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Summary

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Competing interests
  8. References

The aim of this prospective clinical study was to evaluate the location of paravertebral catheters that were placed using the classical landmark puncture technique and to correlate the distribution of contrast dye injected through the catheters with the extent of somatic block. Paravertebral catheter placement was attempted in 31 patients after video-assisted thoracic surgery. In one patient, an ultrasound-guided approach was chosen after failed catheter placement using the landmark method. A fluoroscopic examination in two planes using contrast dye was followed by injection of local anaesthetic and subsequent clinical testing of the extent of the anaesthetised area. In nine patients (29%), spread of contrast dye was not seen within the paravertebral space as intended. Misplaced catheters were in the epidural space (three patients), in the erector spinae musculature (five patients), and in the pleural space (one patient). There was also a discrepancy between the radiological findings and the observed distribution of loss of sensation. We have demonstrated an unacceptably high misplacement rate of paravertebral catheters using the landmark method. Additional research is required to compare the efficacy and safety of continuous paravertebral block using ultrasound-guided techniques or surgical inserted catheters.

Thoracic operations are known to be painful and thus require effective postoperative pain therapy [1]. Thoracic paravertebral block has been shown to be a proven technique to achieve sufficient postoperative analgesia [2, 3]. Unilateral thoracic anaesthesia can be achieved with a multilevel injection technique that can be used as the sole anaesthesia technique for breast surgery [4–7]. Even though a single injection technique has been shown to produce a reliable block, there are conflicting results regarding the use of paravertebral catheters. Continuous paravertebral block is often described as producing a variable degree of block with a limited extent over a few segments only [4, 8]. While the needle tip can be placed with high accuracy using either a landmark technique [9] or ultrasound guidance [8, 10, 11], this variability could be explained by a discrepancy between the needle tip location and the final resting position of the catheter tip once introduced through the needle. This possibility has recently been studied in an imaging study in fixed human cadavers [12]. Indeed, it was demonstrated that catheter tips were misplaced in more than 80% of patients, despite having the needle tips correctly located in the paravertebral compartment.

The aim of this prospective observational clinical study was to evaluate the final resting position of catheter tips inserted using a landmark-based paravertebral approach by means of contrast dye injection and fluoroscopic examination (primary outcome). We also assessed the correlation between the sensory block produced after local anaesthetic injection through the catheter with the distribution of contrast dye (secondary outcome measure).

Methods

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Competing interests
  8. References

After obtaining ethical approval from the ethics committee of the Canton Bern, 35 patients were prospectively enrolled. All patients were scheduled for video-assisted thoracosopic surgery. Exclusion criteria were: lack of consent; age < 18 years; known allergy to iodinated contrast material or local anaesthetics; severe hepatic dysfunction (Child-Pugh class B or C); Waldenström disease; renal insufficiency (calculated glomerular filtration rate < 30 ml.min−1); multiple myeloma; and pregnancy (this was specifically excluded in women of child-bearing age).

Patients were anaesthetised according to the standard clinical practice of our department. All paravertebral catheters (Perifix® standard epidural catheter sets with three end-holes; B Braun Inc., Melsungen, Germany) were placed at the end of surgery using the classical landmark technique as described by Eason and Wyatt [13], with the patient in the lateral decubitus position under general anaesthesia. Catheters were placed by four different consultant anaesthetists familiar with the technique, between vertebral levels T5-T8 (with the predominant target being T6-T7). The insertion level was evaluated using the clinical judgment of the anaesthetist performing the block. After placement of the paravertebral catheter, the patient was turned to the supine position. Ten millilitres of contrast dye (Iopamidol, Iopamiro300®; Braco Suisse SA, Mendisio, Switzerland), diluted with an equal volume of saline 0.9%, was injected through the paravertebral catheter, and fluoroscopy used to demonstrate spread in both the antero-posterior and lateral planes. Fluoroscopy imaging was performed in real time during the injection, after each 2–3 ml, as well as at the end of the injection. All images were recorded and saved. Following the fluoroscopic examinations, a test dose of 3 ml bupivacaine 0.25% mixed with adrenaline 5 μg.ml−1 was injected through the catheter. If no significant rise in heart rate or arterial pressure was observed and there was no radiological evidence that the catheter was located in the epidural space, a bolus of 0.3 ml.kg−1 of bupivacaine 0.25% mixed with adrenaline 5 μg.ml−1 was administered. Thereafter, the patient was woken up and transferred to the post-anaesthesia care unit (PACU). No information on catheter tip location or contrast dye spread was provided to the PACU staff to preserve blinding.

A radiologist not involved in the fluoroscopic examination and blinded to the measured extent of the resulting paravertebral block evaluated all radiological images offline. Contrast dye spread was rated as follows [12]: paravertebral, extrapleural close to the intervertebral neural foramen; paravertebral, intercostals (extrapleural lateral); paravertebral, vertebral (extrapleural anterior); pre-vertebral; erector spinae muscle; epidural; or intra-pleural.

