Measurement of cerebral blood volume using near-infrared spectroscopy and indocyanine green elimination. (1/161)

Methods for measuring cerebral blood volume (CBV) have traditionally used radioisotopes. More recently, near-infrared spectroscopy (NIRS) has been used to measure CBV by using a technique involving O(2) desaturation of cerebral tissue, where the observed change in the concentration of oxygenated hemoglobin is a marker of the volume of blood contained within the brain. A new integration method employing NIRS is described by using indocyanine green (ICG) as the intravascular marker. After bolus injection, concentration-time integrals of cerebral tissue ICG concentration ([ICG](tissue)) measured by NIRS are compared with corresponding integrals of the cerebral blood ICG concentrations ([ICG](blood)) estimated by high-performance liquid chromatography of peripheral blood samples with allowance for cerebral-to-large-vessel hematocrit ratio. It is shown that CBV = integral [ICG]tissue/[ICG]blood. Measurements in 10 adult volunteers gave a mean value of 1.1 +/- 0.39 (SD) ml/100 g illuminated tissue. This result, although lower than previous NIRS estimations, is consistent with the long extracerebral path of light in the adult head. Scaling of results is required to take into account this component of the optical pathlength.  (+info)

Measurement of blood volume in surgical and intensive care practice. (2/161)

Clinical studies to assess the benefits of blood transfusion or haemodilution in critical illness should take account of measured CBV before, during and after intervention. As mentioned above, surrogate measures of CBV are inadequate and studies based on these must be considered incomplete, because they cannot distinguish between effects of changes in haemoglobin concentration and changes in blood volume. The choice of a suitable technique for measuring CBV depends on the facilities available locally. In general, methods based on labelled red cells are more reliable but are technically demanding and time consuming. Those based on albumin are likely to yield false high values and this is particularly true in all patients with impaired capillary integrity. The most promising plasma marker is hydroxyethyl starch which may be particularly useful when the polysaccharide is labelled with a fluorescent dye. Attaching fluorescein to hydroxyethyl starch is not difficult and, should demand be sufficient, it may well become available from manufacturers who are already capable of providing other fluorescent polysaccharides. The clinical benefits of such a development would include more rational schedules of i.v. fluid and blood transfusion management in surgical and intensive care patients.  (+info)

The female reproductive cycle is an important variable in the response to trauma-hemorrhage. (3/161)

Although immune functions in proestrus females are maintained after hemorrhage as opposed to decreased responses in males, it remains unknown whether such a sexual dimorphism also exists with regard to cardiovascular and hepatocellular functions under those conditions. To study this, male and female (estrus and proestrus) rats underwent a 5-cm midline laparotomy and were bled to and maintained at a mean blood pressure of 40 mmHg until 40% of the maximal bleed-out volume was returned in the form of Ringer lactate (RL). Rats were then resuscitated with four times the shed blood volume with RL. At 24 h thereafter, cardiac index; heart performance; hepatocellular function; and plasma estradiol, testosterone, and prolactin levels were measured. Cardiovascular and hepatocellular functions were depressed in males and estrus females (P < 0.05) but were not depressed in proestrus females after resuscitation. Plasma estradiol and prolactin levels were highest in proestrus females (P < 0.05), whereas males had high testosterone and the lowest estradiol levels (P < 0.05). Thus the female reproductive cycle is an important variable in the response to hemorrhage. Because low testosterone and high estradiol and prolactin levels appear to be beneficial for organ functions after trauma-hemorrhage, antagonism of testosterone receptors and/or increases in estradiol and prolactin levels in males and estrus females, respectively, may be novel approaches for improving organ functions under such conditions.  (+info)

Local cerebral blood volume determined by three-dimensional reconstruction of radionuclide scan data. (4/161)

We developed a method to determine in man absolute values of local cerebral blood volume (LCBV) localized throughout the brain in three dimensions and presented in a cross-sectional picture format. Previously, absolute values of LCBV have been determined in vivo by stimulated X-ray fluorescence, but these determinations have been limited to one point in the brain at a time. All other previous estimates of LCBV by external emission counting have been contaminated by the significant contribution of blood in the overlying scalp and cranium. In our method, a transverse section scan is made after the injection of -99m-Tc-labeled red blood cells into a peripheral vein. Data processing then gives a point-to-point estimate of absolute radionuclide concentration analogous to an autoradiograph. After the concentration of blood activity is determined, counting data are converted to a two-dimensional map of LCBV representing a cross section at a known level of the brain. In a series of five baboons, the following equation was obtained for the regression plane that relates LCBV in the center of the brain to arterial carbon dioxide tension (P-ALPHA-CO2) and mean arterial blood pressure (MABP): LCBV equals 2.88 + 0.049P-ALPHA-CO2 MINUS 0.013MABP. In patients, LCBE values ranged from 2 to 4 ml/100 g depending on location; higher values corresponded to regions of cerebral cortex. Differences in blood volumes of focal brain lesions were also quantified.  (+info)

Regulation of extracellular volume and interstitial fluid pressure in rat bone marrow. (5/161)

