Thoracic Paravertebral Catheters in Cadavers
Interesting analysis, if a little disheartening. 11/20 catheters with correct paravertebral spread isn’t reassuring. Still, this may explain the variability inherent to this block’s success.
During paravertebral block, the anterolateral limit of the paravertebral space, which consists of the pleura, should preferably not be perforated. Also it is possible that, during the block, the constant superior costotransverse ligament can be missed in the loss-of-resistance technique. We therefore aimed to develop a new technique for an ultrasound-guided puncture of the paravertebral space.
We performed 20 punctures and catheter placements in 10 human cadavers. A sonographic view showing the pleura and the superior costotransverse ligament was obtained with a slightly oblique scan using a curved array transducer. After inline approach, injection of 10 ml normal saline confirmed the correct position of the needle tip, distended the space, and enabled catheter insertion. The spread of contrast dye injected through the catheters was assessed by CT scans.
The superior costotransverse ligament and the paravertebral space were easy to identify. The needle tip reached the paravertebral space without problems under visualization. In contrast, the introduction of the catheter was difficult. The CT scan revealed a correct paravertebral spread of contrast in 11 cases. Out of the remaining, one catheter was found in the pleural space, in six cases there was an epidural, and in two cases there was a prevertebral spread of contrast dye.
We successfully developed a technique for an accurate ultrasound-guided puncture of the paravertebral space. We also showed that when a catheter is introduced through the needle with the tip lying in the paravertebral space, there is a high probability of catheter misplacement into the epidural, mediastinal, or pleural spaces.
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I have tried this approach in anaesthetised patients on >10 occasions. In contrast to comments above, I have found the needle difficult to identify, let alone the tip, despite some experience with paravertebral imaging and inplane blocks in general.
Needle localisation is best demonstrated by injections of saline as the needle is advanced. Expansion of the paravertebral space is visualised as the pleura is pushed deep above and below the level of insertion and correlates with success. The catheter still tends to be difficult to feed, so depositing it at the end of the needle seems to suffice. The last time I followed this approach I managed to deliver excellent analgesia for 12 unilateral fractured ribs that lasted for 1/52 before the block failed!
I would be intersted to know more specifics. We have only the ultrasound spread noted by the original proceduralist to confirm needle position in the space. Before we conclude that all of these needles were in the right place, but only 55% of the catheters ended up in the right place, I would like to see some type of confirmation(i.e. U/S picture confirmed by a seperate ultrasonographer)Second, what kind of catheter were they using? Was it stiff? How much catheter did they thread into the space?
So I would say cautionary, but not disheartening.
Again this brings up the point as to whether we should just move towards epidurals for the management of rib fracture and thoracotomy pain. There is no definitive end point and many a time I find myself not sure if the paravertebral catheter was in the right place.