Determination of cardiac output by thermodilution during hypothermia

Cardiovascular changes induced by targeted mild hypercapnia after out of hospital cardiac arrest. A sub-study of the TAME cardiac arrest trial

AIM

Hypercapnia may elicit detrimental haemodynamic effects in critically ill patients. We aimed to investigate the consequences of targeted mild hypercapnia versus targeted normocapnia on pulmonary vascular resistance and right ventricular function in patients resuscitated from out-of-hospital cardiac arrest (OHCA).

METHODS

Pre-planned, single-centre, prospective, sub-study of the Targeted Therapeutic Mild Hypercapnia After Resuscitated Cardiac Arrest (TAME) trial. Patients were randomised to mild hypercapnia (PaCO2 = 6.7-7.3 kPa) or normocapnia (PaCO2 = 4.7-6.0 kPa) for 24 hours. Haemodynamic assessment was performed with right heart catheterisation and serial blood-gas analyses every4th hour for 48 hours.

RESULTS

We studied 84 patients. Mean pH was 7.24 (95% CI 7.22-7.30) and 7.32 (95% CI 7.31-7.34) with hypercapnia and normocapnia, respectively (P-group < 0.001). Pulmonary vascular resistance index (PVRI), pulmonary artery pulsatility index, and right atrial pressure did not differ between groups (P-group > 0.05). Mean cardiac index was higher with mild hypercapnia (P-group < 0.001): 2.0 (95% CI 1.85-2.1) vs 1.6 (95% CI 1.52-1.76) L/min/m2. Systemic vascular resistance index was 2579 dyne-sec/cm-5/ m2 (95% CI 2356-2830) with hypercapnia, and 3249 dyne-sec/cm-5/ m2 (95% CI 2930-3368) with normocapnia (P-group < 0.001). Stroke volumes (P-group = 0.013) and mixed venous oxygen saturation (P-group < 0.001) were higher in the hypercapnic group.

CONCLUSION

In resuscitated OHCA patients, targeting mild hypercapnia did not increase PVRI or worsen right ventricular function compared to normocapnia. Mild hypercapnia comparatively improved cardiac performance and mixed venous oxygen saturation.

ICU management based on PiCCO parameters reduces duration of mechanical ventilation and ICU length of stay in patients with severe thoracic trauma and acute respiratory distress syndrome

BACKGROUND

This study aimed to assess whether a management algorithm using data obtained with a PiCCO system can improve clinical outcomes in critically ill patients with acute respiratory distress syndrome (ARDS).

RESULTS

The PaO₂/FiO₂ ratio increased over time in both groups, with a sharper increase in the PiCCO group. There was no difference in 28-day mortality (3.2 vs. 3.6%, P = 0.841). Days on mechanical ventilation (3 vs. 5 days, P = 0.002) and ICU length of stay (6 vs. 11 days, P = 0.004) were significantly lower in the PiCCO group than in the CVP group. Treatment costs were lower in the PiCCO group than in the CVP group. Multivariate logistic regression model showed that the monitoring method (PiCCO vs. CVP) was independently associated with the length of ICU stay [odds ratio (OR) 3.16, 95% confidence interval (95% CI) 1.55-6.63, P = 0.001], as well as shock (OR 3.41, 95% CI 1.74-6.44, P = 0.002), shock and ARDS (OR 3.46, 95% CI 1.79-6.87, P = 0.002), and APACHE II score (OR 1.17, 95% CI 1.02-1.86, P = 0.014).

CONCLUSIONS

This study investigated the usefulness of the PiCCO system in improving outcomes for patient with severe thoracic trauma and ARDS and provided new evidence for fluid management in critical care settings.

Myocardial calcium overload during graded hypothermia and after rewarming in an in vivo rat model

AIM

Mechanisms underlying cardiac contractile dysfunction during and after rewarming from hypothermia remain largely unknown. We have previously reported myocardial post-hypothermic calcium overload to be the culprit. The aim of the present study was to measure changes in myocardial [Ca(2+) ](i) during graded hypothermia and after rewarming in an anesthetized, intact rat model, using the (45) Ca(2+) technique.

