Abstract ID: A44

Abstract Title: INTRANEURAL INJECTIONS RESULT IN HIGH INJECTION PRESSURE AND DELAYED NEUROLOGIC RECOVERY AFTER SCIATIC NERVE BLOCK IN PIGS

Authors: Kapur E¹, Voljevica A², Divanovic K³, Vuckovic I⁴
Medical University of Sarajevo Sarejevo Bosnia-Herzegovina ¹, Medical University of Sarajevo Sarejevo Bosnia-Herzegovina ², Medical University of Sarajevo Sarejevo Bosnia-Herzegovina ³, Medical University of Sarajevo Sarejevo Bosnia-Herzegovina ⁴
Poster Type: Either

ABSTRACT BODY

Introduction:
Studies in animals have suggested that intraneural application of local anesthetics may cause mechanical injury and pressure ischemia of nerve fascicles.(1,2) Previous studies, however, have used small animal models and clinically irrelevant injection speed or equipment. Consequently, the results of those studies remain of questionable relevance to clinical practice. In this study we used equipment and injection methods in common clinical use to study the consequences and pressure dynamics of intraneural injection. Our hypothesis is that an intraneural injection is heralded by higher injection pressure and leads to neurologic impairment in pigs.

Materials and Methods:
The study was conducted in accordance with the principles of laboratory animal care and was approved by the Laboratory Animal Care and Use Committee. Ten pigs of mixed breed (21-26 kg, 4-6 months old) were studied. After general anesthesia, the sciatic nerves (n=20) were exposed bilaterally. Under direct vision, a 25-gauge insulated nerve block needle (ProBlock, LifeTech, Stafford, TX) was placed either extraperineurally (n=10) or subperineurially (n=10), and 4 mL of preservative-free lidocaine 2% was injected using an automated infusion pump (15 ml/min). Injection pressure data were acquired using an in-line manometer coupled to a computer via an analog-to-digital conversion board. After injection, the animals were awakened and subjected to serial neurologic examinations during the 24 post-intervention hours.

Results:
All but two perineural injections resulted in injection pressures below 20 psi, Figure 1. In contrast, intraneural injections resulted in significantly higher peak pressures (p<0.01), Figure 2. In 7 (70%) intraneural injections, the injections pressures were over 20 psi (20-50 psi), Figure 2. Neurologic function returned to baseline within 24 hours in all sciatic nerve receiving perineural injections, Figure 3. In contrast, residual neurologic impairment was present in 7 sciatic nerves after intraneural injection; residual neurologic impairment was associated with injection pressures > 20 psi, Figure 3.

Discussion:
Intraneural injection of local anesthetic in sciatic nerve block model in pigs is associated with high injection pressure (> 20 psi) and delayed neurologic recovery. These findings support the concept of poor compliance of nerve fascicles and suggests that injection pressure > 20 psi can be used as a marker of intrafascicular injection. 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.

REFERENCES
1. Acta Anesth Scand 1978; 22:622-34.
2. Reg Anesth Pain Med. 2004;29:417-23.

ATTACHED FILES

Reg Anesth Pain Med 2005; 30(3):A44