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.     

Evaluation of a minimally invasive non-calibrated pulse contour cardiac output monitor (FloTrac/Vigileo) in anaesthetized dogs

ObjectiveTo evaluate the accuracy of a new cardiac output monitor (FloTrac/Vigileo), originally designed for humans, in dogs. This pulse contour cardiac output monitoring system cannot be calibrated and measures cardiac output (

t) from a standard arterial catheter.Study designProspective experimental trial.AnimalsEight adult Beagle dogs weighing 13.1 (9.8–17.1) kg [median (range)].MethodsAnaesthesia in the dogs was maintained using isoflurane. A pulmonary artery catheter and a metatarsal arterial catheter (22 gauge) were placed. Cardiac output was measured simultaneously 331 times by thermodilution and FloTrac technique. A broad spectrum of

t measurements was achieved through alterations of isoflurane concentration, administration of propofol boluses and dobutamine infusions. Agreement between the methods was quantified with Bland Altman analysis and disagreement was assessed with linear mixed models.ResultsMedian (10th and 90th percentile) cardiac output as measured with thermodilution was 2.54 (1.47 and 5.15) L minute^?1 and as measured with FloTrac 8.6 (3.9 and 17.3) L minute^?1. FloTrac measurements were consistently higher with a mean bias of 7 L minute^?1 and limits of agreement of ?3.15 to 17.17 L minute^?1. Difference between the methods was most pronounced in high

t measurements. Linear mixed models showed an estimated difference between the two methods of 8.05 (standard error 1.18) L minute^?1 and a significant interaction between mean arterial pressure and method. Standard deviation (4.45 higher) with the FloTrac method compared to thermodilution was increased.ConclusionCompared to thermodilution measurements, the FloTrac system was influenced to a higher degree by arterial blood pressure, resulting in consistent overestimation of cardiac output.Clinical RelevanceThe FloTrac monitor, whose algorithms were developed based on human data, cannot be used as an alternative for thermodilution in dogs.     

Ability of pulse wave transit time to detect changes in stroke volume and to estimate cardiac output compared to thermodilution technique in isoflurane-anaesthetised dogs

Objective

To evaluate the ability of pulse wave transit time (PWTT) to detect changes in stroke volume (SV) and to estimate cardiac output (CO) compared with the thermodilution technique in isoflurane-anaesthetized dogs.

Comparison of cardiac output determined by arterial pulse pressure waveform analysis method (FloTrac/Vigileo) versus lithium dilution method in anesthetized dogs

Objective – To compare the determination of cardiac output (CO) via arterial pulse pressure waveform analysis (FloTrac/Vigileo) versus lithium dilution method. Design – Prospective study. Setting – University teaching hospital. Animals – Six adult dogs. Interventions – Dogs were instrumented for CO determinations using lithium dilution (LiDCO) and FloTrac/Vigileo methods. Direct blood pressure, heart rate, arterial blood gases, and end‐tidal isoflurane (ETIso) and CO₂ concentrations were measured throughout the study while CO was manipulated with different depth of anesthesia and rapid administration of isotonic crystalloids at 60 mL/kg/h. Measurements and Main Results – Baseline CO measurements were obtained at 1.3% ETIso and were lowered by 3% ETIso. Measurements were obtained in duplicate or triplicate with LiDCO and averaged for comparison with corresponding values measured continuously with the FloTrac/Vigileo method. For 30 comparisons between methods, a mean bias of ?100 mL/kg/min and 95% limits of agreement between ?311 and +112 mL/kg/min (212 mL/kg/min) was determined. The mean (mL/kg/min) of the differences of LiDCO?Vigileo=62.0402+?0.8383 × Vigileo, and the correlation coefficient (r) between the 2 methods 0.70 for all CO determinations. The repeatability coefficients for the individual LiDCO and FloTrac/Vigileo methods were 187 and 400 mL/kg/min, respectively. Mean LiDCO and FloTrac/Vigileo values from all measurements were 145 ± 68 mL/kg/min (range, 64–354) and 244 ± 144 mL/kg/min (range, 89–624), respectively. The overall mean relative error was 48 ± 14%. Conclusion – The FloTrac/Vigileo overestimated CO values compared with LiDCO and the relative error was high, which makes this method unreliable for use in dogs.     

