Cardiac output measurement using a modified carbon dioxide Fick method: a validation study in ventilated lambs

Capnodynamics - noninvasive cardiac output and mixed venous oxygen saturation monitoring in children

Hemodynamic monitoring in children is challenging for many reasons. Technical limitations in combination with insufficient validation against reference methods, makes reliable monitoring systems difficult to establish. Since recent studies have highlighted perioperative cardiovascular stability as an important factor for patient outcome in pediatrics, the need for accurate hemodynamic monitoring methods in children is obvious. The development of mathematical processing of fast response mainstream capnography signals, has allowed for the development of capnodynamic hemodynamic monitoring. By inducing small changes in ventilation in intubated and mechanically ventilated patients, fluctuations in alveolar carbon dioxide are created. The subsequent changes in carbon dioxide elimination can be used to calculate the blood flow participating in gas exchange, i.e., effective pulmonary blood flow which equals the non-shunted pulmonary blood flow. Cardiac output can then be estimated and continuously monitored in a breath-by-breath fashion without the need for additional equipment, training, or calibration. In addition, the method allows for mixed venous oxygen saturation (SvO₂) monitoring, without pulmonary artery catheterization. The current review will discuss the capnodyamic method and its application and limitation as well as future potential development and functions in pediatric patients.

Preoperative Function Assessment of Ex Vivo Kidneys with Supervised Machine Learning Based on Blood and Urine Markers Measured during Normothermic Machine Perfusion

Establishing an objective quality assessment of an organ prior to transplantation can help prevent unnecessary discard of the organ and reduce the probability of functional failure. In this regard, normothermic machine perfusion (NMP) offers new possibilities for organ evaluation. However, to date, few studies have addressed the identification of markers and analytical tools to determine graft quality. In this study, function and injury markers were measured in blood and urine during NMP of 26 porcine kidneys and correlated with ex vivo inulin clearance behavior. Significant differentiation of kidneys according to their function could be achieved by oxygen consumption, oxygen delivery, renal blood flow, arterial pressure, intrarenal resistance, kidney temperature, relative urea concentration, and urine production. In addition, classifications were accomplished with supervised learning methods and histological analysis to predict renal function ex vivo. Classificators (support vector machines, k-nearest-neighbor, logistic regression and naive bayes) based on relevant markers in urine and blood achieved 75% and 83% accuracy in the validation and test set, respectively. A correlation between histological damage and function could not be detected. The measurement of blood and urine markers provides information of preoperative renal quality, which can used in future to establish an objective quality assessment.

Capnodynamics-Measuring cardiac output via ventilation

Recent studies have identified stable hemodynamics as a contributing factor to improve outcome in pediatric anesthesia. So far, most of the hemodynamic monitoring methods applied in children have been complex to apply and often not satisfactory validated. Standard mainstream carbon dioxide analysis in combination with real-time mathematical analysis of the measured capnography data has enabled the development of dynamic capnography, a non-invasively cardiac output monitoring method that can be applied without user practice or need for calibrations. Capnodynamic cardiac output assessment has been extensively validated against gold standard reference methods, both in experimental and clinical settings. This review will describe the principle behind dynamic capnography measurement of cardiac output and mixed venous oxygen saturation. Additionally, the methods limitations and challenges when applied in children will be delineated.

Effect of supplemental dexmedetomidine in interventional embolism on cerebral oxygen metabolism in patients with intracranial aneurysms

Objective

To investigate the effect of supplemental dexmedetomidine in interventional embolism on cerebral oxygen metabolism in patients with intracranial aneurysms.

Methods

Ninety patients who underwent interventional embolism of intracranial aneurysms were equally divided into Group A and Group B. In Group A, dexmedetomidine was injected intravenously 10 minutes before inducing anesthesia, with a loading dose of 0.6 µg/kg followed by 0.4 µg/kg/hour. Group B received the same amount of normal saline by the same injection method. Heart rate (HR), mean arterial pressure (MAP), arterial–jugular venous oxygen difference [D(a-jv) (O₂)], cerebral oxygen extraction [CE (O₂)], and intraoperative propofol use were recorded before inducing anesthesia (T₀) and at five time points thereafter.

Results

The amount of propofol in Group A was lower vs Group B. At all five time points after T₀, HR, MAP, D(a-jv) (O₂), and CE (O₂) in Group A were significantly lower vs Group B, with significant differences for jugular venous oxygen saturation (S_jvO₂) and the oxygen content of the internal jugular vein (C_jvO₂) between the groups.

Conclusion

Dexmedetomidine resulted in less intraoperative propofol, lower D(a-jv) (O₂) and CE (O₂), and improved cerebral oxygen metabolism.

Capnodynamic determination of cardiac output in hypoxia-induced pulmonary hypertension in pigs

BACKGROUND

Effective pulmonary blood flow (CO_EPBF) has recently been validated for its ability to measure cardiac output (CO) in children and animals. This study compared CO_EPBF with the Fick method (CO_Fick) and CO measurements using an invasive pulmonary artery flow probe (CO_TS). The aim of the study was to validate CO_EPBF against these reference methods in a porcine model of hypoxia-induced selective pulmonary hypertension.

METHODS

Ten anaesthetised mechanically ventilated piglets (median weight 23.9 kg) were exposed to a hypoxic gas mixture inducing selective pulmonary hypertension. Pulmonary hypertension was subsequently reversed with inhaled nitric oxide. Simultaneous recordings of CO_EPBF, CO_Fick, and CO_TS were performed throughout the protocol and examined for agreement and trending ability.

