Fluid therapy in uncontrolled hemorrhage--what experimental models have taught us

Blood volume and hemodynamics during treatment of major hemorrhage with Ringer solution, 5% albumin, and 20% albumin: a single-center randomized controlled trial

BACKGROUND

Volume replacement with crystalloid fluid is the conventional treatment of hemorrhage. We challenged whether a standardized amount of 5% or 20% albumin could be a viable option to maintain the blood volume during surgery associated with major hemorrhage. Therefore, the aim of this study was to quantify and compare the plasma volume expansion properties of 5% albumin, 20% albumin, and Ringer-lactate, when infused during major surgery.

METHODS

In this single-center randomized controlled trial, fluid replacement therapy to combat hypovolemia during the hemorrhagic phase of cystectomy was randomly allocated in 42 patients to receive either 5% albumin (12 mL/kg) or 20% albumin (3 mL/kg) over 30 min at the beginning of the hemorrhagic phase, both completed by a Ringer-lactate replacing blood loss in a 1:1 ratio, or Ringer-lactate alone to replace blood loss in a 3:1 ratio. Measurements of blood hemoglobin over 5 h were used to estimate the effectiveness of each fluid to expand the blood volume using the following regression equation: blood loss plus blood volume expansion = factor + volume of infused albumin + volume of infused Ringer-lactate.

RESULTS

The median hemorrhage was 848 mL [IQR: 615-1145]. The regression equation showed that the Ringer-lactate solution expanded the plasma volume by 0.18 times the infused volume while the corresponding power of 5% and 20% albumin was 0.74 and 2.09, respectively. The Ringer-lactate only fluid program resulted in slight hypovolemia (mean, - 313 mL). The 5% and 20% albumin programs were more effective in filling the vascular system; this was evidenced by blood volume changes of only + 63 mL and - 44 mL, respectively, by long-lasting plasma volume expansion with median half time of 5.5 h and 4.8 h, respectively, and by an increase in the central venous pressure.

CONCLUSION

The power to expand the plasma volume was 4 and almost 12 times greater for 5% albumin and 20% albumin than for Ringer-lactate, and the effect was sustained over 5 h. The clinical efficacy of albumin during major hemorrhage was quite similar to previous studies with no hemorrhage.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05391607, date of registration May 26, 2022.

Advances in the Physiology of Transvascular Exchange and A New Look At Rational Fluid Prescription

The Starling principle is a model that explains the transvascular distribution of fluids essentially governed by hydrostatic and oncotic forces, which dynamically allow vascular refilling according to the characteristics of the blood vessel. However, careful analysis of fluid physiology has shown that the principle, while correct, is not complete. The revised Starling principle (Michel-Weinbaum model) provides relevant information on fluid kinetics. Special emphasis has been placed on the endothelial glycocalyx, whose subendothelial area allows a restricted oncotic pressure that limits the reabsorption of fluid from the interstitial space, so that transvascular refilling occurs mainly from the lymphatic vessels. The close correlation between pathological states of the endothelium (eg: sepsis, acute inflammation, or chronic kidney disease) and the prescription of fluids forces the physician to understand the dynamics of fluids in the organism; this will allow rational fluid prescriptions. A theory that integrates the physiology of exchange and transvascular refilling is the "microconstant model", whose variables include dynamic mechanisms that can explain edematous states, management of acute resuscitation, and type of fluids for common clinical conditions. The clinical-physiological integration of the concepts will be the hinges that allow a rational and dynamic prescription of fluids.

Standardized blood volume changes monitored by capnodynamic hemodynamic variables: An experimental comparative study in pigs

BACKGROUND

The capnodynamic method, based on Volumetric capnography and differential Fick mathematics, assess cardiac output in mechanically ventilated subjects. Capnodynamic and established hemodynamic monitoring parameters' capability to depict alterations in blood volume were investigated in a model of standardized hemorrhage, followed by crystalloid and blood transfusion.

METHODS

Ten anesthetized piglets were subjected to controlled hemorrhage (450 mL), followed by isovolemic crystalloid bolus and blood re-transfusion. Intravascular blood volume, and all hemodynamic variables, were determined twice after each intervention. The investigated hemodynamic variables were: cardiac output and stroke volume for capnodynamics and pulse contour analysis, respectively, pulse pressure and stroke volume variability and mean arterial pressure. One-way ANOVA and Tukey's test for multiple comparisons were used to identify significant changes. Trending was assessed by correlation and concordance.

