Joshua W. Lampe

State of the Art in Therapeutic Hypothermia

Historically, hypothermia was induced prior to surgery to enable procedures with prolonged ischemia, such as open heart surgery and organ transplant. Within the past decade, the efficacy of hypothermia to treat emergency cases of ongoing ischemia such as stroke, myocardial infarction, and cardiac arrest has been studied. Although the exact role of ischemia/reperfusion is unclear clinically, hypothermia holds significant promise for improving outcomes for patients suffering from reperfusion after ischemia. Research has elucidated two distinct windows of opportunity for clinical use of hypothermia. In the early intra-ischemia window, hypothermia modulates abnormal cellular free radical production, poor calcium management, and poor pH management. In the more delayed post-reperfusion window, hypothermia modulates the downstream necrotic, apoptotic, and inflammatory pathways that cause delayed cell death. Improved cooling and monitoring technologies are required to realize the full potential of this therapy. Herein we discuss the current state of clinical practice, clinical trials, recommendations for cooling, and ongoing research on therapeutic hypothermia.

Patient-centric blood pressure-targeted cardiopulmonary resuscitation improves survival from cardiac arrest.

RATIONALE Although current resuscitation guidelines are rescuer focused, the opportunity exists to develop patient-centered resuscitation strategies that optimize the hemodynamic response of the individual in the hopes to improve survival. OBJECTIVES To determine if titrating cardiopulmonary resuscitation (CPR) to blood pressure would improve 24-hour survival compared with traditional CPR in a porcine model of asphyxia-associated ventricular fibrillation (VF). METHODS After 7 minutes of asphyxia, followed by VF, 20 female 3-month-old swine randomly received either blood pressure-targeted care consisting of titration of compression depth to a systolic blood pressure of 100 mm Hg and vasopressors to a coronary perfusion pressure greater than 20 mm Hg (BP care); or optimal American Heart Association Guideline care consisting of depth of 51 mm with standard advanced cardiac life support epinephrine dosing (Guideline care). All animals received manual CPR for 10 minutes before first shock. Primary outcome was 24-hour survival. MEASUREMENTS AND MAIN RESULTS The 24-hour survival was higher in the BP care group (8 of 10) compared with Guideline care (0 of 10); P = 0.001. Coronary perfusion pressure was higher in the BP care group (point estimate +8.5 mm Hg; 95% confidence interval, 3.9-13.0 mm Hg; P < 0.01); however, depth was higher in Guideline care (point estimate +9.3 mm; 95% confidence interval, 6.0-12.5 mm; P < 0.01). Number of vasopressor doses before first shock was higher in the BP care group versus Guideline care (median, 3 [range, 0-3] vs. 2 [range, 2-2]; P = 0.003). CONCLUSIONS Blood pressure-targeted CPR improves 24-hour survival compared with optimal American Heart Association care in a porcine model of asphyxia-associated VF cardiac arrest.

A rodent model of emergency cardiopulmonary bypass resuscitation with different temperatures after asphyxial cardiac arrest

BACKGROUND The use of emergency cardiopulmonary bypass (ECPB) resuscitation after cardiac arrest may offer hope for survival when standard ACLS therapies fail. However, whether cooling adds benefit to ECPB is unknown and we lack an ECPB rodent model for experimental studies. We sought to (a) develop a 72 h survival rodent model using ECPB to treat asphyxial cardiac arrest and (b) use this new model to evaluate early mild and moderate hypothermia versus normothermia during ECPB resuscitation. METHODS After 8 min of normothermic asphyxia, three groups of rats were resuscitated with ECPB at 37 degrees C (NORM), 34 degrees C (MILD) and 30 degrees C (MOD) for 1h (n=10 each). During the second resuscitation hour, ECPB was discontinued, ventilatory support was provided and body temperatures were maintained at 37 degrees C for NORM, 34 degrees C for MILD, and from 30 degrees C gradually up to 34 degrees C in 1h for MOD animals. From hours 3 to 8, body temperature was maintained at 37 degrees C for NORM and 34 degrees C for MILD and MOD animals. RESULTS All rats were initially resuscitated by ECPB. After 72 h, neurological outcome and survival in the MILD (60% survival) and MOD (80%) groups were significantly better than in the NORM (0%) group (p<0.05). Overall performance recovery in the MOD group was best (vs. the NORM group), while the MILD group had an intermediate outcome. CONCLUSIONS A rodent model of ECPB is feasible and useful for resuscitation studies. The addition of early mild and moderate hypothermia to ECPB resuscitation significantly improves survival compared with normothermic ECPB in rats.

Immediate short-duration hypothermia provides long-term protection in an in vivo model of traumatic axonal injury.

