Blood volume determination by the carbon monoxide method using a new delivery system: accuracy in critically ill humans and precision in an animal model

Physiology of Human Hemorrhage and Compensation

Hemorrhage is a leading cause of death following traumatic injuries in the United States. Much of the previous work in assessing the physiology and pathophysiology underlying blood loss has focused on descriptive measures of hemodynamic responses such as blood pressure, cardiac output, stroke volume, heart rate, and vascular resistance as indicators of changes in organ perfusion. More recent work has shifted the focus toward understanding mechanisms of compensation for reduced systemic delivery and cellular utilization of oxygen as a more comprehensive approach to understanding the complex physiologic changes that occur following and during blood loss. In this article, we begin with applying dimensional analysis for comparison of animal models, and progress to descriptions of various physiological consequences of hemorrhage. We then introduce the complementary side of compensation by detailing the complexity and integration of various compensatory mechanisms that are activated from the initiation of hemorrhage and serve to maintain adequate vital organ perfusion and hemodynamic stability in the scenario of reduced systemic delivery of oxygen until the onset of hemodynamic decompensation. New data are introduced that challenge legacy concepts related to mechanisms that underlie baroreflex functions and provide novel insights into the measurement of the integrated response of compensation to central hypovolemia known as the compensatory reserve. The impact of demographic and environmental factors on tolerance to hemorrhage is also reviewed. Finally, we describe how understanding the physiology of compensation can be translated to applications for early assessment of the clinical status and accurate triage of hypovolemic and hypotensive patients. © 2021 American Physiological Society. Compr Physiol 11:1531-1574, 2021.

Evans Blue Dye: A Revisit of Its Applications in Biomedicine

Evans blue (EB) dye has owned a long history as a biological dye and diagnostic agent since its first staining application by Herbert McLean Evans in 1914. Due to its high water solubility and slow excretion, as well as its tight binding to serum albumin, EB has been widely used in biomedicine, including its use in estimating blood volume and vascular permeability, detecting lymph nodes, and localizing the tumor lesions. Recently, a series of EB derivatives have been labeled with PET isotopes and can be used as theranostics with a broad potential due to their improved half-life in the blood and reduced release. Some of EB derivatives have even been used in translational applications in clinics. In addition, a novel necrosis-avid feature of EB has recently been reported in some preclinical animal studies. Given all these interesting and important advances in EB study, a comprehensive revisiting of EB has been made in its biomedical applications in the review.

Effects of inhaled CO administration on acute lung injury in baboons with pneumococcal pneumonia

Inhaled carbon monoxide (CO) gas has therapeutic potential for patients with acute respiratory distress syndrome if a safe, evidence-based dosing strategy and a ventilator-compatible CO delivery system can be developed. In this study, we used a clinically relevant baboon model of Streptococcus pneumoniae pneumonia to 1) test a novel, ventilator-compatible CO delivery system; 2) establish a safe and effective CO dosing regimen; and 3) investigate the local and systemic effects of CO therapy on inflammation and acute lung injury (ALI). Animals were inoculated with S. pneumoniae (10(8)-10(9) CFU) (n = 14) or saline vehicle (n = 5); in a subset with pneumonia (n = 5), we administered low-dose, inhaled CO gas (100-300 ppm × 60-90 min) at 0, 6, 24, and/or 48 h postinoculation and serially measured blood carboxyhemoglobin (COHb) levels. We found that CO inhalation at 200 ppm for 60 min is well tolerated and achieves a COHb of 6-8% with ambient CO levels ≤ 1 ppm. The COHb level measured at 20 min predicted the 60-min COHb level by the Coburn-Forster-Kane equation with high accuracy. Animals given inhaled CO + antibiotics displayed significantly less ALI at 8 days postinoculation compared with antibiotics alone. Inhaled CO was associated with activation of mitochondrial biogenesis in the lung and with augmentation of renal antioxidative programs. These data support the feasibility of safely delivering inhaled CO gas during mechanical ventilation and provide preliminary evidence that CO may accelerate the resolution of ALI in a clinically relevant nonhuman primate pneumonia model.

