Thermodilution Pulmonary Artery Catheter Research Articles

Effect of Pulmonary Artery Pressure on Changes in Right Ventricular Function according to Norepinephrine Infusion in Patients with Valvular Heart Disease

Background: Increasing coronary perfusion pressure by using a vasopressor is one of the important treatment strategies in pulmonary hypertension. In present study, we evaluated whether chronic pulmonary hypertension influences the effect of norepinephrine (NE) on right ventricular function and hemodynamic variables in patients with valvular heart disease. Methods: Forty eight patients undergoing valve replacement surgery were divided into two groups according to pulmonary artery pressure, i.e., a control (n = 28) and a pulmonary hypertension group (n = 20). A thermodilution pulmonary artery catheter for continuous monitoring of cardiac output, right ventricular (RV) ejection fraction and RV volume was inserted before the induction of anesthesia. When systemic hypotension occurred following induction of anesthesia, norepinephrine was infused at rates of 0.03 and then 0.06/kg/min for 10 minutes, respectively and hemodynamic variables were measured after anesthesia induction, and at the end point of each infusion rate. Results: No significant differences occurred in systemic or pulmonary hemodynamic variables according to the infusion of norepinephrine between the two groups. And, no significant changes were observed in right ventricular performance according to the infusion of norepinephrine in two groups. Conclusions: Norepinephrine did not show different systemic or pulmonary hemodynamic effects in patients with or without chronic pulmonary hypertension. Norepinephrine did not increase the right ventricular ejection fractions or cardiac outputs of patients with chronic pulmonary hypertension.

Effects of Lung Volume Reduction Surgery on Left Ventricular Diastolic Filling and Dimensions in Patients With Severe Emphysema

Data on the influence of lung volume reduction surgery (LVRS) on cardiac function and hemodynamics are scarce and controversial. Previous studies have focused mainly on right ventricular function and pulmonary hemodynamics. Here, we evaluated the effects of LVRS on left ventricular (LV) end-diastolic filling pattern, dimensions, stiffness, and performance, as well as pulmonary and systemic hemodynamics. A prospective, open, controlled study. Patients with severe emphysema undergoing LVRS (10 patients). Patients scheduled for pulmonary lobectomy due to carcinoma (ie, the lobectomy group) served as control subjects (10 patients). LV dimensions and mitral flow velocities were measured by transesophageal, two-dimensional, Doppler echocardiography, and central hemodynamics were measured by a pulmonary artery thermodilution catheter. Measurements were performed during anesthesia in the supine position, before and after surgery, without and with passive leg elevation. Baseline cardiac index (CI) [- 21%], stroke volume index (SVI) [- 31%], stroke work index (SWI) [- 26%], and LV end-diastolic area index (EDAI) [- 15%] were significantly (p < 0.001) lower, whereas LV end-diastolic stiffness (LVEDS) did not differ in the LVRS group compared to the lobectomy group. The time from peak early diastolic filling to zero flow (E-dec time) [58%] and the deceleration slope of early diastolic filling (E-dec slope) [45%] were significantly higher (p < 0.01), whereas peak early diastolic filling velocity (E-max) [- 31%; p < 0.01] and the proportion of E-max vs peak late diastolic filling velocity (A-max) [ie, the E/A ratio] (- 27%; p < 0.001) were significantly lower compared to the lobectomy group. LVRS significantly increased CI (40%; p < 0.001), SVI (34%; p < 0.001), SWI (58%; p < 0.001), LV EDAI (18%; p < 0.001), E-max (44%; p < 0.01), A-max (15%; p < 0.05) and E/A ratio (28%; p < 0.01), decreased E-dec time (- 31%; p < 0.05) and E-dec slope (- 98%; p < 0.01), and had no effect on LVEDS. In the lobectomy group, surgery affected none of these variables. LV function is impaired in patients with severe emphysema due to small end-diastolic dimensions. LVRS increases LV end-diastolic dimensions and filling, and improves LV function.

Decreased cardiac output in humans during laparoscopic antireflux surgery: direct measurements.