RESULT

Concordance against intravascular volume changes for capnodynamic cardiac output and stroke volume were 96 and 94%, with correlations r = .78 and .68, (p < .0001) with significant changes for 6 and 5 of the 6 measuring points, respectively. Mean arterial pressure and pulse pressure variation had a concordance of 85% and 87%, r = .67 (p < .0001) and r = -.45 (p < .0001), respectively, and both changed significantly for 3 of 6 measuring points. Pulse contour stroke volume variation, stroke volume and cardiac output, showed concordance and correlation of 76%, r = -.18 (p = .11), 63%, r = .28 (p = .01) and 50%, r = .31 (p = .007), respectively and significant change for 1, 1 and 0 of the measuring points, respectively.

CONCLUSION

Capnodynamic cardiac output and stroke volume did best depict the changes in intravascular blood volume. Pulse contour parameters did not follow volume changes in a reliable way.

Investigation of biomarkers for impending fluid overload in a feline acute haemorrhage-resuscitation model

OBJECTIVE

To determine biomarkers for impending fluid overload during intravenous fluid administration in a feline haemorrhage-resuscitation model.

STUDY DESIGN

Randomized crossover study.

ANIMALS

A group of six domestic cats (mean age and weight: 21 months; 4.9 kg, respectively).

METHODS

The cats underwent three treatments, 2 months apart. They were anaesthetized and instrumented to measure a range of physiological, blood gas, haematological and biochemical variables over time. Samples were taken during a health check, before haemorrhage, after haemorrhage and then at 30 minute intervals during fluid resuscitation and 24 hours later. The three treatments were: 1) control, sham haemorrhage and resuscitation; 2) lactated Ringer's solution (LRS); and 3) 6% tetrastarch 130/0.4 (Vol) where the cats underwent a controlled haemorrhage then resuscitation by administering LRS and Vol at 60 and 20 mL kg^-1 hour^-1, respectively, for 120 minutes. Fluid overload was identified by nasal discharge and radiographic evidence. Biomarkers were variables that exceeded the reference interval for cats during treatment. Potential biomarkers were analysed using receiver operating characteristic curves (p < 0.05).

RESULTS

Mean ± standard deviation total blood loss was 10.2 ± 2.3, 29.3 ± 9.0 and 29.1 ± 6.3 mL kg^-1 for control, LRS and Vol, respectively. The total volume of LRS and Vol administered was 120 and 40 mL kg^-1, respectively. Haematocrit, albumin, magnesium, chloride-to-sodium ratio and sodium-chloride difference were identified as potential biomarkers. These variables exceeded the reference intervals from 30 minutes of resuscitation onwards. A chloride-to-sodium ratio > 0.84 was the most sensitive (90%) and specific (75%) of all potential biomarkers.

CONCLUSIONS AND CLINICAL RELEVANCE

Changes in physiological variables, haematocrit and albumin were poor biomarkers of impending fluid overload compared with electrolytes. Finding the ideal biomarker to identify impending fluid overload of commonly used intravenous fluids should improve the safety of their administration in cats.

Indices of muscle and liver dysfunction after surviving hemorrhage and prolonged hypotension

BACKGROUND

This study determined the long-term effects of prolonged hypotension (PH) on liver, muscle, and kidney dysfunction. The hypothesis was that longer duration of PH after hemorrhage will result in greater organ dysfunction.

METHODS

Baboons were sedated and hemorrhaged (30% blood volume). Systolic blood pressure greater than 80 mm Hg was maintained for 1 hour (1 hr-PH; n = 5), 2 hours (2 hr-PH; n = 5), or 3 hours (3 hr-PH; n = 5). After PH, hemorrhage volume was replaced. Animals were recovered and monitored for 21 days. Control animals were hemorrhaged and immediately resuscitated (0 hr-PH, n = 3). Data are Mean ± Standard Deviation, and analyzed by 2-way repeated measures ANOVA and Holm-Sidak test.

