The dynamics of vascular volume and fluid shifts of lactated Ringer's solution and hypertonic-saline-dextran solutions infused in normovolemic sheep

Crystalloid Coload Reduced the Incidence of Hypotension in Spinal Anesthesia for Cesarean Delivery, When Compared to Crystalloid Preload: A Meta-Analysis

Objective

To determine whether crystalloid infusion just after intrathecal injection (coload) would be better than infusion before anesthesia (preload) for hypotension prophylaxis in spinal anesthesia for cesarean delivery.

Methods

We searched PubMed, EMBASE, Cochrane Central Register of Controlled Trials, and other databases for randomized controlled trials comparing coload of crystalloid with preload in parturients receiving spinal anesthesia for cesarean delivery. Primary outcome was intraoperative incidence of hypotension. Other outcomes were intraoperative need for vasopressors, hemodynamic variables, neonatal outcomes (umbilical artery pH and Apgar scores), and the incidence of maternal nausea and vomiting. We used RevMan 5.2 and STATA 12.0 for the data analyses.

Results

Ten studies with 824 cases were included. The incidence of hypotension was significantly higher in the preload group compared with the coload group (57.8% versus 47.1%, odds ratio [OR] = 1.62, 95% confidence interval [CI] = 1.11–2.37, and P = 0.01). More patients needed intraoperative vasopressors (OR = 1.71, 95% CI = 1.07–2.04, and P = 0.02) when receiving crystalloid preload. In addition, the incidence of nausea and vomiting was higher in the preload group (OR = 3.40, 95% CI = 1.88–6.16, and P < 0.0001). There were no differences in neonatal outcomes between the groups.

Conclusions

For parturients receiving crystalloid loading in spinal anesthesia for cesarean delivery, coload strategy is superior to preload for the prevention of maternal hypotension.

The role of hypertonic saline dextran in trauma resuscitation

Modern trauma management has recognized the importance of using conservative fluid resuscitation regimes in order to prevent complications from fluid overload arising. Hypertonic/hyperoncotic fluids appear to provide an ideal means of facilitating this, requiring only small volumes to rapidly elevate blood pressure. Hypertonic saline dextran (HSD) was introduced in 1985 but its take up has been slow, a large part of this has been due to the lack of human trials and concerns about complications.

The current evidence has been reviewed and it is clear that HSD is an efficient means of correcting hypotension, doing so mainly by the mobilizing endogenous water. It is becoming apparent that early administration has the potential to modulate the inflammatory cascade in patients at risk of developing adult respiratory distress syndrome (ARDS) and multiorgan failure. This is reflected in the handful of human trials that show a trend towards increased survival (particularly for head injuries) and a possible reduction in ARDS. The side effect profile appears to be good, even in the presence of dehydration or penetrating trauma.

Published human trials have methodological problems and lack of power of study this has led to a reliance on animal studies. Clearly there is great potential, but before large-scale prehospital usage can be justified further well-conducted randomized human trials are needed.

Pilot study on the effect of subcutaneous administration of lactated Ringer's solution on biochemistry parameters in healthy euvolemic cats

Subcutaneous fluid administration is a commonly used therapy in veterinary practice. Its safety and efficacy have been demonstrated in human clinical studies, but have only rarely been discussed in the veterinary literature. This prospective observational study was performed to evaluate changes during a 24 h period in serum biochemistries associated with administration of lactated Ringer's solution subcutaneously to healthy cats. Lactated Ringer's solution was administered subcutaneously once to ten healthy, euvolemic cats at a dose of 22 mL kg⁻¹. Blood biochemistry analytes were sampled at baseline and at serial time points for a total of 24 h. Changes in biochemical analytes at each time point were compared to baseline and evaluated for statistical significance. Serum blood urea nitrogen (BUN) was significantly less than baseline at 4, 6, 12, 18, and 24 h post‐infusion. Serum creatinine was significantly less than baseline at 2, 4 and 6 h. Packed cell volume (PCV) was significantly less than baseline at 6, 12, 18, and 24 h. Total plasma proteins were significantly less than baseline at all time points. Serum electrolytes did not change from baseline at any time point. Urine specific gravity was significantly increased from baseline only at 6 h post‐Lactated Ringer's solution (LRS) administration. Subcutaneous administration of lactated Ringer's solution appears to result in haemodilution with minimal change to serum electrolyte concentrations in clinically normal, euvolemic cats.