All patients received an infusion of bupivacaine 0.25% mixed with fentanyl 2 μg.ml−1 and adrenaline 5 μg.ml−1 at 5–12 ml.h−1 via the paravertebral catheter; this was started immediately after transferring the patients to the PACU. They were also prescribed analgesia consisting of regular paracetamol (1 g four times a day) and metamizole (also 1 g four times a day). In the event a patient reported a pain score > 3 on the visual analogue scale (VAS; 0 = no pain to 10 = worst imaginable pain), a bolus of intravenous morphine 2 mg was given as a rescue analgesic. If the cumulative morphine requirement in the first 2 h after surgery was more than 20 mg, morphine via patient-controlled analgesia (PCA) was prescribed. Four hours after surgery, clinical assessment of the paravertebral block was performed by the PACU staff, who are experienced in testing and documenting the extent of paravertebral block. The following data were recorded at the same time: area of loss of pinprick and cold sensation; requirement for additional rescue analgesia; and postoperative pain score (using the VAS).

Data collection, data management and statistical analysis were conducted using SPSS® (version 19; IBM Corp, New York, NY, USA). Success rate for the placement of paravertebral catheters using the classical landmark technique was defined as the number of radiologically correctly placed catheters in the paravertebral space divided by the total number of catheters. Dependency of clinical effect and contrast dye spread were determined using the Spearman correlation coefficient. Since no hypothesis was tested in this prospective clinical observational study, we did not perform a power analysis, and we planned to recruit a convenience sample of 30 patients.

Results

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Competing interests
  8. References

A total of 34 patients were assessed for eligibility and 30 patients completed the study with the placement of a unilateral paravertebral catheter and radiological examination according to the study protocol (Fig. 1). Patients' characteristics and details concerning paravertebral catheter placement and surgery are displayed in Table 1. Three patients were not studied pre-operatively because they received an epidural catheter following a surgical decision to perform an open thoracotomy. In one patient, radiological assessment revealed that the catheter tip and contrast dye were clearly intra-pleural; the catheter was immediately removed and not replaced. This patient was included in the radiological evaluation but not in the non-radiological postoperative evaluation concerning clinical effectiveness of the block. In an additional patient, difficulties were encountered in paravertebral catheter placement requiring the catheter to be placed using an ultrasound-guided approach. No further radiological or clinical assessment was performed in this patient due to the use of ultrasound.

image

Figure 1.  This adapted CONSORT diagram illustrates enrolment, allocation to paravertebral catheter and fluoroscopic assessment of contrast dye spread, as well as the clinical follow-up and evaluation of sensory spread and quality of analgesia. PACU, post-anaesthesia care unit.

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Table 1. Patients' and surgical characteristics in 29 patients in whom a paravertebral catheter was inserted using a landmark-based technique. Values are number (%) or median (IQR [range]).
  
  1. BMI, body mass index.

Women10 (33%)
Age; years55 (43–68 [21–77])
BMI; kg.m−224 (21–27 [18–35])
Thoracic spine level of insertion
 T511 (37%)
 T613 (43%)
 T75 (17%)
 T81 (3%)
Distance from skin to transverse process; cm2.8 (2.0–3.0 [1.0–5.0])
Depth of insertion; cm9.0 (8.0–10.0 [7.0–12.0])
Catheter length beyond needle tip; cm5.0 (4.5–5.0 [3.0–7.5])
Conversion to thoracotomy6 (20%)

In 21 patients (71%), contrast dye (i.e. location of the catheter tip) was identified within the paravertebral space either close to the intervertebral neural foramen, extrapleural laterally at the level of the ribs, extrapleurally at the level of the vertebral bodies or anterior to the vertebral bodies. Hence, the failure rate concerning radiological identification of an adequate contrast dye distribution within the paravertebral space was 29%. This failure rate increased to 32%, if the patient in whom the classic landmark approach was impossible and ultrasound was used was included. In the 21 successful patients, the cranial caudal spread of the contrast dye covered one to eight vertebral segments (median three segments). In the remaining nine patients, contrast dye was not seen in the paravertebral space. Among these patients, spread of dye was seen within the epidural space (three cases), erector spinae muscles (five cases) and the pleural space (one case).

After injection of the local anaesthetic bolus dose through the catheter, the clinical correlation in terms of loss in sensation was not always congruent with the radiological findings (Spearman's rho = 0.049, p = 0.797). Of the 29 patients who had a paravertebral catheter inserted and used, seven patients displayed insufficient postoperative pain control, with a VAS score of more than 4/10 and a morphine requirement of more than 20 mg in the first 2 h, corresponding to a clinical failure rate of 23%. Among these seven patients, the contrast dye distribution was as follows: one patient had contrast spread in the anterior compartment of the paravertebral space resulting in only a small area with loss of sensation; two patients had the catheter located in the muscles posterior to the paravertebral space; and four patients had an insufficient clinical effect, requiring PCA, despite demonstrating spread of contrast dye in the defined paravertebral space.

Altogether, five catheters were in the erector spinae muscles, but despite this clear misplacement three of these patients were pain-free and some had a widespread unilateral loss of sensation – one even had a bilateral block. Three patients where the catheter was seen in the epidural space had a bilateral dense block as expected.

