Systemic Absorption of Lidocaine After Hematoma Block

When a subject with an eligible distal forearm fracture is identified, the subject will be approached for enrollment and consent. Fracture hematoma size will then be estimated using bedside ultrasound operated by trained pediatric emergency faculty or fellows. Ultrasound measurement of the dimensions of the fracture hematomas will be performed at the subject's bedside in the Emergency Department by pediatric emergency physicians trained in ultrasound use and in the specific methods for fracture hematoma size measurement. Obtaining the measurements of hematoma size will be performed by a standard protocol: The fractured bone will be scanned longitudinally on the dorsal-lateral surface to obtain the largest measurement of the length and depth of the associated fracture hematoma. Transverse scan will be obtained on the dorsal-lateral surface to determine width at the largest measurement. These measurements will then be used to calculate the total volume of the hematoma. If no dorsal hematoma is noted, an attempt at identifying volar hematoma may be made and its presence noted.

50% nitrous oxide/50% oxygen then will be administered to the subject by face mask for a minimum of 2 minutes before venous catheter insertion (50% nitrous oxide will continue to be administered until fracture reduction is completed). Nitrous oxide currently is administered regularly in the St. Louis Children's Emergency Department for painful procedures including fracture reduction, abscess incision and drainage, laceration repair and venous catheter placement. Nitrous oxide 50% blended with 50% oxygen will be administered for this study by credentialed emergency unit staff using a continuous flow delivery system that includes scavenging of exhaled nitrous oxide. Standard monitoring for deep sedation will be used as described in the clinical protocol.

A venous catheter then will be inserted into the uninjured arm. A lidocaine hematoma block will be injected by an orthopedic surgery resident using 2.5 mg/kg, maximum of 100mg, of 1% buffered lidocaine. The recommended lidocaine dose for hematoma block in children is 3-5 mg/kg. However, in a previous study, in another pediatric trial, and in the single report of plasma lidocaine levels in adults, 2.5 mg/kg of 1% lidocaine based upon the patient's weight, maximum 100 mg, was found effective and without adverse effects.

The Pediatric Sedation State Scale will be administered by the sedation provider, and a research assistant when available, and used for subsequent analysis to quantify subjects' responses to the injection of the hematoma block and fracture reduction. This scale has been validated for procedural sedation. Pediatric Sedation State Scale scores will be determined before nitrous oxide is begun (baseline), as the hematoma block is placed, at 60 second intervals during reduction and moulding, and 15 minutes after moulding is completed. The PSSS during each interval will be averaged when multiple time points are available.

Serial blood samples will be drawn through the indwelling venous catheter by a nurse or medic at 5, 10, 20, 40 and 60 minutes after injection of the hematoma block. Serial plasma lidocaine levels will be measured as follows. 5 mL samples of blood will be obtained via the indwelling venous catheter at 5, 10, 20, 40 and 60 minutes after injection of the lidocaine hematoma block. The samples of blood will be collected in standard red top vacutainer blood tubes and processed, frozen and stored in the SLCH/BJC Lab.

At 5 minutes after the hematoma block injection, the orthopedic surgeon will attempt fracture reduction. If the subject has minimal response to squeezing the fracture site prior to 5 minutes post injection, reduction may begin at that time. Nitrous oxide administration will be stopped and administration of 100% oxygen will begin when the orthopedic surgeon indicates satisfactory fracture reduction as determined by bedside fluoroscopy (standard procedure), a cast or splint has been applied, and, if necessary, the cast has been split. Oxygen administration will be stopped when the subject's exhaled nitrous oxide concentration falls below 10% or the subject pulls the nitrous oxide mask off the face.

If the subject resists the fracture reduction or verbally indicates significant pain, ketamine sedation will be administered via the indwelling venous catheter and fracture reduction completed under deep sedation. Post procedure pain score via the Wong-Baker Faces scale, and post procedure surveys will be administered 15 minutes after nitrous administration is stopped. After the subject's recovery from sedation, the subject, subject's parents/guardians, physician providing sedation (inhaled nitrous) and the orthopedic surgeon will be asked to rate their satisfaction with the sedation and analgesia for the fracture reduction using a Likert scale ranging from 1 (not satisfied at all) to 10 (very satisfied). Recovery from sedation satisfactory for discharge home is indicated by a score of 10 on the Modified Aldrete Scale below, and the child can sit up unaided along with control of pain and vomiting. Family will be contacted via telephone 48 hours after their visit to assess for any late adverse effects.

Adverse events will be documented on a data collection sheet using consensus-based definitions that include the event, time and any intervention employed. In addition, the subject will be asked about symptoms typically seen with procedural sedation and lidocaine toxicity including: vomiting, nausea, tinnitus, circumoral or tongue numbness, metallic taste in mouth, nystagmus, vision changes, muscle twitching, tremors, seizure, respiratory depression, chest pain, difficulty breathing, palpitations, ECG changes on monitor (type noted, ECG strip printed), and any other unpleasant or euphoric symptom.