Hemodynamic Treatment Research Articles

A Comparison of Three Minimally Invasive Cardiac Output Devices with Thermodilution in Elective Cardiac Surgery

This study compared the cardiac output responses to haemodynamic interventions as measured by three minimally invasive monitors (Oesophageal Doppler Monitor the VigileoFlotrac and the LiDCOrapid) to the responses measured concurrently using thermodilution, in cardiac surgical patients. The study also assessed the precision and bias of these monitors in relation to thermodilution measurements. After a fluid bolus of at least 250 ml, the measured change in cardiac output was different among the devices, showing an increase with thermodilution in 82% of measurements, Oesophageal Doppler Monitor 68%, VigileoFlotrac 57% and LiDCOrapid 41%. When comparing the test devices to thermodilution, the kappa statistic showed at best only fair agreement, Oesophageal Doppler Monitor 0.34, LiDCOrapid 0.28 and VigileoFlotrac -0.03. After vasopressor administration, there was also significant variation in the change in cardiac output measured by the devices. Using Bland-Altman analysis, the precision of the devices in comparison to thermodilution showed minimal bias, but wide limits of agreement with percentage errors of Oesophageal Doppler Monitor 64.5%, VigileoFlotrac 47.6% and LiDCOrapid 54.2%. These findings indicate that these three devices differ in their responses, do not always provide the same information as thermodilution and should not be used interchangeably to track cardiac output changes.

Microcirculatory alterations: potential mechanisms and implications for therapy

Multiple experimental and human trials have shown that microcirculatory alterations are frequent in sepsis. In this review, we discuss the characteristics of these alterations, the various mechanisms potentially involved, and the implications for therapy. Sepsis-induced microvascular alterations are characterized by a decrease in capillary density with an increased number of stopped-flow and intermittent-flow capillaries, in close vicinity to well-perfused capillaries. Accordingly, the surface available for exchange is decreased but also is highly heterogeneous. Multiple mechanisms may contribute to these alterations, including endothelial dysfunction, impaired inter-cell communication, altered glycocalyx, adhesion and rolling of white blood cells and platelets, and altered red blood cell deformability. Given the heterogeneous nature of these alterations and the mechanisms potentially involved, classical hemodynamic interventions, such as fluids, red blood cell transfusions, vasopressors, and inotropic agents, have only a limited impact, and the microcirculatory changes often persist after resuscitation. Nevertheless, fluids seem to improve the microcirculation in the early phase of sepsis and dobutamine also can improve the microcirculation, although the magnitude of this effect varies considerably among patients. Finally, maintaining a sufficient perfusion pressure seems to positively influence the microcirculation; however, which mean arterial pressure levels should be targeted remains controversial. Some trials using vasodilating agents, especially nitroglycerin, showed promising initial results but they were challenged in other trials, so it is difficult to recommend the use of these agents in current practice. Other agents can markedly improve the microcirculation, including activated protein C and antithrombin, vitamin C, or steroids. In conclusion, microcirculatory alterations may play an important role in the development of sepsis-related organ dysfunction. At this stage, therapies to target microcirculation specifically are still being investigated.

Intraoperative Monitoring with Transesophageal Echocardiography in Cardiac Surgery

Since its clinical introduction in the 80s, intraoperative transesophageal echocardiography (TEE) has represented one of the greatest advances in modern cardiac anesthesia. It is a semi-invasive technique that allows direct and fast visualization of structural anatomy of the heart and great vessels as well as contributes to hemodynamic and functional evaluation of the cardiovascular system. Thus, it has become an important monitor in aiding the diagnosis of cardiac pathologies and anesthesia and surgical interventions. The objective of this report was to perform a comprehensive review on the use of intraoperative TEE in cardiac surgery. This article reviews some aspects of ultrasound physics, imaging techniques, echocardiographic cuts used more oftenly, indications, and main clinical applications in addition to contraindications and complications. Intraoperative TEE is a safe method of cardiovascular monitoring, which is useful in the formulation of a surgical strategy, orientation of hemodynamic interventions, and immediate assessment of surgical outcomes. Once qualified to use the method, the anesthesiologist expands its role in perioperative medicine, providing clinical information necessary to the anesthetic-surgical procedure in cardiac surgery.

