EFFECT OF ACUTE BRAIN DEATH ON RELEASE OF ATRIUM AND B-TYPE NATRIURETIC PEPTIDES IN AN ANIMAL MODEL

Brain stem death induces pro-inflammatory cytokine production and cardiac dysfunction in sheep model

Introduction

Organs procured following brain stem death (BSD) are the main source of organ grafts for transplantation. However, BSD is associated with inflammatory responses that may damage the organ and affect both the quantity and quality of organs available for transplant. Therefore, we aimed to investigate plasma and bronchoalveolar lavage (BAL) pro-inflammatory cytokine profiles and cardiovascular physiology in a clinically relevant 6-h ovine model of BSD.

Methods

Twelve healthy female sheep (37–42 Kg) were anaesthetized and mechanically ventilated prior to undergoing BSD induction and then monitored for 6 h. Plasma and BAL endothelin-1 and cytokines (IL-1β, 6, 8 and tumour necrosis factor alpha (TNF-α)) were assessed by ELISA. Differential white blood cell counts were performed. Cardiac function during BSD was also examined using echocardiography, and cardiac biomarkers (A-type natriuretic peptide and troponin I were measured in plasma.

Results

Plasma concentrations big ET-1, IL-6, IL-8, TNF-α and BAL IL-8 were significantly (p < 0.01) increased over baseline at 6 h post-BSD. Increased numbers of neutrophils were observed in the whole blood (3.1 × 10⁹ cells/L [95% confidence interval (CI) 2.06–4.14] vs. 6 × 10⁹ cells/L [95%CI 3.92–7.97]; p < 0.01) and BAL (4.5 × 10⁹ cells/L [95%CI 0.41–9.41] vs. 26 [95%CI 12.29–39.80]; p = 0.03) after 6 h of BSD induction vs baseline. A significant increase in ANP production (20.28 pM [95%CI 16.18–24.37] vs. 78.68 pM [95%CI 53.16–104.21]; p < 0.0001) and cTnI release (0.039 ng/mL vs. 4.26 [95%CI 2.69–5.83] ng/mL; p < 0.0001), associated with a significant reduction in heart contractile function, were observed between baseline and 6 h.

Conclusions

BSD induced systemic pro-inflammatory responses, characterized by increased neutrophil infiltration and cytokine production in the circulation and BAL fluid, and associated with reduced heart contractile function in ovine model of BSD.

Systemic and Myocardial Oxygen Transport Responses to Brain Death in Pigs

BACKGROUND

Brain death is associated with profound disturbances of systemic and myocardial oxygen transport, but little is known regarding the acute response of systemic oxygen consumption (VO(2)).

METHODS

Brain death was induced in 6 pigs (30.6 +/- 3.0 kg) by balloon inflation into the cranial cavity. VO(2) was continuously measured by respiratory mass spectrometry. Blood pressures and gases were measured from the aorta, superior vena cava, and coronary sinus, with arterial epinephrine and norepinephrine, prior to brain death, at 1, 10, and 90 minutes after brain death. Cardiac output (CO), systemic vascular resistance (SVR), oxygen delivery (DO(2)), oxygen extraction (EO(2)), and myocardial oxygen (mEO(2)) and lactate extractions (mE(1ac)) were calculated. Left ventricular contractility was assessed by micromanometer tipped catheters.

RESULTS

VO(2) increased from 4.8 +/- 0.9 to 6.3 +/- 0.9 mL/min/kg 1 minute after brain death (P < .001), and subsequently decreased to below baseline at 90 minutes (P < .001). Left ventricular contractility, CO, and DO(2) increased 1 minute after brain death (P < .001), followed by a rapid decrease to baseline within 10 minutes (P < .001). SVR and EO(2) decreased after brain death (P < .01) and remained low. Lactate remained unchanged. mE(1ac) decreased after brain death despite a decrease in mEO(2) (P < .01), and returned to baseline at 90 minutes.

CONCLUSIONS

The initial surge in VO(2) after brain death is offset by the greater increase in DO(2), thus tissue perfusion remains adequate. The lower than baseline VO(2) and SVR at the end of the study period may indicate general metabolic and hemodynamic compromise. The information regarding the profound metabolic alterations imposed by brain death may have implications for management of brain death donors.

Selected physiologic compatibilities and incompatibilities between human and porcine organ systems

The shortage of donor organs is a major barrier to clinical organ transplantation. Although xenotransplantation is considered one of the alternatives to human organ transplantation, there are immunologic and physiologic incompatibilities between humans and pigs. With the exception of coagulation, the major potential physiologic incompatibilities relating to function of the kidney, heart, liver, lungs, pancreatic islets, and hormones are reviewed. Some of these physiologic differences can be overcome by producing genetically altered pigs to improve compatibility with humans. The possibility of producing such pigs for organ transplantation is considered.

Organ-specific regulation of pro-inflammatory molecules in heart, lung, and kidney following brain death

BACKGROUND

Nonspecific inflammatory events following brain death may increase the intensity of the immunological host response. The present study investigated the course of pro-inflammatory molecules in heart, lung, kidney, and plasma after brain death induction.

MATERIALS AND METHODS

Brain death was induced in five pigs by inflation of an intracranial Foley catheter and five pigs were sham-operated as controls. Each experiment was terminated 6 h after brain death/sham operation and the organs were harvested. We measured the mRNA and protein levels for TNF-alpha, IL-1beta, and IL-6 in heart, lung, kidney, and plasma. Additionally, the mRNA expression for IL-6R, ICAM-1, MCP-1, and TGF-beta was determined in each organ.

RESULTS

After 6 h, the plasma cytokine levels were higher in the brain-dead animals than in the sham-operated. In heart, lung, and kidney there was an increase in IL-6 and IL-1beta following brain death, while TNF-alpha was up-regulated in lung only (P < 0.05). MCP-1 and TGF-beta were significantly higher in heart and lung and IL-6R increased in heart after brain death (P < 0.05).

CONCLUSIONS

Brain death was associated with non-uniform cytokine expression patterns in the investigated organs. These expression patterns may cause variable pro-inflammatory priming resulting in different degrees of damage and explain the organ-specific variation in outcomes after transplantations.