METHODS

Rats were randomized and cooled to 15 °C. Hearts were excised and perfusion-washed to remove extracellular calcium after 0.5 h of hypothermia (n = 9), 4 h of hypothermia (n = 8), and after 4 h of hypothermia and 2 h rewarming (n = 9). A normothermic group, kept at 37 °C for 5 h, served as control (n = 6). [Ca(2+) ](i) was determined in perchloric acid extracts of heart tissue. Spontaneous cardiac electromechanic work was maintained during hypothermia without cardiac arrest or ischaemia.

RESULTS

Between 0.5 and 4 h at 15 °C, a six-fold increase in cardiac [Ca(2+) ](i) was observed (0.55 ± 0.10 vs. 2.93 ± 0.76 μmol (g dry wt)(-1) ). Rewarming resulted in a 33% decline in [Ca(2+) ](i) , but the actual value was significantly above the value measured in control hearts.

CONCLUSION

We show that calcium overload is a characteristic feature of the beating heart during deep hypothermia, which aggravates by increasing duration of exposure. The relatively low decline in [Ca(2+) ](i) during the rewarming period indicates difficulties in recovering calcium homoeostasis, which in turn may explain cardiac contractile dysfunction observed after rewarming.

Use of the PiCCO system in critically ill patients with septic shock and acute respiratory distress syndrome: a study protocol for a randomized controlled trial

BACKGROUND

Hemodynamic monitoring is very important in critically ill patients with shock or acute respiratory distress syndrome(ARDS). The PiCCO (Pulse index Contour Continuous Cardiac Output, Pulsion Medical Systems, Germany) system has been developed and used in critical care settings for several years. However, its impact on clinical outcomes remains unknown.

METHODS/DESIGN

The study is a randomized controlled multi-center trial. A total of 708 patients with ARDS, septic shock or both will be included from January 2012 to January 2014. Subjects will be randomized to receive PiCCO monitoring or not. Our primary end point is 30-day mortality, and secondary outcome measures include ICU length of stay, days on mechanical ventilation, days of vasoactive agent support, ICU-free survival days during a 30-day period, mechanical-ventilation-free survival days during a 30-day period, and maximum SOFA score during the first 7 days.

DISCUSSION

We investigate whether the use of PiCCO monitoring will improve patient outcomes in critically ill patients with ARDS or septic shock. This will provide additional data on hemodynamic monitoring and help clinicians to make decisions on the use of PiCCO.

TRIAL REGISTRATION

http://www.clinicaltrials.gov NCT01526382.

Altered brain myelin sheath morphology after rewarming in situ

In this study cerebral ultrastructure was examined in an in vivo rat model, after rewarming from profound hypothermia (15-13 degrees C). Animals held at 37 degrees C served as controls. After rewarming, brains were examined by electron microscope. Micrographs were taken randomly, analyzed anonymously, and quantified by morphometry. Serum analysis of the stress marker S-100beta was carried out in identical groups. The most striking findings in rewarmed animals, when compared to controls, were alterations of myelin sheaths (p<.008) and elevated S-100beta (p<.0001). This indicates that cells in the central nervous system are susceptible to injury in an experimental model of accidental hypothermia and rewarming.

Cardiac output monitoring using indicator-dilution techniques: basics, limits, and perspectives

The ability to monitor cardiac output is one of the important cornerstones of hemodynamic assessment for managing critically ill patients at increased risk for developing cardiac complications, and in particular in patients with preexisting cardiovascular comorbidities. For >30 years, single-bolus thermodilution measurement through a pulmonary artery catheter for assessment of cardiac output has been widely accepted as the "clinical standard" for advanced hemodynamic monitoring. In this article, we review this clinical standard, along with current alternatives also based on the indicator-dilution technique, such as the transcardiopulmonary thermodilution and lithium dilution techniques. In this review, not only the underlying technical principles and the unique features but also the limitations of each application of indicator dilution are outlined.

