Estimation of hepatic distributional volumes using non-labeled reference markers.

Hepatic distributional volumes were investigated in the in situ perfused rat liver. Perfusion experiments were conducted using Krebs bicarbonate buffer delivered via the portal vein in single-pass mode at a total flow rate of 15 mL/min. A bolus dose of normal erythrocytes (RBC, vascular marker) and Evans blue (EB, extracellular marker) respectively was administered in the presence and absence of protein. At the end of the experiment, liver total water content was determined by desiccation and freeze-drying methods. Similar moment analysis results and superimposable effluent curves were obtained in the presence (RBC, mean transit time [MTT]: 7.31 +/- 0.45 s and volume of distribution [V]: 0.17 +/- 0.01 mL/g; EB, MTT: 10.9 +/- 0.62 s and V: 0.25 +/- 0.02 mL/g) and in the absence (RBC, MTT: 7.55 +/- 0.84 s and V: 0.18 +/- 0.02 mL/g; EB, MTT: 9.24 +/- 0.77 s and V: 0.20 +/- 0.02 mL/g) of protein, which indicates that the hepatic distribution of RBC and EB within the liver is not influenced by protein. Furthermore, the almost identical results obtained with the desiccation and freeze-drying methods clearly suggest that the freeze-drying method can be used as an alternative to desiccation for the estimation of liver water content.

Accuracy and repeatability of pediatric cardiac output measurement using Doppler: 20-year review of the literature.

OBJECTIVE: Review of the accuracy and repeatability of Doppler cardiac output (CO) measurements in children. DESIGN: Publications in the scientific literature retrieved using a computerized Medline search from 1982-2002 and a manual review of article bibliographies. Studies comparing Doppler flow measurements with thermodilution, Fick, or dye dilution methods in the pediatric critical care setting were identified to assess the bias, precision, and intra- and interobserver repeatability of Doppler CO measurement. Where results were not suitable for comparison and the original measurements available, data were re-analyzed using appropriate statistical methods and presented in comparative tables. RESULTS: The precision of pediatric Doppler CO measurements compared to thermodilution, dye dilution, or Fick methods is around 30% and repeatability varies from less than 1% to 22%. Bias is generally less than 10% but varies considerably. CONCLUSIONS: The bias, precision, and repeatability from study to study indicate that Doppler CO measurements are acceptably reproducible in children, with best results when used to track changes rather than absolute values, and using the transesophageal approach.

Plasma volume by Evans blue: effects of eating and comparison with other methods at altitude.

HYPOTHESIS: Measurements of plasma volume (PV) and its changes (delta%PV) by Evans blue (EB) dye are presumed to be valid only in fasting subjects. In addition, delta%PVEB with acute altitude exposure has not been compared with other methods employing the concentration or dilution of naturally occurring blood (hematocrit (Hct), hemoglobin (Hb)) and plasma (density, proteins) components, but should be similar if capillary permeability and the sampled vein/whole body Hct ratio remain unchanged. METHODS: PVEB was determined in six subjects while fasting or eating on different days, with injection and sampling in the same arm, 4-h extrapolation to time zero and correcting readings with the 620-740 A method. For 93 experiments at altitude, delta%PVEB was obtained similarly from a 3-h extrapolation near the end of a 12-h chamber exposure to 426 mm Hg (-4,880 m =16,000 ft) and at the same time on the preceding control day. RESULTS: Mean PVEB with and without eating was not significantly different (SE of absolute difference = +/- 2.8%). The EB decay curves had significantly more scatter with eating than fasting. The fasting vs. non-fasting values for the single 20-min post-injection point also gave a close comparison (r = +0.97). At altitude the loss in PV measured with EB was significantly greater (delta%PVEB = -6.3%) than losses estimated from Hct-Hb (-2.9%), plasma protein (-3.7%), and plasma density (-3.9%). The expected larger PV loss in subjects tolerant to altitude sickness compared with intolerant ones was most clearly shown by delta%PVEB (8.8%). CONCLUSIONS: Obtaining more samples can offset reproducibility lost by eating. The delta%PVEB were largest and nearest to values previously reported at altitude, perhaps because the single baseline and altitude samples utilized by the other methods are more sensitive to subtle, transient fluctuations in body water and vasomotor tone associated with apprehension, vomiting, fluid intake, and regional vasodilation and constriction.

Measurement of blood concentration of indocyanine green by pulse dye densitometry--comparison with the conventional spectrophotometric method.

