Robert A. Gunther

A comparison of several hypertonic solutions for resuscitation of bled sheep

Small volumes (4 ml/kg) of 2400 mOsm NaCl restore cardiac output and mean arterial pressure to 80% of baseline after hemorrhage (65% of blood volume) in unanesthetized sheep. An equal volume of normal saline is less effective. To identify an optimal hypertonic solution, we screened six 2400 mOsm solutions in 18 randomized experiments in 8 sheep: NaCl, NaHCO3, NaCl/sodium acetate, NaCl/mannitol, NaCl/6% Dextran 70, and glucose. Cardiovascular function, as determined by cardiac output and mean arterial pressure, was restored best with NaCl, NaCl/NaAc, and NaCl/Dex. These three solutions were then evaluated using 18 sheep in 36 experiments. Following a 1-hr baseline period, the sheep were bled to a mean arterial pressure of 50 mm Hg for 2 hr. One of the solutions was then given in a volume of 4 ml/kg over 2 min and the sheep were monitored for 3 hr. Within 3 min of the infusion, cardiac output increased to greater than 100% of baseline for all three solutions. The NaCl-Dex solution sustained a significantly higher cardiac output over the 3-hr observation period than the other solutions. Plasma volume increased for all solutions following infusion. NaCl-Dex maintained plasma volume significantly better than the other solutions. As a further control, an isotonic solution of 6% Dextran 70 in normal saline was studied. It was not as effective as the hypertonic NaCl-Dex in maintaining cardiac output, mean arterial pressure, or plasma volume. Osmolality increased 10% (309 to 326 mOsm/kg H2O), plasma [NA] increased 7% (151 to 161 meq/liter), and plasma [K] decreased from 3.9 to 2.6 meq/liter following the hypertonic infusions. The sheep appeared to tolerate these electrolyte changes well. We conclude that a single bolus infusion of 2400 mOsm NaCl with 6% Dextran 70 best resuscitates sheep that have been subjected to a moderate degree of hemorrhagic shock compared to several other solutions. Its beneficial effects are caused in part by a sustained reestablishment of plasma volume. More studies are needed to document the safety of dextran in the clinical setting of hemorrhagic shock. Small volumes of hypertonic solutions may be valuable in the initial fluid resuscitation of patients in hemorrhagic shock.

A bovine model of vaccine enhanced respiratory syncytial virus pathophysiology

A critical issue has been the observation that vaccination of children with a formalin-inactivated respiratory syncytial virus (RSV) vaccine is associated with disease enhancement. We have taken advantage of bovine RSV and our experience with this disease in calves to develop a natural model that parallels human disease. Using formalin-inactivated bovine RSV vaccine calves were either sham-vaccinated/infected, vaccinated/infected, or vaccinated/sham-infected and their clinical signs, pulmonary function, and histological lung lesions quantitatively scored. Interestingly there was significantly greater disease in vaccinated/infected calves and histological lesions in calves were similar to those of affected children. Finally, we note that vaccination did not induce neutralizing antibodies, but IgG antibodies were detected by ELISA. Our model of RSV enhanced disease is important because it provides quantifiable evidence of disease severity that can be applied to evaluate the mechanisms of immunopathology and the safety of candidate RSV vaccines.

The effects of hypoproteinemia on blood-to-lymph fluid transport in sheep lung.

We studied the effects of reducing the plasma protein concentration on flow and composition of pulmonary lymph in 12 unanesthetized sheep. Whole blood was removed while red cells were returned and lactated Ringers was infused at a rate sufficient to maintain pulmonary vascular pressures at baseline values. A 44–54% reduction in plasma protein concentration resulted in a decrease in the plasma oncotic pressure from 18.6 ± 1.1 to 7.8 ± 0.9 mm Hg. Within an hour after plasmapheresis, lymph flows increased to a maximum of 4 times baseline. Subsequently, lymph flow gradually decreased and were close to baseline at 24 hours. The plasma-to-lymph oncotic gradient was reestablished in 5 hours due to decreased lymph protein. Maintained elevation of lymph flow with hydrostatic and oncotic gradients at baseline values suggest that the blood-to-lymph barrier offers leas resistance to fluid transport. The calculated filtration coefficient increased 2- to 3-fold after plasmapheresis. Protein clearances remained normally coupled to lymph flows. Thus the enhanced fluid transport cannot be attributed to a permeability change In the large pore pathways. Hypoproteinemia may alter the interstitial gel so that there is less resistance to fluid movement. Such changes in fluid conductivity between blood capillaries and lymphatics may augment the lymphatic safety factor against pulmonary edema during hypoproteinemia.