In a porcine model, we demonstrated that laparoscopic Nissen fundoplication causes a significant drop in cardiac output (30%) because it exposes both the peritoneal cavity and the mediastinum to CO(2) under pressure. To determine if this occurs in humans, we examined cardiovascular physiology during laparoscopic Nissen fundoplication. Because of invasiveness required in this pilot trial, only six patients were studied. The arterial blood pressure (via radial arterial catheter) and the pulmonary artery diastolic pressure and cardiac index (via pulmonary artery thermodilution catheter) were measured at seven points in time during each laparoscopic Nissen fundoplication. The systolic blood pressure decreased in all patients, and the cardiac index decreased in all but one patient. The exception was a patient with Huntington disease, in whom the cardiac output did not decrease. In four of the five patients, the cardiac output was lowest during hiatal dissection, and in the fifth, it was lowest after reverse Trendelenburg positioning. No significant change in the pulmonary artery diastolic pressure was noted. All patients received adequate intravenous fluid replacement (average, 58 +/- 16 mL/kg) to support blood pressure. In one patient, with a particularly large paraesophageal hernia, profound hypotension (40/25 mm Hg) developed during the mediastinal phase of the procedure, and this patient required alpha-adrenergic support followed by laparotomy to eliminate a surgical cause (none found). Although it is a tremendous advance for patients, laparoscopic Nissen fundoplication can be associated with a significant reduction in cardiac output and blood pressure. Surgeons and anesthesiologists must be alert to changes reflecting these decreases during procedures, which violate both the peritoneal cavity and the mediastinum. We propose careful hemodynamic monitoring during these procedures, especially in patients with coronary artery disease or significant left ventricular dysfunction.

Lung perfusion, shunt fraction, and oxygenation during one-lung ventilation in pigs: The effects of desflurane, isoflurane, and propofol

Objective: To study how desflurane, isoflurane, and propofol affect pulmonary perfusion, shunt fraction, and systemic oxygenation during one-lung ventilation (OLV) in vivo. Design: Prospective animal study with a crossover design. Setting: Animal laboratory of a university hospital. Participants: Twelve female pigs. Interventions: The pigs were anesthetized, tracheally intubated, and mechanically ventilated. After placement of femoral arterial and thermodilution pulmonary artery catheters, a left-sided, double-lumen tube (DLT) was placed via tracheotomy. After DLT placement, FIO2 was adjusted at 0.8, and anesthesia was continued in random order with 1 minimal alveolar concentration of desflurane, 1 minimal alveolar concentration of isoflurane, or propofol. Measurements and Main Results: Measurements of respiratory and hemodynamic parameters were made after stabilization at each anesthetic. During OLV, perfusion of the nonventilated lung and shunt fraction were comparable during all 3 anesthetics. PaO2 was lower during desflurane and isoflurane anesthesia as compared with propofol anesthesia. Mixed venous PO2 and cardiac output were lower with desflurane and isoflurane as compared with propofol. Conclusions: In a clinically relevant model of OLV cardiac output, PaO2 and mixed venous PO2 decreased during desflurane and isoflurane as compared with propofol, whereas perfusion of the nonventilated lung and shunt fraction remained comparable. Copyright 2003, Elsevier Science (USA). All rights reserved.

Correlation Between Noninvasive and Invasive Cardiac Index (CI): Utilization of Noninvasive Echocardiographic Doppler-Derived Index of Myocardial Performance (IMP

PURPOSE: Dr Tei described a doppler index for the assessment of global left ventricular performance termed the Index of myocardial performance (IMP). IMP encompasses left ventricular (LV) systolic contraction, ejection, and diastolic relaxation, and is independent of heart rate (HR), and mean blood pressure (MBP). Diminished LV function is associated with prolongation of IMP (>0.55 seconds). Doppler IMP can be utilized to calculate CI noninvasively. The purpose of this study was to assess whether noninvasive post-cardiopulmonary bypass (CPB) derived CI calculated by the equation [CI × IMP {pre-CPB} = CI × IMP {post-CPB} correlated with standard invasive thermodilution pulmonary artery catheter (PAC) derived CI.

