Effect of lingual gauze swab placement on pulse oximeter readings in anaesthetised dogs and cats

Investigation of the association between oxygen reserve index and arterial partial oxygen pressure in anesthetized dogs

OBJECTIVE

To evaluate the relationship between oxygen reserve index (ORI) and arterial partial pressure of oxygen (PaO2) in anesthetized dogs.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of eight healthy adult Beagle dogs with a median age of 38 (range 20-87) months and a median body mass of 8.6 (range 7.0-13.8) kg.

METHODS

After induction of general anesthesia with propofol, dogs were mechanically ventilated and anesthesia maintained with isoflurane carried in oxygen. Arterial blood samples were collected from a catheter placed in the femoral artery. ORI was measured by placing a CO-oximeter sensor on the tongue. Inspired oxygen fraction (FiO2) was increased from 21% to > 95% in increments of 5%. PaO2 and ORI were recorded and compared at different times. The relationship between ORI and PaO2 was investigated using a nonlinear function, the Hill equation, and a linear regression analysis was performed, as appropriate.

RESULTS

A total of 128 pairs of values were compared for all dogs. Applying the Hill equation to the relationship between ORI and PaO2 resulted in R2 = 0.80 (p < 0.001) with a Hill coefficient of 3.7. It was predicted that ORI ranged 0.1-0.9 as PaO2 ranged 127.0-417.9 mmHg and that in the more linear portion of the range, PaO2 of 127.0-289.9 mmHg ORI ranged 0.1-0.7. Linear regression analysis in the more linear portion showed a weak correlation (R2 = 0.29, p = 0.006).

CONCLUSIONS AND CLINICAL RELEVANCE

In the present study, the Hill equation predicted the relationship between PaO2 and ORI for PaO2 ranging 127.0-417.9 mmHg in anesthetized dogs. However, in the linear portion of the PaO2, the coefficient of determination was low, indicating that ORI is not a surrogate for PaO2.

Non-invasive assessment of oxygenation status using the oxygen reserve index in dogs

BACKGROUND

The oxygen reserve index (ORi) is a real-time, continuous index measured with multi-wavelength pulse CO-oximetry technology. It estimates mild hyperoxemia in humans, which is defined as a partial pressure of oxygen (PaO2) level between 100 and 200 mmHg. The objectives of this study were to assess the correlation between ORi and PaO2, as well as to determine its ability in detecting mild hyperoxemia in dogs.

METHODS

This prospective observational study enrolled 37 anaesthetised and mechanically ventilated dogs undergoing elective procedures. Simultaneous measurements of ORi and PaO2 were collected, using a multi-wavelength pulse CO-oximeter with a probe placed on the dog's tongue, and a blood gas analyser, respectively. A mixed-effects model was used to calculate the correlation (r2) between simultaneous measurements of ORi and PaO2. The trending ability of ORi to identify dependable and proportional changes of PaO2 was determined. The diagnostic performances of ORi to detect PaO2 ≥ 150 mmHg and ≥ 190 mmHg were estimated using the area under the receiver operating characteristic curve (AUROC). The effects of perfusion index (PI), haemoglobin (Hb), arterial blood pH and partial pressure of carbon dioxide (PaCO2) on AUROC for PaO2 ≥ 150 mmHg were evaluated.

RESULTS

A total of 101 paired measurements of ORi and PaO2 were collected. PaO2 values ranged from 74 to 258 mmHg. A strong positive correlation (r2 = 0.52, p < 0.001) was found between ORi and PaO2. The trending ability ORi was 90.7%, with 92% sensitivity and 89% specificity in detecting decreasing PaO2. An ORi value ≥ 0.53 and ≥ 0.76 indicated a PaO2 ≥ 150 and ≥ 190 mmHg, respectively, with ≥ 82% sensitivity, ≥ 77% specificity and AUROC ≥ 0.75. The AUROC of ORi was not affected by PI, Hb, pH and PaCO2.

CONCLUSIONS

In anaesthetised dogs, ORi may detect mild hyperoxaemia, although it does not replace blood gas analysis for measuring the arterial partial pressure of oxygen. ORi monitoring could be used to non-invasively assess oxygenation in dogs receiving supplemental oxygen, limiting excessive hyperoxia.

Two different smartwatches exhibit high accuracy in evaluating heart rate and peripheral oxygen saturation in cats when compared with the electrocardiography and transmittance pulse oximetry

OBJECTIVE

To evaluate the accuracy for 2 smartwatches with oximetry technology and optical wrist heart rate (HR) or single-lead Electrocardiography (ECG) technology (Fenix 5X Plus [GF5xp], Garmin Ltd and Apple Watch 6 [AppW6], Apple Inc, respectively) versus reference methods (ECG and transmittance pulse oximetry [TPO], respectively) in measuring HR and peripheral oxygen saturation of hemoglobin (SpO2) in cats.

ANIMALS

10 male client-owned cats aged 8 to 12 months and weighing 3.2 to 4.5 kg.