Fresh frozen plasma and spray-dried plasma mitigate pulmonary vascular permeability and inflammation in hemorrhagic shock

BACKGROUND

In retrospective and prospective observational studies, fresh frozen plasma (FFP) has been associated with a survival benefit in massively transfused trauma patients. A dry plasma product, such as spray-dried plasma (SDP), offers logistical advantages over FFP. Recent studies on FFP have demonstrated that FFP modulates systemic vascular stability and inflammation. The effect of SDP on these measures has not been previously examined. This study compares SDP with FFP using in vitro assays of endothelial function and in vivo assays of lung injury using a mouse model of hemorrhagic shock (HS) and trauma.

METHODS

FFP, SDP, and lactated Ringer's (LR) solution were compared in vitro using assays of endothelial cell (EC) permeability, cytokine production and content, gene expression, as well as tight and adherens junction stability. All resuscitation products were also compared in a murine model of HS. Mean arterial pressures and physiologic measures were assessed. Pulmonary vascular permeability was measured using tagged dextran. Lung tissues were stained for CD68, VE-cadherin, and occludin.

RESULTS

Treatment of ECs with FFP and SDP, but not LR, preserved the integrity of EC monolayers in vitro and resulted in similar EC gene expression patterns and cytokine/growth factor production. FFP and SDP also reduced HS-induced pulmonary vascular permeability in vivo to the same extent. In mice with HS, mean arterial pressures and base excess were corrected by both FFP and SDP to levels observed in sham-treated mice. Treatment after HS with FFP and SDP but not LR solution reduce alveolar wall thickening, leukocyte infiltration, and the breakdown of EC junctions, as measured by staining for VE-cadherin, and occludin.

CONCLUSION

Both FFP and SDP similarly modulate pulmonary vascular integrity, permeability, and inflammation in vitro and in vivo in a murine model of HS and trauma.

Effects of intravenous administration of lactated Ringer's solution on hematologic, serum biochemical, rheological, hemodynamic, and renal measurements in healthy isoflurane-anesthetized dogs

OBJECTIVE

To determine the hematologic, serum biochemical, rheological, hemodynamic, and renal effects of IV administration of lactated Ringer's solution (LRS) to healthy anesthetized dogs.

DESIGN

4-period, 4-treatment cross-over study.

ANIMALS

8 healthy mixed-breed dogs.

PROCEDURES

Each dog was anesthetized, mechanically ventilated, instrumented, and randomly assigned to receive LRS (0, 10, 20, or 30 mL/kg/h [0, 4.5, 9.1, or 13.6 mL/lb/h]), IV, on 4 occasions separated by at least 7 days. Blood hemoglobin concentration and serum total protein, albumin, lactate, and electrolyte concentrations; PCV; colloid osmotic pressure; arterial and venous pH and blood gases (Po2; Pco2); whole blood and plasma viscosity; arterial and venous blood pressures; cardiac output; results of urinalysis; urine production; glomerular filtration rate; and anesthetic recovery times were monitored. Oxygen delivery, vascular resistance, stroke volume, pulse pressure, and blood and plasma volume were calculated.

RESULTS

Increasing rates of LRS administration resulted in dose-dependent decreases in PCV; blood hemoglobin concentration and serum total protein and albumin concentrations; colloid osmotic pressure; and whole blood viscosity. Plasma viscosity; serum electrolyte concentrations; data from arterial and venous blood gas analysis; glomerular filtration rate; urine production; heart rate; pulse, central venous, and arterial blood pressures; pulmonary vascular resistance; and oxygen delivery did not change. Pulmonary artery pressure, stroke volume, and cardiac output increased, and systemic vascular resistance decreased.

CONCLUSIONS AND CLINICAL RELEVANCE

Conventional IV infusion rates of LRS to isoflurane-anesthetized dogs decreased colligative blood components; increased plasma volume, pulmonary artery pressure, and cardiac output; and did not change urine production or oxygen delivery to tissues.