Effect of lower limb compression devices on thermodilution cardiac output measurement

OBJECTIVE

The aim of this study was to determine whether lower limb (calf) sequential compression devices (SCDs) have a significant effect on thermodilution cardiac output measurements using a pulmonary artery catheter.

DESIGN

Prospective clinical investigation.

SETTING

Surgical and neurosurgical intensive care units in a university hospital.

PATIENTS

A total of 43 patients with pulmonary artery catheters and bilateral lower limb SCDs.

MEASUREMENTS AND MAIN RESULTS

Cardiac output was measured (average of three) when the SCDs were off (T1), during the first 2-4 secs of the inflation cycle (T2), during seconds 4-8 of the inflation cycle (T3), and when the SCDs were off again (T4). Cardiac output measurements were consistently lower when measured during the SCD inflation cycle. The decrease in cardiac output ranged from 7.58% to 49.5%, with a mean reduction of 24.51% in the first 2-4 seconds and 20.61% during seconds 4-8 (p < .001). Two patients displayed an increase in cardiac output during the inflation cycle; one patient had an increase of 2.78% and the other an increase of 13.5%. In 11 patients, measurements were also made using a pulse contour-analysis cardiac output device, but no changes in pulse contour-analysis cardiac output were observed during the same time period.

CONCLUSIONS

Thermodilution cardiac output measurements via a pulmonary artery catheter should not be done during the inflation cycle of lower limb SCDs because they produce a falsely low cardiac output.

Comparisons between electromagnetic and X-beam transit-time flow measurements for evaluating drug actions on cardiac output in the conscious dog

INTRODUCTION

Cardiac output remains an important preclinical measurement for evaluating the cardiovascular effects of drugs. We evaluated the performance of the Triton Active Redirection Transit-Time, ART(2), which represents a new class of X-beam flow systems and compared it in vivo and in vitro to an electromagnetic flow (EMF) system for measuring large vessel flow.

METHODS

In vivo, simultaneous aortic flow measurements were obtained during alpha- and beta-adrenergic receptor stimulation in 5 conscious dogs instrumented with both ART(2) and EMF probes on their ascending aortas. In vitro, simultaneous measurements of volume flow using the ART(2), EMF, and timed-volume collection were made using a novel benchtop flow apparatus that ensured probe alignment and precise timed-volume flow measurements. Accuracy and sensitivity of both systems were assessed by recording flow measurements while varying rates, temperature and hematocrit.

RESULTS

In vivo aortic flow measurements between ART(2) and EMF were closely correlated (linear regression r(2) values ranged from 0.84 to 0.99), with the ART(2) system recording lower flow values than the EMF. In vitro ART(2) flow rates were in excellent agreement with timed-volume flow, while EMF flow rates were lower (p<0.05) and exhibited more variation and dependency upon temperature or hematocrit than the ART(2). Saline flows measured by ART(2) and EMF averaged 97+/-2% and 91+/-5% accuracy, respectively, over the temperature range 32 degrees C to 42 degrees C. For blood hematocrit values between 35% and 45%, ART(2) accuracy averaged 98+/-2%, compared to 89+/-5% accuracy with the EMF.

DISCUSSION

The ART(2) flow measurements in conscious dogs correlated closely to concurrent measurements obtained with the EMF over a wide range of flow rates, even though the absolute aortic flow values differed. Since it accurately measured flow in vitro, the ART(2) system is an appropriate alternative for evaluating cardiovascular effects of disease progression or drug administration in experimental animals.

