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

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

OBJECTIVE

Transpulmonary 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 DESIGN

Prospective experimental trial.

ANIMALS

A total of seven anesthetized male Yorkshire piglets.

METHODS

Piglets 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.

RESULTS

Bland-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 °.

CONCLUSIONS

TPUD 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 RELEVANCE

The use of room temperature injectates allows an easy, readily available clinical application of TPUD CO monitoring while preserving the trending ability of the monitor.

Advanced Hemodynamic Monitoring in the Neonatal Intensive Care Unit

Clinical assessment of cardiac output by interpretation of indirect parameters has proven to be inaccurate, irrespective of the level of experience of the clinician. Objective cardiac output monitoring is feasible in newborn infants in intensive care. The most promising methods include transthoracic echocardiography, transcutaneous Doppler, electrical biosensing technologies, transpulmonary ultrasound dilution, and arterial pulse contour analysis. Simultaneous assessment of blood pressure and cardiac output enables the identification of the earliest stage of shock. Comprehensive hemodynamic monitoring is pivotal for an individualized pathophysiology-based hemodynamic management.

The effect of positive end-expiratory pressure on cardiac output and oxygen delivery during cardiopulmonary resuscitation

Background

Positive end-expiratory pressure (PEEP) is used to optimize oxygenation by preventing alveolar collapse. However, PEEP can potentially decrease cardiac output through cardiopulmonary interactions. The effect of PEEP on cardiac output during cardiopulmonary resuscitation (CPR) is not known.

Methods

This was a preclinical randomized, controlled, animal study conducted in an animal research facility on 25 Landrace-Yorkshire pigs. After inducing cardiac arrest, CPR was performed with LUCAS 3. During CPR, pigs were ventilated at a PEEP of 0, 5, 10, 15, 20 cmH₂O (randomly determined via lottery) for 9 min. Cardiac output, obtained via ultrasound dilution, and PaO₂ were measured, and oxygen delivery calculated for each PEEP.

Results

A mixed-effects repeated-measures analysis of variance was used to compare the baseline value adjusted mean cardiac output, PaO₂, and oxygen delivery between PEEP groups. Least significant difference test was used to conduct pairwise comparisons between PEEP groups. To determine optimum PEEP, Gaussian mixture model was applied to the adjusted means of cardiac output and oxygen delivery. Increasing PEEP to 10 and higher resulted in significant declines in cardiac output. A PEEP of 15 and higher resulted in significant declines in oxygen delivery. As PEEP was increased from 0 to 20, PaO₂ increased significantly. Gaussian mixture model identified the 0–5 PEEP group as providing optimal cardiac output and oxygen delivery, with PEEP of 5 providing the highest oxygen delivery.

Conclusions

A PEEP of 0–5 resulted in the optimal oxygen delivery and cardiac output during CPR, with PEEP of 5 resulting in higher oxygen delivery, and a slightly lower, statistically insignificant cardiac output than PEEP of 0.

Neonatal Hemodynamics: From Developmental Physiology to Comprehensive Monitoring

Maintenance of neonatal circulatory homeostasis is a real challenge, due to the complex physiology during postnatal transition and the inherent immaturity of the cardiovascular system and other relevant organs. It is known that abnormal cardiovascular function during the neonatal period is associated with increased risk of severe morbidity and mortality. Understanding the functional and structural characteristics of the neonatal circulation is, therefore, essential, as therapeutic hemodynamic interventions should be based on the assumed underlying (patho)physiology. The clinical assessment of systemic blood flow (SBF) by indirect parameters, such as blood pressure, capillary refill time, heart rate, urine output, and central-peripheral temperature difference is inaccurate. As blood pressure is no surrogate for SBF, information on cardiac output and systemic vascular resistance should be obtained in combination with an evaluation of end organ perfusion. Accurate and reliable hemodynamic monitoring systems are required to detect inadequate tissue perfusion and oxygenation at an early stage before this result in irreversible damage. Also, the hemodynamic response to the initiated treatment should be re-evaluated regularly as changes in cardiovascular function can occur quickly. New insights in the understanding of neonatal cardiovascular physiology are reviewed and several methods for current and future neonatal hemodynamic monitoring are discussed.

