Mixed Venous Saturation Research Articles

Risk modeling for ventricular assist device support in post-cardiotomy shock

BackgroundPost-cardiotomy shock (PCS) has a complex etiology. Although treatment with inotrops and intra-aortic balloon pump (IABP) support improves cardiac performance, end-organ injuries are common and lead to prolonged ICU stay, extended hospitalization and increased mortality. Early consideration of mechanical circulatory support may prevent such complications and improve outcome. MethodsBetween January 1997 and January 2002, 321 patients required IABP and inotropic support for PCS following coronary artery bypass grafting (CABG) at our institution. Perioperative variables including age, mixed venous saturation (MVO2), inotropic requirements and LV function were analyzed using multivariate statistical methods. All explanatory variables with a univariate p value <0.10 were entered into a stepwise logistic regression model to predict hospital mortality. Odds ratios from significant variables (p<0.05) in the regression model were used to compose a risk score. ResultsOverall hospital mortality was 16%. The independent risk factors for mortality in this population were: MVO2<60% (OR=3.2), milrinone>0.5μg/kg/min (OR=3.2), age>75 (OR=2.7), adrenaline>0.1μg/kg/min (OR=1.5). A 15-point risk score was developed based on the regression model. Hospital mortality in patients with a score >6 was 46% (n=13/28), 3–6 was 31% (n=9/29) and <3 was 11% (n=29/264). ConclusionsA significant proportion of patients with PCS continue to face high mortality despite IABP and inotropic support. Advanced age, heavy inotropic dependency and poor oxygen delivery all predicted increased risk for death. Further investigation is needed to assess whether early institution of VAD support could improve outcome in this high-risk group of patients.

Effects of arterial oxygen tension and cardiac output on venous saturation: a mathematical modeling approach

OBJECTIVES:Hemodynamic support is aimed at providing adequate O2 delivery to the tissues; most interventions target O2 delivery increase. Mixed venous O2 saturation is a frequently used parameter to evaluate the adequacy of O2 delivery.METHODS:We describe a mathematical model to compare the effects of increasing O2 delivery on venous oxygen saturation through increases in the inspired O2 fraction versus increases in cardiac output. The model was created based on the lungs, which were divided into shunted and non-shunted areas, and on seven peripheral compartments, each with normal values of perfusion, optimal oxygen consumption, and critical O2 extraction rate. O2 delivery was increased by changing the inspired fraction of oxygen from 0.21 to 1.0 in steps of 0.1 under conditions of low (2.0 L.min-1) or normal (6.5 L.min-1) cardiac output. The same O2 delivery values were also obtained by maintaining a fixed O2 inspired fraction value of 0.21 while changing cardiac output.RESULTS:Venous oxygen saturation was higher when produced through increases in inspired O2 fraction versus increases in cardiac output, even at the same O2 delivery and consumption values. Specifically, at high inspired O2 fractions, the measured O2 saturation values failed to detect conditions of low oxygen supply.CONCLUSIONS:The mode of O2 delivery optimization, specifically increases in the fraction of inspired oxygen versus increases in cardiac output, can compromise the capability of the “venous O2 saturation” parameter to measure the adequacy of oxygen supply. Consequently, venous saturation at high inspired O2 fractions should be interpreted with caution.

Abstract 16642: Clinical Outcomes and Improved Survival in Patients With Protein Losing Enteropathy After the Fontan Operation

