Calculation Of Cardiac Output Research Articles

Central venous-arterial carbon dioxide difference as an indicator of cardiac index

The mixed venous-arterial (v-a) pCO(2) difference has been shown to be inversely correlated with the cardiac index (CI). A central venous pCO(2), which is easier to obtain, may provide similar information. The purpose of this study was to examine the correlation between the central venous-arterial pCO(2) difference and CI. Prospective, cohort study. Intensive care unit of an urban tertiary care hospital. Eighty-three consecutive intensive care unit patients. Simultaneous blood gases from the arterial, pulmonary artery (PA), and central venous (CV) catheters were obtained. At the same time point, cardiac indices were measured by the thermodilution technique (an average of three measurements). The cardiac indices obtained by the venous-arterial differences were compared with those determined by thermodilution. The correlation (R(2)) between the mixed venous-arterial pCO(2) difference and cardiac index was 0.903 (p <0.0001), and the correlation between the central venous-arterial pCO(2) difference and cardiac index was 0.892 (p <0.0001). The regression equations for these relationships were natural log (CI)=1.837-0.159 (v-a) CO(2) for the PA and natural log (CI)=1.787-0.151 (v-a) CO(2) for the CV (p <0.0001 for both). The root-mean-squared error for the PA and CV regression equations were 0.095 and 0.101, respectively. Venous-arterial pCO(2) differences obtained from both the PA and CV circulations inversely correlate with the cardiac index. Substitution of a central for a mixed venous-arterial pCO(2) difference provides an accurate alternative method for calculation of cardiac output.

USE OF LITHIUM DILUTION AND PULSE CONTOUR ANALYSIS CARDIAC OUTPUT DETERMINATION IN ANAESTHETISED HORSES – A CLINICAL EVALUATION

Pulse contour analysis is a relatively new method of continuously monitoring cardiac output. The objective of this study was to evaluate the suitability of the human algorithm for calculation of continuous cardiac output from the pulse waveform, for use in anaesthetised horses. Cardiac output was measured in 27 anaesthetised clinical cases comparing lithium dilution (LiDCO) with a preceding, calibrated cardiac output measured from the pulse waveform (PulseCO) using a commercial system (LiDCOplus, LiDCO Ltd., Cambridge, UK). These comparisons were repeated every 20–30 min. Positive inotropes or vasopressors were administered when clinically indicated. Cardiac output values obtained ranged from 15.2–52.2 L/min, with cardiac indices from 30.7–114.9 ml/kg/min.Eighty‐nine comparisons were obtained. The mean bias was 0.24 ml/kg/min +/−6.48 ml/kg/min. The limits of agreement were −12.72–13.2 ml/kg/min. The 95% confidence interval for the upper limit of agreement was 12.07–14.33 ml/kg/min and for the lower limit of agreement was −11.59–13.85 ml/kg/min. Linear regression analysis demonstrated a correlation coefficient (r2) of 0.89 and produced an equation of PulseCO (mls kg−1 minute−1)=0.9226LiDCO (mls kg−1minute−1) +5.354.This method of pulse contour analysis is a relatively non‐invasive and reliable way of monitoring continuous cardiac output in the horse under anaesthesia. The ability to easily continuously monitor cardiac output may improve morbidity and mortality in the anaesthetised horse.

