Effect of variation in systemic blood flow on plasma TNF-alpha in a pig model with left ventricular assist device.

Tumor necrosis factor-alpha (TNF-alpha) release has been implicated in a sepsis-like syndrome following cardiopulmonary bypass (CPB). This also may be important in patients who have had a left ventricular assist device (LVAD) implanted. This report investigates the effect of reducing systemic blood flow on hemodynamic response, mixed venous oxygen saturation (SvO(2)), and the release of TNF-alpha. LVADs were implanted in 9 pigs. The aorta was clamped, and thus the LVAD flow represented the entire systemic blood flow. Plasma TNF-alpha in the femoral artery (FA) and superior mesenteric vein (SMV) was measured at baseline and following systemic blood flow changes. Simultaneously, hemodynamic parameters and oxygen saturation in the pulmonary artery (SvO(2)) were measured. Following reductions in systemic blood flow, plasma TNF-alpha increased gradually to a maximum level at a systemic blood flow of 20%. There was no significant difference between TNF-alpha levels in the SMV and the FA. There was a significant (p < 0.05) correlation between cardiac index, stroke volume index, and TNF-alpha. The SvO(2) decreased significantly (p < 0.05) at a systemic blood flow of 30 and 20%. A rise in TNF-alpha occurred when the SvO(2) was less than 75%. The data demonstrate that a reduction in systemic blood flow causes an increase in plasma TNF-alpha. This can lead to the development of a sepsis-like syndrome in a group of patients who already are hemodynamically compromised. While weaning short-term LVAD support, rapid diminution of the cardiac output and the pump flow must be avoided.

Intestinal tissue oxygenation and tumor necrosis factor-alpha release during systemic blood flow changes in pigs with left ventricular assist devices.

We previously demonstrated that tumor necrosis factor-alpha (TNF-alpha) increased following a reduction in systemic blood flow to 60% or less of the original cardiac output using a left ventricular assist device (LVAD). The aim of this study was to investigate the effect of reducing systemic blood flow on tissue oxygenation in the gastrointestinal tract (GIT) and the consequences of this on TNF-alpha release. LVADs were implanted in 9 pigs. The aorta was clamped, and thus the LVAD flow represented the entire systemic blood flow. Plasma TNF-alpha of the superior mesenteric vein was measured at baseline and during systemic blood flow changes. Simultaneously, pH, lactate, oxygen delivery index (DO(2)I), oxygen consumption index (VO(2)I), and oxygen extraction (O(2)ER) in the GIT were measured. The pH decreased and the lactate level increased significantly (p < 0.05) at a systemic blood flow of 50% or less. The VO(2)I was positively correlated with DO(2)I. The O(2)ER increased significantly (p < 0.05) with reductions in systemic blood flow to 30% or less. There was a significant (p < 0.01) correlation between TNF-alpha and O(2)ER at levels higher than 55%. These data demonstrate that the GIT oxygenation is inadequate with a reduction in systemic blood flow to 50% and that GIT oxygenation becomes critical at a reduction of 30%. During LVAD weaning, careful attention must be given to the GIT. The pH and lactate may be good markers of the adequacy of tissue oxygenation in the GIT.

The gastrointestinal tract: an underestimated organ as demonstrated in an experimental LVAD pig model.

BACKGROUND: Although hemodynamic stability and renal function are important and are monitored closely in patients with implanted left ventricular assist devices (LVAD), the gastrointestinal tract may be underestimated in the early postoperative period with regard to adequate perfusion. We investigated renal, intestinal, and whole body metabolic changes in response to variations in LVAD flow and inspired oxygen concentration (FiO2). METHODS: Left ventricular assist devices were implanted in 10 adult pigs (weight, 55 +/- 1.76 kg). Renal vein (RV), superior mesenteric vein (SMV), and pulmonary artery (PA) blood oxygen saturation and lactate concentration were measured and used as tissue perfusion markers. These measurements were made at baseline and after changes in LVAD flow or FiO2. RESULTS: Oxygen saturation in the PA, SMV, and RV decreased significantly after a reduction in LVAD flow (P < 0.05), with a greater reduction in the SMV than in the PA and RV (p < 0.05 at LVAD flow 3.5L/min; p < 0.01 at LVAD flow 2.0 and 1.0 L/min). The lactate concentration in the PA and SMV increased significantly (p < 0.01) with decreased flow, with a greater increase in the SMV than in the PA (p< 0.05), whereas it remained unchanged in the RV. Oxygen saturation in the PA, SMV, and RV decreased significantly after a reduction in FiO2 (p < 0.05). Lactate concentration in the PA, SMV, and RV increased significantly at FiO2 of 0.10 (p < 0.05). Lactate concentration in the PA and SMV was significantly higher than that in the RV at Fi)2 of 0.10 (p < 0.01). CONCLUSIONS: The results show that the gastrointestinal tract is at high risk during low perfusion or low FiO2, whereas the kidneys' metabolic function appears to be less disturbed. In clinical practice, this emphasizes the need to ensure adequate blood flow and respiratory function, especially after extubation, in patients with implanted LVAD. This might avoid intestinal ischemia and subsequent endotoxemia. Gastrointestinal tonometry may help in the assessment of intestinal perfusion.