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.

Retrospective evaluation of the impact of hypoxemia during thoracic surgery in dogs on outcome: a multicenter analysis of 94 cases.

OBJECTIVE: To investigate the statistical association of severe intraoperative hypoxemia in thoracic surgery with mortality, postoperative hospitalization times and cost of care. STUDY DESIGN: Retrospective study. ANIMALS: Dogs that underwent thoracic surgery in three veterinary hospitals between October 1, 2018 and October 1, 2020. METHODS: Anesthesia and hospitalization records from 112 dogs were reviewed and 94 cases met inclusion criteria. Recorded data included signalment, disease etiology, pulmonary or extrapulmonary nature of disease, surgical procedure performed, episodes of severe intraoperative hypoxemia defined as a pulse oximetry reading (SpO2) <90% of 5 minutes or longer duration, survival to discharge, time from extubation to hospital discharge and total invoice cost for clinical visit. Dogs were divided into two groups, those that experienced severe hypoxemia (group A) and those in which SpO2 reading <90% was not observed throughout the procedure (group B). RESULTS: Group A had a greater risk of mortality (odds ratio 10.6, 95% confidence interval 1.9-106.7; p = 0.002), prolonged hospitalization (median 62 hours versus 46 hours; p = 0.035) and more expensive cost of care (median US$10,287 versus $8506; p = 0.056) than group B. No significant difference was found for the type of surgical procedure or pulmonary versus extrapulmonary nature of disease. CONCLUSIONS AND CLINICAL RELEVANCE: Severe intraoperative hypoxemia was statistically associated with an increased risk of mortality and longer postoperative hospitalization times. Although not achieving statistical significance, there was a trend toward increased costs to the client for animals with intraoperative hypoxemia.

Use of CO-oximetry to confirm carboxyhemoglobinemia in cats involved in secondary arson homicide.

The body of a deceased human and 4 deceased cats were found in a house while a fire was being extinguished. As a result of these findings, arson, homicide, and animal death investigations were opened. As part of the animal death investigation, all of the cats were submitted for veterinary forensic autopsies. All cats had soot on the fur and had soot deposits within the oral cavity, esophagus, and respiratory tract. Two cats had soot within the stomach. Cardiac blood was analyzed for carboxyhemoglobin using a CO-oximeter, and all cats had levels >65%. The cause of death was determined to be due to toxic smoke inhalation from the structure fire. Case findings support the potential use of CO-oximeter for determination of carboxyhemoglobin levels in cats and continued research in this area of forensic practice.

Sample stability and heparin interference in ionized calcium and ionized magnesium measurements in horses using the Stat Profile Prime Plus co-oximetry electrolyte analyzer.

BACKGROUND: The determination of iCa and iMg is important in veterinary medicine, but their immediate determination in whole blood is not always possible. Their stability in other sample types and the existence of interferences must be evaluated before its use. OBJECTIVES: We aimed to analyze the effects of storage time on the stability of iCa, iMg, and other analytes in whole blood, plasma, and serum samples in horses and assess the interference of heparin in these measurements. METHODS: Whole blood, heparin-plasma, and serum samples from 10 horses were stored at 4°C and analyzed 1, 2, 3, 4, 5, 6, 7, 8, 24, 48, and 168 hours after sample collection using the Stat Profile Prime Plus Vet equipment (Nova Biomedical, Waltham, MA, USA). Results were analyzed by ANOVA or mixed-effect models. RESULTS: The concentration of iCa, iMg, total calcium (tCa), total magnesium (tMg), and the ratios iCa/tCa and iMg/tMg did not differ up to 168 hours when compared to the initial time. Total Ca, iMg, and tMg were not significantly different among sample types, but iCa concentrations were slightly but significantly lower in plasma. Freezing at -20°C did not affect iCa, iMg, tCa, and tMg. The pH increased in serum and plasma after 8 hours, and a mild negative correlation existed between plasma iCa concentration and pH. A negative correlation was observed also between the ratios iCa/tCa or iMg/tMg and pH in plasma and serum. A significant decrease in iCa and iMg was detected when comparing homemade syringes at high heparin concentration (~200-300 U heparin/mL) and commercial lithium-heparin tubes (20-30 U/mL). CONCLUSIONS: Samples stored at 4°C can be used to determine iCa and iMg concentrations up to 7 days after collection. Other metabolites are stable for up to 8 hours; heparin interference should be taken into account if using homemade heparin syringes.

