Extracorporeal Monitoring Research Articles

Evaluation of the paratrend 7 intravascular blood gas monitor during cardiac surgery: Comparison with the C4000 in-line blood gas monitor during cardiopulmonary bypass

To evaluate the performance of the Paratrend 7 intravascular blood gas monitor (Biomedical Sensors, High Wycombe, UK, Ltd) during cardiac surgery and compare it with that of an in-line blood gas monitor placed in the arterial limb of an extracorporeal circuit during cardiopulmonary bypass. A prospective study. Consecutive patient enrolment. In the cardiac surgical intensive care units at a tertiary referral center. Insertion of the Paratrend 7 intravascular sensor through the radial arterial catheter after induction of anesthesia. Simultaneous measurements of pH, PCO2, and PO2 were made from the sensor and the blood gas analyzer, and the bias and precision were calculated on all the measured parameters. The bias and precision of the intravascular sensor during bypass for pH, PCO2, and PO2 were 0.01 and 0.06 pH units, 0.5 and 2.5 mmHg (2% and 8%), and 3 and 45 torr (0.5% and 14%), respectively. The bias and precision for the prebypass and the postbypass phases were comparable. The bias and precision of the extracorporeal monitor for pH, PCO2, and PO2 were 0.04 and 0.1 pH units, -0.3 and 4 mmHg (-1% and 15%) and 8 and 48 mmHg (4 and 18%), respectively. There were no instances of any complications attributable to the intravascular sensor. The intravascular sensor used in this study functioned well during cardiopulmonary bypass and the postbypass phase. The performance of the intravascular sensor was better than the in-line blood gas monitor during cardiopulmonary bypass.

Overview of Monitoring in Endoscopy

Gastrointestinal endoscopy has evolved rapidly over the past 30 years and has become one of the larger specialities in medicine. An increasing number of diagnostic and therapeutic procedures are being performed with the aid of the flexible endoscope. With this expansion in the use of endoscopy came the routine administration of premedication. The endoscopist thus became a part-time anaesthetist. The lack of proper studies to evaluate the untoward effects of diazepam and, later, midazolam, at their introduction led to an unfortunate increase in reports of fatalities after the introduction of midazolam. Later studies showed the safety of these agents when properly administered, but the affair served to focus attention on monitoring in gastrointestinal endoscopy. The benefits of using extracorporeal monitoring equipment during endoscopy has not been proved in clinical trials, and because of this those bodies that issue guidelines on medical practice, such as the American Society for Gastrointestinal Endoscopy, have not mandated the use of these devices. The guidelines issued have emphasized the importance of training and recertification in advanced cardiac life support. Many endoscopists are reluctant to recognize their role as anaesthetist, and to adopt new practices recommended in the guidelines. However, these changes represent the evolution of medicine and reflect the desire to ensure a uniform high quality of care and as such should not be resisted.

Amperometric enzyme electrode system for extracorporeal lactate monitoring based on lactate dehydrogenase.

A lactate electrode for practical extracorporeal monitoring has been produced, using lactate dehydrogenase retained over an H2O2 sensor. Soluble NAD+ cofactor was used, and phenazine ethosulphate (PES+) in solution permitted electron transfer from NADH to O2 to generate H2O2. The system was optimised using O2 electrodes, but was employed for blood with H2O2 detection to avoid effects due to variations in background pO2. At pH 9.8 in carbonate buffer containing 0.5 mM NAD+ and 1 mM PES+, the electrodes had sufficient stability and sensitivity to allow measurement of diluted whole blood. Calibration graphs were linearised over the range 0.01–0.5 mM lactate either by means of a square root concentration scale or by use of inverse coordinates. The response time in the extracorporeal flow system was slow (6–10 min), but this was found to be adequate to follow lactate rises during mild exercise.

The Characteristics of a New Glucose Sensor for Use in an Artificial Pancreatic Beta Cell

A new glucose sensor has been developed for the continuous extracorporeal monitoring of blood glucose concentrations in conjunction with an artificial pancreatic beta cell simulator. This sensor has a rapid ninety percent response time (less than 1 min), is stable for periods of up to 140 hours of accumulated use and can be calibrated without the use of a reference glucose analyzer. Its reliability has been confirmed in over 100 clinical studies. A comparison of this sensor to other glucose sensors designed for artificial pancreatic beta cell devices is made and the sensor is shown to be the most advanced glucose sensor presently available for extracorporeal continuous glucose monitoring in man.

Continuous Extracorporeal Monitoring of Animal Blood Using the Glucose Electrode

A continuous extracorporeal monitoring system for blood glucose employing an electrochemical sensor is described. The sensor, about the size of a nickel, is rapid, is specific for glucose, generates its own power, and consists of two galvanic oxygen electrodes. Over one oxygen electrode is affixed a plastic matrix to which glucose oxidase is covalently bound; a blank matrix is over the other, which serves as a reference. Oxygen is consumed in the glucose-oxidase-containing matrix, decreasing the current from the underlying oxygen electrode. The current decrease is nonlinearly proportional to the glucose concentration. The sensor is clamped between small blocks of plastic fitted with inlet and outlet nipples so that blood pumped from the animal passes over the two electrodes and thence to an automated chemical analysis for comparison. Blood is collected and anticoagulant added in a double-lumen catheter. Blood is withdrawn at the rate of 1 cc. per hour. Results obtained by use of the system in rabbits are reported. The capacity of the system to continuously monitor changes in blood glucose produced by repeated glucose tolerances is shown in hypo-, normo-, and hyperglycemic animals. Some properties of the system and its calibration are discussed.