Background: Patients (pts) with protein losing enteropathy (PLE) following the Fontan operation (op) have a reported 50% mortality at 5 years (yrs) post diagnosis. We review our clinical outcomes in this pt population. Methods: From 1997 to 2010, 42 pts (55% M) with PLE following the Fontan op were identified from clinical databases. Data were collected by retrospective chart review. Results: Mean age at PLE diagnosis was 18.9 yrs + 11 (4.7-57.9 yrs) and initial Fontan op was 10.1 yrs + 10.8 (1.8-37.6 yrs). Mean time from Fontan op to PLE diagnosis was 8.4 yrs + 14.2 (30 days-27yrs). Types of Fontan op included: atriopulmonary connection (28, 67%), lateral tunnel or intraatrial conduit (6, 14%), or extracardiac conduit (8, 19%). Mean time from diagnosis to last follow-up was 8 yrs + 6 (1-22yrs). Survival was 88% at 5 yrs. There were 11 deaths, mean age 32 yrs + 7.7 (22-47 yrs). Mean time interval from diagnosis to death was 7.5 yrs + 5.4 (1-18yrs). Causes of death include: sepsis (7), complications after Fontan conversion (1), and unknown (3). Decreased survival was seen in pts with high Fontan pressure (mean &gt;15mmHg, p=0.04), decreased ventricular function (EF &lt; 55%, p=0.03), and NYHA class &gt;2 at diagnosis (p=0.04). Pts who died had higher pulmonary vascular resistance (3.8 + 1.6 WU vs 2.1 + 1.1 WU, p=0.017), lower cardiac index (1.6 L/min/m 2 + 0.4 vs 2.7 L/min/m 2 + 0.7, p&lt;0.0001), and lower mixed venous saturation (53% versus 66%, p=0.01) compared to survivors. All factors were obtained at initial PLE diagnosis. Pts treated with medical therapy only (n=15) resulted in symptomatic improvement in 7 pts (47%), no improvement in 5 (33%), and death in 3 (20%). Pts treated with medical + surgical/interventional catheterization procedures (n=27) resulted in symptomatic improvement in 10 pts (37%), no improvement in 9 (33%), and death in 8 (30%). Treatments used more in survivors included spironolactone (21, 68%), octreotide (7, 21%), sildenafil (6, 19%), fenestration creation (15, 48%), and relief of Fontan obstruction (7, 23%). Of the 31 survivors, 17 pts remain well-controlled. Conclusions: PLE remains difficult to treat, but in the current era, survival has improved with advances in treatment. Further study is needed to understand the mechanism of disease and ideal treatment strategy.

Near-infrared spectroscopy as a hemodynamic monitor in critical illness

Near-infrared spectroscopy has moved from a research tool to a widely used clinical monitor in the critically ill pediatric patient over the last decade. The physiological and clinical evidence supporting this technology in practice is reviewed here. A search of MEDLINE and PubMed was conducted to find validation studies, controlled trials, and other reports of near-infrared spectroscopy use in children and adults in the clinical setting. Guidelines published by the American Heart Association, the American Academy of Pediatrics, and the International Liaison Committee on Resuscitation were reviewed including further review of references cited. The biophysical properties of near-infrared spectroscopy devices allow measurement of capillary-venous oxyhemoglobin saturation in tissues a few centimeters beneath the surface sensor with validated accuracy in neonates, infants, and small patients. The biologic basis for the relationship of capillary-venous oxyhemoglobin saturation to cerebral injury has been described in animal and human studies. Normal ranges for cerebral and somatic capillary-venous oxyhemoglobin saturation have been described for normal newborns and infants and children with congenital heart disease and other disease states. The capillary-venous oxyhemoglobin saturation from both cerebral and somatic regions has been used to estimate mixed venous saturation and to predict biochemical shock, multiorgan dysfunction, and mortality in different populations. The relationship of cerebral capillary-venous oxyhemoglobin saturation to neuroimaging and functional assessment of outcome is limited but ongoing. Although there are numerous conflicting reports in small populations, expert opinion would suggest that special use may exist for near-infrared spectroscopy in patients with complex circulatory anatomy, with extremes of physiology, and in whom extended noninvasive monitoring is useful. Class II, level B evidence supports the conclusion that near-infrared spectroscopy offers a favorable risk-benefit profile and can be effective and beneficial as a hemodynamic monitor for the care of critically patients.