Pulse pressure variation is comparable with central venous pressure to guide fluid resuscitation in experimental hemorrhagic shock with endotoxemia

INTRODUCTION

Pulse pressure variation (PPV) has been proposed as a promising resuscitation goal, but its ability to predict fluid responsiveness has been questioned in various conditions. The purpose of this study was to assess the performance of PPV in predicting fluid responsiveness in experimental hemorrhagic shock with endotoxemia, while comparing it with goals determined by a conventional set of guidelines.

METHODS

Twenty-seven pigs were submitted to acute hemorrhagic shock with intravenous infusion of endotoxin and randomized to three groups: (i) control; (ii) conventional treatment with crystalloids to achieve and maintain central venous pressure (CVP) 12 to 15 mmHg, mean arterial pressure of 65 mmHg or greater, and SvO2 (mixed venous oxygen saturation) of 65% or greater; (iii) treatment to achieve and maintain PPV of 13% or less. Parametric data were analyzed by two-way analysis of variance and Tukey test and differences in crystalloid volumes by t test. Predictive values of variables regarding fluid responsiveness were evaluated by receiver operating characteristic curves and multiple logistic regression.

RESULTS

Both treatments produced satisfactory hemodynamic recovery, without statistical differences in fluid administration (P = 0.066), but conventional treatment induced higher CVP (P = 0.001). Areas under receiver operating characteristic curves were larger for CVP (0.77; 95% confidence interval, 0.68-0.86) and PPV (0.74; 95% confidence interval, 0.65-0.83), and these variables were further selected by multiple logistic regression as independent predictors of responsiveness. Optimal PPV cutoff was 15%, with false-positive results involving mean pulmonary arterial pressure of 27 mmHg or greater.

CONCLUSIONS

Acute resuscitation guided by PPV was comparable with the strategy guided by CVP, mean arterial pressure, and SvO2. Central venous pressure and PPV were individually limited but independently predictive of fluid responsiveness.

Impact of Plasma-Lyte pH 7.4 on acid-base status and hemodynamics in a model of controlled hemorrhagic shock

OBJECTIVE

Intravenous infusion of crystalloid solutions is a cornerstone of the treatment of hemorrhagic shock. However, crystalloid solutions can have variable metabolic acid-base effects, perpetuating or even aggravating shock-induced metabolic acidosis. The aim of this study was to compare, in a controlled volume-driven porcine model of hemorrhagic shock, the effects of three different crystalloid solutions on the hemodynamics and acid-base balance.

METHODS

Controlled hemorrhagic shock (40% of the total blood volume was removed) was induced in 18 animals, which were then treated with normal saline (0.9% NaCl), Lactated Ringer's Solution or Plasma-Lyte pH 7.4, in a blinded fashion (n = 6 for each group). Using a predefined protocol, the animals received three times the volume of blood removed.

RESULTS

The three different crystalloid infusions were equally capable of reversing the hemorrhage-induced low cardiac output and anuria. The Lactated Ringer's Solution and Plasma-Lyte pH 7.4 infusions resulted in an increased standard base excess and a decreased serum chloride level, whereas treatment with normal saline resulted in a decreased standard base excess and an increased serum chloride level. The Plasma-Lyte pH 7.4 infusions did not change the level of the unmeasured anions.

CONCLUSION

Although the three tested crystalloid solutions were equally able to attenuate the hemodynamic and tissue perfusion disturbances, only the normal saline induced hyperchloremia and metabolic acidosis.

Comparability of haemoglobin mass measured with different carbon monoxide-based rebreathing procedures and calculations

BACKGROUND

Measurements of haemoglobin mass (Hb(mass)) with the carbon monoxide (CO) rebreathing method provide valuable information in the field of sports medicine, and have markedly increased during the last decade. However, several different approaches (as a combination of the rebreathing procedure and subsequent calculations) for measuring Hb(mass) are used, and routine measurements have indicated that the Hb(mass) differs substantially among various approaches. Therefore, the aim of this study was to compare the Hb(mass) of the seven most commonly used approaches, and then to provide conversion factors for an improved comparability of Hb(mass) measured with the different approaches.

METHODS

Seventeen subjects (healthy, recreationally active, male, age 27.1 ± 1.8 y) completed 3 CO-rebreathing measurements in randomized order. One was based on the 12-min original procedure (CO(original)), and two were based on the 2-min optimized procedure (CO(new)). From these measurements Hb(mass) for seven approaches (CO(originalA-E); CO(newA-B)) was calculated.

