Development of an instrument to indirectly monitor arterial pCO2 during cardiopulmonary bypass.

Arterial blood carbon dioxide tension (PaCO2) during cardiopulmonary bypass (CBP) is important to the conduct of perfusion with alpha-stat or pH-stat strategy. Temperature changes during CBP complicate any attempts to monitor carbon dioxide tension in the exhaust outlet of an oxygenator (PexCO2) because CO2 becomes more soluble with decreasing temperatures. Normally, this would have been the obvious and easy choice of method to indirectly measure the patient's PaCO2. Several tests have been performed with ordinary capnographs modified to measure pCO2 at the oxygenator exhaust gas port. These tests have shown varying degrees of precision (Br I Anaesth 1999; 82(6): 843-46; 1 Extra-Corpor Technol 2003; 35(3): 218-23; Br JAnaesth 2000; 84: 536; J Extra-Corpor Technol 1994; 26: 64-67). Some of the best results have been achieved by Potger et al. (JExtra-Corpor Technol 2003; 35(3): 218-23), who found a strong correlation between the arterial temperature-corrected PexCO2 when using a standard capnograph monitoring the PaCO2 measured from a blood gas analyser (PbCO2). Our group has developed a new instrument, especially designed for oxygenator gas exhaust monitoring. The new instrument has automatic temperature correction, enabling it to show both original and corrected pCO2 values, simultaneously. Ordinary capnograph functions, such as zeroing, flow control and calibration routines, are included. The solution consists of a pCO2 sensor module, a temperature sensor, a water trap and a dedicated PC mounted on a heart-lung machine. Since the heart-lung machine was already equipped with a computer for data logging and a temperature sensor, only a box containing the pCO2 sensor module and the water trap had to be added. The PC uses a specially written program designed to collect data, make the necessary calculations and display the results on the computer screen. A temperature correction was developed based on a linear regression analysis for a data-set of 15 patients, assuming that the deviation between the measured PexCO2 from the oxygenator exhaust outlet and the PbCO2 from the blood gas analyser was linearly dependent on arterial temperature alone. Eighty-six blood gas samples were compared to the corrected PexCO2 values. The final product displayed good qualities of stability and was accurate when temperature fluctuated from 32 to 38 degrees C, even during rewarming, which has been reported to be a problem for other PexCO2 investigations (J Extra-Corpor Technol 2003; 35(3): 218-23).

Clinical evaluation of an instrument to measure carbon dioxide tension at the oxygenator gas outlet in cardiopulmonary bypass.

This paper presents the clinical testing of a new capnograph designed to measure the carbon dioxide tension at the oxygenator exhaust outlet in cardiopulmonary bypass (CPB). During CPB, there is a need for reliable, accurate and instant estimates of the arterial blood CO2 tension (PaCO2) in the patient. Currently, the standard practice for measuring PaCO2 involves the manual collection of intermittent blood samples, followed by a separate analysis performed by a blood gas analyser. Probes for inline blood gas measurement exist, but they are expensive and, thus, unsuitable for routine use. A well-known method is to measure PexCO2, ie, the partial pressure of CO2 in the exhaust gas output from the oxygenator and use this as an indirect estimate for PaCO2. Based on a commercially available CO2 sensor circuit board, a laminar flow capnograph was developed. A standard sample line with integrated water trap was connected to the oxygenator exhaust port. Fifty patients were divided into six different groups with respect to oxygenator type and temperature range. Both arterial and venous blood gas samples were drawn from the CPB circuit at various temperatures. Alfa-stat corrected pCO2 values were obtained by running a linear regression for each group based on the arterial temperature and then correcting the PexCO2 accordingly. The accuracy of the six groups was found to be (+/- SD): +/- 4.3, +/- 4.8, +/- 5.7, +/- 1.0, +/- 3.7 and +/- 2.1%. These results suggest that oxygenator exhaust capnography is a simple, inexpensive and reliable method of estimating the PaCO2 in both adult and pediatric patients at all relevant-temperatures.

Fondaparinux sodium compared with enoxaparin sodium: a cost-effectiveness analysis.

INTRODUCTION: Patients undergoing major orthopedic surgery face considerable risk of venous thromboembolism (VTE), which may be fatal unless they receive prophylactic treatment. Fondaparinux sodium is a new antithrombotic agent that is indicated for prophylaxis of VTE after major orthopedic surgery. This paper presents a cost-effectiveness analysis of fondaparinux sodium and enoxaparin sodium, the latter being the most commonly used agent for prophylaxis of VTE. METHODS: The analysis is based on an international simulation model, using Norwegian unit costs, and Norwegian data of 55 000 patients undergoing orthopedic surgery between 1999 and 2001. We estimated the expected incidence of VTE and VTE-related deaths, and expected costs of VTE-related care for each of the two prophylactic agents for different periods. RESULTS AND CONCLUSION: The results indicate that fondaparinux sodium is likely to be more effective than enoxaparin sodium in preventing the incidence of VTE. By day 90, fondaparinux sodium is expected to avoid 180 more VTE events, and between 8 and 33 more VTE-related deaths per 10,000 patients than enoxaparin sodium. Fondaparinux sodium is also a cost-saving option in short follow-up periods for hip fracture surgery. For extended follow-up periods (i.e. 5 years), fondaparinux sodium is also likely to represent the lower cost treatment option after total knee and hip replacement. The sensitivity analyses show that the main results are robust to changes in the most important parameters. Results are, however, sensitive to the price difference between the two drugs.