Electromagnetic flow-probe implantation for cardiac output measurements in rabbits

A technique suitable for continuous measurement of beat-to-beat cardiac output in conscious rabbits for relatively longer periods is described. The method consists, essentially, of implanting a specially constructed electromagnetic flow probe around either the pulmonary artery or the aorta during left thoracotomy (second intercostal space) in animals anesthetized with hypnorm. With care, the procedure is successful in a large proportion of the animals. Little postoperative care is required and the flow probe remains functional for several weeks up until the animals were killed to recover the probe for reimplantation. The cardiac output values (ml/min/kg) in conscious rabbits were: normal 183 +/- 9; unilateral renal hypertensive animals, 108 +/- 10 and bilateral renal hypertensive animals, 153 +/- 15. Isoprenaline increased, and propranolol decreased, the cardiac output in conscious normotensive rabbits.     

Continuous monitoring of cardiac output by analysis of the pulse contour

One method of continuous cardiac output monitoring by analysis of the radial pulse contour (Qcp) relates left ventricular stroke volume and systolic blood pressure by calculating the impedence characteristic of the aorta (Zao). It was assessed during haemodynamic monitoring by comparing it with the thermodilation method in the pulmonary artery (Qtd) in 20 patients with cardiac failure due to dilated cardiomyopathy (6 cases) and ischaemic cardiomyopathy (14 cases) treated by inotropic agents or vasodilators. Over an average monitoring period of 35 hours 159 measurements of cardiac output were performed by the two methods. There was an excellent correlation between the two methods (r = 0.90; p < 0.001; Qcp = 0.97 Qtd). The systematic error (bias) between the two methods was about 2.5%. The accuracy of Qcp compared with Qtd was 12.5%. During infusion with a vasoactive agent (Piroximone), the method based on pulse contour analysis did not reflect sudden variations in cardiac output. The systematic error between the two methods rose to 19% of the value measured, reflecting the lack of adaptation of parameters of correction in this situation and which necessitated recalibration of Zao at least once after injection of the drug.     

Continuous cardiac output and mixed venous oxygen saturation monitoring

Continuous assessment of cardiac output and SVO2 in the critically ill may be helpful in both the monitoring variations in the patient's cardiovascular state and in determining the efficacy of therapy. Commercially available continuous cardiac output (CCO) monitoring systems are based on the pulsed warm thermodilution technique. In vitro validation studies have demonstrated that this method provides higher accuracy and greater resistance to thermal noise than standard bolus thermodilution techniques. Numerous clinical studies comparing bolus with continuous thermodilution techniques have shown this technique similarly accurate to track each other and to have negligible bias between them. The comparison between continuous thermal and other cardiac output methods also demonstrates good precision of the continuous thermal technique. Accuracy of continuous oximetry monitoring using reflectance oximetry via fiberoptics has been assessed both in vitro and in vivo. Most of the studies testing agreement between continuous SVO2 measurements and pulmonary arterial blood samples measured by standard oximetry have shown good correlation. Continuous SVO2 monitoring is often used in the management of critically ill patients. The most recently designed pulmonary artery catheters are now able to simultaneously measure either SVO2 and CCO or SVO2 and right ventricular ejection fraction. This ability to view simultaneous trends of SVO2 and right ventricular performance parameters will probably allow the clinician to graphically see the impact of volume loading or inotropic therapy over time, as well as the influence of multiple factors, including right ventricular dysfunction, on SVO2. However, the cost-effectiveness of new pulmonary artery catheters application remains still questionable because no established utility or therapeutic guidelines are available.     

