TITLE: Analgesia in post-thoracotomy patients: Comparison between thoracic epidural and thoracic paravertebral blocks

  ABSTRACT.BACKGROUND:
Acute postoperative pain can cause detrimental effects on multiple organ systems, leading to chronic pain syndromes.

ABSTRACT.OBJECTIVE:
To compare thoracic epidural block (TEB) and paravertebral block (PVB) for relief of postoperative pain in adult patients undergoing thoracotomy.

ABSTRACT.MATERIALS AND METHODS:
In this randomized, single-blinded, prospective study, 60 adult patients of both sexes, belonging to ASA physical status I and II, were scheduled for elective thoracotomy under general anesthesia. They were randomly divided into two groups, A and B of 30 each, who were comparable in terms of demographic parameters and body weight. Group A received TEB and Group B received PVB. All the patients underwent thoracotomy under general anesthesia using a uniform standard anesthetic technique. Thirty minutes before the anticipated end of skin suture, blocks were activated in both the groups with 7.5 ml for TEB and 15 ml for thoracic PVB of 0.25% bupivacaine, along with 1 ml of fentanyl for postoperative analgesia.

ABSTRACT.RESULTS:
Patients receiving PVB for postoperative analgesia experienced better analgesia than those receiving TEB from the immediate postoperative period that lasted longer. Intragroup comparison showed that in the cases receiving TEB, there was a significant statistical difference in preoperative and postoperative values with regard to the mean systolic blood pressure (SBP), mean arterial pressure and mean pulse rate. However, in patients receiving PVB, significant difference in preoperative and postoperative values was seen in mean SBP only.

ABSTRACT.CONCLUSIONS:
We observed longer duration of analgesia with PVB compared to TEB.

BODY.INTRODUCTION:
The primary objective of postoperative analgesia is to provide subjective comfort and alleviate the suffering of a patient, who is recuperating from surgery. Acute postoperative pain can cause detrimental effects on multiple organ systems and development of chronic pain syndromes after certain surgeries (phantom limb pain after amputation, post-thoracotomy syndrome).[1]  Moreover, pain increases skeletal muscle tension and this can lead to decreased thoracic compliance, splinting and hypoventilation, particularly in patients undergoing abdominal and thoracic surgery. The American Pain Society now recommends that pain should be treated as the "5th vital sign" and monitored regularly along with pulse and blood pressure.[2]  An effective regimen of postoperative analgesia not only shortens the time to recovery after surgery, but also helps in avoiding the pulmonary, hemodynamic and metabolic complications of acute post surgical pain. Thoracotomy and upper abdominal surgery are associated with severe postoperative pain and marked impairment of respiratory function.[3]  Two broad groups of the analgesic option available are systemic analgesia and regional analgesia. Compared to systemic opioids, neuroaxial analgesia and peripheral nerve blockade techniques can provide superior analgesia while avoiding majority of side effects of opioids. Among the non-epidural techniques for pain management are thoracic paravertebral block (PVB) which achieves similar quality of analgesia as that of epidural analgesia, but with lesser incidence of hypotension and urinary retention. So, the most promising technique appears to be thoracic PVB and is a valuable alternative to thoracic epidural analgesia.[4] Epidural analgesia with local anesthetic, opioid or both has become commonplace and has been regarded as the "gold standard".[5] Epidural blockade has been shown to reduce the intraoperative surgical stress response and has possible advantages for cardiovascular, respiratory, coagulation, gastrointestinal, metabolic and immune function.[6]  With thoracic epidurals causing hypotension, neurologic injury, and are contraindicated in the presence of coagulopathy or local sepsis, thoracic PVB has enjoyed a resurgence in recent years.[7] Placement of local anesthetic within the paravertebral space produces unilateral somatic and sympathetic block, which is advantageous for unilateral surgical procedures of the chest and abdomen; it is simple, safe, easy to learn and with a low incidence of complications.[89]  Paravertebral blockade is an appealing option in patients in whom epidural analgesia may be contraindicated (local sepsis, coagulopathy, pre-existing neurologic disease and difficult thoracic spine anatomy). PVB is presented as an alternative to epidural analgesia, but anatomically the two methods represent epidural analgesia from two different approaches.[10]  The main aim of this study was to compare thoracic epidural block (TEB) and PVB for relief of postoperative pain in adult patients undergoing thoracotomy.

