Clark M. Smith

Hemolysis during long-term extracorporeal membrane oxygenation

We studied the cause of hemolysis during extracorporeal membrane oxygenation (ECMO) by monitoring hematologic and coagulation profiles in seven consecutive infants treated with this procedure. A constrained vortex pump was used in all patients, and the average duration of ECMO was 224 +/- 111 (SD) hours. In all patients, plasma free hemoglobin was low during the first 48 hours after the initiation of ECMO. Later, when visible clots appeared in the ECMO circuit, plasma hemoglobin progressively rose. A rise in the level of fibrin degradation products and a fall in the fibrinogen level were observed concurrently with a rise in the plasma hemoglobin level. After complete circuit changes in six patients, plasma free hemoglobin, fibrin split products, and fibrinogen all returned to baseline values. Neither circuit component changes nor exchange transfusion was effective in normalizing the levels of plasma free hemoglobin, fibrin split products, and fibrinogen. We conclude that when ECMO is administered for prolonged periods, circuit thrombosis occurs and hemolysis ensues. Additional studies are needed to assess the contribution of the constrained vortex pump to this process.

Inactivation of heparin during extracorporeal circulation in infants

Heparin anticoagulation is necessary to prevent clotting during procedures involving the extracorporeal circulation of blood. Our preliminary observations suggested that heparin was inactivated in the extracorporeal circuit during extracorporeal membrane oxygenation. We tested this hypothesis by comparing heparin pharmacokinetics in five infants during extracorporeal circulation with kinetics, respectively determined in each patient and in the isolated circuit immediately after discontinuation of the procedure. Heparin clearance was 1.6 ± 0.5 ml/kg/min in the patient and 2.1 ± 0.8 ml/kg/min in the separated circuit. In each patient, the total of heparin clearances in the patient and circuit, 3.7 ± 1.0 ml/kg/min, was virtually identical with the heparin clearance during the procedure, 3.8 ± 1.9 ml/kg/min (r = 0.94, p < 0.01). We conclude that more than one half of the heparin administered to infants during extracorporeal membrane oxygenation is eliminated by the extracorporeal circuit itself or by blood components in the circuit. These data explain the relatively large heparin doses needed to maintain anticoagulation in infants during extracorporeal circulation. In light of these findings, a reexamination of the normal mechanisms of elimination of heparin activity appears to be warranted.

Whole blood activated clotting time in infants during extracorporeal membrane oxygenation

Bleeding complications are the principal cause of morbidity and mortality in infants treated with extracorporeal membrane oxygenation (ECMO). The whole blood activated clotting time (ACT) test is used universally to monitor heparin therapy during this procedure. To enhance our understanding of this test and improve our management of anticoagulation, we studied the relationship between the ACT and blood heparin concentration in nine infants during ECMO. The activated clotting time correlated with the simultaneously determined heparin concentration (r = .55, p less than .001 for all patients samples; r = .92, p less than .001 for mean patients values). Within the range of values found in our patients, platelet count, fibrinogen, and fibrin degradation products did not affect the ACT-heparin concentration relationship. However, the interpretation of an individual ACT result was limited by its low precision: the mean difference of duplicate determinations was 9.2%, and the estimation of heparin concentration by a single ACT had a coefficient of variation of 32%. Two commercially available techniques using different activators gave results that differed numerically but correlated well with each other. Both provided similar precision in the estimation of heparin concentration. The ACT is a low cost, bedside test whose accuracy and precision allow the achievement of target heparin concentrations required in infants during ECMO. Multiple determinations, either in duplicate or serially, are needed to achieve satisfactory precision. These data will be useful in designing future studies to determine the optimal serum heparin concentration to provide adequate anticoagulation, but avoid bleeding complications.

Spontaneous resolution of severe childhood myelofibrosis.

transfusion malaria in splenectomized than in nonsplenectomized patients. Of the seven patients who developed transfusion malaria, six had had splenectomy. A history of malaria before the 1952 eradication program in Sardinia was reported in 2.6% of blood donors. Attempts to identify donors responsible for transmission by careful examination of blood smears were negative. There was no statistically significant difference (P > 0.10) in the number of transfusions received from blood donors with a previous history of malaria between patients with and without overt malaria. DISCUSSION This study showed a higher incidence of Plasmodium malariae transfusion malaria in splenectomized than in nonsplenectomized patients with thalassemia major. This finding suggests that splenectomized subjects are more prone to develop overt P. malariae transfusion malaria than nonsplenectomized patients receiving the same lifelong transfusion treatment from the same pool of blood donors. Therefore, transfusion malaria should be included in the list of high-risk infections after splenectomy. The most interesting finding in this study was overt malaria occurring within 15 days of splenectomy in four cases out of seven. Transmission of malaria may have occurred before splenectomy but the disease remained latent with low parasitemia because of the protective role of the spleen, as in the experimental infection by Plasmodium inui in monkeys) According to this experimental

Iron deficiency among incarcerated juvenile delinquents.

