Experimental treatment with beta blockers of hemodynamic and myocardial changes in organ donors

Mesenteric hypoperfusion and inflammation induced by brain death are not affected by inhibition of the autonomic storm in rats

OBJECTIVES

Brain death is typically followed by autonomic changes that lead to hemodynamic instability, which is likely associated with microcirculatory dysfunction and inflammation. We evaluated the role of the microcirculation in the hemodynamic and inflammatory events that occur after brain death and the effects of autonomic storm inhibition via thoracic epidural blockade on mesenteric microcirculatory changes and inflammatory responses.

METHODS

Male Wistar rats were anesthetized and mechanically ventilated. Brain death was induced via intracranial balloon inflation. Bupivacaine (brain death-thoracic epidural blockade group) or saline (brain death group) infusion via an epidural catheter was initiated immediately before brain death induction. Sham-operated animals were used as controls (SH group). The mesenteric microcirculation was analyzed via intravital microscopy, and the expression of adhesion molecules was evaluated via immunohistochemistry 180 min after brain death induction.

RESULTS

A significant difference in mean arterial pressure behavior was observed between the brain death-thoracic epidural blockade group and the other groups, indicating that the former group experienced autonomic storm inhibition. However, the proportion of perfused small vessels in the brain death-thoracic epidural blockade group was similar to or lower than that in the brain death and SH groups, respectively. The expression of intercellular adhesion molecule 1 was similar between the brain death-thoracic epidural blockade and brain death groups but was significantly lower in the SH group than in the other two groups. The number of migrating leukocytes in the perivascular tissue followed the same trend for all groups.

CONCLUSIONS

Although thoracic epidural blockade effectively inhibited the autonomic storm, it did not affect mesenteric hypoperfusion or inflammation induced by brain death.

Takotsubo cardiomyopathy: its possible impact during adult donor care

Takotsubo cardiomyopathy, the syndrome caused by an extreme release and circulation of catecholamines, shares several histopathological and clinical similarities with cardiac changes after brain death noted in animal investigations and human observation. Overwhelming stimulation of myocardial inotropic β receptors may alter their responsiveness and induce other biochemical processes, producing reduced cardiac contractility. Treatment methods in Takotsubo cardiomyopathy that use extracorporeal circulatory support and medications that do not rely on β-receptor stimulation and preemptive blockade of β receptors or calcium channels before brain death may be relevant to donor care.

Takotsubo Cardiomyopathy: Its Possible Impact during Adult Donor Care

Takotsubo cardiomyopathy, the syndrome caused by an extreme release and circulation of catecholamines, shares several histopathological and clinical similarities with cardiac changes after brain death noted in animal investigations and human observation. Overwhelming stimulation of myocardial inotropic β receptors may alter their responsiveness and induce other biochemical processes, producing reduced cardiac contractility. Treatment methods in Takotsubo cardiomyopathy that use extracorporeal circulatory support and medications that do not rely on β-receptor stimulation and preemptive blockade of β receptors or calcium channels before brain death may be relevant to donor care.

Brain death provokes very acute alteration in myocardial morphology detected by echocardiography: preventive effect of beta-blockers

Our objective was to evaluate immediate acute changes in myocardial function during the autonomic storm of brain death (BD). Wistar rats were divided into four groups (n = 8/group): controls without any treatment, β-blocker (Esmolol®, 10 mg/kg), calcium channel blocker (Diltiazem®, 10 mg/kg), or alpha-blocker (Prazosin®, 0.3 mg/kg). Treatments were administered intravenously 5 min before BD induction. Echocardiography (ATL-5000, 8 MHz) was performed to measure left ventricular (LV) dimensions and fractional shortening at baseline, during BD induction and 5 min and 15 min after BD. In controls, BD was immediately associated with an increase in wall thickness and a decrease in LV cavity dimension. This myocardial wall hypertrophy was completely prevented by β-blockers, but not with calcium- and alpha-blockers. Extensive myocardial interstitial edema was found in all groups, except in the β-blocker group. Myocardial wall hypertrophy was also prevented during a longer follow-up of 180 min after BD in β-blocker group as opposed to controls. In conclusion, BD is associated with an immediate and severe myocardial damage related to an important interstitial edema which is prevented by β-blockers.

Improvement of Donor Myocardial Function after Treatment of Autonomic Storm During Brain Death

BACKGROUND

In experimental brain death models, autonomic storm (AS) triggers severe myocardial dysfunction, which can be attenuated by pharmacologic treatment. The aim of this study was to determine the incidence of AS in a cohort of human organ donors and to evaluate the potential interest of AS treatment on myocardial function, cardiac harvesting and transplantation.

METHODS

The cohort consisted of 152 patients. Among them, 46 patients were initially considered as potential cardiac donors (main criteria: age < 60 years, no history of cardiac disease). AS diagnosis included increased systolic arterial pressure > 200 mm Hg associated with tachycardia >140 beats/min. Heart acceptance criteria were associated creatine kinase (CK), troponin Ic, and left ventricle ejection fraction (LVEF) estimated by echocardiography and visual inspection.

RESULTS

AS was observed in 29 patients (63%). Hypertension was treated in 12 patients (esmolol n = 6, urapidil n = 5, nicardipine). Cardiac harvesting was performed in 28 donors (61%). LVEFs were significantly higher after AS treatment (no AS: 55.4 +/- 13.4%, untreated AS: 49.0 +/- 18.8%, treated AS: 63.9+ +/- 10.3%, P = 0.049). AS treatment was found to be independently associated with LVEF in > 50% of the cases (P = 0.034). Treatment of AS or the lack of AS were associated with an increased probability of successful cardiac transplantation (OR = 8.8; 95% CI 2.1-38.3, P = 0.002).

CONCLUSIONS

Treatment of hypertension during AS may attenuate brain death-induced myocardial dysfunction and increase the number of available cardiac grafts.

Stable myocardial function and endocrine dysfunction during experimental brain death

BACKGROUND

The origin of cardiac impairment during brain death (BD) is controversial. Using a pig experimental model we sought to assess hormonal changes during the first stage of brain death and how these changes contribute to hemodynamic alteration and myocardial dysfunction.

METHODS

Twenty-two pigs were randomized into 2 groups: a control (C) group and a BD group. BD was induced by sub-dural inflation of a balloon catheter. Micromanometers and ultrasonic flow probes were placed on the myocardium to measure cardiovascular parameters. Blood samples and hemodynamic parameters were analyzed before and after induction of BD.

RESULTS

A biphasic release of catecholamines was observed, with an initial peak occurring 1 minute after BD induction, followed by a second peak at 60 minutes. Similarly, a biphasic evolution of dP/dt(max) and systolic blood pressure (SBP) was observed at BD, in parallel with catecholamine evolution. In the BD group, both cortisol and aldosterone decreased progressively over time. Circulating triiodothyronine (T3), levothyroxine (T4), prolactin and melatonin concentrations were similar to those of the control group. The difference in arteriovenous (AV) lactate level in arterial and coronary sinus blood was not significantly different between the 2 groups, suggesting an absence of myocardial ischemia. Furthermore, myocardial contractility was not altered during the 3 hours of BD.

CONCLUSIONS

During the initial period after induction of brain death, cerebral and thyroid hormones remained stable while cortico- and medullo-surrenal hormones varied significantly. We suggest that suprarenal gland impairment is among the first events occurring during brain death. Paradoxically, hemodynamic parameters and myocardial function were not found to be altered.