title: Accuracy of Masimo Radical-7® Pulse CO-oximetryTM in anaesthetized dogs
Creators: name: Tayari, Hamaseh
Publisher: name: University of Glasgow
Year: 2021

description: Total haemoglobin concentration tHb, arterial haemoglobin saturation (SaO2), and arterial oxygen content (CaO2) are indicative of a patient’s ability to transport oxygen (O2) and can be used to guide clinical decisions. Laboratory-based methodologies such as the haematology analyser, laboratory CO-Oximetry, and point-of-care analysers have been used to assess these values, but despite being accurate all these instruments require a blood sample, allow only intermitted monitoring, are operator-dependent, and introduce a delay in obtaining results. Pulse CO-oximetry, by combining the principles of CO-Oximetry with pulse oximetry enables noninvasive measurements of the Hb (SpHb) and derived values. Whilst the Masimo pulse COoximeter has given the approval by the Food and Drug Administration (FDA) and European Medical Agency (EMA), there is still debate within the scientific literature regarding its accuracy. In a recent version of the pulse CO-oximeter software, a so-called in-vivo adjustment that allows initial calibration of the SpHb against a measured laboratory value has been introduced with the intent to increase accuracy (Miyashita et al. 2014; Frasca et al. 2015; De Rosa 2020).To date, in veterinary medicine only three studies have investigated the performances of pulse CO-oximetry, but none of them have investigated the accuracy of SpHb after in-vivo adjustment. With the hypotheses that in-vivo adjustment would increase the accuracy of subsequent SpHb measurements, the aim of this thesis was to assess the agreement of pulse CO-oximeter derived values of tHb [H], CaO2 and SaO2, using an optical fluorescencebased blood gas analyser and oximeter (VetStat®) as the reference method. This thesis hypothesises that the accuracy of SpHb and SpO2 will be influenced by perfusion index (PI), mean arterial pressure (MAP) and tongue thickness. Furthermore, clinical significance and trending accuracy were tested with error grid and four quadrant plot analysis. A total of 39 data pairs of tHb were obtained before in-vivo adjustment in as many dogs. The mean [Hb]-SpHb difference was -2.7 g dL−1 with limit of acceptance (LoA) of -4.9 to -0.5 g dL−1. After in-vivo adjustment from the same dogs, 104 data pairs were obtained; the mean [Hb]-SpHb difference, after in-vivo adjustment, was -0.2 g dL−1 with LoA of -1.1 to 0.6g dL−1. The mean SaO2-SpO2 difference was 0.86% with LoA of -0.8 to 2.5% and between CaO2 -SpOC was 0.66 ml dL-1with LoA of -2.59 to 3.91 ml dL-1. Zone A of the error grid encompassed approximately 98% of data pairs for SpHb. The concordance rate for consecutive changes in SpHb and [Hb] performed with four quadrant plot analysis was 92.6%. Before in-vivo adjustment, pulse CO-oximetry derived values overestimated the spectrophotometric-based blood gas analyser [Hb] and CaO2 values. Following in-vivo adjustment, the accuracy, precision, and LoA markedly improved. The accuracy of SpHb and SpO2 were not influenced by PI, MAP and tongue thickness and pulse CO-oximetry, after in-vivo adjustment, adequately tracked the changes of Hb within the time confirming a good trending accuracy. Furthermore, the Masimo’s performance was evaluated in dogs referred to the University of Glasgow Small Animal Hospital for a variety of emergency surgeries and presented in hypovolemic states, and/or acute haemorrhagic states. The findings from our observational study shown an acceptable [Hb]-SpHb difference, and a consistent fall in SpHb values during bleeding episodes. This finding may support the use of pulse CO-oximetry devices as an intraoperative starting point for deciding when to perform an invasive tHb measurement. Nevertheless, in all patients receiving synthetic colloids and/or vasoactive drugs (noradrenaline infusion) the increase in [Hb]-SpHb difference suggests that values displayed by the Masimo Radical-7 under these circumstances should be considered carefully and always confirmed by an invasive blood sample. In conclusion, pulse co-oximetry and SpHb monitoring, after in-vivo adjustment, cannot completely replace invasive measurements, but show definite promise for use during surgical procedures.