Gastric emptying and intestinal transit of various enteral feedings following severe burn injury

BACKGROUND

Burn-induced delayed gastric emptying and intestinal transit limits enteral feeding/resuscitation.

AIMS

To study (1) the effects of burn injury on gastric emptying and intestinal transit at different time points following enteral feeding/fluids, and (2) the effects of enteral resuscitative fluids on gastric emptying, intestinal transit, and plasma volume expansion.

METHODS

Rats were randomized into sham-burn and burn groups. They were either enterally untreated or treated by a gavage of one or multiple doses of oral rehydration solution (ORS) or, Vivonex(®), all mixed with phenol red as a marker, at different time points from 1 to 6 h after burn. Gastric emptying, intestinal transit and hematocrit values were assessed. Gastric emptying of a semi-solid methylcellulose meal served as a standard control for gastric emptying studies.

RESULTS

We found that (1) burn did not alter the gastric emptying of ORS, but delayed its intestinal transit at all time points; (2) burn delayed the gastric emptying of both methylcellulose or Vivonex and the intestinal transit of Vivonex, 6 h after burn; and (3) multiple doses of ORS normalized the elevated post-burn hematocrit values. The percentage of plasma volume expansion at 6 h resulting from the multiple-dose ORS was superior to that of Vivonex by 50%. Addition of Erythromycin to Vivonex improved its gastric emptying, intestinal transit, and plasma volume expansion.

CONCLUSIONS

Burn delays the gastric emptying of semi-solids, but not the ORS. Enteral electrolyte solution (ORS) and feeding (Vivonex) provided plasma volume expansion. Prokinetic drugs may be able to maximize the effectiveness of early post-burn feeding.

Effects of fluid resuscitation with hypertonic saline dextrane or Ringer's acetate after nonhemorrhagic shock caused by pulmonary contusion

BACKGROUND

Injured lungs are sensitive to fluid resuscitation after trauma. Such treatment can increase lung water content and lead to desaturation. Hypertonic saline with dextran (HSD) has hyperosmotic properties that promote plasma volume expansion, thus potentially reducing these side effects. The aim of this study was to (1) evaluate whether fluid treatment counteracts hypotension and improves survival after nonhemorrhagic shock caused by lung contusion and (2) analyze whether resuscitation with HSD is more efficient than treatment with Ringer's acetate (RA) in terms of blood oxygenation, the amount of lung water, circulatory effects, and inflammatory response.

METHODS

Twenty-nine pigs, all wearing body armor, were shot with a 7.62-mm assault rifle to produce a standardized pulmonary contusion. These animals were allocated into three groups: HSD, RA, and an untreated shot control group. Exposed animals were compared with animals not treated with fluid and shot with blank ammunition. For 2 hours after the shot, the inflammatory response and physiologic parameters were monitored.

RESULTS

The impact induced pulmonary contusion, desaturation, hypotension, increased heart rate, and led to an inflammatory response. No change in blood pressure was observed after fluid treatment. HSD treatment resulted in significantly less lung water (p < 0.05) and tended to give better Pao2 (p = 0.09) than RA treatment. Tumor necrosis factor-α release and heart rate were significantly lower in animals given fluids.

CONCLUSION

Fluid treatment does not affect blood pressure or mortality in this model of nonhemorrhagic shock caused by lung contusion. However, our data indicate that HSD, when compared with RA, has advantages for the injured lung.

Arteriovenous differences in plasma dilution and the distribution kinetics of lactated ringer's solution

BACKGROUND

Conventional concept suggests that infused crystalloid fluid is first distributed in the plasma volume and then, since the capillary permeability for fluid is very high, almost instantly equilibrates with the extracellular fluid space. We challenge whether this view is consistent with findings based on volume kinetic analysis.

METHODS

Fifteen volunteers received an IV infusion of 15 mL/kg of lactated Ringer's solution during 10 min. Simultaneous arterial and venous blood hemoglobin (Hgb) samples were obtained and Hgb concentrations measured. The arteriovenous (AV) difference in Hgb dilution in the forearm was determined and a volume kinetic model was fitted to the series of Hgb concentrations in arterial and venous blood.

