Continuous intra-arterial blood-gas monitoring in infants and children with cyanotic heart disease

Recommendations for haemodynamic and neurological monitoring in repair of acute type a aortic dissection

During treatment of acute type A aortic dissection there is potential for both pre- and intra-operative malperfusion. There are a number of monitoring strategies that may allow for earlier detection of potentially catastrophic malperfusion (particularly cerebral malperfusion) phenomena available for the anaesthetist and surgeon. This review article sets out to discuss the benefits of the current standard monitoring techniques available as well as desirable/experimental techniques which may serve as adjuncts in the monitoring of these complex patients.

Assessment of a continuous blood gas monitoring system in animals during circulatory stress

BACKGROUND

The study was aimed to determine the measurement accuracy of The CDI™ blood parameter monitoring system 500 (Terumo Cardiovascular Systems Corporation, Ann Arbor MI) in the real-time continuous measurement of arterial blood gases under different cardiocirculatory stress conditions

METHODS

Inotropic stimulation (Dobutamine 2.5 and 5 μg/kg/min), vasoconstriction (Arginine-vasopressin 4, 8 and 16 IU/h), hemorrhage (-10%, -20%, -35%, and -50% of the theoretical volemia), and volume resuscitation were induced in ten swine (57.4 ± 10.7 Kg).Intermittent blood gas assessments were carried out using a routine gas analyzer at any experimental phase and compared with values obtained at the same time settings during continuous monitoring with CDI™ 500 system. The Bland-Altman analysis was employed.

RESULTS

Bias and precision for pO2 were - 0.06 kPa and 0.22 kPa, respectively (r2 = 0.96); pCO2 - 0.02 kPa and 0.15 kPa, respectively; pH -0.001 and 0.01 units, respectively ( r2 = 0.96). The analysis showed very good agreement for SO2 (bias 0.04,precision 0.33, r2 = 0.95), Base excess (bias 0.04,precision 0.28, r2 = 0.98), HCO3 (bias 0.05,precision 0.62, r2 = 0.92),hemoglobin (bias 0.02,precision 0.23, r2 = 0.96) and K+ (bias 0.02, precision 0.27, r2 = 0.93). The sensor was reliable throughout the experiment during hemodynamic variations.

CONCLUSIONS

Continuous blood gas analysis with the CDI™ 500 system was reliable and it might represent a new useful tool to accurately and timely monitor gas exchange in critically ill patients. Nonetheless, our findings need to be confirmed by larger studies to prove its reliability in the clinical setting.

Experiences with continuous intra-arterial blood gas monitoring: precision and drift of a pure optode-system

OBJECTIVE

The utility of continuous intra-arterial blood gas analysis (CBGA) with combined electrochemical and optode sensors has been demonstrated. More recently, a pure optode sensor with a changed sensing element architecture has become available. The aim was to determine the measurement accuracy and long-term stability of the new sensor.

DESIGN

A prospective explorative study was performed. Simultaneous measurements of intermittent blood gas analyses (IBGA) (ABL 610, Radiometer, Copenhagen) and CBGA (Diametrics Medical, High Wycombe, Bucks., UK) were compared using Bland-Altman analysis.

PATIENTS

Twenty-five patients admitted to the ICU and requiring mechanical ventilation for an expected minimum of about 96 h were included.

RESULTS

Mean monitoring time was 106.1 (range 15-231) hours. Bias and precision for PO(2 )were -0.2 kPa (1%)+/-1.8 kPa (9.5%); PCO(2): 0.03 kPa (0.6%)+/-0.44 kPa (9.3%); pH: -0.001 (0.01%)+/-0.04 (0.45%). The sensor showed no change of measurement characteristics during 4 days of measurement. However, in 69 cases continuous monitoring was interrupted (reversible sudden drops of PO(2) measurement) possibly caused by thrombotic deposition and/or sensor bending and accidental sensor retraction.

CONCLUSIONS

The precision and bias of the PCO(2)- and pH-sensing elements were in line with the findings of the older sensor technology. The possibility that the PO(2) optode could offer greater accuracy than the older technology is suggested by comparisons with results reported in previous studies. No sensor drift occurred during long-term measurement over more than 4 days.