Arterial oxygenation and oxygen delivery after hemoglobin-based oxygen carrier infusion in canine hypovolemic shock: a dose-response study.

OBJECTIVE To compare effects of 6% hetastarch (Hextend) and hemoglobin-based oxygen carrier hemoglobin glutamer-200 (Hb-200) (bovine; Oxyglobin) on hemodynamics, arterial oxygen content, and systemic oxygen delivery in a canine hemorrhagic shock model. DESIGN Randomized laboratory investigation. SETTING University surgical research facility. SUBJECTS Twenty-four anesthetized healthy, adult, mongrel dogs (28 +/- 1 kg; 7 female, 17 male). INTERVENTIONS Dogs were instrumented for determinations of heart rate, arterial, central venous, pulmonary arterial, and pulmonary arterial occlusion pressures, and cardiac index. Total solids, colloid oncotic pressure, arterial oxygen content, Hb, lactate, pH, and blood gases were analyzed in blood samples. Recordings were made before, after 1 hr of hemorrhagic shock, and immediately and 3 hrs after infusion of either 30 mL/kg hetastarch (group 1), 10 mL/kg Hb-200 + 20 mL/kg hetastarch (group 2), 20 mL/kg Hb-200 + 10 mL/kg hetastarch (group 3), or 30 mL/kg Hb-200 (group 4). MEASUREMENTS AND MAIN RESULTS Hemorrhage (35 +/- 1 mL/kg) reduced mean arterial pressure to 50 mm Hg and caused significant decreases in total Hb, mean pulmonary arterial pressure, cardiac index and systemic oxygen delivery, increases in heart rate and systemic vascular resistance, and lactic acidosis. In group 1, hetastarch infusion was accompanied by increases of pulmonary arterial pressure, cardiac index, and blood oxygen extraction above baseline, and decreases of systemic vascular resistance, total Hb, total solids, arterial oxygen content, and systemic oxygen delivery below baseline (p <.05). Other data returned to baseline. In groups 2 to 4, hemodynamic functions (except pulmonary arterial pressure) recovered, yet neither total Hb (i.e., plasma and red blood cell Hb) nor arterial oxygen content increased despite increases in plasma Hb of 2 to 5 g/dL and proportionate increases in total solids. Systemic oxygen delivery improved dose-dependently with Hb-200 but did not return to baseline (p <.05), reaching values comparable to hetastarch group only at 30 mL/kg Hb-200. In all groups, oxygen extraction remained above baseline. Metabolic acidosis and lactatemia resolved significantly faster in groups 2 to 4, and colloid oncotic pressure after resuscitation was greater in groups 2 to 4 than in controls (p <.05). CONCLUSIONS In hemorrhagic shock, Hb-200 infusion may not improve oxygen delivery more than hetastarch, likely due to hemodilution caused by its high colloid oncotic pressure, but may facilitate diffusive oxygen transport to tissues.

Effectiveness of hypertonic saline-dextran 70 for initial fluid resuscitation of major burns

