Abstract ID: A1
Abstract Title: High Injection Pressure Predicts Delayed Neurologic Recovery After Intraneural Injection In Canine Sciatic Nerve
Poster Type: Either
ABSTRACT BODY
Introduction: A recent study in dogs suggested that the combination of intraneural placement of a needle and high pressure injection of a local anesthetic might lead to fascicular injury. However, the use of epinephrine may have confounded the results and contributed to the poor neurologic outcome. Our hypothesis is that occurrence of high pressure during sciatic nerve injection of epinephrine-free lidocaine in dogs is associated with an increased risk of neurologic injury.
Materials and Methods: The study was conducted in accordance with the principles of laboratory animal care. Ten dogs (10-18 kilograms) of mixed breed (twenty sciatic nerves) were studied. Induction of general endotracheal anesthesia was performed and the sciatic nerves were exposed bilaterally. Under microscopic guidance, a 25-gauge needle was inserted intraneurally (within the perineurium). All nerves received an intraneural injection of 4 ml of lidocaine 2% using an automated infusion pump programmed to deliver 4 ml/min. During injection, injection pressures were continuously recorded using an in-line manometer coupled to a computer. After injection, the dogs were awakened and subjected to serial neurological examinations by veterinarians blinded to the pressure data.
Results: The pressure data tended to be grouped in two ranges; approximately half of all injections were <11 psi (low injection pressure), whereas the remaining half were > 20 psi (high injection pressure), Figure 1. All sciatic nerves in which low injection pressures were recorded regained normal function in all 4 studied neurologic parameters within several hours after injection (range 4 to 48 hrs), Figure 2 shows recovery from nociception. In contrast, recovery of sciatic nerves in which high injection pressures were recorded demonstrated a delayed or incomplete recovery by the end of the study period (1 week; p<0.01), Figure 3 shows the delayed recovery from ataxia.
Discussion: Our findings confirm that high injection pressure is associated with neurologic sequelae. In current clinical practice, there is no consensus on techniques or methods to reduce the risk of intraneural injection, and neurologic injury can occur even with experienced practitioners. Although there is a paucity of clinical data, educational material in regional anesthesia suggest that abnormal resistance to injection may be indicative of intraneural injection and carries a risk of nerve injury. Indeed, in our study, only animals in which high injection pressures were recorded demonstrated delayed or incomplete recovery. The most likely explanation why some but not all nerves were injured after intraneural injection was because some needles were inserted intraneurally but extrafascicularly (low injection pressure) while others were inserted intrafascicularly (high injection pressure). If these results are applicable to clinical practice, monitoring injection pressures may prove to be a convenient means to avoid intrafascicular injections and decrease risk of neurologic injury.
ATTACHED FILES
Reg Anesth Pain Med 2004; 29(2):A1