A bovine hemoglobin-based oxygen carrier as pump prime for cardiopulmonary bypass: Reduced systemic lactic acidosis and improved cerebral oxygen metabolism during low flow in a porcine model

Cerebral ischemia can occur during cardiopulmonary bypass, especially during low flow. HBOC-201 (OPK Biotech, Cambridge, Mass) is a hemoglobin-based oxygen-carrying solution that enhances oxygen delivery. This project evaluated the benefits on total body and cerebral oxygen delivery and consumption using HBOC-201 during cardiopulmonary bypass. Twelve immature swine were assigned to one of 2 groups. One group used HBOC-201 in pump prime, and the other used donor porcine blood. Cardiopulmonary bypass was initiated and then flow was serially decreased from 100% to 75%, to 50%, and then back to full flow. At each interval, (15)O positron emission tomographic analysis was performed, and blood was collected. Total body and cerebral oxygen delivery and consumption were calculated. Statistical analysis was performed with a Tukey-Kramer adjusted P value based on a repeated measures linear model on log-transformed data. Total and plasma hemoglobin levels were higher in the HBOC-201 group. Oxygen delivery and consumption were not statistically different but did tend to be higher in the HBOC-201 group. Mixed venous saturation was lower in the HBOC-201 group but not significant. Mild metabolic acidosis with increased lactate levels developed in the blood group. Mean cerebral blood flow decreased in both groups when total flow was 50%. In the HBOC-201 group cerebral oxygen metabolism was maintained. The addition of HBOC-201 for cardiopulmonary bypass appears to improve oxygen use and minimize anaerobic metabolism. Cerebral oxygen use was preserved in the HBOC-201 group, even during decrease in blood flow. These findings support the reported improved oxygen-unloading properties of HBOC-201 and might provide a benefit during cardiopulmonary bypass.

Improved survival in patients with inoperable chronic thromboembolic pulmonary hypertension

Patients with inoperable chronic thromboembolic pulmonary hypertension (Inop-CTEPH) treated with conventional therapy have a poor survival. We compare the 3-year survival between those treated with conventional therapy and those treated with conventional therapy and a combination of novel drugs. We also evaluate the clinical course. A total of 34 Inop-CTEPH consecutive patients were evaluated from 1991 to 2009 including right heart catheterization (RHC) and perfusion lung scan (PLS): 7 underwent surgical treatment while 27 were confirmed inoperable. Of these 27 patients, 12 evaluated from 1991 to 2003 (Group 1) were treated with conventional therapy and 15 evaluated from 2004 to 2009 (Group 2) were treated with conventional and novel therapies. At baseline, no group difference emerged at RHC. Based on clinical course, novel drugs and oxygen supplementation were given to patients of Group 2. Seven of these who had worse clinical course repeated RHC and four of them also PLS during therapy. Those without repeat RHC had baseline pulmonary artery mean pressure and brain natriuretic peptide (NT-proBNP) lower and mixed venous saturation (SvO2) and exercise test higher (p=0.022, 0.015, 0.044 and 0.003, respectively). During therapy, those with repeat RHC had total pulmonary vascular resistance reduced (p=0.012), base excess increased (p=0.002) and significant redistribution of pulmonary blood flow at PLS. At the 3-year follow-up, survival was 86% in Group 2 and 31% in Group 1 (p=0.031). In Inop-CTEPH patients, the clinical course may help to select drugs and the level of oxygen supply that can improve hemodynamics, gas exchange and long-term survival.

Selected Abstracts Presented at the 21st Meeting of The European Society for Computing and Technology in Anaesthesia and Intensive Care (ESCTAIC)