RESULTS

Hb(mass) estimations differed among these approaches (p < 0.01). Hb(mass) averaged 960 ± 133 g (CO(newB)), 981 ± 136 g (CO(newA)), 989 ± 130 g (CO(originalE)), 993 ± 126 g (CO(originalA,D)), 1030 ± 130 g (CO(originalB)), and 1053 ± 133 g (CO(originalC)). Procedural variations had a minor influence on measured Hb(mass).

CONCLUSIONS

The relevant discrepancies between the CO-rebreathing approaches originate mainly from different underlying calculations for Hb(mass). Provided Hb(mass) enabled the development of conversion factors to compare average Hb(mass) values measured with different CO-rebreathing approaches. These factors can be used to develop reasonable Hb(mass) reference ranges for both clinical and athletic purposes.

Measuring circulating blood volume in newborn infants using pulse dye densitometry and indocyanine green

BACKGROUND

Circulating blood volume (BV) is an important, but often unconsidered, variable in newborn infants undergoing intensive care. The data on validation and repeatability of BV measurement are limited.

AIM

To validate and test the repeatability of measuring BV in newborn infants using indocyanine green (ICG) and pulse dye densitometry (PDD).

METHODS

Validation--Paired measurements of BV were made using the fetal hemoglobin (HbF) dilution and the PDD method. Repeatability--The BV was measured twice at an interval of 30-40 min in a second group of infants.

RESULTS

Validation--Data from three of 13 infants studied were excluded because of probe dislodgement or ICG injection error. The median (range) birth weight of the 10 infants whose data were analyzed was 1032 g (740-2384 g) and seven (70%) were receiving either mechanical ventilation or nasal CPAP. The median BV measured by HbF dilution was 66.2 ml x kg(-1) (43.7-81.0 ml x kg(-1)) and by the PDD method was 68.9 ml x kg(-1) (49.3-101.0 ml x kg(-1)). The mean difference was 5.92 ml x kg(-1) (SD 17.33 ml x kg(-1)). Repeatability--Twelve infants were studied and three excluded because of probe dislodgement/motion artifact or ICG injection error. The median weight of the nine infants whose data were analyzed was 1208 g (795-2600 g). The median (range) BV1 and BV2 were 70.5 ml x kg(-1) (53.1-160 ml x kg(-1)) and 87.5 ml x kg(-1) (38.0-248.0 ml x kg(-1)), respectively. Mean difference of the two BV estimates (BV1-BV2) was -24.6 ml x kg(-1) (SD 33.3 ml x kg(-1)) and coefficient of repeatability was 66.5 ml x kg(-1).

CONCLUSION

Pulse dye densitometry can be used to measure BV in the newborn infant at the cotside but the repeatability measurements suggest that its use is limited.

Circulating blood volume determination using electronic spin resonance spectroscopy

There have been numerous methods proposed to measure the circulating blood volume (CBV). Nevertheless, none of them have been massively and routinely accepted in clinical diagnosis. This study describes a simple and rapid method, on a rabbit model, using the dilution of autologous red cells labeled with a nitroxide radical (Iodoacetamide-TEMPO), which can be detected by electronic spin resonance (ESR) spectroscopy. Blood samples were withdrawn and re-injected using the ears' marginal veins. The average CBV measured by the new method/body weight (CBV(IAT)/BW) was 59 +/- 7 mL/kg (n = 33). Simultaneously, blood volume determinations using the nitroxide radical and (51)Cr (CBV(Cr)) were performed. In the plot of the difference between the methods (CBV(IAT) - CBV(Cr)) against the average (CBV(IAT) + CBV(Cr))/2, the mean of the bias was -1.1 +/- 6.9 mL and the limits of agreement (mean difference +/-2 SD) were -14.9 and 12.7 mL. Lin's concordance correlation coefficient p(c) = 0.988. Thus, both methods are in close agreement. The development of a new method that allows a correct estimation of the CBV without using radioactivity, avoiding blood manipulation, and decreasing the possibility of blood contamination with similar accuracy and precision of that of the "gold standard method" is an innovative proposal.

Systemic arterial pressure wave reflections during acute hemorrhage*

OBJECTIVE

To determine the effects of hemorrhage on wave-reflection-induced systolic pressure augmentation in the aorta.

DESIGN

Randomized, controlled laboratory experiment.

