Thermodilution right ventricular ejection fraction. Catheter positioning effects

Behaviour and stability of thermodilution signals in a closed extracorporeal circuit: a bench study

Thermodilution is the gold standard for cardiac output measurement in critically ill patients. Its application in extracorporeal therapy is limited, as a portion of the thermal indicator is drawn into the extracorporeal circuit. The behaviour of thermodilution signals in extracorporeal circuits is unknown. We investigated thermodilution curves within a closed-circuit and assessed the impact of injection volume, flow and distance on the behaviour of the thermodilution signals and catheter constants. We injected 3, 5, 7 and 10 ml of thermal indicator into a heated closed circuit. Thermistors at distances of 40, 60, 80, and 100 cm from the injection port recorded the thermodilution signals (at flow settings of 0.5, 1, 1.5, and 2 L/min). Area under the curve (AUC), rise time, exponential decay and catheter constants were analysed. Linear mixed-effects models were used to evaluate the impact of circuit flow, distance and injection volume. Catheter positioning did not influence AUC (78 injections). Catheter constants were independent of flow, injection volume or distance to the injection port. The distance to the injection port increased peak temperature and rise time and decreased exponential time constant significantly. The distance to the injection port did not influence catheter constants, but the properties of the thermodilution signal itself. This may influence measurements that depend on the exponential decay of the thermodilution signal such as right ventricular ejection fraction.

Assessment of Right Heart Function during Extracorporeal Therapy by Modified Thermodilution in a Porcine Model

BACKGROUND

Veno-arterial extracorporeal membrane oxygenation therapy is a growing treatment modality for acute cardiorespiratory failure. Cardiac output monitoring during veno-arterial extracorporeal membrane oxygenation therapy remains challenging. This study aims to validate a new thermodilution technique during veno-arterial extracorporeal membrane oxygenation therapy using a pig model.

METHODS

Sixteen healthy pigs were centrally cannulated for veno-arterial extracorporeal membrane oxygenation, and precision flow probes for blood flow assessment were placed on the pulmonary artery. After chest closure, cold boluses of 0.9% saline solution were injected into the extracorporeal membrane oxygenation circuit, right atrium, and right ventricle at different extracorporeal membrane oxygenation flows (4, 3, 2, 1 l/min). Rapid response thermistors in the extracorporeal membrane oxygenation circuit and pulmonary artery recorded the temperature change. After calculating catheter constants, the distributions of injection volumes passing each circuit were assessed and enabled calculation of pulmonary blood flow. Analysis of the exponential temperature decay allowed assessment of right ventricular function.

RESULTS

Calculated blood flow correlated well with measured blood flow (r2 = 0.74, P < 0.001). Bias was -6 ml/min [95% CI ± 48 ml/min] with clinically acceptable limits of agreement (668 ml/min [95% CI ± 166 ml/min]). Percentage error varied with extracorporeal membrane oxygenation blood flow reductions, yielding an overall percentage error of 32.1% and a percentage error of 24.3% at low extracorporeal membrane oxygenation blood flows. Right ventricular ejection fraction was 17 [14 to 20.0]%. Extracorporeal membrane oxygenation flow reductions increased end-diastolic and end-systolic volumes with reductions in pulmonary vascular resistance. Central venous pressure and right ventricular ejection fractions remained unchanged. End-diastolic and end-systolic volumes correlated highly (r2 = 0.98, P < 0.001).

CONCLUSIONS

Adapted thermodilution allows reliable assessment of cardiac output and right ventricular behavior. During veno-arterial extracorporeal membrane oxygenation weaning, the right ventricle dilates even with stable function, possibly because of increased venous return.