Study of platelet-activating factor acetylhydrolase in the perioperative period of patients undergoing cardiac surgery

This study was conducted to determine whether brief, intermittent exposure to hypoxia with little change in nutrient intake would affect fetal growth. Pregnant rats were exposed to 1 or 2 h of hypoxia (FiO2 = 0.09-0.095) from days 15 to 19 of gestation. Exposure to 1 h of hypoxia decreased fetal body weight and length, liver weight and increased the brain/liver weight ratio (p < 0.05) as compared to controls. Two hours of hypoxia decreased fetal body weight and length, and heart, lung, kidney, gut, brain and liver weights (p < 0.01), but did not affect the brain/liver weight ratio. Two hours of hypoxia decreased maternal food intake and weight gain (p < 0.05), but fetal growth was not significantly altered in pair-fed controls. These data demonstrate that brief, intermittent periods of intrauterine hypoxia have significant effects on fetal growth.     

Multiplane transesophageal echocardiographic doppler imaging accurately determines cardiac output measurements in critically ill patients

OBJECTIVES: To compare cardiac output and stroke volume measured by multiplane transesophageal Doppler echocardiography with that measured by the thermodilution technique. DESIGN: Prospective direct comparison of paired measurements by both techniques in each patient. SETTING: Cardiac surgery and myocardial infarction intensive care units. PATIENTS: Twenty-nine patients, mean age (+/- SD) 67 +/- 8 years. Nineteen had undergone open heart surgery and 10 had suffered acute myocardial infarction. METHODS: Cardiac output and stroke volume were measured simultaneously by the thermodilution technique and multiplane transesophageal Doppler echocardiography via the transgastric view (119 +/- 8 degrees) with the sample volume positioned at the level of the left ventricular outflow tract. RESULTS: Stroke volume and cardiac output measurements were obtained in 29 of 33 patients (88%). Mean values were 50 +/- 13 mL and 4.8 +/- 1.3 L/min by Doppler and 51 +/- 14 mL and 4.9 +/- 1.4 L/min by thermodilution (r = 0.90, r = 0.91, p < 0.001). The mean differences in values obtained with the two techniques were 1 +/- 6 mL (2 +/- 12%) and 0.1 +/- 0.7 L/min (2 +/- 12%). CONCLUSIONS: Multiplane transesophageal echocardiography enhances the ability to estimate accurately cardiac output and stroke volume by providing new access to left ventricular outflow tract in critically ill patients.     

Management of specific medical conditions in the perioperative period

BACKGROUND: Reversal of ischemia after myocardial infarction by revascularization is worthwhile only if viability exists in a sufficiently large portion of the left ventricle. METHODS AND RESULTS: To determine myocardial hypoperfusion reversibility and its influence on segmental and global function, we studied 50 patients after myocardial infarction. Three technetium 99m-tetrofosmin scintigraphies were performed: 1 at rest, 1 after 0.6 mg sublingual nitroglycerin (NTG), and 1 after injection at peak stress. First-pass multigated radionuclide angiography was obtained at rest and after NTG. Each patient also underwent a stress redistribution-reinjection thallium-201 scintigraphy. During stress 99mTc-tetrofosmin, 104 segments had normal uptake, 51 showed moderately reduced uptake, and 186 had severely reduced uptake. Of these 186 segments, 33 (18%) improved at rest, and 41 (22%) improved only after NTG. Fifty-nine (79%) of these segments with improved uptake were also found to have reversible defects on 201TI imaging. In the 26 patients with ventricular dysfunction, a 73% agreement was found between the functional and 99mTc-tetrofosmin uptake post-NTG improvement, whereas a 69% agreement was found with thallium reinjection. No significant differences were seen between 99mTc-tetrofosmin and 201T1 imaging. CONCLUSION: Nitroglycerin administration during 99mTc-tetrofosmin scintigraphy improves the detection of myocardium with reversible hypoperfusion in patients with a previous myocardial infarction.     

