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

ObjectiveTo 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 designProspective observational clinical study.AnimalsA group of 39 adult dogs.MethodsIn 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).ResultsA 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.ConclusionsBefore 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.     

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

ObjectivesTo 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 designRandomized crossover study.AnimalsA convenience sample of eight wild-caught male white rhinoceros.MethodsWhite 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.ResultsCompared 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 relevanceA 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.     

High inspired oxygen concentrations increase intrapulmonary shunt in anaesthetized horses

OBJECTIVES: To compare pulmonary function and gas exchange in anaesthetized horses during and after breathing either O2-rich gas mixtures or air. ANIMALS: Six healthy standard bred trotters (age range 3-12 years; mass range 423-520 kg), four geldings and two mares. Study design Randomized, cross-over experimental study. METHODS: Horses were anaesthetized on two occasions with tiletamine-zolazepam after pre-anaesthetic medication with acepromazine, romifidine and butorphanol. After endotracheal intubation and positioning in left lateral recumbency, animals were allowed to breathe spontaneously. One of two, randomly allocated inspired gas treatments was provided: either i) room air (fractional concentration of inspired O2 [FIO2] = 0.21) provided throughout anaesthesia; or ii) an O2-rich gas mixture (FIO2 = >0.95) for 15 minutes, followed by room air. The alternative treatment was delivered at the second anaesthetic. Respiratory and haemodynamic variables and the distribution of ventilation-perfusion (VA/Q) ratios (using the multiple inert gas elimination technique) were determined in the standing conscious horse (baseline) after sedation and during anaesthesia. RESULTS: Breathing O2-rich gas was associated with a decreased respiratory rate (p = 0.015) increased PaCO2 (p < 0.001) and increased PaO2 (p = 0.004) compared with breathing air. All horses developed intrapulmonary shunt during anaesthesia, but shunt was significantly greater (13 +/- 5%) when O2-rich gas was delivered compared with air breathing (5 +/- 2%; p = 0.013). Ten minutes after O2-rich gas was replaced by air, shunt remained larger in horses that had initially received oxygen compared with those breathing air (p = 0.042). Mixed venous oxygen tensions were significantly lower during sedation than at baseline (p < 0.001) and during anaesthesia (p < 0.001). CONCLUSIONS: During dissociative anaesthesia, arterial oxygenation was greater when horses breathed gas containing more than 95% oxygen, compared with when they breathed air. However, breathing O2-rich gas increased intrapulmonary shunt and caused hypoventilation. The intrapulmonary shunt created during anaesthesia by high inspired O2 concentrations remained larger when FIO2 was reduced to 0.21, indicating that absorption atelectasis produced during O2-rich gas breathing persisted throughout anaesthesia. CLINICAL RELEVANCE: In healthy horses undergoing short-term dissociative anaesthesia, air breathing ensures a level of oxygen delivery that meets tissue demand. There is no benefit to horses in breathing O2-rich gas after the gas supply is discontinued. On the contrary, the degree of shunt induced by breathing O2-rich gas persists. The clinical relevance of this during recovery requires investigation.     

Comparison of different methods to calculate venous admixture in anaesthetized horses

Objective

The aim of this study was to compare different methods to determine venous admixture (${\dot{Q}}_{\text{s}}/{\dot{Q}}_{\text{t}}$) in anaesthetized horses. The first objective was to estimate ${\dot{Q}}_{\text{s}}/{\dot{Q}}_{\text{t}}$ using jugular venous blood oxygen content (${\dot{Q}}_{\text{s}}/{\dot{Q}}_{\text{t}\text{jugular}}$), and a fixed value for the oxygen extraction (F-shunt). The second objective was to assess the influence of blood pressure and positioning on oxygen extraction. The third objective was to perform regression analysis between jugular and mixed venous blood oxygen tensions.

