Selected techniques of regional anaesthesia for orthopaedic surgery
Department of Endoscopic Surgery in Zory
Central blocks, continuous subarachnoid-epidural anaesthesia, including combined spinal-epidural anaesthesia (CSE) are used for long and painful procedures of lower limbs. They provide quick and good-quality anaesthesia as well as satisfactory postoperative analgesia. After their administration, ambulation is quick and rehabilitation instituted early, which is essential for the postoperative course of orthopaedic procedures.
Peripheral blocks are an excellent alternative, especially in patients at high perioperative risk, who require anticoagulants.
The novel techniques of location of peripheral nerves and plexuses, i.e. nerve stimulation- and ultrasound-guidance, improve the efficacy of blocks and shorten the duration of anaesthesia. Moreover, they improve safety and comfort of patients.
The paper presented during the 8th Polish ESRA Zonal Symposium, Wisła 27-29 May 2010
Anaesthesia for orthopaedic surgery requires knowledge of various techniques of regional anaesthesia. Limb surgery may be conducted under central or peripheral blockades, which provide good perioperative analgesia. Continuous analgesia ensures effective relief of postoperative pain, early ambulation and successful rehabilitation of patients.
CONTINUOUS SPINAL-EPIDURAL ANAESTHESIA
Central blocks, spinal or epidural are routinely administered by the majority of anaesthesiologists. Combined continuous spinal-epidural (CSE) anaesthesia is considerably rarer in everyday practice, despite its numerous assets.
The pioneer of this technique was Ryszard Rodziński, a surgeon from Lvov who published several studies on the combined use of spinal anaesthesia, used since 1898, and sacral epidural anaesthesia, known since 1901 .
The combination of both central blocks eliminates some disadvantages and limitations of each method and exposes their merits . It provides fast and good analgesia, eliminates the risk of too short or improper level of anaesthesia, which is the drawback of spinal anaesthesia. In CSE anaesthesia, its duration can be prolonged at any time, range extended or effects prolonged over the postoperative period.
Indications for CSE anaesthesia for orthopaedic surgery include procedures of anticipated duration >90 min, those associated with severe postoperative pain and in which early ambulation is recommended or in high-risk patients where extensive sympathetic blockade is contraindicated.
TECHNIQUES OF ANAESTHESIA
First, the extradural space is localized and the catheter introduced. In another space (mostly beneath) spinal blockade is performed. The technique enables control of proper catheter position (pain, paraesthesia, CSF leak) before the supply of a local anaesthetic to the subarachnoid space. Its drawback, however, is that two insertions are needed.
In another technique, described by Cook , the needle is first inserted into the subarachnoid space. Once its proper position is confirmed, the needle lumen should be closed with a central stylet to prevent the leak of CSF. The second epidural needle is used to localize another intervertebral space and the epidural catheter is introduced. After confirming the proper catheter position, a local anaesthetic is first administered into the subarachnoid space. According to the author of this technique, such anaesthesias are associated with markedly lower percentages of failures and lower risk of complications, e.g. insertion of the epidural catheter into the subarachnoid space or damage to the catheter by the spinal needle.
Irrespective of the space penetrated first, the method is intricate, requiring the puncture of two intervertebral spaces, which increases the risk of vessel punctures and CNS infections.
Single-insertion technique – “needle-through-needle”
In 1937, Soresi  described the CSE anaesthesia technique using one needle. The local anaesthetic was first injected to the epidural space; the same needle was advanced and the drug deposited in the subarachnoid space. Special sets are currently used for this technique.
In most cases, the spinal needle is introduced into the epidural one and sticks out for 10-20 mm; thanks to that, the subarachnoid and epidural spaces can be simultaneously localized. In this technique, the local anaesthetic is first administered to the subarachnoid space and once the spinal needle is removed, the catheter is inserted into the epidural space.
The advantage of this technique is the puncture of only one intervertebral space, which increases comfort of patients. The simplicity of the technique and the smaller number of manipulations during anaesthesia diminishes the risk of vessel punctures and CNS infections. Its major limitation is that the epidural catheter position cannot be checked before the administration of local anaesthetic to the subarachnoid space.
Technique with a double-lumen needle
Using a single insertion of a double-lumen needle into the intervertebral space, the epidural space is first localized and the catheter introduced, followed by the insertion of the spinal needle through the lower lumen; finally the anaesthetic is administered.
To improve the efficacy and safety of CSE anaesthesia, various methods have been described. One of them is nerve stimulation , in which special epidural catheters, connected with a stimulator, have to be used. Proper placement of the catheter is confirmed by muscle contraction within the lower limbs in response to electrical stimulation of 1-10 mA. This method can be used in the technique of two insertions or one insertion with a double-lumen needle.
Another method improving the efficacy and safety of CSE anaesthesia is ultrasonography . The method is not easy due to difficulties in visualizing the spinal canal (numerous artefacts caused by bony tissue) and various technical problems. A specially designed head of the probe solved some of the problems; using this head the puncture needle may be introduced under ultrasound guidance. The method has been successfully used during CSE anaesthesia for elective Caesarean sections .