EDITOR’S PERSPECTIVE

The Right Ventricle During Selective Lung Ventilation for Thoracic Surgery

The right ventricle (RV) has been an area of evolving interest after decades of being ignored and considered less important than the left ventricle. Right ventricular dysfunction/failure is an independent predictor of mortality and morbidity in cardiac surgery; however, very little is known about the incidence or impact of RV dysfunction/failure in thoracic surgery. The pathophysiology of RV dysfunction/failure has been studied in the context of acute respiratory distress syndrome (ARDS), cardiac surgery, pulmonary hypertension, and left ventricular failure, but limited data exist in literature addressing the issue of RV dysfunction/failure in the context of thoracic surgery and one-lung ventilation (OLV). Thoracic surgery and OLV present as a unique situation where the RV is faced with sudden changes in afterload, preload, and contractility throughout the perioperative period. The authors discuss the possible pathophysiologic mechanisms that can affect adversely the RV during OLV and introduce the term RV injury to the myocardium that is affected adversely by the various intraoperative factors, which then makes it predisposed to acute dysfunction. The most important of these mechanisms seems to be the role of intraoperative mechanical ventilation, which potentially could cause both ventilator-induced lung injury leading to ARDS and RV injury. Identification of at-risk patients in the perioperative period using focused imaging, particularly echocardiography, is paramount. The authors also discuss the various RV-protective strategies required to prevent RV dysfunction and management of established RV failure.

Inotropes Improve Right Heart Function in Patients Undergoing Aortic Valve Replacement for Aortic Stenosis

The administration of inotropes after aortic valve replacement (AVR) for aortic stenosis (AS) is controversial. Issues include the risk of left ventricular (LV) systolic outflow obstruction (LVOTO) and the proper treatment of diastolic dysfunction for patients in whom LV systolic function is often preserved and subsequently improved. In this study, we assessed the hemodynamic benefits of inotropes for patients undergoing AVR for AS. Thirty-four patients were prospectively randomized to one of three groups: epinephrine, milrinone, or placebo. Hemodynamic and echocardiographic data were obtained before and immediately after cardiopulmonary bypass (CPB). Data were also obtained before and after increases in ventricular preload to assess the effects of inotropes on diastolic function. The use of inotropes was associated with significantly larger increases in right ventricular (RV) (placebo, 0.5%; epinephrine, +9%; milrinone, +8%; P < 0.01) and LV (placebo, +7%; epinephrine, +18%; milrinone, +20%; P = 0.07) ejection fractions (EF) and cardiac output after CPB. Changes in cardiac output and index were more strongly correlated with changes in RVEF (r = 0.56, P < 0.01; r = 0.47, P < 0.01, respectively) than with LVEF (r = 0.22, r = 0.08). Of all patients receiving epinephrine or milrinone, only one (1 of 22) had a decrease in RVEF, whereas 6 of 12 patients receiving placebo had a reduction in RVEF from pre-CPB to post-CPB. Correspondingly, for LVEF, 1 of 22 patients receiving inotropes had a decrease in LVEF, whereas 3 of 12 placebo patients had a reduction in LVEF from pre-CPB to post-CPB. No patient had evidence of LVOTO. Inotropes improved hemodynamics after AVR for AS. This was attributable more to improved RV function than to changes in LV function. Although there were no changes in diastolic function, it is possible that this study did not allow significant timing to observe benefits of inotropes on diastolic function in this setting.

IMPLICATIONS

Compared with placebo, both epinephrine and milrinone similarly improved biventricular performance after aortic valve replacement, with a greater impact on right ventricular function. Choice of either inotropic drug should be driven by blood pressure and hemodynamic goals in this setting.

Prognostic usefulness of the tricuspid annular plane systolic excursion in patients with congestive heart failure secondary to idiopathic or ischemic dilated cardiomyopathy

The prognostic value of ultrasound evaluation of right ventricular (RV) performance in patients with congestive heart failure (CHF) is still a matter of investigation. We studied 140 consecutive patients with chronic CHF and a left ventricular ejection fraction <35%. All patients underwent a complete echocardiographic evaluation that systematically included the measurement of the tricuspid annular plane systolic excursion (TAPSE). During a follow-up period of 24 +/- 14 months, 45 patients died and 7 underwent emergency heart transplantation. At the multivariate survival analysis (Cox regression model) backward stepwise selection identified a prognostic model with 2 parameters: New York Heart Association (NYHA) class III or IV and TAPSE < or =14 mm (p <000). In a subgroup of 97 patients in sinus rhythm in whom mitral inflow Doppler variables could be measured, survival was further analyzed according to a model in which the significant parameters were included in the same order as usually used in routine clinical practice: clinical variables first, left ventricular function data second, mitral Doppler variables third, and indexes of right ventricular (RV) function last. TAPSE < or =14 mm added significant (p <0.03) prognostic information to NYHA class III or IV, left ventricular ejection fraction of <20%, and mitral deceleration time of < 125 ms. In conclusion, in patients with CHF, TAPSE adds significant prognostic information to the NYHA clinical classification, to the echocardiographic evaluation of left ventricular function, and to mitral Doppler variables. Furthermore, the measurement of TAPSE is easy to obtain in all patients, irrespective of heart rate and rhythm.