Use of lithium dilution and pulse contour analysis cardiac output determination in anaesthetized horses: a clinical evaluation

OBJECTIVE: To assess the suitability of a human algorithm for calculation of continuous cardiac output from the arterial pulse waveform, in anaesthetized horses. STUDY DESIGN: Prospective clinical study. ANIMALS: Twenty-four clinical cases undergoing anaesthesia for various conditions. MATERIALS AND METHODS: Cardiac output (Qt), measured by lithium dilution (QtLiDCO), was compared with a preceding, calibrated Qt measured from the pulse waveform (QtPulse). These comparisons were repeated every 20-30 minutes. Positive inotropes or vasopressors were administered when clinically indicated. Cardiac indices from 30.7 to 114.9 mL kg(-1) minute(-1) were recorded. Unusually shaped QtLiDCO curves were rejected and the measurement was repeated immediately. RESULTS: Eighty-nine comparisons were made between QtLiDCO and QtPulse. The bias between the mean (+/-SD) of the two methods (QtLiDCO - QtPulse) was -0.07 L minute(-1)(+/-3.08) (0.24 +/- 6.48 mL kg(-1) minute(-1)). The limits of agreement were -12.72 and 13.2 mL kg(-1) minute(-1) (Bland & Altman 1986; Mantha et al. 2000). Linear regression analysis demonstrated a correlation coefficient (r2) of 0.89. Cardiac output in individual patients varied from 49.1 to 183% of the initial measurement at the time of calibration. Linear regression of log-transformed Qt variation for each method found a mean difference of 9% with limits of agreement of -4.1 to 22.1%. CONCLUSIONS AND CLINICAL RELEVANCE: This method of pulse contour analysis is a relatively noninvasive and reliable way of monitoring continuous Qt in the horse under anaesthesia. The ability to easily monitor Qt might decrease morbidity and mortality in the anaesthetized horse.     

An investigation into the detection of the pulse in conscious and anaesthetized dogs

ObjectivesTo record the success rate of veterinary professionals and students at identifying the pulse in conscious and anaesthetized dogs. To explore the influence of clinical experience, pulse location, anaesthesia and likely confounding variables on the success of pulse palpation.Study designProspective, observational, randomized study.AnimalsA total of 54 client-owned dogs scheduled for general anaesthesia.MethodsFor each dog, three participants (senior anaesthetist, anaesthesia resident/nurse, veterinary student/animal care assistant) attempted pulse palpation at three locations (femoral, radial and dorsal pedal pulse) in conscious and anaesthetized dogs. The time to pulse palpation was measured with a stopwatch for each attempt and data were modelled using a multivariate Cox regression survival analysis (significance p < 0.05).ResultsThe overall success rate of pulse palpation was 77%, with a median time of 10.91 seconds (interquartile range 9.09 seconds). Success rate was lower in conscious dogs (67%) than in anaesthetized dogs (87%). There was a 77% lower likelihood of success at the radial than at the femoral pulse [hazard ratio (HR) 0.23, 95% confidence interval (CI) 0.38–0.69, p < 0.001]. Veterinary students/animal care assistants had a 71% lower likelihood of success than senior anaesthetists (HR 0.29, 95% CI 0.22–0.39, p < 0.001). Age, weight and American Society of Anesthesiologists physical status had no significant influence. Premedication/anaesthetic drugs, heart rate or mean arterial pressure had no significant influence on the time to pulse palpation in anaesthetized dogs. The median time to palpation was less than 10 seconds for all experience groups at the femoral location.ConclusionsPalpation of the femoral location had the greatest likelihood of success with the least amount of time. Monitoring the femoral pulse during induction of anaesthesia is suggested as a method for confirming spontaneous circulation. Pulse palpation improves with clinical experience.     

A study of cardiovascular function under controlled and spontaneous ventilation in isoflurane–medetomidine anaesthetized horses

Objective To determine, in mildly hypercapnic horses under isoflurane–medetomidine balanced anaesthesia, whether there is a difference in cardiovascular function between spontaneous ventilation (SV) and intermittent positive pressure ventilation (IPPV). Study design Prospective randomized clinical study. Animals Sixty horses, undergoing elective surgical procedures under general anaesthesia: ASA classification I or II. Methods Horses were sedated with medetomidine and anaesthesia was induced with ketamine and diazepam. Anaesthesia was maintained with isoflurane and a constant rate infusion of medetomidine. Horses were assigned to either SV or IPPV for the duration of anaesthesia. Horses in group IPPV were maintained mildly hypercapnic (arterial partial pressure of carbon dioxide (PaCO₂) 50–60 mmHg, 6.7–8 kPa). Mean arterial blood pressure (MAP) was maintained above 70 mmHg by an infusion of dobutamine administered to effect. Heart rate (HR), respiratory rate (f_R), arterial blood pressure and inspiratory and expiratory gases were monitored continuously. A bolus of ketamine was administered when horses showed nystagmus. Cardiac output was measured using lithium dilution. Arterial blood‐gas analysis was performed regularly. Recovery time was noted and recovery quality scored. Results There were no differences between groups concerning age, weight, body position during anaesthesia and anaesthetic duration. Respiratory rate was significantly higher in group IPPV. Significantly more horses in group IPPV received supplemental ketamine. There were no other significant differences between groups. All horses recovered from anaesthesia without complications. Conclusions There was no difference in cardiovascular function in horses undergoing elective surgery during isoflurane–medetomidine anaesthesia with SV in comparison with IPPV, provided the horses are maintained slightly hypercapnic. Clinical relevance In horses with health status ASA I and II, cardiovascular function under general anaesthesia is equal with or without IPPV if the PaCO₂ is maintained at 50–60 mmHg.     