RESULTS

Hemorrhage resulted in mild hypotension. Minimal resuscitation was required during the hypotensive phase, and survival rate was 100%. Significant increases (p < 0.001) in alanine aminotransferase, aspartate aminotransferase, creatine phosphokinase, and lactate dehydrogenase occurred on Day 1 after PH, and were significantly greater (p < 0.001) in the 2 hr- and 3 hr-PH groups than the 0 hr-PH group. Maximum alanine aminotransferase levels (U/L) were 140 ± 56 (0 hr-PH), 170 ± 130 (1 hr-PH), 322 ± 241 (2 hr-PH), and 387 ± 167 (3 hr-PH). Maximum aspartate aminotransferase levels (U/L) were 218 ± 44 (0 hr-PH), 354 ± 219 (1 hr-PH), 515 ± 424 (2 hr-PH), and 711 ± 278 (3 hr-PH). Maximum creatine phosphokinase values (U/L) were 7834 ± 3681 (0 hr-PH), 24336 ± 22268 (1 hr-PH), 50494 ± 67653 (2 hr-PH), and 59857 ± 32408 (3 hr-PH). Maximum lactic acid dehydrogenase values (U/L) were 890 ± 396 (0 hr-PH), 2055 ± 1520 (1 hr-PH), 3992 ± 4895 (2 hr-PH), and 4771 ± 1884 (3 hr-PH). Plasma creatinine and blood urea nitrogen were unaffected by PH (p > 0.10).

CONCLUSION

These results indicate that PH up to 3 hours in duration results in transient liver and muscle dysfunction that was most severe after 2 hr-PH and 3 hr-PH. Prolonged hypotension produced minimal effects on the kidney.

LEVEL OF EVIDENCE

Basic science research, Level of evidence not required for basic science research.

Understanding volume kinetics

The distribution and elimination kinetics of the water volume in infusion fluids can be studied by volume kinetics. The approach is a modification of drug pharmacokinetics and uses repeated measurements of blood hemoglobin and urinary excretion as input variables in (usually) a two-compartment model with expandable walls. Study results show that crystalloid fluid has a distribution phase that gives these fluids a plasma volume expansion amounting to 50%-60% of the infused volume as long as the infusion lasts, while the fraction is reduced to 15%-20% within 30 minutes after the infusion ends. Small volumes of crystalloid barely distribute to the interstitium, whereas rapid infusions tend to cause edema. Fluid elimination is very slow during general anesthesia due to the vasodilatation-induced reduction of the arterial pressure, whereas elimination is less affected by hemorrhage. The half-life is twice as long for saline than for Ringer solutions. Elimination is slower in conscious males than conscious females, and high red blood cell and thrombocyte counts retard both distribution and re-distribution. Children have faster turnover than adults. Plasma volume expansions are similar for glucose solutions and Ringer's, but the expansion duration is shorter for glucose. Concentrated urine before and during infusion slows down the elimination of crystalloid fluid. Colloid fluids have no distribution phase, an intravascular persistence half-life of 2-3 hours, and-at least for hydroxyethyl starch-the ability to reduce the effect of subsequently infused crystalloids. Accelerated distribution due to degradation of the endothelial glycocalyx layer has not yet been demonstrated.

Resuscitation Fluid Choices to Preserve the Endothelial Glycocalyx

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2019. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2019. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Anesthesia-Associated Relative Hypovolemia: Mechanisms, Monitoring, and Treatment Considerations

Although the utility and benefits of anesthesia and analgesia are irrefutable, their practice is not void of risks. Almost all drugs that produce anesthesia endanger cardiovascular stability by producing dose-dependent impairment of cardiac function, vascular reactivity, and compensatory autoregulatory responses. Whereas anesthesia-related depression of cardiac performance and arterial vasodilation are well recognized adverse effects contributing to anesthetic risk, far less emphasis has been placed on effects impacting venous physiology and venous return. The venous circulation, containing about 65–70% of the total blood volume, is a pivotal contributor to stroke volume and cardiac output. Vasodilation, particularly venodilation, is the primary cause of relative hypovolemia produced by anesthetic drugs and is often associated with increased venous compliance, decreased venous return, and reduced response to vasoactive substances. Depending on factors such as patient status and monitoring, a state of relative hypovolemia may remain clinically undetected, with impending consequences owing to impaired oxygen delivery and tissue perfusion. Concurrent processes related to comorbidities, hypothermia, inflammation, trauma, sepsis, or other causes of hemodynamic or metabolic compromise, may further exacerbate the condition. Despite scientific and technological advances, clinical monitoring and treatment of relative hypovolemia still pose relevant challenges to the anesthesiologist. This short perspective seeks to define relative hypovolemia, describe the venous system’s role in supporting normal cardiovascular function, characterize effects of anesthetic drugs on venous physiology, and address current considerations and challenges for monitoring and treatment of relative hypovolemia, with focus on insights for future therapies.

