Factors affecting distribution of spinal anesthesia

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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.

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