Systemic Absorption of Lidocaine After Hematoma Block

This study will measure in children how much numbing medicine, lidocaine, is absorbed into the bloodstream after it is injected into a blood clot (hematoma) around a forearm fracture for pain control when the broken bone is moved back into place (fracture reduction). This is called a hematoma block and is commonly used in the Emergency Unit. To help with anxiety and to add additional pain control, nitrous oxide (laughing gas) is given while the lidocaine hematoma block is placed and continued during the fracture reduction. Advantages of using this technique for pain control instead of an intravenous anesthetic such as ketamine include faster recovery and discharge home, and longer pain control. Of concern, if too much lidocaine is absorbed into the bloodstream, seizures and irregular heart beating may occur. Bloodstream concentrations of lidocaine after a hematoma block have been measured in only one study of 8 adults and found to be at significant but safe levels. No study has been published in children to measure bloodstream lidocaine levels when a hematoma block is used. Because children's bones are still growing and more metabolically active than adult bones, the investigators believe it is important to determine whether lidocaine blood levels in children are also at safe levels when using a standard lidocaine hematoma block for reduction of fractures. The investigators also want to determine whether bloodstream lidocaine levels correlate with type of fracture. The investigators also aim to determine if there is a difference in absorption pattern between different types of distal radius fractures, if there is a correlation between fracture type and systemic lidocaine absorption, and if there is a correlation between fracture type and ability to provide adequate pain and sedation control with lidocaine hematoma block/inhaled nitrous combination. The investigators believe blood lidocaine levels after hematoma block in children will peak at safe levels, but will be higher than those observed in adults.