Case presentation Literature review Summary & Recommendations 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 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 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 Immediately after spinal, pt positioned supine, O2 by FM, propofol infusion started Kefzol 2g IV given Nurses placing foley, pt responsive, breathing comfortably… 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 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’’ 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… Hocking et al, 2004 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 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. McClure et al, 1982 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 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 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 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 Most important factors influencing spread of local anesthetics in spinal anesthesia: › Baricity of solution › Patient position › Dose used 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?) 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.