Epidural anaesthesia

Helen Lindsay

 

In terms of pain scores and the quality of analgesia following major open abdominal surgery, an effective epidural is regarded as the gold standard when compared to parental opioids (1, 2).  Benefit is assumed to be associated with this in terms of patient satisfaction and improved recovery with reduced morbidity, however the evidence is conflicting.  While the benefit of superior analgesia also appears to apply when compared to alternative local anaesthetic techniques, the clinical significance of this benefit is uncertain. 

In a systematic review of all randomised control trials prior to 1997, neuraxial block was associated with a statistically significant reduction in mortality, deep vein thrombosis, pulmonary embolus, transfusion, pneumonia and respiratory depression (3).  Two randomised controlled trials were published subsequently (4, 5).  They were much larger than those completed previously and designed to have adequate power to confirm beneficial effect.  When compared to a ‘balanced technique’ with opioids these studies found no association between the use of an epidural and a reduction in major complication (4) other than respiratory failure in high risk patients having high risk procedures, with a number needed to treat of 15 (5). 

Another meta-analysis comparing epidural with systematic analgesia has since confirmed the association between epidural use and a reduced odds of pneumonia (6).  Although it is noted that this effect was weaker in a sub-analysis where opioid patient controlled analgesia (PCA) was part of the systemic analgesia intervention.  The size of the relative benefit also reduced over the time-frame of the study from 1971 to 2006, with a reduction in the incidence of post-operative pneumonia in the systemic analgesia group from 34% to 12%, while a rate of 8% remained stable in the epidural group.  A similar reduction in relative benefit is described in relation to thromboembolic complications with the introduction of modern thromboprophylactic guidelines (7).   A retrospective cohort study of over 250,000 patients undergoing elective intermediate-high risk non-cardiac surgery from 1994-2004 has also affirmed that epidural use was associated with a reduced relative risk of death at 30 days (RR 0.89, 95% CI 0.81-0.98, P=0.02), but again that this benefit was small, with a number needed to treat of 477 (8).  It also indicated a real benefit in the composite group of all surgical procedures, orthopaedic and thoracic surgery but not for abdominal and vascular surgery. 

In contrast, a post-hoc analysis of POISE trial patients neuraxial block was associated with an increased risk of a composite outcome that included cardiovascular death, non-fatal myocardial infarction and non-fatal cardiac arrest within 30 days of randomization to the trial (287 (7.3%) in the neuraxial group, 229 (5.7%) in the non-neuraxial group; OR 1.24, 95% CI 1.02-1.49, P=0.03) (9).  While the authors noted this to be a concerning finding conflicting with results previously published, there is a plausible means of causation with the association of epidural use with hypotension (5, 6, 9), and an increasing body of literature suggesting that perioperative hypotension is a risk factor for adverse perioperative outcome (10, 11).  There are however recognized limitations of the study due to the nature of its design.  The patients studied were a very specific subset of patients at high risk of postoperative cardiovascular morbidity, who were not randomised to receive a neuraxial block but rather treated at the discretion of the their anaesthetist.  While the paper extensively describes techniques to reduce bias, including the use of propensity score techniques, its major limitation was the inability to control for unmeasured and unknown confounding factors.  Recognizing this Leslie et al. state that the study does not provide evidence that epidurals should be contra-indicated in high-risk patients.  Rather they propose that epidural can no longer be justified by clinicians or patients based on beneficial perioperative cardiovascular outcomes. 

Every analgesic modality currently available comes with its benefits and compromises, and epidurals are no exception.  Firstly epidurals do not always work, with a failure rate of up to 30% quoted in the literature (12).  Secondly they are associated with rare but significant complications (13).  To limit this risk there are various absolute and relative contraindications that may restrict the utility of epidurals, sepsis and coagulopathy being particularly relevant to patients presenting for abdominal surgery.  Thirdly epidurals are relatively resource intensive and the provision of infrastructure necessary for safe and effective practice may not be feasible.  These factors create a necessity for viable alternative peripheral regional techniques.  However there are various theoretical benefits of peripheral regional techniques over epidural that may make them preferable even when epidural is possible.  These benefits include:

• Greater ease of placement in the anaesthetized patient.