The volume and fluid pressure characteristics of the intact bone marrow is incompletely understood. We used microspheres and lipoproteins for measurements of intravascular volume (IVV) and EDTA for interstitial fluid volume (IFV) within the rat bone marrow. Interstitial fluid pressure (IFP) was determined with micropipettes connected to a servo-controlled counter-pressure system. Both the microspheres and the lipoproteins yielded estimates of IVV of approximately 1 ml/100 g. After a brief reactive hyperemia, IVV increased to 2.5 ml/100 g, whereas IFV decreased with approximately 1.5 ml/100 g, so that total extracellular volume did not change. Baseline bone marrow IFP was 9.7 mmHg. The hyperemia led to a transient twofold increase in IFP, whereas a marked blood loss decreased IFP by almost one-half. These novel data suggest that extracellular volume and IFP within the bone marrow can be measured with tracer methods and the micropuncture technique. The responses of IVV, IFV, and IFP during changes in blood flow to the bone marrow suggest a tight regulation and are thus compatible with those for a low-compliant tissue.  (+info)

Clinical evaluation of circulating blood volume in critically ill patients--contribution of a clinical scoring system. (6/161)

The circulating blood volume (CBV) of critically ill patients may be difficult to estimate on the basis of history and physical examination. The aim of this study was to evaluate the ability of seven clinical signs and central venous pressure (CVP) to predict CBV in critically ill patients; CBV was evaluated with the [125I]human serum albumin technique. A scoring system was constructed using a combination of independence Bayes method and logistic regression. Sixty-eight patients constituted a 'model development' sample and 30 patients a validation sample. Thirty-six patients (53%) in the model development sample were found to have a low CBV (measured CBV at least 10% lower than the predicted mean normal CBV). Neither the haemodynamic variables monitored in ICU, nor the spot urinary sodium concentrations were different between patients with and without a low CBV. Individually, none of the clinical signs tested have a good positive or negative predictive value. For CVP, only extreme values seem to have clinical significance. To construct the score, the signs tested were ranked according to their discriminating efficacy. The probability of a low CBV was obtained by adding the weights of each sign tested and converting the score obtained into a probability. On a validation sample of 30 patients, the predictions are reliable as assessed by Z statistics ranging between -2 and +2. Our results suggest that: (1) individually, no clinical sign presented a clinical useful predictive value; and (2) a clinical scoring system may be helpful for the evaluation of CBV in critically ill patients.  (+info)

Mechanisms of edema formation after intracerebral hemorrhage: effects of extravasated red blood cells on blood flow and blood-brain barrier integrity. (7/161)

BACKGROUND AND PURPOSE: Red blood cell (RBC) lysis contributes to brain edema formation after intracerebral hemorrhage (ICH), and RBC hemolysate (oxyhemoglobin) has been implicated to be a spasminogen in subarachnoid hemorrhage. Whether cerebral ischemia contributes to brain edema formation after ICH remains unclear, however. The aims of this study were to test whether extravasation of RBCs induces cerebral ischemia and/or blood-brain barrier disruption in a rat ICH model characterized by perihematomal brain edema. METHODS: In this study, 87 pentobarbital-anesthetized Sprague-Dawley rats were used. In each animal, saline, packed RBCs, or lysed RBCs were injected into the right caudate nucleus. Sham injections served as controls. Regional cerebral blood flow, brain water and ion contents, blood-brain barrier integrity, and plasma volume were measured. RESULTS: Intraparenchymal infusion of lysed RBCs caused severe brain edema by the first day but did not induce ischemic cerebral blood flows. In contrast, blood-brain barrier permeability increased during the first day after infusion of lysed RBCs (a 3-fold increase) and 3 days after infusion of packed RBCs (a 4-fold increase). CONCLUSIONS: These results suggest that ischemia is not present at 24 or 72 hours after hematoma induction by injection of intact or lysed RBCs. RBC constituents that appear after delayed lysis, however, increase blood-brain barrier permeability, which contributes to edema formation.  (+info)

Absence of beneficial effect of acute normovolemic hemodilution combined with aprotinin on allogeneic blood transfusion requirements in cardiac surgery. (8/161)

BACKGROUND: The efficacy of acute normovolemic hemodilution (ANH) in decreasing allogeneic blood requirements remains controversial during cardiac surgery. METHODS: In a prospective, randomized study, 80 adult cardiac surgical patients with normal cardiac function and no high risk of ischemic complications were subjected either to ANH, from a mean hematocrit of 43% to 28%, or to a control group. Aprotinin and intraoperative blood cell salvage were used in both groups. Blood (autologous or allogeneic) was transfused when the hematocrit was less than 17% during cardiopulmonary bypass, less than 25% after cardiopulmonary bypass, or whenever clinically indicated. RESULTS: The amount of whole blood collected during ANH ranged from 10 to 40% of the patients' estimated blood volume. Intraoperative and postoperative blood losses were not different between control and ANH patients (total blood loss, control: 1,411 +/- 570 ml, n = 41; ANH: 1,326 +/- 509 ml, n = 36). Allogeneic blood was given in 29% of control patients (median, 2; range, 1-3 units of packed erythrocytes) and in 33% of ANH patients (median, 2; range, 1-5 units of packed erythrocytes; P = 0.219). Preoperative and postoperative platelet count, prothrombin time, and partial thromboplastin time were similar between groups. Perioperative morbidity and mortality were not different in both groups, and similar hematocrit values were observed at hospital discharge (33.7 +/- 3.9% in the control group and 32.6 +/- 3.7% in the ANH group; nonsignificant) CONCLUSIONS: Hemodilution is not an effective means to lower the risk of allogeneic blood transfusion in elective cardiac surgical patients with normal cardiac function and in the absence of high risk for coronary ischemia, provided standard intraoperative cell saving and high-dose aprotinin are used.  (+info)