SETTING

University research laboratory.

SUBJECTS

Twenty-five anesthetized pigs randomized to surgical controls (n = 7), hemorrhage (n = 9, H), and hemorrhage with reinfusion (n = 9, HR).

INTERVENTIONS

Hemorrhage of 1 mL/kg/min over 20 mins followed by observation (H) or reinfusion (HR) of shed blood.

MEASUREMENTS AND MAIN RESULTS

High-fidelity systemic arterial pressure waveforms, from ascending aorta to femoral artery, were transduced and archived digitally using intravascular semiconductor catheter-tipped pressure transducers. Wave-reflection-induced systolic pressure augmentation was determined using the augmentation index in the ascending aorta (AIaa) and distal descending aorta (AIda). Pulse wave velocity, wave travel times, and lumped pressure wave reflection sites were also calculated. AI values were positive at baseline with greater decreases in AIda compared with AIaa observed following hemorrhage, with negative values achieved for AIda alone. AI returned to control values following reinfusion. Lumped reflection site positions and pressure contour maps suggested that a single lumped reflection site (lower abdomen/pelvis) at baseline was replaced by two discrete sites (upper abdomen and pelvis) following hemorrhage, which only recovered following reinfusion. Hemorrhage was associated with hemodynamic conditions that favored late return of wave reflection from the trunk and with the absence of significant changes in systemic vascular resistance.

CONCLUSIONS

Hemorrhage-induced early return of pressure wave reflection from the abdominal vasculature is associated with systolic pressure augmentation in the ascending aorta and has the potential to worsen afterload conditions and decrease coronary artery perfusion and cardiac performance. Hemorrhage-induced splanchnic vasoconstriction causing pressure wave reflection may explain these loading conditions in the ascending aorta, and systolic pressure augmentation may be a more useful guide to left ventricular afterload than systemic vascular resistance.

Blood volume measurements using an integrated fiberoptic monitoring system in a porcine septic shock model

OBJECTIVES

To compare the accuracy of an integrated fiberoptic monitoring system using transpulmonary thermo-dye dilution technique to measure blood volume (BV) with standard method using chromium-51-tagged erythrocytes in septic shock.

DESIGN

Prospective blinded animal laboratory study.

SETTING

University department of anesthesiology.

SUBJECTS

Thirty-five anesthetized and mechanically ventilated pigs (21.4 +/- 2.2 kg) were investigated over a period of 6 hrs.

INTERVENTIONS

Septic shock was induced with fecal peritonitis (0.75 g . kg per body weight autologous feces). A central venous catheter was used for injection of the indicator dyes.

MEASUREMENTS AND MAIN RESULTS

BV was measured by detecting indocyanine green using a 4-Fr aortic catheter with an integrated fiberoptic and thermistor connected to a computer system for calculation of transpulmonary indicator dilution BV (BVTPID). Cr-tagged erythrocytes were used as standard method of BV measurement (BV-Cr). Hemodynamic treatment scheme was aimed at maintenance of a central venous pressure of 12 mm Hg. Data were analyzed using Bland-Altman analyses. One hundred and five data pairs of simultaneous BV measurements were yielded during hemodynamic stability with a mean BVTPID of 64.2 +/- 17.8 mL . kg. Mean BV-Cr was 83.1 +/- 17.0 mL . kg. Linear regression equation was BVTPID = 0.58 x BV-Cr + 15.8 (r = .56, p < .01). Mean bias was 18.9 mL . kg (95% confidence interval, 15.7-22.1 mL . kg), with limits of agreement of -13.9 to 51.7 mL . kg.

CONCLUSIONS

Transpulmonary indicator dilution for blood volume measurement agrees moderately with standard method using Cr-tagged erythrocytes in porcine septic shock.

Low arterial pressure during cardiopulmonary bypass in piglets does not decrease fluid leakage

BACKGROUND

Cardiopulmonary bypass (CPB) is associated with increased fluid filtration occasionally leading to post-operative organ dysfunction. One of the factors determining fluid filtration is the capillary hydrostatic pressure which depends on arterial pressure, venous pressure and pre- to post-capillary resistance ratio. The purpose of this study was to assess whether lowering of the mean arterial pressure and/or the central venous pressure could reduce fluid extravasation during normothermic and hypothermic CPB.