Validation of a new spectrometer for noninvasive measurement of cardiac output

Acetylene is a blood-soluble gas and for many years its uptake rate during rebreathing tests has been used to calculate the flow rate of blood through the lungs (normally equal to cardiac output) as well as the volume of lung tissue. A new, portable, noninvasive instrument for cardiac output determination using the acetylene uptake method is described. The analyzer relies on nondispersive IR absorption spectroscopy as its principle of operation and is configured for extractive (side-stream) sampling. The instrument affords exceptionally fast (30 ms, 10%–90%, 90%–10%, at 500 mL min−1 flow rates), interference-free, simultaneous measurement of acetylene, sulfur hexafluoride (an insoluble reference gas used in the cardiac output calculation), and carbon dioxide (to determine alveolar ventilation), with good (typically ±2% full-scale) signal-to-noise ratios. Comparison tests with a mass spectrometer using serially diluted calibration gas samples gave excellent (R2&amp;gt;0.99) correlation for all three gases, validating the IR system’s linearity and accuracy. A similar level of agreement between the devices also was observed during human subject C2H2 uptake tests (at rest and under incremental levels of exercise), with the instruments sampling a common extracted gas stream. Cardiac output measurements by both instruments were statistically equivalent from rest to 90% of maximal oxygen consumption; the physiological validity of the measurements was confirmed by the expected linear relationship between cardiac output and oxygen consumption, with both the slope and intercept in the published range. These results indicate that the portable, low-cost, rugged prototype analyzer discussed here is suitable for measuring cardiac output noninvasively in a point-of-care setting.

Six years follow-up of an implanted SvO(2) sensor in the right ventricle.

Mixed venous oxygen saturation (SvO(2)) is a standard invasive measure used in the management of congestive heart failure patients. The reliability of a long-term SvO(2) sensor remains unproven. Nine patients (NYHA Class I/II, n=2/7) were implanted with a dual chamber pacemaker modified to utilize a right ventricular SvO(2) lead (Medtronic Inc., Models 8007/4327A IPG/Lead). Invasive studies compared sensor SvO(2) to reference (Optical Swan-Ganz catheter) at 0, 3 and 9 months. Symptom limited tests (Bike(max)) with metabolic assessment and arterial oxygen saturation measurements performed 1-7 days, 3.5 and 9.5 months post-implant allowed for cardiac output calculations. Long-term sensor performance was confirmed by submaximal tests, Bike(subm) in years 1-3, and Walk(in-place) every 6 months for the duration of follow-up. Sensor SvO(2) readings were stable over time when compared to the Swan-Ganz Catheter. Non-invasive CO measured during Bike(max) was in normal ranges for this patient population, 3.7+/-0.9 l/min at rest and 8.4+/-2.2 l/min at peak-exercise. Resting SvO(2) values from Bike(subm) and Walk(in-place) did not change significantly over time (P>0.1 vs. 1 year) and neither did the change from rest to peak exercise during Bike(subm) (P>0.05 vs. 1 year) or Walk(in-place) (P>0.05 vs. 4 year). While limited in size, this small pilot study suggests that long-term monitoring of SvO(2) by implanted devices may be feasible. The clinical value remains to be proven in future studies.

Balancing tissue perfusion demands: cardiovascular dynamics of Cancer magister during exposure to low salinity and hypoxia.

Decapod crustaceans inhabit aquatic environments that are frequently subjected to changes in salinity and oxygen content. The physiological responses of decapod crustaceans to either salinity or hypoxia are well documented; however, there are many fewer reports on the physiological responses during exposure to these parameters in combination. We investigated the effects of simultaneous and sequential combinations of low salinity and hypoxia on the cardiovascular physiology of the Dungeness crab, Cancer magister. Heart rate, as well as haemolymph flow rates through the anterolateral, hepatic, sternal and posterior arteries were measured using a pulsed-Doppler flowmeter. Summation of flows allowed calculation of cardiac output and division of this by heart rate yielded stroke volume. When hypoxia and low salinity were encountered simultaneously, the observed changes in cardiac properties tended to be a mix of both factors. Hypoxia caused a bradycardia, whereas exposure to low salinity was associated with a tachycardia. However, the hypoxic conditions had the dominant effect on heart rate. Although hypoxia caused an increase in stroke volume of the heart, the low salinity had a more pronounced effect, causing an overall decrease in stroke volume. The patterns of haemolymph flow through the arterial system also varied when hypoxia and low salinity were offered together. The resulting responses were a mix of those resulting from exposure to either parameter alone. When low salinity and hypoxia were offered sequentially, the parameter experienced first tended to have the dominant effect on cardiac function and haemolymph flows. Low salinity exposure was associated with an increase in heart rate, a decrease in stroke volume and cardiac output, and a concomitant decrease in haemolymph flow rates. Subsequent exposure to hypoxic conditions caused a slight decrease in rate, but other cardiovascular variables were largely unaffected. In contrast, when low salinity followed acclimation to hypoxic conditions, apart from an increased heart rate, there were no other cardiovascular changes associated with the low salinity episode. The implications of these changes in cardiovascular dynamics are discussed in relation to physiological mechanisms and the ecology of decapod crustaceans, in hypoxic or low salinity environments.