Changes in plasma dopamine-beta-hydroxylase activity during the perioperative period of cardiac surgery: an index of sympathetic nerve activity

To evaluate the usefulness of plasma dopamine-beta-hydroxylase (DBH) activity as an index of sympathetic nerve activity during cardiac operations, we examined the serial changes in plasma DBH activity, in relation to the plasma noradrenaline (NA) level and hemodynamic parameters, in patients who underwent cardiac surgery. The plasma DBH activity decreased significantly after cardiopulmonary bypass, and remained low during dopamine (DA) infusion until 72 h after the operation. However, recovery of the hemodynamic parameters, being the mean arterial pressure, heart rate and cardiac index, was seen as early as 1-3 h postoperatively. It was therefore assumed that the plasma DBH activity takes a long time to recover after an operation. The time-course changes in the plasma NA level were quite different from the changes in DBH activity, with an apparent negative correlation being observed between them. Thus, there is a possibility that exogenously administered DA, as well as increased plasma NA, might inhibit DBH activity during cardiac surgery. Moreover, since catecholamines are often administered upon completion of cardiac surgery, measurement of the plasma catecholamine level would be inappropriate for evaluating real sympathetic nerve activity. From the results of this study, it is surmised that measurement of the plasma DBH activity could be useful for estimating the intrinsic sympathetic nerve activity of patients who have undergone cardiac surgery.     

Continuous measurement of cardiac output by the Fick principle in infants and children: comparison with the thermodilution method

OBJECTIVE: To compare a system that continuously monitors cardiac output by the Fick principle with measurements by the thermodilution technique in pediatric patients. DESIGN: Prospective direct comparison of the above two techniques. SETTING: Pediatric intensive care unit of a university hospital. PATIENTS: 25 infants and children, aged 1 week to 17 years (median 10 months), who had undergone open heart surgery were studied. Only patients without an endotracheal tube leak and without a residual shunt were included. METHODS: The system based on the Fick principle uses measurements of oxygen consumption taken by a metabolic monitor and of arterial and mixed venous oxygen saturation taken by pulse- and fiberoptic oximetry to calculate cardiac output every 20s. INTERVENTIONS: In every patient one pair of measurements was taken. Continuous Fick and thermodilution cardiac output measurements were performed simultaneously, with the examiners remaining ignorant of the results of the other method. RESULTS: Cardiac output measurements ranged from 0.21 to 4.55 l/min. A good correlation coefficient was found: r2 = 0.98; P < 0.001; SEE = 0.41 l/min. The bias is absolute values and in percent of average cardiac output was - 0.05 l/min or - 4.4% with a precision of 0.32 l/min or 21.3% at 2 SD, respectively. The difference was most marked in a neonate with low cardiac output. CONCLUSION: Continuous measurement of cardiac output by the Fick principle offers a convenient method for the hemodynamic monitoring of unstable infants and children.     

Effects of iced and room temperature injectate on cardiac output measurements in critically ill patients with low and high cardiac outputs

OBJECTIVE: To determine the effect of injectate temperature (iced or room temperature) on cardiac output values in critically ill adults with low and high cardiac outputs. DESIGN: Quasi-experimental. SETTINGS: Two multidisciplinary intensive care units in two large, metropolitan, private, nonprofit hospitals in Texas. SUBJECTS: A convenience sample of 21 critically ill men and women who averaged 61 years of age (range 31 to 82 years) and whose most recent cardiac output measured with room temperature injectate was low (< or = 3.5 L/min) or high (> or = 8.0 L/min). INTERVENTION: Iced injectate and room temperature injectate (randomly ordered) were used to measure cardiac output in each subject. OUTCOME MEASURES: Cardiac output value with iced injectate versus cardiac output value with room temperature injectate. RESULTS: We found significant differences between cardiac output measurements with room temperature and those with iced injectate in eleven critically ill patients with low cardiac outputs (< or = 3.5 L/min) and in ten critically ill patients with high cardiac outputs (> or = 8.0 L/min). In the low cardiac output group, cardiac outputs using room temperature injectate averaged 0.37 L/min (range 0.1 to 1.10 L/min) higher than cardiac outputs using iced injectate (p = 0.001). In the high cardiac output group, measurements with room temperature injectate averaged 1.17 L/min L/min (range 0.3 to 3.0 L/min) higher than cardiac outputs with iced injectate (p = 0.005). Percent differences between room temperature and iced injectate values averaged 13% (range 3% to 27%) in patients with low cardiac outputs and 11% (range 3% to 29%) in patients with high cardiac outputs. Seven (77%) of the patients in the low cardiac output group and four (40%) of the patients in the high cardiac group had a 10% or greater difference--which many clinicians describe as a clinically significant difference--between room temperature and iced injectate cardiac output values. CONCLUSION: Although research is clearly needed to substantiate these findings, we suggest that nurses use iced injectate in patients with low and high cardiac outputs (< or = 3.5 L/min or > or = 8.0 L/min) to ensure accurate measurement of cardiac output.     