The Changes of Right Ventricular Function and Hemodynamic Parameters During Coronary Anastomosis in Beating Heart Surgery

Background: Hemodynamic derangement during the displacement of the beating heart in off-pump coronary artery bypass graft surgery (OPCAB) might be related with right ventricular (RV) dysfunction. This study evaluated the influence of displacing and stabilizing the heart, for the anastomosis of coronary arteries, on hemodynamic alterations and RV function in patients undergoing OPCAB. Methods: Twenty patients with triple vessel coronary artery disease underwent OPCAB using single pericardial sutures: a tissue stabilizer was included. The hemodynamic variables and right ventricular ejection fraction (RVEF) were obtained using a right-heart ejection fraction thermodilution pulmonary artery catheter after the induction of anesthesia, before and after anastomosis of each coronary artery and after sternal closure. Results: No significant hemodynamic changes were observed during the displacement of the heart or the placement of a stabilizer on all of the coronary arteries, except the obtuse marginal artery (OM) before anastomosis. RVEF, left ventricular stroke work index (LVSWI), stroke volume index and cardiac index (CI) decreased and mean pulmonary artery pressure increased significantly whist positioning the graft to the OM. Right ventricular volumes were not significantly changed, although central venous pressure and pulmonary capillary wedge pressure increased. Changing CI had a close relationship with LVSWI ( = 0.537, P ＜ 0.05) but not with RVEF ( = 0.118). These hemodynamic compromises recovered to baseline values after sternal closure. Conclusions: The displacement of the beating heart for positioning during anastomosis of the graft to the OM caused significant hemodynamic instability and LV functional changes in addition to RV functional changes seemed to be responsible for hemodynamic derangements.

Pathophysiological responses following phosgene exposure in the anaesthetized pig.

This study aimed to develop a reproducible model of phosgene-induced lung injury in the pig to facilitate the future development of therapeutic strategies. Ten female young adult large white pigs were used. Following induction of anaesthesia using a halothane/oxygen/nitrous oxide mixture, arterial and venous catheters were inserted together with a pulmonary artery thermodilution catheter, and a suprapubic urinary catheter by laparotomy. Anaesthesia was maintained throughout the experiment by intravenous infusion of ketamine, midazolam and alfentanil. On completion of surgery the animals were allowed to equilibrate for 1 h and then were divided into two groups. Group 1 (n = 5) was exposed to phosgene for 10 min (mean Ct = 2443 +/- 35 mg min m(-3)) while spontaneously breathing, whereas control animals (Group 2 n = 5) were exposed to air. At 30 min post-exposure, anaesthesia was deepened in order to allow the initiation of intermittent positive pressure ventilation and the animals were monitored for up to 24 h. Cardiovascular and respiratory parameters were monitored every 30 min and blood samples were taken for arterial and mixed venous blood gas analysis and clinical chemistry. A detailed post-mortem and histopathology was carried out on all animals following death or euthanasia at the end of the 24-h monitoring period. Control animals (Group 2) all survived until the end of the 24-h monitoring period with normal pathophysiological parameters. Histopathology showed only minimal passive congestion of the lung. Following exposure to phosgene (Group 1) there was one survivor to 24 h, with the remainder dying between 16.5 and 23 h (mean = 20 h). Histopathology from these animals showed areas of widespread pulmonary oedema, petechial haemorrhage and bronchial epithelial necrosis. There was also a significant increase in lung wet weight/body weight ratio (P < 0.001). During and immediately following exposure, a transient decrease in oxygen saturation and stroke volume index was observed. From 6 h there were significant decreases in arterial pH (P < 0.01), P(a)O(2) (P < 0.01) and lung compliance (P < 0.01), whereas oxygen delivery and consumption was reduced from 15 h onwards in phosgene-exposed animals. Mean pulmonary artery pressure of phosgene-exposed animals was increased from 15 h post-exposure, with periods of increased pulmonary vascular resistance index being recorded from 9 h onwards. We have developed a reproducible model of phosgene-induced lung injury in the anaesthetized pig. We have followed changes in cardiovascular and pulmonary dynamics for up to 24 h after exposure in order to demonstrate evidence of primary acute lung injury from 16 h post-exposure. Histopathology showed evidence of widespread damage to the lung and there was also a significant increase in lung wet weight/body weight ratio (P < 0.001).