Changes in blood volume indicators and dynamic indicators measured with transpulmonary ultrasound velocity during blood depletion and repletion in a neonatal swine model

BACKGROUND

Dynamic indicators such as pulse pressure and stroke volume variations can be measured to track changes in preload during hemorrhage, and evaluate fluid therapy. However, these dynamic indicators require mechanical ventilation, and might be affected by cardiac dysrhythmias and changes in vascular tone. Blood volume indicators may offer alternatives for assessing changes in volume status.

AIMS

The aims of this study were to measure changes in blood volume indicators and dynamic indicators during removal of blood in two stages and subsequent blood replacement in anesthetized, mechanically ventilated, neonatal pigs.

METHODS

In eight anesthetized, mechanically ventilated piglets (5-6 weeks old), cardiac index, stroke volume index, total end-diastolic volume, central blood volume, active circulating volume, pulse pressure variation, and stroke volume variation were measured during blood removal in two stages (15 mL kg^-1 each stage) and blood replacement (30 mL kg^-1 ). Values after each intervention were measured for each parameter.

RESULTS

All indicators differed from baseline after removal of 15 mL kg^-1 of blood, except for stroke volume variation. Differences between both stages of hemorrhage were only observed for indexed stroke volume, total end-diastolic volume, central blood volume, and pulse pressure variation.

CONCLUSION

Total end-diastolic volume and central blood volume changed during blood depletion and repletion, and differed between stages of hemorrhage. These indicators might be useful for assessing volume status instead of, or in addition to cardiac index and dynamic indicators.

Detection and quantification of left-to-right shunting using transpulmonary ultrasound dilution (TPUD): a validation study in neonatal lambs

OBJECTIVES

We investigated the accuracy of left-to-right shunt detection using transpulmonary ultrasound dilution (TPUD) and compared the agreement between pulmonary over systemic blood flow (Qp/Qs) ratio measured by TPUD [Qp/Qs(tpud)] and ultrasonic flow probes [Qp/Qs(ufp)].

METHODS

Seven newborn lambs under general anesthesia were connected to the TPUD monitor (COstatus™) after insertion of arterial and central venous catheters. A Gore-Tex® shunt, inserted between the descending aorta and left pulmonary artery, was intermittently opened and closed while cardiac output was varied by blood withdrawals. Flow probes were placed around the main pulmonary artery (Qufp) and the descending aorta proximal (Qpre) and distal (Qpost) to the shunt insertion. Qp/Qs(ufp) was calculated as (Qufp+Qpre-Qpost)/Qufp.

RESULTS

Seventy-two paired measurement sessions were analyzed. Shunts were detected by TPUD with a positive predictive value of 86%, a negative predictive value of 100%, a sensitivity of 100% and a specificity of 83%. The Bland-Altman analysis comparing Qp/Qs(tpud) and Qp/Qs(ufp) showed an overall mean bias (SD) of 0.1 (0.3), limits of agreement (LOA) of ±0.6 and a percentage error of 34.8%.

CONCLUSIONS

The qualitative diagnostic accuracy of TPUD for shunt detection is high. Modification of the algorithm seems required as shunt quantification by TPUD is accurate, but not yet very precise.

Hemodynamic volumetry using transpulmonary ultrasound dilution (TPUD) technology in a neonatal animal model

To analyze changes in cardiac output and hemodynamic volumes using transpulmonary ultrasound dilution (TPUD) in a neonatal animal model under different hemodynamic conditions. 7 lambs (3.5-8.3 kg) under general anesthesia received arterial and central venous catheters. A Gore-Tex(®) shunt was surgically inserted between the descending aorta and the left pulmonary artery to mimic a patent ductus arteriosus. After shunt opening and closure, induced hemorrhagic hypotension (by repetitive blood withdrawals) and repetitive volume challenges, the following parameters were assessed using TPUD: cardiac output, active circulating volume index (ACVI), central blood volume index (CBVI) and total end-diastolic volume index (TEDVI). 27 measurement sessions were analyzed. After shunt opening, there was a significant increase in TEDVI and a significant decrease in cardiac output with minimal change in CBVI and ACVI. With shunt closure, these results reversed. After progressive hemorrhage, cardiac output and all volumes decreased significantly, except for ACVI. Following repetitive volume resuscitation, cardiac output increased and all hemodynamic volumes increased significantly. Correlations between changes in COufp and changes in hemodynamic volumes (ACVI 0.83; CBVI 0.84 and TEDVI 0.78 respectively) were (slightly) better than between changes in COufp and changes in heart rate (0.44) and central venous pressure (0.7). Changes in hemodynamic volumes using TPUD were as expected under different conditions. Hemodynamic volumetry using TPUD might be a promising technique that has the potential to improve the assessment and interpretation of the hemodynamic status in critically ill newborns and children.

