Spinal vs. Epidural Anesthesia
Spinal and epidural anesthesia are both forms of local anesthesia injected near the spinal cord.1 Both block pain from an entire region of the lower body, such as the lower abdomen, pelvis, and lower extremities, and are used in various operations. Spinal anesthesia, also known as a spinal block, involves the injection of an anesthetic into the cerebrospinal fluid of the subarachnoid space, which is part of the spinal cord.2 The injection site is first numbed with a local anesthetic, after which the needle is inserted into the spinal canal, usually without use of a catheter.1 Epidural anesthesia is administered into the space between the spinal column and outer membrane of the spinal cord (this membrane is known as the dura mater; “epidural” means “upon the dura”).
Several important differences exist between these two types of anesthesia. A catheter is typically used during the administration of epidural anesthesia, while the use of one for spinal anesthesia is uncommon.3 The onset of action of the two also differs: a spinal block takes effect within 5 minutes of administration, while an epidural takes approximately 25-30 minutes to induce the loss of sensation.4 Epidural anesthesia is most commonly used during childbirth. Epidural anesthesia, which uses a catheter, is a better option for childbirth than spinal anesthesia, since a single injection often is not sufficient to last throughout the entire birth and a catheter allows for the continuous administration of anesthesia.5
Complications for both have been reported, but both are overall extremely safe. A 2014 review of the National Anesthesia Clinical Outcomes Registry (NACOR) showed that among 80,000 cases of anesthesia (which included both spinal and epidural), complications existed in 2.78% of cases, with most resulting from errors such as over- or under-dosing or the use of expired drugs.6 Of particular concern for anesthesiologists during obstetric anesthesia is a dural puncture or “wet-tap,” which occurs when the needle punctures the dura and causes a leak of spinal fluid. A dural puncture can cause a postdural puncture headache, and, in rare cases, can lead to cerebral venous thrombosis, subdural hematoma, and seizures.7 While the NACOR review reported that dural punctures only occurred in 0.19% of cases, other estimates place this number as high as 1.5%.8
Combined spinal and epidural anesthesia (CSE) is designed to address the shortcomings of both. Spinal anesthesia has a fixed duration of action and carries a risk of extended block, while epidural anesthesia has a higher incidence of insufficient block. In CSE, the two are combined, with the goal of having the advantages of one anesthesia to compensate for the disadvantages of the other.9 In the single-space technique (SST), the spinal anesthetic and epidural are inserted into the same location, while the two are administered about 1-2 lumbar segments distal from one another in the double-space technique (DST).10 Skin punctures are less common when SST is used, which may decrease the risk for other complications, although no quantitative studies have been performed comparing the safety of the two methods.11 Perhaps unsurprisingly, the dosages for spinal and epidural anesthesia are each lower than they are when administered alone.12
References
1. Epidural and Spinal Anesthesia | Michigan Medicine. https://www.uofmhealth.org/health-library/rt1583.
2. Varaday, S. Subarachnoid Spinal Block: Overview, Periprocedural Care, Technique. Medscape (2020).
3. “Epidurals and Spinals: Information about Their Operation for Anyone Who May Benefit from an Epidural or Spinal .” NHS Royal Berkshire, Apr. 2016, www.royalberkshire.nhs.uk/patient-information-leaflets/Anaesthetics/Anaesthetics%20epiduraandspinalsls.htm.
4. Burm, A.G. Clinical Pharmacokinetics of epidural and spinal anesthesia. Clin. Pharmacokinet. 5, 283-311 (1989).
5. Pregnancy and birth: Epidurals and painkillers for labor pain relief. InformedHealth.org [Internet] (Institute for Quality and Efficiency in Health Care (IQWiG), 2018).
6. Obstetric Outcomes Data from the Anesthesia Quality Institute National Anesthesia Clinical Outcomes Registry. http://www.asaabstracts.com/strands/asaabstracts/abstract.htm?year=2014&index=13&absnum=3862.
7. Plewa, M. C. & McAllister, R. K. Postdural Puncture Headache. in StatPearls (StatPearls Publishing, 2021).
8. Inadvertent dural puncture/wet tap and PDPH management – Clinical Pain Advisor. https://www.clinicalpainadvisor.com/home/decision-support-in-medicine/anesthesiology/inadvertent-dural-puncture-wet-tap-and-pdph-management/.
9. Felsby, S. & Juelsgaard, P. Combined Spinal and Epidural Anesthesia. Anesth. Analg. 80, 821–826 (1995).
10. Brownridge, P. Central neural blockade and caesarian section. Part 1: Review and case series. Anesth. Intensive Care 1 33-41 (1979).
11. Morgan, P. Spinal anaesthesia in obstetrics. Can J Anaesth 12 1145-63 (1995).
12. Rawal, N., Schollin, J. & Wesström, G. Epidural versus combined spinal epidural block for cesarean section. Acta Anaesthesiol. Scand. 32, 61–66 (1988).