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.

Reliability of pulse oximetry at four different attachment sites in immobilized white rhinoceros (Ceratotherium simum).

OBJECTIVES: To determine the reliability of peripheral oxygen haemoglobin saturation (SpO2), measured by a Nonin PalmSAT 2500A pulse oximeter with 2000T transflectance probes at four attachment sites (third eyelid, cheek, rectum and tail), by comparing these measurements to arterial oxygen haemoglobin saturation (SaO2), measured by an AVOXimeter 4000 co-oximeter reference method in immobilized white rhinoceros (Ceratotherium simum). STUDY DESIGN: Randomized crossover study. ANIMALS: A convenience sample of eight wild-caught male white rhinoceros. METHODS: White rhinoceros were immobilized with etorphine (0.0026 ± 0.0002 mg kg-1, mean ± standard deviation) intramuscularly, after which the pinna was aseptically prepared for arterial blood sample collection, and four pulse oximeters with transflectance probes were fixed securely to their attachment sites (third eyelid, cheek, rectum and tail). At 30 minutes following recumbency resulting from etorphine administration, the animals were given either butorphanol (0.026 ± 0.0001 mg kg-1) or an equivalent volume of saline intravenously. At 60 minutes following recumbency, insufflated oxygen (15 L minute-1 flow rate) was provided intranasally. In total, the SpO2 paired measurements from the third eyelid (n = 80), cheek (n = 67), rectum (n = 59) and tail (n = 76) were compared with near-simultaneous SaO2 measurements using Bland-Altman to assess bias (accuracy), precision, and the area root mean squares (ARMS) method. RESULTS: Compared with SaO2, SpO2 measurements from the third eyelid were reliable (i.e., accurate and precise) above an SaO2 range of 70% (bias = 1, precision = 3, ARMS = 3). However, SpO2 measurements from the cheek, rectum and tail were unreliable (i.e., inaccurate or imprecise). CONCLUSIONS AND CLINICAL RELEVANCE: A Nonin PalmSAT pulse oximeter with a transflectance probe inserted into the space between the third eyelid and the sclera provided reliable SpO2 measurements when SaO2 was > 70%, in immobilized white rhinoceros.

Technical note: a nose ring sensor system to monitor dairy cow cardiovascular and respiratory metrics.

Monitoring cardiovascular and respiratory measurements corresponds to the precision livestock farming (PLF) objective to continuously monitor and assess dairy cows' welfare and health. Changes in heart rate, breathing rate, and oxygen saturation (SpO2) are valuable metrics in human and veterinary medicine to assess stress, pain, illness, and detect critical conditions. The common way to measure heart rate is either manually or with a stethoscope. Under research conditions, heart rate is usually measured with a sports watch chest belt. Breathing rate is obtained by counting the cow's flank movements which is a time-consuming and labor-intensive method that requires training and is prone to human error. No devices are available on the market that enable practical and easy pulse oximetry in farm animals. This study presents a wireless nose ring sensor system (NoRS) composed of thermal and photoplothysmography sensors that attach to the nostrils of four Holstein dairy cows. The NoRS's thermocouple measured the cow's nasal cavity air temperature; an optic sensor measured the IR (660 nm) and RED (660 nm) signals reflected from the cow's nasal septum. Breathing was calculated from the thermocouple signal's center frequency with a fast Fourier transformation or the signal peak count (i.e., oscillations). The breathing rate was compared to breathing observed by concurrently counting the flank movements. Heart rate and SpO2 were measured by integrated pulse oximetry and heart rate monitor module (MAX30101 TinyCircuit) assembled on the NoRS circuit. Heart rate was also measured with FFT and by counting the number of peaks from the optic sensor's raw IR and RED signals. These measures were compared to an off-the-shelf hand-held pulse oximeter's heart rate and SpO2 readings during the same time. The comparisons revealed highly significant correlations for the heart rate readings where the strength of the correlation was sensitive to the method. The correlation between breathing rate and the veterinarian's visual observations was low, albeit significant. Thus, inhale-exhale cycle counting constitutes a more precise approach than flank movement counts. The hand-held device's 96% SpO2 is compatible with near-saturation values expected in healthy cows. The mean NoRS SpO2 reading was 3% less. After further piloting under field conditions, the NoRS will require no animal restraining to automatically and continuously record cows' breathing rate, heart rate, and SpO2.