• Reduced risk of complication with concurrent anticoagulation use or peri-operative coagulopathy.

• Less hypotension and hemodynamic instability in the absence of a sympathetic block, being useful in the shocked, critically unwell patient, or in general surgical patients where iatrogenic fluid overload is potentially associated with worse clinical outcome (14).

• Increased potential for mobility, with no lower limb block and a reduced need for mandatory infusion devices/IV poles. 

• A reduced risk of urinary retention and the need for invasive catheterization.

• The infectious complication risk is yet to be defined in terms of placement in the septic patient, but the implications of an epidural abscess are of graver significance. 

 

While adequate analgesia is an important aspect of a patient’s post-operative experience and may have implications in the development of chronic post-operative pain (2), pain scores provide a very narrow assessment of recovery.  Increasingly there is a shift to assessing functionality, with measures such as the resumption of normal bowel habit, mobilization and time to discharge.  This point is highlighted in more recent randomised control trials that specifically looked at colorectal surgery.  In a systematic review comparing outcomes between post-operative epidural analgesia and parenteral opioids, pain scores and the rate of ileus were reduced in the epidural group, while the rate of pruritus, urinary retention and hypotension (not defined) were increased, and the length of stay was not significantly different between each intervention group (15).   Similar results where found in a randomised control trial in patients having open liver resection surgery comparing thoracic epidural with local infiltration through surgically placed subfascial wound catheters and an opioid PCA (16). While superior pain scores at rest and with movement were achieved in the epidural group (see Figure 5), the time to first mobilization was similar, the median number of steps taken in the first 48 hours was significantly greater (2 steps in the epidural group, 6 steps in the local infiltration group, P=0.040), and the median length of stay in hospital was significantly reduced in the local infiltration group (6.0 days in the epidural group,  4.5 days in the local group, P=0.044).

Figure 5: Mean scores following open liver resection, in patients randomised to either thoracic epidural or local infiltration through a surgical placed subfascial wound catheter and an opioid PCA. Courtesy of Revie et al (16)

 

The feasibility of a randomised control trial to definitively provide evidence of a benefit or harm with epidural use is likely to be impractical (17).  The entity of what an epidural can constitute is hugely variable in terms of where it is placed, dosed and managed.  Any benefit is likely to vary depending on the surgery completed, and the study population to power a study investigating potential adverse events would require upward of 50,000 subjects (18).  The current evidence base suggests that patient selection is key, recognizing that a low incidence of major complication must be balanced against the limited evidence of modest benefits in terms of improved pain control and reduced pulmonary complication in high risk patients having high risk surgery (7).  Currently no robust evidence base provides for rationalization of the benefits of reduction in the surgical stress response and ileus, versus the risks of hypotension and the uncertain impact on anastomotic breakdown.  Regular institutional audit providing cost-benefit data is a recommended tool to inform this decision and help guide clinicians as to the role of epidural and alternative analgesia techniques in their practice and institution (7).

 

 References

1. Block BM, Liu SS, Rowlingson AJ, Cowan AR, Cowan JA, Jr., Wu CL. Efficacy of postoperative epidural analgesia: a meta-analysis. Jama. 2003;290(18):2455-63.

2. Macintrye PE SD, Schug SA, Visser EJ, Wakler SM,. Acute Pain Management: Scientific Evidence. 3rd ed. Melbourne: Australia New Zealand College of Anaesthetists & Faculty of Pain Medicine; 2010.

3. Rodgers A, Walker N, Schug S, McKee A, Kehlet H, van Zundert A, et al. Reduction of postoperative mortality and morbidity with epidural or spinal anaesthesia: results from overview of randomised trials. BMJ (Clinical research ed). 2000;321(7275):1493.