A prospective, multicenter, randomized trial did not demonstrate improved outcomes in severe traumatic brain injured patients treated with mild hypothermia [Clifton, G.L., Miller, E.R., Choi, S.C., Levin, H.S., McCauley, S., Smith, K.R., Jr., Muizelaar, J.P., Wagner, F.C., Jr., Marion, D.W., Luerssen, T.G., Chesnut, R.M., Schwartz, M., 2001. Lack of effect of induction of hypothermia after acute brain injury. N. Engl. J. Med. 344, 556-563.]. However, the mean time to target temperature was over 8 h and patient inclusion was based on Glasgow Coma Scale score so brain pathology was likely diverse. There remains significant interest in the benefits of hypothermia after traumatic brain injury (TBI) and, in particular, traumatic axonal injury (TAI), which is believed to significantly contribute to morbidity and mortality of TBI patients. The long-term beneficial effect of mild hypothermia on TAI has not been established. To address this issue, we developed an in vivo rat optic nerve stretch model of TAI. Adult male Sprague-Dawley rats underwent unilateral optic nerve stretch at 6, 7 or 8 mm piston displacement. The increased number of axonal swellings and bulbs immunopositive for non-phosphorylated neurofilament (SMI-32) seen four days after injury was statistically significant after 8 mm displacement. Ultrastructural analysis 2 weeks after 8 mm displacement revealed a 45.0% decrease (p<0.0001) in myelinated axonal density in the optic nerve core. There was loss of axons regardless of axon size. Immediate post-injury hypothermia (32 degrees C) for 3 h reduced axonal degeneration in the core (p=0.027). There was no differential protection based on axon size. These results support further clinical investigation of temporally optimized therapeutic hypothermia after traumatic brain injury.

Feasibility of intra-arrest hypothermia induction: A novel nasopharyngeal approach achieves preferential brain cooling.

AIM In patients with cardiopulmonary arrest, brain cooling may improve neurological outcome, especially if applied prior to or during early reperfusion. Thus it is important to develop feasible cooling methods for pre-hospital use. This study examines cerebral and compartmental thermokinetic properties of nasopharyngeal cooling during various blood flow states. METHODS Ten swine (40+/-4kg) were anesthetized, intubated and monitored. Temperature was determined in the frontal lobe of the brain, in the aorta, and in the rectum. After the preparatory phase the cooling device (RhinoChill system), which produces evaporative cooling in the nasopharyngeal area, was activated for 60min. The thermokinetic response was evaluated during stable anaesthesia (NF, n=3); during untreated cardiopulmonary arrest (ZF, n=3); during CPR (LF, n=4). RESULTS Effective brain cooling was achieved in all groups with a median cerebral temperature decrease of -4.7 degrees C for NF, -4.3 degrees C for ZF and -3.4 degrees C for LF after 60min. The initial brain cooling rate however was fastest in NF, followed by LF, and was slowest in ZF; the median brain temperature decrease from baseline after 15min of cooling was -2.48 degrees C for NF, -0.12 degrees C for ZF, and -0.93 degrees C for LF, respectively. A median aortic temperature change of -2.76 degrees C for NF, -0.97 for LF and +1.1 degrees C for ZF after 60min indicated preferential brain cooling in all groups. CONCLUSION While nasopharyngeal cooling in swine is effective at producing preferential cerebral hypothermia in various blood flow states, initial brain cooling is most efficient with normal circulation.

Persistently Altered Brain Mitochondrial Bioenergetics After Apparently Successful Resuscitation From Cardiac Arrest.

Background Although advances in cardiopulmonary resuscitation have improved survival from cardiac arrest (CA), neurologic injury persists and impaired mitochondrial bioenergetics may be critical for targeted neuroresuscitation. The authors sought to determine if excellent cardiopulmonary resuscitation and postresuscitation care and good traditional survival rates result in persistently disordered cerebral mitochondrial bioenergetics in a porcine pediatric model of asphyxia-associated ventricular fibrillation CA. Methods and Results After 7 minutes of asphyxia, followed by ventricular fibrillation, 5 female 1-month-old swine (4 sham) received blood pressure–targeted care: titration of compression depth to systolic blood pressure of 90 mm Hg and vasopressor administration to a coronary perfusion pressure >20 mm Hg. All animals received protocol-based vasopressor support after return of spontaneous circulation for 4 hours before they were killed. The primary outcome was integrated mitochondrial electron transport system (ETS) function. CA animals displayed significantly decreased maximal, coupled oxidative phosphorylating respiration (OXPHOSCI+CII) in cortex (P<0.02) and hippocampus (P<0.02), as well as decreased phosphorylation and coupling efficiency (cortex, P<0.05; hippocampus, P<0.05). Complex I– and complex II–driven respiration were both significantly decreased after CA (cortex: OXPHOSCI P<0.01, ETSCII P<0.05; hippocampus: OXPHOSCI P<0.03, ETSCII P<0.01). In the hippocampus, there was a significant decrease in maximal uncoupled, nonphosphorylating respiration (ETSCI+CII), as well as a 30% reduction in citrate synthase activity (P<0.04). Conclusions Mitochondria in both the cortex and hippocampus displayed significant alterations in respiratory function after CA despite excellent cardiopulmonary resuscitation and postresuscitation care in asphyxia-associated ventricular fibrillation CA. Analysis of integrated ETS function identifies mitochondrial bioenergetic failure as a target for goal-directed neuroresuscitation after CA. IACUC Protocol: IAC 13-001023.