Monitoring cardiovascular and respiratory measurements responds to the precision livestock farming objective to continuously monitor and assess dairy cows' welfare and health. Changes in heart rate, breathing rate, and oxygen saturation are valuable metrics in human and veterinary medicine that are used to assess stress, pain, illness, and detect critical conditions. This article describes a wireless nose ring sensor system (NoRS) developed to read heart rate, breathing rate, and oxygen saturation from the cow's nostrils and tested on four Holstein dairy cows. These measures were compared to heart rate and oxygen saturation readings obtained from an off-the-shelf hand-held pulse oximeter and a veterinarian's concurrent count of flank movements. The comparison revealed highly significant correlations between the heart rate readings and a low, albeit significant correlation for breathing rate. The mean NoRS oxygen saturation reading was 3% less than the hand-held device. Although commonly used techniques for detecting vital parameters such as heart rate, breathing rate, and oxygen saturation only provide information about the time of examination, the NoRS is a wearable device that can monitor cardiovascular and respiratory measurements remotely and over time.

Retrospective evaluation of carboxyhemoglobin and methemoglobin levels in dogs and cats with respiratory disease.

OBJECTIVE: To evaluate carboxyhemoglobin (COHb) and methemoglobin (MetHb) levels in dogs and cats with respiratory disease in the ICU. DESIGN: Retrospective study. SETTING: University veterinary teaching hospital. ANIMALS: The ICU census was searched for dogs (n = 466) and cats (n = 97) hospitalized within the ICU between January 2016 and January 2019 in whom blood gas with co-oximetry was performed. Dogs and cats were stratified into those with primary respiratory and nonrespiratory categories; the underlying cause of the disease was also noted. Venous blood gas, co-oximeter, PaO2 /FiO2 (PF ratio), physical examination findings, and outcome were recorded. MEASUREMENTS AND MAIN RESULTS: The median COHb and MetHb in dogs hospitalized in the ICU were 2.6% (0.1%-5.6%) and 1.1% (0.1%-2.9%), respectively. The median COHb and MetHb in cats hospitalized in the ICU were 2.2% (0.1%-5.4%) and 1.0% (0%-2.1%), respectively. Dogs with respiratory disease had a higher COHb than dogs without respiratory disease (median, 2.7% [range, 0.3%-5.0%] vs. 2.5% [0.1%-5.6%]; P = 0.0148). COHb was positively associated with survival in cats (median, 2.2% [range, 0.1%-5.4%] vs. 1.9% [0.1%-3.9%]; P = 0.0433). Both COHb and MetHb were higher in septic dogs than in nonseptic dogs (median COHb, 2.8% [range 0.3%-4.5%] vs. 2.6% [0.1%-5.6%]; P = 0.02 and median MetHb, 1.1% [0.1%-2.9%] vs. 1.1% [0.1%-2.4%]; P = 0.01, respectively). CONCLUSIONS: There may be a positive association between COHb and respiratory disease in dogs; prospective studies are needed to evaluate this further. No association between COHb and respiratory disease in cats or MetHb and respiratory disease in either species was detected. Additional prospective studies are needed to determine whether COHb and MetHb are biomarkers for sepsis in dogs and whether COHb is an indicator of mortality in cats.

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.

Accuracy and trending capability of haemoglobin measurement by noninvasive pulse co-oximetry in anaesthetized horses.

OBJECTIVE: To assess the accuracy and trending capability of continuous measurement of haemoglobin concentration [Hb], haemoglobin oxygen saturation (SaO2) and oxygen content (CaO2) measured by the Masimo Radical-7 pulse co-oximeter in horses undergoing inhalational anaesthesia. STUDY DESIGN: Prospective observational clinical study. ANIMALS: A group of 23 anaesthetized adult horses. METHODS: In 23 healthy adult horses undergoing elective surgical procedures, paired measurements of pulse co-oximetry-based haemoglobin concentration (SpHb), SaO2 (SpO2), and CaO2 (SpOC) and simultaneous arterial blood samples were collected at multiple time points throughout anaesthesia. The arterial samples were analysed by a laboratory co-oximeter for total haemoglobin (tHb), SaO2 and manually calculated CaO2. Bland-Altman plots, linear regression analysis, error grid analysis, four-quadrant plot and Critchley polar plot were used to assess the accuracy and trending capability of the pulse co-oximeter. Data are presented as mean differences and 95% limits of agreement (LoA). RESULTS: In 101 data pairs analysed, the pulse co-oximeter slightly underestimated tHb (bias 0.06 g dL-1; LoA -1.0 to 1.2 g dL-1), SaO2 (bias 1.4%; LoA -2.0% to 4.8%), and CaO2 (bias 0.3 mL dL-1; LoA -2.1 to 2.7 mL dL-1). Zone A of the error grid encompassed 99% of data pairs for SpHb. Perfusion index (PI) ≥ 1% was recorded in 58/101 and PI < 1% in 43/101. The concordance rate for consecutive changes in SpHb and tHb with PI ≥ 1% and < 1% was 80% and 91% with four-quadrant plot, and 45.8% and 66.6% with Critchley polar plot. CONCLUSIONS: Pulse co-oximetry has acceptable accuracy for the values measured, even with low PI, whereas its trending ability requires further investigation in those horses with a higher [Hb] variation during anaesthesia.

