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Circulating erythrocyte numbers may be decreased by intravascular hemolysis or by sequestration of red cells followed by their destruction within the mononuclear phagocytic system. The mechanisms of intravascular hemolysis from physical or chemical agents include hypotonic lysis, pore formation within the erythrocyte membrane by a broad range of biotoxins, and heat damage to the spectrin skeleton.

Extravascular sequestration and destruction are initiated by oxidizing agents such as oxygen, arsine gas, and chlorates. Allied mechanisms appear to be responsible for erythrocytolysis and for neocytolysis, the selective destruction of young red cells, a phenomenon unique to microgravity.

In addition, hemolysis can be induced by other agents, although their mechanism of action has not been defined. Table 51–1 lists some of these agents. Descriptions of erythrocyte damage caused by lead, copper, and radiation are also included in the text.

Table 51–1. Drugs and Chemicals That Have Been Reported to Cause Hemolytic Anemia

Acronyms and Abbreviations

Acronyms and abbreviations that appear in this chapter include: AsH3, arsenic hydride (arsine gas); EDTA, ethylenediaminetetraacetic acid; G-6-PD, glucose-6-phosphate dehydrogenase; HFE, hemochromatosis gene; NADPH, reduced nicotinamide adenine dinucleotide phosphate.

There are two principle means by which circulating red cells may be removed other than by bleeding (see Chap. 32). The first is intravascular hemolysis. The second is red cell sequestration and destruction by the mononuclear phagocytic system.

Chaps. 46 and 48 discuss the hemolysis that results when certain drugs are administered to patients deficient in glucose-6-phosphate dehydrogenase (G-6-PD) or with unstable hemoglobins. Immune mechanisms may also play a role in drug- or toxin-induced hemolytic anemias, and are discussed in Chap. 53. Microangiopathic hemolytic anemias (see Chap. 50) can also be caused by drugs such as mitomycin. The present chapter deals with drugs, toxins, and other physical agents that can cause red cell destruction, which are not discussed in other chapters.

Hypotonic Lysis

When large amounts of distilled water gain access to the systemic circulation, either by intravenous injection or when used as an irrigating solution during surgery, hemolysis will occur.1 Severe hemolysis may also result from water inhalation in near-drowning.2 Another rare, but not insignificant, example is hypotonic lysis secondary to water intoxication which occurs from polydipsia in the setting of psychiatric illness or hazing rituals.3

Pore Formation Within the Red Blood Cell Membrane

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