METHODS

Seven piglets were given nitroprusside to a mean arterial pressure of 35-40 mmHg during 60 min of normothermic and 90 min of hypothermic CPB (LP group). They were compared with a control group (C group, n = 7) without blood pressure interventions. Blood chemistry, net fluid balance, plasma volume, colloid osmotic pressure in plasma and interstitial fluid, intravascular protein masses, fluid extravasation rate and total tissue water content were measured or calculated.

RESULTS

Mean arterial pressure was significantly lower in the LP group than in the C group during CPB. Plasma volume tended to increase in the LP group (P > 0.05), but remained essentially unchanged in the C group. Net fluid balance in the LP group was more positive than in the C group 30 min after CPB start [1.02 (0.15) vs. 0.56 (0.13) ml/kg/min (Mean (SEM) P < 0.05)]. Fluid extravasation rate tended to be higher in the LP group and total tissue water content of the gastrointestinal tract, left myocardium and skin was significantly elevated compared with the C group.

CONCLUSION

During CPB, lowering of the mean arterial pressure using nitroprusside did not reduce fluid extravasation. On the contrary, the data may implicate an increase in edema formation during low pressure CPB.

Clinically practical blood volume assessment with fluorescein-labeled HES

BACKGROUND

Standard techniques for measuring blood volume (BV) entail administering radioactivity and human albumin. This is laborious, expensive, and impractical in acute settings. An alternative method suitable for widespread routine application was assessed.

STUDY DESIGN AND METHODS

Seventy-nine ambulant outpatients and 18 intensive care unit (ICU) patients were prospectively recruited. Measurements of RBC volume (RCV) and plasma volume (PV) were performed with radiochromium-labeled RBCs (51Cr), radioiodinated albumin (125I), and fluorescein-labeled HES (FITC-HES). Small molecules overestimate PV because of vascular endothelial dysfunction (ED) and increased capillary permeability; a reference value for PV was therefore derived with the RCV and Hct.

RESULTS

Mean PV with 125I dilution was 230 mL (SD, 185 mL) greater than that with FITC-HES in outpatients. This difference was more exaggerated, 345 mL (SD, 371 mL), in ICU patients likely to have ED. Both the PV measured with FITC-HES and the 125I dilution correlated closely with the PV derived with RCV and Hct (r = 0.950 and 0.925, respectively) in the ICU patients.

CONCLUSION

FITC-HES estimates PV more accurately than 125I. FITC-HES should replace radioactive tracers for assessing BV. Comparing the estimates of PV with molecules of differing molecular weights may have clinical utility as an indicator of ED.

Use of xenon as a sedative for patients receiving critical care

OBJECTIVE

Many sedative regimens are used in the intensive care setting, but none are wholly without adverse effect. Xenon is a noble gas with sedative and analgesic properties. It has been used successfully as a general anesthetic and has many desirable properties, not least of which is a minimal effect on the myocardium. In theory, xenon may provide sedation without adverse effect for certain groups of critically ill patients. The objective of this study was to assess the feasibility of using xenon as an intensive care sedative.

DESIGN

Double-blind, randomized study.

SETTING

Tertiary-level intensive care unit.

SUBJECTS

Twenty-one patients admitted to an intensive care unit following elective thoracic surgery.

INTERVENTIONS

A standard intensive care sedation regimen (intravenous propofol at 0-5 mg.kg-1.hr-1 and alfentanil 30 microg.kg-1.hr-1) was compared with a xenon sedation regimen delivered using a novel bellows-in-bottle delivery system. MEASUREMENTS AND MAIN RESULTS Each sedative regimen was continued for 8 hrs. The hemodynamic effects, additional analgesic requirements, recovery from sedation, and effect on hematological and biochemical variables were compared for the two sedation regimens. All patients were successfully sedated during the xenon regimen. The mean +/- SD end-tidal xenon concentration required to provide sedation throughout the duration of the study was 28 +/- 9.0% (range, 9-62%). Arterial systolic, diastolic, and mean pressures showed a greater tendency for negative gradients in patients receiving the propofol regimen (p <.05, p <.1, and p <.01, respectively). Recovery following xenon was significantly faster than from the standard sedation regimen (p <.0001). Hematological and biochemical laboratory markers were within normal clinical limits in both groups.