Use of blood colour for assessment of arterial oxygen saturation in immobilized impala (Aepyceros melampus).

OBJECTIVE: To determine the relationship between arterial blood colour [as defined by the International Commission on Illumination (CIE) L∗a∗b∗ colour space] and haemoglobin oxygen saturation [functional saturation (SaO2) and fractional saturation (FO2Hb)], and if arterial blood colour can be used to predict arterial haemoglobin oxygen saturation. STUDY DESIGN: Descriptive study as an adjunct to two prospective randomized crossover studies. ANIMALS: A group of 10 wild caught adult female impala (Aepyceros melampus) weighing 34.1 ± 5.2 kg (mean ± standard deviation). METHODS: Impala were immobilized with potent opioids (0.09 mg kg-1 of etorphine or thiafentanil). A total of 163 arterial blood samples were collected anaerobically into heparinized syringes from arterial cannulae and analysed immediately using spectrocolourimetry and co-oximetry. Data were analysed by modelling the relationship between predicted arterial blood colour CIE L∗a∗b∗ components and SaO2 and FO2Hb. The models were then used to predict values for L∗, a∗ and b∗ to produce a colour palette for the range of SaO2 and FO2Hb used. The modified version of the Farnsworth-Munsell hue test was used to assess the subjective ordering of the resulting colour palette by 20 observers. RESULTS: The second-order polynomial (quadratic) model produced the best fit for all three arterial blood colour CIE L∗a∗b∗ components for both SaO2 and FO2Hb. The regression models were used to generate predicted arterial blood colour CIE L∗a∗b∗ components for the midpoint of each decile over a range of SaO2 and FO2Hb percentages (15% to 95%). The resulting colour palettes were correctly ordered by all observers in the SaO2 range of 45-95% saturation. CONCLUSIONS AND CLINICAL RELEVANCE: An association between arterial blood colour (as defined by CIE L∗a∗b∗ components) and SaO2 and FO2Hb exists, and arterial blood colour can be used to give a clinically useful estimate of arterial haemoglobin oxygen saturation in impala.

CO-oximetry measurements and antioxidant effects of ascorbic acid and methylene blue in equine methemoglobinemic blood.

OBJECTIVES: To determine the effects of time after sampling on CO-oximetry measurements of equine blood samples and the effects of adding ascorbic acid (AscAc) and methylene blue (MetBlue) to samples with methemoglobinemia. DESIGN: Experimental study. SETTING: University teaching hospital. ANIMALS: Thirty healthy adult horses assigned to 5 groups. INTERVENTIONS: Repeated CO-oximetry determinations were performed on venous (n = 6) and arterial blood samples (n = 7) stored at 0°C for 48 hours. Methemoglobinemia was induced in vitro in 17 additional blood samples. Six were used as untreated controls, 6 had AscAc added, and 5 had MetBlue added. Total hemoglobin, oxyhemoglobin, carboxyhemoglobin, methemoglobin (MetHb), and oxygen saturation of hemoglobin (SO2 ) were measured. MEASUREMENTS AND MAIN RESULTS: Oxyhemoglobin and SO2 increased from 69.8% ± 10.2% and 90% ± 3% to 82.8% ± 7.9% and 99% ± 3%, respectively, after 8 hours in venous blood (mean ± SD, P < 0.001). There was an effect of treatment (P = 0.032) and of time (interaction P = 0.003) on MetHb% in methemoglobinemic samples. The difference in absolute MetHb% from time 0 was as follows: 7.0% (interquartile range [IQR] = 21.2), -0.2% (IQR = 3.5), and -4.4% (IQR = 5.2) at 48 hours in control, AscAc, and MetBlue groups, respectively (P < 0.05). There was no effect of time on MetHb% in the AscAc group (23% [IQR = 52.6] at time 0 to 23.2% [IQR = 56.9] after 48 h). CONCLUSIONS: Storage of blood in ice water to determine O2 Hb and SO2 using a CO-oximeter should not exceed 4 hours. Measurement of MetHb% could be delayed by up to 48 hours if AscAc is added to the sample. MetBlue significantly decreased MetHb% over time. The limitations of this study include the fact that the antioxidant effects of AscAc and MetBlue were evaluated in vitro and not in vivo. Further studies are needed to evaluate different storage temperatures and syringe types.

