What factors contribute to the elevation of serum free fatty acid levels in newborns in the cardiac surgical setting?

Elevations in serum free fatty acid (FFA) levels during heart surgery have been reported in humans and experimental animals, causing increased arrhythmias, decreased heart function, and contributing to mortality. Factors such as heparin administration, age, cardiopulmonary bypass (CPB), and cyanosis or hypoxia have been implicated but not proven. This study was designed to clarify the contribution of these factors using an experimental pig model as follows: (i) adult (n = 10) versus 3-day-old piglets (n = 18) had FFA levels assessed before and after heparin administration; (ii) 3-day-old piglets, the additional effect of CPB (n = 8) or just severe hypoxia (PaO₂ = 20-25 mm Hg; n = 6) exposure on FFA levels. This work demonstrated that significant elevations in serum FFA were mainly due to heparin administration, with modest contributions by young age, CPB, and hypoxia. Our preliminary clinical investigations also suggest that children undergoing CPB are at risk of being exposed to high FFA levels and that these patients only suffered a decrease in heart function when these elevations were present in conjunction with cyanosis and (or) prolonged ischemic time. These initial findings require further confirmation. Given these findings, pharmacotherapeutics geared towards limiting FFA elevations should be considered, especially in young children undergoing pediatric cardiac surgery.

Extension and validation of the GLYCAM force field parameters for modeling glycosaminoglycans

Glycosaminoglycans (GAGs) are an important class of carbohydrates that serve critical roles in blood clotting, tissue repair, cell migration and adhesion, and lubrication. The variable sulfation pattern and iduronate ring conformations in GAGs influence their polymeric structure and nature of interaction. This study characterizes several heparin-like GAG disaccharides and tetrasaccharides using NMR and molecular dynamics simulations to assist in the development of parameters for GAGs within the GLYCAM06 force field. The force field additions include parameters and charges for a transferable sulfate group for O- and N-sulfation, neutral (COOH) forms of iduronic and glucuronic acid, and Δ4,5-unsaturated uronate (ΔUA) residues. ΔUA residues frequently arise from the enzymatic digestion of heparin and heparin sulfate. Simulations of disaccharides containing ΔUA reveal that the presence of sulfation on this residue alters the relative populations of 1H2 and 2H1 ring conformations. Simulations of heparin tetrasaccharides containing N-sulfation in place of N-acetylation on glucosamine residues influence the ring conformations of adjacent iduronate residues.

[Use of heparin and its derivatives in nursing care]

Heparin is an injectable anti-coagulant indicated in the treatment of venous thromboembolic diseases. In the case of major kidney failure, unfractionated heparins (UFHs) can be administered while low molecular weight heparins (LMWHs) are contraindicated at a curative dose. Platelet count must be monitored in patients treated with UFHs and when an LMWH is prescribed in a surgical context.

Clinical experience with argatroban for heparin-induced thrombocytopenia in a large teaching hospital

BACKGROUND

Argatroban is a direct thrombin inhibitor approved for the prophylaxis or treatment of thrombosis in patients with heparin-induced thrombocytopenia (HIT). The product monograph does not guide clinicians beyond specifying the initial dose of 2 μg/kg per minute (or 0.5 μg/kg per minute for patients with hepatic impairment). Some authors have suggested that in the intensive care unit (ICU) and for patients with acute cardiac disease and those with renal or hepatic dysfunction, this dose may result in a supratherapeutic activated partial thromboplastin time (aPTT).

OBJECTIVES

To evaluate the efficacy and safety of argatroban in adult patients with suspected HIT in a large teaching hospital, and to review dosing for patients in the ICU, patients with acute cardiac disease, and patients with renal or hepatic dysfunction.

METHODS

Charts of patients with suspected HIT who had received argatroban for at least 24 h between October 1, 2005, and October 1, 2007, at the Foothills Medical Centre, Calgary, Alberta, were examined retrospectively.

RESULTS

Thirty patients met the inclusion criteria, with charts available for review. Of these, 21 (70%) patients had an initial argatroban dose of 2 μg/kg per minute and 4 (13%) had an initial dose of 0.5 μg/kg per minute. The median duration of therapy was 6 days, and the mean dose was 2.14 μg/kg per minute. There were 122 dosage adjustments, the most common change being 0.5 μg/kg per minute, followed by adjustments of 1 and 0.1 μg/kg per minute. Six patients had supratherapeutic aPTT values (above 100 s), and none experienced major bleeding.

CONCLUSIONS

The results of this study suggest that an initial argatroban dose of 2 μg/kg per minute is appropriate for patients with no hepatic dysfunction. Patients with acute cardiac disease and critically ill patients may require lower doses of argatroban; however no dosage adjustments are required for patients with renal dysfunction.