Discussion

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Competing interests
  8. References

This study has demonstrated an unacceptably high failure rate of correct placement of the tip of a catheter in the paravertebral space using a landmark-guided approach. In approximately one third of all the insertion attempts, the tip of the catheter was incorrectly placed and contrast dye distribution within the paravertebral space was not achieved. Despite this low success rate, some of the misplaced catheters produced a clinically satisfactory block. On the other hand, a number of catheters apparently placed correctly nonetheless provided inadequate analgesia.

There are two different possible definitions of failure in this context. The clinical failure rate, as perceived by the patient who was in pain, was 23% in this investigation, despite the fact that catheter placements occurred in a study setting and were performed by an anaesthetist who routinely performs these blocks. If failure is defined according to the location and the extent of contrast dye spread, then the failure rate was even higher (32%). These failures were probably related to incorrect placement of the needle tip – either too deep or too shallow – using the landmark technique and could potentially be resolved by refinement of clinical skills or by using an ultrasound-guided approach. The other failures, however, were more probably catheter-related ones. Once the needle tip reaches the paravertebral space close to the intervertebral neural foramen, catheters can follow several directions: towards the epidural space; towards the anterior compartment of the paravertebral space (close to the sympathetic chain); or even prevertebrally. Obviously, those catheters tracking into the epidural space produced an extensive bilateral block. On the other hand, one of the prevertebral catheters and one of the catheters lying in the anterior compartment close to the sympathetic chain resulted in only a small area of loss of sensation and thus a clinically inadequate block. Some catheters stayed close to the neural foramen or came to rest laterally superficial to the pleura. These catheters were generally effective in terms of analgesic effect as well as area of loss of sensation.

It is well documented that with a multi-level single injection paravertebral technique, unilateral anaesthesia of the thorax can be achieved with a high success rate, irrespective whether a landmark-based technique [4, 5, 14, 15] or an ultrasound-guided approach [8] has been chosen. There is, however, some controversy surrounding the use of catheters for continuous paravertebral block because of limited cranio-caudal spread of local anaesthetic [16] as well as the possible discrepancy between the needle tip position and the final catheter tip location [12]. The present investigation adds some new information to this discussion but the following question remains: why does a meta-analysis comparing epidural anaesthesia to paravertebral block favour the paravertebral block [3]? The reason could be that most of the studies included involved thoracotomy, where the paravertebral catheter was placed under direct vision by the surgeon. This achieves continuous extrapleural infusion of local anaesthetic solution [16, 17], which is conceptually comparable to our cases where the contrast dye was found to lie extra-pleurally. It is intuitively more accurate to place such catheters under direct vision compared to using a landmark-guided, posterior percutaneous approach. Whether or not it would be possible to improve the observed discrepancy between needle tip position and final catheter tip placement using a different catheter material (for example coiled catheters) remains to be tested in a clinical trial [17].

Comparing spread of contrast dye and loss of sensation as tested clinically, we could observe a correlation but the findings were rarely identical. Similar findings have been reported for single-injection paravertebral blocks [15] and for imaging studies in infants receiving caudal blocks [18, 19]. The probable explanation for this is the time delay between the injection of the contrast dye and the subsequent local anaesthetic bolus injection and continuous infusion. Also, the volume of local anaesthetic injected was larger than the volume of contrast dye injected and the local anaesthetic had a longer time to spread by the time the resultant sensory block was assessed clinically, 4 h later. This subsequent spread could also explain why one patient with a catheter located in the erector spinae muscle had a bilateral block. In this case (and also in two other cases) where the catheter was clearly not placed in the epidural space, the ensuing bilateral block probably still resulted from epidural spread of local anaesthetic [10]. This issue has been raised previously [20, 21] and our results support this theory.

This prospective observational clinical study has some limitations. Even though the anaesthetists inserting the catheter were aware of the potential discrepancy between final catheter location and initial needle tip position, the distance the catheter was advanced beyond the needle tip was relatively high. Since we used a stiff catheter, it may be possible that inserting the catheter further into the space makes misplacement more likely. Nevertheless, a previous cadaver study demonstrated a similar misplacement rate, even though the catheter was inserted between 1 and 3 cm from the needle tip [12]. We decided to use the landmark approach for this study as it has been used successfully over many years, and decided that it might also avoid potential unforeseen problems associated with an ultrasound-guided approach using a completely different needle direction. In retrospect, we could probably have avoided the misplacement of catheters into the musculature of the spine or into the pleural cavity if we had used ultrasound.

The radiological assessment of spread of contrast dye in this prospective observational clinical study documented an unacceptably high misplacement rate of paravertebral catheters using the landmark method. Efficacy and safety of continuous paravertebral block may be superior using ultrasound-guided techniques or surgical inserted catheters; however, an additional study comparing these methods is required.

Acknowledgements

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Competing interests
  8. References

We would like to thank Dirk Schröder and his team of technicians for helping with the fluoroscopic examinations. We also thank Dr. Patrick Conroy in Dublin for his advice and for proofreading the manuscript. This study was supported by an institutional research grant from the University Department of Anaesthesiology and Pain Therapy, University Hospital and University of Bern, Bern, Switzerland.

References

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Competing interests
  8. References