Comparison of continuous, stat, and intermittent cardiac output measurements in patients undergoing minimally invasive direct coronary artery bypass surgery

Objective: To compare intermittent cardiac output (ICO) with continuous cardiac output (CCO) and stat cardiac output (SCO) measurements in patients undergoing minimally invasive direct coronary artery bypass (MIDCAB) surgery. Design: Prospective, clinical study. Setting: Single, tertiary referral center. Participants: Twenty adult patients undergoing off-pump MIDCAB surgery from January through June 2000. Interventions: Each patient had a 7.5F 5-lumen pulmonary artery thermodilution catheter (CCO catheter, Baxter Healthcare Corporation, Irvine, CA) inserted for measurement of cardiac output (CO). ICO, CCO, and SCO were compared at 10 predefined time points. Results: A total of 400 data pairs for CO were obtained. ICO values ranged from 1.8 to 8.4 L/min; CCO, 1.9 to 7.5 L/min; and SCO, 2.25 to 6.35 L/min. Correlation between ICO and CCO was significant (correlation coefficient, r = 0.78, p < 0.001), accompanied by a bias of −0.095 L/min and precision of 0.729 L/min. Similarly, the correlation between ICO and SCO was significant (r = 0.79, p < 0.001), accompanied by good accuracy (bias, 0.084 L/min) and precision (0.843 L/min). There were statistically significant decreases in mean arterial pressure, CO, cardiac index, stroke volume, stroke volume index, and left and right ventricular stroke work indices during anastomosis of the left internal mammary artery to left anterior descending artery. These parameters returned to baseline preinduction values 1 minute after completion of the anastomosis. Conclusion: Excellent correlation, accuracy, and precision were found among the 3 methods of measuring CO in patients undergoing MIDCAB surgery. Further studies are needed to assess their accuracy in multivessel off-pump coronary artery bypass graft surgery and in patients with poor left ventricular function.

Utility of esophageal Doppler as a minimally invasive hemodynamic monitor: a review.

The current bedside "gold standard" for cardiac output (CO) monitoring is thermodilution using a pulmonary artery catheter (PAC) but there is a number of risks associated with its use. The primary objective of this review was to evaluate the utility of esophageal Doppler (ED) as a minimally invasive monitor of CO. Medline literature search from 1966 to 2001 with citation review for studies comparing ED to PAC thermodilution for CO in perioperative and critically ill patients. Twenty-five publications were identified comparing ED and PAC measurement of CO in a broad range of patients. There was a good overall correlation between CO determined by ED and thermodilution (n = 18 studies, median R = 0.89, range 0.52 to 0.98) and minimal bias (n = 13, median -0.01, range 1.38 to 2 L x min(-1)). The precision of ED was only fair overall as assessed by limits of agreement. The ED technique was found to be responsive in detecting changes in thermodilution CO and was reliable demonstrating both low intra- and inter-observer variation. ED was reportedly easy to insert after minimal training and was safe, with no significant complications identified. ED is a practical, reliable, and valid device for measuring CO in perioperative and critically ill patients. Further studies with larger numbers of patients are needed to determine if the limited precision observed is inherent to the technique, the diagnoses of patients studied, or the small sample sizes.

Lung volume reduction surgery improves left ventricular diastolic function

Background and goal: Lung volume reduction surgery (LVRS) improves pulmonary function and increases exercise performance in patients with severe emphysema (1). We evaluated the effects of LVRS on left ventricular function, assuming that LVRS improves diastolic function by reducing the pulmonary tamponade of the heart. Materials and Methods: Ten patients scheduled for LVRS were studied after informed consent. After induction of anaesthesia, a pulmonary artery thermodilution catheter was inserted for measurements of pulmonary hemodynamics. A multiplane transesophageal echocardiographic transducer visualised the left ventricle for measurements of end-diastolic area (EDA), and for analysis of mitral Doppler flow profiles. Images were stored on VHS videotape and analysed using a PC-based off-line analysis system (2). Pulmonary capillary wedge pressure (PCWP) and EDA were measured before and after surgery in the supine position and during passive leg elevation to establish the left ventricular end-diastolic pressure-area curve. For statistical analysis, a paired Students t-test and a repeated measures ANOVA was used. Results are reported as Mean S.E.M. *p 0.05. **p 0.01. Results:

The effects of increasing concentrations of isoflurane and desflurane on pulmonary perfusion and systemic oxygenation during one-lung ventilation in pigs.