Small-volume resuscitation (4 ml/kg) with hypertonic saline-dextran (HSD) has been shown effective in hemorrhagic shock. In the present study the effectiveness of an initial 4 ml/kg bolus infusion of HSD on cardiovascular function and fluid resuscitation requirements after a major burn injury was evaluated in anesthetized sheep following a 40% BSA scald burn. One hour after injury resuscitation was initiated by a rapid intravenous bolus infusion (4 ml/kg) of either hypertonic saline-dextran (7.5% NaCl in 6% dextran 70) (HSD) or the same volume of normal (isotonic) saline (NS). Lactated Ringers was later infused as needed to maintain cardiac output at 90% of baseline. HSD rapidly and effectively restored cardiac output and mean arterial pressure significantly better than the same volume of NS. Hemodynamic improvement by HSD was short lived, and need for further fluid therapy was only marginally delayed (HSD 38 +/- 8 min, NS 20 +/- 3 min; p = 0.06) (mean +/- SEM). The total requirements for fluid therapy during the first 6 hr postburn were not reduced by the initial HSD bolus (HSD 3,145 +/- 605 ml, NS 2,905 +/- 495 ml; n.s.), nor was skin edema formation reduced. We conclude that in anesthetized sheep HSD resuscitation was only transiently effective in treating burn shock. This may be attributed to the sustained increase in vascular permeability and continued plasma leak following thermal injury.

DOSE-RESPONSE CHARACTERISTICS OF HYPERTONIC SALINE DEXTRAN SOLUTIONS

In an effort to find the best hypertonic saline-dextran solution (HSD) for prehospital use, 33 chronically catheterized sheep were bled using a fixed pressure shock model (50 mm Hg x 2 hours) and resuscitated with 4 ml/kg of HSD solution (2-minute bolus). In the first set of experiments colloid was varied and sodium chloride was held constant, as 7.5% NaCl was paired with either 0%, 6%, or 12% dextran 70. A dose-response relationship existed, with cardiac output increasing 20% with each sequential dextran 70 concentration. Mean arterial blood pressure was higher in animals that were resuscitated with either the 7.5% NaCl/6% dextran 70 or 7.5% NaCl/12% dextran 70 solution (p less than 0.05). Using the optimal dextran 70 concentration from the first set of experiments (i.e., 12%), solute was varied in a second set of experiments comparing 0.9%, 3.8%, 7.5%, or 10% NaCl/12% dextran 70. Again, dose-response features were demonstrated, as cardiac output increased as a function of NaCl concentration. However, this response plateaued with the 7.5% NaCl concentration and no advantage was obtained by increasing the NaCl concentration to 10%. We conclude that a 4-ml/kg bolus of 7.5% NaCl/12% dextran 70 solution may be a more effective form of therapy than those previously evaluated. This new solution is now being included in our ongoing clinical trials.

Use of a chronic prefemoral lymphatic fistula for monitoring systemic capillary integrity in unanesthetized sheep

Abstract Alterations in fluid and protein flux across the soft tissue capillary resulting in edema formation is a common occurrence in the critically ill patient. The pathophysiology and therapeutic modalities for treating edema are poorly defined in large part due to the difficulty of monitoring capillary integrity. We have described a preparation using lymph flow (Q L ) from the prefemoral efferent lymphatic in sheep, which we have found to accurately reflect changes in capillary fluid and protein flux. The lymph fistula is easy to prepare and chronic studies can be performed in the unanesthetized state. A lung lymph fistula can be formed in the same animal which allows for the comparison of the pulmonary and systemic capillary effects of injury. We have found that prefemoral Q L responds in a predictible manner to changes in Starling forces reflecting in changes in fluid flux. We also determined that the soft tissue capillary responds differently to different systemic insults, increasing both fluid and protein flux with a contralateral burn injury and demonstrating no effect from endotoxemia. Prefemoral and lung lymph flow also responded differently to the same insult indicating the importance of studying both capillary systems simultaneously. These findings reflect the need to monitor the systemic capillary. We consider this lymph preparation to be very useful for this purpose.

The effects of hemoglobin glutamer-200 (bovine) on the microcirculation in a canine hypovolemia model: a noninvasive computer-assisted intravital microscopy study.