Continuous intravascular blood gas monitoring: development, current techniques, and clinical use of a commercial device

This review focuses on the development, current techniques, and clinical use of continuous intravascular blood gas monitoring (CIBM) devices in anaesthesia and intensive care. The operating principles, range of application, performance, limitations, costs, and impact on patient treatment and outcome, are discussed. Studies of early and currently available CIBM devices were analysed. At present, the Paratrend 7+ (PT7+) for adults and Neotrend (NT) for newborns are the only commercially available CIBM systems. The PT7+ contains three optical sensors to measure PO(2), PCO(2) and pH, as well as a thermocouple to measure temperature. The NT is a modification of the PT7+ to continuously monitor PO(2), PCO(2), pH and temperature in newborns. Under laboratory conditions, good performance over a wide range of blood gas values was observed with the Paratrend 7 (PT7. Performance in the clinical setting was not as satisfactory, especially for PO(2) values. However, the performance and accuracy of CIBM devices appear to be sufficient for clinical use and they are being used clinically in selected patient groups. Several factors affecting the performance of CIBM are considered.

Esophageal capnometry during hemorrhagic shock and after resuscitation in rats

BACKGROUND

Splanchnic perfusion following hypovolemic shock is an important marker of adequate resuscitation. We tested whether the gap between esophageal partial carbon dioxide tension (PeCO2) and arterial partial carbon dioxide tension (PaCO2) is increased during graded hemorrhagic hypotension and reversed after blood reinfusion, using a fiberoptic carbon dioxide sensor.

MATERIALS AND METHOD

Ten Sprague-Dawley rats were anesthetized, tracheotomized, and cannulated in one femoral artery and vein. A calibrated fiberoptic PCO2 probe was inserted into the distal third of the esophagus for determination of luminal PeCO2 during maintained anesthesia (pentobarbital 15 mg/kg per hour), normothermia (38 +/- 0.5 degrees C), and fluid balance (saline 5 ml/kg per hour). Three out of 10 rats were used to determine the limits of hemodynamic stability during gradual hemorrhage. Seven of the 10 rats were then subjected to mild and severe hemorrhage (15 and 20-25 ml/kg, respectively). Thirty minutes after severe hemorrhage, these rats were resuscitated by reinfusion of the shed blood. Arterial gas exchange, hemodynamic variables, and PeCO2 were recorded at each steady-state level of hemorrhage (at 30 and 60 min) and after resuscitation.

RESULTS

The PeCO2-PaCO2 gap was significantly increased after mild and severe hemorrhage and returned to baseline (prehemorrhagic) values following blood reinfusion. Base deficit increased significantly following severe hemorrhage and remained significantly elevated after blood reinfusion. Significant correlations were found between base deficit and PeCO2-PaCO2 (P < 0.002) and PeCO2 (P < 0.022). Blood bicarbonate concentration decreased significantly following mild and severe hemorrhage, but its recovery was not complete at 60 min after blood reinfusion.

CONCLUSION

Esophageal-arterial PCO2 gap increases during graded hemorrhagic hypotension and returns to baseline value after resuscitation without complete reversal of the base deficit. These data suggest that esophageal capnometry could be used as an alternative for gastric tonometry during management of hypovolemic shock.

Transcutaneous and intra-arterial blood gas monitoring--a comparison during apnoea testing for the determination of brain death

Intra-arterial (i.a.) and transcutaneous (t.c.) blood gas monitoring were compared with in vitro blood gas analysis (abg) during apnoea testing for the determination of brain death in a prospective observational study. All three methods were used simultaneously in 19 patients in whom brain death was suspected. Brain death was confirmed in each case adhering to the recommendations of the Scientific Advisory Board of the German Federal Chamber of Physicians which demand a PCO2 of at least 60 mmHg. In vitro parameters ranged from 23.2 to 80.4 mmHg (PCO2), 52.7 to 509.9 mmHg (PO2), and 7.072 to 7.591 (pH). The intra-individual correlations between both monitoring methods (rPCO2=0.958, rPO2=0.859) and between each of them and abg (r>0.960) were high. Absolute deviations from abg for the corrected as well as uncorrected measurements were similar for both methods, except with regard to group bias where an advantage for the i.a. values emerged. Since many of the i.a. measurements failed and the disposable i.a. probes cost much more than the t.c. electrodes, the i.a. technique at present holds no advantage over t.c. measurements in testing for apnoea in suspected brain death except where simultaneous monitoring of pH and temperature are desired.