During one-lung ventilation (OLV), hypoxic pulmonary vasoconstriction (HPV) reduces venous admixture and attenuates the decrease in arterial oxygen tension by diverting blood from the nonventilated lung to the ventilated lung. In vitro, desflurane and isoflurane depress HPV in a dose-dependent manner. Accordingly, we studied the effects of increasing concentrations of desflurane and isoflurane on pulmonary perfusion, shunt fraction, and PaO(2) during OLV in vivo. Fourteen pigs (30-42 kg) were anesthetized, tracheally intubated, and mechanically ventilated. After placement of femoral arterial and thermodilution pulmonary artery catheters, a left-sided double-lumen tube (DLT) was placed via tracheotomy. After DLT placement, FIO(2) was adjusted at 0.8 and anesthesia was continued in random order with 3 concentrations (0.5, 1.0, and 1.5 minimal alveolar concentrations) of either desflurane or isoflurane. Differential lung perfusion was measured with colored microspheres. All measurements were made after stabilization at each concentration. Whereas mixed venous PO(2), mean arterial pressure, cardiac output, nonventilated lung perfusion, and shunt fraction decreased in a dose-dependent manner, PaO(2) remained unchanged with increasing concentrations of desflurane and isoflurane during OLV. In conclusion, increasing concentration of desflurane and isoflurane did not impair oxygenation during OLV in pigs. In an animal model of one-lung ventilation, increasing concentrations of desflurane and isoflurane dose-dependently decreased shunt fraction and perfusion of the nonventilated lung and did not impair oxygenation. The decreases in shunt fraction are likely the result of anesthetic-induced marked decreases in cardiac output and mixed venous saturation.

Changes in systolic and diastolic function during multivessel off-pump coronary bypass grafting.

To measure the changes in systolic and diastolic left ventricular function that occur during off-pump coronary artery bypass grafting (OPCAB) as a consequence of positioning the heart and interrupting coronary flow. 2-D Transoesophageal echocardiography was used to derive systolic wall motion indices and pulsed Doppler parameters of diastolic function including the E/A ratio, PVS/PVD ratio, and deceleration time. A continuous cardiac output thermodilution pulmonary artery catheter was used to provide hemodynamic measures of left ventricular function. Data was obtained prior to, during and following coronary grafting. Thirty-four consecutive anastomoses were evaluated, including eight circumflex (LCX), 17 left anterior descending artery (LAD) and nine right coronary artery (RCA) anastamoses. Significant changes in diastolic and systolic cardiac function were identified in those patients who underwent LCX grafting. Specifically during LCX grafting, both wall motion score index (2.4+/-1.4 vs 1.5+/-0.63 and 1.9+/-0.91) and the E/A ratio were significantly increased (3.5+/-1.4 vs 1.1+/-0.33 and 1.2+/-0.44) when compared to RCA and LAD grafting, respectively. The PVS/PVD ratio was significantly decreased during left circumflex grafting (0.7+/-0.45 vs 1.1+/-0.19 and 1.0+/-0.58) when compared to RCA and LAD grafting, respectively. All functional parameters returned to baseline by the end of surgery. Multivessel OPCAB can be achieved with mild impairment of left ventricular function that returns to baseline by the end of the procedure. Impairment of diastolic function is most marked during circumflex grafting as demonstrated by a restrictive filling pattern. Measures of diastolic function may be helpful in developing better strategies for exposure of the circumflex graft site.

Comparison of bioimpedance versus thermodilution cardiac output during cardiac surgery: Evaluation of a second-generation bioimpedance device

Objective: To compare a second-generation thoracic electrical bioimpedance (TEB) hemodynamic monitoring system with the clinically used pulmonary artery catheter thermodilution (TD-PAC) system. Design: Blinded, simultaneous measurements at specified key time points during surgery. Setting: University teaching hospital cardiac surgical operating rooms. Participants: Forty-seven patients undergoing primary elective coronary artery bypass surgery. Interventions: Timed cardiac output measurements by thermodilution and continuous monitoring of bioimpedance were performed. Measurements and Main Results: Cardiac index (TEB and TD-PAC) and other hemodynamic parameters were measured at 4 time points: (1) after anesthesia induction, (2) with the mediastinum open, (3) immediately after cardiopulmonary bypass, and (4) at the end of the case. Pearson's correlation and Bland-Altman analysis were carried out. Cardiac index by TEB and TD-PAC had an overall correlation of r = 0.71 (p < 0.0001). The Bland-Altman statistics showed a mean difference of −0.28 L/min/m2 and precision of 0.67 L/min/m2. The best correlation was at time 1, and the lowest correlation was at time 4. Mediastinal opening and cardiopulmonary bypass had little or no effect on the correlation between technologies. Conclusion: TEB reporting of cardiac index during coronary artery surgery generally agreed with TD-PAC cardiac index except at the end of the case (time 4). Copyright © 2001 by W.B. Saunders Company

Heart rate variability and hemodynamic alterations in canines with normal cardiac function during exposure to pressure support, continuous positive airway pressure, and a combination of pressure support and continuous positive airway pressure.