Effects of sympathetic stimulation during cooling on hypothermic as well as posthypothermic hemodynamic function

This experimental study was performed to explore hemodynamic effects of a moderate dose epinephrine (Epi) during hypothermia and to test the hypothesis whether sympathetic stimulation during cooling affects myocardial function following rewarming. Two groups of male Wistar rats (each, n = 7) were cooled to 15 °C, maintained at this temperature for 1 h, and then rewarmed. Group 1 received 1 μg/min Epi, i.v., for 1 h during cooling to 28 °C, a dose known to elevate cardiac output (CO) by approximately 25% at 37 °C. Group 2 served a saline solution control. At 37 °C, Epi infusion elevated CO, left ventricular systolic pressure, maximum rate of left ventricle pressure rise, and mean arterial pressure. During cooling to 28 °C, these variables, with the exception of mean arterial pressure, decreased in parallel to those in the saline solution group. In contrast, in the Epi group, mean arterial pressure remained increased and total peripheral resistance was significantly elevated at 28 °C. Compared with corresponding prehypothermic values, most hemodynamic variables were lowered after 1 h at 15 °C in both groups (except for stroke volume). After rewarming, alterations in hemodynamic variables in the Epi-treated group were more prominent than in saline solution controls. Thus, before cooling, continuous Epi infusion predominantly stimulates myocardial mechanical function, materialized as elevation of CO, left ventricular systolic pressure, and maximum rate of left ventricle pressure rise. Cooling, on the other hand, apparently eradicates central hemodynamic effects of Epi and during stable hypothermia, elevation of peripheral vascular vasopressor effects seem to take over. In contrast to temperature-matched, non-Epi stimulated control rats, a significant depression of myocardial mechanical function occurs during rewarming following a moderate sympathetic stimulus during initial cooling.

Is oxygen supply a limiting factor for survival during rewarming from profound hypothermia?

It has been postulated that unsuccessful resuscitation of victims of accidental hypothermia is caused by insufficient tissue oxygenation. The aim of this study was to test whether inadequate O2supply and/or malfunctioning O2extraction occur during rewarming from deep/profound hypothermia of different duration. Three groups of rats ( n = 7 each) were used: group 1 served as normothermic control for 5 h; groups 2 and 3 were core cooled to 15°C, kept at 15°C for 1 and 5 h, respectively, and then rewarmed. In both hypothermic groups, cardiac output (CO) decreased spontaneously by >50% in response to cooling. O2consumption fell to less than one-third during cooling but recovered completely in both groups during rewarming. During hypothermia, circulating blood volume in both groups was reduced to approximately one-third of baseline, indicating that some vascular beds were critically perfused during hypothermia. CO recovered completely in animals rewarmed after 1 h ( group 2) but recovered to only 60% in those rewarmed after 5 h ( group 3), whereas blood volume increased to approximately three-fourths of baseline in both groups. Metabolic acidosis was observed only after 5 h of hypothermia (15°C). A significant increase in myocardial tissue heat shock protein 70 after rewarming in group 3, but not in group 2, indicates an association with the duration of hypothermia. Thus mechanisms facilitating O2extraction function well during deep/profound hypothermia, and, despite low CO, O2supply was not a limiting factor for survival in the present experiments.

Cardiovascular effects of epinephrine during rewarming from hypothermia in an intact animal model

Rewarming from accidental hypothermia is often complicated by “rewarming shock,” characterized by low cardiac output (CO) and a sudden fall in peripheral arterial pressure. In this study, we tested whether epinephrine (Epi) is able to prevent rewarming shock when given intravenously during rewarming from experimental hypothermia in doses tested to elevate CO and induce vasodilation, or lack of vasodilation, during normothermia. A rat model designed for circulatory studies during experimental hypothermia and rewarming was used. A total of six groups of animals were used: normothermic groups 1, 2, and 3 for dose-finding studies, and hypothermic groups 4, 5, and 6. At 20 and 24°C during rewarming, group 4 (low-dose Epi) and group 5 (high-dose Epi) received bolus injections of 0.1 and 1.0 μg Epi, respectively. At 28°C, Epi infusion was started in groups 4 and 5 with 0.125 and 1.25 μg/min, respectively. Group 6 served as saline control. After rewarming, both CO and stroke volume were restored in group 4, in contrast to groups 5 and 6, in which both CO and stroke volume remained significantly reduced (30%). Total peripheral resistance was significantly higher in group 5 during rewarming from 24 to 34°C, compared with groups 4 and 6. This study shows that, in contrast to normothermic conditions, Epi infused during hypothermia induces vasoconstriction rather than vasodilation combined with lack of CO elevation. The apparent dissociation between myocardial and vascular responses to Epi at low temperatures may be related to hypothermia-induced myocardial failure and changes in temperature-dependent adrenoreceptor affinity.

