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Crit Care. 2010; 14(Suppl 1): P168.
Published online 2010 March 1. doi:  10.1186/cc8400
PMCID: PMC2933998

Combined oximetry and transcutaneous capnography is a reliable non-invasive monitoring in patients after cardiac surgery

Introduction

The aim of this study was to validate the revised V-Sign™ 2 ear lobe sensor for combined assessment of pulse rate (PR), pulse oximetry (SpO2) and transcutaneous carbon dioxide tension (PtcCO2) in adults after cardiac surgery.

Methods

In 20 patients coevally readings of blood gases were compared with values of the V-Sign™ 2 ear lobe sensor. Measurements were performed during periods of hypercapnia, normocapnia and hypocapnia and then in intervals of 30 minutes up to 5 hours. Agreement was assessed by Bland-Altman analysis and single regression analysis.

Results

Two hundred and ninety-six data pairs were analysed. Detection failures for PtcCO2 were 1.3%, for SpO2 10% and for PR 5%. PtcCO2 and PaCO2 ranged between 3.58 and 7.70 kPa. Mean bias and limits of agreement (LOA) between PtcCO2 and PaCO2 was excellent (Table (Table1).1). The best agreement between PtcCO2 and PaCO2 was found during periods of hyperventilation and hypoventilation with a mean bias (LOA) of +0.18 kPa (-0.31/+0.67 kPa) and 0.07 kPa (-0.45/+0.59 kPa), respectively. At about 5 hours no relevant drift was observed between PtcCO2 and PaCO2. V-Sign™ 2 SpO2 moderately agreed and slightly underestimated SaO2 determined by direct oximetry, whereas pulse rate values detected by the V-Sign™ 2 ear lobe sensor agreed well with those of the ECG (Table (Table11).

Table 1
Agreement between V-Sign™ 2 sensor and co-oximetry and ECG

Conclusions

Transcutaneous capnography using the V-Sign™ 2 ear lobe sensor reliably detects the ventilation state of patients after cardiac surgery. This non-invasive approach has the potential to reduce the number of arterial blood gas samples.


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