Accuracy of the transpulmonary ultrasound dilution method for detection of small anatomic shunts

The purpose of this study was to investigate the qualitative and quantitative accuracy of transpulmonary ultrasound dilution (UD) (COstatus™, Transonic Systems) for the detection of small anatomic shunts. It was a prospective, observational study in a multi-disciplinary pediatric intensive care unit. Seventy-three critically ill children (67 post cardiac surgery), with a median (IQR) age of 10 (3-50.3) months and a median (IQR) weight of 8 (3.43-13) kg were enrolled. Ultrasound dilution (UD) measurements were performed on patients within 1 h of undergoing two-dimensional echocardiography, which was used as the comparator technique. Shunt was diagnosed by characteristic changes on the UD curve shape, and was considered "test-positive" only if two or more measurements suggested the presence of the shunt. The UD technology also provided an estimate of pulmonary to systemic blood flow ratio (Qp:Qs). 12/73 (16.4 %) patients had a shunt identified by both UD and echocardiography. The overall accuracy (95 % CI) was 86.1 % (75.6-96.6 %), with a sensitivity of 85.7 % (57.2-98.2 %) and specificity of 86.4 % (75.0-94.0 %). The estimated Qp:Qs ranged from 0.7 to 1.4, which was consistent qualitatively with the echocardiographic findings on color flow doppler. Shunt was detected by UD alone in eight children; six of these had clinical conditions known to compromise dilution curve analysis (valve regurgitation, asymmetric pulmonary blood flow). Shunt was detected by echocardiography alone in two children; in both cases the shunt was tiny. UD is an accurate method for the detection of small anatomical shunts, both qualitatively and quantitatively.

Validation of an ultrasound dilution technology for cardiac output measurement and shunt detection in infants and children

OBJECTIVE

To validate cardiac output measurements by ultrasound dilution technology (COstatus monitor) against those obtained by a transit-time ultrasound technology with a perivascular flow probe and to investigate ultrasound dilution ability to estimate pulmonary to systemic blood flow ratio in children.

DESIGN

Prospective observational clinical trial.

SETTING

Pediatric cardiac operating theater in a university hospital.

MATERIAL AND METHODS

In 21 children (6.1 ± 2.6 kg, mean ± SD) undergoing heart surgery, cardiac output was simultaneously recorded by ultrasound dilution (extracorporeal arteriovenous loop connected to existing arterial and central venous catheters) and a transit-time ultrasound probe applied to the ascending aorta, and when possible, the main pulmonary artery. The pulmonary to systemic blood flow ratio estimated from ultrasound dilution curve analysis was compared with that estimated from transit-time ultrasound technology.

RESULTS

Bland-Altman analysis of the whole cohort (90 pairs, before and after surgery) showed a bias between transit-time ultrasound (1.01 ± 0.47 L/min) and ultrasound dilution technology (1.03 ± 0.51 L/min) of -0.02 L/min, limits of agreement -0.3 to 0.3 L/min, and percentage error of 31%. In children with no residual shunts, the bias was -0.04 L/min, limits of agreement -0.28 to 0.2 L/min, and percentage error 19%. The pooled co efficient of variation was for the whole cohort 3.5% (transit-time ultrasound) and 6.3% (ultrasound dilution), and in children without shunt, it was 2.9% (transit-time ultrasound) and 4% (ultrasound dilution), respectively. Ultrasound dilution identified the presence of shunts (pulmonary to systemic blood flow ≠ 1) with a sensitivity of 100% and a specificity of 92%. Mean pulmonary to systemic blood flow ratio by transit-time ultrasound was 2.6 ± 1.0 and by ultrasound dilution 2.2 ± 0.7 (not significant).

CONCLUSION

The COstatus monitor is a reliable technique to measure cardiac output in children with high sensitivity and specificity for detecting the presence of shunts.

Determination of cardiac output by ultrasound dilution technique in infants and children: a validation study against direct Fick principle

BACKGROUND

In critically ill children, monitoring of cardiac output (CO) is essential to guide haemodynamic management and facilitate cardiovascular therapy. The ultrasound dilution technique (UDT), a novel minimally invasive indicator method, was recently introduced to determine CO. We validated UDT against the 'gold standard' reference technique, the direct Fick principle, in infants and children.

