Introduction: Recently, the manufacturer of the only commercially available continuous intravascular blood gas monitoring system introduced a new, pure optode probe, the Paratrend P7+ (Diametrics Medical, High Wycombe, UK). We performed a comparison between intermittent blood gas analyses (IBGA) using a conventional blood gas analyser (ABL5, Radiometer, Copenhagen) and the results of the P7+ probe, by simultaneous measurements. The aim of our study was to evaluate the applicability and performance of the new probe for jugular venous and arterial blood gas determinations .
Method: Ten patients (7 male, 3 female) aged 68.9 ± 5.6 years old, ASA II-III, undergoing carotid endarterectomy under general anaesthesia were studied. After surgical exposure of the internal carotid artery, a 6.0 Fr introducer sheath was inserted into the ipsilateral jugular vein. The tip of P7+ was advanced through and placed into the jugular bulb. Oxygen was administered to the patient at inspiratory oxygen concentration (FiO2) of 1.0. Before surgical closure of the wound the probe was repositioned backwards in protective tubing. All patients were extubated and transferred to ICU where supplemental oxygen at FiO2 0.7 to 0.3 was administered through a Venturi mask. A 20G arterial catheter was introduced in the radial artery and patient's own P7+ probe was advanced through it. Simultaneous recording of P7+ readings and IBGA using commercially prepared syringes (Quik A.B.G.TM, MarquestTM) were performed at both insertion sites. Statistical analysis with the method of Bland and Altman was employed.
Results: The P7+ probe could be placed in the jugular vein and subsequently in the radial artery with neither malfunction due to kinking or “wall effect”, nor complications. Mean monitoring time was for jugular vein 40 ± 4.5 min and for radial artery 420 ± 45min. We analysed a total of 97 parallel blood gas samples (43 venous and 54 arterial). The ranges for IBGA were: PO2 3.7 to 47.3kPa (mean 17.3 ± 12.7), PCO2 4.5 to 7.5kPa (mean 5.7 ± 0.5), and pH 7.25 to 7.5 units (mean 7.38 ± 0.04). The coefficient correlation (r) between continuous and conventional blood gas measurements was for PO2 0.97, for PCO2 0.63, and for pH 0.6. The calculated bias and precision values (1 SD of bias) were for PO2 0.82/3.4kPa, for PCO2 −0.51/0.48 kPa and for pH 0.052/0.03 units, respectively.
Discussion: According to our data, the PO2 values as measured by the new Paratrend P7+ probe and conventional blood gas analyser, correlated sufficiently for both jugular and arterial blood. The precision of the sensor for PO2 was less satisfactory than for PCO2 and pH.
1 Menzel M, Henze D, Soukup J, et al. Experiences with continuous intra-arterial blood gas monitoring. Minerva Anestesiol