Continuous pH and Pco2 monitoring during respiratory failure in children with the Paratrend 7 inserted into the peripheral venous system

Correlation and Interchangeability of Venous and Capillary Blood Gases in Non-Critically Ill Neonates

BACKGROUND

Venous blood gas (VBG) is frequently used in the neonatal unit as alternative for capillary blood gas (CBG). However, studies reporting correlation are conflicting and data on interchangeability in neonates are lacking.

OBJECTIVE

We investigated the correlation and interchangeability of the components between VBG and CBG in infants admitted to the neonatal intensive care unit.

METHODS

In a prospective study in the neonatal unit in Leiden University Medical Center (Netherlands), simultaneously VBG and CBG were withdrawn in neonates when both venous puncture and intravenous access as blood gas monitoring was indicated. From each blood gas analysis, a Pearson correlation, intraclass correlation, and Bland-Altman analysis was performed. Clinically acceptable difference for each blood gas value was defined up-front by means of an absolute difference: pH ± 0.05; partial pressure of carbon dioxide (pCO₂) (±0.67 kPa = 5 mmHg); partial pressure of oxygen (pO₂) (±0.67 kPa = 5 mmHg); base excess ± 3 mmol/l; and bicarbonate (HCO₃^-) ± 3 mmol/l.

RESULTS

In 93 patients [median gestational age 31 (IQR 29-34) weeks], 193 paired samples of VBG and CBG were collected. The Pearson correlation between VBG and CBG was very strong for pH (r = 0.79; P < 0.001), BE (r = 0.90; P < 0.001) and bicarbonate (r = 0.87; P < 0.001); strong for pCO₂ (r = 0.68; P < 0.001); and moderate for pO₂ (r = 0.31; P < 0.001). The percentage of the interchangeability within our acceptable absolute difference for pH was 88%, pCO₂ 72%, pO₂ 55%, BE 90%, and bicarbonate 94%.

CONCLUSION

VBG and CBG in neonates are well correlated and mostly interchangeable, except for pO₂.

A platinum oxide-based microvoltammetric pH electrode suitable for physiological investigations

Herein, we report the in vitro investigation of a physiologically relevant Pt oxide-based microvoltammetric pH electrode.

Sidestream microstream end tidal carbon dioxide measurements and blood gas correlations in neonatal intensive care unit

OBJECTIVE

The study was designed to assess the use of newer sidestream microstream end tidal carbon dioxide (ETCO(2) ) device in predicting blood carbon dioxide (PCO(2) ) measurements in very low birth weight (VLBW = birth weight <1,500 g) and non-VLBW NICU neonates.

STUDY DESIGN

Sidestream microstream ETCO(2) detectors were allowed time to calibrate and reach steady state prior to blood gas measurements. Blood CO(2) (PCO(2) ) and simultaneous ETCO(2) were recorded. Ratio of dead space to tidal volume (VD/VT) was calculated using modified Bohr's equation. Correlation coefficient, estimates of difference, standard deviation, and 95% limits of agreement between ETCO(2) and PCO(2) concentrations were calculated.

RESULTS

Two hundred eighty-six paired samples were collected from 48 ventilated NICU patients. Average PCO(2) and ETCO(2) were 58.4 and 50.6 with a correlation of 0.76. Subgroup analysis showed a correlation of 0.73 in 204 paired blood from 34 VLBW infants and 0.82 in 82 paired samples from non-VLBW infants. Estimates of difference ± standard deviation between PCO(2) and ETCO(2) concentrations in these three groups, respectively (ALL, VLBW, and non-VLBW) were 7.84 ± 9.96, 8.2 ± 10.16, and 6.95 ± 9.45. The correlation coefficient significantly improved in the VLBW group to 0.86 with dead space to tidal volume ratio (VD/VT) <30% (0.86 vs. 0.42; P < 0.001).

CONCLUSION

ETCO(2) measurements using sidestream microstream technology in VLBW demonstrated that the correlation of ETCO(2) and PCO(2) was moderate, but the agreement was less than adequate (bias > 5 mmHg in all groups). The results improved with lower VD/VT, suggesting that sidestream capnography is more reliable in conditions of less severe lung disease.

Detection of carbon dioxide thresholds using low-flow sidestream capnography in ventilated preterm infants

BACKGROUND

Monitoring CO2 levels in preterm infants receiving mechanical ventilation is designed to avoid the harmful consequences of hypocapnia or hypercapnia. Capnography is of questionable accuracy for monitoring PCO2 in preterm infants.

OBJECTIVES

To determine the accuracy of sidestream capnography in ventilated preterm infants by comparing end-tidal carbon dioxide (EtCO2) values to mixed venous carbon dioxide pressure (PvCO2) and to transcutaneous carbon dioxide pressure (TcPCO2).