RESULTS

The AV difference in plasma dilution was only positive during the infusion and for 2.5 min thereafter, which represents the period of net flow of fluid from plasma to tissue. Kinetic analysis showed that volume expansion of the peripheral fluid space began to decrease 14 min (arterial blood) and 20 min (venous blood) after the infusion ended. Distribution of lactated Ringer's solution apparently occurs much faster in the forearm than in the body as a whole. Therefore, the AV difference in the arm does not accurately reflect the distribution of Ringer's solutions or whole-body changes in plasma volume.

CONCLUSIONS

The relatively slow whole-body distribution of lactated Ringer's solution, which boosts the plasma volume expansion during and for up to 30 min after an infusion, is probably governed by a joint effect of capillary permeability and differences in tissue perfusion between body regions.

Application of the sodium dilution principle to calculate extracellular fluid volume changes in horses during dehydration and rehydration

OBJECTIVE

To apply the principle of sodium dilution to calculate the changes in the extracellular fluid (ECF) volume (ECFV) and intracellular fluid volume (ICFV) that occur during dehydration and rehydration in horses.

ANIMALS

8 healthy horses of various breeds.

PROCEDURES

Horses were dehydrated over 4 hours by withholding water and administering furosemide. Saline (0.9% NaCl) solution was administered IV during the next 2 hours (20 mL/kg/h; total 40 mL/kg). Horses were monitored for an additional hour following IV fluid administration. Initial ECFV was determined by use of multifrequency bioelectrical impedance analysis, and serum sodium concentration was used to calculate total ECF sodium content. Sodium and fluid volume losses were monitored and calculated throughout the study and used to estimate changes in ECFV and ICFV during fluid balance alterations.

RESULTS

Changes during dehydration and rehydration primarily occurred in the ECFV. The sodium dilution principle estimated an overexpansion of the ECFV beyond the volume of fluid administered, indicating a small contraction of the ICFV in response to fluid administration. Serum and urinary electrolyte changes were recorded and were consistent with those of previous reports.

CONCLUSIONS AND CLINICAL RELEVANCE

The sodium dilution principle provided a simple method that can be used to estimate the changes in ECFV and ICFV that occur during fluid administration. Results suggested an overexpansion of the ECFV in response to IV saline solution administration. The sodium dilution principle requires further validation in healthy and clinically ill horses, which could provide clinical applications similar to those in other species.

Effect of esmolol on fluid therapy in normovolemia and hypovolemia

beta-Adrenergic agonists can enhance vascular volume expansion after a fluid bolus. The present study addresses how the beta-adrenergic antagonist esmolol influences volume expansion and fluid balance during normovolemia (series 1) and hypovolemia (series 2). Sheep were instrumented, and the spleen was removed. For series 1, continuous infusion of 50 to 100 microg.kg(-1).min(-1) esmolol (n = 6) or control (no drug; n = 6) was begun 30 min before administration of a 24-mL kg(-1) 20-min bolus of 0.9% NaCl. For series 2, anesthetized sheep were infused with 50 to 100 microg.kg(-1).min(-1) esmolol (n = 6) or control (no drug; n = 6) 30 min before a-20 mL kg(-1) hemorrhage. Fluid resuscitation (0.9% NaCl) was begun 30 min after hemorrhage. The 24-mL kg(-1) 20-min bolus was followed by titrated fluid therapy. Hemoglobin, fluid in, and urinary output were used to calculate changes in plasma volume (DeltaPV), extravascular volume (DeltaEVV = fluid in - urinary output - DeltaPV), volume expansion efficiency (VEE = fluid in / DeltaPV), and fluid distribution ratio (DeltaPV/DeltaEVV). Hemodynamics for both series were similar with the exception of heart rate. In series 1, peak DeltaPV was 9.1 +/- 1.0 mL kg(-1) in control and 3.7 +/- 1.0 mL kg(-1) at study end. Esmolol resulted in a lower peak DeltaPV (6.4 +/- 2.0 mL kg(-1)) and a negative DeltaPV (-0.4 +/- 0.6 mL kg(-1)) at study's end. Urinary output was lower, and EVV was greater with esmolol. In series 2, esmolol increased fluid requirements (67 +/- 7 mL kg(-1)) compared with control (54 +/- 5 mL kg(-1)). Esmolol reduced DeltaPV/DeltaEVV. These data suggest that esmolol impairs the vascular retention of fluid and may increase the amount of volume support during fluid resuscitation.