Variations in intrathoracic pressure generated by different ventilator weaning modes may significantly affect intrathoracic hemodynamics and cardiovascular stability. Although several investigators have attributed cardiovascular alterations during ventilator weaning to augmented sympathetic tone, there is limited investigation of changes in autonomic tone during ventilator weaning. Heart rate variability (HRV), the analysis of beat-to-beat changes in heart rate, is a noninvasive indicator of autonomic tone that might be useful in the identification of patients who are at risk for weaning difficulty due to underlying cardiac dysfunction. The authors describe HRV and hemodynamics in response to 3 ventilatory conditions: pressure support (PS) 10 cmH2O, continuous positive airway pressure (CPAP) 10 cmH2O, and a combination of PS 10 cmH2O and CPAP 10 cmH2O (PS + CPAP) in a group of canines with normal ventricular function. Six canines were studied in the laboratory. Continuous 3-lead electrocardiographic data were collected during baseline (controlled mechanical ventilation) and following transition to each of the ventilatory conditions (PS, CPAP, PS + CPAP) for analysis of HRV. HRV was evaluated using power spectral analysis to define the power under the curve in a very low frequency range (0.0033 to < 0.04 Hz, sympathetic tone), a low frequency range (0.04 to < 0.15 Hz, primarily sympathetic tone), and a high frequency range (0.15 to < 0.40 Hz, parasympathetic tone). A thermodilution pulmonary artery catheter measured cardiac output and right ventricular end-diastolic volume to describe global hemodynamics. There were significant increases in very low frequency power (sympathetic tone) with a concomitant significant reduction in high-frequency power (parasympathetic tone) with exposure to PS + CPAP. These alterations in HRV were associated with significantly increased heart rate and reduced right ventricular end-diastolic volume. Although there was a small but significant increase in cardiac output with exposure to PS, HRV was unchanged. These data indicate that there was a relative shift in autonomic balance to increased sympathetic and decreased parasympathetic tone with exposure to PS + CPAP. The increase in intrathoracic pressure reduced right ventricular end-diastolic volume (preload). This hemodynamic alteration generated a change in autonomic tone, so that cardiac output could be maintained. Individuals with autonomic and/or cardiovascular dysfunction may not be capable of this type of response and may fail to successfully wean from mechanical ventilation.

Invasive and noninvasive haemodynamic monitoring of acutely ill sepsis and septic shock patients in the emergency department.

The objective of this study was to describe early circulatory events of patients presenting to the emergency department (ED) with severe sepsis or septic shock. Invasive and noninvasive monitoring were used to evaluate sequential patterns of both central haemodynamics and peripheral tissue perfusion/oxygenation and to test the hypothesis that increased cardiac output is an early compensation to increased body metabolism. This is a prospective observational study of 45 patients who entered the ED with severe sepsis or septic shock in an urban academic ED. Invasive clinical monitoring was performed using a radial artery catheter and a thermodilution pulmonary artery catheter. Noninvasive monitoring consisted of an improved thoracic electrical bioimpedance device to estimate cardiac output; pulse oximetry for arterial saturation to reflect changes in pulmonary function, and transcutaneous oxygen (PtcO2) and carbon dioxide tensions (PtcCO2) as a reflection of tissue perfusion. Survivors had higher cardiac index, mean arterial pressure (MAP), and better tissue perfusion as measured by PtcO2, oxygen delivery, and oxygen consumption. Oxygen extraction ratio was higher in the nonsurvivors (p < 0.05) and there were episodes of high PtcCO2 values in the nonsurvivors. No significant differences were found in the heart rate, PAOP (wedge pressure) and SaO2 by pulse oximetry between the two groups. It is concluded that ED monitoring septic patients provides a unique opportunity to document early physiologic interactions between cardiac, pulmonary, and tissue perfusion functions in surviving and nonsurviving patients with septic shock. The data is consistent with the concept that increased cardiac output is an early compensatory response to increased body metabolism. Real time haemodynamic monitoring of patients in the ED provides early warning of outcome and may be used to guide therapy.