METHODS

Twenty-six children (median age: 6 yr 2 months; median weight: 19.2 kg) underwent diagnostic heart catheterization. In each child, CO was determined by the Fick principle using direct measurement of oxygen consumption and invasive oximetry. Consecutively, haemodynamically stable conditions provided; three independent measurements of CO were conducted with UDT. CO values were compared using bias and limits of agreement calculated using the Bland-Altman approach and linear regression analysis for the complete study group and for a subgroup with body weight <20 kg (n=14).

RESULTS

The mean (standard deviation) CO values were 3.76 (1.73) litre min(-1) (range 1.38-6.97) for the direct Fick principle and 3.49 (1.72) litre min(-1) (range 1.31-7.00) for UDT. An excellent correlation (r=0.96) was found between both methods (P<0.0001). The Bland-Altman analysis demonstrated good clinical agreement with a mean bias of 0.26 litre min(-1), limits of agreement of -0.66 and 1.19 litre min(-1), and percentage error of 25.9%. Comparable results were obtained for patients <20 kg (mean bias=0.19 litre min(-1), percentage error=25.5%).

CONCLUSIONS

CO measurements by UDT agree favourably with Fick-derived CO data and both techniques were found to be equivalent and interchangeable. UDT represents a valid and applicable method for repetitive CO determinations in infants and children.

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.

Prematurity and congenital heart disease

Significant advances in technology and therapy have led to dramatic improvements in the survival of preterm babies over the last 2 decades. Similarly, improvements in surgical and cardiac intensive care techniques have increased the feasibility of supporting even very small babies to the point of surgical repair, leading some to adopt an approach of early and complete surgical repair in preterm infants, with the aim of minimizing potential preoperative morbidity associated with extended medical management or surgical palliation. (1,2) However, multiple diagnostic and therapeutic challenges complicate the care of premature infants. Major errors in echocardiography are more common in neonates weighing less than 2.5 kg, (3) and the ideal timing and type of surgical intervention in premature infants remains unknown. These problems are compounded by the need for critical care practices that optimize management of immature cardiopulmonary, gastrointestinal, and neurological systems. This review will summarize some of the recent advances in neonatal and perinatal medicine, which have the potential to contribute to improved management of preterm infants with critical cardiac disease.

Hemodynamic recovery after hypovolemic shock with lactated Ringer's and keratin resuscitation fluid (KRF), a novel colloid

Death after severe hemorrhage remains an important cause of mortality in people under 50 years of age. Keratin resuscitation fluid (KRF) is a novel resuscitation solution made from keratin protein that may restore cardiovascular stability. This postulate was tested in rats that were exsanguinated to 40% of their blood volume. Test groups received either low or high volume resuscitation with either KRF or lactated Ringer's solution. KRF low volume was more effective than LR in recovering cardiac function, blood pressure and blood chemistry. Furthermore, in contrast to LR-treated rats, KRF-treated rats exhibited vital signs that resembled normal controls at 1-week.

Pressure recording analytical method for measuring cardiac output in critically ill children: a validation study

BACKGROUND

Pressure recording analytical method (PRAM) is a novel, arterial pulse contour-based method for measuring cardiac output (CO). Validation studies of PRAM in children are few, and have not assessed both absolute accuracy and ability to track changes in CO across a broad case mix. We aimed to compare CO as measured by PRAM with that using a transpulmonary dilution method in a cohort of critically ill children.

METHODS

Forty-eight, mechanically ventilated children with a median (inter-quartile) weight of 10.7 (5.5-15) kg with arterial and central venous catheters in situ were studied. CO was measured simultaneously using PRAM and the comparator method, transpulmonary ultrasound dilution (UD). Measurements were repeated before and after therapeutic interventions that were intended to augment CO (e.g. fluid bolus).

RESULTS

In total, 210 paired measurements were compared. The mean (sd) CO was 1.9 (1.2) litre min(-1) with UD when compared with 1.92 (0.5) litre min(-1) using PRAM. The mean bias was 0.02 litre min(-1) with wide limits of agreement: ± 2.21 litre min(-1), giving a percentage error of 116%. The concordance between PRAM and UD for measuring changes in CO was also poor, with only 37% of measurements falling within the pre-defined polar plot limits of ±30°.

