Cardiac surgery patients present considerable variation in pre‐operative hemodynamic variables
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Abstract:
It is essential to control hemodynamics in cardiac surgery. Patients are often monitored extensively in order to optimize hemodynamic performance. However, pre-operative values are normally unknown. Furthermore, hemodynamic goals may seem arbitrary and the lack of an evidence-based consensus may lead to both under- and over-treatment. The aim of this study was to evaluate the variables most commonly used for hemodynamic guidance in the post-operative period.Ten patients scheduled for elective cardiac surgery were followed with invasive hemodynamic monitoring the night before surgery. All data were recorded automatically and electronically.We found considerable inter-patient differences and intra-patient variation. The greatest intra-patient variation was found in the cardiac index (CI), ranging from 1.9 to 5.3 l/min/m(2). Four patients had periodic CI <2.4 l/min/m(2). Eight patients showed SpO2 values < or =92, four of them in more than 15% of the observations. Six patients had an SvO2 <70% in more than 40% of the observations and two an SvO2 < 64% in more than 20% of the observations.This study is unique because hemodynamic reference data in cardiac surgery patients have not been published previously. The intra-patient variations were unexpectedly high in most hemodynamic variables and demonstrate the difficulties of using hemodynamic parameters as a guidance for treatment and indicate that goal-oriented therapy using currently accepted values may result in over-treatment in some patients.Keywords:
Cardiac index
Measurements of cardiac output with the thermodilution technique add to data for clinical decision making and therefore must be valid and reliable. However, the results of studies on the accuracy of values obtained with room-temperature and iced injectates, especially in patients with high or low cardiac output, have been conflicting.To determine the effect of the temperature of the injectate (iced or room temperature) on cardiac output values obtained with the thermodilution technique in critically ill adults with known low cardiac output.A convenience sample of 50 subjects (41 men and 9 women) who had a cardiac index of less than 2.5 (calculated as cardiac output in liters per minute divided by body surface area in square meters) before the study had cardiac output measured by using a closed system and manual injections of room-temperature and iced injectates.A paired t test indicated no significant difference between iced and room-temperature injectates for cardiac output (iced, 3.62 L/min; room temperature, 3.71 L/min; t = 0.99; P = .327) and cardiac index (iced, 1.95; room temperature, 1.99; t = 0.71; P = .482).The findings support the practice of using room-temperature injectate to measure cardiac output in patients with low cardiac output.
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The main haemodynamic indices were studied in rabbits of two age groups (young -- 10--12 month, and old -- 3--4 years) under normal conditions and those with experimentally induced renal hypertension. Significant changes were observed in the proportion of the main parameters of haemodynamics -- cardiac output per 1 min and total peripheral resistance -- in the presence of persistent arterial hypertension, which permitted to single out three haemodynamic forms of experimentally induced renal hypertension. The first and second haemodynamic forms are characterized by a sharp enhancement of the total peripheral resistance and diverse changes in the values of cardiac output per 1 min.: the third haemodynamic form is predmoninatly characterized by an elevation of the cardiac output. The compensatory hyper-function of the myocardium in the first and second forms of renal hypertension develops usually isometrically, in the third form -- according to the mixed variant.
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Vascular surgery
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Data on the cardiac output and circulatory dynamics obtained by cardiac catheter studies in 51 subjects with chronic severe anemia are presented. Patients are divided into two groups: group A consists of 26 subjects with an average hemoglobin value of 3.0 Gm. per 100 ml. (range 1.5 to 3.8 Gm.); group B, 25 patients with a hemoglobin level of 4.0 to 6.5 Gm., average 4.5 Gm. Group A subjects have a somewhat faster heart rate (99 against 92 a minute), higher cardiac index (8.0 versus 6.3 liters per minute per square meter), and stroke index (88 and 68 ml. per beat per square meter) than group B patients. The oxygen consumption values in both groups are normal (average 158 and 160 ml. per minute per square meter), while more oxygen is extracted by the tissue in group A subjects (61 and 53 per cent) whereas less oxygen is transported to the tissue (261 and 321 ml. per minute per square meter). The stroke volume seems to bear a closer relationship to the high cardiac output than such other parameters as heart rate, right heart filling pressure, and velocity of blood flow. Apparently the presence of slow heart rate does not negate high cardiac output. Data also suggest that systemic vascular resistance may play an important role in the high cardiac output as the two are inversely related, and by increasing the peripheral arterial pressure the output can be significantly reduced. Restudy data after the treatment of the anemia (hemoglobin 10.0 to 12.5 Gm. per 100 ml.) show appreciable reduction in the cardiac output and in the right heart filling pressure, increase in the peripheral vascular resistance and oxygen transport values, and widening of the arteriovenous oxygen differences with concomitant decrease in the oxygen extraction by the tissue.