SELECTED ABSTRACTS PRESENTED AT THE 21ST MEETING OF THE EUROPEAN SOCIETY FOR COMPUTING AND TECHNOLOGY IN ANAESTHESIA AND INTENSIVE CARE (ESCTAIC) Amsterdam, The Netherlands, 6th–9th October, 2010 Edited by: A. A. van Dusseldorp, C. Boer, D. S. Karbing, L. Krummreich, S. E. Rees, S. A. Loer LIST OF ABSTRACTS Soraya Abbasi: The Role of Physiological Models in Critiquing Mechanical Ventilation Treatments Gracee Agrawal: Real-time Detection of Suppression in EEG Christa Boer: Clinical Experience with Perioperative Non-invasive Beat-to-beat Arterial Blood Pressure Monitoring Nadja Bressan: Infusion Rate Control Algorithm for Target Control Infusion using Optimal Control Chih-Yen Chiang: Rule-based Evaluation for the Patientcontrolled Analgesia Clinical Effectiveness Wolfgang Friesdorf: Professional Design of Clinical Working Systems According to Human Factors Fred de Geus: CAROLA: An Open Source PDMS, After 25 Years Still Experimental? Yori Gidron: The Effects of Stress and Hemispheric Lateralization on Managerial Decisions Johan Groeneveld: Value of Central or Mixed Venous O2 Saturation in Guiding Treatment in the Intensive Care Unit Gabriel M. Gurman: Professional Stress and the Anesthesiologist-how Evident is it? Eliahu Heldman: Salivary Cortisol as a Measure of Professional Stress; An Overview and a Description of a Study with Paramedics Martin Hurrell: Implementation of a Standards-based, CDA-Compliant Anesthesia Record Mathieu Jeanne: Analgesia Nociception Index Online Computation and Preliminary Clinical Test During Cholecystectomy Under Remifentanil-Propofol Anaesthesia Christian Jeleazcov: Pharmacodynamic Modeling of Changes in Pulse Waveform During Induction of Propofol Anaesthesia in Volunteers: Comparison between Invasive and Continuous Non-invasive Measurements of Pulse Pressure Pierre Kalfon: Assessing Performances of Glucose Control Algorithms on a set of Virtual ICU Patients Cor Kalkman: Automation and Automation Surprises: Lessons from Aviation. Should Health Care Brace Itself. Dan S Karbing: Use of the INVENT System for Standardized Quantification of Clinical Preferences Towards Mechanical Ventilator Settings Talma Kushnir: Moods and Burnout Among Physicians: Associations with Prescribing Medications Communicating with Patients, and Referrals for Specialists and Diagnostic Tests Johannes J van Lieshout: Non-invasive Pulse Contour Cardiac Output by Nexfin Technol Egbert Mik: Monitoring Mitochondrial Oxygenation Journal of Clinical Monitoring and Computing (2011) 25:3–43 DOI: 10.1007/s10877-011-9276-2 Springer 2011

H-FABP in Pre Capillary Pulmonary Hypertension: Comparison to Other Surrogate Parameters for Prediction of Severity and Outcome

Background: Heart-type fatty acid-binding protein (H-FABP) is a promising novel biomarker for risk stratification of patients with chronic thromboembolic pulmonary hypertension (CTEPH). Whether disease severity in a group of patients with pre capillary pulmonary hypertension (PH) can be predicted by determination of plasma H-FABP levels remains unknown. Methods: 41 consecutive patients with a mean (±SD) age of 60.6 ± 2.1 years and severe PH were studied with a mean follow up to 541 days (95% CI: 420; 661 days). H-FABP, but also the biomarkers NT-Pro-BNP and big-endothelin (Big-ET1), were correlated to parameters derived from right sided cardiac catheterization and cardio-pulmonary exercise test. Results: At baseline H-FABP levels ranged from 620 to 15200 pg/ml (3648 ± 502 pg/ml) and were weakly but significantly correlated to VO2AT (r = –0.37, p = 0.04) and VO2 peak (r =–0.38, p = 0.03). However, invasively measured hemodynamic parameters of PH and right ventricular dysfunction did not correlate with H-FABP levels. In- terestingly, moderate to high correlations between H-FABP and NT-Pro-BNP (r = 0.51, p = 0.01) and Big-ET1 (r = 0.65, p = 0.01) and between Big-ET1 and NT-Pro-BNP (r = 0.5, p = 0.01) could be observed. In contrast to H-FABP, NT-Pro-BNP, and even more Big-ET1, showed significant correlations to different invasively measured hemodynamic parameters of the disease indicating severity and consequently prognosis of severe pre-capillary pulmonary hypertension. However, in a multivariate Cox regression analysis, PVR, mixed venous oxygen saturation and the VE/VCO2 slope (>60) as well as the heart rate recovery within one minute (HRR) but none of the biomarkers were identified as independent factors of poor prognosis. In con- trast, peak workload and mixed venous saturation were identified as risk markers in the idiopathic pulmonary arterial hypertension subgroup. Conclusions: In contrast to the predictive value of H-FABP in CTEPH H-FABP fails to be a reliable marker in PH or to be a novel predictor of mid and long term outcome. The data suggest that an increased slope of VE/VCO2 and a decreased extent of HRR within one minute represent more promising diagnostic non invasive parameters.