A population of 163 incarcerated delinquents (126 males and 37 females aged 12–18 years) was studied to determine the prevalence of iron deficiency and to compare hemoglobin (Hgb), mean corpuscular volume (MCV), serum ferritin (SF), and erythrocyte protoparphyrin/hemoglobin (EP/Hgb) as predictors of response to iron therapy. Thirty-two percent of females and 6% of males had SF ≤ 12 ng/ml; 51% of females and 24% of males had SF ≤ 20 ng/ml. The mean SF was 17.7 ng/ml for females and 29.2 ng/ml for males. Of the 163 subjects, 53 were at risk for iron deficiency based on SF, Hgb, EP/Hgb, or MCV criteria. Twenty-one completed treatment with iron, and nine had greater than 1 g rise in Hgb. The following tests identified responders: SF ≤ 12 ng/ml-5/9; SF ≤ 20 ng/ml-9/9; Hgb ≤ third percentile-4/9; Hgb ≤ tenth percentile-7/9; MCV ≤ tenth percentile-2/9; EP/Hgb ≥ 3.0 μg/g Hgb-2/9; EP/Hgb ≥ 2.5 μg/g Hgb-4/9. Serum ferritin ≤ 20 ng/ml had a false positive rate of 57%; Hgb ≤ tenth percentile and EP/Hgb ≥ 2.5 μ g/g Hgb had no false positives. The significance of the high prevalence of iron deficiency among a population of incarcerated adolescents is not clear. Serum ferritin ≤ 20 ng/ml offers the most sensitive screening test to suggest iron-responsive anemia, but it has poor specificity; Hgb ≤ tenth percentile is an alternative screening test that is more available, less expensive, nearly as sensitive, and more specific; EP/Hgb ≥ 2.5 μg/g Hgb, MCV ≤ tenth percentile, SF ≤ 12 ng/ml, and Hgb ≤ third percentile did not prove to be good screening tests because of poor sensitivity.

Evaluation of the yield stress of normal blood as a function of fibrinogen concentration and hematocrit.

The yield stress is a sensitive index of blood fluidity at low shear. Seven healthy adults were studied at hematocrits varying between 40 and 80% and fibrinogen concentrations from 0.0 to 0.935 g/dl. Multivariable analysis was used to determine the functional dependence of yield stress on hematocrit and fibrinogen level. The major findings from this analysis include a decreasing effect of fibrinogen at high concentrations (saturation effect), a relative insensitivity of yield stress to fibrinogen at low concentration (threshold effect), and a strong interaction between the effects of hematocrit and fibrinogen concentration on yield stress. Our results give the normal range of yield stress for a given value of fibrinogen and hematocrit and can be used to predict the effect of reductions in hematocrit or fibrinogen on the yield stress of normal blood.

A new method for measuring the yield stress in thin layers of sedimenting blood.

A new method is presented to describe the low shear rate behavior of blood. We observed the response of a thin layer of sedimenting blood to a graded shear stress in a wedge-shaped chamber. The method allows quantitation of the degree of phase separation between red cells and plasma, and extracts the yield stress of the cell phase as a function of hematocrit. Our studies showed that the behavior of normal human blood underwent a transition from a solid-like gel to a Casson fluid. This transition began at the Casson predicted yield stress. The viscoelastic properties of blood were examined at shear stresses below the yield stress. The measured Youngs elastic moduli were in good agreement with published data. The yield stress of blood showed a linear dependence on hematocrit up to 60%, and increased more rapidly at higher hematocrit.

Autoimmune Neutropenia of Infancy and Early Childhood

Forty-one children were identified with autoimmune neutropenia of infancy and early childhood (absolute neutrophil count [ANC] less than 500/microliters and demonstrable serum antineutrophil antibodies). There were 21 boys and 20 girls; the median age at diagnosis was 11 months (range 5-38 months). No life-threatening infections occurred. There was a gradual upward trend in ANC in all patients over many months, with 87% having an ANC > 1000/microliters by 24 months from diagnosis. Among various clinical and laboratory parameters analyzed statistically, only younger age at diagnosis was associated with earlier neutrophil recovery. There was no association between degree or duration of neutropenia and sex, race, antibody reactivity, or presence of serious illness at diagnosis.

Hemoglobin Minneapolis-Laos [β-118 (GH1) Phe→Tyr] A New Hemoglobin Variant with Normal Functional Properties

Routine screening of hemoglobin samples from Southeast Asian immigrants by isoelectric focusing (1) revealed an individual with an abnormal hemoglobin component which migrated with approximately the same mobility as fetal hemoglobin. The proband was a 27 year old male of Laotian origin. His newborn son was found to be heterozygous for this variant and HbE. The probands wife was homozygous for HbE. The probands hematological findings were as follows: RBC -5.13 million, PCV -48.8%, MCV 95 fl, and Hb -16.7 g/dl. His red cells were normochromic and normocytic.

Influence of calcium antagonists on thrombin-induced calcium mobilization and platelet-vessel wall interactions

Elevation of cytosolic ionized calcium plays a critical role in human platelet activation. We have evaluated three well-characterized calcium antagonists for their ability to prevent thrombin-induced calcium mobilization in Fura 2 AM-loaded platelets and also their ability to inhibit platelet-vessel wall interactions. Thrombin (0.2 U/ml) caused significant elevation of cytosolic calcium (basal 84 +/- 18, activated 546 +/- 76 nM; n = 3). Verapamil, diltiazem, and nifedipine (100 microM) did not exert any inhibitory effect on thrombin-mediated calcium elevation. Untreated platelets perfused through a Baumgartner chamber containing a rabbit aorta preparation reacted with exposed and denuded subendothelium. The percentage of the total area covered by control platelet thrombi was 39.6 +/- 3.4. Diltiazem and Nifedipine significantly reduced the percentage of area covered by platelet thrombi, but the drugs were not as effective as aspirin (8.2 +/- 1.4). Calcium antagonists studied did not inhibit thrombin-stimulated elevation of cytosolic calcium in blood platelets. Although these drugs have been shown to prevent in vitro platelet aggregation and offer some protection against risks for atherosclerosis and thrombosis, they failed to significantly inhibit platelet-vessel wall interactions leading to formation of spread platelets and aggregates.