BODY.MATERIALS AND METHODS:
The randomized, parallel group control trial was carried out in the Department of Anesthesiology at Institute of Postgraduate Medical Education and Research, Kolkata, between February 2007 and August 2008. The study protocol was approved by the Institutional ethics committee. Sixty adult patients between the age of 20 and 65 years, belonging to both sexes and of ASA physical status I and II, undergoing posterolateral thoracotomy (for resection of hydatid cyst, lobar resection, chest wall tumor, closed mitral commissurotomy, and so on) were selected as the study population. All of them were prepared for general anesthesia as a standard procedure.  All the patients or their caregivers undergoing thoracotomy were explained about the purpose of the study and were ensured strict confidentiality. Exclusion criteria included unwilling patients, general contraindications for epidural anesthesia, disorders of homeostasis or thoracic spine abnormalities, displaying signs and symptoms of systemic infection or patients having local sepsis or those with diabetes mellitus, hypertension, ischemic heart disease, chronic obstructive pulmonary disease and other major systemic illness, history of allergy to the study medications, renal insufficiency or liver dysfunction. Exclusion criteria also included patients having chronic pain as the analgesic requirements of these patients would be very different from other patients. Written informed consent was obtained from each of the patients prior to the study. They were given the options not to participate in the study if they wanted.  The subjects were then subsequently randomized into two groups, A and B, to receive two different types of spinal block and a particular block, epidural and paravertebral, respectively, representing equal numbers and equal distribution of sexes in both the groups. The patients were explained about the nature of thoracotomy pain and were asked for rescue analgesia postoperatively, whenever necessary.  In Group A patients, a thoracic epidural 18-G multiorifice catheter was placed 2 cm inside the epidural space through a 16-G Tuohy epidural needle using a Para median approach at T5–T6 interspace, maintaining strict aseptic precaution. The epidural space was identified by loss of resistance technique using saline. A test dose of 3 ml of 2% lignocaine with 1:200,000 adrenaline was administered through the epidural catheter port on negative aspiration of cerebrospinal fluid (CSF) and blood. This was to rule out accidental intrathecal or intravascular placement. Similarly, in Group B patients, a multiorifice 18-G epidural catheter was placed through a 16-G epidural Tuohy needle 2 cm inside T5–T6 paravertebral space, gliding the needle over the transverse process of T6 vertebra on the proposed side of operation. Loss of resistance technique with saline was used to identify the space. Also, 3 ml of 2% lignocaine with 1:200,000 adrenaline was administered through the epidural catheter on negative aspiration for blood, CSF and air. After the catheter placement, the patients were put back to horizontal supine position and subsequently general anesthesia was instituted with endotracheal tube and controlled ventilation. The induction agent was thiopentone sodium (5 mg/kg BW, i.v.). Muscle relaxant used was vecuronium bromide (100 μg/kg BW, i.v.) initially for intubation and 20 μg/kg BW i.v. top-ups. For intraoperative analgesia, fentanyl (3 μg/kg BW, i.v.) initially and 0.5 μg/kg BW i.v. top-ups was given until the activation of block. Maintenance was done with isoflurane (0.5–1%) in 50% N2O and O2.  In both the groups, TEB or PVB as applicable, was activated 30 minutes prior to the anticipated completion of surgery and the time was noted. In Group A, 7.5 ml of 0.25% bupivacaine at the proposed site along with 50 μg fentanyl (1 ml) was administered through the epidural catheter as a single injection.[11] In Group B, 15 ml of 0.25% bupivacaine (calculated as 3 ml/paravertebral segmental space for achieving analgesia in dermatomes of T4, T5, T6, T7, T8 segments) along with 50 μg fentanyl (1 ml) was administered through the catheter.[12]  Hemodynamic parameters [Pulse rate (P), systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP)] were recorded as baseline and at regular intervals (half-an-hour interval) from activation of block throughout the procedure. Thirty percent fall of BP from baseline value was considered as hypotension. Assessment of the duration of analgesia was followed up by the subjective compliant of the patients and the first top-up dose was regarded as the effective duration of analgesia. When the patients requested for rescue analgesic, was considered the end point of the study. So, we have presented only summative data noted prior to start of the operation and at the end point of the study in the "Results" section.

BODY.MATERIALS AND METHODS.STATISTICAL ANALYSIS:
The data were entered into MS Excel spread sheets and analysis was carried out. The procedures involved were transcription, preliminary data inspection, content analysis and interpretation. Parameters used to compare the groups statistically were demographic characteristics, duration of analgesia, hemodynamic parameters. Numerical parametric data were presented as mean±standard deviation, compared by t-test, and a P value of less than 0.5 was considered as significant. The statistical analyses were done by using Graph Pad InStat "version 3" software.