ICU survival and the central to mixed venous oxygen difference

We read with interest the recent study on central venous saturation (ScvO2) and mixed venous saturation (SvO2) in 53 patients with severe sepsis [1]. For several reasons, however, we feel the authors' broadly stated conclusion that 'a positive (ScvO2 - SvO2) value is not associated with improved outcome' is unwarranted. First, in Figure 3 of their paper, graphing the number of measurements rather than the number of subjects is counterintuitive; your readers may find the latter a more clinically useful metric. The meaning of the columns is obscure because a single subject can contribute measurements to both columns (less than and greater than zero). Second, the total number of measurements depicted in each Figure 3 column is crucial information, but is not provided. After physically measuring the height of the columns, we estimate 278 total measurements, rather than 265 as noted in the text. Third, we question how the P-value (P = 0.13) for a total population can be numerically equal to the lowest P-value of two constituent groups of similar size. Finally, the authors should consider acknowledging the possibility of a type II error when stating their conclusion. Specifically, if the total number of measurements were doubled, keeping the proportions the same, the P-value would decrease to 0.08 (Chi square with Pearson's correlation). If tripled, then the P-value becomes P < 0.0001. We welcome new studies on survival and (ScvO2 - SvO2) difference, and do not believe the current study casts doubt on our finding [2] that a positive difference is strongly associated with survival.

Neurohumoral and inflammatory markers for prediction of right ventricular failure after implantation of a left ventricular assist device

Implantation of a left ventricular assist device (LVAD) is an established treatment for end-stage heart failure. Right ventricular dysfunction develops in 20%-50% of patients after device implantation, leading to prolonged hospital stays and elevated mortality rates. However, prediction of right ventricular failure remains difficult. A total of 40 patients who received an LVAD for chronic end-stage heart failure between May 2001 and December 2002 were evaluated. The patients were divided retrospectively into two groups: group I (n = 26), with no apparent postoperative right ventricular failure; and group II (n = 14), with right ventricular failure after implantation defined by the presence of two of the following criteria during the first week after surgery: mean arterial pressure ≤ 55 mmHg, central venous pressure ≥ 16 mmHg, mixed venous saturation ≤ 55%, cardiac index <2 l/min/m(2), inotropic support score >20 units or an apparent need for mechanical right ventricular support. Hemodynamic, echocardiographic, neurohumoral, and inflammatory parameters were evaluated 24 h before implantation of the LVAD. Levels of procalcitonin, neopterin, n-terminalpro-brain natriuretic peptide, and big endothelin-1 were significantly lower in group I: 0.106 vs. 0.322 ng/ml, P = 0.048; 10.5 vs. 20.7 ng/ml, P = 0.018; 6322 vs. 17174 pg/ml, P = 0.032; 1.6 vs. 19.5 pg/ml, P = 0.02, respectively. Levels of creatinine kinase and creatinine were significantly lower in group I than in group II: 24 vs. 40 U/l, P = 0.034; 1.3 vs. 2.3 mg/dl, P = 0.008, respectively. Preoperative evaluation of markers of inflammation and neurohumoral activation may provide additional information for predicting right ventricular failure after implantation of an LVAD.

SvO2 to monitor resuscitation of septic patients: let's just understand the basic physiology

Real-time monitoring of mixed venous oxygen blood saturation (SvO2) or of central venous oxygen blood saturation is often used during resuscitation of septic shock. However, the meaning of these parameters is far from straightforward. In the present commentary, we emphasize that SvO2 - a global marker of tissue oxygen balance - can never be simplistically used as a marker of preload responsiveness, which is an intrinsic marker of cardiac performance. In some septic shock patients, because of profound hypovolemia or myocardial dysfunction, SvO2 can be low but obviously cannot alone indicate whether a fluid challenge would increase cardiac output. In other patients, because of a profound impairment of oxygen extraction capacities, SvO2 can be abnormally high even in patients who are still able to respond positively to fluid infusion. In any case, other reliable dynamic parameters can help to address the important question of fluid responsiveness/unresponsiveness. However, whether fluid administration in fluid responders and high SvO2 would be efficacious to reduce tissue dysoxia in the most injured tissues is still uncertain.