METHODS

Simultaneous recordings of EtCO2, TcPCO2 and PvCO2 in 37 ventilated preterm infants. The PvCO2-EtCO2 gradient was calculated. The Bland-Altman technique and the intra-class correlation coefficient (ICC) were used to assess agreement between methods. The area under the curve (AUC) was calculated.

RESULTS

Ninety-nine EtCO2/PvCO2 pairs were studied from 37 preterm infants with a mean gestational age of 27.7 +/- 1.9 weeks and a mean birth weight of 1,003 +/- 331 g. The mean PvCO2-EtCO2 gradient was 11.2 +/- 8.0 mmHg, and the ICC was 0.28. The mean PvCO2-TcPCO2 gradient was 0 +/- 7.8 mmHg, and the ICC was 0.78. AUCs for EtCO2 and TcPCO2 were similar in detecting high or low PvCO2.

CONCLUSION

Despite an insufficient correlation between EtCO2 and PvCO2, capnography was able to detect low and high CO2 warning levels with a similar efficacy to that of TcPCO2, and may therefore be of clinical interest.

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.

Clinical Performance of an In-Line, ex Vivo Point-of-Care Monitor: A Multicenter Study

Background: The management of critically ill infants and neonates includes frequent determination of arterial blood gas, electrolyte, and hematocrit values. An objective of attached point-of-care patient monitoring is to provide clinically relevant data without the adverse consequences associated with serial phlebotomy.

Methods: We prospectively determined the mean difference (and SD of the difference) from laboratory methods of an in-line, ex vivo monitor, the VIA LVM Blood Gas and Chemistry Monitoring System® (VIA LVM Monitor; Metracor Technologies, Inc.), in 100 critically ill neonates and infants at seven children’s hospitals. In doing so, we examined monitor stability with continuous use. In vivo patient test results from laboratory benchtop analyzers were compared with those from the VIA LVM Monitor on paired samples. In a separate in vitro comparison, benchtop analyzer and monitor test results were compared on whole-blood split samples.

Results: A total of 1414 concurrent, paired-sample measurements were obtained. The mean differences (SD of differences) from laboratory methods and r values for the combined data for the VIA LVM Monitor from the seven sites were 0.001 (0.026) and 0.97 for pH, 0.7 (3.6) mmHg and 0.94 for Pco2, 4.2 (9.6) mmHg and 0.98 for Po2, 0.0 (2.9) mmol/L and 0.87 for sodium, 0.1 (0.2) mmol/L and 0.96 for potassium, and 0.3% (2.9%) and 0.90 for hematocrit. Performance results were similar among the study sites with increasing time of monitor use and between in vivo paired-sample and in vitro split-sample test results.

Conclusion: The VIA LVM Monitor can be used to assess critically ill neonates and infants.

Continuous pH monitoring using the Paratrend 7 inserted into a peripheral vein in a patient with shock and congenital lactic acidosis

The authors present a 25-year-old woman who was admitted to the ICU for treatment of shock, respiratory failure, and acidosis related to congenital lactic acidosis from pyruvate dehydrogenase deficiency. To aid in ongoing management of the metabolic acidosis, the Paratrend blood gas monitoring sensor was inserted through a peripheral venous site to provide a continuous measurement of pH and partial pressure of carbon dioxide (Pco2). With the venous insertion of the Paratrend, a clinically useful correlation with arterial blood gas values was noted. Linear regression analysis of the pH values from the venous blood gas analyses and the Paratrend monitor revealed r2 = 0.71 with p = 0.001 and r2 = 0.78 with a p = 0.0003 for the Pco2 values. Our preliminary experience suggests that venous placement of the Paratrend monitor can be used to provide clinically useful, continuous measurement of pH and Pco2.

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.

Continuous pH and pCO2 Monitoring Using the Paratrend Inserted Through a Pulmonary Artery or Central Venous Catheter

The Paratrend continuous blood gas monitoring system was placed through a pulmonary artery or central venous catheter as a means of continuously monitoring pH, pCO2, and mixed venous oxygen saturation in three neonates at risk for cardiorespiratory dysfunction, two following surgery for congenital heart disease and one with septic shock. After calibration with an arterial/mixed venous blood gas value, the Paratrend monitor provided a clinically useful continuous measurement of pH and pCO2. The difference between the Paratrend and the arterial values for pH and pCO2 were 0.02 ± 0.009 and 2.4 ± 0.8 mmHg, respectively. There was a significant discrepancy between the oxygen saturation reading from the Paratrend and the actual measured mixed venous value (9 ± 5%). The possible applications of the Paratrend placed through a pulmonary artery or central venous catheter are discussed.