Effect of gelatin-polysuccinat on cerebral oxygenation and microcirculation in a porcine haemorrhagic shock model

BACKGROUND

During early treatment of haemorrhagic shock maintenance of cerebral and end-organ oxygen supply by fluid resuscitation is mandatory. Gelatin-polysuccinat (GP) recently regained attention despite a still unclear risk profile and widely unknown effects on cerebral and peripheral microcirculation. This study investigates the effects of GP versus balanced electrolyte solution (BEL) with focus on cerebral regional oxygen saturation and peripheral microcirculation in a porcine haemorrhagic shock model.

METHODS

After Animal Care Committee approval haemorrhagic shock was induced by arterial blood withdrawal in 27 anaesthetized pigs. Consequently, the animals received rapid fluid resuscitation by either GP or BEL to replace the removed amount of blood, or remained untreated (n = 3 × 9). Over two hours cerebral regional oxygen saturation by near-infrared spectroscopy and peripheral buccal microcirculation by combined white-light spectrometry and laser-Doppler flowmetry were recorded. Secondary parameters included extended haemodynamics, spirometry, haematological and blood gas parameters.

RESULTS

Both fluid resuscitation regimes sufficiently stabilized the macro- and microcirculation in haemorrhagic shock with a more pronounced effect following GP infusion. GP administration led to a persisting, critical impairment of cerebral regional oxygen saturation through considerable haemodilution. Survival rates were 100% in both fluid resuscitation groups, but only 33% in the untreated control.

CONCLUSION

Equal amounts of GP and BEL sufficiently stabilize systemic circulation and microcirculatory perfusion. Forced fluid resuscitation by GP should be applied with caution to prevent haemodilution-induced impairment of cerebral oxygen delivery.

The half-life of infusion fluids: An educational review

Supplemental Digital Content is available in the text

An understanding of the half-life (T_1/2) of infused fluids can help prevent iatrogenic problems such as volume overload and postoperative interstitial oedema. Simulations show that a prolongation of the T_1/2 for crystalloid fluid increases the plasma volume and promotes accumulation of fluid in the interstitial fluid space. The T_1/2 for crystalloids is usually 20 to 40 min in conscious humans but might extend to 80 min or longer in the presence of preoperative stress, dehydration, blood loss of <1 l or pregnancy.

The longest T_1/2 measured amounts to between 3 and 8 h and occurs during surgery and general anaesthesia with mechanical ventilation. This situation lasts as long as the anaesthesia. The mechanisms for the long T_1/2 are only partly understood, but involve adrenergic receptors and increased renin and aldosterone release. In contrast, the T_1/2 during the postoperative period is usually short, about 15 to 20 min, at least in response to new fluid.

The commonly used colloid fluids have an intravascular persistence T_1/2 of 2 to 3 h, which is shortened by inflammation. The fact that the elimination T_1/2 of the infused macromolecules is 2 to 6 times longer shows that they also reside outside the bloodstream. With a colloid, fluid volume is eliminated in line with its intravascular persistence, but there is insufficient data to know if this is the same in the clinical setting.

Pharmacokinetics of centhaquin citrate in a dog model

OBJECTIVES

Centhaquin citrate is a novel agent that is being developed for use in the resuscitation of patients with haemorrhagic shock. While pharmacokinetics have been described in small animal models, the pharmacokinetic parameters of centhaquin citrate in large mammals have yet to be described.

METHODS

Four healthy Beagle dogs (two males and two females) were given an intravenous bolus of 1.0 mg/kg centhaquin citrate. Plasma concentrations were measured at baseline and at ten time points within 24 h after administration. Multiple compartmental models were built and compared. The nonparametric adaptive grid function within the Pmetrics package for R was used for parameter estimation. Predicted concentrations were calculated using population mean and individual Bayesian posterior parameters.