Cardiac Output Assessed by Invasive and Minimally Invasive Techniques

Cardiac output (CO) measurement has long been considered essential to the assessment and guidance of therapeutic decisions in critically ill patients and for patients undergoing certain high-risk surgeries. Despite controversies, complications and inherent errors in measurement, pulmonary artery catheter (PAC) continuous and intermittent bolus techniques of CO measurement continue to be the gold standard. Newer techniques provide less invasive alternatives; however, currently available monitors are unable to provide central circulation pressures or true mixed venous saturations. Esophageal Doppler and pulse contour monitors can predict fluid responsiveness and have been shown to decrease postoperative morbidity. Many minimally invasive techniques continue to suffer from decreased accuracy and reliability under periods of hemodynamic instability, and so few have reached the level of interchangeability with the PAC.

Peripheral Circulatory Features during High-Frequency Jet Ventilation

The paper gives the results of a study of peripheral circulatory features during high-frequency jet ventilation (HFJV). The main specific features of peripheral circulation and oxygen transport during HFJV are formulated on the basis of a study of cardiac output (impedance cardiography), peripheral vascular resistance, peripheral vascular blood filling (photoplethysmogram analysis), adaptive peripheral blood flow reactions (spectral analysis of peripheral vascular pulsation). HFJV gives rise to the peculiar pattern of peripheral hemodynamics and tissue gas exchange, which is characterized by higher oxygen uptake without a decrease in mixed venous blood saturation, with normal extraction coefficient and preserved low peripheral vascular resistance. During HFJV, unlike traditional ventilation, the main peripheral hemodynamic feature is the increased capillary bed blood volume caused by the blood flow involvement of reserve capillaries under control of volume (parasympathetic) regulation of adaptive peripheral hemodynamic reactions. Key words: high-frequency jet ventilation, oxygen transport, peripheral hemodynamics.

Efeitos hemodinâmicos e metabólicos da movimentação passiva dos membros inferiores em pacientes sob ventilação mecânica

Limb movements, passively performed by a physiotherapist, have been shown to result in significant increases in critically ill patients' metabolic and hemodynamic variables. This study objective was to determine whether passive cycling leg movement increases hemodynamic and metabolic variables in sedated mechanical ventilation dependent patients. Five sedated mechanical ventilation dependent patients in a 18-bed intensive care unit of a university hospital were evaluated. Passive cycling leg movements were performed for 10min at a 30 movements/min rate. Complete hemodynamical data were recorded and arterial and mixed venous blood sample were collected 5 minutes before and after 5 minutes after the maneuver completion. All patients had increased oxygen consumption (VO2). The VO2 increase occurred with a concomitant drop in mixed venous blood saturation (SvO2), likely from both oxygen extraction ratio (O2ER) and cardiac index (CI) increase. passive cycling leg movements may influence hemodynamical and metabolic status in sedated mechanical ventilation-dependent patients.

