Toward development of a point-of-care assay of enoxaparin anticoagulant activity in whole blood.

There is need for a rapid assay to determine the efficacy of low-molecular-weight-heparin (LMWH) in whole blood. Heparinase was used to eliminate, and thereby quantify, the anticoagulant activity of the low-molecular-weight-heparin, enoxaparin. The percent change in the clotting time of whole blood in the presence of heparinase yielded the anticoagulant contribution of enoxaparin. A minimally activated assay (MAA) of whole blood clotting time was evaluated for the detection and relative quantification of enoxaparin. The assay cartridge consisted of a plain glass tube and detection magnet, with no additional sources of activation. Comparisons were also made with a point-of-care, activated partial thromboplastin time (aPTT) assay. Plasma or whole blood was spiked with enoxaparin at concentrations ranging from 0.1 to 1.0 anti-factor Xa IU/ml. A commercial preparation of heparinase I was used to digest enoxaparin, and clotting times were determined with and without heparinase incubation. Heparinase digestion caused an average shortening of clotting time of 21.1% (47.3 s) in blood spiked with 0.4 anti-Xa IU/ml enoxaparin, an amount expected in the therapeutic range; also, 0.1 anti-Xa IU/ml of enoxaparin could be reliably detected. The assay performed comparably when transferred to a point-of-care setting with heparinase being added directly to citrated blood collection tubes, followed by either MAA or aPTT assay. Strong correlations were obtained with both assays between the percent change in clotting time (after heparinase) and the added concentration of enoxaparin, or in comparison with the chromogenically measured concentration of enoxaparin. The assays for an individual blood sample can be completed within 10 min.

Pushing the Envelope in Obstetric Care: A Case Report of Cesarean Delivery in a Parturient with a BMI >100 kg m-2.

An increasing number of women with a body mass index (BMI) ≥ 60 kg m-2, referred to as super-super obesity, are requiring anesthetic care for labor and delivery. Management of these patients presents obstetric, anesthetic, and logistical challenges. We report our experience in the management of cesarean delivery in a parturient with a BMI of 112 kg m-2. Use of epidural anesthesia and performance of a supraumbilical transverse surgical incision with caudal placement of the panniculus resulted in optimal hemodynamic and ventilatory parameters. Effective multidisciplinary planning and communication is key. We present this case to highlight decision-making strategies and elucidate our approach in the management of this complex obstetric case.

Anesthesiologists' Preferences regarding Visitor Presence during Placement of Neuraxial Labor Analgesia.

INTRODUCTION: Neuraxial labor analgesia has become an integral part of modern obstetric anesthetic practice. Presence of a familiar person during its placement may be beneficial to the patient. A survey was sent to anesthesiologists practicing obstetric anesthesia in the USA to determine their views. METHODS: The survey queried the following: existence of a written policy; would they allow a visitor; visitor's view, sitting or standing; reasons to allow or not allow a visitor; and influence by other staff on the decision. The responses were analyzed using multiple chi-square analyses. RESULTS: Most practitioners supported allowing a visitor during placement. Reduction of patient anxiety and fulfillment of patient request were the major reasons for allowing a visitor. Sitting position and no view of the workspace were preferred. Visitor interference and safety were cited as the major reasons for precluding a visitor. Nonanesthesia providers rarely influenced the decision. Epidural analgesia was the preferred technique. Essentially no bias was found in the responses; there was statistical uniformity regardless of procedures done per week, years in practice, professional certification, geographic region (rural, urban, or suburban), or academic, private, or government responders. CONCLUSION: The practice of visitor presence during the placement of neuraxial labor analgesia is gaining acceptance.

Neural Network Prediction of ICU Length of Stay Following Cardiac Surgery Based on Pre-Incision Variables.

BACKGROUND: Advanced predictive analytical techniques are being increasingly applied to clinical risk assessment. This study compared a neural network model to several other models in predicting the length of stay (LOS) in the cardiac surgical intensive care unit (ICU) based on pre-incision patient characteristics. METHODS: Thirty six variables collected from 185 cardiac surgical patients were analyzed for contribution to ICU LOS. The Automatic Linear Modeling (ALM) module of IBM-SPSS software identified 8 factors with statistically significant associations with ICU LOS; these factors were also analyzed with the Artificial Neural Network (ANN) module of the same software. The weighted contributions of each factor ("trained" data) were then applied to data for a "new" patient to predict ICU LOS for that individual. RESULTS: Factors identified in the ALM model were: use of an intra-aortic balloon pump; O2 delivery index; age; use of positive cardiac inotropic agents; hematocrit; serum creatinine ≥ 1.3 mg/deciliter; gender; arterial pCO2. The r2 value for ALM prediction of ICU LOS in the initial (training) model was 0.356, p <0.0001. Cross validation in prediction of a "new" patient yielded r2 = 0.200, p <0.0001. The same 8 factors analyzed with ANN yielded a training prediction r2 of 0.535 (p <0.0001) and a cross validation prediction r2 of 0.410, p <0.0001. Two additional predictive algorithms were studied, but they had lower prediction accuracies. Our validated neural network model identified the upper quartile of ICU LOS with an odds ratio of 9.8(p <0.0001). CONCLUSIONS: ANN demonstrated a 2-fold greater accuracy than ALM in prediction of observed ICU LOS. This greater accuracy would be presumed to result from the capacity of ANN to capture nonlinear effects and higher order interactions. Predictive modeling may be of value in early anticipation of risks of post-operative morbidity and utilization of ICU facilities.