Determination of physiological dead space in anaesthetized horses: a method-comparison study

Objective

To compare two methods of Bohr–Enghoff physiological dead space to tidal volume ratio (Vd/Vt_{Bohr–Enghoff}) determination using a mixing chamber and an E-CAiOVX metabolic monitor.

Evaluation of Masimo signal extraction technology pulse oximetry in anaesthetized pregnant sheep

ObjectiveEvaluation of the accuracy of Masimo signal extraction technology (SET) pulse oximetry in anaesthetized late gestational pregnant sheep.Study designProspective experimental study.AnimalsSeventeen pregnant Merino ewes.MethodsAnimals included in study were late gestation ewes undergoing general anaesthesia for Caesarean delivery or foetal surgery in a medical research laboratory. Masimo Radical-7 pulse oximetry (SpO₂) measurements were compared to co-oximetry (SaO₂) measurements from arterial blood gas analyses. The failure rate of the pulse oximeter was calculated. Accuracy was assessed by Bland &; Altman's (2007) limits of agreement method. The effect of mean arterial blood pressure (MAP), perfusion index (PI) and haemoglobin (Hb) concentration on accuracy were assessed by regression analysis.ResultsForty arterial blood samples paired with SpO₂ and blood pressure measurements were obtained. SpO₂ ranged from 42 to 99% and SaO₂ from 43.7 to 99.9%. MAP ranged from 24 to 82 mmHg, PI from 0.1 to 1.56 and Hb concentration from 71 to 114 g L^?1. Masimo pulse oximetry measurements tended to underestimate oxyhaemoglobin saturation compared to co-oximetry with a bias (mean difference) of ?2% and precision (standard deviation of the differences) of 6%. Accuracy appeared to decrease when SpO₂ was <75%, however numbers were too small for statistical comparisons. Hb concentration and PI had no significant effect on accuracy, whereas MAP was negatively correlated with SpO₂ bias.Conclusions and clinical relevanceMasimo SET pulse oximetry can provide reliable and continuous monitoring of arterial oxyhaemoglobin saturation in anaesthetized pregnant sheep during clinically relevant levels of cardiopulmonary dysfunction. Further work is needed to assess pulse oximeter function during extreme hypotension and hypoxaemia.     

The effect of hyoscine on dobutamine requirement in spontaneously breathing horses anaesthetized with halothane

OBJECTIVE: To determine whether hyoscine has a sparing effect on the volume of dobutamine required to maintain mean arterial pressure (MAP) at 70 mmHg in horses anaesthetized with halothane. STUDY DESIGN: Prospective, randomized, controlled clinical trial. ANIMALS: Twenty adult horses weighing 507 +/- 97 kg (mean +/- SD), aged 10 +/- 5 years. MATERIALS AND METHODS: Pre-anaesthetic medication in all horses was intramuscular (IM) acepromazine (40 mug kg(-1)) and intravenous (IV) detomidine (0.02 mg kg(-1)). Anaesthesia was induced with ketamine (2.2 mg kg(-1) IV) and diazepam (0.02 mg kg(-1) IV), and maintained with halothane in oxygen. Horses breathed spontaneously. Flunixin (1.1 mg kg(-1) IV) was given to provide analgesia. Heart rate, ECG, invasive arterial pressure, respiratory rate, percentage end-tidal carbon dioxide, percentage end-tidal halothane and partial pressure of oxygen and carbon dioxide in arterial blood and blood pH were monitored. Dobutamine was infused by an infusion pump to maintain MAP at 70 mmHg. Horses were randomly assigned to receive saline or hyoscine (0.1 mg kg(-1)) IV 30 minutes after induction. The heart rate, MAP and volume of dobutamine infused over 30-minute periods were measured and analysed statistically using a one-way anova. RESULTS: After administration of hyoscine, heart rate increased for 10 minutes (p < 0.01) and MAP for 5 minutes (p < 0.01). There was no difference in the volume of dobutamine infused over 30 minutes between horses given hyoscine or saline, although there was a wide individual variation in dobutamine requirements. No side effects of hyoscine were seen. CONCLUSIONS: The increase in heart rate and blood pressure that occurs after 0.1 mg kg(-1) hyoscine is given IV in anaesthetized horses, is of short duration and does not significantly alter the amount of dobutamine required to maintain arterial pressure over the next 30 minutes. Clinical relevance The short duration of action of 0.1 mg kg(-1) hyoscine IV may limit its usefulness for correction of hypotension in horses anaesthetized with halothane. Further work is necessary to investigate the effects of higher or repeated doses or constant rate infusions of hyoscine.     

