Clinical assessment of a flow-through fluorometric blood gas monitor

Monitoring of Blood Gases during Extracorporeal Circulation with an Artificial Lung

During cardiopulmonary bypass, the heart-lung machine and the patient's gas exchange systems (uptake and elimination) form an undissociable couple. Changes in one of the components lead to corresponding changes in the other. In the artificial lung, like in the natural lung and peripheral tissues, gas exchanges depend on several parameters: blood inlet conditions, blood flow rate, temperature, composition of the gas mixture used for ventilation, blood tissue perfusion, O2 consumption, etc. The perfusionist's primary objective is to obtain from the artificial lung adequate O2 delivery to and CO2 removal from the tissues. This paper discusses the main parameters which must be taken into account and analyses the main sensors currently available for in-line measurement of blood gases.

Use of monitoring devices during anesthesia for cardiac surgery: a survey of practices at public hospitals within the United Kingdom and Ireland

A questionnaire was sent to all 42 public hospitals, within the United Kingdom (UK) and Ireland, known to conduct elective cardiac surgery. Information was sought with regard to the availability of intraoperative monitoring equipment. A one hundred percent response rate was achieved. Pulse oximetry, inspired oxygen analysis, and expired carbon dioxide analysis were not utilized at 4, 8, and 10 hospitals, respectively. Similarly, continuous monitoring of arterial oxygen tension and oxygen fraction in the gas flow to the bypass machine was not conducted in 28 and 32 hospitals, respectively. This survey revealed that essential anesthetic monitoring devices, as defined by the United Kingdom Association of Anesthetists, are not in routine usage during the pre-bypass and post-bypass phases of anesthesia for cardiac surgery within the British Isles.

Continuous intravascular blood gas monitoring

The benefit of a continuous intra-arterial blood gas monitor is apparent to any physician who has ever waited for the return of blood gas values at the bedside of a critically ill patient. The potential for rapid detection and prompt treatment of blood gas changes, coupled with immediate evaluation of the effectiveness of a therapeutic intervention, appears great. Whereas these systems may offer a tremendous advance in the physician's ability to track and treat alterations in cardiopulmonary physiology, no large-scale in vivo human trials have yet been reported. The only data available on accuracy, bias, precision, drift, and complication rate are from relatively small trials. Hopefully, when large-scale trials are completed, these systems will live up to their tremendous potential.

Clinical assessment of a continuous intraarterial blood gas monitoring system

We evaluated the clinical performance of a continuous intraarterial blood gas monitoring (CIABG) system which includes a fluorometric intravascular sensor. Seventeen patients undergoing elective surgery were monitored perioperatively with the CIABG system (PB3300; Puritan Bennett, Carlsbad, CA). Conventional laboratory blood gas analyses (BGA) were performed simultaneously whenever indicated, and the values were compared with those obtained from the CIABG system. Monitoring time ranged from 24 to 72 hr. The biases (average error between PB3300 and BGA) of pH, PCO2 and PO2 were 0.003 pH unit, -2.8 mmHg, and 0.9 mmHg in the operating room (OR), and 0.005 pH unit, 3.9 mmHg, and 8.5 mmHg in the intensive care unit (ICU), respectively. The precision (standard deviation of the bias) of pH, PCO2 and PO2 were 0.030 pH unit, 2.1 mmHg, and 29.9 mmHg in the OR and 0.035 pH unit, 3.8 mmHg, and 14.7 mmHg in the ICU, respectively. Although the PB3300 system was clinically useful as a trend monitor, the system's precision and reliability were unacceptable for estimation of true blood gas values.