Hemodynamic patterns of survivors and nonsurvivors during high risk elective surgical operations.

Postoperative survivors' and nonsurvivors' hemodynamic and oxygen transport patterns have been extensively studied, and the early postoperative circulatory events leading to organ failures and death have been documented. Outcome was improved when potentially lethal circulatory patterns were treated during the early (the first 8-12 hours) postoperative period; but after the appearance of organ failure, reversal of nonsurvival patterns did not improve the outcome. The purpose of this study was to describe prospectively intraoperative circulatory deficiencies that precede shock, organ failures, and death. The ultimate aim was to elucidate nonsurvivor patterns at the earliest possible time to develop more effective preventive strategies for lethal organ failures. This approach is based on the assumption that it is easier and more effective to prevent the initiators of shock, such as hypovolemia, hypoxemia, poor tissue perfusion, and tissue hypoxia, than to treat the mediators of organ failure, such as cytokines, antigens, eicosinoids, and heat shock proteins. We monitored 356 high risk elective surgical patients with preoperative and intraoperative hemodynamic monitoring by the pulmonary artery (PA) thermodilution catheter. The conventionally monitored mean arterial pressure and heart rate remained in the normal range in both groups; the nonsurvivor pattern included decreased cardiac index, stroke index, stroke work, oxygen delivery, and oxygen consumption. Low oxygen consumption was partly compensated by increased oxygen extraction rates, and arterial pressures were maintained by increasing systemic vascular resistance. The early temporal pattern of nonsurvivors' changes were similar to those described during the postoperative period that preceded development of organ failure and death. This suggests that lethal circulatory dysfunctions may begin during the intraoperative period but become more apparent before and after organs fail during later postoperative stages.

The effects of increasing concentrations of desflurane on systemic oxygenation during one-lung ventilation in pigs.

During one-lung ventilation (OLV), hypoxic pulmonary vasoconstriction reduces venous admixture and attenuates the decrease in arterial O2 tension by diverting blood from the nonventilated to the ventilated lung. In vitro, increasing concentrations of desflurane depresses hypoxic pulmonary vasoconstriction in a dose-dependent manner. Accordingly, we investigated the effects of increasing concentrations of desflurane on oxygenation during OLV in vivo. Thirteen pigs (25-30 kg) were anesthetized (induction: propofol 2-3 mg/kg IV; maintenance: N2O/O2 50%/50%, desflurane 3%, propofol 50 microg x kg(-1) min(-1), and vecuronium 0.2 mg x kg(-1) x h(-1) IV), orotracheally intubated, and mechanically ventilated. After placement of femoral arterial and thermodilution pulmonary artery catheters, a leftsided, 28F, double-lumen tube was placed via tracheotomy. After double-lumen tube placement, N2O and desflurane were discontinued, propofol was increased to 200 microg x kg(-1) x min(-1), and the fraction of inspired oxygen was adjusted at 0.8. Anesthesia was then continued in random order with desflurane 5%, 10%, or 15% end-tidal concentrations while propofol was discontinued. Whereas mixed venous PO2, mean arterial pressure, cardiac output, and shunt fraction decreased in a dose-dependent manner, PaO2 remained unchanged with increasing concentrations of desflurane during OLV. These findings indicate that, in vivo, increasing concentrations of desflurane do not necessarily worsen oxygenation during OLV. Oxygenation during one-lung ventilation depends on reflex vasoconstriction in the nonventilated lung. In vitro, desflurane inhibits this reflex dose-dependently. Our results indicate that, in vivo, this does not necessarily translate to dose-dependent decreases in oxygenation during one-lung ventilation.

Biphasic changes in left ventricular function during hyperdynamic endotoxemia.