Aerosolized salbutamol (albuterol) improves PaO2 in hypoxaemic anaesthetized horses – a prospective clinical trial in 81 horses

Objective To compare the arterial pH and blood gas values, heart rate and mean arterial blood pressure, in hypoxaemic anaesthetized horses, before and after treatment, with a salbutamol (albuterol) aerosol. Animal population Eighty‐one client‐owned horses weighing between 114 and 925 kg. Fifty‐seven underwent emergency abdominal surgery and 24 were anaesthetized for elective procedures. Materials and methods Pre‐anaesthetic medication included xylazine, detomidine, butorphanol and morphine, alone or in various combinations. Induction of anaesthesia was achieved with guaifenesin and ketamine, diazepam and ketamine, or guaifenesin and thiopental. The trachea of all animals was intubated and anaesthesia maintained with either halothane (33 horses) or isoflurane (48 horses) in oxygen. Heart rate and rhythm were monitored continuously. Arterial blood pressure was monitored directly, and arterial blood collected for pH and blood gas analyses. When arterial PaO₂ fell below 9.3 kPa (70 mm Hg) and failed to respond to corrective measures including positive pressure ventilation and treatment of hypotension (mean arterial blood pressures <70 mm Hg), a salbutamol aerosol (2 µg kg^?1) was delivered via the endotracheal tube. Twenty minutes later, a second arterial blood sample was analysed. Results There were no significant differences in mean arterial blood pressure, heart rate, arterial pH, base excess and bicarbonate before and after treatment. Arterial O₂ tension increased significantly from a mean ± SD of 8.3 ± 1.7 kPa (62.4 ± 13.1 mm Hg) before administration to 15.9 ± 9.8 kPa (119.4 ± 57.7 mm Hg) after treatment. There was a small but significant decrease in PaCO₂ from 7.4 ± 1.5 kPa (55.2 ± 11.2 mm Hg) to 7.0 ± 1.3 kPa (52.9 ± 9.8 mm Hg) between sample times. No changes in heart rhythm were observed. A high percentage (approximately 70%) of animals sweated following treatment. Conclusions Salbutamol administered at a dose of 2 µg kg^?1 via the endotracheal tube of anaesthetized horses with PaO₂ values less than 9.3 kPa (70 mm Hg) resulted in an almost two‐fold increase in PaO₂ values within 20 minutes of treatment. No changes in heart rate or mean arterial blood pressure were associated with the use of salbutamol in this study. The improvement in PaO₂ may be a result of bronchodilatation and improved ventilation, increased perfusion secondary to an increase in cardiac output, or a combination of these two factors. Cardiac output and ventilation–perfusion distribution were not measured in this study; therefore, the reason for the increase in PaO₂ values cannot be conclusively determined. Clinical relevance Administration of a salbutamol aerosol is a simple but effective technique that can be used to improve PaO₂ values in hypoxaemic horses during inhalant anaesthesia with no apparent detrimental side effects.     