Comparison of venous hemoglobin saturation measurements obtained by in vivo oximetry and calculated from blood gas analysis in critically ill dogs.

OBJECTIVE: To compare in vivo central venous hemoglobin saturation measurement (ScvO2 ) using a fiber optic catheter with saturation calculated from blood gas analysis in critically ill dogs. DESIGN: Prospective observational study. SETTING: University veterinary teaching hospital intensive care unit. ANIMALS: A convenience sample of 20 dogs with severe illness. INTERVENTIONS: Dogs were instrumented with either a central venous catheter with an integrated fiber optic cable or a conventional catheter with a fiber optic probe inserted through its distal port. Baseline saturation was measured with the fiber optic system (FSO2 ), then monitored continuously. Central venous blood was collected for analysis and FSO2 was recorded by the principal investigator (PI) or nursing staff participating in data collection (staff) at baseline and at 1, 2, 3, and 6 hours. Hemoglobin oxygen saturation (SO2 ) values calculated using human Bohr coefficients were taken directly from the analyzer (GPSO2 ), and were also calculated using temperature-correction and canine Bohr coefficients (RSO2 ). MEASUREMENTS AND MAIN RESULTS: Ninety-seven paired measurements from 20 dogs were analyzed. FSO2 obtained by the PI (n = 41) had better agreement with both GPSO2 (concordance correlation coefficient ρc = 0.926 vs 0.5562) and RSO2 (ρc = 0.75 for PI vs 0.54) than did staff (n = 56). RSO2 values were always smaller than GPSO2 . FSO2 - GPSO2 differences were smaller when measurements were collected by the PI versus Staff (mean difference 0.21 vs -6.6, respectively, P < 0.02). Thirty-six of 41 FSO2 values obtained by PI were within 5% of GPSO2 . CONCLUSIONS: Concordance between FSO2 and either calculation method was low, but was better when performed by PI. The larger difference between methods when using RSO2 suggests a positive bias by FSO2 . Difficulty obtaining stable measurements may have contributed to the poor concordance between methods within Staff.

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.

Oxygen reserve index as a noninvasive indicator of arterial partial pressure of oxygen in anaesthetized donkeys: a preliminary study.

OBJECTIVE: To evaluate the oxygen reserve index (ORI) as a noninvasive estimate of the PaO2 during moderate hyperoxaemia [100-200 mmHg (13.3-26.6 kPa)], and to determine ORI values identifying PaO2 > 100, > 150 (20.0 kPa) and > 200 mmHg in anaesthetized donkeys with an inspired fraction of oxygen (FiO2) > 0.95. STUDY DESIGN: Prospective observational study. ANIMALS: A group of 28 adult standard donkeys aged (mean ± standard deviation) 4 ± 2 years and weighing 135 ± 15 kg. METHODS: Donkeys were sedated intramuscularly with xylazine and butorphanol; anaesthesia was induced with ketamine and diazepam and maintained with isoflurane in oxygen. An adhesive sensor probe was applied to the donkey's tongue and connected to a Masimo pulse co-oximeter to determine ORI values. An arterial catheter was inserted into an auricular artery. After ORI signal stabilization, the value was noted and PaO2 determined by blood gas analysis. The Pearson correlation coefficient was used to assess the relationship between ORI and PaO2 for oxygen tension < 200 mmHg (< 26.6 kPa). The Youden index was used to identify the value of ORI that detected PaO2 > 150 and 200 mmHg (20.0 and 26.6 kPa) with the highest sensitivity and specificity. RESULTS: A total of 106 paired measurements were collected. A mild positive correlation was observed between ORI and PaO2 for values < 200 mmHg (26.6 kPa; r = 0.52). An ORI > 0.0, > 0.1 and > 0.3 indicated a PaO2 > 100, > 150 and > 200 mmHg (13.3, 20.0 and 26.6 kPa) with negative predictive values > 94%. CONCLUSIONS AND CLINICAL RELEVANCE: ORI may provide a noninvasive indication of PaO2 > 100, > 150 and > 200 mmHg (13.3, 20.0 and 26.6 kPa) in anaesthetized donkeys with an FiO2 > 0.95, although it does not replace blood gas analysis for assessment of oxygenation.

