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Factors affecting distribution of spinal anesthesia

Factors affecting distribution of spinal anesthesia. Vivianne Tawfik, MD, PhD CA-1 Department of Anesthesia. Overview. Case presentation Literature review Summary & Recommendations. Case presentation. 59yo F s/f L total knee replacement

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Factors affecting distribution of spinal anesthesia

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  1. Factors affecting distribution of spinal anesthesia Vivianne Tawfik, MD, PhD CA-1 Department of Anesthesia

  2. Overview • Case presentation • Literature review • Summary & Recommendations

  3. Case presentation • 59yo F s/f L total knee replacement • PMHx: HTN, tobacco use (15 pack-years), chronic knee pain, obesity • Allergies: Tetracycline- hives • Meds: Atenolol, lisinopril, HCTZ, ASA, tramadol, tylenol, naprosyn

  4. Case (cont) • ECG: NSR • TTE: overall normal, EF 65%, mod LVH • Pre-op labs: WNL • Vitals: 62, 140/84, 5’6”, 117 kg • Airway: Mal 4, limited mouth opening but normal ROM

  5. Case (cont) • Anesthesia plan: • Femoral nerve catheter + spinal + MAC • Spinal difficult to place 2/2 obesity requiring multiple attempts • Spinal drugs delivered: • Isobaric bupivicaine 0.5% 2.5 cc + astromorph 200 mcg

  6. Case (cont) • Immediately after spinal, pt positioned supine, O2 by FM, propofol infusion started • Kefzol 2g IV given • Nurses placing foley, pt responsive, breathing comfortably…

  7. Case (cont) • Three minutes later, patient spitting up saliva, eyes roll back, unresponsive, apneic, hypotensive (BP 65/42) • Bag mask ventilation started, oral airway placed with good air movement • After ~5 minutes patient responsive, complaining of need to clear her throat and difficulty breathing • Decision made to intubate and initiate GA

  8. Intrathecal drug spread • Interpatient variability in LA spread noted by August Bier in 1899 • Termed “Lauenhaft” or “waywardness” • Methods used to test level (back in 1899): • ‘‘ . . . sensual perception of needle pricks to the thigh, tickling of the soles of the feet, a small incision in the thigh, pushing a large helved needle down to the femur, strong pinching with dental forceps, application of a burning cigar, pulling out pubic hairs, a strong blow with an iron hammer against the tibia, vigorous blows with the knuckles against the tibia, and strong pressure on a testicle’’

  9. LA spread • Stage 1: Spread of LA by CSF displacement and local currents caused by injection • Stage 2: Interplay between densities of CSF and LA solution under influence of gravity • Multiple factors affecting these mechanisms…

  10. Factors affecting intrathecal drug spread Hocking et al, 2004

  11. Baricity • Ratio of the density (mass/volume) of the LA solution divided by the density of CSF (1.0003) • Hypobaric = LA + water, <0.9990 • Isobaric = LA + saline • Hyperbaric = LA + dextrose, > 1.0010 • Affected by gravity and positioning

  12. Volume/Dose/Concentration • Difficult to change one factor alone • Most studies show no effect of volume or concentration • Dose may have a small effect on block height: • Two studies showed significantly lower blocks with 10mg vs. 15 or 20 mg isobaric bupivicaine Bernards CM.

  13. Effect of speed of injection and volume on LA spread McClure et al, 1982

  14. Patient position • Should have no effect on a “truly” isobaric solution • Using a hyperbaric solution injected in a sitting patient used for “saddle block” • Can have an influence on LA spread up to 60 minutes after the dose is given

  15. Technique-related effects • Level of injection • Can have some effect as an increase in injection site of one level can lead to significantly increased cephalad spread • Barbotage • Repeated aspiration and re-injection of CSF to produce currents- likely minimal effect

  16. Technique-related effects • Needle type/alignment • Possible small effect if opening is aimed cephalad • Para-median approach usually results in cephalad spread b/c of higher level of initial injection than with midline approach

  17. Patient characteristics • Sex • Females have lower CSF density which can affect baricity of solution • Age • At extremes of age there is an increase in the maximum spread • Height • No effect because increases in height usually related to longer limbs, not longer spine • Weight • Possible higher block in obesity related to: • Epidural fat compression of the dural sac • Higher initial site of injection than intended 2/2 poor landmarks • Distribution of adipose in the supine position

  18. Summary • Most important factors influencing spread of local anesthetics in spinal anesthesia: • Baricity of solution • Patient position • Dose used

  19. Back to our case… • Isobaric solution could have been slightly hypobaric as CSF density is variable • Dose of injection was 12,5mg • Patient supine but obesity likely resulted in slight Trendelenberg position • Injected relatively quickly as case already delayed from multiple attempts at spinal • Obesity likely led to higher site of injection than intended (L1-2?)

  20. References • Bernards CM. Epidural and spinal anesthesia. Chapter 37. • Hocking G, Wildsmith JAW. Intrathecal drug spread. Br. J. Anes. 2004. 93(4): 568-78. • McClure JH, Brown DT, Wildsmith JAW. Effect of injected volume and speed of injection on the spread of spinal aneshesia with isobaric amethocaine. Br. J. Anes. 1982. 54: 917. • Stienstra R, Veering BT. Intrathecal drug spread: Is it controllable? RegAnes Pain Med. 1998. 23(4): 347-351.

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