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

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.

Evaluation of the performance of two new generation pulse oximeters in cats at different probe positions and under the influence of vasoconstriction

Objectives

The aim of this study was to compare the failure rate of two new generation pulse oximeters at different probe positions, and with and without vasoconstriction, in anaesthetised cats.

Methods

This prospective clinical study included 103 cats in which the new generation pulse oximeters, the Rad-5 (Masimo) and EDAN H100N (EDAN), were evaluated. Premedication consisted of the vasoconstrictive drug combination butorphanol (0.2 mg/kg IV) and dexmedetomidine (5 µg/kg IV), or butorphanol only (0.2 mg/kg IV). Pulse oximeter failure rate at the tongue was compared between both groups. Pulse oximeter failure rate was also analysed at the alternative probe positions of the lip, pinna, knee fold and toe in the butorphanol group. Student’s t-test, Wilcoxon matched pairs signed rank test, Mann−Whitney U-test, Friedman test and χ² test were performed. A P value <0.05 was considered to be statistically significant.

Results

Overall failure to achieve an adequate signal was 37.6% with the Masimo and 48.0% with the EDAN pulse oximeter (P <0.0001). At the standard probe position on the tongue, the Masimo failed in 4.5%, while the EDAN failed in 35.3% (P <0.0001). Vasoactive premedication increased the failure rate for the Masimo from 3.8% to 5.2% (P = 0.3414) and for the EDAN from 22.4% to 49.0% (P <0.0001). At the alternative probe positions of the lip and knee fold, failure rates for the Masimo were lower (39.7% and 81.4%) than with the EDAN (52.6% and 94.4%; P = 0.0231 and P = 0.0005, respectively), while the Masimo failed more often at the pinna (63.5%) than the EDAN (47.4%; P = 0.0044). At the alternative probe position of the toe, the failure rate for the Masimo (32.7%) was not different from the EDAN (38.5%; P = 0.7547).

Conclusions and relevance

The Masimo pulse oximeter had lower signal failure rates at the standard probe position on the tongue and at 2/4 alternative probe positions. The standard probe position on the tongue had the lowest failure rate for both devices. Dexmedetomidine-induced vasoconstriction increased the failure rate for the EDAN but not for the Masimo pulse oximeter.

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.

Thinking Out-of-the-Box: A Non-Standard Application of Standard Pulse-Oximetry and Standard Near-Infrared Spectroscopy in a COVID-19 Patient

PURPOSE

Purpose of this report is to describe the feasibility of lingual pulse oximetry and lingual near-infrared spectroscopy (NIRS) in a COVID-19 patient to assess lingual tissue viability after several days of mechanical ventilation in the prone position.

MATERIALS & METHODS

In a COVID-19 ICU-patient, the tongue became grotesquely swollen, hardened and protruding from the oral cavity after 20 h of mechanical ventilation uninterrupted in the prone position. To assess the doubtful viability of the tongue, pulse-oximetric hemoglobin O2-saturation (SpO2; Nellcor, OxiMax MAX-NI, Covidien, MA, USA) and NIRS-based, regional tissue O2-saturation measurements (rSO2; SenSmart, Nonin, MN, USA) were performed at the tongue.

RESULTS

At the tongue, regular pulse-oximetric waveforms with a pulse-oximetric hemoglobin O2-saturation (SpO2) of 88% were recorded, i.e. only slightly lower than the SpO2 reading at the extremities at that time (90%). Lingual NIRS-based rSO2 measurements yielded stable tissue rSO2-values of 76-78%, i.e. values expected also in other adequately perfused and oxygenated (muscle-) tissues.

CONCLUSION

Despite the alarming, clinical finding of a grotesquely swollen, rubber-hard tongue and clinical concerns on the adequacy of the tongue perfusion and oxygenation, our measurements of both arterial pulsatility (SpO2) and NIRS-based tissue oxygenation (rSO2) suggested adequate perfusion and oxygenation of the tongue, rendering non-vitality of the tongue, e.g. by lingual venous thrombosis, unlikely. To our knowledge, this is the first clinical report of lingual rSO2 measurement.

Dexmedetomidine and ketamine simultaneous administration in tigers (Panthera tigris): pharmacokinetics and clinical effects

Background

The study determines the pharmacokinetic profiles of dexmedetomidine (DEX), ketamine (KET) and its active metabolite, norketamine (NORKET), after simultaneous administration. Moreover, the study evaluates the sedative effects of this protocol, its influence on the main physiological variables and the occurrence of adverse effects.

Methods

Eighteen captive tigers were initially administered with a mixture of DEX (10 µg/kg) and KET (2 mg/kg) by remote intramuscular injection. In case of individual and specific needs, the protocol was modified and tigers could receive general anaesthesia, propofol or additional doses of DEX and KET.

Results

Based on the immobilisation protocol, nine animals were assigned to the standard protocol group and the other nine to the non-standard protocol group. Higher area under the first moment curve (AUMC_0-last) and longer mean residence time (MRT_0-last) (P<0.05) were observed in the non-standard protocol group for DEX, KET and NORKET, and higher area under the concentration-time curve from administration to the last measurable concentration (AUC_0-last) only for KET. The KET metabolisation rate was similar (P=0.296) between groups. No differences between groups were detected in terms of stages of sedation and recoveries. All physiological variables remained within normality ranges during the whole observation period. During the hospitalisation period, no severe adverse reactions and signs of resedation were observed.

Conclusion

The simultaneous administration of 10 µg/kg of DEX and 2 mg/kg of KET can be considered an effective protocol for chemical immobilisation of captive tigers, along with dosage adjusments or when other drugs are needed.