A study of measurement of noninvasive blood pressure with the oscillometric device,Sentinel, in isoflurane‐anaesthetized horses

ObjectiveTo assess accuracy of noninvasive blood pressure (NIBP) measured by oscillometric device Sentinel compared to invasive blood pressure (IBP) in anaesthetized horses undergoing surgery. To assess if differences between the NIBP measured by the Sentinel and IBP are associated with recumbency, cuff placement, weight of the horse or acepromazine premedication and to describe usefulness of the Sentinel.Study designProspective study examining replicates of simultaneous NIBP and IBP measurements.AnimalsTwenty-nine horses.MethodsInvasive blood pressure was measured via a catheter in the facial artery, transverse facial artery or metatarsal artery. NIBP was measured using appropriate size cuffs placed on one of two metacarpal or metatarsal bones or the tail in random order. With both techniques systolic (SAP), mean (MAP), and diastolic (DAP) arterial blood pressures and heart rates (HR) were recorded. A mixed effects model compared the IBP to the NIBP values and assessed potential effects of catheter placement, localisation of the cuffs in combination with recumbency, weight of the horse or acepromazine premedication.ResultsNoninvasive blood pressure yielded higher measurements than IBP. Agreement varied with recumbency and cuff position. Estimated mean differences between the two methods decreased from SAP (lateral recumbency: range -5.3 to -56.0 mmHg; dorsal recumbency: range 0.8 to -20.7 mmHg), to MAP (lateral recumbency: range -1.8 to -19.0 mmHg; dorsal recumbency: range 13.9 to -16.4 mmHg) to DAP (lateral recumbency: range 0.5 to -6.6 mmHg; dorsal recumbency: range 21.0 to -15.5 mmHg). NIBP measurement was approximately two times more variable than IBP measurement. No significant difference between IBP and NIBP due to horse's weight or acepromazine premedication was found. In 227 of 1047 (21.7%) measurements the Sentinel did not deliver a result.Conclusion and clinical relevanceAccording to the high variability of NIBP compared to IBP, NIBP measurements as measured by the Sentinel in the manner described here are not considered as an appropriate alternative to IBP to measure blood pressure in anaesthetized horses.     

Measurement of tidal volume using Respiratory Ultrasonic Plethysmography in anaesthetized,mechanically ventilated horses

ObjectiveTo compare tidal volume estimations obtained from Respiratory Ultrasonic Plethysmography (RUP) with simultaneous spirometric measurements in anaesthetized, mechanically ventilated horses.Study designProspective randomized experimental study.AnimalsFive experimental horses.MethodsFive horses were anaesthetized twice (1 week apart) in random order in lateral and in dorsal recumbency. Nine ventilation modes (treatments) were scheduled in random order (each lasting 4 minutes) applying combinations of different tidal volumes (8, 10, 12 mL kg^?1) and positive end-expiratory pressures (PEEP) (0, 10, 20 cm H₂O). Baseline ventilation mode (tidal volume = 15 mL kg^?1, PEEP = 0 cm H₂O) was applied for 4 minutes between all treatments. Spirometry and RUP data were downloaded to personal computers. Linear regression analyses (RUP versus spirometric tidal volume) were performed using different subsets of data. Additonally RUP was calibrated against spirometry using a regression equation for all RUP signal values (thoracic, abdominal and combined) with all data collectively and also by an individually determined best regression equation (highest R²) for each experiment (horse versus recumbency) separately. Agreement between methods was assessed with Bland-Altman analyses.ResultsThe highest correlation of RUP and spirometric tidal volume (R² = 0.81) was found with the combined RUP signal in horses in lateral recumbency and ventilated without PEEP. The bias ± 2 SD was 0 ± 2.66 L when RUP was calibrated for collective data, but decreased to 0 ± 0.87 L when RUP was calibrated with individual data.Conclusions and clinical relevanceA possible use of RUP for tidal volume measurement during IPPV needs individual calibration to obtain limits of agreement within ± 20%.     