PROCEDURES

All cats that were presented for elective castration at the Atatürk University Animal Hospital between March 10 and April 15, 2022, were considered for enrollment. Monitoring of HR and SpO2 during anesthesia was performed with a 3-lead ECG and transmittance pulse oximetry, respectively, connected to a multiparameter monitor (reference methods) along with a GF5xp and a AppW6. Agreement between reference methods and the smartwatches were assessed by the Bland-Altman plot, in which the differences (%) between methods were plotted against their mean HR or SpO2 (reference method measurement - test device measurement) and the limits of agreement (mean ± 1.96 × SD).

RESULTS

Compared with ECG measurements of HR, GF5xp had superior bias (-0.1%) and limit of agreement (LoA, 3.0 to -3.3%) versus those of the AppW6 (bias, 0.2%; LoA, 3.7 to -3.4%). Compared with TPO measurements of SpO2, AppW6 had superior bias (0.2%) and LoA (3.0% and -2.5%) versus those of the GF5xp (bias, -2.1%; LoA, 0.2 to -4.4%).

CLINICAL RELEVANCE

Results indicated that the GF5xp and AppW6 exhibited high accuracy in evaluating HR and SpO2 in cats when compared with the reference methods. However, it should be noted that these comparisons were made in anesthetized patients without any systemic disease.

[Pulmonary function testing in the cat - an overview]

This article provides an overview of currently available pulmonary function tests in cats, divided into invasive and non-invasive methods. Invasive techniques comprise arterial blood gas analysis and measurement of pulmonary mechanics. Non-invasive techniques include pulse oximetry and capnography, as well as methods not yet integrated into everyday practice such as tidal breathing airflow-volume loops, whole-body barometric plethysmography and thorax compression. In this article, the background, execution, interpretation, and limitations of each test are discussed. Proper performance and assessment of pulmonary function measurements may aid in understanding the pathophysiology of feline respiratory disease and in increasing objectivity when assessing the existing disease and treatment efficacy.

Repeatability and accuracy of fingertip pulse oximeters for measurement of hemoglobin oxygen saturation in arterial blood and pulse rate in anesthetized dogs breathing 100% oxygen

OBJECTIVE

To evaluate the repeatability and accuracy of fingertip pulse oximeters (FPO) for measurement of hemoglobin oxygen saturation in arterial blood and pulse rate (PR) in anesthetized dogs breathing 100% O₂.

ANIMALS

29 healthy client-owned anesthetized dogs undergoing various surgical procedures.

PROCEDURES

In randomized order, each of 7 FPOs or a reference pulse oximeter (PO) was applied to the tongue of each intubated anesthetized dog breathing 100% O₂. Duplicate measurements of oxygen saturation (Spo₂) and PR were obtained within 60 seconds of applying an FPO or PO. A nonparametric version of Bland-Altman analysis was used. Coefficient of repeatability was the interval between the 5th and 95th percentiles of the differences between duplicate measurements. Bias was the median difference, and the limits of agreement were the 5th and 95th percentiles of the differences between each FPO and the PO. Acceptable values for the coefficient of repeatability of Spo₂ were ≤ 6%. Agreements were accepted if the limits of agreement had an absolute difference of ≤ ± 3% in Spo₂ and relative difference of ≤ ± 10% in PR.

RESULTS

Coefficient of repeatability for Spo₂ was acceptable for 5 FPOs, but the limits of agreement for Spo₂ were unacceptable for all FPOs. The limits of agreement for PR were acceptable for 2 FPOs.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that some FPOs may be suitable for accurately monitoring PRs of healthy anesthetized dogs breathing 100% O₂, but mild underestimation of Spo₂ was common.

Appraisal of the 'penumbra effect' using lingual pulse oximetry in anaesthetized dogs and cats

OBJECTIVE

Factors described as contributors to the 'penumbra effect' in relation to pulse oximetry include optical shunting, circulatory anastomoses and probe parallelity. This study aimed to clarify the main underlying mechanism involved.

STUDY DESIGN

Prospective clinical trial.

ANIMALS

A total of 30 dogs and 15 cats (client-owned).

METHODS

In anaesthetized dogs and cats, a pulse oximeter probe was placed on the tongue to measure haemoglobin oxygen saturation (SpO₂) and perfusion index. In 15 dogs, the probe was positioned at the root (baseline) of the tongue, then at 0.5 and 1 cm rostral to it, to investigate the effect of circulatory anastomoses on SpO₂ values. In cats (which do not have lingual arteriovenous anastomoses), the probe was positioned at the root and apex of the tongue. To assess the effect of probe parallelity on SpO₂ values in dogs, two lines were drawn parallel to the planes of the light-emitting diode and the detector surfaces and the intersection angle calculated using ImageMeter Pro, Google Play. In a further 15 dogs, the probe was placed at the tongue edge (0% optical shunt), with 50% optical shunt, then with the 50% optical shunt shielded. Data were analysed using Friedman's test, Student t test and Pearson's correlation coefficient (p < 0.05).

RESULTS

In dogs, SpO₂ values were significantly higher at 1.0 cm than at baseline (p < 0.0001). In cats, there were no significant differences in SpO₂ values at each location. There was no significant difference in SpO₂ between 0% and 50% optical shunt in dogs. SpO₂ had a moderate negative correlation with tongue thickness and negligible correlation with intersection angle.

CONCLUSIONS AND CLINICAL RELEVANCE

Circulatory anastomoses are probably responsible for observed changes in SpO₂ as the probe is placed towards an extremity, rather than optical shunting or probe parallelity.