Combination of intraneural injection and high injection pressure leads to fascicular injury and neurologic deficits in dogs.
BACKGROUND
Unintentional intraneural injection of local anesthetics may cause mechanical injury and pressure ischemia of the nerve fascicles. One study in small animals showed that intraneural injection may be associated with higher injection pressures. However, the pressure heralding an intraneural injection and the clinical consequences of such injections remain controversial. Our hypothesis is that an intraneural injection is associated with higher pressures and an increase in the risk of neurologic injury as compared with perineural injection.


METHODS
Seven dogs of mixed breed (15-18 kg) were studied. After general endotracheal anesthesia, the sciatic nerves were exposed bilaterally. Under direct microscopic guidance, a 25-gauge needle was placed either perineurally (into the epineurium) or intraneurally (within the perineurium), and 4 mL of lidocaine 2% (1:250,000 epinephrine) was injected by using an automated infusion pump (4 mL/min). Injection pressure data were acquired by using an in-line manometer coupled to a computer via an analog digital conversion board. After injection, the animals were awakened and subjected to serial neurologic examinations. On the 7th day, the dogs were killed, the sciatic nerves were excised, and histologic examination was performed by pathologists blinded to the purpose of the study.


RESULTS
Whereas all perineural injections resulted in pressures < or =4 psi, the majority of intraneural injections were associated with high pressures (25-45 psi) at the beginning of the injection. Normal motor function returned 3 hours after all injections associated with low injection pressures (< or =11 psi), whereas persistent motor deficits were observed in all 4 animals having high injection pressures (> or =25 psi). Histologic examination showed destruction of neural architecture and degeneration of axons in all 4 sciatic nerves receiving high-pressure injections.


CONCLUSIONS
High injection pressures at the onset of injection may indicate an intraneural needle placement and lead to severe fascicular injury and persistent neurologic deficits. If these results are applicable to clinical practice, avoiding excessive injection pressure during nerve block administration may help to reduce the risk of neurologic injury.
Hadzic
Admir
A
Department of Anesthesiology, St. Luke's-Roosevelt Hospital Center, New York, NY 10025, USA. admir@nysora.com
Dilberovic
Faruk
F
Shah
Shruti
S
Kulenovic
Amela
A
Kapur
Eldan
E
Zaciragic
Asija
A
Cosovic
Esad
E
Vuckovic
Ilvana
I
Divanovic
Kucuk-Alija
KA
Mornjakovic
Zakira
Z
Thys
Daniel M
DM
Santos
Alan C
AC
D000779:Anesthetics, Local / Q000008:administration & dosage; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004195:Disease Models, Animal; D004285:Dogs; D005260:Female; D007260:Infusion Pumps; D007267:Injections / Q000009:adverse effects; D008012:Lidocaine / Q000008:administration & dosage; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D009407:Nerve Block / Q000009:adverse effects* / Q000379:methods; D011312:Pressure / Q000009:adverse effects; D012584:Sciatic Nerve / Q000187:drug effects / Q000293:injuries* / Q000648:ultrastructure
D000779:Anesthetics, Local; D008012:Lidocaine