Imaging Macromolecular Interactions at an Interface

Important physiological, pathological, and technological processes occur at continuous and dispersed phase interfaces. Understanding these processes is limited by inability to quantitate molecular events occurring at the interface. To provide a model-independent measurement of protein concentration and mobility at the interface, we employed confocal laser scanning microscopy (CLSM). Fluorescently labeled albumin and fibrinogen were studied singly, pairwise, and with a surfactant, Pluronic F-127, in aqueous droplets. CLSM enables measurement of molecular behaviors manifest as surface inhomogeneity and of biophysical quantities including partitioning between the bulk and the gas-liquid (GL) interface. We conclude that albumin and fibrinogen behave substantially differently at the GL interface, adsorption from multispecies solutions is fundamentally different than adsorption from solutions of single species, and surfactants can inhibit proteins from occupying the interface.

Blood Pressure- and Coronary Perfusion Pressure-Targeted Cardiopulmonary Resuscitation Improves 24-Hour Survival From Ventricular Fibrillation Cardiac Arrest.

Objectives:Treatment algorithms for cardiac arrest are rescuer centric and vary little from patient to patient. The objective of this study was to determine if cardiopulmonary resuscitation–targeted to arterial blood pressure and coronary perfusion pressure rather than optimal guideline care would improve 24-hour survival in a porcine model of ventricular fibrillation cardiac arrest. Data Sources:Preclinical animal laboratory using female 3-month-old swine. Study Selection:A randomized interventional study. Data Extraction:After induction of anesthesia and 7 minutes of untreated ventricular fibrillation, 16 female 3-month-old swine were randomized to 1) blood pressure care: titration of chest compression depth to a systolic blood pressure of 100 mm Hg and vasopressor dosing to maintain coronary perfusion pressure of greater than 20 mm Hg or 2) guideline care: chest compression depth targeted to 51 mm and standard guideline vasopressor dosing. Animals received manual cardiopulmonary resuscitation for 10 minutes before the first defibrillation attempt and standardized postresuscitation care for 24 hours. Data Synthesis:Twenty-four–hour survival was more likely with blood pressure care versus guideline care (0/8 vs 5/8; p < 0.03), and all survivors had normal neurologic examinations. Mean coronary perfusion pressure prior to defibrillation was significantly higher with blood pressure care (28 ± 3 vs 10 ± 6 mm Hg; p < 0.01). Chest compression depth was lower with blood pressure care (48 ± 0.4 vs 44 ± 0.5 mm Hg; p < 0.05), and the number of vasopressor doses was higher with blood pressure care (median, 3 [range, 1–7] vs 2 [range, 2–2]; p < 0.01). Conclusions:Individualized goal-directed hemodynamic resuscitation targeting systolic blood pressure of 100 mm Hg and coronary perfusion pressure of greater than 20 mm Hg improved 24-hour survival compared with guideline care in this model of ventricular fibrillation cardiac arrest.

Protein Assembly at the Air–Water Interface Studied by Fluorescence Microscopy

Protein assembly at the air-water interface (AWI) occurs naturally in many biological processes and provides a method for creating biomaterials. However, the factors that control protein self-assembly at the AWI and the dynamic processes that occur during adsorption are still underexplored. Using fluorescence microscopy, we investigated assembly at the AWI of a model protein, human serum albumin minimally labeled with Texas Red fluorophore. Static and dynamic information was obtained under low subphase concentrations. By varying the solution protein concentration, ionic strength, and redox state, we changed the microstructure of protein assembly at the AWI accordingly. The addition of pluronic surfactant caused phase segregation to occur at the AWI, with fluid surfactant domains and more rigid protein domains revealed by fluorescence recovery after photobleaching experiments. Protein domains were observed to coalesce during this competitive adsorption process.

Gas embolism and surfactant-based intervention : Implications for long-duration space-based activity

Abstract:  Intravascular gas embolism can occur with decompression in space flight, and it commonly occurs during cardiac and vascular surgery. Intravascular bubbles may be deposited into any end organ such as the heart or the brain. Surface interactions between the bubble and the endothelial cells lining the vasculature result in serious impairment of blood flow and can lead to heart attack, stroke, or even death. Surfactant‐based intervention is a novel treatment for gas embolism. Intravascular surfactant can adsorb onto the gas–liquid interface and compete with blood‐borne macromolecules for interfacial occupancy. Surfactants can retard the progress of pathophysiological molecular and cellular events stimulated by the bubble surface, including endothelial cell injury and initiation of blood clotting. Bulk and surface transport of a surfactant to provide competition for interfacial occupancy is a therapeutic strategy because surfactant adsorption can dominate protein (or other macromolecule) adsorption. The presence of surfactant along the gas–liquid interface also induces variation in the interfacial tension, which in turn affects the blood flow and the bubble motion. We describe the interplay between biological transport processes and physiological events occurring and the cellular and molecular level in vascular gas embolization. Special consideration is given to modeling the transport and hydrodynamic interactions associated with surfactant‐based intervention.