Letters to the Editor

Hemodynamic and perfusion end points for volemic resuscitation in sepsis. Shock 34(Suppl 1):34-39, 2010 To the Editor: We would like to congratulate Drs da Silva Ramos and Pontes Azevedo on their elegant review about end points of volume resuscitation in sepsis (1). Except for lactate, base deficit, and venous oximetry, the authors focused on macrocirculatory variables. We wish to comment on potential caveats connected with the use of macrocirculatory variables as resuscitation end points and propose alternative targets for volume replacement in sepsis. So far, fluid resuscitation has been guided by responses of macrocirculatory variables to fluid loading. Hence, a positive fluid response is commonly defined as an increase of 10% or greater in arterial blood pressure and/or cardiac output. Physiologically, this may hold true, given that the heart acts as a preload-dependent servo pump (2). However, in sepsis, when cardiac dysfunction and disturbed cardiovascular regulation are highly prevalent, this concept may bear potential pitfalls. Although patients with cardiac dysfunction may fail to respond to fluid loading because of impaired cardiac reserve, peripheral hypovolemia and tissue hypoperfusion may persist, requiring further fluid loading. On the other hand, a patient with intact heart function may respond to fluid loading even if tissue perfusion has been restored. Given that tissue hypoperfusion is one of the key pathogenetic features of organ dysfunction sepsis and septic shock (3), hemodynamic interventions-fluid resuscitation included-should target tissue perfusion. Doing so, macrocirculatory parameters, such as those discussed by the authors, exhibit a notoriously weak association with tissue perfusion in critically ill patients (4). Accordingly, a clinical study reported that changes in MAP and cardiac index failed to predict microcirculatory changes in response to early fluid resuscitation in severe sepsis. The predictive value of both variables to foresee improvements in microcirculatory flow was only marginally better than flipping a coin (area under the receiver operating characteristic curve for MAP and cardiac index: 0.51 and 0.62, respectively). Interestingly, only changes in lactate levels were related to microcirculatory but not macrocirculatory changes (5). If tissue hypoperfusion is the problem, why not consider tissue perfusion as the end point for fluid resuscitation? As summarized in a recent review (6), several (experimental) devices may help the clinician to quantify tissue perfusion. From a clinical point of view, however, assessment of skin perfusion (e.g., by examination of skin temperature and capillary refill time) may be used as a sensitive, easy, cheap, and readily available means to evaluate peripheral volemia and tissue perfusion and guide volume loading at the bedside. Considering that the skin hosts the highest density of vasoconstrictor hormone receptors (7), it is the first of all organs where vasoconstriction occurs and peripheral hypovolemia can be noted. With few exceptions (e.g., serious hypothermia/hyperthermia, arterial occlusive disease), cold and mottled skin reflects relevant vasoconstriction and can serve as an early indicator of reduced systemic blood flow due to hypovolemia or reduced cardiac pump function. If fluid resuscitation with or without inotropic support has reestablished peripheral perfusion and signs of tissue hypoperfusion persist (e.g., oliguria or elevated lactate) (8), other hemodynamic interventions, such as vasopressor infusion, are indicated. Mats Dahlqvist Walter R. Hasibeder Martin W. Dünser

Searching for mechanisms that matter in early septic acute kidney injury: an experimental study

