This chapter will discuss anemia, thrombocytopenia, coagulation disorders, and oncologic emergencies that are seen in the critical care setting.
Two-thirds of patients admitted to the intensive care unit (ICU) will have a hemoglobin level less than 12 g/dL, and 97% will have anemia by day 8.1-4 The lifespan of a red blood cell (RBC) is 120 days, and normal aging leads to increased oxygen hemoglobin affinity, decreased repair of oxidant injury, and decreased ability to membrane deformability during transit.1,5 Red blood cell formation begins at 20 mL/d and can increase to 200 mL/d in hemolysis and heavy blood loss in a healthy patient.6 Increasing levels of erythropoietin stimulate red cell production, inhibit erythroid precursor apoptosis, and enhance the removal of senescent RBCS. In addition to erythropoietin, healthy RBC production requires iron, zinc, folate, vitamin B12, thyroxine, androgens, cortisol, and catecholamines.1
Anemia in the ICU is due to blood loss and decreased production.1 Insensible blood loss occurs from phlebotomy, especially for patients with arterial catheters; stress gastritis exacerbated by mechanical ventilation, nutritional deficiencies, antithrombotic medication, and renal failure; and invasive procedures and surgical interventions.1,7-12 Decreased production may be secondary to nutritional deficiencies, anemia of inflammation (AI), and medications. In AI, cytokines such as interleukin-1 (IL-1), tumor necrosis factor-α (TNF-α), and IL-6 increase hepatic hepcidin synthesis, which inhibits iron absorption and delivery to the bone marrow compartment and blocks iron release from bone marrow macrophages to the erythron.1,13-16 Medications such as norepinephrine and phenylephrine inhibit hematopoietic maturation and angiotensin-converting enzyme inhibitors (ACEI), calcium channel blockers, theophylline, and β-adrenergic blockers suppress the secretion of erythropoietin by the kidney in response to anemia-induced hypoxemia.17-20
Anemia has been shown to be associated with adverse effects and poor outcomes in patients with normal renal function, chronic renal failure, chronic obstructive pulmonary disease (COPD), congestive heart failure, and acute myocardial infarction.21-31 Anemia can persist up to 6 months after ICU stay.32
Anemias are classified based on the mean corpuscular volume (MCV) and the reticulocyte count (Table 23-1). The next step in the diagnosis of anemia is examining the leukocyte count and differential, the platelet count, and the blood smear (Table 23-2). Anemias are normocytic, microcytic, and macrocytic, and within each category, they are subdivided into normoproliferative, hypoproliferative, and hyperproliferative, if the reticulocyte count is normal, decreased, or increased, respectively. Healthy reticulocyte production should increase 1.5-fold for a hematocrit (Hct) of 30% to 40%, should double with Hct of 20% to 30%, and should triple with Hct of 15% or less; these increases are designated maturation factors. The reticulocyte production index (RPI) is used to determine proliferation status:
RPI = (Reticulocyte Count × Hct of Patient/45)/Maturation Factor