Hypertonic saline modulation of intestinal tissue stress and fluid balance

Crystalloid-based resuscitation of severely injured trauma patients leads to intestinal edema. A potential mechanism of intestinal edema-induced ileus is a reduction of myosin light chain phosphorylation in intestinal smooth muscle. We sought to determine if the onset of edema initiated a measurable, early mechanotransductive signal and if hypertonic saline (HS) can modulate this early signal by changing intestinal fluid balance. An anesthetized rat model of acute interstitial intestinal edema was used. At laparotomy, the mesenteric lymphatic was cannulated to measure lymph flow and pressure, and a fluid-filled micropipette was placed in the intestinal submucosa to measure interstitial pressure. Rats were randomized into four groups (n=6 per group): sham, mesenteric venous hypertension+80 mL/kg 0.9% isotonic sodium chloride solution (ISCS 80), mesenteric venous hypertension+80 mL/kg 0.9% ISCS+4 mL/kg 7.5% saline (ISCS 80+HS), or 4 mL/kg 7.5% saline (HS alone) to receive the aforementioned intravenous fluid administered over 5 min. Measurements were made 30 min after completion of the preparation. Tissue water, lymph flow, and interstitial pressure were measured. Resultant applied volume induced stress on the smooth muscle (sigmaravi-muscularis) was calculated. Mesenteric venous hypertension and crystalloid resuscitation caused intestinal edema that was prevented by HS. Intestinal edema caused an early increase in intestinal interstitial pressure that was prevented by HS. Hypertonic saline did not augment lymphatic removal of intestinal edema. sigmaravi-muscularis was increased with onset of edema and prevented by HS, paralleling the interstitial pressure data. Intestinal edema causes an early increase in interstitial pressure that is prevented by HS. Prevention of the edema-induced increase in interstitial pressure serves to blunt the mechanotransductive signal of sigmaravi-muscularis.

Closed-loop control of fluid therapy for treatment of hypovolemia

Closed-loop algorithms and resuscitation systems are being developed to control IV infusion rate during early resuscitation of hypovolemia. Although several different physiologic variables have been suggested as an endpoint to guide fluid therapy, blood pressure remains the most used variable for the initial assessment of hemorrhagic shock and the treatment response to volume loading. Closed-loop algorithms use a controller function to alter infusion rate inversely to blood pressure. Studies in hemorrhaged conscious sheep suggest that: (1) a small reduction in target blood pressure can result in a significant reduction in volume requirement; (2) nonlinear algorithms may reduce the risk of increased internal bleeding during resuscitation; (3) algorithm control functions based on proportional-integral, fuzzy logic, or nonlinear decision tables were found to restore and maintain blood pressure equally well. Proportional-integral and fuzzy logic algorithms reduced mean fluid volume requirements compared with the nonlinear decision table; and (4) several algorithms have been constructed to the specific mechanism of injury and the volume expansion properties of different fluids. Closed-loop systems are undergoing translation from animal to patient studies. Future smart resuscitation systems will benefit from new noninvasive technologies for monitoring blood pressure and the development of computer controlled high flow intravenous pumps.

Hypertonic 15% sodium pyruvate offers no initial resuscitation advantage compared with 8% hypertonic NACl in sheep with multiple hemorrhages

Initial fluid resuscitation of hemorrhagic shock might be enhanced by the infusion of monocarboxylate-energy substrates. We evaluated hemodynamics, metabolism, and fluid dynamics for initial resuscitation of hemorrhage using small volume 15% sodium pyruvate solution (HPY) compared with osmotically matched 8% hypertonic saline (HS). Instrumented conscious sheep were hemorrhaged 25 mL/kg at time zero through 15 min (T0-T15) and 5 mL/kg for 5 min at T50 to T55 and T70 to T75. Fluid resuscitation from T30 to T180 was performed by a computer-controlled closed-loop system, which titrated infusion rate to a mean arterial pressure of 90 mmHg. Initial infusion was 4 mL/kg of either HPY or HS, followed by the administration of lactated Ringer. Both HPY and HS restored cardiac index similarly. The lactate/pyruvate ratio was used to assess metabolic debt and was significantly higher (T180), whereas oxygen delivery was significantly lower (T120) with HPY versus HS. Total fluid administered was similar, with 43.7 +/- 6.2 mL/kg for HPY and 39.4 +/- 6.8 mL/kg for HS. Plasma volume was similarly increased and approached baseline values for both groups. Initial resuscitation with small volume HPY offered no hemodynamic or metabolic advantage compared with small volume HS when the fluids were infused to an end point pressure.