Lack of Agreement Between Thermodilution and Fick Cardiac Output in Critically Ill Patients

s: Individual comparison of cardiac output via intermittent thermodilution and Fick technique over a wide range of cardiac outputs. Prospective clinical investigation. Multidisciplinary ICUs of two teaching hospitals in Vancouver, British Columbia. Eighteen critically ill patients who had pulmonary and systemic arterial catheters and in whom active support was being withdrawn. Measurement of thermodilution cardiac output and calculation of Fick cardiac output while support was withdrawn. Active support was withdrawn in a three-step process: removal of vasopressors followed by decrease in fraction of inspired oxygen to 0.21, and finally removal of mechanical ventilation. Simultaneous Fick and thermodilution cardiac outputs were obtained over a wide range. Fick calculated cardiac outputs were obtained using the Fick equation with oxygen uptake (O(2)) being measured with indirect calorimetry. O(2) determinations were made using five measurements over 5 min, with the mean being used for subsequent analysis. Thermodilution cardiac outputs were determined by the mean of five measurements, with the first being discarded. Coefficient of variation was calculated for the O(2) and thermodilution cardiac outputs. One hundred thirty-six simultaneous cardiac outputs were obtained in 18 patients with a mean APACHE (acute physiology and chronic health evaluation) II score of 25.5. The range of cardiac outputs was 1.39 to 16.95 L/min. Linear regression analysis found a good correlation of the data sets, with an R of 0.85. Bias and precision calculations found a bias of - 0.17 L/min with the upper and lower limits of agreement being 2.96 L/min and - 3.30 L/min, respectively. In patients with high cardiac outputs (> 7 L/min), the bias was - 1.90 with the limits of agreement being 1.87 L/min and - 5.67 L/min. The coefficient of variation for O(2) was 4.6% and for thermodilution cardiac output was 7.75%. There was good consistency of each of the measurements with a low coefficient of variation. The bias for the whole group was small, but the limits of agreement extended into a clinically relevant area, resulting in a lack of agreement. In patients with high cardiac outputs, the Fick tended to consistently produce higher cardiac outputs compared to thermodilution, suggesting a systematic error.

Primer caso de síndrome cardiopulmonar por hantavirus secundario a mordedura de ratón

We describe the first case of Hantavirus cardiopulmonary syndrome (HCPS) occurring after a rodent bite. A student was bitten when he was manipulating a trap in which an Oligoryzomys longicaudatus was trapped. Fourteen days later he developed moderate HCPS. He needed supplemental oxygen, but he did not need mechanical ventilation nor vasoactive drugs treatment. The hemodynamic condition was monitored utilizing the Pulse Contour Cardiac Output (PiCCO) computer. The transcardiopulmonary thermodilution technique is less invasive than the pulmonary arterial catheter, and allows the measurement of the extravascular lung water index. This index seems to be helpful in the management of moderate HCPS. We describe the epidemiological data, clinical features, hemodynamic condition and treatment of this patient

Ventricular Function Determination During Extracorporeal Membrane Oxygenation (ECMO) Following Norwood Operation: A Case Report