Assessment of Right Ventricular Function

In contrast to studies suggesting that the right ventricle (RV) often functions primarily as a conduit for blood flow from the venous circulation to the lungs, recent data show that the chamber plays a major role in maintenance of global cardiovascular homeostasis un der many conditions. Accordingly, clinicians involved with the perioperative care of surgical patients must be familiar with factors influencing RV performance. Com prised of two embryologically distinct regions, the inflow and outflow tracts, the crescent-shaped RV exhib its characteristics of filling and contraction that are different from those of the left ventricle (LV). Further more, although the basic determinants of ventricular function (rate and rhythm, preload, afterload, and con tractility) are the same for both the LV and RV, the relative contribution of each determinant to overall function of each chamber is somewhat different. This review approaches assessment of RV function from two directions. First, the anatomic and physiological differ ences between the RV and LV are described and used to show why some methods derived for complex character ization of LV function cannot be directly applied to the RV. Second, the application and limitations of methods used for perioperative assessment of RV function are discussed.

Clinical estimation of left and right ventricular volume with open chest compared with transesophageal echocardiography and fast-response thermodilution

OBJECTIVE

A clinical measure--inspection of the relation of the heart (acute margin) to the diaphragm--has shown a strong positive correlation to transesophageal echocardiographic (TEE) determination of left ventricular end-diastolic area (LVEDA) during weaning from cardiopulmonary bypass (CPB). The present study examines the correlation between right ventricular end-diastolic volumes (RVEDV) before and after CPB when using the same clinical measure of left ventricular dimension.

DESIGN

Prospective study.

SETTING

Operating room, university hospital.

PARTICIPANTS

Patients scheduled for elective coronary artery bypass grafting.

INTERVENTIONS

After induction of anesthesia and endotracheal intubation, a transesophageal echo-probe was inserted. A pulmonary artery right ventricular ejection fraction/volumetric TD catheter was placed in the pulmonary artery.

MEASUREMENTS AND MAIN RESULTS

Before going on CPB, a mark was made with cautery at the line of contact between the acute margin and the diaphragm. After CPB, the patients were transfused to the same level. At these two times, TEE recordings of the LVEDA and hemodynamic measurements including calculations of RVEDV were obtained. The LVEDA before and after CPB showed a positive correlation, r = 0.81, p < 0.001. The RVEDV after CPB showed a weak correlation, r = 0.54, p < 0.05, to RVEDV before CPB. There were no significant changes in right ventricular (RV) wall tension calculated as right atrial pressure x RVEDV and pulmonary artery systolic pressure x right ventricular end-systolic volume products. The only significant change regarding hemodynamic parameters was a decrease in mean arterial pressure.

CONCLUSIONS

It is concluded that there is only a weak correlation regarding RVEDV before and after CPB when the patient is transfused to the line of contact, whereas this clinical measure correlates well with LVEDA.

Right ventricular function after coronary artery bypass grafting in patients with and without revascularization of the right coronary artery

OBJECTIVES

To evaluate the influence of revascularization of a stenosis of the right coronary artery on right ventricular function.

DESIGN

Prospective study.

SETTING

Single institutional study in a university hospital.

PARTICIPANTS

20 patients with different degrees of stenosis of the right coronary artery undergoing elective coronary artery bypass grafting.

INTERVENTIONS

In 10 patients, bypass surgery included revascularization of a significant stenosis of the right coronary artery (group 1). In 10 other patients, the pathology of the right coronary artery was judged to be not significant, without indication for revascularization (group 2).