Patient Directed Bypass: Cooling for Aortic Surgery – A Preliminary Concept

No consensus exists as to the temperature to cool to on bypass for surgery involving the aortic arch. Excluding normothermic surgery, which is rarely performed for arch work, circulatory arrest, anterograde, and retrograde cerebral perfusion either in isolation or in combination remain the techniques of “cerebral protection.” To date, no account of individual patient body or cerebral function variation is involved. Utilizing an electronic perfusion database we retrospectively analyzed 10 patients undergoing aortic arch work with regard to mixed venous saturations during cooling. Perfusion related variables were registered and uploaded to www.perfsort.net. We regarded a saturation of 100% as being indicative of no oxygen extraction, implying no metabolic activity—the theoretical goal prior to a circulatory arrest period. There is enormous variation in the temperature at which metabolic activity of the body stops. We had a range from 17–25 degrees. Patients were cooled for an average of 6 (SD 3.4) degrees below which oxygen extraction had ceased to occur. Potentially we are adding 111 minutes (SD 62) of unnecessary bypass time. This may imply that excessive cooling is occurring in some individuals undergoing arch surgery. Patient directed cooling for aortic arch surgery may help to reduce the morbidity/physical insult associated with severe hypothermia. This work is very preliminary but may help us to depart from the one size fits all paradigm that exists in current clinical practice. Correlation with bispectral index, electroencephalogram monitoring and neurological outcomes is needed.

Exercise Testing and Training in Children With Congenital Heart Disease

The primary function of the cardiopulmonary system is to provide blood flow (and oxygen) in quantities sufficient to support the metabolic needs of the body. The capacity of the cardiopulmonary system to fulfill this function is maximally stressed when an individual's metabolic rate is increased, a condition that occurs most commonly during physical activity/exercise. A number of physiological changes accompany and facilitate the accommodation of the circulatory system to the hemodynamic demands of exercise (Figure 1). In normal individuals, these changes (which during upright exercise include a tripling of the resting heart rate, a >60% reduction in systemic and pulmonary vascular resistance, and a >50% increase in stroke volume) can ultimately produce a >5-fold increase in cardiac output. The increase in cardiac output is accompanied by enhanced ventricular preload (as the ventricles move up their Starling curves to accommodate the increased workload), a doubling of systolic and mean pulmonary artery pressures (most of the increase in pulmonary artery pressures is due to the concomitant rise in left-sided filling pressures; the increase in transpulmonary pressure gradient is relatively small), and a more modest increase in systemic arterial pressures.1,–,4 Figure 1. Some of the physiological changes that accompany and facilitate the accommodation of the circulatory system to the hemodynamic demands of exercise. RAp indicates right atrial pressure; LAp, left atrial pressure; PVR, pulmonary vascular resistance; SVR, systemic vascular resistance; PAp, pulmonary artery pressure; and AOp, aortic pressure. Congenital heart disease (CHD) may, in a variety of ways and to a variable extent, adversely affect these hemodynamic adaptations. For instance, patients with a Fontan procedure lack a pulmonary ventricle. They therefore cannot increase their pulmonary blood flow and pressures normally (and consequently cannot maintain their ventricular preload and systemic blood flow) during exercise.5 Patients with tetralogy of Fallot and …

E0597 Serum HDL-C levels correlated with the haemodynamic and severity in patients with idiopathic pulmonary arterial hypertension

AimsAlthough dyslipidemia was an established risk factor for cardiovascular disease, its role in the pathogenesis of pulmonary arterial hypertension (PAH) is still unclear. The aims of the current study were...

Impaired Systemic Oxygen Extraction During Exercise in Heart Failure with Preserved Ejection Fraction

