Assessment of cardiac output measurement in dogs by transpulmonary pulse contour analysis

Objective – To determine if metatarsal artery pressure (COmet) is comparable to femoral artery pressure (COfem) as the input for transpulmonary pulse contour analysis (PiCCO) in anesthetized dogs, using the lithium dilution method (LiDCO) as a standard for cardiac output (CO) measurement. Design – Prospective randomized study. Setting – University research laboratory. Animals – Ten healthy purpose‐bred mixed breed dogs were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases, and CO. Interventions – The CO was measured using LiDCO and PiCCO techniques. Animals had their right femoral and left distal metatarsal artery catheterized for proximal (COfem) and distal (COmet) PiCCO analysis, respectively. Measurements were obtained from each animal during low, normal, and high CO states by changing amount of inhalant anesthetics and heart rate. Measurements were converted to CO indexed to body weigh (CI_BW=CO/kg) for statistical analysis. Agreement was determined using Bland and Altman analysis and concordance correlation coefficients. Measurements and Main Results – Thirty paired measurements were taken. The LiDCO CI_BW (± SD) was 68.7 ± 30.3, 176.0 ± 53.0, and 211.1 ± 76.5 mL/kg/min during low, normal, and high CO states, respectively. There was a significant effect of CI_BW state on bias and relative bias with COmet (P<0.001 and P=0.003, respectively). Bias of the COmet method (± SD) was ?116.6 (70.5), 20.1(76.4), and 91.3 (92.0) mL/kg/min at low, normal, and high CI_BW, respectively. Bias of the COfem (± SD) was ?20.3 (19.0), 8.6 (70.9), and ?2.9 (83.0) mL/kg/min at low, normal, and high CI_BW, respectively. The mean relative bias for COfem was ?6.7 ± 44% (limits of agreements: ?81.2 to 67.9%). Conclusion – Compared with lithium dilution, the pulse contour analysis provides a good estimation of CO, but requires femoral artery catheterization in anesthetized 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.     

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.     

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.     

Evaluation of transpulmonary ultrasound dilution cardiac output in piglets: accuracy,precision and trending ability with room temperature injectate

ObjectiveTranspulmonary ultrasound dilution (TPUD) is a minimally invasive technique to measure cardiac output (CO) using a 1 mL kg^–1 isotonic 37 °C saline injectate indicator. The objective was to evaluate the performance of TPUD using a room temperature saline injectate.Study designProspective experimental trial.AnimalsA total of seven anesthetized male Yorkshire piglets.MethodsPiglets aged 1 month and weighing 7.7–9.0 kg were anesthetized with detomidine–ketamine–hydromorphone–isoflurane and a pulmonary artery flow probe (PAFP) placed via a median sternotomy. The thoracic cavity remained open during measurement of CO by PAFP and TPUD. The TPUD indicators of 1 mL kg^–1 0.9% saline at 37 °C and 20 °C were compared during infusions of phenylephrine and dobutamine, blood withdrawal and replacement. Bias, limits of agreement (LoAs) and percentage error (PE) between each iteration of PAFP and TPUD were measured with Bland–Altman plots. Trending ability via concordance, angular bias and radial LoA were compared.ResultsBland–Altman plots showed negligible bias with varying LoAs. PEs of 22% and 38% were found for 37 °C and 20 °C saline injectates, respectively. In the four-quadrant plots, the concordance rate was 94% and 100% for measurements obtained with 37 °C and 20 °C saline injectates, respectively. Angular bias for both were < ±5 °, with radial LoA < ±7 °.ConclusionsTPUD was accurate when using 1 mL kg^–1 of isotonic saline at 37 °C in a range of CO within 0.2–0.8 L minute^–1, and it reliably tracked positive and negative changes in CO. Room temperature (20 °C) indicator was less accurate but equally able to track direction of changes in CO.Clinical relevanceThe use of room temperature injectates allows an easy, readily available clinical application of TPUD CO monitoring while preserving the trending ability of the monitor.     

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.     

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.     

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.

Volumetric evaluation of fluid responsiveness using a modified passive leg raise maneuver during experimental induction and correction of hypovolemia in anesthetized dogs

ObjectiveTo demonstrate if modified passive leg raise (PLR_M) maneuver can be used for volumetric evaluation of fluid responsiveness (FR) by inducing cardiac output (CO) changes during experimental induction and correction of hypovolemia in healthy anesthetized dogs. The effects of PLR_M on plethysmographic variability index (PVI) and pulse pressure variation (PPV) were also investigated.Study designProspective, crossover study.AnimalsA total of six healthy anesthetized Beagle dogs.MethodsDogs were anesthetized with propofol and isoflurane. They were mechanically ventilated under neuromuscular blockade, and normothermia was maintained. After instrumentation, all dogs were subjected to four stages: 1, baseline; 2, removal of 27 mL kg^–1 circulating blood volume; 3, after blood re-transfusion; and 4, after 20 mL kg^–1 hetastarch infusion over 20 minutes. A 10 minute stabilization period was allowed after induction of each stage and before data collection. At each stage, CO via pulmonary artery thermodilution, PVI, PPV and cardiopulmonary variables were measured before, during and after the PLR_M maneuver. Stages were sequential, not randomized. Statistical analysis included repeated measures anova and Tukey’s post hoc test, considering p < 0.05 as significant.ResultsDuring stage 2, PLR_M at a 30° angle significantly increased CO (mean ± standard deviation, 1.0 ± 0.1 to 1.3 ± 0.1 L minute^–1; p < 0.001), with a simultaneous significant reduction in PVI (38 ± 4% to 21 ± 4%; p < 0.001) and PPV (27 ± 2% to 18 ± 2%; p < 0.001). The PLR_M did not affect CO, PPV and PVI during stages 1, 3 and 4.Conclusions and clinical relevanceIn anesthetized dogs, PLR_M at a 30° angle successfully detected FR during hypovolemia, and identified fluid nonresponsiveness during normovolemia and hypervolemia. Also, in hypovolemic dogs, significant decreases in PVI and PPV occurred in response to PLR_M maneuver.