catheter is inadvertently placed into the subarachnoid space at the very beginning. To avoid this error so test dose – two to three milliliters of local anesthetic – is administered into the epidural catheter first. If the catheter is in the correct place after five minutes such small amount will not produce any effects, and full dose of local anesthetic mixture is administered. If combined spinal-epidural block is performed the test dose becomes meaningless, and in that case the main epidural dose is administered slowly and the patient is closely observed for the signs and symptoms of high block.

Another cause of high block is the migration of the properly placed epidural catheter into the epidural space. The catheter is made of plastic, the substance foreign to human tissues, and it can in certain conditions damage the dura and move into the subarachnoid space. To avoid this patients with epidurals have the level of the block checked at regular intervals, usually every hour.

Another, relatively unique situation that may lead to high block is when a patients with working labor epidural has to undergo urgent cesarean section. There are three options of providing anesthesia for surgery in this situation: giving general anesthetic, using the same epidural catheter or administering a spinal. Labor epidurals topped up for surgery are sometimes inadequate for surgery, and some anesthetists prefer removing existing epidural catheter and administering a spinal anesthetic. In rare cases the combination of working epidural and spinal results in excessive dose of local anesthetic mixture and high block. The presence of labor epidural is considered relative contra-indication to spinal anesthetic by some authors. One way to prevent high block in this situation is to stop epidural infusion as soon as the decision to proceed with the cesarean is made. This way the concentration of local anesthetic around spinal cord falls, and additional administration of drug does not lead to spread high enough to create problems. Ultimately the choice of anesthesia for cesarean section in each particular case depends on clinical circumstances.

Modern anesthetic techniques have made labor epidural much safer and the incidence of dangerously high block is low. Even if high block occurs its consequences are not as dire as a decade ago, thanks to the introduction into clinical practice sensory selective local anesthetic ropivacaine, which is currently most commonly used in epidurals. Ropivacaine affects motor nerve fibers to lesser degree than other local anesthetics, and even if the block is high phrenic nerve is not affected by this drug. It is also used in a very low concentration, thus further reducing the chances of serious respiratory problems. Most likely symptoms of high block are numbness and tingling in the hands, flushing and possibly lightheadedness.

In any case, legally epidural can only be performed in the hospital or clinic environment fully equipped for dealing with complications, including resuscitation and full life support. The protocols in places where epidurals are performed imply close monitoring of the patients, and high block is easily detected at its early stages.

The incidence of high block resulting from labor epidurals is low. A prospective analysis of more than 10,000 epidurals conducted in 1998 observed unexpectedly high blocks in eight patients or 0.07%, two of which required induction of general anesthesia, intubation and ventilation.

The treatment of high block is fairly straightforward. The infusion is stopped and supportive measures are provided. If breathing is affected the patient is given oxygen, placed in upright position and sometimes given respiratory assistance with a breathing device. It is not necessary to remove the epidural catheter that has migrated into the subarachnoid space. It can still be used with smaller doses of drugs and closer observation of the patient.

References:

1. Paech MJ, Godkin R, Webster S. Complications of obstetric epidural analgesia and anaesthesia: a prospective analysis of 10,995 cases. Int J Obstet Anesth. 1998 Jan;7(1):5-11

2. Gupta A, Enlund G, Bengtsson M, Sjöberg F. Spinal anaesthesia for caesarean section following epidural analgesia in labour: a relative contraindication.Int J Obstet Anesth. 1994 Jul;3(3):153-6.

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Dr. Eugene Smetannikov is a practicing anesthesiologist with the interest in obstetric anesthesia. He is the author of the most comprehensive book on the subject, The Truth About Labor Epidural