MEASUREMENTS AND MAIN RESULTS

Using the fast-response thermodilution pulmonary artery catheter, right ventricular function was estimated perioperatively. After termination of extracorporeal circulation, there was an increase in right ventricular volumes in group 2 (p < 0.05) and an initial decrease in group 1 (p < 0.05), with higher volumes in group 2 compared with group 1 (p < 0.05). The ejection fraction increased in group 1 (p < 0.05) and decreased in group 2 after operation (p < 0.05), with higher values in group 1 compared with group 2 (p < 0.05). In addition to these findings, the pressure-volume relationship showed a leftward and upward shift in group 1 and a rightward shift in group 2 postoperatively.

CONCLUSIONS

These results indicate that right ventricular depression can occur after bypass grafting in patients with a moderate stenosis of the right coronary artery that is not revascularized. Revascularization of more severe stenosis of the right coronary artery appears to preserve postoperative right ventricular function.

Right ventricular end-diastolic volume as a measure of preload

Right ventricular (RV) end-diastolic volume index (RVEDVI) measured by a modified thermodilution pulmonary artery catheter has been proposed as an improved measure of cardiac preload, compared with pulmonary capillary wedge pressure (PCWP). This study compared the correlation of RVEDVI and PCWP with cardiac index (CI) to determine which parameter better reflected ventricular preload. Modified thermodilution catheters were placed in 38 critically ill patients. Hemodynamic parameters were recorded in these patients at 2- to 4-hour intervals for 1 to 7 days. Complete data sets (1,008) were obtained. Regression analysis was performed comparing PCWP, RVEDVI, RV ejection fraction (RVEF) to CI in the entire group and in individual patients. Because mathematical coupling may exist between RVEDVI and CI, the correlation between these variables was corrected for mathematical coupling using the method described by Stratton. Simple regression analysis of data from all patients, uncorrected for mathematical coupling, yielded a significant correlation between CI and RVEDVI (r = 0.60, p < 0.0001), RVEF (r = 0.37, p < 0.0001), and PCWP (r = 0.01, p < 0.001). Correction for mathematical coupling between RVEDVI and CI resulted in a minor changes of the correlation coefficient to 0.56. In individual patients, a significant, uncorrected correlation (p < 0.05) was found between RVEDVI and CI in 27 of the 38 patients, whereas 11 patients had a significant correlation between PCWP and CI. RVEDVI correlated more closely with CI than did PCWP, even after correlation for mathematical coupling. In both the group as a whole and in individual patients, RVEDVI was a better indicator of cardiac preload.

Evaluation of the clinical usefulness of thermodilution volumetric catheters

OBJECTIVE

To determine if treatment modalities (fluid, inotropes, and blood) would be altered based on preload measurements of right ventricular end-diastolic volume index measured by fast response thermodilution catheter, as compared with pulmonary artery occlusion pressure (PAOP).

DESIGN

A prospective clinical trial.

SETTING

An 11-bed surgical intensive care unit (ICU) at The Queen's Medical Center, an affiliate of the University of Hawaii Surgical Residency program.

PATIENTS

Surgical ICU patients who required pulmonary artery catheters, except those patients with arrhythmias or history of tricuspid valve disease.

INTERVENTIONS

During the first 48 hrs after catheter insertion, hemodynamic data were obtained at least every 4 hrs. Treatment of low preload was initiated only if clinical indications were present. These indications included a mean arterial pressure of < 70 mm Hg, heart rate of > 120 beats/min, urine output of < 40 mL/hr, stroke volume of < 40 mL/m2 with oxygen delivery of < 450 mL/min/m2, and lactic acidosis. Volume infusion was considered if PAOP was < 18 mm Hg and right ventricular end-diastolic volume index was < 140 mL/m2. Treatment was given tohigh preload, defined as a PAOP of > 18 mm Hg to prevent pulmonary edema. When PAOP and right ventricular end-diastolic volume index gave conflicting information, other clinical parameters were assessed to determine treatment.

