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a Department of Thoracic Surgery, Hospital Universitari Sagrat Cor., C/Viladomat 288, 08029 Barcelona, Spain
b Department of Anesthesia, Hospital Universitari Sagrat Cor., C/Viladomat 288, 08029 Barcelona, Spain
Received 25 July 2007; received in revised form 4 December 2007; accepted 10 December 2007.
* Corresponding author. Tel.: +34 934948922; fax: +34 934052641. (Email: juanjofibla{at}hotmail.com).
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Abstract |
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 Top Abstract 1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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Key Words: Post-thoracotomy pain • Paravertebral block • Paravertebral analgesia
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1. Introduction |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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Given the fact that systemic opioids are not potent enough to control neurogenic pain without detrimental effects on respiratory outcome [2], epidural analgesia is considered as the gold standard for thoracic analgesia [3].
However thoracic epidural analgesia carries the risk of dural puncture, epidural hematoma, epidural abscess, and side effects such as hypotension, bradycardia, and urinary retention and these commonly occur. Regional anesthesia by thoracic paravertebral block (TPVB) could be a good alternative for post-thoracotomy pain [4].
A thoracic paravertebral infusion of a local anesthetic provides effective pain relief with few side effects. This technique also reduces the occurrence of chronic post-thoracotomy neuralgia and stress responses, and preserves pulmonary function [5].
TPVB efficacy depends on adequate catheter placement and on the potency, concentration and volume of the local anesthetic [6].
Bupivacaine has been the most frequently used local anesthetic according to published studies. It is a contrasted potent drug; however it has been reported toxic when limit dosages are overpassed [7].
Ropivacaine is a new local anesthetic that could be a useful alternative to bupivacaine for TPVB. It is considered less cardiotoxic and neurotoxic than bupivacaine at equipotent doses and also less potent than bupivacaine at equal milligram doses. These properties could be important because higher concentrations and volumes of local anesthetics are needed for this technique [8].
We decided to compare these drugs, one with a higher concentration and a lower volume, the other at a lower concentration but with a higher volume.
We conducted a randomized controlled trial to evaluate the effectiveness of a multimodal approach for pain treatment after thoracic surgery including a thoracic paravertebral infusion of bolus of bupivacaine 0.5% (10 ml/6 h) vs ropivacaine 0.2% (15 ml/6 h), intercalated with 2 g of endovenous methamizol every 6 h.
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2. Materials and methods |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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Patients of every group (AT and PT) were allocated randomly to the analgesic technique (bupivacaine 0.5%, 10 ml/6 h or ropivacaine 0.2%, 15 ml/6 h).
General anesthesia was induced with 1.5–2 mg/kg of propofol, 2 µm/kg of fentanyl, and 0.6 mg/kg of atracurium and maintained with sevoflurane, nitrous oxide, and oxygen. All patients were intubated with a double-lumen endobronchial tube for one-lung ventilation.
An anterior or posterolateral thoracotomy was implemented in the forth (AT) or fifth (PT) intercostal space. One tube for wedge resections and two tubes for lobectomies were placed after resection in the seventh or eighth intercostal space; after pneumonectomy chest tube was removed in the operating room. The same policy of chest tube placement was followed in both groups in order that this would not bias the results of the study. The paravertebral catheter was placed by the surgeon before closing the thoracotomy.
The puncture site was situated 2.5–3 cm laterally to the thoracotomy close to the spinous process and an 18-gauge Tuohy needle was inserted perpendicularly to the skin. The needle entering into the paravertebral space was located visually. A catheter was then inserted 2–3 cm. After careful aspiration through the catheter, an initial bolus of 15 ml of bupivacaine 0.5% or 20 ml of ropivacaine 0.2% was infused.
The total dose, volume and concentration of bupivacaine and ropivacaine were selected regarding previous studies, all of which showed the efficacy of plain bupivacaine and ropivacaine in concentrations ranging from 0.2% to 0.5%, starting with a bolus dose of 15–20 ml followed by bolus of 10 or 15 ml, respectively. In our center, the disposable concentrations of local anesthetics for surgical use are bupivacaine 0.5% and ropivacaine 0.2%.
We employed higher volumes of ropivacaine to compensate for its lower concentration (15 ml/6 h). We avoided higher volumes of anesthetic to prevent complications.
Patients received a bolus of 10 ml of bupivacaine or 15 ml of ropivacaine every 6 h with 2 g of endovenous methamizol intercalated every 6 h and meperidine, a synthetic opioid, as rescue drug (bolus of 50 mg subcutaneous).