Rapid point-of-care assay of enoxaparin anticoagulant efficacy in whole blood.

There is the need for a clinical assay to determine the extent to which a patient's blood is effectively anticoagulated by the low-molecular-weight-heparin (LMWH), enoxaparin. There are also urgent clinical situations where it would be important if this could be determined rapidly. The present assay is designed to accomplish this. We only assayed human blood samples that were spiked with known concentrations of enoxaparin. The essential feature of the present assay is the quantification of the efficacy of enoxaparin in a patient's blood sample by degrading it to complete inactivity with heparinase. Two blood samples were drawn into Vacutainer tubes (Becton-Dickenson; Franklin Lakes, NJ) that were spiked with enoxaparin; one sample was digested with heparinase for 5 min at 37 °C, the other sample represented the patient's baseline anticoagulated status. The percent shortening of clotting time in the heparinase-treated sample, as compared to the baseline state, yielded the anticoagulant contribution of enoxaparin. We used the portable, battery operated Hemochron 801 apparatus for measurements of clotting times (International Technidyne Corp., Edison, NJ). The apparatus has 2 thermostatically controlled (37 °C) assay tube wells. We conducted the assays in two types of assay cartridges that are available from the manufacturer of the instrument. One cartridge was modified to increase its sensitivity. We removed the kaolin from the FTK-ACT cartridge by extensive rinsing with distilled water, leaving only the glass surface of the tube, and perhaps the detection magnet, as activators. We called this our minimally activated assay (MAA). The use of a minimally activated assay has been studied by us and others. (2-4) The second cartridge that was studied was an activated partial thromboplastin time (aPTT) assay (A104). This was used as supplied from the manufacturer. The thermostated wells of the instrument were used for both the heparinase digestion and coagulation assays. The assay can be completed within 10 min. The MAA assay showed robust changes in clotting time after heparinase digestion of enoxaparin over a typical clinical concentration range. At 0.2 anti-Xa I.U. of enoxaparin per ml of blood sample, heparinase digestion caused an average decrease of 9.8% (20.4 sec) in clotting time; at 1.0 I.U. per ml of enoxaparin there was a 41.4% decrease (148.8 sec). This report only presents the experimental application of the assay; its value in a clinical setting must still be established.

The effect of preoperative antiplatelet/anticoagulant prophylaxis on postoperative blood loss in cardiac surgery.

UNLABELLED: In this study we sought to determine whether preoperative treatment with antiplatelet and/or anticoagulant drugs influences postoperative blood loss after coronary artery bypass graft surgery. Although prophylactic treatment to prevent ischemic events preoperatively is often necessary, the treatment frequently continues until there may be a risk of increased bleeding (i.e., within 5-7 days before surgery). With patient consent, a preincision blood sample was collected prospectively from 93 adult subjects who presented randomly. They consisted of 3 groups regarding their primary preoperative regimen: 1) no preoperative treatment within the week before surgery; 2) platelet adenosine diphosphate (ADP) receptor antagonist; 3) ADP receptor antagonist plus IV heparin. Postoperative chest tube drainage (24 h) in the group that received ADP antagonist alone was more (P < 0.05) than either of the other groups: 503 +/- 56; 633 +/- 55; 439 +/- 29 mL (mean +/- SEM) for Groups 1, 2, and 3, respectively. Combined treatment with ADP antagonist plus heparin infusion appeared to prevent the increased blood loss with the ADP antagonist alone. Preincision and postoperative plasma fibrinogen concentrations were largest (P < 0.05) in the group that received the combination treatment; mean +/- SEM for groups 1, 2, and 3 preincision, 311 +/- 17, 366 +/- 16, and 423 +/- 18 mg/dL, and postoperatively, 229 +/- 16, 267 +/- 13, and 312 +/- 16 mg/dL. Postoperative fibrinogen showed strong dependence on preoperative fibrinogen in all groups (r = 0.576 to 0.825; P = 0.01 to 10(-6)). Prevention of the increased blood loss in the ADP receptor antagonist group by the addition of a heparin infusion may have been attributable to a conservation of coagulation factors, as evidenced by the increased plasma fibrinogen concentrations with combined prophylactic treatment. IMPLICATIONS: The objective of this study was to determine whether preoperative treatment with antiplatelet and/or anticoagulant drugs influences the extent of blood loss in the 24-h period after cardiac surgery.