Effect of changes in oscillatory amplitude on PaCO(2) and PaO(2) during high frequency oscillatory ventilation

Continuous blood gas monitoring using an in-dwelling optode method: comparison to intermittent arterial blood gas sampling in ECMO patients

INTRODUCTION

The ability to measure postmembrane arterial blood gases is essential in the management of critically ill neonates treated with extracorporeal membrane oxygenation (ECMO). A new technology using, the Paratrend 7 system (Diametrics Medical, High Wycombe,UK) allows for continuous measurement of pH, PCO(2) and PO(2), and calculates oxygen saturation, bicarbonate, and base excess.

OBJECTIVE

To evaluate and compare the results of continuous blood gas measurement using the Paratrend 7 system with a standard system of blood gas analysis in our intensive care unit.

DESIGN

Prospective, controlled, interventional study.

SETTING

The neonatal intensive care unit of a tertiary referral center.

PATIENTS

Neonates who required extracorporeal life support and were expected to have frequent postmembrane arterial blood sampling during the testing period.

RESEARCH DESIGN AND METHOD

To enable Paratrend 7 sensor access to the ECMO circuit, the postmembrane access port extension set that is routinely used for blood drawn for blood gas analysis was used. The study began with the insertion of the Paratrend 7 sensor. Subjects remained on the study until the ECMO was discontinued and/or frequent blood gases were no longer needed. The blood gas results from the Paratrend 7 system were not used in clinical management of the patient. BLOOD GAS MEASUREMENT: During the study period, with each blood sample drawn for laboratory analysis, a printout from the Paratrend 7 monitor was recorded for comparison.

RESULTS

A total of 242 pairs of blood gas samples were collected from 10 neonates. The mean bias/precision for pH was -0.02/0.04; for PO(2) 68.35/93.44 mm Hg; and for PCO(2) 1.75/4.23 mm Hg. The correlation (r value) between the sensor reading and the blood gases were 0.89 for pH, 0.96 for PO(2), and 0.73 for PCO(2) (Table 1).

CONCLUSION

The blood gases compared in the two methods had a strong correlation for pH, PCO(2) and PO(2). Results of this study indicate that this technology provides an accurate means of monitoring continuous blood gas parameters in neonatal ECMO patients. Use of the Paratrend 7 should allow reduced health-care provider exposure to blood and decreased patient iatrogenic blood loss.

Hypercapnic respiratory failure and partial upper airway obstruction during high frequency oscillatory ventilation in an adult burn patient

PURPOSE

To present a case of severe hypercapnic respiratory failure in an adult burn patient and to describe our clinical problem solving approach during support with an unconventional mode of mechanical ventilation.

CLINICAL FEATURES

A 19-yr-old male with smoke inhalation and flame burns to 50% total body surface area was admitted to the Ross Tilley Burn Centre. High frequency oscillatory ventilation (HFOV) was initiated on day three for treatment of severe hypoxemia. By day four, the patient met consensus criteria for acute respiratory distress syndrome. On day nine, alveolar ventilation was severely compromised and was characterized by hypercapnea (PaCO(2) 136 mmHg) and acidosis (pH 7.10). Attempts to improve CO(2) elimination by a decrease in the HFOV oscillatory frequency and an increase in the amplitude pressure failed. An intentional orotracheal tube cuff leak was also ineffective. A 6.0-mm nasotracheal tube was inserted into the supraglottic hypopharynx to palliate presumed expiratory upper airway obstruction. After nasotracheal tube placement, an intentional cuff leak of the orotracheal tube improved ventilation (PaCO(2) 81 mmHg) and relieved the acidosis (pH 7.30). The improvement in ventilation (with normal oxygen saturation) was sustained until the patient's death from multiple organ dysfunction four days later.

CONCLUSION

During HFOV in burn patients, postresuscitation edema of the supraglottic upper airway may cause expiratory upper airway obstruction. The insertion of a nasotracheal tube, combined with an intentional orotracheal cuff leak may improve alveolar ventilation during HFOV in such patients.

Continuous blood gas monitoring using an in-dwelling optode method: clinical evaluation of the Neotrend sensor using a luer stub adaptor to access the umbilical artery catheter

INTRODUCTION

Arterial blood gases are essential in the management of critically ill neonates. A new technology using the Neotrend system (Diametrics Medical) allows for continuous measurement of pH, PaCO(2), and PaO(2), and calculates oxygen saturation, bicarbonate, and base excess.

OBJECTIVE

To evaluate and compare the results of continuous blood gas measurement using the Neotrend system with a standard system of blood gas analysis in our intensive care unit.

DESIGN

Prospective, controlled, interventional study.

SETTING

The neonatal intensive care unit of a tertiary referral center.

PATIENTS

Neonates with respiratory distress who required respiratory support and frequent arterial blood gas sampling and had a UAC.

RESEARCH DESIGN AND METHOD

To enable Neotrend sensor access to an existing Argyle umbilical artery catheter (UAC) the catheter was cut at the 25-cm mark and connected to an 18-gauge blunt needle luer stub adaptor (Vygon 95440). The study began with the insertion of the Neotrend sensor. Subjects remained on the study until the UAC was discontinued and/or frequent blood gases were no longer needed. The blood gas results from the Neotrend system were not used in clinical management of the patient. BLOOD GAS MEASUREMENT: During the study period, with each blood sample drawn for laboratory analysis, a printout from the Neotrend monitor was recorded for comparison.

RESULTS

A total of 217 pairs of blood gas samples were collected from seven neonates. The mean bias/precision for pH was 0.01/0.04; for PaO(2) 0.72/18.5 mm Hg; and for PaCO(2) 3.96/2.63 mm Hg. The correlation (r value) between the sensor reading and the blood gases were 0.85 for pH, 0.96 for PaO(2), and 0.92 for PaCO(2).

CONCLUSION

The blood gases compared in the two methods had a strong correlation for pH, PaCO(2), PaO(2), and oxygen saturation. Although the bicarbonate and base excess values showed suboptimal statistical correlation, the difference was not clinically relevant. Results of this study indicate that this technology provides an accurate means of monitoring continuous blood gas parameters in neonatal patients. It also allows reduced healthcare provider exposure to blood and decreased patient iatrogenic blood loss.