MEASUREMENTS AND MAIN RESULTS

Twenty-seven patients requiring 70 catheters were evaluated for the study. Thirteen patients with 46 pairs of data points completed the study. Fourteen patients were excluded from analysis due to irregular heart rate, poor quality of cardiac output at the time of volume infusion, or lack of major volume manipulation. PAOP and right ventricular end-diastolic volume index measurements agreed in 42 of 46 instances (PAOP of < 18 mm Hg, right ventricular end-diastolic volume index of < 140 mL/m2), leading to fluid treatment. In one instance, PAOP was > 18 mm Hg, right ventricular end-diastolic volume index was < 140 mL/m2, and the patient had normal blood pressure and good urine output. PAOP was used in this instance as a guide to diurese the patient, which led to improvement of heart rate and stroke volume index. Three measurements in two patients with high intra-abdominal pressure indicated a PAOP of > 18 mm Hg with right ventricular end-diastolic volume index of < 140 mL/m2. A rigid abdomen accompanied hypotension, tachycardia and low urine output. Thus, a fluid bolus was administered, resulting in improved blood pressure, stroke volume, and heart rate. PAOP were obtained at end-expiration. Positive end-expiratory pressure (PEEP) was removed for < 1 sec, if patients were on PEEP > or = 10 cm H2O, to avoid the effects of high intrapleural pressure on PAOP readings. Cardiac output was measured at end-expiration, and stroke volume index and right ventricular end diastolic volume index were derived.

CONCLUSIONS

In this small sample of surgical patients with sepsis, adult respiratory distress syndrome, and hemorrhagic shock (n = 13), the additional information derived from right ventricular end-diastolic volume index did not change treatment in 43 of 46 instances. However, patients with increased intra-abdominal pressures may show misleadingly high PAOP despite low preload. These patients clearly benefitted from the additional information derived from ventricular volume measurements. Additionally, clinicians who are reluctant to take off-PEEP PAOP may also find this catheter useful.

Right ventricular function during weaning from respirator after coronary artery bypass grafting. Comparison of two different weaning techniques

The purpose of this investigation was to determine right ventricular function during weaning from controlled ventilation comparing a biphasic positive airway pressure ventilatory support system (BiPAP [Respironics]) with pressure support ventilation (PSV). In 22 patients following coronary artery bypass grafting, both weaning techniques were used in randomized chronological order for 60 min each. Right ventricular end-systolic (RVESV) and end-diastolic volume (RVEDV) and ejection fraction (RVEF) were evaluated using the fast-response Swan-Ganz catheter. In comparison to PSV, the BiPAP system resulted in a significantly higher mean pulmonary artery pressure (20.6 +/- 5.0 vs 19.3 +/- 4.2 mm Hg, p = 0.0158), pulmonary vascular resistance index (206 +/- 55 vs 181 +/- 61 dyn.s.cm-5.m2, p = 0.0355), RVESV (92.2 +/- 36.3 vs 77.2 +/- 30.4 ml, p = 0.0017), and RVEDV (176.4 +/- 48.5 vs 161.8 +/- 43.3 ml, p = 0.0061), while the RVEF was significantly lower (46.0 +/- 11.9 vs 51.8 +/- 12.4 percent, p = 0.0012). No differences in left ventricular function or arterial blood gas analyses were measured during both study periods. In summary, the RV afterload was higher with the BiPAP system compared with PSV which suggested that this was due to differences in the respiratory support between both weaning modes. Because of the Frank-Starling mechanism, this higher afterload did cause a small but significant increase in RV volumes and a significant decrease in RV ejection fraction with the BiPAP system.

Assessment of right ventricular contractile performance after pulmonary resection

Right ventricular (RV) performance deteriorates after pulmonary resection. The mechanism remains unclear and could be related to changes in loading conditions or contractility. To assess the role of alteration in RV contractility, we developed a simple and reliable means to measure RV contractile performance in adult patients. Using thermodilution methods and rapid volume infusion in the preoperative setting, the relationship between RV stroke work (RVSWI) and end-diastolic volume (RVEDVI), termed the preload recruitable stroke work relation, was plotted using linear regression. Experimental studies have demonstrated that the preload recruitable stroke work relation is a linear and load-insensitive index of RV contractile performance. Our study confirms this finding in adult patients: RVSWI = 0.33 (RVEDVI) - 20.4 (n = 108; r = 0.94; p < 0.01). Examination of RV pump function and hemodynamic parameters in the early postresection period (up to 24 hours postoperatively) revealed significant changes in loading conditions, but isochronal RVEDVI and RVSWI values were within the confidence limits of the preload recruitable stroke work relation. Thus, depressed RV contractility does not appear to play a predominant role in this early postoperative period. Further study in a larger patient population will be required to verify this observation and to assess RV performance beyond 24 hours after resection.