IntroductionIn almost half of all sepsis patients, acute kidney injury (AKI) develops. However, the pathobiologic differences between sepsis patients with and without AKI are only poorly understood. We used a unique opportunity to examine dynamic inflammatory, renal hemodynamic, and microvascular changes in two clinically relevant large-animal models of sepsis. Our aim was to assess variability in renal responses to sepsis and to identify both hemodynamic and nonhemodynamic mechanisms discriminating individuals with AKI from those in whom AKI did not develop.MethodsThirty-six pigs were anesthetized, mechanically ventilated, and instrumented. After a recovery period, progressive sepsis was induced either by peritonitis (n = 13) or by continuous intravenous infusion of live Pseudomonas aeruginosa (n = 15). Eight sham operated-on animals served as time-matched controls. All animals received standard intensive care unit (ICU) care, including goal-directed hemodynamic management. Before, and at 12, 18, and 22 hours of sepsis, systemic and renal (ultrasound flow probe) hemodynamics, renal cortex microcirculation (laser Doppler), inflammation (interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), oxidative stress (thiobarbituric acid reactive species (TBARS), nitrite/nitrate concentrations (NOx), and renal oxygen kinetics and energy metabolism were measured.ResultsIn 14 (50%) pigs, AKI developed (62% in peritonitis, 40% in bacteria infusion model). Fecal peritonitis resulted in hyperdynamic circulation, whereas continuous bacteria infusion was associated with normodynamic hemodynamics. Despite insults of equal magnitude, comparable systemic hemodynamic response, and uniform supportive treatment, only those pigs with AKI exhibited a progressive increase in renal vascular resistance. This intrarenal vasoconstriction occurred predominantly in the live-bacteria infusion model. In contrast to AKI-free animals, the development of septic AKI was preceded by early and remarkable inflammatory response (TNF-α, IL-6) and oxidative stress (TBARS).ConclusionsThe observed variability in susceptibility to septic AKI in our models replicates that of human disease. Early abnormal host response accompanied by subsequent uncoupling between systemic and renal vascular resistance appear to be major determinants in the early phase of porcine septic AKI. Nonuniform and model-related renal hemodynamic responses that are unpredictable from systemic changes should be taken into consideration when evaluating hemodynamic therapeutic interventions in septic AKI.

Pulmonary Artery Catheter for Coronary Artery Bypass Graft

Pulmonary Artery Catheter for Coronary Artery Bypass Graft

A Systematic Review and Meta-Analysis on the Use of Preemptive Hemodynamic Intervention to Improve Postoperative Outcomes in Moderate and High-Risk Surgical Patients

Complications from major surgery are undesirable, common, and potentially avoidable. The long-term consequences of short-term surgical complications have recently been recognized to have a profound influence on longevity and quality of life in survivors. In the past 30 years, there have been a number of studies conducted attempting to reduce surgical mortality and morbidity by deliberately and preemptively manipulating perioperative hemodynamics. Early studies had a high control-group mortality rate and were criticized for this as being unrepresentative of current practice and raised opposition to its implementation as routine care. We performed this review to update this body of literature and to examine the effect of changes in current practice and quality of care to see whether the conclusions from previous quantitative analyses of this field remain valid. Randomized clinical trials evaluating the use of preemptive hemodynamic intervention to improve surgical outcome were identified using multiple methods. Electronic databases (MEDLINE, EMBASE, and the Cochrane Controlled Clinical Trials register) were screened for potential trials, reference lists of identified trials were examined, and additional sources were sought from experts and industry representatives. Identified studies that fulfilled the entry criteria were examined in full and subjected to quantifiable analysis, subgroup analysis, and sensitivity analysis where possible. There were 29 studies identified, 23 of which reported surgical complications. In total, the 29 trials involved 4805 patients with an overall mortality of 7.6%. The use of preemptive hemodynamic intervention significantly reduced mortality (pooled odds ratio [95% confidence interval] of 0.48 [0.33-0.78]; P = 0.0002) and surgical complications (odds ratio 0.43 [0.34-0.53]; P < 0.0001). Subgroup analysis showed significant reductions in mortality for studies using a pulmonary artery catheter, supranormal resuscitation targets, studies using cardiac index or oxygen delivery as goals, and the use of fluids and inotropes as opposed to fluids alone. By contrast, there was a significant reduction in morbidity for each of the 4 subgroups analyzed. The use of a preemptive strategy of hemodynamic monitoring and coupled therapy reduces surgical mortality and morbidity.

Should we target blood pressure in sepsis?

To review blood pressure targets and their implementation in sepsis. Review of the hemodynamic intervention trials in sepsis. Explicit blood pressure targets have been recommended for septic patients. The Surviving Sepsis Guidelines recommend vasopressors to achieve and maintain a mean arterial blood pressure of at least 65 mm Hg in patients not responding to initial fluid resuscitation. Patients remaining hypotensive despite efforts to increase blood pressure have up to twice as high mortality as those whose hypotension can be corrected with fluids and vasopressors. The actual blood pressure targets and their implementation are the main determinants of the patient's exposure to vasopressors. Several randomized controlled trials on hemodynamic interventions in septic shock show that patients continue to receive vasopressors despite the fact that blood pressure targets have been exceeded, and thus vasopressors should be reduced. Accordingly, patients are likely to be exposed to higher amounts of vasopressors and over longer periods of time than would be necessary if the predefined targets would be strictly implemented. Post hoc analyses suggest that in patients without refractory hypotension, the cumulative vasopressor load is independently associated with mortality. Accordingly, reduction of exposure to vasopressors has the potential of improving outcomes. This can be achieved by adhering to the lower currently proposed blood pressure limits. In addition, the lowest tolerable blood pressure levels should be reevaluated.