Patients’ pain was evaluated with a VAS graded from 0, no pain, to 10, the worst pain imaginable, recorded 1 h after the paravertebral analgesic bolus.
The study period lasted 72 h, and data collection was performed by a third person (the assigned ward nurse) who was not aware of the randomization and wrote the VAS score in the patient Kardex.
The following data were assessed: (1) 1st, 6, 24, 48, 72 h pain scores, (2) any requirement for rescue analgesia (meperidine), and (3) adverse events related to the analgesia technique, respiratory depression (respiratory rate <8 breaths per minute), cardiotoxicity, confusion, sedation, urinary retention, nausea, vomiting, and pruritus. SPSS v13 package (Chicago, IL, US) was used for statistical data analysis. The data samples were split into four data sets attending to each factor. Adjustment of data sets to a normal distribution was always verified for the applicability of parametric statistics (Kolmogorov–Smirnov test). Subsequently the comparison of serial measurements (variables) was performed by ANOVA for repeated measures with Greenhouse–Geisser correction. When normal distribution was not applicable data were analyzed by using non-parametric statistics (Mann–Whitney U test).
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3. Results |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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No pruritus or periods of excessive somnolence were detected in either of the groups. There were no intraoperative or postoperative complications in any of the patients in regard to catheter placement or local anesthetic infusion.
Patient characteristics and operative data were comparable between the groups (Table 1 ). Differences between both local anesthetic and thoracotomy variety can be seen in Tables 2 and 3 .
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Per hours there were statistically differences between VAS 1 and 24 h (Table 2).
Initial VAS scores (first hour after bolus) were low in both groups (3.1/3.8) with a peak of pain in 6 and 24 h control (values over 6). VAS pain scores decreased progressively being lower after 72 h (3.4/4.0).
VAS scores in function of the thoracotomy performed (AT or PT) showed lower scores in AT group that were statistically significant mean and per hour (p < 0.01) (Table 3).
Eleven patients (16%) needed meperidine as rescue drug at some moment (six with ropivacaine and five with bupivacaine), there were no differences in the requirements for rescue analgesia between the two groups (p > 0.05).
No complications attributable to postoperative pain (retention of secretions, atelectasis or pneumonia) were recorded. No postoperative bronchoscopies or minitracheotomies were performed.
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4. Discussion |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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TPVB was described at the beginning of the 20th century. Recently, because of the possibility of inserting a catheter into the thoracic paravertebral space, it has been evaluated for postoperative analgesia after thoracotomy [10].
Thoracic paravertebral space is a vertically and horizontally open space located between the intercostal and epidural space. Local anesthetic injection can diffuse through this space to upper and lower nerve roots. Consequently analgesia achieved using a paravertebral block can span several segments. The intensity of the block will depend on the potency, concentration and volume infused of the local anesthetic [6,11].
The insertion of the thoracic paravertebral catheter has been described by a surgical approach under direct vision as in the current study or by a skin puncture generally performed by the anesthesiologist [12].
Since 2002 in our department (with the agreement of anesthesiology) we have been employing a multimodal treatment of post-thoracotomy pain consisting of a TPVB with bolus of bupivacaine intercalated with methamizol and subcutaneous meperidine as rescue drug.
We have observed in the day-practice an effective control of post-thoracotomy pain with this strategy.
We decided to evaluate our pain management policy comparing the most frequently employed local anesthetic (bupivacaine) with the more recently implanted (ropivacaine) in two groups with different thoracotomy approaches (AT and PT).
It has been shown that at the usual doses of bupivacaine, early threshold plasma levels for central nervous system toxicity are often exceeded and occasional episodes of temporary confusion can arise, probably caused by bupivacaine accumulation [13].
Compared with bupivacaine, ropivacaine produces a greater sensorimotor differential block with the benefit of a shorter elimination half-life, with a possibly lower potential for accumulation. The risk of toxicity with ropivacaine is lower that with bupivacaine, however at equal milligram doses ropivacaine is slightly less potent than bupivacaine in a potency ratio of 1:1.2 [14].
Because of concerns of this potential bupivacaine toxicity, clinicians have turned to propose ropivacaine for TPVB as a safer option [15].
We decided to test both drugs. The concentrations disposable at our center were 0.5% for bupivacaine and 0.2% for ropivacaine.