CONCLUSIONS

There is an unacceptably poor agreement between UD and PRAM. We do not recommend the use of PRAM for measuring CO in critically ill children with the current algorithm.

Comparison of transpulmonary thermodilution and ultrasound dilution technique: novel insights into volumetric parameters from an animal model

Especially in critically ill children with cardiac diseases, fluid management and monitoring of cardiovascular function are essential. Ultrasound dilution technique (UDT) was recently introduced to measure cardiac output (CO) and volumetric parameters, such as intrathoracic and end-diastolic blood volume. We compared UDT with the well-established transpulmonary thermodilution (TPTD) method (PiCCO) for determining CO measurements and derived volumes in a juvenile animal model. Experiments were performed in 18 ventilated, anesthetized piglets during normovolemia and after isovolemic hemodilution. At baseline and 20 min after each step of isovolemic hemodilution, 3 independent measurements of CO and volumetric parameters were conducted with TPTD and UDT, consecutively, under hemodynamically stable conditions. We observed comparable results for CO measurements with both methods (mean 1.98 l/min; range 1.12-2.87) with a percentage error of 17.3% (r = 0.92, mean bias = 0.28 l/min). Global end-diastolic volume (GEDV) and intrathoracic blood volume (ITBV) by TPTD were almost two times greater than analogous volumes [central blood volume (CBV); total end-diastolic volume (TEDV)] quantified by UDT (CBV = 0.58 × ITBV + 27.1 ml; TEDV = 0.48 × GEDV + 23.1 ml). CO measurements by UDT were found to be equivalent and hence interchangeable with TPTD. Discrepancies in volumetric parameters could either be due to the underlying algorithm or different types of indicators (diffusible vs. nondiffusible). Compared with the anatomically defined heart volume, TPTD seems to overestimate end-diastolic volumes. Future studies will be necessary to assign these results to critically ill children and to validate volumetric parameters with reference techniques.

Ultrasound dilution: an accurate means of determining cardiac output in children

BACKGROUND

Cardiac output is a useful measure of myocardial performance. Cardiac output monitoring is frequently performed in critically ill adults to guide physicians' treatment strategies. However, standard methods of determining cardiac output in children are not without risk and can be problematic secondary to their invasive nature and other technical problems. The COstatus system (Transonic Systems, NY), which is based on ultrasound dilution technology, works off in situ catheters and uses an innocuous indicator to allow for routine measurements of cardiac output and blood volumes in pediatric patients. The purpose of this study was to validate cardiac output measured by the COstatus system with those obtained by the clinical standard technique of pulmonary artery thermodilution.

METHODS

This was a prospective evaluation performed at a single institution. Any child with a structurally normal heart undergoing hemodynamic evaluation in the cardiac catheterization laboratory was included. A prograde right heart catheterization was performed, and cardiac output was first determined by using the pulmonary artery thermodilution technique. Thermodilution results were then compared with cardiac output measurements obtained using the COstatus system. The results were analyzed by standard correlation, Bland-Altman, and Critchley and Critchley analyses.

RESULTS

Twenty-eight patients were evaluated with a median age of 8 yrs and a median weight of 31 kg. The mean thermodilution cardiac index = 3.18 L/min (± 1.35 L/min), and the mean COstatus system cardiac index = 3.17 L/min (± 1.31 L/min). Standard Pearson correlation tests revealed an excellent correlation coefficient of 0.95 (p < .0001). Bland-Altman analysis revealed good clinical agreement with a mean difference of -0.004 L/min with a precision of 0.8 L/min at 2 SD. A percentage error of 25.4% was noticed in this study, which is less than the clinically acceptable limit.

CONCLUSION

The ultrasound dilution technique of determining cardiac output using the COstatus system provides a less invasive method than the traditional pulmonary artery thermodilution for accurately determining cardiac output in children. This is the first validation of the COstatus system in pediatric patients. Further studies are required to establish its accuracy in pediatric patients with cardiac shunts and other hemodynamically unstable conditions.