Heart Failure With Preserved Ejection Fraction in Outpatients With Unexplained Dyspnea: A Pressure-Volume Loop Analysis

The aim of the present study was to diagnose heart failure with preserved ejection fraction (HFPEF) in outpatients with unexplained chronic dyspnea and to elucidate its underlying mechanisms in this population using invasive pressure-volume loop analysis. The diagnosis of HFPEF in stable outpatients with unexplained dyspnea is difficult. Thirty patients (age 67 +/- 8.6 years, 27% males) with preserved left ventricular (LV) ejection fraction (>50%) and unexplained chronic New York Heart Association functional class II to III dyspnea underwent heart catheterization. Patients with significant coronary artery stenosis (>50%) were excluded. Pressure-volume loops were assessed using a conductance catheter at rest, hand-grip exercise, leg lifting, and nitroprusside and dobutamine infusion. Twenty (66%) patients showed LV end-diastolic pressure >16 mm Hg (HFPEF), whereas the remaining 10 patients served as controls. Patients with HFPEF had significantly higher end-diastolic stiffness (0.205 +/- 0.074 vs. 0.102 +/- 0.017, p < 0.001) at rest, and their end-diastolic pressure-volume relationship showed a consistent upward and leftward shift during all hemodynamic interventions compared with controls. Regarding the underlying mechanism of HFPEF, 14 (70%) patients had markedly increased end-diastolic stiffness, which was considered a sufficient single pathology to induce increased LV end-diastolic pressure. Four (20%) patients showed a concomitant presence of moderately increased stiffness and severe LV dyssynchrony, and the remaining 2 (10%) patients, with normal stiffness, showed significant exercise-induced mitral regurgitation at hand-grip exercise. If the invasive pressure measurements were absent, only 5 (25%) of the outpatients with HFPEF fulfilled the European Society of Cardiology definition of HFPEF. A significant proportion of stable outpatients with unexplained chronic dyspnea may have HFPEF. In the patients whom we studied, increased LV stiffness, dyssynchrony, and dynamic mitral regurgitation were the major mechanisms underlying development of HFPEF.

An adaptive transfer function for deriving the aortic pressure waveform from a peripheral artery pressure waveform

We developed a new technique to mathematically transform a peripheral artery pressure (PAP) waveform distorted by wave reflections into the physiologically more relevant aortic pressure (AP) waveform. First, a transfer function relating PAP to AP is defined in terms of the unknown parameters of a parallel tube model of pressure and flow in the arterial tree. The parameters are then estimated from the measured PAP waveform along with a one-time measurement of the wave propagation delay time between the aorta and peripheral artery measurement site (which may be accomplished noninvasively) by exploiting preknowledge of aortic flow. Finally, the transfer function with its estimated parameters is applied to the measured waveform so as to derive the AP waveform. Thus, in contrast to the conventional generalized transfer function, the transfer function is able to adapt to the intersubject and temporal variability of the arterial tree. To demonstrate the feasibility of this adaptive transfer function technique, we performed experiments in 6 healthy dogs in which PAP and reference AP waveforms were simultaneously recorded during 12 different hemodynamic interventions. The AP waveforms derived by the technique showed agreement with the measured AP waveforms (overall total waveform, systolic pressure, and pulse pressure root mean square errors of 3.7, 4.3, and 3.4 mmHg, respectively) statistically superior to the unprocessed PAP waveforms (corresponding errors of 8.6, 17.1, and 20.3 mmHg) and the AP waveforms derived by two previously proposed transfer functions developed with a subset of the same canine data (corresponding errors of, on average, 5.0, 6.3, and 6.7 mmHg).

