Hemolysis can lead to a severe crisis, primarily resulting from loss of oxygen-carrying capacity of arterial blood. Hemolytic crisis can lead to signs of anemia, shock, and even death. Other signs, such as thrombosis and icterus, may result from the consequences of hemolysis. Several diagnostic steps are necessary to not only diagnose hemolysis but also to determine if an underlying cause of the hemolytic crisis exists.<\/span><\/p>\n Take-Home Points<\/strong><\/p>\n <\/div><\/div><\/p>\n A<\/span>nemia in small animals is defined as decreased circulating red blood cells (RBCs), which is practically defined as reduced PCV, hematocrit, hemoglobin concentration, or total RBC count below the reference interval.1<\/sup> Because breed differences, geographic location, and methods of measuring these values can alter the reference interval, a local, age- and breed-specific definition of anemia is recommended.<\/p>\n In response to anemia, rapid compensatory mechanisms result in increased cardiac output and redistribution of blood flow through autoregulation and altered systemic vascular resistance, usually resulting in constriction of blood vessels in nonessential or peripheral tissues. When anemia continues over a longer period, other compensatory mechanisms (which may take days) include increased blood flow, increased oxygen onloading and offloading from the hemoglobin molecule (through increased 2,3-diphosphoglycerate), and eventually, production of new RBCs under the influence of erythropoietin. When anemia is severe or acute enough, these mechanisms are insufficient and\/or have a maximal level of compensatory ability, potentially leading to shock or death.<\/p>\n Anemia secondary to hemolysis can result in a state in which oxygen consumption becomes dependent on oxygen delivery (FIGURE 1<\/b><\/span>). Tissue oxygen delivery is dependent on several physiologic concepts (BOX 1<\/b><\/span>). Most of the oxygen in the blood is carried on hemoglobin, which is effective as an oxygen-carrying molecule only when it is in the tetrameric form, found inside RBCs. When hemoglobin is not present in sufficient quantities, the delivery of oxygen to tissues decreases. A small amount of oxygen is also dissolved in the plasma; however, that amount is trivial compared with the amount attached to the hemoglobin molecule.<\/p>\n FIGURE 1. Oxygen delivery (DO2<\/sub>) and oxygen consumption (VO2<\/sub>) relationship curve. There are 2 portions of the relationship curve. The red flat line is the DO2<\/sub>-independent portion of the VO2<\/sub> curve; in this portion of the curve, more oxygen is delivered to tissues than is required to meet physiologic needs and is the status for most healthy animals. In anemic patients, delivery of oxygen decreases (moving toward the left of the curve), depending on the severity of the anemia. If anemia (and DO2<\/sub>) becomes severe enough, a critical point of oxygen delivery (DO2crit<\/sub>), may be reached, where the amount of oxygen being delivered to the body matches the amount being consumed. Below this point (further toward the left), there is no longer enough oxygen being delivered to the tissues to meet physiologic demands, and VO2<\/sub> becomes dependent on the amount of oxygen being delivered, leading to tissue hypoxia and clinical signs of anemia.<\/p><\/div>\n CO = HR \u00d7 SV<\/p>\n Cao2<\/sub> = (Sao2<\/sub> \u00d7 Hgb \u00d7 1.37) + (Pao2<\/sub> \u00d7 0.003)<\/p>\n <\/div><\/div>\n In the presence of hemolysis, hemoglobin is no longer an effective oxygen-carrying molecule. The clinical signs of poor oxygen delivery are the same as those of most states of shock. In this context, poor oxygen delivery is from anemia (low hemoglobin resulting from oxygen delivery to the tissues falling below the critical point). Signs of anemia can include tachycardia; tachypnea; weakness; lethargy; pale mucous membranes (FIGURE 2<\/b><\/span>) with prolonged capillary refill time; altered mentation; cool extremities\/skin; collapse; and, if severe enough, death. Patients exhibiting these clinical signs often need rapid intervention, not only to treat the anemia (e.g., transfusions) but also for diagnostics to investigate the underlying cause of the anemia.<\/p>\n\n
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Clinical Signs<\/b><\/span><\/h2>\n