Page 94 - JSOM Fall 2024

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Loco-regional anesthesia risks and toxicity will be discussed without epinephrine and 4mg/kg with epinephrine. Add-
further in the pharmacology section. ing epinephrine in a dose between 1:200,000 (5µg/mL) and
1:100,000 (10µg/mL) to local anesthetics has many benefits
Administration of Regional Anesthesia regarding nerve blockage. The main benefits are reductions in
in Austere Environments bleeding and systemic resorption of local anesthetic (improv-
Today’s conflicts may be punctuated by hybrid threats that ing onset and duration), allowing the provider to increase the
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could widen the battlefield into a multi-domain battlespace. local anesthetic dose to the referred toxicity dose with epi-
Multi-domain operations describe operations occurring in the nephrine. 21,22 This effect is mainly due to the vasoconstriction
five domains (land, air, maritime, cyber, and space) with the created in the tissue around the nerves. With a 1:200,000 con-
aim of regaining superiority in a contested and access-denied centration of epinephrine, blood flow is reduced up to 80%.
world (anti-access/area denial [A2/AD]). This leads to reduced A supplementary trigger system (inherent negative aspiration
freedom of movement for Forces and, consequently, a decrease remaining the most important trigger system) to alert the pro-
in evacuation capacity. Because SOF medical elements tend vider to slight tachycardia indicative of intravascular injection
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to operate fully embedded into irregular elements, adhering can be benficial. In the case of intravascular injection, the
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to their medical standards within current conflict limitations injection must be stopped, the needle withdrawn a few milli-
(peer-to-peer, A2/AD) medical providers will be increasingly meters, and negative aspiration performed.
pushed into Prolonged Casualty Care (PCC) situations.
In the early postoperative period, patients may complain of
PCC is medical care provided in the field and outside of doctri- paresthesia, mainly due to postoperative neurological symp-
nal medical planning timelines in order to decrease patient mor- toms (PONS), which up to 15% of patients may experience.
tality and morbidity while using limited personnel and material However, those symptoms rarely persist, and the incidence
resources until the patient reaches the next level of care. The of prolonged paresthesia or neuropathy fluctuates between
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after-action review of the Marjah firefight in January 2016 0.014% and 0.04%. 4,23
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demonstrates how troops who were in contact fire and sur-
rounded by the enemy for 17 hours had difficulty managing While performing any loco-regional anesthetic technique, pro-
pain in a patient with a gunshot wound to the leg and how nerve viders can apply easy preventive measures, including:
blocks could have been a potential solution in this situation.
• Always calculating the toxicity dose for the patient’s weight
Diffusion blocks seem the most suitable solution for Special • Preferentially using the least cardiotoxic agents (e.g., short-
Forces medics in austere environments because they require acting agents or levobupivacaine [of note, the cardiotox-
less skill sustainment than the ultrasound technique, which icity of bupivacaine contributed to the development of
also requires an ultrasound machine with high enough resolu- levobupivacaine])
tion and a linear probe. Diffusion blocks are thus safer for the • Administering low-concentration solutions
patient, cheaper, and technology/power independent. They can • Performing slow and fractionated injection
be used for surgery, wound care, or fracture reduction. One • Iteratively searching for blood reflux (aspirating each
good example of a diffusion block is the fascia iliaca compart- 5–10mL)
ment block, 17,18 which can be used instead of a femoral block. • Interrupting any injection as soon as signs of cardiotoxicity
Performed at a safe distance of the femoral nerve and femo- or neurotoxicity appear
ral artery, the fascia iliaca compartment block, with a larger
amount of local anesthetic (up to 40mL of 0.5% or 0.25% Signs and symptoms of local anesthesia toxicity can easily be
levobupivacaine), will block the femoral, lateral femoral cuta- recognized through the SAMS acronym: speech difficult (me-
neous, and obturator nerves. The wide-awake local anesthesia tallic taste in the mouth, lingual paresthesia), altered central
no tourniquet (WALANT) wrist and ankle block, lateral and nervous system (dizziness), muscles twitching (ringing in the
medial antebrachial cutaneous, and digital blocks are other ex- ears and blurred vision), and seizures. Primary treatment con-
amples of interesting diffusion blocks that allow providers to sists of stopping of the injection and using a benzodiazepine as
administer effective site-specific pain relief in a safe way. 19,20 per national seizure protocols.

Pharmacology Conclusion
Although the majority of local anesthetic intoxication events
are due to accidental intravenous injection, it is important to SOF medics often work in an isolated team in austere environ-
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understand that systemic toxicity of local anesthetics can have ments, with reduced freedom of movement and very limited
several consequences. The risk of toxicity depends on the site of medical support. The patient’s autonomic stability and pain are
injection (the rate of reabsorption is proportional to the degree two sides of an equation that medics have to balance in PCC.
of vascularity of the site (e.g., intravenous> subcutaneous); the The former can lead to the patient’s death in the worst-case
type of local anesthetic used (e.g., bupivacaine has a fast-in, scenario, and the latter to PTSD if the balance is not properly
slow-out pattern, while lidocaine has a fast-in, fast-out pat- achieved. Loco-regional anesthesia, integrated with multimodal
tern); its concentration or dose or the metabolism of the pa- analgesia, can address both aspects of the balance by provid-
tient; and whether epinephrine is used. ing adequate pain management while maintaining the patient’s
neurological, ventilatory, and hemodynamic status.
Although a range of local anesthetic drugs exists, the most
popular are lidocaine, for its short duration of effect (up to Our survey of 35 medical providers showed that, although the
2hr), and levobupivacaine, for its long duration effect (up to vast majority had already received a lecture on loco-regional
4hr). 7,12 Lidocaine toxicity is 4mg/kg without epinephrine and anesthesia, 83% (29) were not trained for it, and 54% (19) had
7mg/kg with epinephrine. Levobupivacaine toxicity is 3mg/kg never heard about multimodal analgesia. Although this topic

92 | JSOM Volume 24, Edition 3 / Fall 2024