Morphologic changes in tubular cells from in situ kidneys following experimental hypothermia and rewarming

Although renal failure may occur following rewarming from deep accidental hypothermia, this subject has received little attention in experimental hypothermia and clinical case reports. In order to explore the integrity of hypothermic and posthypothermic renal morphology we used an experimental animal model of accidental hypothermia where the heart supports the circulation throughout cooling and rewarming without accompanying cardioplegia or ischemia. Ultrastructural changes in renal tubular cells from three groups of pentobarbital anesthetized Wistar rats: 1) controls (n=6) maintained at 37 degrees C for 4 h, 2) hypothermic rats (n=6) core-cooled and maintained at 15-13 degrees C for 4 h, and 3) rewarmed rats (n=10), were studied as a sensitive indicator of renal damage. Electron micrographs (EM) from hypothermic kidneys showed rounded up mitochondria with loss of contrast. These changes were observed in several though not all of the biopsies, but they were found in all kidneys. Areas exhibiting focal tubular necrosis were seen on most EM from three of these kidneys. EM from rewarmed kidneys showed alterations of mitochondrial ultrastructure with similarities to those observed after hypothermia, but in general the changes were more prominent. Extracellular edema, intracellular edema, swelling of mitochondria, margination of chromatin, necrosis of single tubular cells, and disrupting necrotic debris into tubular lumen could be found in micrographs from 7 of the 10 kidneys examined. Rewarming from experimental hypothermia, without episodes of ischemia or hypoxia, thus induces ultrastructural changes in renal tubular cells similar to changes observed in acute tubular necrosis, associated with renal failure.

Cardiac output can be reliably measured noninvasively after coronary artery bypass grafting operation

OBJECTIVE

To evaluate the reliability of whole-body impedance cardiography in the measurement of cardiac output after coronary artery bypass grafting operation in comparison with the thermodilution method.

DESIGN

Prospective, consecutive sampling.

PATIENTS

A total of 82 patients undergoing coronary artery bypass surgery were investigated. In a group of 41 patients who were intubated, cardiac output measurements were taken simultaneously with whole-body impedance cardiography and the thermodilution method within the first 3 hrs after the operation (early intensive care unit [ICU] period). In another group of 41 patients, the measurements were taken before the operation and in the second 12 hrs after cardiac surgery (late ICU period).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The agreement between the thermodilution and whole-body impedance cardiography cardiac output measurements was good before the operation, bias 0.04 +/- 1.64 L/min (n = 41), and in the late ICU period, bias 0.00 +/- 1.84 L/min (+/-2 SD) (n = 41). The results were within 20% in 81%-85% of the cases. The agreement was satisfactory in the early ICU period, bias 0.38 +/- 2.74 L/min (n = 41). It was presumed that thermal instability of the patients was one possible source of measurement errors in the thermodilution method, causing reduced agreement between the methods in this period. The repeatability values (rv = 2.83 x SDs) for whole-body impedance cardiography were 0.44 L/min before the operation, 0.30 L/min in the early ICU period, and 0.65 L/min in the late ICU period, being significantly better than for the thermodilution method (0.79, 0.51, and 1.11 L/min, respectively) in all phases of the investigation (p < .001). The agreement between the thermodilution method and whole-body impedance cardiography is similar to reported comparisons between invasive methods in analogous settings.