4. Park WY, Thompson JS, Lee KK. Effect of epidural anesthesia and analgesia on perioperative outcome: a randomized, controlled Veterans Affairs cooperative study. Annals of surgery. 2001;234(4):560-9; discussion 9-71.

5. Rigg JR, Jamrozik K, Myles PS, Silbert BS, Peyton PJ, Parsons RW, et al. Epidural anaesthesia and analgesia and outcome of major surgery: a randomised trial. Lancet. 2002;359(9314):1276-82.

6. Popping DM, Elia N, Marret E, Remy C, Tramer MR. Protective effects of epidural analgesia on pulmonary complications after abdominal and thoracic surgery: a meta-analysis. Archives of surgery (Chicago, Ill : 1960). 2008;143(10):990-9; discussion 1000.

7. Rawal N. Epidural technique for postoperative pain: gold standard no more? Regional anesthesia and pain medicine. 2012;37(3):310-7.

8. Wijeysundera DN, Beattie WS, Austin PC, Hux JE, Laupacis A. Epidural anaesthesia and survival after intermediate-to-high risk non-cardiac surgery: a population-based cohort study. Lancet. 2008;372(9638):562-9.

9. Leslie K, Myles P, Devereaux P, Williamson E, Rao-Melancini P, Forbes A, et al. Neuraxial block, death and serious cardiovascular morbidity in the POISE trial. British journal of anaesthesia. 2013;111(3):382-90.

10. Walsh M, Devereaux PJ, Garg AX, Kurz A, Turan A, Rodseth RN, et al. Relationship between intraoperative mean arterial pressure and clinical outcomes after noncardiac surgery: toward an empirical definition of hypotension. Anesthesiology. 2013;119(3):507-15.

11. Sun LY, Wijeysundera DN, Tait GA, Beattie WS. Association of Intraoperative Hypotension with Acute Kidney Injury after Elective Noncardiac Surgery. Anesthesiology. 2015.

12. Hermanides J, Hollmann MW, Stevens MF, Lirk P. Failed epidural: causes and management. British journal of anaesthesia. 2012;109(2):144-54.

13. Cook TM CD, Wildsmith JA. Major complications of central neuraxial block London: The Royal College of Anaesthetists, 2009.

14. Wilkinson KM, Krige A, Brearley SG, Lane S, Scott M, Gordon AC, et al. Thoracic Epidural analgesia versus Rectus Sheath Catheters for open midline incisions in major abdominal surgery within an enhanced recovery programme (TERSC): study protocol for a randomised controlled trial. Trials. 2014;15:400.

15. Marret E, Remy C, Bonnet F. Meta-analysis of epidural analgesia versus parenteral opioid analgesia after colorectal surgery. The British journal of surgery. 2007;94(6):665-73.

16. Revie EJ, McKeown DW, Wilson JA, Garden OJ, Wigmore SJ. Randomized clinical trial of local infiltration plus patient-controlled opiate analgesia vs. epidural analgesia following liver resection surgery. HPB : the official journal of the International Hepato Pancreato Biliary Association. 2012;14(9):611-8.

17. Choi PT, Beattie WS, Bryson GL, Paul JE, Yang H. Effects of neuraxial blockade may be difficult to study using large randomized controlled trials: the PeriOperative Epidural Trial (POET) Pilot Study. PloS one. 2009;4(2):e4644.

18. Barrington MJ, Scott DA. Do we need to justify epidural analgesia beyond pain relief? Lancet. 2008;372(9638):514-6.

CONTACT

Administrative contact

Please contact Karen Patching -
Desk phone: +64 (0) 9 375 7085
Email: karenp@adhb.govt.nz

c/- Department of Anaesthesia & Perioperative Medicine
Level 8 - Support Building, Auckland City Hospital
PO Box 92024, Auckland, New Zealand