Extracorporeal membrane oxygenation has been used successfully to support both cardiac and pulmonary function following Stage I Norwood operation. Determination of the return of native cardiac function and pulmonary function can be easily accomplished because of the single ventricle physiology. The pulmonary function can be assessed while on full flow ECMO by isolating the membrane oxygenator gas compartment, allowing evaluation of native pulmonary gas exchange through the modified Blalock–Taussig shunt. Cardiac output can be calculated by using the following oxygen delivery equation: Total O2 delivery ECMO oxygen delivery + ventricular oxygen delivery. The ventricular O2 saturation used in the formula for oxygen delivery is same as the mixed venous O2 saturation returning to the ECMO pump because of the large atrial communication following the Norwood operation. A 3.2 kilogram patient was placed on a pediatric ECMO circuit utilizing a heparin-coated centrifugal pump and a microporous membrane oxygenate after failure to wean from bypass because of a low oxygen saturation and poor ventricular function. On day 1 of support, the systemic arterial oxygen saturation was 100% and matched the ECMO arterial saturation. On day 2 of the support, the patient's arterial saturation decreased to 96%, and the ECMO mixed venous saturation was 87%. Using the oxygen delivery formula, the ventricular cardiac output was calculated to be 175 mL/min, with an ECMO flow of 400 mL/min for a total cardiac output of 575 mL/min. The native ventricular contribution was, therefore, 30% of total cardiac output. Calculation of cardiac output would normally require a left ventricular sample in a patient with biventricular physiology. The single ventricle physiology in the post-operative Norwood patient makes this calculation a useful tool for assessing return of ventricular function in these patients.

Calculation of cardiac output by measurement from tricuspid inflow using a 3-D digital color doppler method: an in vivo validation study

Calculation of cardiac output by measurement from tricuspid inflow using a 3-D digital color doppler method: an in vivo validation study

Noninvasive cardiac output assessment during heart surgery.

To evaluate the reliability of a new noninvasive method for the assessment of cardiac output with the partial carbon dioxide rebreathing technique. This technique was applied to patients undergoing heart surgery. Values of cardiac index obtained with this equipment were compared with the artero-venous CO2 gradient, a reliable index of cardiovascular status. Positive and negative predictive values of the test were assessed. A total of 21 simultaneous measurement of the cardiac index and of the artero-venous CO2 gradient were obtained. The positive predictive value of the test was 67% while the negative predictive value was 100%, indicating that a normal value of cardiac index recorded with the rebreathing technique predicts with a good reliability a normal cardiovascular state. Working through a series of mathematical algorithms, accuracy in the computation of cardiac output can be decreased with this equipment; however, this limitation seems to be outweighed by the simplicity and noninvasive nature of the methods.

Empirical estimators of gamma fits to tracer-dilution curves and their technical basis and practical scope

A gamma fit facilitates smoothing and extrapolation of distorted tracer-dilution curves in blood flow studies. Theoretically based empirical estimators were developed as simple alternatives to direct regression approaches from simulated gamma distributions with a wide range of shape asymmetry. Key curve features of peak height p, full width w at half peak height, rising and falling limb inflection tangents and asymmetry of the peak time with respect to the p/2 height occurrences were related to the parameters of the distribution by multiple linear regression after suitable transformations. The product pw was simply related to the total area A under the curve, pw/A being 0.93 ± 0.01 in 70 cardiac output determinations from ten surgical patients. Shape and scale parameters were closely related to the standard deviation, inflection point properties and w for the curves. Mensuration devices suitable for cardiac output computers were developed that calculated total areas from incomplete portions under gamma curves and by-passed the need for parameter estimation. There was limited point in estimating the distribution parameters just to derive particle transit times, because of the ad hoc nature of the fitting form, which did not allow for the back-dispersion by Brownian motion of tracer molecules diluting in blood flow. Nonetheless, the accuracy of area prediction using a gamma fit was adequate for most clinical purposes and comparable to that via the random walk function, giving good insight to established results and computing procedures.

