E. Hamilton

Microbubbles Improve Sonothrombolysis In Vitro and Decrease Hemorrhage In Vivo in a Rabbit Stroke Model

Introduction:Tissue plasminogen activator (tPA) is the thrombolytic standard of care for acute ischemic stroke, but intracerebral hemorrhage (ICH) remains a common and devastating complication. We investigated using ultrasound (US) and microbubble (MB) techniques to reduce required tPA doses and to decrease ICH. Materials and Methods:Fresh blood clots (3–5 hours) were exposed in vitro to tPA (0.02 or 0.1 mg/mL) plus pulsed 1 MHz US (0.1 W/cm2), with or without 1.12 × 108/mL MBs (Definity or albumin/dextrose MBs [adMB]). Clot mass loss was measured to quantify thrombolysis. New Zealand white rabbits (n = 120) received one 3- to 5-hour clot angiographically delivered into the internal carotid artery. All had transcutaneous pulsed 1 MHz US (0.8 W/cm2) for 60 minutes and intravenous tPA (0.1–0.9 mg/kg) with or without Definity MBs (0.16 mL/mg/kg). After killing the animals, the brains were removed for histology 24 hours later. Results:In vitro, MBs (Definity or adMB) increased US-induced clot loss significantly, with or without tPA (P < 0.0001). At 0 and 0.02 mg/mL, tPA clot loss was greater with adMBs compared with Definity (P ≤ 0.05). With MB, the tPA dose was reduced 5-fold with good efficacy. In vivo, both Definity MB and tPA groups had less infarct volume compared with controls at P < 0.0183 and P = 0.0003, respectively. Definity MB+tPA reduces infarct volume compared with controls (P < 0.0001), and ICH incidence outside of strokes was significantly lower (P = 0.005) compared with no MB. However, infarct volume in Definity MB versus tPA was not different at P = 0.19. Conclusion:Combining tPAand MB yielded effective loss of clot with very low dose or even no dose tPA, and infarct volumes and ICH were reduced in acute strokes in rabbits. The ability of MBs to reduce tPA requirements may lead to lower rates of hemorrhage in human stroke treatment.

Production of uniformly sized serum albumin and dextrose microbubbles

Uniformly-sized preparations with average microbubble (MB) diameters from 1 to 7 μm were produced reliably by sonicating decafluorobutane-saturated solutions of serum albumin and dextrose. Detailed protocols for producing and size-separating the MBs are presented, along with the effects that changing each production parameter (serum albumin concentration, sonication power, sonication time, etc.) had on MB size distribution and acoustic stability. These protocols can be used to produce MBs for experimental applications or serve as templates for developing new protocols that yield MBs with physical and acoustic properties better suited to specific applications. Size stability and ultrasonic performance quality control tests were developed to assure that successive MB preparations perform identically and to distinguish the physical and acoustic properties of identically sized MBs produced with different serum albumin-dextrose formulations and sonication parameters. MBs can be stored at 5 °C for protracted periods (2 weeks to one year depending on formulation).

Influences of Microbubble Diameter and Ultrasonic Parameters on In Vitro Sonothrombolysis Efficacy

PURPOSE To quantify the effects of microbubble (MB) size, elasticity, and pulsed ultrasonic parameters on in vitro sonothrombolysis (ultrasound [US]-mediated thrombolysis) efficacy. MATERIALS AND METHODS Monodispersive MBs with diameters of 1 μm or 3 μm were exposed to pulsed US (1 MHz or 3 MHz) to lyse rabbit blood clots. Sonothrombolysis efficacy (clot mass loss) was measured as functions of MB size and concentration, ultrasonic frequency and intensity, pulse duration (PD), pulse repeat frequency (PRF), and duty factor. RESULTS Sonothrombolysis at 1 MHz was more effective using 3-μm MBs and at 3 MHz using 1-μm MBs. Sonothrombolysis was more effective at 1 MHz when≥75% of MBs remained intact, especially for 3-μm MBs; improving sonothrombolysis by increasing PRF from 100 Hz to 400 Hz at 3 MHz was associated with increasing 3-μm MB survival. However, 60% of 1-μm MBs were destroyed during maximal sonothrombolysis at 3 MHz, indicating that considerable MB collapse may be required for sonothrombolysis under these conditions. CONCLUSIONS The ability to control MB size and elasticity permits using a wide range of US parameters (eg, frequency, intensity) to produce desired levels of sonothrombolysis. Comparable, maximal sonothrombolysis efficacy was achieved at 20-fold lower intensity with 3-μm MBs (0.1W/cm(2)) than with 1-μm MBs (2.0W/cm(2)), a potential safety issue for in vivo sonothrombolysis. US parameters that maximized MB survival yielded maximal sonothrombolysis efficacy except with 1-μm MBs at 3MHz where most MBs were destroyed.

Propofol for Treatment of Refractory Alcohol Withdrawal Syndrome: A Review of the Literature.

The authors evaluated all available evidence on the use of propofol as an adjuvant for the treatment of resistant alcohol withdrawal syndrome (AWS) in comparison to other therapies. A comprehensive PubMed search (1966–December 2015) was conducted using the search terms propofol, alcohol withdrawal, and drug therapy. Articles were cross‐referenced for other citations. Clinical studies, case series, and case reports published in the English language assessing the use of propofol in adult patients for treatment of AWS were reviewed for inclusion. Propofol is a sedative‐hypnotic that exerts its actions through agonism of GABAA receptors at a different binding site than benzodiazepines and reduces glutamatergic activity through N‐methyl‐d‐aspartase (NMDA) receptor blockade. Dosages from 5 to 100 μg/kg/minute reduced AWS symptoms with frequent development of hypotension and requirement for mechanical ventilation. Patients on propofol often experienced longer durations of mechanical ventilation and length of stay, which may be attributed to more‐resistant cases of AWS. When propofol was compared with dexmedetomidine as adjuncts in AWS, both agents showed similar benzodiazepine‐ and haloperidol‐sparing effects. Dexmedetomidine was associated with more numerical rates of bradycardia, while propofol was associated with more numerical instances of hypotension. Dexmedetomidine was used more frequently in nonintubated patients. The available data assessing the utility of propofol for AWS exhibited significant heterogeneity. Propofol may be useful in a specific population of patients with AWS, limited to those who are not clinically responding to first‐line therapy with benzodiazepines. Specifically, propofol should be considered in patients who are refractory to or not candidates for other adjuvant therapies, patients already requiring mechanical ventilation, or those with seizure activity or refractory delirium tremens. In severe, refractory AWS, adjuvant therapy with propofol may be considered but requires further research to recommend its use either preferentially or as monotherapy.