Plasma Heparin And Antithrombin III Response Following Endotracheal Administration Of Heparin

Plasma heparin and antithrombin III (AT III) concentrations were determined using chromogenic peptide substrates in patients undergoing various forms of minor surgery. After anaesthesia, patients were given small volumes of concentrated heparin (25,000 IU/ml) at various doses based on body weight. Administration was by the endotracheal route via a fine cannula by either instillation or insufflation.Calibration curves for low-dose heparin (in the range 0.02 to 0.20 IU/ml) were constructed for each patient using pretreatment platelet free plasma. The total amount of heparin neutralizing activity in each plasma was determined and the observed heparin concentration was adjusted to compensate for the interference caused by heparin neutralizing activity released in vivo.Heparin administered by endotracheal insufflation was more effective than heparin given by instillation in producing satisfactory levels of heparin in the plasma. Peak levels were attained 6 to 24 hours after administration and the effect lasted for several days. By altering the dose, the peak level of heparin could be adjusted in order to achieve a low concentration without affecting the duration of the anticoagulant action.A parallel moderate decrease in the AT III level was observed within 6 to 24 hours of administration, with recovery toward the pre-treatment level beginning by 48 hours.Endotracheal insufflation of heparin provides a convenient method of obtaining a prolonged effect at levels low enough to avoid bleeding, yet sufficient to prevent thromboembolic complications following various surgical procedures. Since the anticoagulant effect lasts for at least several days, this method provides an attractive alternative to 8 or 12 hourly subcutaneous injections of heparin.