Clinical evaluation of the CDI System 400 blood gas monitor

The CDI 400 blood gas monitor was evaluated by investigating its clinical performance in 30 patients undergoing cardiac surgery requiring cardiopulmonary bypass. Arterial and venous blood samples were withdrawn during stable hypothermic conditions. Reference analysis was performed on the ABL4 blood gas analyzer. A total of 229 samples were included for calculations of bias and precision. Simple regression analysis was utilized to illustrate the relationship between the tested monitor and its reference. Results revealed an acceptable agreement for pH and arterial pO2 measurements. Venous pO2 bias and precision were poor (+0.76 +/- 1.07 kPa). Arterial and venous pCO2 were generally overestimated (+0.5 +/- 0.4 kPa and +0.2 +/- 0.4 kPa). Performance given as correlation coefficients indicated a similar pattern. Slopes and intercepts deviated from the line of identity for all parameters analysed. In summary: the CDI 400 is a valid instrument in guiding the perfusionist with crucial trend information. However, its general performance implies that a reference blood gas analyser is still needed.

What's new in monitoring the coronary surgery patient?

Monitoring has been extensively reviewed in most textbooks of cardiothoracic surgery and anaesthesia, particularly in the recent textbooks on monitoring edited by Carol L Lake 1 and Casey D Blitt 2 and in the Journal of Clinical Monitoring. Although monitoring properly includes both pre- and postoperative periods, this review will concentrate exclusively on the operative period. I will also concentrate on new approaches or information which relate to more traditional approaches to monitoring. The emphasis in this review will not be on what we can monitor, but rather on what we should monitor. In this regard, I will analyse accuracy and identify sources of error and try to answer the following questions. Does the device or parameter measure (monitor) what we want to know? Does it improve patient outcome and safety? Is it cost-effective? Unfortunately, data are not always available to answer all these questions at present, but hopefully the discussions will make us aware of what we do and do not know, and what we should look for in the near future.

Oxygenator exhaust capnography: a method of estimating arterial carbon dioxide tension during cardiopulmonary bypass

An in vivo study was undertaken during hypothermic (28 degrees C) cardiopulmonary bypass to compare oxygenator exhaust capnography as a means of estimating arterial carbon dioxide tension (PaCO2) with bench blood gas analysis. A total of 123 pairs of measurements were made in 40 patients. Oxygenator exhaust capnographic measurements systematically underestimated PaCO2 measured by a bench blood gas analyzer. During the cooling and stable hypothermic phases of cardiopulmonary bypass, the relationship was reasonably accurate, but became far more variable during rewarming. Oxygenator exhaust capnography could be used as an inexpensive means of continuously monitoring PaCO2 during the cooling and stable hypothermic phases of cardiopulmonary bypass but should not be used during rewarming.

In vitro assessment of a flow-through fluorometric blood gas monitor

The Gas-STAT blood gas monitor uses fluorometric techniques to continuously monitor blood gas tensions and acid-base status in the extracorporeal perfusion circuit during cardiac surgery. We evaluated the in vitro performance of this instrument by using a tonometry loop to simulate the clinical environment and to provide controlled gas tensions and pH in the circulating fluid. In this article we report the in vitro study in which 35 Gas-STAT blood gas sensors were used to assess the precision, stability, response time, and specificity of the instrument and to confirm the sterile integrity of its flow-through cells. The blood gas monitor exhibited precision values for pH, carbon dioxide tension (PCO2), and oxygen tension (PO2) of 0.1%, 1.3%, and 1.0%, respectively; stabilities were 0.002 units/h for pH, 0.5 mm Hg/h for PCO2, and 1.4 mm Hg/h for PO2; time constants (tau, a response to within 1/e of a new gas tension, approximately 63%) were 81 seconds for PCO2 and 72 seconds for PO2. No significant interference was detected in in vitro tests of 30 drugs and metabolites typically encountered during cardiac surgery. Bacterial challenge of the flow-through cell membranes showed that they provide an effective barrier isolating the sensors from contaminants in the fluid path. Our quality control consisted of measurement of a midrange gas standard as an unknown immediately following sensor calibration; this simple program is proposed as a complement to the manufacturer's operating procedures.(ABSTRACT TRUNCATED AT 250 WORDS)