KEY FINDINGS

Centhaquin citrate pharmacokinetic parameters were best described using a two-compartment model. Median (IQR) values for Ke , Vc , Vp , Kcp and Kpc were 4.9 (4.4-5.2) h(-1) , 328.4 (304.0-331.9) l, 1000.6 (912.3-1042.4) l, 10.6 (10.3-11.1) h(-1) and 3.2 (2.9-3.7) h(-1) , respectively.

CONCLUSIONS

Pharmacokinetic parameters of centhaquin citrate in a large mammal have been described. A large volume of distribution and rapid elimination were observed, consistent with previous work in rats.

An Evolving Uncontrolled Hemorrhage Model Using Cynomolgus Macaques

BACKGROUND

Trauma-induced hemorrhagic shock produces hemodynamic changes that often result in a systemic inflammatory response that can lead to multiple organ failure and death. In this prospective study, the pathophysiology of a nonhuman primate uncontrolled hemorrhagic shock model is evaluated with the goal of creating an acute systemic inflammatory syndrome response and a reproducible hemorrhage.

METHODS

Nonhuman primates were divided into 2 groups. A laparoscopic left hepatectomy was performed in groups A and B, 60% and 80%, respectively, resulting in uncontrolled hemorrhage. Resuscitation during the prehospital phase lasted 120 min and included a 0.9% saline bolus at 20 mL/kg. The hospital phase involved active warming, laparotomy, hepatorrhaphy for hemostasis, and transfusion of packed red blood cells (10 mL/kg). The animals were recovered and observed over a 14-day survival period with subsequent necropsy for histopathology.

RESULTS

Baseline demographics and clinical parameters of the two groups were similar. Group A (n = 7) underwent a 57.7% ± 2.4% left hepatectomy with a 33.9% ± 4.0% blood loss and 57% survival. Group B (n = 4) underwent an 80.0% ± 6.0% left hepatectomy with 56.0% ± 3.2% blood loss and 75% survival. Group B had significantly lower hematocrit (P < 0.05) for all postinjury time points. Group A had significantly elevated creatinine on postoperative day 1. Nonsurvivors succumbed to an early death, averaging 36 h from the injury. Histopathologic evaluation of nonsurvivors demonstrated kidney tubular degeneration.

CONCLUSIONS

Nonhuman primates displayed the expected physiologic response to hemorrhagic shock due to liver trauma as well as systemic inflammatory response syndrome with resultant multiple organ dysfunction syndrome and either early death or subsequent recovery. Our next step is to establish a clinically applicable nonhuman primate polytrauma model, which reproduces the prolonged maladaptive immunologic reactivity and end-organ dysfunction consistent with multiple organ failure found in the critically injured patient.

Context-sensitive fluid therapy in critical illness

Microcirculatory alterations are frequently observed in critically ill patients undergoing major surgery and those who suffer from trauma or sepsis. Despite the need for adequate fluid administration to restore microcirculation, there is no consensus regarding optimal fluid therapy for these patients. The recent recognition of the importance of the endothelial glycocalyx layer in capillary fluid and solute exchange has largely changed our views on fluid therapy in critical illness. Given that disease status largely differs among critically ill patients, fluid therapy must not be considered generally, but rather tailored to the clinical condition of each patient. This review outlines the current understanding of context-sensitive volume expansion by fluid solutions and considers its clinical implications for critically ill patients. The modulation of capillary hydrostatic pressure through the appropriate use of vasopressors may increase the effectiveness of fluid infusion and thereby reduce detrimental effects resulting from excessive fluid administration.

Damage control: The modern paradigm

It is more than 20 years since the term ‘Damage control’ was introduced to describe an emerging surgical strategy of abbreviated laparotomy for exsanguinating trauma patients. This strategy of temporisation and prioritisation of physiological recovery over completeness of anatomical repair was associated with improved survival in a subset of patients with combined major vascular and multiple visceral injuries. The ensuing years saw the rapid adoption of these principles as standard of care for massively injured and physiologically exhausted patients. Resuscitation of severely injured patients has changed significantly in the last decade with the emergence of a new resuscitation paradigm termed ‘damage control resuscitation’. Originating in combat support hospitals, damage control resuscitation emphasises the primacy of haemorrhage control while directly targeting the ‘lethal triad’ of coagulopathy, acidosis, and hypothermia. Integral to damage control resuscitation is the appropriate application of damage control surgery and together they constitute the modern damage control paradigm. This review aims to discuss the modern application of damage control resuscitation and damage control surgery and to review the evidence supporting its constituent components, as well as considering deficiencies in current knowledge and areas for future research.