We sought to correlate in vivo microvascular, systemic function, hemodynamic, and oxygenation changes in autologous shed blood (n = 4) and hemoglobin glutamer-200 (Hb-200) (n = 4) resuscitations in hypovolemic dogs. Hemorrhage (∼40% blood loss) reduced mean arterial pressure to ∼50 mm Hg and caused significant (P < 0.01) decreases in hematocrit, total hemoglobin, mean pulmonary arterial pressure, cardiac output, and oxygen delivery and significant (P < 0.01) increases in heart rate, systemic vascular resistance, and lactic acidosis. Significant (P < 0.01) changes in conjunctival microvascular variables also occurred, including a 19% decrease in venular diameter and 79% increase in average blood flow velocity. Shed blood resuscitation returned microvascular, systemic function, hemodynamic, and oxygenation variables to prehemorrhagic baseline values. In contrast, Hb-200 failed to restore hematocrit, total hemoglobin, cardiac output, oxygen delivery index, and systemic venous resistance to baseline, but it restored other systemic functions and all hemodynamic and microvascular changes. In addition, Hb-200 resuscitation in hypovolemic dogs (∼40% blood loss) did not cause extreme hemodilution or fatal outcome. This study confirms that real-time (in vivo) microvascular studies, which were conducted only in small rodent models in the past, can be performed simultaneously with systemic function, hemodynamic, and oxygenation studies in a large animal model for relevant data correlation.

Comparison of Treatment Modalities for Hemorrhagic Shock

Allogeneic blood resuscitation is the treatment of choice for hemorrhagic shock. When blood is unavailable, plasma expanders, including crystalloids, colloids, and blood substitutes, may be used. Another treatment modality is vasopressin, a vasoconstrictor administered to redistribute blood flow, increase venous return, and maintain adequate cardiac output. While much information exists on systemic function and oxygenation characteristics following treatment with these resuscitants, data on their effects on the microcirculation and correlation of real-time microvascular changes with changes in systemic function and oxygenation in the same animal are lacking. In this study, real-time microvascular changes during hemorrhagic shock treatment were correlated with systemic function and oxygenation changes in a canine hemorrhagic shock model (50–55% total blood loss with a MAP of 45–50 mmHg as a clinical criterion). Following splenectomy and hemorrhage, the dogs were assigned to five resuscitation groups: autologous/shed blood, hemoglobin-based oxygen carrier/Oxyglobin®, crystalloid/saline, colloid/Hespan® (6% hetastarch), and vasopressin. Systemic function and oxygenation changes were continuously monitored and periodically measured (during various phases of the study) using standard operating room protocols. Computer-assisted intravital video-microscopy was used to objectively analyze and quantify real-time microvascular changes (diameter, red-cell velocity) in the conjunctival microcirculation. Measurements were made during pre-hemorrhagic (baseline), post-hemorrhagic (pre-resuscitation), and post-resuscitation phases of the study. Pre-hemorrhagic microvascular variables were similar in all dogs (venular diameter = 42±4 µm, red-cell velocity = 0.55±0.5 mm/sec). All dogs showed significant (P < 0.05) post-hemorrhagic microvascular changes: ∼ 20% decrease in venular diameter and ∼ 30% increase in red-cell velocity, indicative of sympathetic effects arising from substantial blood loss. Microvascular changes correlated with post-hemorrhagic systemic function and oxygenation changes. All resuscitation modalities except vasopressin restored microvascular and systemic function changes close to pre-hemorrhagic values. However, only autologous blood restored oxygenation changes to pre-hemorrhagic levels. Vasopressin treatment resulted in further decreases in venular diameter (∼ 50%) as well as red-cell velocity (∼ 70%) without improving cardiac output. Our results suggested that volume replenishment—not oxygen-carrying capability—played an important role in pre-hospital/en route treatment for hemorrhagic shock. Vasopressin treatment resulted in inadvertent detrimental outcome without the intended benefit.

The HemoCue, a point of care B-hemoglobin photometer, measures hemoglobin concentrations accurately when mixed in vitro with canine plasma and three hemoglobin-based oxygen carriers (HBOC).