Quantification of recirculation by thermodilution during venovenous extracorporeal membrane oxygenation

Purpose: The aim of this study was to determine whether recirculation could be quantified by a thermodilution technique during venovenous (VV) extracorporeal membrane oxygenation (ECMO) in a rabbit model. Methods: Five New Zealand white rabbits, mean weight, 4.5 (range, 3.7 to 5.7) kg, were anesthetized, instrumented, cannulated with a double-lumen catheter, and placed on VV ECMO. Serial injections of ice-cold saline were performed at the arterial arm of the circuit, and the resultant temperature change at various pump flows was measured at the venous arm of the circuit using a thermistor-tipped catheter and a cardiac output computer. Results were compared with the respective 100% recirculation measured with all the circuit flow passing through the bridge. Results: Using linear regression, recirculation percentage could be calculated as: 19 + 0.1 × pump flow (R2 = 0.81, P <.005). Recirculation correlated positively with pump flow. Variability between results at each flow was less than 10%. Conclusions: Recirculation can be quantified during VV ECMO by measuring the change in temperature in the venous arm using a cardiac output computer after injection of a known quantity of ice-cold saline in the arterial side of the circuit. The effect of interventions to reduce recirculation can be assessed conveniently and reliably. J Pediatr Surg 35:1411-1414. Copyright © 2000 by W.B. Saunders Company.

Hemodynamic responses to hypoxia and hypercapnia during acute normovolemic hemodilution in anesthetized cats.

The present study was undertaken to evaluate the effects of hypoxia and hypercapnia on circulatory parameters during acute normovolemic hemodilution. Cats anesthetized with a mixture of alpha-chloralose and urethane were maintained by positive pressure ventilation. Muscles were paralysed by intramuscular vecuronium (0.1 mg/kg) to eliminate reflex respiratory movements. Cats were exposed to hypoxia (12% O(2) and 7% O(2)) and hypercapnia (4% CO(2) and 7% CO(2)) at normal hematocrit (Ht 40.1 +/- 2.8%) and then at graded levels of normovolemic hemodilution (Ht 24.0 +/- 2.0% and Ht 13.0 +/- 1.5%, respectively). Left ventricular pressure (LVP), LV dP/dt(max), arterial blood pressure (ABP), heart rate (HR), and right atrial pressure (RAP) were recorded on a polygraph. Cardiac output (CO) was measured using a cardiac output computer. Hemodilution per se did not produce any significant change in ABP, RAP or LV dP/dt(max), however, it produced a significant rise in HR and a significant fall in total peripheral resistance (TPR). Exposure to hypoxic gas mixtures caused significant increases in HR and CO at control Ht; but after hemodilution it caused the reverse effects. Hypercapnia did not produce any significant effect on ABP, LV dP/dt(max) or RAP either at control Ht or after hemodilution. Hypercapnia produced a fall in HR, CO and stroke volume (SV) at normal Ht and percent fall in HR response was enhanced following hemodilution. The reversal of chronotropic response to hypoxia and enhanced bradycardia response to hypercapnia, under conditions of acute normovolemic hemodilution would be deleterious as the tissues would become more hypoxic. Such a response may be attributed to altered control mechanisms under such conditions of severe stress.

Influence of hypoxia on cardiac functions in the grass shrimp ( Palaemonetes pugio Holthuis)

Crustaceans frequently encounter hypoxic water and have evolved a variety of compensatory mechanisms to deal with low O 2 conditions. Typically, large decapod crustaceans attempt to maintain cardiac output by increasing stroke volume to compensate for the hypoxia-induced bradycardia. Grass shrimp ( Palaemonetes pugio), small hypoxic tolerant decapod crustaceans, were used to investigate cardiac responses to hypoxia in a smaller crustacean using videomicroscopy and dimensional analysis techniques. In addition, these techniques were compared to the more established dye dilution technique for calculation of cardiac output. No significant difference was found between the two methods for determining cardiac output in grass shrimp. Cardiac parameters (heart rate f H, stroke volume V S, and cardiac output V b) were monitored in grass shrimp exposed to progressive hypoxia ( P O 2 s=20, 13.3, 10, 5.3, and 2 KPa O 2). Shrimp exhibit a cardiac response to hypoxia that is atypical when compared to larger crustaceans. Cardiac output was maintained until water P O 2 fell below 10 KPa O 2. This maintenance of V b is consistent in both large and small decapods, however the mechanism differs. In grass shrimp, V S was P O 2 dependent and declined significantly while f H increased significantly when P O 2 was reduced to 13.3 KPa O 2.