It is a fact that higher levels of block are obtained increasing concentration of the anesthetic. On the other hand a higher volume of anesthetic is supposed to block more intercostal nerves, compensating a lower concentration [6].
In this study we employed a summed concentration per day of 225 mg of bupivacaine with a volume of 45 ml. Summed ropivacaine per day was 130 mg with a volume of 65 ml. We did not administrate higher volumes than 15 ml/6 h in order to prevent possible complications given the lack of experience in the use of higher volumes of ropivacaine.
Regarding the need for rescue analgesia both anesthetics obtained similar results. However bupivacaine mean VAS values were better than those with ropivacaine (p < 0.05); also after 1 and 24 h (Table 2).
The differences are small but may show the importance of concentration over volume. Concentrations of local anesthetic usually employed in TPVB are low because of the risk of toxicity. Some reports suggest that it may be necessary to use higher concentrations to achieve better VAS scores [16,17]. However there are insufficient studies to determine if these higher concentrations of local anesthetic would provide better pain control without toxicity.
In our series we saw no toxicity related to local anesthetic, and obtained slightly better VAS values in the group with higher concentrations.
It is important to remark that, different from an epidural block, paravertebral block with a local anesthetic is not a direct nerve root block. In this technique the nerves are blocked by diffusion through the paravertebral space. Therefore higher concentrations and volumes should be needed.
Theoretically the day dose in bolus of bupivacaine for TPVB (the more toxic of local anesthetics employed) cannot exceed 400 mg [18]. Our patients received a total dose per day of 225 mg of bupivacaine.
On these bases and according to our results we believe that under strict control, higher concentrations and volumes of local anesthetics could be given to improve post-thoracotomy pain. Further studies employing higher doses and concentrations should be performed.
In our results, first hour values were significantly lower (3.1/3.8) in comparison to post-6 h values (6.9/7.1), when the peak of pain was seen. Other authors have showed the peak of pain precisely in the first hour post-thoracotomy [19]. This could be explained because of the accumulation of residual anesthetics given during the surgery. Most of the procedures were lung resections that required high dosages of intraoperative anesthetics that are not completely eliminated in the first postoperative hour.
Besides, opioid receptors are partially impregnated for several hours after surgery. The pain peak 6 h after surgery could be explained because at that time there are no opioids in blood. Local anesthetic is infused from 0 analgesia. The rest of the values followed a decrease with both anesthetics from the 6 h peak (second dose of local anesthetic). The lowest scores were collected in the 72 h control.
Regarding the literature, TPVB is mainly performed by continuous infusion of the anesthetic [20]. In our management we employed bolus. We believe that this facilitates postoperative management of the patients. In our department we only send post-pneumonectomy patients to intensive care units (ICU) for 24 h. The rest are managed in the ward. And an important part of the feasibility of this policy is the multimodal pain approach.
Nurses in the ward subministrate all the drugs, the bolus of local anesthetic every 6 h intercalated with 2 ml of methamizol, and rescue subcutaneous meperidine if needed. Volumes and concentrations of local anesthetic obtained are similar and toxicity is rare.
We believe that TPVB bolus facilitates postoperative care and monitoring is simplified. Consequently this policy could be more suitably adapted to patients in surgical wards avoiding highly monitored ICU.
Analyzing our data regarding the type of thoracotomy it is remarkable the difference in mean VAS values between AT and PT (Table 3) with a strong statistically significance (p < 0.01) in the mean and all the postoperative hours.
In conclusion, our patients received satisfactory analgesia, as assessed by pain scores. Bupivacaine got better VAS scores (p < 0.05) in mean and after first and 24 h, however the two groups had no difference in the requirement for rescue analgesia. AT showed to be a less painful incision in comparison to PT with statistically significant values both with bupivacaine and ropivacaine (p < 0.01).
No toxicity was observed. Higher concentrations and volumes of local anesthetics could be used to obtain better VAS scores.
Paravertebral catheter placement done by the surgeon ensures the exact location of the infusion of the local anesthetic (visual check).
The multimodal treatment including the TPVB alternated with endovenous methamizol and subcutaneous meperidine as rescue, during the first 72 h (the most painful postoperative period) provides effective analgesia after thoracic surgery.
This management could be considered an alternative to thoracic epidural analgesia.
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Footnotes |
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Presented at the 15th European Conference on General Thoracic Surgery, Leuven, Belgium, June 3–6, 2007. |
References |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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