Cardiac Output and Left Atrial Pressure Monitoring by Right Ventricular Pressure Waveform Analysis for Potential Implantable Device Application

A well-tested and safe implantable device is now available for long-term ambulatory monitoring of the right ventricular pressure (RVP) waveform of congestive heart failure patients. However, cardiac output (CO) and left atrial pressure (LAP) are more useful for assessing cardiac function and managing volume status. We developed a new technique to estimate relative CO change and LAP by long time interval analysis of the RVP waveform. To demonstrate feasibility, we performed four chronic canine experiments in which the RVP waveform and accurate reference measurements were simultaneously recorded during common hemodynamic interventions. The overall root-mean-squared-errors of the estimated relative CO change and LAP were 16.0% and 2.0 mmHg. For comparison, the corresponding errors for the previously proposed intra-beat RVP waveform analysis techniques were 21% and 160% higher. With further successful testing, the new technique may potentially be employed with an established implantable device for chronic monitoring of essential hemodynamic variables.

An evaluation of serial blood lactate measurement as an early predictor of shock and its outcome in patients of trauma or sepsis

Context:Attainment of hemodynamic parameters to within a normal range may leave patients in compensatory shock. In such patients, serial blood lactate evaluation can be useful in predicting shock.Aims:To ascertain the role of serum lactate as a predictor of shock and its outcome in patients of trauma and sepsis.Settings and Design:A prospective, non-interventional study.Materials and Methods:The study included 50 patients (5 to 60 years old) of trauma admitted within 12 hours of injury and patients of suspected or proven sepsis. Those with chronic medical illnesses, alcohol intoxication, or poisoning were excluded. Blood lactate levels were analyzed at admission and 12, 24, and 36 hours of inclusion with records of corresponding hemodynamic variables, investigations, and interventions. The outcome was recorded as survival or non-survival.Statistical Analysis Used:Statistical analysis was done with a student's t test and repeated measure ANOVA (Analysis of Variance).Results:An analysis revealed higher mean lactate levels in non-survivors as compared with survivors. Mean lactate levels in non-survivors did not attain normal levels, while that of survivors reached normal levels by 24 hrs in trauma patients and 36 hrs in sepsis patients. The predicted mortality rates by a lactate level >40 mg/dl at admission, 12, 24, and 36 hours were 52.6%, 61.5%, 83.3%, and 100%, respectively for both the subgroups combined. Non-survivors had a higher incidence of MODS (Multi Organ Dysfunction Syndrome).Conclusions:Serial lactate values followed over a period of time can be used to predict impending complications or grave outcome in patients of trauma or sepsis. Interventions that decrease lactate values to normal early may improve chances of survival and can be considered effective therapy. Lactate values need to be followed for a longer period of time in critical patients.

Continuous cardiac output and left atrial pressure monitoring by long time interval analysis of the pulmonary artery pressure waveform: proof of concept in dogs

We developed a technique to continuously (i.e., automatically) monitor cardiac output (CO) and left atrial pressure (LAP) by mathematical analysis of the pulmonary artery pressure (PAP) waveform. The technique is unique to the few previous related techniques in that it jointly estimates the two hemodynamic variables and analyzes the PAP waveform over time scales greater than a cardiac cycle wherein wave reflections and inertial effects cease to be major factors. First, a 6-min PAP waveform segment is analyzed so as to determine the pure exponential decay and equilibrium pressure that would eventually result if cardiac activity suddenly ceased (i.e., after the confounding wave reflections and inertial effects vanish). Then, the time constant of this exponential decay is computed and assumed to be proportional to the average pulmonary arterial resistance according to a Windkessel model, while the equilibrium pressure is regarded as average LAP. Finally, average proportional CO is determined similar to invoking Ohm's law and readily calibrated with one thermodilution measurement. To evaluate the technique, we performed experiments in five dogs in which the PAP waveform and accurate, but highly invasive, aortic flow probe CO and LAP catheter measurements were simultaneously recorded during common hemodynamic interventions. Our results showed overall calibrated CO and absolute LAP root-mean-squared errors of 15.2% and 1.7 mmHg, respectively. For comparison, the root-mean-squared error of classic end-diastolic PAP estimates of LAP was 4.7 mmHg. On future successful human testing, the technique may potentially be employed for continuous hemodynamic monitoring in critically ill patients with pulmonary artery catheters.