Validation of cardiac output measurement by ultrasound dilution technique with pulmonary artery thermodilution in a pediatric animal model

Novel COstatus system (Transonic Systems, Inc., NY), based on ultrasound dilution (UD), works off in situ arterial and central venous catheters in pediatric patients to measure cardiac output (CO). The purpose of the present study was to validate CO measurement by UD (COUD) with pulmonary artery (PA) thermodilution (COTD) in a prospective animal study. Ten anesthetized pigs (16-45 kg) were instrumented with pediatric PA, central venous, and peripheral artery catheters. For COUD measurements, normothermic saline (0.5-1.0 ml/kg body weight, up to a maximum of 30 ml) was injected into the venous limb of an arteriovenous loop that was connected between in situ catheters. For COTD measurements, 5-10 ml cold saline was injected into the PA catheter. Sixty-four averaged sets were obtained for comparison. COTD mean was 2.98 ± 1.21 l/min (range 1.33-6.29), and COUD mean was 2.68 ± 1.16 l/min (range 1.33-5.85). This study yielded a correlation r = 0.96, COUD = 0.91*(COTD) - 0.04 l/min; bias was 0.3 l/min with limits of agreement as -0.39 to 0.99 l/min; and the percentage error was 23.73% between the methods. CO measurements by UD agreed well with thermodilution measurements in the pediatric swine model.

Flow-regulated extracorporeal arteriovenous tubing loop for cardiac output measurements by ultrasound velocity dilution: validation in post-cardiac surgery intensive care unit patients

Assessment of cardiac output (CO) is crucial in the management of the critically ill, especially in post cardiac surgery intensive care unit (ICU) patients. In this study, we validated CO measured by the novel ultrasound dilution (COUD) with those measured by pulmonary artery (PA) thermodilution (COTD) in 26 adult post cardiac surgery patients. For COUD, blood was circulated through an extracorporeal arteriovenous (AV) loop from the radial artery catheter to the introducer of PA catheter for 5-8 minutes. Three to four injections of 25 ml body temperature isotonic saline were performed into the venous limb of the AV loop. For COTD, five injections of 10 ml ice cold saline were performed. A total of 77 COUD and COTD measurement sets were compared. Cardiac output measured by thermodilution ranged from 3.28 to 9.4 L/min, whereas COUD ranged from 2.85 to 10.1 L/min. The correlation between the methods was found to be r = 0.91, COUD = 0.93(COTD) + 0.42 L/min. Bias and precision (mean difference ± 2SDs) was -0.004 ± 1.34 L/min between the two methods. The percentage error (2SD/mean) was 22.2%, which is below the clinically acceptable limit (<30%). Cardiac output measured by ultrasound dilution and thermodilution methods agreed well in post cardiac surgery ICU patients and hence can be interchangeably used.

Comparison of cardiac output and blood volumes in intrathoracic compartments measured by ultrasound dilution and transpulmonary thermodilution methods

PURPOSE

To compare cardiac output (CO) and blood volumes measured by COstatus(®) (Transonic Systems Inc., NY, USA) versus PiCCO (Philips IntelliVue MP40 with PiCCO-technology module M3012A#10, Netherlands) in adult ICU patients.

METHODS

This was a prospective single-center study. Each of the 30 patients studied received a 5-Fr Pulsiocath femoral arterial and a standard central venous catheter. Twenty ml of iced 5% dextrose solution was injected for PiCCO measurements. For COstatus measurements, an extracorporeal arteriovenous loop, with two sensors placed on it, was connected between the Pulsiocath femoral arterial and central venous catheters. Blood was circulated through this loop at 12 ml/min for 5-8 min using a pump. Twenty ml of warm saline was injected into the venous side for measurements. For each method, three injections were averaged for comparison.

RESULTS

A good agreement for measured CO (range 3.65-16.3 l/min) with a percentage error of 20% was observed, with r = 0.95, bias = -0.037 l/min. PiCCO's global end-diastolic volume (GEDV) was 2.5 times larger than the analogous COstatus's total end-diastolic volume (TEDV) [TEDV = 0.28 × GEDV + 176 ml]. PiCCO's intrathoracic blood volume (ITBV) was larger than the analogous COstatus's central blood volume (CBV) [CBV = 0.73 × (ITBV) +78 ml].

CONCLUSIONS

CO measured by COstatus was found to be equivalent and hence interchangeable with PiCCO in this study population. COstatus blood volumes were found to be within the expected physiological range whilst PiCCO blood volumes were significantly higher, which was also observed in other studies. Future studies using 3D echo/MRI are required to validate these blood volumes.

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.