Pharmacokinetics of centhaquin citrate in a rat model

OBJECTIVE

Centhaquin citrate is a novel agent being developed for use in the treatment of haemorrhagic shock. It has decreased mortality in rat, rabbit and pig models of hypovolaemic shock compared to hypertonic saline and lactated Ringer's resuscitation. The pharmacokinetics of centhaquin citrate have not been described to date.

METHODS

Sixteen male Sprague Dawley rats were given an intravenous bolus of 0.45 mg/kg centhaquin citrate. Rats were divided into two groups; plasma concentrations were measured at five time points for each group within 24 h after administration. Competing compartmental pharmacokinetic models were assessed. The nonparametric adaptive grid function within the Pmetrics package for R was used for parameter estimation. Predicted concentrations were calculated using population median and individual Bayesian posterior parameters.

KEY FINDINGS

A two-compartment model of centhaquin citrate best fit the data. Median (IQR) values for elimination coefficient (Ke), volume of distribution (V) and intercompartmental transfer rates (Kcp, Kpc) were 8.8 (5.2-12.8) h(-1), 6.4 (2.8-10.4) l, 11.9 (4.6-15.0) h(-1) and 3.7 (2.3-9.1) h(-1), respectively.

CONCLUSION

This is the first report of the pharmacokinetic parameters of centhaquin citrate in a rat model. Centhaquin citrate was found to have a short half-life with a large volume of distribution.

Coagulation competence for predicting perioperative hemorrhage in patients treated with lactated Ringer's vs. Dextran--a randomized controlled trial

BACKGROUND

Perioperative hemorrhage may depend on coagulation competence and this study evaluated the influence of coagulation competence on blood loss during cystectomy due to bladder cancer.

METHODS

Forty patients undergoing radical cystectomy were included in a randomized controlled trial to receive either lactated Ringer's solution or Dextran 70 (Macrodex ®) that affects coagulation competence.

RESULTS

By thrombelastography evaluated coagulation competence, Dextran 70 reduced "maximal amplitude" (MA) by 25 % versus a 1 % reduction with the administration of lactated Ringer's solution (P <0.001). Blinded evaluation of the blood loss was similar in the two groups of patients - 2339 ml with the use of Dextran 70 and 1822 ml in the lactated Ringer's group (P = 0.27). Yet, the blood loss was related to the reduction in MA (r = -0.427, P = 0.008) and by multiple regression analysis independently associated with MA (P = 0.01). Thus, 11 patients in the dextran group (58 %) developed a clinical significant blood loss (>1500 ml) compared to only four patients (22 %) in the lactated Ringer's group (P = 0.04).

CONCLUSIONS

With the use of Dextran 70 vs. lactated Ringer's solution during cystectomy, a relation between hemorrhage and coagulation competence is demonstrated. Significant bleeding develops based on an about 25 % reduction in thrombelastography determined maximal amplitude. A multivariable model including maximal amplitude discriminates patients with severe perioperative bleeding during cystectomy.

TRIAL REGISTRATION

The study was accepted on January 7(th), 2013 at www.clinicaltrialsregister.eu EudraCT 2012-005040-20.

Markers for blood-brain barrier integrity: how appropriate is Evans blue in the twenty-first century and what are the alternatives?