A renewed interest in peripheral nerve blocks has been observed, which is associated with novel, safer and more effective local anaesthetics. The widespread use of low-molecular heparins and oral anticoagulants in patients with cardiovascular diseases hinders administration of central blocks; therefore, peripheral blocks have become a good alternative.
The peripheral nerves may be identified using the anatomical landmarks, by inducing paraesthesia, or using nerve stimulation and ultrasound guidance.
The first two methods are not currently recommended due to a high risk of complications and a relatively low percentage of successes. Their use excludes the possibility of objective assessment of proper placement of a needle in the tissues, the only confirmation being paresthesias (usually unpleasant), reported by the patient.
Peripheral plexuses and nerves are localized using the electric current to stimulate the nervous motor fibres. Stimulation induces the contraction of an appropriate group of tissues, which confirms the proper needle placement. At present, low current intensities (0.2-0.5 mA) are used, which increases the safety and comfort of patients. The remaining parameters of the device include the frequency (1-2 Hz) and time of impulse (0.1-0.3 ms). The time of impulse during localization of motor nerves should be 0.1 ms. In order to identify sensory nerves , particularly the saphenous nerve in the distal thigh, longer impulses are required – 0.3 ms, which corresponds to chronaxia of the sensory nerves. If the stimulating needle is too near the sensory nerve searched for, the patient will feel paresthesias within the innervation region, which additionally confirms its proper placement.
The best blocking effect is provided when the motor response is induced by the electric current of 0.2-0.5 mA . It should be remembered that the response to stimulation persisting at <0.2 mA may be suggestive of too close position of the needle in relation to the nerve. In such cases, there is a risk of nerve damage during the supply of local anaesthetic; the needle should be gently withdrawn until the motor response during 0.2 mA stimulation vanishes.
Furthermore, stimulation may be used for identification of individual nerves. For instance, the brachial plexus block by axillary approach when the local anaesthetic may be administered into the region of each nerve separately. Such a block provides better quality of anaesthesia with a smaller local anaesthetic dose. The prerequisite of successful block with stimulation is the knowledge of anatomy, topography and type of motor response during stimulation of individual nerves.
Another technique facilitating the localization of nerves and plexuses is transdermal stimulation. The majority of the latest stimulators are additionally equipped; thanks to that, the desirable motor response of muscles can be obtained by touching the skin over the nerve with a stimulator, before the needle insertion. Transdermal stimulation increases the efficacy of block, shortens the time of anaesthesia and improves the patient`s comfort.
The newest technique used to identify the peripheral nerves and plexuses is ultrasonography, which was introduced into clinical practice in the mid-90ties of the previous century . Ultrasonography enables visualization of anatomical structures and objective monitoring of local anaesthetic distribution.
Thanks to the high-quality devices (linear head 8-13 MHz) and high resolution of images, the finest anatomical structures can be visualized. In order to use this method successfully, the operator should know classical anatomy and topography of the region blocked as well as ultrasound anatomy of the nervous structures and adjacent tissues. Each plexus and nerve has a characteristic ultrasound appearance. Individual nerves differ in shape, appearance and echogenicity.
With ultrasound guidance, the spread of local anaesthetic during its supply can be observed and the needle position corrected, if need be.
Numerous studies demonstrate that ultrasound guided blocks may be efficiently used with markedly lower doses of anaesthetics – even 20-30% lower than in the other techniques described .
Ultrasound-guidance enables the control of needle position. When the “in plane” method is used, the entire needle length is visible, i.e. the needle is inserted along the longitudinal dimension of the head. In the “out of plane” method, the needle is visible as a point, i.e. introduced along the transverse head dimension. The choice of method depends on the type of block, imagination and manual skills of an anaesthesiologist. Both methods may be used interchangeably.
Irrespective of the method used, ultrasonography diminishes the risk of puncturing the blood vessels or pleural cavity thus improves the safety of block and patient`s comfort. Additionally, multiple punctures of the anaesthetized area are not needed.
Combined stimulation and ultrasonography
The studies attempting to demonstrate the superiority of one of the techniques in question seem pointless  as each technique has its merits and limitations.
The limitations of nerve stimulation include low sensitivity hindering identification of the nerve with a needle, which is likely to be associated with varied resistance of healthy tissues or lack of motor response in cases of peripheral neuropathy. In ultrasonography, on the other hand, imaging of all anatomical structures is not always accurate. Technical problems, such as an acoustic shadow induced by bony structures, acoustic enhancement below big blood vessels or air in the tissues, may markedly worsen the quality of imaging and thus impair visualization of the nervous structures and the needle.
The combination of both techniques improves the efficacy and safety of peripheral nerve blocks. If sensitivity of stimulation is low, an appropriate needle placement should be confirmed ultrasonographically. Difficulties in imaging the nervous structures, e.g. due to anatomical anomalies, may be overcome by confirming the proper nerve localization using a stimulator.
In many cases of brachial plexus blocks by the axillary approach, the radial nerve is located just below the axillary artery, in the region of acoustic enhancement caused by blood vessels; hence, ultrasound visualization of the nerve is infeasible. In such cases, the motor response to radial nerve stimulation confirms its position and appropriate needle placement.
Ultrasonography and nerve stimulation are supplementary. Their simultaneous application increases the efficacy of blocks to almost 100% [13, 14].
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