Assessment of pulse co-oximetry technology after in vivo adjustment in anaesthetized dogs

Abstract

Objective: To compare values of haemoglobin concentration (SpHb), arterial haemoglobin saturation (SpO₂) and calculated arterial oxygen content (SpOC), measured noninvasively with a pulse co-oximeter before and after in vivo adjustment (via calibration of the device using a measured haemoglobin concentration) with those measured invasively using a spectrophotometric-based blood gas analyser in anaesthetized dogs.

Study design: Prospective observational clinical study.

Animals: A group of 39 adult dogs.

Methods: In all dogs after standard instrumentation, the dorsal metatarsal artery was catheterised for blood sampling, and a pulse co-oximeter probe was applied to the tongue for noninvasive measurements. Paired data for SpHb, SpO₂ and SpOC from the pulse co-oximeter and haemoglobin arterial oxygen saturation (SaO₂) and arterial oxygen content (CaO₂) from the blood gas analyser were obtained before and after in vivo adjustment. Bland-Altman analysis for repeated measurements was used to evaluate the bias, precision and agreement between the pulse co-oximeter and the blood gas analyser. Data are presented as mean differences and 95% limits of agreement (LoA).

Results: A total of 39 data pairs were obtained before in vivo adjustment. The mean invasively measured haemoglobin-SpHb difference was -2.7 g dL^-1 with LoA of -4.9 to -0.5 g dL^-1. After in vivo adjustment, 104 data pairs were obtained. The mean invasively measured haemoglobin-SpHb difference was -0.2 g dL^-1 with LoA of -1.1 to 0.6 g dL^-1. The mean SaO₂-SpO₂ difference was 0.86% with LoA of -0.8% to 2.5% and that between CaO₂-SpOC was 0.66 mL dL^-1 with LoA of -2.59 to 3.91 mL dL^-1.

Conclusions: Before in vivo adjustment, pulse co-oximeter derived values overestimated the spectrophotometric-based blood gas analyser haemoglobin and CaO₂ values. After in vivo adjustment, the accuracy, precision and LoA markedly improved. Therefore, in vivo adjustment is recommended when using this device to monitor SpHb in anaesthetised dogs.

Keywords: anaesthesia; dog; haemoglobin; oxygen saturation; pulse co-oximetry.