Cardiac contractility was studied in a clinically relevant conscious swine model simulating human hemodynamics during endotoxemia. The slope of the end-systolic pressure-volume relationship [end-systolic elastance (EES)] was used as a load-independent contractility index. Chronic instrumentation in 10 pigs included two pairs of endocardial ultrasonic crystals for measuring internal major and minor axial dimensions of the left ventricle, a micromanometer for left ventricular pressure measurement, and a thermodilution pulmonary artery catheter. After a 10-day recovery period, control measurements of cardiac hemodynamic function were obtained. The following week, Escherichia coli endotoxin (10 micrograms . kg-1. h-1) was administered intravenously for 24 h. EES increased 1 h after endotoxin infusion and decreased beyond 7 h. The later hemodynamic changes resembled human cardiovascular performance during endotoxemia more closely than the changes during the acute phase. EES decreased in the later phase. A similar biphasic response of EES has been reported during a tumor necrosis factor-alpha (TNF) challenge. Even though plasma TNF was highest at 1 h and declined thereafter in this study, no consistent relationship between TNF and EES was identified, and TNF levels did not correlate directly with the changes in EES.

REVERSAL OF MEDETOMIDINE INDUCED SEDATION BY ATIPAMEZOLE IN SHEEP

S391 INTRODUCTION: Medetomidine is a highly selective alpha-2 agonist with sedative properties. The alpha-2 antagonist, atipamezole, reverses medetomidine induced sedation in animals. Sedative doses of alpha-2 agonists may change cardiac output and organ blood flow. The aim of this study was to investigate changes in cardiac output and organ blood flow induced by medetomidine and reversed by atipamezole in sheep. METHODS: With the approval of the Animal Care Committee, we studied 8 sheep. Animals were chronically instrumented with catheters in the left atrium, femoral artery and vein and a thermodilution pulmonary artery catheter. Medetomidine was infused in the femoral vein using a computer-controlled infusion pump targeting plasma levels of 0, 0.8, 1.6, 3.2, 6.4 and 12.8 ng/ml for 20 minutes each, followed by a 5 minute infusion of atipamezole (170 ug/kg). Hemodynamic values and organ blood flow (using coloured microspheres) were measured just prior to medetomidine infusion (baseline), at the end of each of the 5 medetomidine infusion steps, and 30 minutes after administration of atipamezole. Data were analyzed by repeated measures ANOVA followed by Dunnett's test. P<0.05 was considered significant. Data are mean +/- SD RESULTS: All animals fell asleep during medetomidine infusion and awoke within 5 minutes from the start of atipamezole infusion. Medetomidine (12.8 ng/ml) increased mean arterial pressure (MAP) from 107 +/- 10 to 134 +/- 16 mmHg, systemic vascular resistance (SVR) from 1310 +/- 207 to 3467 +/- 1299 dynes[center dot]s[center dot]cm-5, decreased heart rate from 96 +/- 14 to 67 +/- 23 bpm and cardiac output (CO) from 6.3 +/- 1.0 to 3.3 +/- 0.7 l/min. Blood flow decreased in heart, brain, kidney, skeletal muscle and intestine but increased in liver (Table 1). After atipamezole SVR and MAP returned to baseline, CO remained below baseline at 5.8 +/- 1.1 l/min and HR increased above baseline to 124 +/- 33 bpm. Blood flow increased to above baseline values in skeletal muscle but remained significantly below baseline in heart, brain and kidney (Table 1).Table 1: Percentage changes from baseline in organ blood flowDISCUSSION: Atipamezole did not reverse medetomidine induced reduction in cardiac, cerebral and renal blood flow. However, skeletal muscle blood flow increased to above baseline values. These results in sheep imply that high doses of alpha-2 agonists reversed by antagonists may cause considerable redistribution of organ blood flow in humans.

Preload assessment in patients with an open abdomen.

Intra-abdominal hypertension and abdominal compartment syndrome cause significant morbidity and mortality in surgical and trauma patients. Maintenance of intravascular preload and use of open abdomen techniques are essential. The accuracy of pulmonary artery occlusion pressure (PAOP) and central venous pressure (CVP) in patients with intra-abdominal hypertension has been questioned. Twenty surgical and trauma patients with intra-abdominal hypertension requiring open abdominal decompression were monitored using volumetric thermodilution pulmonary artery catheters. Hemodynamic, oxygenation, inspiratory, and intravesicular pressure measurements were collected prospectively. PAOP, CVP, and right ventricular end-diastolic volume index (RVEDVI) were compared as estimates of preload status. Multiple regression analysis demonstrated that cardiac index correlated significantly better with RVEDVI (r = 0.69) than with PAOP (r = -0.27) or CVP (r = -0.28) during resuscitation after open abdominal decompression (p < 0.0001). RVEDVI is superior to PAOP and CVP as an estimate of preload status in patients with an open abdomen.