Ultrasonographic appearance of intraneural injections in the porcine model.

BACKGROUND: Ultrasonographic (US) images of apparent intraneural injection of local anesthetic solutions have been reported. We aimed to define US signs of intraneural (ie, subepineural) injection using a histologic standard in an animal model and compare these signs with other potential markers of intraneural injection, including low nerve stimulation current thresholds and high injection pressures. METHODS: In 6 anesthetized adult swine, bilateral brachial plexus and femoral nerves were contacted by needles and penetrated. India ink was injected intraneurally under US monitoring. The minimum current that elicited a motor response was recorded. Injection pressures were measured using a digital manometer. Nerves were then excised, processed, and subjected to histologic analysis. RESULTS: Nerve expansion during injection was visualized under ultrasonography in all procedures. Electrical current intensity to elicit motor response to nerve stimulation varied between 0.2 and 3.3 mA with the needle tip positioned intraneurally. The mean injection pressure was 7.40 +/- 8.07 psi (range, 0.07-31.5 psi), with 80% of injections between 0.61 and 15.0 psi. None of 24 intraneural injections resulted in histologic evidence of intrafascicular injection (95% confidence interval, 0.0%-16.3%). CONCLUSIONS: Ultrasonographic images compatible with nerve swelling during an injection are consistent with true intraneural injections as demonstrated by histologic analysis. Under the conditions studied, intensity of the stimulating current required to elicit motor response was not associated with intraneural needle placement. In the absence of fascicular injury, intraneural injections were associated with low injection pressure, although false-positive results can occur.

Inclusion of a nitric oxide congener in the insufflation gas repletes S-nitrosohemoglobin and stabilizes physiologic status during prolonged carbon dioxide pneumoperitoneum.

A method to maintain organ blood flow during laparoscopic surgery has not been developed. Here we determined if ethyl nitrite, an S-nitrosylating agent that would maintain nitric oxide bioactivity (the major regulator of tissue perfusion), might be an effective intervention to preserve physiologic status during prolonged pneumoperitoneum. The study was conducted on appropriately anesthetized adult swine; the period of pneumoperitoneum was 240 minutes. Cohorts consisted of an anesthesia control group and groups insufflated with CO2 alone or CO2 containing fixed amounts of ethyl nitrite (1-300 ppm). Insufflation with CO2 alone produced declines in splanchnic organ blood flows and it reduced circulating levels of S-nitrosohemoglobin (i.e., nitric oxide bioactivity); these reductions were obviated by ethyl nitrite. In a specific example, preservation of kidney blood flow with ethyl nitrite kept serum creatinine and blood urea nitrogen concentrations constant whereas in the CO2 alone group both increased as kidney blood flow declined. The data indicate ethyl nitrite can effectively attenuate insufflation-induced decreases in organ blood flow and nitric oxide bioactivity leading to reductions in markers of acute tissue injury. This simple intervention provides a method for controlling a major source of laparoscopic-related morbidity and mortality: tissue ischemia and altered postoperative organ function.