Electrical velocimetry for noninvasive cardiac output and stroke volume variation measurements in dogs undergoing cardiovascular surgery

Objective

To compare electrical velocimetry (EV) noninvasive measures of cardiac output (CO) and stroke volume variation (SVV) in dogs undergoing cardiovascular surgery with those obtained with the conventional thermodilution technique using a pulmonary artery catheter.

RESEARCH PAPER: Comparison between two methods for cardiac output measurement in propofol‐anesthetized dogs: thermodilution and Doppler

ObjectiveTo compare cardiac output (CO) measured by Doppler echocardiography and thermodilution techniques in spontaneously breathing dogs during continuous infusion of propofol. To do so, CO was obtained using the thermodilution method (CO_TD) and Doppler evaluation of pulmonary flow (CO_DP) and aortic flow (CO_DA).Study designProspective cohort study.AnimalsEight adult dogs weighing 8.3 ± 2.0 kg.MethodsPropofol was used for induction (7.5 ± 1.9 mg kg^?1 IV) followed by a continuous rate infusion at 0.7 mg kg^?1 minute^?1. The animals were positioned in left lateral recumbency on an echocardiography table that allowed for positioning of the transducer at the 3rd and 5th intercostal spaces of the left hemithorax for Doppler evaluation of pulmonary and aortic valves, respectively. CO_DP and CO_DA were calculated from pulmonary and aortic velocity spectra, respectively. A pulmonary artery catheter was inserted via the jugular vein and positioned inside the lumen of the pulmonary artery in order to evaluate CO_TD. The first measurement of CO_TD, CO_DP and CO_DA was performed 30 minutes after beginning continuous infusion (T0) and then at 15‐minute intervals (T15, T30, T45 and T60). Numeric data were submitted to two‐way anova for repeated measurements, Pearson’s correlation coefficient and Bland &; Altman analysis. Data are presented as mean ± SD.ResultsAt T0, CO_TD was lower than CO_DA. CO_DA was higher than CO_TD and CO_DP at T30, T45 and T60. The difference between the CO_TD and CO_DP, when all data were included, was ?0.04 ± 0.22 L minute^?1 and Pearson’s correlation coefficient (r) was 0.86. The difference between the CO_TD and CO_DA was ?0.87 ± 0.54 L minute^?1 and r = 0.69. For CO_TD and CO_DP, the difference was ?0.82 ± 0.59 L minute^?1 and r = 0.61.ConclusionDoppler evaluation of pulmonary flow was a clinically acceptable method for assessing the CO in propofol‐anesthetized dogs.     

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.     

Lack of agreement between thermodilution and echocardiographic determination of cardiac output during normovolemia and acute hemorrhage in clinically healthy, anesthetized dogs

Objective and hypothesis: To determine whether or not there is agreement between the thermodilution and echocardiographic measurement of cardiac output (CO) during normovolemia and acute hemorrhage. The hypothesis was that there will be agreement between echocardiographic measurement of CO (ECO) and thermodilution measurement of CO (TDCO) during normovolemia and acute hemorrhage. Design: CO was measured by both thermodilution and echocardiography during α‐chloralose anesthesia in dogs before and 15 and 30 minutes following acute arterial hemorrhage. Setting: Laboratory investigation. Animals: Eighteen clinically healthy dogs, weighing 20–25 kg, anesthetized with α‐chloralose. Interventions: Acute arterial hemorrhage of approximately 50% of the total blood volume. CO was measured by thermodilution and echocardiography before and 15 and 30 minutes following hemorrhage. Measurements and main results: Acute hemorrhage resulted in a significant decrease in CO. There was a lack of agreement between the 2 methods to measure CO at each time and at all anatomic points of measurement in the aorta and pulmonary artery. Conclusion: There is a lack of agreement between the 2 methods; thus, determination of CO by echocardiography may not be a clinically useful tool following hemorrhage in dogs.     

