The Use of Intravenous Lidocaine as an Analgesic Modality in the Austere Environment: Two Cases

Abstract

Providing effective analgesia for trauma in austere settings is particularly difficult and often complicated by equipment and medication limitations and harsh environmental conditions. Common modalities that are employed in conventional clinical practices may not be available or pragmatic in austere environments. Furthermore, side effects such as sedation, altered mentation, or hypoxemia require additional resources and attention. We report 2 cases that demonstrate the use of intravenous lidocaine for the management of acute pain, secondary to trauma, in an austere environment. In the first, the administration of intravenous lidocaine reduced pain, secondary to a tibia fracture, thereby facilitating splinting. In the second, a patient, who had sustained rib fractures, was also treated with intravenous lidocaine. In this case, the analgesic effects of the medication resulted in reduction in pain and improvement in pulmonary function. Of note, the narrow therapeutic window of this modality was made evident as both patients transiently experienced tinnitus following the initial lidocaine bolus. This report describes 2 cases in which intravenous lidocaine was used to manage acute pain, in an austere environment, while avoiding many of the detrimental effects that accompany alternative analgesics.

Introduction

Providing effective acute pain management in an austere prehospital environment is a particularly challenging task. Although numerous factors are likely attributable to complicating this task, a lack of medications, equipment limitations, and limited availability of medically trained personnel are all likely contributors.^1,2 To overcome this challenge, medical providers must look for reliable, pragmatic, compact, lightweight, and durable analgesic modalities. According to current literature, these modalities must not have significant side effects, including excessive sedation or hemodynamic instability. ¹

Although current evidence is not yet robust, ³ there is a growing interest in utilizing intravenous lidocaine as an analgesic modality in both the austere and combat environments.^4,5 However, the narrow therapeutic index, need for ongoing monitoring, necessary infusion equipment, and requirement that lipid emulsion be accessible ⁶ all have been thought to restrict the use of intravenous lidocaine in such environments. The availability of lipid emulsion, an important therapy for local anesthetic systemic toxicity, also influences the decision-making process of implementing regional and systemic local anesthetics.

Despite the previously described limitations, this retrospective report of 2 cases shows the benefit of utilizing intravenous lidocaine to treat acute pain in the austere environment.

Case Report

We report cases from a clinic in Southeast Asia, where pharmacologic analgesics were restricted to ketamine, paracetamol, and lidocaine. While the supply of lidocaine was robust, only 6000 mg of ketamine and 5000 mg of paracetamol were available. For this reason, the clinic typically reserved ketamine use for emergent procedural sedation (eg, cricothyroidotomy, chest tube placement, endotracheal intubation) and paracetamol for management of fever or mild pain. As a result of local counternarcotics policies, opioids were not available. Additional constraints included unreliable electricity, no refrigeration, infrequent resupply, no access to radiography or ultrasonography, no infusion pumps, and a medical staff of only 2 providers, a paramedic and a physician. Since temperature control was not available, a reliable supply of lipid emulsion could not be maintained. Infusions were established by adding 1 mg·kg^-1 of 1% (10 mg·mL^-1) lidocaine to a known volume of crystalloid solution. Then, using the tubing drop factor (drops·mL^-1) and the infusate concentration (mg·mL^-1), the drop rate (drops·min^-1) was calculated for an infusion of 1 mg·kg^-1·h^-1.

Case 1 - we treated a 22-y-old female, who presented with a fractured left tibia and fibula as a result of falling from a moving motorcycle. Upon presentation, the patient complained of pain localized to the site of the fracture, which was specifically described as constant and 8/10 in severity on the defense and veterans pain rating scale (DVPRS).^7,8 The patient was then monitored with continuous pulse oximetry, manual noninvasive blood pressure manometry, and 3-lead electrocardiography. After ensuring that no life-threatening injuries were present, establishing intravenous access, and determining that the affected extremity was neurovascularly intact, we treated the patient with a 1 mg·kg^-1 bolus of intravenous lidocaine over approximately 2 min. Of note, the patient did report transient tinnitus. Within 2 min of completing the bolus, the pain began to subside to 3/10 in severity (DVPRS). This analgesic effect lasted for approximately 40 min and facilitated splinting. The patient was then released with oral paracetamol for analgesia.