Balloon Compression as Treatment for Refractory Vaginal Hemorrhage

Severe vaginal hemorrhage is a rare presenting condition but serious life threat in the emergency department (ED). Initial management has historically been limited to vaginal packing, fluid resuscitation, and emergency surgical intervention. An alternative approach to therapy is presented that can be effectively deployed in the ED. In the present case, balloon compression of the vaginal mucosa was successful in arresting life-threatening hemorrhage. The patient survived subsequent hemodynamic stabilization and surgical intervention and was ultimately discharged home.

Estimation of the Aortic Pressure Waveform and Beat-to-Beat Relative Cardiac Output Changes From Multiple Peripheral Artery Pressure Waveforms

We introduce a patient- and time-specific technique to estimate the clinically more relevant aortic pressure (AP) waveform and beat-to-beat relative changes in cardiac output (CO) from multiple peripheral artery pressure (PAP) waveforms distorted by wave reflections. The basic idea of the technique is to first estimate the AP waveform by applying a new multichannel blind system identification method that we have developed (rather than the conventional generalized transfer function) to the PAP waveforms and then estimate the beat-to-beat proportional CO by fitting a Windkessel model to the estimated waveform in which wave distortion should be attenuated. We present an evaluation of the technique with respect to four swine datasets including simultaneous measurements of two peripheral AP waveforms, a reference AP waveform, and reference aortic flow probe CO during diverse hemodynamic interventions. Our results show an overall AP waveform error of 3.5 mmHg and an overall beat-to-beat CO error of 12.9% (after a single CO calibration in each animal). These estimation errors represent substantial improvements compared to those obtained with several alternative PAP waveform analysis techniques. With further successful testing, the new technique may ultimately be employed for automated and less invasive monitoring of central hemodynamics in various cardiovascular patients.

Non-invasive Cardiac Output by Transthoracic Electrical Bioimpedence in Post-cardiac Surgery Patients: Comparison with Thermodilution Method

Thoracic electrical bioimpedance (TEB) cardiac output (CO) is being explored increasingly as a non-invasive alternative to the pulmonary artery catheter (PAC). This study compared TEB-CO measured using a new instrument--NICOMON (Larsen & Toubro Ltd. India) with thermodilution (Td) CO in post-cardiac surgery patients. Postoperative cardiac surgical patients requiring a PAC for their management were studied. TEB-CO was measured by passing a 4 mA RMS alternating current across the chest and measuring the analog bioimpedence across the thorax. Kubicek equation was used to estimate TEB-CO. Td-CO was measured using a PAC. Bland-Altman analysis was used to compare paired data. One hundred and ninety-seven pairs of CO measurements were made by the two methods among 35 patients. Mean TEB-CO was 5.15 +/- 1.27 l/min and mean Td-CO was 5.22 +/- 1.28 l/min. Pearson correlation coefficient (r) for these measurements was 0.856 (P < 0.01), with bias -0.0651 l and precision: +/-1.37 l/min. The percentage error of measurement of this precision was 26.44%. Cardiac index also correlated among the two methods (r = 0.789; P = 0.01). Thoracic electrical bioimpedance cardiac output compares favorably with thermodilution method among post-cardiac surgery patients. Further studies are indi- cated with this instrument to validate its efficacy in various clinical situations and utility in monitoring hemodynamic interventions.

Kardiovaskuläres Versagen in der Sepsis

Besides adequate and early antimicrobial therapy, goal-directed haemodynamic in-terventions are crucial for survival of severe sepsis and septic shock. Although cardiac output often is restored in the early phase of sepsis syndrome significant left- and right ventricular impairment may already be present. Clinical presentation, invasive blood pressure tracing and echocardiographic evaluation are pivotal for early recognition, diagnosis and monitoring of therapeutic interventions.

