Intestinal oxygen exchange at condition of anemia

Relevance. Although disorders of oxygen delivery is one of the main factors in the development of intestinal dysfunction and bacterial translocation, the critical level of anemia and possibilities of it lowering remain unclear. Aim. Тo study changes of the system as well as the regional mesenterial oxygen exchange in conditions of normovolemic anemia of different severity. Material and methods. In experiment on 60 white rats under the general anaesthesia by ketamine 50 mg/kg stage-by-stage blood donation and it normovolemic replacement by hydroxyethyl starch were performed, gradually reducing haematocrit to 0,30, 0,25 and 0,20 l/l. Arterial, mixed venous, and mesenteric venous PO2, PCO2, and pH were measured. Systemic and intestinal oxygen transports and consumptions (DO2 and VO2) were calculated by standard equations. The content of lactic acid in the intestinal tissues is additionally determined to assess the degree of activity of local anaerobic metabolism. Results. At mild anemia reduction СаО2 by third of initial size essentially did not influence on system and regional DО2 to tissues. Compensation of oxygen deficiency at haematocrit 0,30 л/л was carried out by rising of a cardiac index due to reduction of viscosity of blood. At moderated anemia concentration hemoglobin and СаО2 decreased twice, changes in system DО2 to tissues led to reduction of Са-vО2 by 32,1 % (р < 0,05). Physiological adaptation was carried out through the increasing of О2ЕR by tissues and was effective. In experimental animals with severe degree of anemia (Hb 58,8 ± 2,4 g/l) СаО2 decreased in 2,5 times what led to occurrence of haemic hypoxia according to level of gases contents of blood. The concentration of lactic acid in intestinal tissues increased on 36.1 % (p = 0.05), deficiency of buffer bases till -8,2 ± 1,7 (p = 0.05). Conclusions. In case of severe anaemia, hypoxia of the intestinal tissues develops, which is accompanied by an increase in the local levels of lactic acid and deficiency of base buffers with the development of subcompensated metabolic acidosis.

Thoracic Epidural Anesthesia with Ropivacaine Does Not Compromise the Tolerance of Acute Normovolemic Anemia in Pigs

Background: The initial treatment of an acute blood loss with acellular fluids leads to the dilution of the red cell mass remaining in the vasculature, that is, to acute normovolemic anemia. Whether the compensation and, thus, the tolerance of acute anemia, are affected by sympathetic block induced by thoracic epidural anesthesia has not yet been investigated. Methods: Eighteen anesthetized and mechanically ventilated pigs were instrumented with thoracic epidural catheters and randomly assigned to receive an epidural injection of either 5-ml ropivacaine 0.2% (n = 9) aiming for a Th5–Th10 block or saline (n = 9) followed by continuous epidural infusion of 5 ml/h of either fluid. Subsequently, acute normovolemic anemia was induced by replacement of whole blood with 6% hydroxyethyl starch solution until a “critical” limitation of oxygen transport capacity was reached as indicated by a sudden decrease in oxygen consumption. The critical hemoglobin concentration quantified at this time point was the primary endpoint; secondary endpoints were hemodynamic and oxygen transport parameters. Results: Thoracic epidural anesthesia elicited only a moderate decrease in mean arterial pressure and cardiac index and a transient decrease in oxygen extraction ratio. During progressive anemia, the compensatory increases in cardiac index and oxygen extraction ratio were not compromised by thoracic epidural anesthesia. Critical hemoglobin concentration was reached at identical levels in both groups (ropivacaine group: 2.5 ± 0.6 g/dl, saline group: 2.5 ± 0.6 g/dl). Conclusion: Thoracic epidural anesthesia with ropivacaine 0.2% does not decrease the tolerance to acute normovolemic anemia in healthy pigs. The hemodynamic compensation of acute anemia is fully preserved despite sympathetic block, and the critical hemoglobin concentration remains unaffected.