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 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 1).

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.