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To identify hemodynamic variables that might indicate susceptibility to slowing of heart rate (HR) and to mean arterial pressure (MAP) decrease caused by cold injectate during thermodilution (TD) cardiac output determination, we measured hemodynamic variables in 32 anesthetized patients undergoing major surgery. A total of 608 cardiac output determinations were evaluated for any relationship between the magnitude of HR decreases and basal hemodynamic variables. The magnitude of HR decrease was pronounced in low cardiac index (CI), low mean pulmonary artery pressure (MPAP), and high systemic vascular resistance index (SVRI). Although there was some decrease in MAP associated with cold injectate, neither changes in SVRI nor those in the other hemodynamic variables correlated with the decreases in MAP. These results suggest that decreased CI and MPAP associated with elevated SVRI may be more susceptible to slowing of HR during cardiac output determination by TD in anesthetized patients.
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The results of a long-term observation (for 1 to 4 1/2 years) of haemodynamic changes in 32 non-treated patients with stage II essential hypertension are presented. In 18 patients the lesion did not progress throughout the observation period (group I). At re-examination the haemodynamic parameters in this group of patients did not change significantly, although in some of them the haemodynamic mechanism of maintenance of hypertension underwent certain changes: the cardiac output decreased and the total peripheral resistance increased. In 14 patients (Group 2) their essential hypertension was progressively developing. At the same time a deceleration of the heart contractions rate, a reduction of the cardiac and stroke outputs, a decrease of the circulating blood volume, and an increase of the total peripheral resistance were noted. The reduction of the cardiac output was directly proportional to its initial value (r = +0.78, P less than 0.01) and to the elevation of the arterial pressure (r = +0.71, P less than 0.01). The most distinct changes were noted in 3 patients who developed signs of cardiac insufficiency during the period between the two examinations. The possible mechanisms of haemodynamic changes under the progression of essential hypertension are discussed.
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The evolution of different hemodynamic parameters with ponderal growth has been studied in conscious Wistar rats. The thermodilution method has been used to determine cardiac output and related variables. The results suggest that, between animal weight and the different hemodynamic parameters, there is a direct proportional relationship to blood volume, mean arterial pressure, cardiac output, stroke volume and total peripheral resistance, and an indirect proportional relationship to heart rate, cardiac index and stroke volume index. Body weight, therefore, plays a major role in hemodynamic determination, this having to be kept in mind when designing the experiment.
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Since the technique of thermodilution (TD) cardiac output measurement, per se , causes hemodynamic alterations, the author examined whether the alterations elicited by iced injectate are augmented in the presence of acute blood loss or endotoxemia, compromized conditions frequently associated with critically ill patients. Acute blood loss (N = 8) and endotoxemia (N = 8) were induced by withdrawing arterial blood approximately 20–30 ml kg ‐1 over 30 min and by a slow intravenous infusion of E. coli endotoxin 2.5‐3.0 mg kg ‐l over 10 min, respectively, in anesthetized dogs. The magnitudes of decreases in mean arterial and pulmonary artery pressures during slowing of heart rate (HR) following injection of iced injectate 3 ml were slightly less in acute blood loss than in normovolemia, whereas in endotoxemia the degree of mean arterial pressure decrease during slowing of HR following iced injectate 3 ml was slightly less as compared with that before endotoxemia. However, the alterations in other hemodynamic variables following injection of iced injectate 3 ml were similar between dogs with and without acute blood loss or endotoxemia. No profound hemodynamic changes were observed during any TD cardiac output measurements under both conditions. Cardiac output estimated by TD correlated closely with pulmonary blood flow measured by electromagnetic flowmeter in endotoxemia (r > 0.9) but not during acute blood loss. These results indicate that TD cardiac output determination does not cause serious hemodynamic alterations in endotoxemia or acute blood loss, and can estimate right ventricular output accurately in endotoxemia but not in acute blood loss.
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The hemodynamic changes following acute myocardial infarction have been studied in patients in an intensive care unit. Serial determinations of cardiac output and blood pressure have shown a wide range of hemodynamic patterns in severely ill patients varying from a low cardiac output and high peripheral resistance to a high cardiac output and low peripheral resistance. The progression of changes during the illness and their relation to the clinical findings have been discussed.
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Coronary care unit
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