What's new in monitoring the coronary surgery patient?

Monitoring has been extensively reviewed in most textbooks of cardiothoracic surgery and anaesthesia, particularly in the recent textbooks on monitoring edited by Carol L Lake 1 and Casey D Blitt 2 and in the Journal of Clinical Monitoring. Although monitoring properly includes both pre- and postoperative periods, this review will concentrate exclusively on the operative period. I will also concentrate on new approaches or information which relate to more traditional approaches to monitoring. The emphasis in this review will not be on what we can monitor, but rather on what we should monitor. In this regard, I will analyse accuracy and identify sources of error and try to answer the following questions. Does the device or parameter measure (monitor) what we want to know? Does it improve patient outcome and safety? Is it cost-effective? Unfortunately, data are not always available to answer all these questions at present, but hopefully the discussions will make us aware of what we do and do not know, and what we should look for in the near future.

Usefulness of right ventricular indices in early diagnosis of cardiac tamponade

Early diagnosis of postoperative cardiac tamponade is impeded by its clinical similarity to left ventricular failure. Moreover, the hemodynamic changes necessary to diagnose cardiac tamponade are detected by conventional monitoring technique only after clinical compromise. Early signs of cardiac tamponade and left ventricular failure were studied with emphasis on right ventricular function in anesthetized dogs. One group (n = 20) had cardiac tamponade produced by incrementally increasing pericardial pressure (2 to 20 mm Hg), and another group (n = 20) had acute left ventricular failure produced by successive ligation of the anterior descending coronary artery at the lower, middle, and upper thirds. Besides standard hemodynamic measurements, right ventricular function was examined with a rapid-response thermodilution catheter. During cardiac tamponade, cardiac output, right ventricular ejection fraction, right ventricular stroke volume, and right ventricular end-diastolic volume were significantly decreased from baseline values after a pericardial pressure of 8 mm Hg or more (p less than 0.05). Right atrial and pulmonary arterial pressures were not significantly elevated until 14 and 20 mm Hg of pericardial pressure, respectively. Although cardiac function in the left ventricular failure group was reduced after each ligation, right ventricular ejection fraction remained unchanged. This study suggests that right ventricular indices may facilitate earlier diagnosis of cardiac tamponade with greater accuracy.

Retrograde versus antegrade cardioplegia: impact on right ventricular function

Retrograde cardioplegia administered through the coronary sinus has several documented advantages over antegrade cardioplegia but has been thought to provide inadequate right ventricular myocardial protection. We prospectively compared the effects of retrograde and antegrade cardioplegia on right ventricular performance in patients undergoing myocardial revascularization. Two groups of similar age, extent of disease, and preoperative left ventricular ejection fraction received retrograde (n = 16) or antegrade (n = 14) crystalloid cardioplegia. A right ventricular rapid-response thermistor catheter, previously developed and validated in our institution, was used to measure right atrial pressure, pulmonary artery pressure, right ventricular ejection fraction, end-diastolic volume index, and stroke volume index before bypass (baseline) and at several intervals after bypass. There were no differences in cross-clamp time, heart rate, cardiac enzymes, inotrope requirements, or arrhythmias between the two groups. Right ventricular parameters were equivalent in both groups at all time intervals except 30 minutes after bypass, at which time right ventricular end-diastolic volume index was lower (80 +/- 6 versus 93 +/- 6 mL/m2; p less than 0.05) and right ventricular stroke volume index was higher (35 +/- 3 versus 29 +/- 2 mL/m2, p less than 0.05) in the retrograde group compared with the antegrade group, indicating better right ventricular function with retrograde cardioplegia early after bypass. In both groups, right ventricular end-diastolic volume index was higher than baseline (p less than 0.05) during the first 4 hours after bypass. No other important differences were found.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined dose ratios of dopamine and dobutamine and right ventricular performance after cardiac surgery