Predictable increases in arteriovenous oxygen content difference C(a-v)O2 during exercise in normal individuals and in patients with heart failure with reduced left ventricular ejection fraction (HFrEF) permits estimation of cardiac output (CO[est]) during exercise by the Fick principle (i.e. CO = VO2/C(a-v)O2). Heart failure with preserved ejection fraction (HFpEF) is a common cause of unexplained dyspnea for which accurate non-invasive estimation of exercise CO would be desirable. However, it is unknown whether estimated C(a-v)O2 accurately reflects measured C(a-v)O2 in HFpEF. PURPOSE: To determine if peak exercise C(a-v)O2 is normal and can be used to accurately predict exercise CO(f) in patients with HFpEF. Methods: Simultaneous Fick CO (CO[f]), cardiac filling pressures, arterial blood gases, hemoglobin levels (Hb), and respiratory gas exchange parameters were measured at one-minute intervals during incremental cardiopulmonary exercise testing in 47 patients with HFrEF (Age 61±12, LVEF 34±10%) and 103 patients with HFpEF (Age 58±15yrs, LVEF 64±8%), as defined by rest PCWP>15 mmHg or exercise PCWP>20 mmHg. Estimates of C(a-v)O2 were derived from assuming a normal mixed venous O2Hb saturation at maximal exercise of 24% with an arterial oxygen saturation of 96%, for which C(a-v)O2 = [Hb]×1.34×(0.96-0.24). Conveniently, 1.34×(0.96-0.24). 1, making it possible to divide peak VO2 by [Hb] to derive CO[est]. The actual oxygen saturation achieved during exercise was substituted for the 96% value if oxygen saturation fell below 96%. RESULTS: Patients with HFpEF had similar arterial O2 content to patients with HFrEF (17.9±2.4ml/dl vs. 18.6±2.5ml/dl, P=0.1) but extracted oxygen less avidly during exercise, as evidenced by higher CvO2 content at peak exercise (6.0±1.5 vs. 4.7±1.5ml/dl, respectively, P<0.0001) and higher mixed venous saturations (35±5% vs. 26±8%, P<0.0001). As a result, peak VO2/Hb underestimated CO[f] (i.e. COest = 0.85*(CO[f]) + 0.66). There was a strong correlation between CO[est] and CO[f] in HFpEF (R=0.94, P<0.001) and in HFrEF (R=0.95, P<0.001, Figure). CONCLUSIONS: Patients with HFpEF consistently extract oxygen less avidly at peak exercise than patients with HFrEF, but in both populations measurement of peak VO2, hemoglobin concentration, and oxygen saturation can be utilized to closely approximate invasively measured peak exercise Fick cardiac output.

Refinement of a Novel Empirical Formula to Determine the “True” Mixed Venous Saturation in Patients Undergoing Veno-Venous Extracorporeal Life Support

Veno-venous extracorporeal life support (vvECLS) is an important treatment methodology for adult respiratory failure and complex airway reconstruction. However, the supplemental oxygen provided to the venous circulation artificially raises the observed mixed venous saturation (SvO(2)), thereby eliminating its utility in evaluating the match between oxygen delivery and consumption in the critically ill patient. We previously developed an equation to calculate the "true" or native SvO(2) (NSvO(2)) but recently recognized that the prior model failed to account for both coronary sinus venous return and asymmetric return of venous sources to either the right heart or the ECLS circuit. A more complete model of venous return in the setting of vvECLS was developed to illustrate flow sources and vectors. From these diagrams, a series of equations for blood flow and oxygen content were developed. Using algebraic rearrangements, a more precise formula for the calculation of NSvO(2) was determined. Assuming the following representations: Fc = circuit flow, SatV(5) = circuit arterial oxygen saturation (expressed as a fraction of 1), CSvO(2) = circuit venous oxygen saturation, PAPO(2) = partial pressure of oxygen in the pulmonary artery, PO(2)V(5a) = partial pressure of oxygen in the circuit outflow, and CO = cardiac output,(Equation is included in full-text article.)Refinement of a previously published equation for the calculation of native mixed venous saturation in the setting of veno-venous extracorporeal life support may allow improved evaluation of the value of interventions to improve oxygen delivery.

Should blood flow during cardiopulmonary bypass be individualized more than to body surface area?

Blood flow during cardiopulmonary bypass (CPB) is calculated on body surface area (BSA). Increasing comorbidity, age and weight of today's cardiac patients question this calculation as it may not reflect individual metabolic requirement. The hypothesis was that a measured cardiac index (CI) prior to normothermic CPB is a better estimate. A cross-over study, with random allocation to CPB blood flow for 20 minutes based on either a calculation (2.4 L/min/m(2)) or on CI, with a switch to the opposite flow for another 20 minutes, was performed. Twenty-two elective cardiac surgery patients with normal ventricular function were included. Effect parameters were cerebral oxygenation, mixed venous saturation and arterial lactate. CI varied from 1.9 to 3.1 L/min/m(2) (median 2.4 L/min/m(2)). No differences in effect parameters were seen. In conclusion, a CPB blood flow based on an individual estimate did not improve cerebral and systemic oxygenation compared to a blood flow based on BSA.