Repeated epinephrine doses during prolonged cardiopulmonary resuscitation have limited effects on myocardial blood flow: a randomized porcine study.

BACKGROUND: In current guidelines, prolonged cardiopulmonary resuscitation (CPR) mandates administration of repeated intravenous epinephrine (EPI) doses. This porcine study simulating a prolonged CPR-situation in the coronary catheterisation laboratory, explores the effect of EPI-administrations on coronary perfusion pressure (CPP), continuous coronary artery flow average peak velocity (APV) and amplitude spectrum area (AMSA). METHODS: Thirty-six pigs were randomized 1:1:1 to EPI 0.02 mg/kg/dose, EPI 0.03 mg/kg/dose or saline (control) in an experimental cardiac arrest (CA) model. During 15 minutes of mechanical chest compressions, four EPI/saline-injections were administered, and the effect on CPP, APV and AMSA were recorded. Comparisons were performed between the control and the two EPI-groups and a combination of the two EPI-groups, EPI-all. RESULT: Compared to the control group, maximum peak of CPP (Pmax) after injection 1 and 2 was significantly increased in the EPI-all group (p = 0.022, p = 0.016), in EPI 0.02-group after injection 2 and 3 (p = 0.023, p = 0.027) and in EPI 0.03-group after injection 1 (p = 0.013). At Pmax, APV increased only after first injection in both the EPI-all and the EPI 0.03-group compared with the control group (p = 0.011, p = 0.018). There was no statistical difference of AMSA at any Pmax. Seven out of 12 animals (58%) in each EPI-group versus 10 out of 12 (83%) achieved spontaneous circulation after CA. CONCLUSION: In an experimental CA-CPR pig model repeated doses of intravenous EPI results in a significant increase in APV only after the first injection despite increments in CPP also during the following 2 injections indicating inappropriate changes in coronary vascular resistance during subsequent EPI administration.

Optimal timing of hypothermia in relation to myocardial reperfusion.

Two previous clinical trials investigating hypothermia as an adjunct therapy for myocardial infarction have failed. Recently a pilot study has demonstrated a significant reduction in infarct size. The aims of this study were to elucidate the effects of hypothermia on reperfusion injury and to investigate the optimal hypothermia protocol for a future clinical trial. Pigs (40-50 kg) were anesthetized and a normal pig temperature of 38°C was established utilizing an endovascular temperature modulating catheter. The pigs were randomized to a combination hypothermia group (1,000 ml of 4°C saline solution and endovascular cooling, n = 8), or to normothermic controls (n = 8). A PCI balloon was then inflated in the LAD for 40 min (control) or 45 min with hypothermia induced during the last 5 min. Furthermore, hypothermia induced by cold saline alone (n = 8), and prolonged combination hypothermia during reperfusion (n = 7) were also examined. Infarct size and area at risk were determined ex vivo after 4 h of reperfusion using gadolinium-enhanced MRI and Tc-99-tetrofosmin SPECT, respectively. All pigs in the combination hypothermia group were cooled to <35°C within 5 min. Combination hypothermia reduced IS/AAR by 18% compared with normothermic controls despite 5 min longer ischemic time (61 ± 5 vs. 74 ± 4%, p = 0.03). Cold saline did not reduce IS/AAR. Prolonging hypothermia treatment after onset of reperfusion by an additional 45 min over that used in a previous paper did not confer any additional benefit. The cardioprotective effects of hypothermia treatment are due to an attenuation of myocardial injury during both ischemia and reperfusion. The results suggest that a hypothermia protocol using a cold saline infusion and endovascular cooling enables hypothermia to be induced in a clinical setting without delaying reperfusion therapy.

Hypothermia in cardiogenic shock reduces systemic t-PA release.

Therapeutic hypothermia has been found to improve hemodynamic and metabolic parameters in cardiogenic shock. Tissue plasminogen activator (t-PA) is a pro-thrombolytic enzyme, which also possesses pro-inflammatory properties. Interleukin 6 (IL-6) and tumour necrosis factor alpha (TNF-α) are pro-inflammatory cytokines; interleukin 10 (IL-10) and transforming growth factor beta 1 (TGF-ß1) are anti-inflammatory cytokines. The aim of this experiment was to investigate the mechanism behind the protective effect of therapeutic hypothermia in cardiogenic shock. This was done by studying the effect of hypothermia on basal t-PA levels, peripheral t-PA release, and on the inflammatory response. Cardiogenic shock was induced by inflation of an angioplasty balloon in the proximal left anterior descending artery for 40 min in 16 pigs, followed by 110 min of reperfusion. The animals were randomized to hypothermia (33°C, n = 8), or normothermia (n = 8) at reperfusion. Hemodynamic parameters were continuously monitored. Plasma was sampled every 30 min for analysis of blood-gases and t-PA, and for analysis of inflammatory markers at baseline and at the end of the experiment. t-PA, IL-6 and TGF-ß1 increased during cardiogenic shock. Apart from favourably affecting hemodynamic and metabolic variables, hypothermia was found to reduce basal arterial and venous t-PA levels, and to inhibit the release of t-PA from the peripheral vascular bed. Hypothermia did not alter the inflammatory response. In conclusion, mild hypothermia improves hemodynamic and metabolic parameters in cardiogenic shock. This is associated with a reduction in basal t-PA levels and t-PA release from the peripheral vascular bed, but not with an altered inflammatory response.