CONCLUSIONS

Whole-body impedance cardiography reliably measures cardiac output in patients after coronary artery bypass grafting operation. The excellent repeatability of whole-body impedance cardiography enhances the value of the method in continuous monitoring of patients after the operation.

Continuous versus bolus thermodilution cardiac output measurements--a comparative study

OBJECTIVE

To compare the methods for continuous and bolus thermodilution cardiac output measurements.

DESIGN

In vivo and in vitro experimental studies.

SETTING

Surgical research division in a university hospital.

SUBJECTS

Eight calves and flow bench model.

INTERVENTIONS

Data were collected in vivo from eight calves instrumented with pulmonary artery catheters, which allowed both continuous and bolus thermodilution measurements. The pulmonary artery catheter was placed through the external jugular vein. All in vitro measurements were performed using a flow bench model.

MEASUREMENTS AND MAIN RESULTS

A total of 232 bolus and continuous thermodilution measurements were analysed in vivo to determine the degree of agreement between the two methods. The absolute measurement bias was 0.14 L/min with 95% confidence limits ranging from -0.83 to 1.15 L/min. In vitro analysis of 576 measurements at six different temperature points (range 31 degrees to 41 degrees C), using clinically relevant flows (2 to 9 L/min), showed overestimation of flow values using continuous and bolus thermodilution methods. However, the continuous method showed better accuracy by a lower degree of overestimation. Systematic error was 9.7 +/- 8.4 (SD) % for continuous and 11.1 +/- 6.3% for the bolus method (p < .001). This effect was especially evident at lower flow rates. The influence of various temperatures on the accuracy and reproducibility of both methods of measurement was statistically significant but not clinically relevant. The infusion of lactated Ringer's lactate solution (infusion rates 100 to 1000 mL/hr) affects both methods at a low flow rate of 2 L/min, without causing a significant effect on continuous measurement at a higher flow rate (4 L/min). Shunting of 50% of circulating volume to the distal part of the thermal filament of the pulmonary catheter impaired the accuracy of continuous measurement without affecting results from bolus measurements (systematic error -26.8 +/- 8.2% for continuous and -5.2 +/- 4.1% for bolus thermodilution).

CONCLUSIONS

Continuous thermodilution cardiac output measurement provided higher accuracy and greater resistance to thermal noise than standard bolus measurements. The correct placement of the catheter is essential for precise measurements.

Errors in the measurement of cardiac output by thermodilution

Cardiac output (CO) determination by thermodilution, which was introduced by Fegler in 1954, has gained wide acceptance in clinical medicine and animal experiments because it has several advantages over other methods with respect to simplicity, accuracy, reproducibility, repeated measurements at short intervals, and because there is no need for blood withdrawal. However, errors in determination of CO by thermodilution may be introduced by technical factors and the patients' pathological conditions. The current review summarizes these issues and provides our recommendations, based on the medical literature published between 1954-1992. To obtain more reproducible and accurate CO values by thermodilution, one should make several determinations (1) by using 10 ml injectate at room temperature for adults and 0.15 ml.kg-1 injectate for infants and children; (2) at evenly spaced intervals of the ventilation cycle; (3) when rapid intravenous fluid administration is discontinued; (4) by observing thermodilution curves so that baseline pulmonary artery temperature drift or the existence of intra- and extracardiac shunts are noticed. Finally, CO determination by thermodilution may be unreliable or impossible in patients with low CO states and tricuspid or pulmonary regurgitation. Since non-invasive CO monitoring has not replaced CO determination by thermodilution, intimate knowledge of this method is crucial for anaesthetists to prevent errors in the management of patients.

