2.  Case presentation  Literature review  Summary & Recommendations

3.  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.  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.  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.  Immediately after spinal, pt positioned supine, O2 by FM, propofol infusion started  Kefzol 2g IV given  Nurses placing foley, pt responsive, breathing comfortably…

7.  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.  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.  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. Hocking et al, 2004

11.  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.  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. McClure et al, 1982

14.  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.  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.  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.  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.  Most important factors influencing spread of local anesthetics in spinal anesthesia: › Baricity of solution › Patient position › Dose used

19.  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.  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? Reg Anes Pain Med. 1998. 23(4): 347-351.