A Review of Available Techniques for Cardiac Output Monitoring

Hemodynamic Assessment via Echocardiography During Propofol Anesthetic Induction in Healthy Dogs

Introduction: Propofol is an intravenous anesthetic administered as a bolus or continuous infusion during anesthetic induction and maintenance. Its pharmacokinetic characteristics include hepatic and extrahepatic metabolism with a rapid onset of action and short duration, which provides a smooth anesthetic induction without excitatory effects. Objective: To evaluate whether the isolated use of propofol in anesthetic induction in dogs changes the hemodynamic variables assessed via echocardiography. Study Design: Prospective clinical study. Animals: Twelve healthy dogs. Methods: The dogs were induced with propofol (dose/effect) at 3 mg/kg/minute, and echocardiographic evaluations were performed immediately before anesthetic induction (MB) and immediately after its interruption (MI), at the end of the supply of the anesthetic agent. Results: A significant reduction was observed between the values of the following hemodynamic variables: Ejection Fraction (EF%), which varied from 70% to 65% (p=0.011) between moments, and the Doppler Ejection Index (DEI), which ranged from 27.1 mL/beat/m2 to 22.4 mL/beat/m2 (p=0.044). The heart rate (HR) and the other studied hemodynamic variables showed no significant differences between the evaluated moments. Conclusion and Clinical Relevance: Propofol was a safe anesthetic-inducing agent, maintaining stable hemodynamic indices during anesthetic induction at the used rate.

Evaluation of Electrical Cardiometry for Measuring Cardiac Output and Derived Hemodynamic Variables in Comparison with Lithium Dilution in Anesthetized Dogs

Numerous cardiac output (CO) technologies were developed to replace the 'gold standard' pulmonary artery thermodilution due to its invasiveness and the risks associated with it. Minimally invasive lithium dilution (LiD) shows excellent agreement with thermodilution and can be used as a reference standard in animals. This study evaluated CO via noninvasive electrical cardiometry (EC) and acquired hemodynamic variables against CO measured using LiD in six healthy, anesthetized dogs administered different treatments (dobutamine, esmolol, phenylephrine, and high-dose isoflurane) impacting CO values. These treatments were chosen to cause drastic variations in CO, so that fair comparisons between EC and LiD across a wide range of CO values (low, intermediate, and high) could be made. Statistical analysis included linear regression, Bland-Altman plots, Lin's concordance correlation coefficient (ρ_c), and polar plots. Values of p < 0.05 represented significance. Good agreement was observed between EC and LiD, but consistent underestimation was noted when the CO values were high. The good trending ability, ρ_c of 0.88, and low percentage error of ±31% signified EC's favorable performance. Other EC-acquired variables successfully tracked changes in CO measured using LiD. EC may be a pivotal hemodynamic tool for continuously monitoring circulatory changes, as well as guiding and treating cardiovascular anesthetic complications in clinical settings.

Agreement between Electrical Cardiometry and Pulmonary Artery Thermodilution for Measuring Cardiac Output in Isoflurane-Anesthetized Dogs

In animals, invasive pulmonary artery thermodilution (PATD) is a gold standard for cardiac output (CO) monitoring, but it is impractical in clinical settings. This study evaluates the agreement between PATD and noninvasive electrical cardiometry (EC) for measuring CO and analyzes the other EC-derived hemodynamic variables in six healthy anesthetized dogs subjected to four different hemodynamic events in a sequential order: (1) euvolemia (baseline); (2) hemorrhage (33% blood volume loss); (3) autologous blood transfusion; and (4) 20 mL/kg colloid bolus. The CO measurements obtained using PATD and EC are compared using Bland-Altman analysis, Lin's concordance correlation (LCC), and polar plot analysis. Values of p < 0.05 are considered significant. The EC measurements consistently underpredict the CO values as compared with PATD, and the LCC is 0.65. The EC's performance is better during hemorrhage, thus indicating its capability in detecting absolute hypovolemia in clinical settings. Even though the percentage error exhibited by EC is 49.4%, which is higher than the standard (<30%), EC displays a good trending ability. Additionally, the EC-derived variables display a significant correlation with the CO measured using PATD. Noninvasive EC may have a potential in monitoring trends in hemodynamics in clinical settings.

Ultrasound dilution cardiac output and echocardiography findings in anesthetized mature alpacas (Vicugna pacos) during normotension, hypotension and hypertension