OBJECTIVE: Pulse dye densitometry (PDD) uses two wavelengths (805 and 890 nm) in association with pulse oximetry to compute the arterial blood concentration ratio of indocyanine green (ICG) to hemoglobin (Hb). When Hb is measured in the usual way, this permits the PDD to compute cardiac output, plasma or blood volume, and liver blood flow following an intravenous injection of ICG. In this study, we evaluate the accuracy of the PDD calculation of dye concentration by comparing it with measurement of the dye concentration in blood (Cb) measured by the spectrophotometric cuvette method during dye clearance in patients. METHODS: In 25 patients receiving major abdominal surgery, ICG (10, 20, or 40 mg) was injected into a central vein and arterial ICG concentration was continuously and simultaneously monitored at nose and finger by PDD; concurrently, ICG concentrations were measured by a spectrophotometer at 805 nm in 4 radial arterial blood samples. Repeated measures or one-way ANOVA were used for comparison of ICG concentrations and percent errors by PDD at the nose, finger, and Cb. RESULTS: The percent error (bias) of calculated dye concentration and its standard deviation (precision) was -3.9 +/- 16.8% (p < 0.01) with the probe on a nostril and 3.4 +/- 12.6% using the finger probe. These errors were found to be greatest when the mean transit time of the dye was rapid (-20.7 +/- 6.8% at nose p < 0.01 and -8.5 +/- 2.5% at finger p < 0.05) due to factors other than the time delay of blood sampling. CONCLUSION: These errors are of similar size to those associated with thermal cardiac output measurement, suggesting that PDD should be valuable clinically as a noninvasive tool especially since it provides values for blood volume and liver blood flow.

Correction for apparent prolongation of mean transit time resulting from response time in a thermodilution system.

We investigated a method of correcting an apparent prolongation in the measured mean transit time (MTT), resulting from the response time of the thermodilution system. We measured the mean response times (MRT) for five commercially available thermistor-tipped catheters by recording their step function response curves. MRT is the sum of the time from the point of step change to the point of the first detection of change in temperature (latency time) plus the time from the first detection to the point of 63.2% of full response (time constant). By using a flow loop model filled with saline through a mixing chamber, we recorded pairs of thermodilution curves simultaneously with pairs of catheters, and studied the influence of MRT on MTT over the constant flow rates of 1-6 L/min. The difference in MRT's (delta MRT, second) between a pair of thermodilution systems correlated with the difference in MTT's (delta MTT, second) between a corresponding pair of thermodilution curves, yielding an equation: delta MTT = 1.07 delta MRT = 0.04 (n = 72, r = 0.95), delta MTT/delta MRT = 1.02 +/- 0.18 (mean +/- SD). We conclude that an apparent prolongation of MTT due to response time is removable by subtracting MRT from measured MTT.

[Results of the dye dilution technic in peripheral arteriovenous fistulas and hyperthyroidism]. / Ergebnisse der Farbstoffverdünnungstechnik bei peripheren, arteriovenösen Fisteln und Hyperthyreosen

Dye dilution curves (DDC) from 35 patients with arteriovenous fistulas and from 22 patients with hyperthyreoidism were performed and compared with results in 122 healthy subjects. In most cases Cardiogreen was injected into an antecubital vein during reactive hyperaemia. On the arterial side, dye concentrations were recorded by ear oximetry. The appearance time was shortened in most cases. During dilution time dye curves were interrupted by an early recirculation in hyperthyreoidism, whereas in 29 patients with haemodialysis fistulas this interruption was discrete and detectable only when compared with results after occlusion of the fistulas. Different shapes of dilution curves were observed: 1. in most cases DDC seemed to be normal or near normal, often with an accelerated indicator passage; 2. DDC with an interruption of the dilution limb by an early recirculation; 3. DDD, showing a hump of the dilution limb; 4. asymmetrical DDC or DDC with a flat shoulder of the dilution limb and without a recirculation wave. Patients with hyperthyreoidism and arteriovenous fistulas had no different shapes of dilution curves. The results are discussed with special reference to the DDC in patients with central left-to-right shunts.

The precision of a special purpose analog computer in clinical cardiac output determination.

Three hundred dye-dilution curves taken during our first year of clinical experience with the Waters CO-4 cardiac output computer were analyzed to estimate the errors involved in its use. Provided that calibration is accurate and 5.0 mg of dye are injected for each curve, then the percentage standard deviation of measurement using this computer is about 8.7%. Included in this are the errors inherent in the computer, errors due to baseline drift, errors in the injection of dye and acutal variation of cardiac output over a series of successive determinations. The size of this error is comparable to that involved in manual calculation. The mean value of five successive curves will be within 10% of the real value in 99 cases out of 100. Advances in methodology and equipment are discussed which make calibration simpler and more accurate, and which should also improve the quality of computer determination. A list of suggestions is given to minimize the errors involved in the clinical use of this equipment.