CONCLUSIONS

Xenon provided satisfactory sedation in our group of patients. It was well tolerated with minimal hemodynamic effect. Recovery from this agent is extremely rapid. We have demonstrated the feasibility of using xenon within the critical care setting, without adverse effect.

Changes in circulating blood volume after infusion of hydroxyethyl starch 6% in critically ill patients

BACKGROUND

The cardiovascular response to a volume challenge with hydroxyethyl starch (HES) (200/0.5) 6% depends on the relation between the volume of HES 6% infused and the expansion of the blood volume in critically ill patients. However, only relatively limited data exist on the plasma expanding effect of infusion of HES 6% in critically ill patients. The purpose of the study was to evaluate the variation in the expansion of the circulating blood volume (CBV) in critically ill patients after infusion of 500 ml of colloid (HES (200/0.5) 6%) using the carbon monoxide method.

METHODS

In 20 consecutive patients admitted to the ICU requiring mechanical ventilation and volume expansion, 500 ml of HES (200/0.5) 6% was infused. The CBV was measured immediately before the infusion, 10 min after completing the infusion and then hourly for 8 h.

RESULTS

The median volume expansion immediately after infusion was 470 ml (range 270 ml to 840 ml). The corresponding values after 4 h and 8 h were 265 ml (range -30 ml to 460 ml) and 120 ml (range -210 ml to 360 ml), respectively. The increase in CBV was only statistically significant for 4 h. The coefficient of variation of the method for estimation of CBV was 3.6%.

CONCLUSIONS

The large interindividual variation of the volume expansion after infusion of HES 6% in critically ill patients illustrates one of the difficulties in optimizing colloid therapy and interpretating the changes in hemodynamic variables after a colloid challenge.

A novel approach to measuring circulating blood volume: the use of a hemoglobin-based oxygen carrier in a rabbit model

Hemoglobin-based oxygen carriers (HBOC) may be ideal for monitoring circulating plasma volume (CV-P) and circulating blood volume (CV-B). We used an HBOC (Hemoglobin glutamer-200 [bovine], Oxyglobin; Biopure, Cambridge, MA) as an indicator for relative CV-B in the rabbit model. Accuracy of the technique was determined by comparison with the Evans blue dye (EBD) dilution technique in 19 anesthetized female New Zealand rabbits weighing 2.0 to 10.6 kg. The measurements were performed at baseline, after hemorrhage (1/3 of CV-B), normovolemic hemodilution (replacement of 1/3 CV-B by Hextend; Abbot Laboratories, North Chicago, IL), and hypervolemic hemodilution (additional infusion of Hextend(R) in a volume equal to 1/3 of CV-B). Hemoglobin concentration was measured by using a HemoCue photometer (HemoCue AB, Angelholm, Sweden). EBD concentration was analyzed by using linear regression to estimate Time 0 concentration; Time 0 was defined as EBD injection time. The difference between CV-P values determined by EBD and HBOC dilution was independent from the magnitude of the CV-P value. The relative bias was 1.29 mL, and the precision (one SD) was 2.82 mL. The difference did not reach statistical significance.

IMPLICATIONS

Circulating plasma and blood volumes can be accurately estimated by plasma hemoglobin concentration measurements by using hemoglobin-based oxygen carrier infusion.

Selected contribution: redistribution of pulmonary perfusion during weightlessness and increased gravity

To compare the relative contributions of gravity and vascular structure to the distribution of pulmonary blood flow, we flew with pigs on the National Aeronautics and Space Administration KC-135 aircraft. A series of parabolas created alternating weightlessness and 1.8-G conditions. Fluorescent microspheres of varying colors were injected into the pulmonary circulation to mark regional blood flow during different postural and gravitational conditions. The lungs were subsequently removed, air dried, and sectioned into approximately 2 cm(3) pieces. Flow to each piece was determined for the different conditions. Perfusion heterogeneity did not change significantly during weightlessness compared with normal and increased gravitational forces. Regional blood flow to each lung piece changed little despite alterations in posture and gravitational forces. With the use of multiple stepwise linear regression, the contributions of gravity and vascular structure to regional perfusion were separated. We conclude that both gravity and the geometry of the pulmonary vascular tree influence regional pulmonary blood flow. However, the structure of the vascular tree is the primary determinant of regional perfusion in these animals.