Challenges in anaesthesia and pain management for burn injuries

Burn-injured patients provide unique challenges to those providing anaesthesia and pain management. This review aims to update both the regular burn anaesthetist and the anaesthetist only occasionally involved with burn patients in emergency settings. It addresses some aspects of care that are perhaps contentious in terms of airway management, fluid resuscitation, transfusion practices and pharmacology. Recognition of pain management failures and the lack of mechanism-specific analgesics are discussed along with the opioid crisis as it relates to burns and nonpharmacological methods in the management of distressed patients.

Pharmacokinetic/Pharmacodynamic Model of CW002, an Investigational Intermediate Neuromuscular Blocking Agent, in Healthy Volunteers

BACKGROUND

CW002 is an investigational nondepolarizing, neuromuscular blocking agent with a rapid onset and intermediate duration of action in animals. This is a single ascending dose, healthy subject study exploring tolerability, pharmacokinetics, and potency.

METHODS

Population pharmacokinetic and pharmacokinetic/pharmacodynamic models were developed using plasma drug concentration data from a previously published dose-response study in 28 healthy subjects receiving single doses of CW002 during sevoflurane anesthesia. Subjects included in the models were from five different dose cohorts (cohorts 3, 4, 5, 6, and 8 receiving 0.04, 0.06, 0.08, 0.10, and 0.14 mg/kg, respectively). Serial arterial plasma concentrations and muscle twitch heights were monitored.

RESULTS

A four-compartment model was fit to the concentration-time data, whereas a transit compartment with a sigmoid Emax model was fit to the pharmacokinetic/pharmacodynamic data. The population pharmacokinetics of CW002 was linear with very low interindividual variability in clearance (10.8%). Simulations were conducted to predict the onset and offset of effect at 2×, 3×, and 4× ED95. The time to 80% block was predicted to be 1.5, 0.8, and 0.7 min for 2×, 3×, and 4× ED95 doses, respectively. The simulated 25 to 75% recovery index was independent of dose.

CONCLUSIONS

CW002 has predictable pharmacokinetics and is likely to have a rapid onset with an intermediate duration of action at 3× ED95. This model provides information to inform critical decisions (e.g., dose, study design) for continued development of CW002.

Gap analysis of pharmacokinetics and pharmacodynamics in burn patients: a review

Severe burn injury results in a multifaceted physiological response that significantly alters drug pharmacokinetics and pharmacodynamics (PK/PD). This response includes hypovolemia, increased vascular permeability, increased interstitial hydrostatic pressure, vasodilation, and hypermetabolism. These physiologic alterations impact drug distribution and excretion-thus varying the drug therapeutic effect on the body or microorganism. To this end, in order to optimize critical care for the burn population it is essential to understand how burn injury alters PK/PD parameters. The purpose of this article is to describe the relationship between burn injury and drug PK/PD. We conducted a literature review via PubMed and Google to identify burn-related PK/PD studies. Search parameters included "pharmacokinetics," "pharmacodynamics," and "burns." Based on our search parameters, we located 38 articles that studied PK/PD parameters specifically in burns. Twenty-seven articles investigated PK/PD of antibiotics, 10 assessed analgesics and sedatives, and one article researched an antacid. Out of the 37 articles, there were 19 different software programs used and eight different control groups. The mechanisms behind alterations in PK/PD in burns remain poorly understood. Dosing techniques must be adapted based on burn injury-related changes in PK/PD parameters in order to ensure drug efficacy. Although several PK/PD studies have been undertaken in the burn population, there is wide variation in the analytical techniques, software, and study sample sizes used. In order to refine dosing techniques in burns and consequently improve patient outcomes, there must be harmonization among PK/PD analyses.

Comparison of the pharmacokinetics of linezolid in burn and non-burn rabbits

Linezolid is effective on many resistant organisms for the treatment of severe infections in burns. However, its pharmacokinetics was difficult to predict after major burns. The study aimed to describe the pharmacokinetic properties of linezolid administered intravenously at a dose of 10 mg/kg in severely burned rabbits in comparison to that in non-burns. Linezolid concentrations were quantitatively analyzed by high-performance liquid chromatography. The direct consequence of the physiological changes after burn injury was lower plasma linezolid concentrations. In addition, burn injury induced significantly altered pharmacokinetic parameters with higher inter-individual variability. The distribution volume and clearance rate were increased (2.88 vs. 1.92 L/kg, P > 0.05; 0.28 vs. 0.20 L/h/kg, P < 0.05), and the AUC0-∞ was significantly lower (37.99 vs. 51.47 mg/L h, P < 0.05). However, there were almost no changes in half-life and mean residence time. These results suggested that therapeutic drug monitoring and dosage individualization of linezolid in patients with severe burns were necessary.