The effects of antishock trouser inflation during hypothermic cardiovascular depression in the canine model

The purpose of this study was to investigate the value and to identify any deleterious effects of antishock trouser use during hypothermic cardiovascular depression. Thirteen mongrels were made hypotensive by cooling to a core temperature of approximately 27 degrees C. Eight dogs had antishock trousers inflated for one hour and five dogs served as controls. Metabolic and hemodynamic variables were measured at regular intervals during cooling, during trouser inflation, and after trouser deflation. No study animal experienced ventricular fibrillation. Neither central temperature, pH, or serum potassium nor mean arterial BP or systemic vascular resistance were significantly affected by trouser inflation or deflation. Antishock trouser use during the early phase of hypothermia before rewarming does not appear to result in a central bolus of cold, acidotic, hyperkalemic blood or the precipitation of ventricular fibrillation. There appears to be no significant hemodynamic benefit of antishock trouser use early in the management of hypotension caused by moderate hypothermia.

Surface-induced hypothermia: effects on coronary blood flow autoregulation and vascular reserve

Surface-induced hypothermia has been shown to exert a protective effect in canine models of myocardial infarction. However, its effects on coronary blood flow (CBF) autoregulation and coronary vascular reserve (CVR) have not been investigated. The effects of mild (32 degrees C) and moderate (27 degrees C) hypothermia on CBF autoregulation and CVR (at 60 mm Hg diastolic pressure) were studied using a chronically instrumented canine preparation. Coronary artery pressure-flow relations were obtained over a wide range of coronary diastolic pressures (10 to 106 mm Hg) with autoregulation intact and during adenosine-induced maximal coronary conductance (MCC) at 37, 32, 27 degrees C (n = 7 dogs), and after rewarming (n = 5 dogs). Halothane (1 MAC end-tidal concentration, temperature adjusted) was the anesthetic. Autoregulation remained intact during hypothermia. CBF remained relatively constant between diastolic pressures of 43.1 +/- 9.0 and 84.0 +/- 14.4 mm Hg (mean +/- SD). No significant differences were observed between temperatures in the autoregulated pressure range. CBF correlated well with myocardial oxygen consumption (MVO2) (r2 = 0.81, P less than 0.0001). There were no significant changes in MVO2, CBF, MCC, or CVR at 32 degrees C. At 27 degrees C, MVO2 (3.65 +/- 1.3 at 37 degrees C vs 2.35 +/- 1.4 ml O2.min-1 at 27 degrees C), autoregulated CBF (34.9 +/- 15.1 vs 19.5 +/- 10.8 ml.min-1), the slope of the line of MCC (4.31 +/- 0.7 vs 2.7 +/- 0.4 ml.mm-1.min-1), and CVR (147.1 +/- 24.6 vs 90.1 +/- 27.3 ml.min-1) were all less than control (P less than 0.05). After rewarming to 37 degrees C, no significant changes from control were noted. The authors conclude that coronary autoregulation remains intact at both 32 and 27 degrees C, although MCC and CVR are significantly decreased at 27 degrees C.

The thermal-dye method of lung water measurement is reliable at a low cardiac output

The measurement of lung water by the thermal-dye double indicator dilution technique was evaluated in dogs with normal and edematous lungs during a state of reduced cardiac output. The technique used cold indocyanine green dye to measure extravascular thermal volume (EVTV) as an estimate of extravascular lung water (EVLW). Anesthesia was maintained with pentobarbital. In 15 of 21 animals, pulmonary edema was first induced with oleic acid (0.75 to 0.18 ml/kg). Cardiac output (CO) was then decreased by a combination of propranolol and slow exsanguination (mean CO reduction to 36% of baseline). Extravascular lung water produced in this model ranged from 1.4 to 30.2 ml/kg. Predetermination measurements of EVTV correlated closely with EVLW as determined by gravimetric analysis (EVTV = 1.1 EVLW + 4.7 ml/kg, n = 21, r = 0.93, P less than 0.001). Thermodilution cardiac output measured in the abdominal aorta (used in the calculation of the EVTV) correlated well with simultaneous measurements of cardiac output by both indocyanine green dye dilution and pulmonary artery thermodilution (r = 0.86 and r = 0.88, respectively, pretermination). The thermal-dye technique appears to provide an accurate reflection of lung water in normal and edematous lungs, even in the presence of a low cardiac output.