PurposeAccuracy of measurement of low hemoglobin concentrations using the HemoCue®, a B-hemoglobin photometer (HemoCue AB, Angelholm, Sweden) may exhibit significant variability. Infusion of hemoglobin-based oxygen carriers (HBOC) results in low concentrations of plasma hemoglobin. Our study assessed B-hemoglobin photometer measurement accuracy of three HBOC: (hemoglobin glutamer-200 (bovine; Oxyglobin®, Biopure Corp., Cambridge, MA, USA); hemoglobin glutamer-250 (bovine; Hemopure®, Biopure Corp, Cambridge, MA, USA), and hemoglobin-raffimer, (human; Hemolink™, Hemosol, Inc., Toronto, Ontario, Canada).MethodsIn the laboratory, 45 split canine plasma samples were mixed with hemoglobin glutamer-200 (8.13, 16.25, 32.5 g·L−1 concentrations), 45 samples were mixed with hemoglobin glutamer-250 (8.13, 16.25, 32.5 g·L−1 concentrations), 45 with hemoglobin-raffimer (12.5, 25.0, 50.0 g·L−1 concentrations), and measured. Plasma samples without HBOC served as control. Hemoglobin concentration was determined by a laboratory analyzer (Coulter Corporation, Hiafeah, FL, USA) and B-hemoglobin photometer (HemoCue®, Ångelholm, Sweden). Two independent technicians performed blinded sample measurements and randomly tested each sample five times. Results were analyzed according to Bland and Altman analysis.ResultsB-hemoglobin photometer demonstrated high repeatability for all three HBOCs. Repeatability coefficients were 0.37 g·L−1 and 0.48 g·L−1 for hemoglobin glutamer-200, 0.39 g·L−1 and 0.4 g·L−1 for hemoglobin glutamer-250 and 1.07 g·L−1 and 0.85 g·L−1 for hemoglobin-raffimer. An acceptable agreement was found between the B-hemoglobin photometer and the laboratory analyzer for all three HBOCs tested.ConclusionThe B-hemoglobin photometer accurately determined the concentration of three HBOC solutions dissolved in canine plasma.RésuméObjectifLa précision des mesures de faibles concentrations d’hémoglobine réalisées avec le HemoCue®, photomètre pour B-hémoglobine (HemoCue AB, Angelholm, Suède), peut afficher une variabilité significative. Une perfusion de transporteurs d’oxygène à base d’hémoglobine (TOBH) entraîne de faibles concentrations d’hémoglobine plasmatique. Notre étude a évalué la précision du photomètre pour B-hémoglobine de trois TOBH : (l’hémoglobine glutamère-200 (bovine; Oxyglobin®, Biopure Corp., Cambridge, MA, USA) ; l’hémoglobine glutamère-250 (bovine; Hemopure®, Biopure Corp, Cambridge, MA, USA) et l’hémoglobine-raffimère (humaine; HemolinkTM, Hemosol, Inc., Toronto, Ontario, Canada).MéthodeAu laboratoire, 45 échantillons divisés de plasma canin ont été combinés à de l’hémoglobine glutamère-200 (des concentrations de 8,13 - 16,25 - 32,5 g·L−1), 45 avec de l’hémoglobine glutamère-250 (8,13 - 16,25 - 32,5 g·L−1) et 45 avec de l’hémoglobine-raffimère (12,5 - 25,0 - 50,0 g·L−1), puis mesurés. Les échantillons plasmatiques sans TOBH constituaient les témoins. La concentration d’hémoglobine a été déterminée à l’aide d’un analyseur de laboratoire (Coulter Corporation, Hiafeah, FL, USA) et du photomètre pour B-hémoglobine (HemoCue®, Ångelholm, Sweden). Deux techniciens objectifs ont mesuré les échantillons sansen connaître la nature et ont testé chacun cinq fois de façon aléatoire. Les résultats ont été analysés à partir des méthodes de Bland et Altman.RésultatsLe photomètre pour B-hémoglobine a démontré une grande fidélité pour les trois TOBH. Les coefficients de répétabilité ont été de 0,37 g·L−1 et de 0,48 g·L−1 pour l’hémoglobine glutamère-200 ; 0,39 g·L−1 et 0,4 g·L−1 pour l’hémoglobine glutamère-250 et 1,07 g·L−1 et 0,85 g·L−1 pour l’hémoglobine-raffimère. Il y avait une concordance acceptable entre le photomètre pour B-hémoglobine et l’analyseur de laboratoire en regard des trois TOBH testés.ConclusionLe photomètre pour B-hémoglobine a permis de déterminer avec exactitude la concentration de trois solutions de TOBH dissoutes dans du plasma canin.