BODY.RESULTS:
In this study, 60 adult patients (ASA physical status I and II) were randomly assigned to two groups to receive either TEB or PVB for providing postoperative analgesia. Patients who received TEB were assigned to Group A, and those who received PVB were assigned to Group B. In both the groups, the sexes were equally represented. In a majority of the subjects, there was no incidence of adverse events like failure of placement of block and incidences of dural puncture in both the groups, except in one patient of TEB and three patients of PVB wherein vascular puncture were seen during the block placement. In these four patients, the block was placed by reinsertion of needle later. However, patients in either group did not experience any other additional complications like urinary retention, nausea and vomiting, coughing and other pulmonary complications like pleural puncture.  The mean age and weight of the patients of TEB and PVB were comparable. The body weights were in a range of 52 to 62 kg. There were no statistically significant differences between the two groups with respect to these demographic variables [Table 1].   Table 1 Demographic characteristic of the subjects   Pulse rate (P), SBP, DBP and MAP were monitored at the same points. There was no significant difference in preinduction hemodynamic parameters between the two groups. The hemodynamic profiles of the patients monitored at the end of the study were taken as an indirect indicator of postoperative pain. All the postoperative values were higher than the preoperative values as the direction of change. However, intergroup comparison does not show any significant difference in mean SBP and mean DBP. A statistically significant difference existed between the MAP and mean P among the groups. While comparing the parameters of mean, median and maximum duration of the effective duration of analgesia, patients receiving PVB for postoperative analgesia experienced better analgesia than those receiving TEB from the immediate postoperative period that lasted longer and this difference was statistically significant [Table 2].  Table 2 Comparison of clinical variables between two groups   Intra group comparison showed that in group A cases receiving TEB, there was a significant statistical difference in preoperative and post operative values in regard to mean systolic blood pressure, mean arterial pressure and mean pulse rate per minute. However, there was no difference in mean diastolic blood pressure. However, hypotension was not observed in our series. However, in the PVB group, significant difference in preoperative and postoperative values was seen in mean SBP only. Values with regard to mean DBP, MAP and mean P were statistically insignificant [Table 3].  Table 3 Changes in hemodynamic profiles within groups both preoperative and after activation of block 