Continuous intra-jugular venous blood-gas monitoring with the Paratrend 7 during hypothermic cardiopulmonary bypass

We measured the accuracy of the continuous intra-vascular blood-gas monitoring system (Paratrend 7, PT7) placed in the jugular venous bulb in 18 adult patients having cardiac or aortic surgery with hypothermic cardiopulmonary bypass (CPB). After induction of anaesthesia, a PT7 sensor was inserted through a 20-gauge venous catheter into the right jugular venous bulb. Blood samples were drawn from the venous catheter and measured with a blood gas analyser (BGA). Five to eight paired measurements using the PT7 and blood samples were made per patient, and bias and precision were calculated for each patient using the Bland-Altman method. The ranges for the blood sample measurements were: pH 7.12 to 7.59, PCO(2) 3.7 to 9.6 kPa, PO(2) 3.5 to 16.0 kPa, oxygen saturation 40 to 99%, bicarbonate 18.6 to 34.4 mmol l(-1), and base excess -7.8 to 12.5 mmol l(-1). Bias and precision values were 0.014/0.071 for pH, 0/0.90 kPa for PCO(2), and -0.16/1.18 kPa for PO(2). These values were comparable with those previously made on arterial blood. However, precision for oxygen saturation in each patient varied 2.3 to 23.6% (95% CI: 6.3 to 12.9%), which was unsatisfactory for clinical measurements. Deep hypothermia ( approximately 19.6 degrees C) and marked haemodilution ( approximately 13.5%) during CPB did not influence the reliability of the PT7 sensor. Thus, we concluded that continuous intra-jugular venous blood-gas monitoring is clinically feasible using the PT7 and may provide valuable information during CPB.

Comparing methods of clinical measurement: reporting standards for bland and altman analysis

In this era of medical technology assessment and evidence-based medicine, evaluating new methods to measure physiologic variables is facilitated by standardization of reporting results. It has been proposed that assessing repeatability be followed by assessing agreement with an established technique. If the "limits of agreement" (mean bias +/- 2SD) are not clinically important, then one could use two measurements interchangeably. Generalizability to larger populations is facilitated by reporting confidence intervals. We identified 44 studies that compared methods of clinical measurement published during 1996 to 1998 in seven anesthesia journals. Although 42 of 44 (95.4%) used the limits of agreement methodology for analysis, several inadequacies and inconsistencies in reporting the results were noted. Limits of agreement were defined a priori in 7.1%, repeatability was evaluated in 21.4%, and relationship (pattern) between difference and average was evaluated in 7.1%. Only one of the articles reported confidence intervals. A computer macro for the Minitab statistical package (State College, PA) is described to facilitate reporting of Bland and Altman analysis with confidence intervals. We propose standardization of nomenclature in clinical measurement comparison studies.

IMPLICATIONS

A literature review of anesthesia journals revealed several inadequacies and inconsistencies in statistical reports of results of comparison studies with regard to interchangeability of measurement methods. We encourage journal editors to evaluate submissions on this subject carefully to ensure that their readers can draw valid conclusions about the value of new technologies.

Substantial changes in arterial blood gases during thoracoscopic surgery can be missed by conventional intermittent laboratory blood gas analyses

Substantial and clinically relevant changes in arterial blood gases are likely to occur during thoracoscopic surgery with one-lung ventilation (OLV). We hypothesized that they may be missed when using the conventional intermittent blood gas sampling practice. Therefore, during 30 thoracoscopic procedures with OLV, the sampling intervals between consecutive intermittent laboratory blood gas analyses (BGA) were evaluated with respect to changes of PaO2, PaCO2, and pHa ([H+]) using a continuous intraarterial blood gas monitoring system. Frequency and timing of BGA were based on the clinical judgment of 16 experienced anesthesiologists who were blinded to the continuously measured values. Extreme fluctuations of PaO2 (37-625 mm Hg), PaCO2 (27-56 mm Hg), and pHa (7.24-7.51) were observed by continuous blood gas monitoring. During 63% of all sampling intervals, PaO2 decreased >20% compared with the preceding BGA value, which remained undetected by intermittent analysis. In 10 patients with a continuously measured minimal PaO2 value < or = 60 mm Hg, the preceding BGA overestimated this minimal PaO2 by > 47%. Correspondingly, PaCO2 increases of > 10% were observed in 35% of all sampling intervals, and [H+] increases of > 10% were observed in 24% of all sampling intervals. Because these blood gas changes were not reliably detected by using noninvasive monitoring and their magnitude is not predictable during OLV, intermittent BGA with short sampling intervals is warranted. In critical cases, continuous blood gas monitoring may be helpful.

IMPLICATIONS

The magnitude of blood gas changes during thoracoscopic surgery with one-lung ventilation is not predictable and not reliably detected by noninvasive monitoring. Using a continuous intraarterial blood gas monitoring device, we demonstrated that intermittent laboratory blood gas analysis with short sampling intervals is warranted to detect arterial hypoxemia.