Case 2 - we treated a 38-y-old male, with a prior history of opioid use disorder, who presented with a fractured left posterior fifth rib as a result of falling from a ladder over 2 m high. Of note, this patient was also concurrently serving as a medical assistant. On initial physical assessment, the patient appeared to be splinting with shallow breaths at a respiratory rate of 35 breaths·min⁻¹. Continuous 3-lead electrocardiography, pulse oximetry, and manual noninvasive blood pressure manometry were initiated. The patient’s oxygen saturation on pulse oximetry was 93%, while on room air. The patient complained of a sharp pain, localized to the site of the fracture, was worsened by deep inspirations, and rated at a 9/10 in severity (DVPRS). On examination, bilateral breath sounds could be auscultated, trachea was midline, and no jugular venous distension was observed. After establishing intravenous access, we initiated a 1 mg·kg^-1 bolus of intravenous lidocaine over 2 min, followed by an ongoing infusion of 1 mg·kg^-1·h^-1 for 2 h. Within 5 min of initiating the intravenous lidocaine bolus, the patient felt the pain resolve to a dull pain, with a severity of 4/10 (DVPRS). More importantly, the patient’s respiratory rate improved to 18 respirations per minute, and the saturation on pulse oximetry improved to 98%. The patient did describe transient tinnitus. Once pain was reduced to a more tolerable level, the patient was able to be transported to a nearby location, where he was able to resume his clinical duties and would have access to additional care. However, he did complain that the pain began to increase again approximately 30 min after discontinuation of the intravenous lidocaine infusion.

Discussion

Effective pain control and management of trauma can be difficult in an austere environment, often complicated by limited resources and personnel. Pain control options are frequently limited by what is immediately available, weight or bulk of agent, equipment needed for administration, route of administration, and availability of intravenous access. Lidocaine is often made available in these settings because local and regional anesthetic techniques are currently recommended as both an effective and safe modality in the treatment of acute pain. ² In both of these cases, regional anesthetic techniques would have likely been beneficial. However, a properly trained provider was not available. This pair of cases represent an austere environment, where many commonly used analgesic modalities for moderate to severe pain were not readily available. Although ketamine was available, the immediate supply was limited and its use may have compromised the patients’ sensorium and cognitive function, a costly side effect in this setting. Even when administered in doses as low as 0.1 to 0.4 mg·kg^-1, intravenous ketamine may result in undesirable psychotomimetic effects. ⁹ The risk of local anesthetic systemic toxicity, a constellation of mainly cardiovascular and neurologic side effects, is typically seen when serum lidocaine concentrations exceed 5 to 10 mcg·mL^-1. Prior studies suggest that these toxic levels can be avoided by using low dose infusions and boluses less than 1.5 mg·kg^-1.^10,11 Although the patients described in this study briefly experienced tinnitus, intravenous lidocaine provided analgesia without considerably compromising mental status. Given the contextual limitations, implementation of this modality in austere environments may prove to be advantageous with reduced dosing, careful administration, and even as a component of multimodal analgesia.

Intravenous lidocaine infusions utilized in the treatment of acute pain have been studied in the perioperative setting, where this modality results in reduced pain scores and opioid requirements after abdominal surgeries. Additionally, intravenous lidocaine may have an analgesic benefit in intrathoracic and orthopedic surgeries. ¹² Lidocaine has also been shown to treat chronic neuropathic pain, as seen in diabetic neuropathy or complex regional pain syndromes. It has anti-nociceptive, anti-hyperalgesic, and anti-inflammatory activity ⁶ that can uniquely provide prolonged pain relief without the concomitant sedative or hypnotic effects seen by other analgesic medications. A recent study found that lidocaine administration was associated with a decreased incidence of chronic postsurgical pain. ¹³ These properties of lidocaine likely result not only from the blockade of voltage-gated sodium channels, but also from the inhibitory activity at various other sites, to include the NMDA and muscarinic cholinergic receptors. ⁶

Intravenous lidocaine has a small therapeutic window with a high risk for toxicity. Therefore, use of this modality in conventional clinical settings requires that lipid emulsion be readily available. Side effects for this modality include slurred speech, tinnitus, perioral paresthesias, and, rarely, cardiovascular collapse or seizures.^6,12 Transient tinnitus, which was experienced by the 2 described patients, is considered a minor adverse effect that often occurs even at serum lidocaine concentrations as low as 5 mcg·mL^-1. The more severe effects, such as cardiovascular collapse, typically do not occur until a serum concentration of 10 mcg·mL^-1 is reached. Providers also need to be mindful of the contraindications to systemic lidocaine, such as heart failure, cardiac dysrhythmias, medication allergy, hepatic impairment, renal impairment, or seizure disorders. ¹² Proper training, clinical experience with this modality, and appropriate equipment during the administration of systemic lidocaine are necessary factors that provide safety but also limit employment of this modality.

The cases described here occurred at a single remote clinic, where treatment was restricted by limited resources and personnel. Additional research is required to identify best practices for the administration of intravenous lidocaine for the management of pain in austere and prehospital settings, as well as optimal patient populations and methods of administering the infusions. The scalability and feasibility of using lidocaine infusions for analgesia at points of injury must also be further evaluated. Future clinical investigation may find intravenous lidocaine to be a safe and effective alternative analgesic modality. This modality may warrant consideration in situations where traditional options have been exhausted, are unavailable, or are deemed unsuitable.