Research, con't
Clinically Measured Minimum Stimulation are Similar in both Diabetics and Non-Diabetics
Tae-Hyung Han, MD, PhD
Diabetics are known to require higher stimulating currents to elicit motor response. To examine this hypothesis, we conducted a prospective, case‐control study to clinically quantitate and compare minimum stimulation currents of brachial plexus posterior cord in diabetics vs. non‐diabetics. Patients with type 1 or 2 diabetes (n=41), scheduled for elective upper extremity surgery under infraclavicular block, were recruited. Non‐diabetic adults (n=44) served as controls. A combined technique of ultrasound and neuro stimulation was used. The lowest motor stimulator current intensity of posterior cord was recorded at extensor twitch abolishment. Minimum stimulating currents in controls vs. diabetics were 0.10 (0.02‐0.5) vs. 0.14 (0.02‐0.64) mA, both below 0.5 mA. The current methods and techniques of regional anesthesia are not designed to distinguish minimal stimulation currents between diabetics vs. controls, but to provide successful surgical anesthesia. Upon performing regional anesthesia using nerve stimulator in diabetics, anesthesiologists should expect similar extensor muscle twitch responses to electrical currents as in non-diabetics.
Closed Loop Control of Intracranial Pressure: Development of Novel Continuous Infusion Regimens for Mannitol vs 3% Hypertonic Saline
Tae-Hyung Han, MD, PhD
Hyperosmotic agents are the cornerstone of therapy for increased intracranial pressure (ICP), traditionally given as intermittent bolus. Continuous infusion protocols, rather than intermittent bolus, to achieve and maintain desired serum osmolalities, may improve ICP control clinical outcomes. We studied fifty seven adults undergoing elective craniotomy, examining 20% mannitol (0.5 or 1.0 g/kg) or 3% hypertonic saline (2.5 or 5 ml/kg), given over 15 min. Serial mannitol, Na+ concentrations and serum osmolality were measured over 12 hours. The pharmacokinetics of hyperosmotic agents and osmolar pharmacodynamics were constructed and validated. We found 1) that the human osmolality can be artificially achieved and maintained at the desired target level, and 2) that continuous infusion of hyperosmotic agents, driven by the well characterized pharmacokinetic and pharmacodynamic models, is convenient and safe. Clinical applications of these infusion protocols will require further refinement of the model parameters.
Large Volume of Distribution and High Clearance May Partially Explain Increased Vecuronium Requirement in Burns
Tae-Hyung Han, MD, PhD
Requirements for nondepolarizing muscle relaxants (NDMRs) are increased following major thermal injury. Pharmacodynamics of NDMRs has been well delineated in burns, as delayed onset and faster offset. To better understand their pharmacology in burns, we studied the disposition characteristics of vecuronium in major burns. Adults (n=20) with > 20% TBSA burn were enrolled. Vecuronium 0.12 mg/kg was administered intravenously as a single bolus. Blood samples were collected for up to 12 hours. The plasma concentration decay curve over time showed that threecompartment model was the best fit. Increased volume of distribution in slow peripheral compartment (V3) and enhanced clearance explained faster concentration decay in the burned. BURN and TBSA were significant covariates, improving the model performance. Larger volume of distribution (dilutional) and higher clearance may partially explain increased vecuronium dose requirement in burns. Our findings can be of assistance in NDMR dosing guidelines in burns.