Cardiovascular,respiratory, electrolyte and acid–base balance during continuous dexmedetomidine infusion in anesthetized dogs

ObjectiveTo evaluate the cardiovascular, respiratory, electrolyte and acid–base effects of a continuous infusion of dexmedetomidine during propofol–isoflurane anesthesia following premedication with dexmedetomidine.Study designProspective experimental study.AnimalsFive adult male Walker Hound dogs 1–2 years of age averaging 25.4 ± 3.6 kg.MethodsDogs were sedated with dexmedetomidine 10 μg kg^?1 IM, 78 ± 2.3 minutes (mean ± SD) before general anesthesia. Anesthesia was induced with propofol (2.5 ± 0.5 mg kg^?1) IV and maintained with 1.5% isoflurane. Thirty minutes later dexmedetomidine 0.5 μg kg^?1 IV was administered over 5 minutes followed by an infusion of 0.5 μg kg^?1 hour^?1. Cardiac output (CO), heart rate (HR), ECG, direct blood pressure, body temperature, respiratory parameters, acid–base and arterial blood gases and electrolytes were measured 30 and 60 minutes after the infusion started. Data were analyzed via multiple linear regression modeling of individual variables over time, compared to anesthetized baseline values. Data are presented as mean ± SD.ResultsNo statistical difference from baseline for any parameter was measured at any time point. Baseline CO, HR and mean arterial blood pressure (MAP) before infusion were 3.11 ± 0.9 L minute^?1, 78 ± 18 beats minute^?1 and 96 ± 10 mmHg, respectively. During infusion CO, HR and MAP were 3.20 ± 0.83 L minute^?1, 78 ± 14 beats minute^?1 and 89 ± 16 mmHg, respectively. No differences were found in respiratory rates, PaO₂, PaCO₂, pH, base excess, bicarbonate, sodium, potassium, chloride, calcium or lactate measurements before or during infusion.Conclusions and clinical relevanceDexmedetomidine infusion using a loading dose of 0.5 μg kg^?1 IV followed by a constant rate infusion of 0.5 μg kg^?1 hour^?1 does not cause any significant changes beyond those associated with an IM premedication dose of 10 μg kg^?1, in propofol–isoflurane anesthetized dogs. IM dexmedetomidine given 108 ± 2 minutes before onset of infusion showed typical significant effects on cardiovascular parameters.     

Use of ephedrine and dopamine in dogs for the management of hypotension in routine clinical cases under isoflurane anesthesia

OBJECTIVE: To determine the cardiovascular responses of ephedrine and dopamine for the management of presurgical hypotension in anesthetized dogs. STUDY DESIGN: Prospective, randomized, clinical trial. ANIMALS: Twelve healthy client-owned dogs admitted for orthopedic surgery; six per group METHODS: Prior to surgery, 58 anesthetized dogs were monitored for hypotension [mean arterial pressure (MAP) <60 mmHg] that was not associated with bradycardia or excessive anesthetic depth. Ephedrine (0.2 mg kg(-1), IV) or dopamine (5 microg kg(-1) minute(-1), IV) was randomly assigned for treatment in 12 hypotensive dogs. Ten minutes after the first treatment (Tx(1)-10), ephedrine was repeated or the dopamine infusion rate was doubled. Cardiovascular assessments taken at baseline, Tx(1)-10, and 10 minutes following treatment adjustment (Tx(2)-10) were compared for differences within and between treatments (p < 0.05). RESULTS: Ephedrine increased cardiac index (CI), stroke volume index (SVI), oxygen delivery index (DO(2)I), and decreased total peripheral resistance (TPR) by Tx(1)-10, while MAP increased transiently (<5 minutes). The second ephedrine bolus produced no further improvement. Dopamine failed to produce significant changes at 5 microg kg(-1) minute(-1), while 10 microg kg(-1) minute(-1) increased MAP, CI, SVI significantly from baseline, and DO(2)I compared with Tx(1)-10. The improvement in CI, SVI, and DO(2)I was not significantly different between treatments at Tx(2)-10. CONCLUSIONS AND CLINICAL RELEVANCE: In anesthetized hypotensive dogs, ephedrine and dopamine improved cardiac output and oxygen delivery. However, the pressure-elevating effect of ephedrine is transient, while an infusion of dopamine at 10 microg kg(-1) minute(-1) improved MAP significantly by additionally maintaining TPR.