Alpacas (Vicugna pacos) have physiologic adaptations to live at high altitude. These adaptations may result in unexpected responses to changes in cardiac performance and blood pressure during general anesthesia. There are few studies evaluating cardiovascular variables in anesthetized alpacas. The purpose of this study was to report cardiovascular performance in anesthetized mature alpacas during normotension, hypotension, and hypertension using ultrasound dilution and echocardiography. Six adult alpacas, 3 females and 3 castrated males, weighing 62.6 to 88.7 kg were anesthetized and maintained with isoflurane and placed in right lateral recumbency. Each alpaca underwent ultrasound dilution and echocardiography measurements during three cardiovascular phases, normotension, hypotension via increased isoflurane concentration, and hypertension via phenylephrine infusion. Variables were analyzed with a Friedman test and a post hoc Dunn's test when significant. A p < 0.05 was used for significance. Cardiac output, cardiac index, systemic vascular resistance, stroke volume, total ejection fraction, left ventricular internal diameter during diastole, and total stroke volume indexed to body weight were greater for hypertension compared to hypotension. Total ejection fraction, stroke volume, and left ventricular ejection time were greater for hypertions compared to normotension. There was no difference between ultrasound dilution and echocardiography determined cardiac output measurements within each cardiovascular phase. Phenylephrine appeared to have increased ventricular performance and/or increased preload in anesthetized, mature alpacas. For detecting change in cardiovascular status in anesthetized alpacas, ultrasound dilution and echocardiography may be useful.

Evaluation of Oral Transmucosal Administration of Pentobarbital for Euthanasia of Conscious Wild Birds

This prospective study evaluated oral transmucosal pentobarbital sodium at three doses in 110 wild-caught wild birds requiring euthanasia. Birds received transmucosal pentobarbital at five (430 mg/kg), six (516 mg/kg), and seven times (602 mg/kg) the intravenous dose for mammals. Time to first effects and loss of consciousness, presence of pupillary light and corneal reflexes, apnea, and asystole were recorded each minute. When asystole was not achieved at 5 minutes, IV pentobarbital was administered. Combining data for all doses, loss of consciousness occurred at a median (range) of 2 minutes (0-4.75 min), apnea at 3 minutes (0-6 min), and asystole at 4 minutes (0.5-5 min). Loss of consciousness and apnea occurred significantly faster in the 602 mg/kg dose group than in the 430 mg/kg group (p = 0.009, difference of 0.6 ± 0.2 min; p = 0.024, difference of 0.7 ± 0.3 min), respectively. Apnea and asystole were achieved in 80/110 birds within 5 minutes. Oral transmucosal pentobarbital results in rapid loss of consciousness and respiratory arrest and provides a reliable alternative euthanasia method compared to intravenous administration.

MEASURING CARDIAC OUTPUT THROUGH THERMODILUTION BASED ON MACHINE LEARNING

Cardiac output (CO) refers to the amount of blood ejected from a unilateral ventricle per minute and is an important measure of cardiac function. Thermodilution is the gold standard for CO measurement because of its accuracy. However, the traditional thermodilution method requires calibration of the correction factor before measurement, which makes its practical application difficult. Therefore, conducting CO measurement by using a machine-learning-based thermodilution method is proposed in this paper, and CO is regressed and predicted through the thermodilution curve by a machine learning model. In this paper, we constructed five cardiac vascular models, and three of them were randomly selected to simulate the thermodilution process. Nine features of the thermodilution curve from the time–frequency domains were extracted and fed into the multilayer perceptron model for training. On the basis of a cross-validation method, the accuracy of the final prediction model was 97.99% ([Formula: see text]%). Simultaneously, a trained neural network was used to predict the CO of the remaining two cardiac vascular models, and the resulting error was within 5%. In this paper, an experimental system consisting of a water pump, a three-way valve and a temperature sensor is also designed, and the thermodilution curves at different quantities of flow are tested and regressed and predicted with the above model, with the error being within 10%, which met the requirement for real-world use, and thus, a method was established for measuring CO by using machine-learning-based thermodilution.

Anesthesia-Associated Relative Hypovolemia: Mechanisms, Monitoring, and Treatment Considerations

Although the utility and benefits of anesthesia and analgesia are irrefutable, their practice is not void of risks. Almost all drugs that produce anesthesia endanger cardiovascular stability by producing dose-dependent impairment of cardiac function, vascular reactivity, and compensatory autoregulatory responses. Whereas anesthesia-related depression of cardiac performance and arterial vasodilation are well recognized adverse effects contributing to anesthetic risk, far less emphasis has been placed on effects impacting venous physiology and venous return. The venous circulation, containing about 65–70% of the total blood volume, is a pivotal contributor to stroke volume and cardiac output. Vasodilation, particularly venodilation, is the primary cause of relative hypovolemia produced by anesthetic drugs and is often associated with increased venous compliance, decreased venous return, and reduced response to vasoactive substances. Depending on factors such as patient status and monitoring, a state of relative hypovolemia may remain clinically undetected, with impending consequences owing to impaired oxygen delivery and tissue perfusion. Concurrent processes related to comorbidities, hypothermia, inflammation, trauma, sepsis, or other causes of hemodynamic or metabolic compromise, may further exacerbate the condition. Despite scientific and technological advances, clinical monitoring and treatment of relative hypovolemia still pose relevant challenges to the anesthesiologist. This short perspective seeks to define relative hypovolemia, describe the venous system’s role in supporting normal cardiovascular function, characterize effects of anesthetic drugs on venous physiology, and address current considerations and challenges for monitoring and treatment of relative hypovolemia, with focus on insights for future therapies.