Apyrase treatment of myocardial infarction according to a clinically applicable protocol fails to reduce myocardial injury in a porcine model.

BACKGROUND: Ectonucleotidase dependent adenosine generation has been implicated in preconditioning related cardioprotection against ischemia-reperfusion injury, and treatment with a soluble ectonucleotidase has been shown to reduce myocardial infarct size (IS) when applied prior to induction of ischemia. However, ectonucleotidase treatment according to a clinically applicable protocol, with administration only after induction of ischemia, has not previously been evaluated. We therefore investigated if treatment with the ectonucleotidase apyrase, according to a clinically applicable protocol, would reduce IS and microvascular obstruction (MO) in a large animal model. METHODS: A percutaneous coronary intervention balloon was inflated in the left anterior descending artery for 40 min, in 16 anesthetized pigs (40-50 kg). The pigs were randomized to 40 min of 1 ml/min intracoronary infusion of apyrase (10 U/ml, n = 8) or saline (0.9 mg/ml, n = 8), twenty minutes after balloon inflation. Area at risk (AAR) was evaluated by ex vivo SPECT. IS and MO were evaluated by ex vivo MRI. RESULTS: No differences were observed between the apyrase group and saline group with respect to IS/AAR (75.7 +/- 4.2% vs 69.4 +/- 5.0%, p = NS) or MO (10.7 +/- 4.8% vs 11.4 +/- 4.8%, p = NS), but apyrase prolonged the post-ischemic reactive hyperemia. CONCLUSION: Apyrase treatment according to a clinically applicable protocol, with administration of apyrase after induction of ischemia, does not reduce myocardial infarct size or microvascular obstruction.

Physiologic effect of repeated adrenaline (epinephrine) doses during cardiopulmonary resuscitation in the cath lab setting: A randomised porcine study.

BACKGROUND: This porcine study was designed to explore the effects of repetitive intravenous adrenaline doses on physiologic parameters during CPR. METHODS: Thirty-six adult pigs were randomised to four injections of: adrenaline 0.02 mg(kgdose)(-1), adrenaline 0.03 mg(kgdose)(-1) or saline control. The effect on systolic, diastolic and mean arterial blood pressure, cerebral perfusion pressure (CePP), end tidal carbon dioxide (ETCO2), arterial oxygen saturation via pulse oximetry (SpO2), cerebral tissue oximetry (SctO2), were analysed immediately prior to each injection and at peak arterial systolic pressure and arterial blood gases were analysed at baseline and after 15 min. RESULT: In the group given 0.02 mg(kgdose)(-1), there were increases in all arterial blood pressures at all 4 pressure peaks but CePP only increased significantly after peak 1. A decrease in ETCO2 following peak 1 and 2 was observed. SctO2 and SpO2 were lowered following injection 2 and beyond. In the group given a 0.03 mg(kgdose)(-1), all ABP's increased at the first 4 pressure peaks but CePP only following 3 pressure peaks. Lower ETCO2, SctO2 and SpO2 were seen at peak 1 and beyond. In the two adrenaline groups, pH and Base Excess were lower and lactate levels higher compared to baseline as well as compared to the control. CONCLUSION: Repetitive intravenous adrenaline doses increased ABP's and to some extent also CePP, but significantly decreased organ and brain perfusion. The institutional protocol number: Malmö/Lund Committee for Animal Experiment Ethics, approval reference number: M 192-10.

Mild hypothermia reduces acute mortality and improves hemodynamic outcome in a cardiogenic shock pig model.

INTRODUCTION: Cardiogenic shock is the main cause of death in patients hospitalized due to an acute myocardial infarction. Mild hypothermia reduces metabolism and could offer protective effects for this condition. The aim of our study was to investigate if mild therapeutic hypothermia would improve outcome and hemodynamic parameters in an ischemic cardiogenic shock pig model. METHODS: Twenty-five pigs (40-50 kg) were anesthetized and a normothermic temperature of 38 degrees C was established utilising an endovascular cooling catheter in a closed-chest model. A Swan-Ganz catheter was placed in the pulmonary artery. Hemodynamic parameters were continuously monitored and blood gases were sampled every 30 min. Ischemia was induced by inflation of a PCI balloon in proximal LAD for 40 min. Sixteen pigs that have fulfilled predefined shock criteria were randomized to hypothermia (n=8), or normothermia (n=8). Hypothermia (33 degrees C) was induced after onset of reperfusion by using an endovascular temperature modulating catheter and was maintained until termination of the experiment. RESULTS: The pigs in the hypothermia group were cooled to <34 degrees C in approximately 45 min. 5/8 pigs in the normothermia group died while all pigs in the hypothermia group survived (p<0.01). Stroke volume and blood pressure were significantly higher in the hypothermia group (p<0.05), whereas heart rate was significantly lower in the hypothermia group (p=0.01). Cardiac output did not differ among the groups (p=0.13). Blood gas analysis revealed higher mixed venous oxygen saturation, pH, and base excess in the hypothermia group indicating less development of metabolic acidosis (p<0.05). CONCLUSIONS: In this pig model, mild therapeutic hypothermia reduces acute mortality in cardiogenic shock, improves hemodynamic parameters and reduces metabolic acidosis. These findings suggest a possible clinical benefit of therapeutic hypothermia for patients with acute cardiogenic shock.