An evaluation of pulse oximeters in dogs, cats and horses

Objective Evaluation of five pulse oximeters in dogs, cats and horses with sensors placed at five sites and hemoglobin saturation at three plateaus. Study design Prospective randomized multispecies experimental trial. Animals Five healthy dogs, cats and horses. Methods Animals were anesthetized and instrumented with ECG leads and arterial catheters. Five pulse oximeters (Nellcor Puritan Bennett‐395, NPB‐190, NPB‐290, NPB‐40 and Surgi‐Vet V3304) with sensors at five sites were studied in a 5 × 5 Latin square design. Ten readings (SpO₂) were taken at each of three hemoglobin saturation plateaus (98, 85 and 72%) in each animal. Arterial samples were drawn concurrently and hemoglobin saturation was measured with a co‐oximeter. Accuracy of saturation measurements was calculated as the root mean squared difference (RMSD), a composite of bias and precision, for each model tested in each species. Results Accuracy varied widely. In dogs, the RMSD for the NPB‐395, NPB‐190, NPB‐290, NPB‐40 and V3304 were 2.7, 2.2, 2.4, 1.7 and 2.7% respectively. Failure to produce readings for the NPB‐395, NPB‐190, NPB‐290, NPB‐40 and V3304 were 0, 0, 0.7, 0, and 20%, respectively. The Pearson correlation coefficients for the tongue, toe, ear, lip and prepuce or vulva were 0.95, 0.97, 0.69, 0.87 and 0.95, respectively. In horses, the RMSD for the NPB‐395, NPB‐190, NPB‐290, NPB‐40 and V3304 were 3.1, 3.0, 4.7, 3.3 and 2.1%, respectively while rates of failure to produce readings were 10, 21, 0, 17 and 60%, respectively. The Pearson correlation coefficients for the tongue, nostril, ear, lip and prepuce or vulva were 0.98, 0.94, 0.88, 0.93 and 0.94, respectively. In cats, the RMSD for all data for the NPB‐395, NPB‐190, NPB‐290, NPB‐40 and V3304 were 5.9, 5.6, 7.9, 7.9 and 10.7%, respectively while failure rates were 0, 0.7, 0, 20 and 32%, respectively. The correlation coefficients for the tongue, rear paw, ear, lip and front paw were 0.54, 0.79,.0.64, 0.49 and 0.57, respectively. For saturations above 90% in cats, the RMSD for the NPB‐395, NPB‐190, NPB‐290, NPB‐40 and V3304 were 2.6, 4.4, 4.0, 3.5 and 4.8%, respectively, while failure rates were 0, 1.7, 0, 25 and 43%, respectively. Conclusions and clinical relevance Accuracy and failure rates (failure to produce a reading) varied widely from model to model and from species to species. Generally, among the models tested in the clinically relevant range (90–100%) RMSD ranged from 2–5% while failure rates were highest in the V3304.     

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

ObjectiveTo 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 designProspective observational study.AnimalsA group of 28 adult standard donkeys aged (mean ± standard deviation) 4 ± 2 years and weighing 135 ± 15 kg.MethodsDonkeys 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.ResultsA 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 relevanceORI 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.     

The effect of the inspired oxygen fraction on arterial blood oxygenation in spontaneously breathing,isoflurane anaesthetized horses: a retrospective study

ObjectivesTo investigate the influence of two inspired oxygen fractions (FIO₂) on the arterial oxygenation in horses anaesthetized with isoflurane.Study DesignRetrospective, case-control clinical study.AnimalsTwo hundred equine patients undergoing non-abdominal surgery (ASA class 1–2), using a standardized anaesthetic protocol and selected from anaesthetic records of a period of three years, based on pre-defined inclusion criteria.MethodsIn group O (n = 100), medical oxygen acted as carrier gas, while in group M (n = 100), a medical mixture of oxygen and air (FIO₂ 0.60) was used. Demographic data, FIO₂, arterial oxygen tension (PaO₂) and routinely monitored physiologic data were recorded. The alveolar-arterial oxygen tension difference [P(A-a)O₂] and PaO₂/FIO₂ ratio were calculated. The area under the curve, standardized to the anaesthetic duration, was calculated and statistically compared between groups using t-tests or Mann–Whitney tests as appropriate. Categorical data were compared using Chi-square tests.ResultsNo significant differences in age, body weight, sex, breed, surgical procedure, position, anaesthetic duration or arterial carbon dioxide tension were found. Mean FIO₂ was 0.78 in group O and 0.60 in group M. Compared to group O, significantly lower values for PaO₂ and for P(A-a)O₂ were found in group M. In contrast, the PaO₂/FIO₂ ratio and the percentage of horses with a PaO₂ <100 mmHg (13.33 kPa) were comparable in both groups.ConclusionsAlthough a reduction of the inspired oxygen fraction resulted in a lower PaO₂, the P(A-a)O₂ was also lower and the number of horses with PaO₂ values <100 mmHg was comparable.Clinical relevanceIn healthy isoflurane anaesthetized horses, the use of a mixture of oxygen and air as carrier gas seems acceptable, but further, prospective studies are needed to confirm whether it results in a lower degree of ventilation/perfusion mismatching.