A number of approaches and techniques have been described for performing ultrasound-guided thoracic paravertebral blocks. The ultrasound probe may be placed in a transverse position, a paramedian longitudinal position, or in an oblique plain. The needle may then be inserted in an in-plane or out-of-plane fashion. In addition, a catheter may be inserted using any of these approaches. A 5-12 MHz linear array probe is most commonly used, but a curved array ultrasound probe may be used as well. These blocks may be placed in the prone, lateral decubitus or seated position. Hence, the list of possible techniques available to place a thoracic paravertebral block is quite extensive. At the current time, no single technique has been shown to be more effective, easier to perform, or safer for the patient. A single injection will cover 4-5 dermatomes and is adequate for many procedures such as a mastectomy or pain management for rib fractures. Some practitioners prefer to perform a thoracic paravertebral block at two or three levels. The most commonly used agents are Bupivicaine 0.5% and Ropivicaine 0.5% with epinephrine 1:200,000-1:400,000.
Figure 1. Anatomy of Thoracic Paravertebral Space
The paramedian sagittal thoracic nerve block may be performed in plane and out of plane. An out of plane block may be placed in a parellel fashion with the probe in a longitudinal paramedian position or with the probe in a transverse position. An in plane paramedian sagittal block is placed with the probe in a vertical position approximately 2.5-3 cm lateral to the midline between two transverse processes. Both transverse processes should be visualized, with the superior costotransverse ligament and the pleura visible in between (figure 2). A 20 gauge blunt tipped block needle or a 22G Tuohy needle is introduced in a cephalad direction. The tip of the needle is advanced under direct visualization until it pierces the superior costotransverse ligament. If the superior coststransverse ligament is not easily seen, the needle is advanced until it is directly above the pleura. Due to the steep angle with which the block needle enters the tissue, the needle is often difficult to visualize. For this reason some practitioners choose to inject small aliquots of normal saline intermittently as they advance the needle to confirm the position of the tip. When the needle tip is located immediately above the pleura, the needle is aspirated to confirm the absence of blood or air. After this, 10-20 cc of local anesthetic is injected in 3-4 cc increments. Spread of local anesthetic with depression of the pleura will be clearly visualized. The extent of local anesthetic spread should be evaluated by moving the ultrasound probe superiorly and inferiorly.
When performing an out of plane paramedian sagital block the probe may be placed as described above. In this case the needle is placed at the side of the probe and is advanced with small aliquots of normal saline injected to evaluate the position of the tip by "tissue dissection". When the superior costotransverse ligament is pierced and after careful aspiration, the pleura will be depressed by the injection of normal saline. This is followed by injection of 10-20 cc local anesthetic injected in 3-4cc increments. When a catheter is placed using this technique it is generally threaded approximately 3 cm beyond the tip of the needle( Figure 3). The historical incidence of pneumothorax with TPVB is 0.3-0.5%, so patients receive a chest radiograph postoperatively to rule out pneumothorax before being discharged home.
Figure 2: Longitudinal, out-of-plane approach to thoracic paravertebral block. The transducer is first placed 5-6 cm lateral to the spinous processes to identify ribs, parietal pleura and intercostal spaces (A1-A3). The transducer is then moved progressively medially to identify transverse processes (B1-B3). Transverse processes (TP) appear square and deeper then ribs (round, superficial). The needle is inserted out-of-plane to contact the TP (C1-C2 and C3, line 1) and then walked off the TP (C3, line 2) inferior or superior to TP to enter the paravertebral space and injection local anesthetic (blue). Proper injection displaces the pleura (blue arrows). PVM - paravertebral muscles.
Figure 3. Continuous thoracic paravertebral block. The catheter is inserted 3 cm past the needle tip.
Mastectomy as an Outpatient Procedure Pathway
Mayo clinic has developed a program featuring multimodal pain control, including PVB, celebrex and gabapentin, which enable patients to be discharged home the same day of their operation. At the preop clinic, patients need to learn to change bandages, care for the incision, understand the surgical drain and be familiar with issues that may indicate the need for a doctor’s evaluation. Furthermore, before the implementation of the program, the multidisciplinary breast staff was educated as to the protocol and reassured the requirements of the patient could be met postoperatively prior to discharge home. Not only is TPVB associated with low pain scores, low PONV and high patient satisfaction, it has also proven to be cost-effective. Boughey et al. found that the use of TPVB decreased the overnight admission rate from 97% to 61% after major breast surgery. The benefits of TPVB continue beyond the length of local anesthetic. By blocking the nociceptic inputs, patients at their one-month, six-month and one-year follow up evaluations had significant less pain than their non-block counterparts, indicating a role in preventing chronic postmastectomy pain syndrome.
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发表于 2014-9-10 01:36:30
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