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

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.

Developing a modified Apgar scoring system for newborn lambs.

The Apgar (appearance, pulse, grimace, attitude, respiration) score is an accepted method for assessing newborn viability in humans and domestic animals. The purpose of this research was to modify an existing Apgar scoring system for lambs and compare Apgar score with litter size and birth order, as well as time-to-stand and time-to-suckle. Polypay lambs (n = 75) delivered naturally were used for this study. Pulse (<100 bpm = 0; 100-175 bpm = 1; >175 bpm = 2) and respiration (<45% SpO2 = 0; 45-65% SpO2 = 1; >65% SpO2 = 2) were measured with a pulse oximeter attached to the lamb's ear. Appearance, grimace, and attitude were assessed using mucous membrane color (cyanotic = 0; pale = 1; pink = 2); response to nose stimulation (no response = 0; moves head slightly = 1; shakes head = 2); and response to rump stimulation (no movement = 0; moves but no attempt to stand = 1; attempts to stand = 2), respectively. The Apgar score was measured within 5 min of birth (T0), 15 min (T15) and 60 min (T60) after birth. The time-to-stand and time-to-suckle were recorded and compared to Apgar scores. Apgar scores did not differ by litter size or birth order. There were no significant correlations between the Apgar scores and time-to-stand. There was a moderate positive correlation between attitude and time-to-suckle at T0 (R2 = 0.467), which may affect the ingestion of adequate colostrum in a timely manner. Producers may choose to consider using Apgar scoring so that assistance can be provided to lambs before serious complications arise.

Evaluation of the reliability of pulse oximetry, at different attachment sites, to detect hypoxaemia in immobilized impala (Aepyceros melampus).

OBJECTIVE: Evaluation of the reliability of pulse oximetry at four different attachment sites compared to haemoglobin oxygen saturation measured by a co-oximeter and calculated by a blood gas analyser in immobilized impala. STUDY DESIGN: Randomized crossover study. ANIMALS: A total of 16 female impala. METHODS: Impala were immobilized with etorphine or thiafentanil alone, or etorphine in combination with a novel drug. Once immobilized, arterial blood samples were collected at 5 minute intervals for 30 minutes. Then oxygen was insufflated (5 L minute-1) intranasally at 40 minutes and additional samples were collected. A blood gas analyser was used to measure the arterial partial pressure of oxygen and calculate the oxygen haemoglobin saturation (cSaO2); a co-oximeter was used to measure the oxygen haemoglobin saturation (SaO2) in arterial blood. Pulse oximeter probes were attached: under the tail, to the pinna (ear) and buccal mucosa (cheek) and inside the rectum. Pulse oximeter readings [peripheral oxygen haemoglobin saturation (SpO2) and pulse quality] were recorded at each site and compared with SaO2 and cSaO2 using Bland-Altman and accuracy of the area root mean squares (Arms) methods to determine the efficacy. P value < 0.05 was considered significant. RESULTS: Pulse quality was 'good' at each attachment site. SpO2 measured under the tail was accurate and precise but only when SaO2 values were above 90% (bias = 3, precision = 3, Arms = 4). The ear, cheek and rectal probes failed to give accurate or precise readings (ear: bias = -4, precision = 14, Arms = 15; cheek: bias = 12, precision = 11, Arms = 16; and rectum: bias = 5, precision = 12, Arms = 13). CONCLUSIONS AND CLINICAL RELEVANCE: In order to obtain accurate and precise pulse oximetry readings in immobilized impala, probes must be placed under the tail and SaO2 must be above 90%. Since SaO2 values are usually low in immobilized impala, pulse oximeter readings should be interpreted with caution.

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.