In recent years there has been a resurgence of interest in brain barriers and various roles their intrinsic mechanisms may play in neurological disorders. Such studies require suitable models and markers to demonstrate integrity and functional changes at the interfaces between blood, brain, and cerebrospinal fluid. Studies of brain barrier mechanisms and measurements of plasma volume using dyes have a long-standing history, dating back to the late nineteenth-century. Their use in blood-brain barrier studies continues in spite of their known serious limitations in in vivo applications. These were well known when first introduced, but seem to have been forgotten since. Understanding these limitations is important because Evans blue is still the most commonly used marker of brain barrier integrity and those using it seem oblivious to problems arising from its in vivo application. The introduction of HRP in the mid twentieth-century was an important advance because its reaction product can be visualized at the electron microscopical level, but it also has limitations. Advantages and disadvantages of these markers will be discussed together with a critical evaluation of alternative approaches. There is no single marker suitable for all purposes. A combination of different sized, visualizable dextrans and radiolabeled molecules currently seems to be the most appropriate approach for qualitative and quantitative assessment of barrier integrity.

A prospective, randomized trial of intravenous hydroxocobalamin versus whole blood transfusion compared to no treatment for Class III hemorrhagic shock resuscitation in a prehospital swine model

OBJECTIVES

The objective was to compare systolic blood pressure (sBP) over time in swine that have had 30% of their blood volume removed (Class III shock) and treated with intravenous (IV) whole blood or IV hydroxocobalamin, compared to nontreated control animals.

METHODS

Thirty swine (45 to 55 kg) were anesthetized, intubated, and instrumented with continuous femoral and pulmonary artery pressure monitoring. Animals were hemorrhaged a total of 20 mL/kg over a 20-minute period. Five minutes after hemorrhage, animals were randomly assigned to receive 150 mg/kg IV hydroxocobalamin solubilized in 180 mL of saline, 500 mL of whole blood, or no treatment. Animals were monitored for 60 minutes thereafter. A sample size of 10 animals per group was determined based on a power of 80% and an alpha of 0.05 to detect an effect size of at least a 0.25 difference (>1 standard deviation) in mean sBP between groups. sBP values were analyzed using repeated-measures analysis of variance (RANOVA). Secondary outcome data were analyzed using repeated-measures multivariate analysis of variance (RMANOVA).

RESULTS

There were no significant differences between hemodynamic parameters of IV hydroxocobalamin versus whole blood versus control group at baseline (MANOVA; Wilks' lambda; p = 0.868) or immediately posthemorrhage (mean sBP = 47 mm Hg vs. 41 mm Hg vs. 37 mm Hg; mean arterial pressure = 39 mm Hg vs. 28 mm Hg vs. 34 mm Hg; mean serum lactate = 1.2 mmol/L vs. 1.4 mmol/L vs. 1.4 mmol/L; MANOVA; Wilks' lambda; p = 0.348). The outcome RANOVA model detected a significant difference by time between groups (p < 0.001). Specifically, 10 minutes after treatment, treated animals showed a significant increase in mean sBP compared to nontreated animals (mean sBP = 76.3 mm Hg vs. 85.7 mm Hg vs. 51.1 mm Hg; p < 0.001). RMANOVA modeling of the secondary data detected a significant difference in mean arterial pressure, heart rate, and serum lactate (p < 0.001). Similar to sBP, 10 minutes after treatment, treated animals showed a significant increase in mean arterial pressure compared to nontreated animals (mean arterial pressure = 67.7 mm Hg vs. 61.4 mm Hg vs. 40.5 mm Hg). By 10 minutes, mean heart rate was significantly slower in treated animals compared to nontreated animals (mean heart rate = 97.3 beats/min vs. 95.2 beats/min vs. 129.5 beats/min; p < 0.05). Serum lactate, an early predictor of shock, continued to rise in the control group, whereas it did not in treated animals. Thirty minutes after treatment, serum lactate values of treated animals were significantly lower compared to nontreated animals (p < 0.05). This trend continued throughout the 60-minute observation period such that 60-minute values for lactate were 1.4 mmol/L versus 1.1 mmol/L versus 3.8 mmol/L. IV hydroxocobalamin produced a statistically significant increase in systemic vascular resistance compared to control, but not whole blood, with a concomitant decrease in cardiac output.

CONCLUSIONS

Intravenous hydroxocobalamin was more effective than no treatment and as effective as whole blood transfusion, in reversing hypotension and inhibiting rises in serum lactate in this prehospital, controlled, Class III swine hemorrhage model.

Is there a place for crystalloids and colloids in remote damage control resuscitation?

