Intravenous regional nerve blocks
Intravenous regional anesthesia, or a Bier block, is a rapid and reliable method for producing short-term (< 90 minutes) anesthesia
and muscle relaxation of a distal extremity and can be performed in anesthetized or sedated animals.2,3,30 Because it requires restricted movement for a period of time, dogs often tolerate the procedure with moderate sedation,
while cats often require heavy sedation. Sicker patients often tolerate this technique with minimal sedation, as they usually
accept restraint for longer periods. This technique is indicated for mass removal, wound management, surgical biopsy, or fracture
repair of a distal extremity.
For this technique, place an intravenous catheter into a distal vein of a limb, usually the cephalic vein or the saphenous
vein. Place a rubber tourniquet, or a blood pressure cuff attached to a sphygmomanometer, around the limb proximal to the
intravenous catheter, and tighten it to completely occlude arterial blood flow (pressure must be greater than systolic arterial
pressure) (Figure 3). The advantage to using the sphygmomanometer and blood pressure cuff is that you can measure the pressure required to occlude
arterial flow, avoiding excessive pressure that may cause direct tissue trauma and ischemic damage. Limb exsanguination with
an Esmarch bandage is often described in reference texts for this technique1,2 but, in our experience, is not required in dogs or cats to produce an effective block. Inject lidocaine or mepivacaine into
the catheter (Table 4). Never use bupivacaine, as intravenous administration of bupivacaine is always contraindicated.
Figure 3. A Bier block provides excellent anesthesia to the extremity distal to the tourniquet as long as the tourniquet remains
tightened. Lidocaine is being injected slowly into an intravenous catheter.
Five to 10 minutes are required to achieve surgical anesthesia distal to the tourniquet, which will last up to 90 minutes.
To avoid ischemic tissue damage, do not leave the tourniquet in place for more than 90 minutes.1,2 Sensation will return within five to 10 minutes of removing the tourniquet, and residual analgesia is minimal (20 to 30
minutes), so provide other analgesics postoperatively.2 This technique provides a blood-free surgical site and is also used with injectable antibiotics to obtain high tissue concentrations
in a distal extremity.33,34
This technique is associated with few side effects as there is minimal systemic absorption of local anesthetic as long as
the tourniquet remains in place and prevents blood flow to and venous return from the extremity.1,2 It is important to ensure that the tourniquet is not dislodged too early, as this will result in rapid plasma uptake of
the anesthetic. Using lidocaine or mepivacaine doses below the toxic doses (Tables 2 & 4) will minimize the possibility of toxicosis should the tourniquet become dislodged.
The mechanism by which local anesthetics produce intravenous regional anesthesia is unknown but probably results from local
diffusion of the anesthetic and the blockade of nerve endings and nerve trunks and from leakage under the cuff, resulting
in systemic absorption.1 Some systemic absorption is also thought to occur from interosseous vessels.35