Abstract ID: A3

Abstract Title: COMBINATION OF INTRANEURAL INJECTION AND HIGH INJECTION PRESSURE LEADS TO SEVERE FASCICULAR INJURY AND NEUROLOGIC DEFICITS IN DOGS

Poster Type: Either


ABSTRACT BODY

INTRODUCTION
Severe neurologic injury is rare but a well documented complication after peripheral nerve blocks.[1] Inadvertent intraneural injection of local anesthetic may cause mechanical injury and pressure ischemia of the nerve fascicles.[2,3] One study in small animals demonstrated that intraneural injection may be associated with increased injection force (pressure).[4] However, the pressure heralding an intraneural injection and the clinical consequences of such injection remain controversial. In the current study, we compared the pressure resulting from an intraneural and paraneural injection and neurologic and histologic consequences of such injections.
METHODS
The study was conducted in accordance with the principles of laboratory animal care[5] and was approved by the Laboratory Animal Care and Use Committee. Seven dogs of mixed breed (15-18 kg) were studied. After general endotracheal anesthesia the sciatic nerves were exposed bilaterally. Under a direct microscopic guidance, a 25-gauge needle was placed either paraneurally (into the epineurium) or intraneurally (within the perineurium) and 4 mL of lidocaine (1%) was injected using an automated infusion pump. Pressure data were acquired 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 5th day, the dogs were killed, the sciatic nerves excised and histologic examination performed by pathologists blinded to the purpose of the study.
RESULTS
Pressure data: Whereas low injection pressures were recorded with all paraneural injections (Fig 1), the majority of intraneural injections were associated with higher initial pressures (25-45 psi; Fig 2).
Neurologic Outcome: Normal motor function returned 3 hours after all paraneural injections and after 3 intraneural injections associated with low pressure. Persistent motor deficits were observed in all 4 animals having an intraneural injection where high-pressure („d25 psi) was observed during initial injection.
Histologic Examination: Histologic examination revealed normal sciatic nerve architecture in the 10 nerve specimens associated with low-pressure injection („T11 psi). In contrast, there was destruction of neural architecture and degeneration of axons in all 4 sciatic nerves with high-pressure injection.
DISCUSSION
Intraneural injection is a well accepted mechanism of nerve injury3; however, its role in neurologic injury after peripheral nerve blocks has not been well understood. This study, in a dog model, demonstrates that intraneural needle placement combined with injection pressures greater than 25 psi may lead to severe fascicular injury and persistent neurologic deficits. If these results are applicable to clinical practice, avoiding excessive injection pressure (force) during nerve block administration may help to avoid fascicular injury.
REFERENCES
1 Anesthesiology. 2002;97:1274-80
2 Selander D: Complications of Regional Anesthesia. Edited by Finucane BT. Philadelphia, PA: Churchill Livingstone, 1999, pp 105-15
3 J Neurosurg. 1998;89:12-23
4 Acta Anesth Scand. 1978; 22:622-34
5 National Institutes of Health publication No. 86-23. Bethesda, National Institutes of Health, 1985

ATTACHED FILES

A3_fig1.doc

A3_fig2.doc

A3_fig3.doc

Reg Anesth Pain Med 2004; 29(2):A3