High cardiac output hypertensions

Hyperkinetic circulation, as it is related to the clinical hypertensive diseases, is defined and its implications interpreted. These pathophysiological considerations have an important bearing in understanding the pressor mechanisms underlying hypertension and the application of therapy. Another very important consideration is the value of elucidating the mechanisms for the hyperdynamic circulation, for with a clearer understanding of these, we shall come closer to an explanation of the pathogenesis of hypertension.     

Thermodilution cardiac output monitor

The authors describe the case of a 53-year-old woman who suffered from a hemifacial spasm caused by a venous angioma in the posterior fossa. At operation the parenchymal segment of the angioma was preserved and vascular decompression was performed by placing pieces of shredded Teflon between the vessel and nerve. After decompression the patient was completely free from spasm.     

Metabolic consequences of different perioperative fluid therapies in the neonatal period

The rat CNS has been previously shown to synthesize pregnenolone (PREG) and to convert it into progesterone (PROG) and some of its 5 alpha-reduced metabolites. However, the brain cell types involved in the metabolic conversions of PREG are poorly known. Selective conditions were used to obtain purified cultures of neurons and astrocytes from mouse or rat fetal striatum and cerebral cortex. Neurons converted PREG to only one identified metabolite, 20 alpha-dihydro PREG, whereas astrocytes converted PREG also to PROG, 5 alpha-dihydro PROG, and 3 alpha (3 beta)-5 alpha-tetrahydro PROG. Therefore, astrocytes can convert the neurosteroid PREG into the steroid hormone PROG and the neuromodulatory steroid 3 alpha, 5 alpha-tetrahydro PROG, whereas neurons lack the delta 5-3 beta-hydroxysteroid dehydrogenase isomerase activity (and cholesterol side-chain cleavage activity), necessary for the biosynthesis of PROG. Provision of steroid substrates is another example of cross-talk between glial cells and neurons.     

The principles of augmenting the cardiac output in adults

Augmentation of the patient's cardiac output to optimize tissue oxygenation is a primary role of intensive and cardiac care nurses. This involves three approaches: the use of intravenous colloids and occasionally crystalloids, creating a passive stretching of the myocardium to increase cardiac output, the use of inotropic agents which directly stimulate the heart and finally and less commonly the use of cardiac assist devices, notably the intra aortic balloon pump. The choice of method will be dictated by the presenting clinical data and the perceived benefits to the patient of each approach. The role of nurses as part of the health care team is to practice safe, informed care, through an understanding of both the advantages and disadvantages of each approach to the clinical scenario encountered. This paper contains exploration of each of the three principles with a case study approach, allowing the reader to consider a variety of presenting clinical data and appropriate haemodynamic manipulation.     

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.     

Control of cardiac output in essential hypertension

We reviewed 179 patients who had undergone thoracotomy and resection of a suspected malignant coin lesion of the lung over the past 20 years to see if a policy of early thoracotomy was therapeutically valid. The average diameter of all lesions was 1.6 cm; the average diameter of 27 malignant lesions (15 percent) was 1.8 cm. Follow-up of the 27 patients with malignant neoplasms was 100 percent. The present survival rate of the 19 patients with primary lung cancer is 89 percent (17/19). Of 12 cases of primary lung cancer followed for five years, ten (83 percent) survived. The five-year survival of the eight patients with metastatic lesions was 25 percent (2/8). There were no postoperative deaths and few serious postoperative complications (four patients or 2 percent). Very small primary lung cancers detected and treated early do have the same poor prognosis as larger primary cancers.