Amela Kulenović

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 ≤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 (≤11 psi), whereas persistent motor deficits were observed in all 4 animals having high injection pressures (≥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.

Detection of nerve structures during peripheral nerve blockade in pigs model

Objective: In recent years regional anesthesia has gained great popularity. However, like any other medical procedure, the regional anesthesia carries certain risk of unintended intraneural injection and consequential neurological complications. Studies in animals have suggested that intraneural application of local anesthetics may cause mechanical injury. Previous studies, however, have used small animal models and clinically irrelevant injection speed or equipment. 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: 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 was placed either intraneurally (n = 10) or perineurally (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 next 7 days. Results: All perineural injections resulted in injection pressures below 40 kPa. In contrast, intraneural injections resulted in significantly higher peak pressures (P 140 k Pa. Conclusion: High injection pressure (>140 kPa) predicts intraneural injection and consequential neurologic deficit. As long as the injection pressure is low, injection into poorly compliant tissue can be avoided and neurological complication can be prevented.