Transient Left Ventricular Dysfunction After Percutaneous Patent Ductus Arteriosus Closure in Children

Background and Objectives: The goal of this study was to assess changes in left ventricular (LV) function and to identify pre-closure factors associated with LV dysfunction {fractional shortening (FS) below 29%} after transcatheter patent ductus arteriosus (PDA) closure. Subjects and Methods: Forty-three pediatric patients with PDAs underwent cardiac catheterization for hemodynamic studies and intervention. Doppler echocardiography was performed at pre-closure, post-closure, and follow-up. Results: S’ and A’ of the septum and mitral annulus were significantly decreased at post-closure and follow-up, respectively. In five of eight patients with Qp/Qs ratios over 1.60 and Pp/Ps ratios over 0.32 at pre-closure, the FS was decreased below 29% at post-closure. Qp/Qs ratio over 1.60 and Pp/Ps ratio over 0.32 at pre-closure had a sensitivity of 86% and a specificity of 84% for predicting FS to be below 29% at post-closure. Conclusion: Larger amounts of pre-closure left-to-right shunting and higher pulmonary artery pressure were associated with an increased likelihood of FS <29% after closure. The results of this study suggest that serial assessments of ventricular function are needed after PDA occlusion in patients with high Qp/Qs and Pp/Ps ratios. (Korean Circ J 2008;38:596-600)

The influence of systemic hemodynamics and oxygen transport on cerebral oxygen saturation in neonates after the Norwood procedure

Ischemic brain injury is an important morbidity in neonates after the Norwood procedure. Its relationship to systemic hemodynamic oxygen transport is poorly understood. Sixteen neonates undergoing the Norwood procedure were studied. Continuous cerebral oxygen saturation was measured by near-infrared spectroscopy. Continuous oxygen consumption was measured by respiratory mass spectrometry. Pulmonary and systemic blood flow, systemic vascular resistance, oxygen delivery, and oxygen extraction ratio were derived with measurements of arterial, and superior vena cava and pulmonary venous gases and pressures at 2- to 4-hour intervals during the first 72 hours in the intensive care unit. Mean cerebral oxygen saturation was 66% +/- 12% before the operation, reduced to 51% +/- 13% on arrival in the intensive care unit, and remained low during the first 8 hours; it increased to 56% +/- 9% at 72 hours, still significantly lower than the preoperative level (P < .05). Postoperatively, cerebral oxygen saturation was closely and positively correlated with systemic arterial pressure, arterial oxygen saturation, and arterial oxygen tension and negatively with oxygen extraction ratio (P < .0001 for all). Cerebral oxygen saturation was moderately and positively correlated with systemic blood flow and oxygen delivery (P < .0001 for both). It was weakly and positively correlated with pulmonary blood flow (P = .001) and hemoglobin (P = .02) and negatively correlated with systemic vascular resistance (P = .003). It was not correlated with oxygen consumption (P > .05). Cerebral oxygen saturation decreased significantly in neonates during the early postoperative period after the Norwood procedure and was significantly influenced by systemic hemodynamic and metabolic events. As such, hemodynamic interventions to modify systemic oxygen transport may provide further opportunities to reduce the risk of cerebral ischemia and improve neurodevelopmental outcomes.

Blind identification of the aortic pressure waveform from multiple peripheral artery pressure waveforms

We have developed a new technique to estimate the clinically relevant aortic pressure waveform from multiple, less invasively measured peripheral artery pressure waveforms. The technique is based on multichannel blind system identification in which two or more measured outputs (peripheral artery pressure waveforms) of a single-input, multi-output system (arterial tree) are mathematically analyzed so as to reconstruct the common unobserved input (aortic pressure waveform) to within an arbitrary scale factor. The technique then invokes Poiseuille's law to calibrate the reconstructed waveform to absolute pressure. Consequently, in contrast to previous related efforts, the technique does not utilize a generalized transfer function or any training data and is therefore entirely patient and time specific. To demonstrate proof of concept, we have evaluated the technique with respect to four swine in which peripheral artery pressure waveforms from the femoral and radial arteries and a reference aortic pressure waveform from the descending thoracic aorta were simultaneously measured during diverse hemodynamic interventions. We report that the technique reliably estimated the entire aortic pressure waveform with an overall root mean squared error (RMSE) of 4.6 mmHg. For comparison, the average overall RMSE between the peripheral artery pressure and reference aortic pressure waveforms was 8.6 mmHg. Thus the technique reduced the RMSE by 47%. As a result, the technique also provided similar improvements in the estimation of systolic pressure, pulse pressure, and the ejection interval. With further successful testing, the technique may ultimately be employed for more precise monitoring and titration of therapy in, for example, critically ill and hypertension patients.