BODY.DISCUSSION:
Our study showed no significant statistical differences between the two groups with respect to demographic variables and pre-induction hemodynamic parameters. In the hemodynamic parameters, all the postoperative values were higher than the preoperative values as the direction of change. However, a statistically significant difference was observed between the two groups in terms of MAP and mean P among the groups. PVB achieved better pain control in comparison to TEB, and in the effective duration of analgesia, the difference was statistically significant.  In a similar study by Mathew et al.,[13] the results were quite similar as that of the present study. They observed good postoperative pain relief at rest in paravertebral and extradural groups, up to 20 hours.  Pertunnen et al., in 1995, studied 45 patients randomly allocating them into three groups to receive intercostals block, a continuous thoracic epidural injection and continuous paravertebral infusion of bupivacaine. There was no significant difference between the groups in pain reduction, respiratory depression or adverse event after 20 hours of block placement.[4]  In a systematic review and meta-analysis of 10 relevant randomized trials comparing PVB with TEB for postoperative pain relief in thoracic surgery, Davies et al. concluded that PVB and Thoracic Epidural Anaesthesia (TEA) provide comparable pain relief after thoracic surgery. It was also observed in this study that although there was no difference in pain scores between PVB and TEB, there was a statistically significant reduction in complications with PVB. PVB has a better side effect profile and is associated with a reduction in pulmonary complications. PVB is associated with less urinary retention, less postoperative nausea and vomiting, less hypotension and a reduction in pulmonary complications.[14]  Researchers in different set-ups observed that that paravertebral bupivacaine was comparable with thoracic epidural bupivacaine for pain scores and supplementary analgesic requirements.[15–17]  Bimston et al. reported that pain relief was better in patients who received paravertebral bupivacaine plus fentanyl compared with patients who received thoracic epidural bupivacaine plus fentanyl, whereas there were no significant differences in supplementary analgesic requirements.[18]  A survey of analgesic techniques, after thoracotomy, in Australian hospitals showed that 79% of respondents regarded epidural blockade as the best available technique.[19] A similar survey of UK practice, after upper abdominal surgery, found that 80% of anesthetists considered epidural analgesia to be the best mode of pain relief.[20] Researchers have shown thoracic PVB to be an effective form of analgesia after thoracotomy.[21]  A systematic review of randomized studies at the Division of Cardiothoracic Surgery, University of North Carolina, revealed that the intercostal nerve blockade for post-thoracotomy pain relief can be accomplished by continuous infusion of local anesthetics. They concluded that an extrapleural infusion is at least as effective as an epidural and significantly better than narcotics alone. The other techniques of intercostal blockade do not offer an advantage over narcotics alone.[22]  In a study conducted in the Bradford Royal Infirmary, UK, patients were allocated randomly to receive thoracic epidural bupivacaine or thoracic paravertebral bupivacaine. Both epidural and PVBs were effective in controlling post-thoracotomy pain. Side effects, especially nausea, vomiting and hypotension, were troublesome only in the epidural group. The researchers concluded that with these regimens, PVB was superior to epidural bupivacaine.[23]  In a prospective, randomized study at the University Hospital, Zürich, Switzerland, pain control was analyzed in patients undergoing elective lobectomy or bilobectomy with two groups: one received a continuous extrapleural intercostal nerve blockade (T3 through T6) with bupivacaine through an indwelling catheter, the other was administered a combination of local anesthetics (bupivacaine) and opioid analgesics (fentanyl) through a thoracic epidural catheter. Both the techniques were safe and highly effective in terms of pain relief and recovery of postoperative pulmonary function. The results suggested that extrapleural intercostal analgesia might be a valuable alternative to thoracic epidural analgesia for pain control after thoracotomy and should particularly be considered in patients who do not qualify for thoracic epidural analgesia.[24]  A prospective, randomized, blinded study at University of Parma, Department of Anaesthesiology and Pain Therapy, Italy, was conducted to compare the analgesic efficacy of continuous paravertebral and epidural analgesia for post-thoracotomy pain patient satisfaction with the analgesia technique. The study concluded that continuous thoracic paravertebral analgesia is as effective as epidural blockade in controlling post-thoracotomy pain, but is associated with less hemodynamic effects.[25]  In a meta-analysis conducted at the Department of Thoracic Surgery, Guy's and St Thomas Hospital, Great Maze Pond, London, PVB was found to be of equal efficacy to epidural anesthesia, but with a favorable side effect profile and lower complication rate. The reduced rate of complication was most marked for pulmonary complications and is accompanied by quicker return to normal pulmonary function. They concluded that intercostal analgesia, in the form of PVB, can be at least as effective as epidural analgesia.[26]  However, Messina et al. reported that epidural analgesia is more efficient than paravertebral continuous block at reducing pain after thoracic surgery. In their study, there was a statistically significant increase in median patient-controlled use of morphine in the paravertebral group than in the epidural group.[27]  In the present study, there was no significant change in the HR between the two groups. This concurs with the studies of Mathew et al.[13]  Group A patients with TEB experienced reduction of SBP and MAP postoperatively, though hypotension was not observed in our series. The significant incidence of hypotension in thoracic epidural group compared to PVB group was observed by Mathew et al.[13]

BODY.DISCUSSION.STRENGTH OF STUDY:
Our study findings reflected that the use of PVB was an effective alternative to TEB in a resource-poor set up in the developing countries. To the horizon of our knowledge, this is the earliest study reported from eastern India.

BODY.DISCUSSION.LIMITATIONS OF STUDY:
Our study had several limitations. We did not perform any testing to determine the level and the depth of the thoracic blockade and any pain scoring system, which would have been desirable. The time when the patient asked for rescue analgesia due to pain at rest was considered as the end point of study. It could have been better if we had performed some pulmonary function tests and arterial blood gas analysis to assess the impact of analgesia on the respiratory function to detect any postoperative complications.

BODY.DISCUSSION.FUTURE DIRECTIONS OF THE STUDY:
In the literature, there are reports declaring that there is no statistically significant difference between the PVB and the TEB techniques and mentioning that both techniques can be performed safely. Moreover, further studies were required to determine whether PVB is equivalent to TEB combining LA plus opioid, in terms of pain relief and morbidity.

Question: Compared to Paravertebral block what was the result of Epidural block on Effective duration of analgesia?
Evidence: While comparing the parameters of mean, median and maximum duration of the effective duration of analgesia, patients receiving PVB for postoperative analgesia experienced better analgesia than those receiving TEB from the immediate postoperative period that lasted longer and this difference was statistically significant
Answer: significantly decreased