The effect of combined administration of different dose ratios of dobutamine (DB) and dopamine (DA) (DB/DA ratio of 1:1; 1.5:0.5; 2:0; 0.5:1.5; and 0:2), with the added dose kept constant (10 micrograms/kg/min-20 micrograms/kg/min), on right ventricular function (measured by the thermal washout method with the aid of a rapid-response thermistor) was determined in ten patients after cardiac surgery (between 12 and 24 h after surgery). The following values represent the mean +/- SD of DB only and of the DB/DA-equal combination vs DA only. The DB/DA-equal or DB-dominant combination increased the right ventricular ejection fraction vs DA only (0.39 +/- 0.12 [p less than 0.01] and 0.37 +/- 0.11 [p less than 0.05], respectively, vs 0.32 +/- 0.12) and the stroke volume index (43 +/- 12 ml/m2 [p less than 0.01] and 41 +/- 15 ml/m2, respectively, vs 38 +/- 14 ml/m2) and decreased right ventricular end-diastolic pressure (RVEDP) (10 +/- 4 mm Hg [p less than 0.01] and 11 +/- 4 mm Hg [p less than 0.05], respectively, vs 13 +/- 5 mm Hg) and pulmonary capillary wedge pressure (10 +/- 4 mm Hg [p less than 0.01] and 12 +/- 5 mm Hg [p less than 0.05], respectively, vs 14 +/- 6 mm Hg) to the same degree as DB alone. The DB/DA-equal or DB-dominant combination did not induce tachycardia (heart rate, 105 +/- 11 [p less than 0.05] and 95 +/- 14 beats per minute, respectively, vs 90 +/- 17 beats per minute) or have any effect on the right ventricular end-diastolic volume index (RVEDVI) (115 +/- 30 ml/m2 and 117 +/- 33 ml/m2, respectively, vs 127 +/- 42 ml/m2). Moreover, the diastolic parameters of the right ventricle (the ratio of RVEDVI/RVEDP: 15 +/- 8 [p less than 0.05] and 13 +/- 7, ml/mm Hg/m2, respectively, 11 +/- 5 ml/mm Hg/m2) decreased as the ratio of DA increased. This change in the diastolic properties of the right ventricle might have been caused by release of norepinephrine in the myocardium by DA or by improved coronary perfusion with DB. The DB/DA-equal and DB-dominant combinations were superior to DB or DA alone and to the DA-dominant combination in obtaining enhanced right ventricular performance.

Effect of pulmonary resection on right ventricular function

The effect of pulmonary resection on right ventricular (RV) performance and its possible contribution to morbidity or mortality remain unclear. Using thermodilution methods and a fast-response thermistor positioned in the pulmonary artery, it is now possible to measure RV end-diastolic volume and RV ejection fraction. Using this technique, RV performance during and after major pulmonary resection was studied in 15 patients. Significant RV dysfunction was demonstrated in the postoperative period. Right ventricular end-diastolic volume increased significantly on postoperative day 1 (177 +/- 9 mL) and postoperative day 2 (172 +/- 4 mL) versus early postoperatively (153 +/- 10 mL) (p less than 0.05). By postoperative day 2, RV ejection fraction was significantly decreased (0.36 +/- 0.03) from preoperative (0.45 +/- 0.02) and early postoperative (0.40 +/- 0.01) values (p less than 0.05). Although pulmonary artery pressures rose modestly in the postoperative period, and pulmonary vascular resistance increased by postoperative day 2, pulmonary vascular resistance remained significantly lower or unchanged from baseline values. We speculate that the etiology of the RV dysfunction after pulmonary resection may be multifactorial. Changes in RV afterload or alteration in RV contractility may be factors.