RESULTS

Overall bias (Bland-Altman) between CO_EPBF and CO_TS was 0.2 L min^-1 (limits of agreement -0.5 and +0.9 L min^-1) with a mean percentage error of 25%. Overall bias between CO_EPBF and CO_Fick was -0.1 L min^-1 (limits of agreement -0.9 and +0.6 L min^-1) and a mean percentage error of 25%. The concordance rate was 86% for CO_EPBF when compared with CO_TS using a 10% exclusion zone.

CONCLUSIONS

Estimation of CO with CO_EPBF results in values very close to the gold standard reference methods CO_Fick and CO_TS. CO_EPBF appears to be an accurate tool for monitoring absolute values and changes in CO during hypoxia-induced pulmonary hypertension and inhaled nitric oxide treatment.

Cardiac Output Monitoring in Preterm Infants

Maintaining optimal circulatory status is a key component of preterm neonatal care. Low-cardiac output (CO) in the preterm neonate leads to inadequate perfusion of vital organs and has been linked to a variety of adverse outcomes with heightened acute morbidity and mortality and adverse neurodevelopmental outcomes. Having technology available to monitor CO allows us to detect low-output states and potentially intervene to mitigate the unwanted effects of reduced organ perfusion. There are many technologies available for the monitoring of CO in the preterm neonatal population and while many act as useful adjuncts to aid clinical decision-making no technique is perfect. In this review, we discuss the relative merits and limitations of various common methodologies available for monitoring CO in the preterm neonatal population. We will discuss the ongoing challenges in monitoring CO in the preterm neonate along with current gaps in our knowledge. We conclude by discussing emerging technologies and areas that warrant further study.

Noninvasive photoacoustic measurement of the composite indicator dilution curve for cardiac output estimation

Recently, the measurement of indicator dilution curves using a photoacoustic (PA) technology was reported, which showed promising results on the noninvasive estimation of cardiac output (CO) that is an important hemodynamic parameter useful in various clinical situations. However, in clinical practice, measuring PA indicator dilution curves from an arterial blood vessel requires an ultrasound transducer array capable of focusing on the targeted artery. This causes several challenges on the clinical translation of the PA indicator dilution method, such as high sensor cost and complexity. In this paper, we theoretically derived that a composite PA indicator dilution curve simultaneously measured from both arterial and venous blood vessels can be used to estimate CO correctly. The ex-vivo and in-vivo experimental results with a flat ultrasound transducer verified the developed theory. We believe this new concept would overcome the main challenges on the clinical translation of the noninvasive PA indicator dilution technology.

Neonatal hemodynamics: monitoring, data acquisition and analysis

Monitoring of cardiovascular function is critical to both clinical care and research as the use of sophisticated monitoring systems enable us to obtain accurate, reliable and real-time information on developmental hemodynamics in health and disease. Novel approaches to comprehensive hemodynamic monitoring and data acquisition will undoubtedly aid in developing a better understanding of developmental cardiovascular physiology in neonates. In addition, development and use of state-of-the-art, comprehensive hemodynamic monitoring systems enable the recognition of signs of cardiovascular compromise in its early stages, and provide information on the hemodynamic response to treatment in critically ill patients.

Cardiac output monitoring in newborns

There is an increased interest in methods of objective cardiac output measurement in critically ill patients. Several techniques are available for measurement of cardiac output in children, although this remains very complex in newborns. Cardiac output monitoring could provide essential information to guide hemodynamic management. An overview is given of various methods of cardiac output monitoring with advantages and major limitations of each technology together with a short explanation of the basic principles.

Cardiac output measurement using an ultrasound dilution method: a validation study in ventilated piglets

OBJECTIVE

To assess agreement between a new method of cardiac output monitoring, using ultrasound dilution technology and ultrasound transit time-based measurement of pulmonary blood flow in a piglet model.

DESIGN

Prospective, experimental juvenile animal study.

SETTING

Animal laboratory of a university hospital.

SUBJECTS

Nine random-bred piglets.

INTERVENTIONS

After the animals received general anesthesia, we placed intravascular arterial and central venous catheters with the tip positioned in the abdominal aorta and the right atrium, respectively. The catheters were connected to the ultrasound dilution cardiac output monitor. An ultrasound transit time perivascular flow probe was positioned around the common pulmonary artery and served as the standard reference measurement. Cardiac output was manipulated during the experiment by creating hemorrhagic hypotension. Ultrasound dilution cardiac output was measured intermittently with injection volumes of 0.5 mL/kg and 1.0 mL/kg of isotonic saline at body temperature.

MEASUREMENTS AND MAIN RESULTS

Ultrasound dilution cardiac output (Q) measurement was compared with pulmonary blood flow (Q). Bias, defined as Q minus Q, was calculated for each measurement. Mean bias with standard deviation was calculated for measurements with volumes of injected saline, 0.5 mL/kg and 1.0 mL/kg, and compared using the Mann-Whitney U test. Mean bias (sd) between Q and Q was 0.040 (0.132) and 0.058 (0.136) L/min for measurement with 0.5 mL/kg and 1.0 mL/kg of isotonic saline, respectively (no statistically significant difference).

CONCLUSIONS

Ultrasound dilution cardiac output measurement is reliable in piglets with the use of a small volume of a nontoxic indicator (isotonic saline).