Continuous noninvasive estimation of cardiac output by electrical bioimpedance: an experimental study in dogs.

A new device has been developed to estimate continuously and noninvasively cardiac output from the thoracic electrical bioimpedance (CObi). CObi was compared to cardiac output by thermodilution (COtd) in five anesthetized dogs. Blood pressure, blood volume, and blood flow were manipulated by hemorrhage and infusions of sodium nitroprusside and phenylephrine. These data were used to determine the correlation between CObi and COtd under conditions of hypotensive normal flow and normotensive low flow, as well as during hemorrhagic shock and resuscitation. The CObi device was calibrated in vivo to COtd for each dog at the beginning of each experiment. CObi had a significant positive correlation with COtd throughout the experiments (r = 0.84, slope = 0.91, intercept = 0.55, p less than 0.01), and CObi predicted COtd with a standard error of the estimate of 0.81 L/min. Neither heart rate nor mean arterial pressure was significantly correlated with COtd or CObi. During severe hemorrhagic shock, CObi could not determine cardiac output in two of the dogs when COtd averaged 1.7 L/min. These data indicate that CObi is a blood-flow related variable that can be monitored continuously.

Trials of commercial reagents in anion-exchange coagulation procedures: ortho diagnostics.

The suitability of Ortho Diagnostics one-stage prothrombin time (PT) reagent (Ortho Brain Thromboplastin) and activated partial thromboplastin (aPTT) reagent (Activated Thrombofax) has been evaluated for use in conjunction with the anion-exchange heparin removal maneuver. The PT/HR and aPTT/HR are tests used to follow the anticoagulant influence of coumarins when heparin also is being administered. After establishing a coumarin therapeutic range for Activated Thrombofax, a parallel trial was conducted with Ortho Brain Thromboplastin on coumarin-treated patient plasmas. Determinations also were made after heparin (0.2 mu/mL) was added and then removed by ECTEOLA microchromatography columns. Ortho Brain Thromboplastin was found to induce a shortening bias associated with a spurious improvement in the precision of tests run on anion-exchange treated plasmas that potentially could result in coumarin overdosage. The systematic error did not appear to result either from protracted incubation or the activation of prekallikrein, high molecular weight kininogen, Factor XI or XII. This reagent was found to perform appropriately with plasma not exposed to ECTEOLA. Activated Thrombofax gave reliable and reproducible results before and after heparin removal. This aPTT reagent could be used in the aPTT/HR anticoagulant surveillance scheme.

Use of activated partial thromboplastin time to monitor coumarin anticoagulation.

The activated partial thromboplastin time after heparin removal (aPTT/HR) is an anionexchange procedure that permits the unobstructed monitoring of the progress of coumarin anticoagulation by removing interfering heparin. An all-intrinsic-pathway anticoagulant surveillance scheme based upon the aPTT/HR has been proposed and provisionally tested. The adoption of the new scheme will depend upon the identification of partial thromboplastins that are as predictable and reliable as the tissue thromboplastins in modern one-stage prothrombin times. In this study, the commercial APTT Reagent and Simplastin performed with equal sensitivity and specificity when evaluated by means of prothrombin group factor assays on coumarintreated subject plasmas. It is concluded that this commercial partial thromboplastin (1) is capable of being used for the purpose of following heparin, heparin plus coumarin, and coumarin anticoagulation; (2) is potentially able to identify more of the inherited and acquired derangements that can lead to anticoagulation-associated hemorrhage; and (3) is a universally available alternative to the traditional anticoagulant monitoring approach.