Bolus cardiac output calculation in patients with severe heart failure: Does current nursing procedure lead to the strongest correlation with fick cardiac output measurement

Bolus cardiac output calculation in patients with severe heart failure: Does current nursing procedure lead to the strongest correlation with fick cardiac output measurement

Microbubbles associated with mitral valve prostheses in pediatric patients

Objectives: To assess whether microbubbles are associated with mitral valve prostheses in children and to investigate their relationship to exercise. Background: Bright, highly mobile echoes are seen in left heart chambers of patients with mechanical mitral valve prostheses. The clinical importance of those microbubbles is not yet known but they survive long enough to reach the cerebral circulation. No such studies have been reported in children. Methods: There were 20 male and 10 female patients with a mean age of 10.4 years (range 2–16 years). Transthoracic echocardiography with calculation of cardiac output and ejection fraction was performed at baseline and after exercise following mechanical mitral valve replacement. Studies were evaluated for the presence of microbubbles. The mean time from operation to time of study was 18 months (range 0.2–89 months) Results: Of the 30 children evaluated, 28 (93%) had evidence of microbubbles. Exercise increased the number of microbubbles in 15 of the 26 children. This was positively associated with an increase in cardiac output. Conclusions: (1) Microbubbles are common observed in children with mechanical mitral prostheses and are augmented by exercise. (2) This phenomenon is of a special concern in children due to their expected longevity with the prosthesis.

Circulatory modification in the blue crab Callinectes sapidus, during exposure and acclimation to low salinity

A pulsed-Doppler flowmeter was used to measure heart rate and haemolymph flow rates in each arterial system of the blue crab, Callinectes sapidus, enabling calculation of stroke volume and cardiac output. During exposure to a 6–6–12 h salinity cycle of 100–25–100% seawater, there was an immediate increase in heart rate upon dilution of the medium. After this initial increase it decreased steadily, but remained elevated above levels in 100% seawater. A smaller increase in heart rate occurred when the salinity was raised, declining thereafter and reaching pre-treatment levels after 6 h in 100% SW. There was a slight decrease in stroke volume of the heart, but overall this resulted in an increase in cardiac output when the salinity was lowered. Differential haemolymph flow through each major arterial system also occurred. There was an increase in flow rates through the anterior aorta, anterolateral arteries and sternal artery during the first 2 h of low salinity exposure and smaller increases occurred again when the salinity was raised to 100% seawater. No significant changes in flow were observed in the hepatic arteries or posterior aorta. During a 72 h acclimation period in low salinity, similar increases in cardiac parameters and flow rates were observed in the first 6 h. These values declined to levels comparable to those in 100% seawater, after 40–50 h acclimation in low salinity. The changes in cardiovascular parameters are not directly related to the osmoregulatory physiology of this species, but appear to be due to specific behaviours occurring in response to low salinity. The results obtained here for this efficient osmoregulator are compared and contrasted with similar studies on Cancer magister, which is classified as a weak hyperosmoregulator.