Crystalloids and colloids are used in prehospital fluid resuscitation to replace blood loss and preserve tissue perfusion until definite surgical control of bleeding can be achieved. However, large volumes of fluids will increase bleeding by elevating blood pressure, dislodging blood clots, and diluting coagulation factors and platelets. Hypotensive fluid resuscitation strategies are used to avoid worsening of uncontrolled bleeding. This is largely supported by animal studies. Most clinical evidence suggests that restricting fluid therapy is associated with improved outcome. Remote damage control resuscitation emphasizes the early use of blood products and restriction of other fluids to support coagulation and tissue oxygenation. Controversy regarding the optimal choice and composition of resuscitation fluids is ongoing. Compared with crystalloids, less colloid is needed for the same expansion of intravascular volume. On the other hand, colloids may cause coagulopathy not only related to dilution. The most important advantage of using colloids is logistical because less volume and weight are needed. In conclusion, prehospital fluid resuscitation is considered the standard of care, but there is little clinical evidence supporting the use of either crystalloids or colloids in remote damage control resuscitation. Alternative resuscitation fluids are needed.

Comparison of Ringer's solution with 0.4% glucose or without in intraoperative infusion regimens for the prevention of hypoglycemia in juvenile pigs

Juvenile pigs are prone to hypoglycemia, nevertheless they are commonly used in preclinical studies. The optimal perioperative fluid management with crystalloid solutions in such settings has not yet been studied. The aim of the current study was to correlate the perioperative fluid administration of Ringer's solution, with and without the addition of a minimal amount of glucose (0.4% glucose) to the blood glucose, and the incidence of perioperative hypoglycemia in 20 juvenile pigs (31.7 ± 5.2 kg) undergoing surgery for approximately one hour. Infusion of Ringer's solution without glucose (group Ri, n = 10) led to a significant decrease of the serum blood glucose level from 105.7 ± 27.1 mg/dL at baseline compared with 87.8 ± 31.7 mg/dL post surgery. The pigs (50%) in group Ri were observed to be hypoglycemic (<72 mg/dL). The second group received Ringer's solution containing a final concentration of 0.4% glucose (group Ri-Glu, n = 10) and showed a significant increase in blood glucose level from 104.4 ± 15.8 mg/dL at baseline compared with 122.3 ± 14.3 mg/dL post surgery. No animal in group Ri-Glu was observed to be hypoglycemic. In conclusion, we showed that even minor changes in perioperative crystalloid fluid management significantly influence blood glucose levels. In order to avoid hypoglycemia in juvenile pigs we recommend adding a minimal amount of glucose (0.4% final concentration) to the Ringer's solution given perioperatively during surgery of approximately one hour.

Comparisons of normal saline and lactated Ringer's resuscitation on hemodynamics, metabolic responses, and coagulation in pigs after severe hemorrhagic shock

Background

Ongoing improvements in trauma care now recommend earlier use of blood products as part of damage control resuscitation, but generally these products are not available at far forward battlefield locations. For the military, questions continue to arise regarding efficacy of normal saline (NS) vs. lactated Ringer’s (LR). Thus, this study compared the effects of LR and NS after severe hemorrhage in pigs.

Methods

20 anesthetized pigs were randomized into control (n = 6), LR (n = 7), and NS (n = 7) groups. Hemorrhage of 60% estimated total blood volume was induced in LR and NS groups by removing blood from the left femoral artery using a computer-controlled pump. Afterwards, the pigs were resuscitated with either LR at 3 times the bled volume or the volume of NS to reach the same mean arterial pressure (MAP) as in LR group. Hemodynamics were measured hourly and blood samples were taken at baseline (BL), 15 min, 3 h and 6 h after resuscitation to measure changes in coagulation using thrombelastograph®.

Results

MAP was decreased by hemorrhage but returned to BL within 1 h after resuscitation with LR (119 ± 7 ml/kg) or NS (183 ± 9 ml/kg, p < 0.05). Base excess (BE) was decreased by hemorrhage; resuscitation with LR recovered BE but not with NS. Total peripheral resistance was decreased with NS and LR, with a larger drop shown in NS. Serum potassium was increased with NS, but not affected with LR. Coagulation changes were similar between LR and NS.

Conclusions

NS may be inferior to LR in resuscitation due to its vasodilator effects and the risks of metabolic acidosis and hyperkalemia.