The effects of valvular regurgitation on thermodilution ejection fraction measurements

Through the use of thermodilution principles and rapid response thermistors, it is now possible to measure right ventricular ejection fractions serially in patients. However, to our knowledge, the extent to which tricuspid regurgitation affects the accuracy of thermodilution ejection fraction measurements has not been quantified. The purpose of this study was to compare actual and thermodilution ejection fraction measurements in an in vitro model of tricuspid regurgitation over a wide range of ejection fractions. Stepwise perforation of the inlet valve resulted in regurgitant fractions ranging from 4 to 40 percent. At each increment of inlet valve regurgitation, triplicate sets of thermodilution (EFthermo) ejection fraction measurements were obtained and compared with actual ejection fractions (EFactual). The mean difference between EFactual and EFthermo significantly increased with 8 percent regurgitation and significantly increased with greater increments of inlet valve regurgitation. EFthermo consistently underestimated EFactual over the entire range of regurgitant values. Linear regression analysis revealed a significant correlation between EFactual and EFthermo for all degrees of regurgitation; however, the correlation coefficient significantly declined from control valves with 13 percent regurgitation and declined further with 33 percent regurgitation. Qualitative classification of the inlet valve regurgitation into mild, moderate, and severe regurgitation was performed using pulsed Doppler echocardiography. Mild inlet valve regurgitation resulted in a significantly increased difference between EFactual and EFthermo from control values. A significant increase in the difference between EFactual and EFthermo was observed with both moderate and severe regurgitation. In summary, thermodilution underestimated actual ejection fraction in a direct linear relationship to the degree of inlet valve regurgitation. Thus, in the presence of tricuspid regurgitation, this method may still be useful in serially measuring changes in right ventricular ejection fraction.

In vitro validation of a thermodilution right ventricular ejection fraction method

A thermodilution catheter and computer system has been developed to measure right ventricular ejection fraction and volumes. To evaluate the performance of this method, the thermodilution system was evaluated in an in vitro pulsatile flow model. Thermodilution measurements of ejection fraction (EF), cardiac output (CO), stroke volume (SV), end-diastolic volume (EDV), and end-systolic volume (ESV) were compared with known values in a pulsatile flow bench. Thermodilution EF measurements correlated very well with the pulsatile flow model (r2 = 0.95, m [slope] = 0.85, SEE = 4.0 EFU). Thermodilution CO and SV were highly predictive of actual pulsatile flow (r2 = 0.99, m = 0.99, SEE = 187 ml/min and r2 = 0.98, m = 0.96, SEE = 2.5 ml, respectively). Thermodilution end-diastolic and end-systolic volume measurements resulted in low mean eror, -1.8% and 0.6%, respectively. The standard deviations of the error for EDV and ESV were 11.0% and 16.4%. The thermodilution measurements were repeatable, with CO, SV, and EF coefficients of variation of 3.2%, 3.3%, and 4.7%, respectively. EDV and ESV were slightly more variable, with coefficients of variation of 5.5% and 7.2%, respectively.

In vitro validation of a right ventricular thermodilution ejection fraction system

Right ventricular ejection fraction (RVEF) is used clinically as an index of right ventricular (RV) pump function. Clinical measurements of RVEF are complicated by the need for complex imaging equipment to compute RV volumes. Recently, the use of thermodilution (TD) methods have been suggested as a simplified means to measure RVEF (RVEFTD) in patients using rapid response thermistors. Validation, however, by comparison of RVEFTD and other methods in vivo, is difficult. Accordingly, thermodilution derived EF measurements (EFTD) were compared to known values using an in vitro system, with known ejection fractions (EF) set from 17-78% and stroke rates varying independently from 50-100 strokes/min. EFTD was computed by fitting the downslope of the TD curve to a monoexponential function and computing the time constant of thermal decay. A significant correlation existed between EFTD and actual EF over the entire study (r = 0.96, p less than 0.001). Bias analysis showed that the points were within a 95% confidence interval of +/- 12%. Multivariate analysis showed that stroke rate did not significantly affect TD measurements (r = 0.03, p greater than 0.7). This study demonstrates that TD accurately predicts EF using an in vitro system and appears to be independent of stroke rate. Thus, TD methods may provide an accurate, simple and reliable means to serially measure RVEF in the clinical setting.