Indicator dilution measurement of lung water: considerations of the method

Background: Pulmonary oedema is life threatening. A method is needed for reliable measurement of lung water in man in order to clarify aetiology, pathophysiology, prognosis, and to evaluate treatments against pulmonary oedema.Methods: The double‐indicator dilution method with bolus injection and optical detection of heavy water and indocyanine green in arterial blood for the measurement of cardiac output, central blood volume and lung water was applied in two human and two experimental studies. In parallel, the thermo‐dye technique was tested in one of the experimental studies. The results from these four studies, together with results presented in the literature, were analysed according to the criteria set forth by The National Institute of Health, USA 1985, for the measurement of lung water in man, that is versatility, reproducibility, sensitivity, and accuracy.Results: for the heavy water‐indocyanine green method: Versatility: No adverse reaction was recorded in the two human studies. A central venous line and a peripheral arterial line, or access to an arterio‐venous fistula, were needed for bolus injection and concentration analysis. In‐line optical detection of heavy water and indocyanine green did not expose the subjects to radio‐labelled isotopes and the blood loss was low compared to timed blood volume collection. Reproducibility: The coefficient of variation was below 10% for cardiac output and central blood volume, and 10–17% for lung water. Sensitivity: Changes in lung water that were below the level of gas exchange disturbance could be detected in a group of subjects. Accuracy: Cardiac output, mean transit time and lung water for heavy water were linearly related to independent reference measures. Evidence for barrier limitations for heavy water in the clinical setting were weak. The indicator dilution method is unreliable for shock states and pulmonary embolism.Results: for the thermo‐dye method: Versatility: The method did not expose the subjects to radio‐labelled isotopes and there was no blood loss, but the method requires a central venous line and a thermistor‐equipped fibre‐optic catheter placed in the aorta.Reproducibility: The coefficient of variation was approximately 10% for cardiac output, central blood volume and lung water. Sensitivity: In healthy lungs, small differences in lung water can be detected. In pulmonary oedema, the large increase in deviation cripples the sensitivity of the method. Accuracy: Recovery of the thermal indicator and the error in its mean transit time were dependent on the distribution volume for the indicator cold. This undermines reliable calculation of cardiac output and lung water.Conclusions: The method using optical detection of heavy water and indocyanine green in blood for the measurement of cardiac output, central blood volume and lung water in humans is an improvement with regard to radio‐labelled methods, with the same reproducibility. The method allows for detection of small changes in lung water under the range where gas‐exchange disturbance occurs. The method provides values close to gravimetric lung water values in both healthy and grossly oedematous lungs, independent of cardiac output and distribution volume, with the exception of shock states and severe vascular obstruction.

Detrimental effect of hypothermia during acute normovolaemic haemodilution in anaesthetized cats.

Haemodynamic responses to hypothermia were studied at normal haematocrit and following the induction of acute normovolaemic haemodilution. Experiments were performed on 20 cats anaesthetized with a mixture of chloralose and urethane in two groups. In one group (n = 10) the effects of hypothermia on various haemodynamic variables were studied at normal haematocrit (41.0 +/- 1.7%) and in the second group of cats (n = 10) the effects of hypothermia on various haemodynamic variables were studied after the induction of acute normovolaemic haemodilution (14.0 +/- 1.0%). The haemodynamic variables left ventricular pressure, left ventricular contractility, arterial blood pressure, heart rate and right atrial pressure were recorded on a polygraph. Cardiac output was measured using a cardiac output computer. In both groups hypothermia was induced by surface cooling with the help of ice. Cardiovascular variables were recorded at each 1 degree C fall in body temperature. Hypothermia produced a significant (P < 0.05) drop in heart rate, cardiac output, arterial blood pressure and left ventricular contractility in both groups. However, the percentage decrease in these variables in response to hypothermia was significantly (P < 0.05) higher in cats with low haematocrit than in those with normal haematocrit. The severity of hypothermia--induced cardiovascular effects is evident from the drastic decrease in heart rate, cardiac output, arterial blood pressure and myocardial contractility in cats with low haematocrit, indicating a higher risk of circulatory failure under anaemic conditions at low temperatures.

Adolf Fick (1829-1901), physiologist: a heritage for anesthesiology and critical care medicine.

Adolf Fick (1829-1901), physiologist: a heritage for anesthesiology and critical care medicine.