Dynamics of vascular volume and hemodilution of lactated Ringer's solution in patients during induction of general and epidural anesthesia

OBJECTIVE

To investigate the dynamics of vascular volume and the plasma dilution of lactated Ringer's solution in patients during the induction of general and epidural anesthesia.

METHODS

The hemodilution of i.v. infusion of 1000 ml of lactated Ringer's solution over 60 min was studied in patients undergoing general (n=31) and epidural (n=22) anesthesia. Heart rate, arterial blood pressure and hemoglobin (Hb) concentration were measured every 5 min during the study. Surgery was not started until the study period had been completed.

RESULTS

General anesthesia caused the greater decrease of mean arterial blood pressure (MAP) (mean 15% versus 9%; P<0.01) and thereby followed by a more pronounced plasma dilution, blood volume expansion (VE) and blood volume expansion efficiency (VEE). A strong linear correlation between hemodilution and the reduction in MAP (r=-0.50; P<0.01) was found. At the end of infusion, patients undergoing general anesthesia retained 47% (SD 19%) of the infused fluid in the circulation, while epidural anesthesia retained 29% (SD 13%) (P<0.001). Correspondingly, a fewer urine output (mean 89 ml versus 156 ml; P<0.05) and extravascular expansion (454 ml versus 551 ml; P<0.05) were found during general anesthesia.

CONCLUSION

We concluded that the induction of general anesthesia caused more hemodilution, volume expansion and volume expansion efficiency than epidural anesthesia, which was triggered only by the lower MAP.

Normotensive and hypotensive closed-loop resuscitation using 3.0% NaCl to treat multiple hemorrhages in sheep

OBJECTIVE

NaCl solutions (7.5%) have been reported to be effective for resuscitation in animals and trauma patients, but these solutions are not approved for use in the United States. We hypothesized that infusion of Food and Drug Administration-approved 3% NaCl provides superior cardiovascular and metabolic function while reducing the overall fluid requirement for resuscitation of hemorrhage. Our objective was to compare four groups, hypotensive and normotensive resuscitation of hemorrhage using 3% NaCl (HS) or lactated Ringer's (LR).

DESIGN

Sheep were hemorrhaged in three separate bleeds, 25 mL/kg at T0 mins and 5 mL/kg at both T50 and T70 mins.

SETTING

University laboratory.

SUBJECTS

Instrumented conscious sheep.

INTERVENTIONS

Resuscitation was started at T30 mins and continued until T180. Normotensive and hypotensive resuscitation to mean arterial pressures of 90 mm Hg and 65 mm Hg, respectively, was performed with LR or HS using a closed-loop resuscitation system.

MEASUREMENTS AND MAIN RESULTS

All four groups were successfully resuscitated to near target levels. Two animals in the hypotensive treatment protocols died during the second and third bleeding, one with the LR65 group and one with the HS65 group. Mean infused volumes were 59.9 +/- 7.0 and 18.0 +/- 5.9 in the LR90 and LR65 groups, respectively, and were 19.6 +/- 2.2 mL/kg and 13.3 +/- 5.7 mL/kg in the HS90 and HS65 treatments (p < .05; LR90 vs. each of the groups). Cardiac indexes were significantly higher with normotensive vs. hypotensive treatment. However, there was no hemodynamic advantage apparent with HS vs. LR when compared with the normotensive or hypotensive treatments. Some animals had high lactate levels (>10 mmol) with both of the hypotensive treatments and also with the HS90 treatment, while not one of the 11 LR90 treatment animals had lactate levels >8 mmol.

CONCLUSIONS

Volume sparing was apparent with HS, but no hemodynamic or metabolic advantage was apparent when used for either normotensive or hypotensive resuscitation. Trends toward lower base excess values and higher occurrences of deaths only in the hypotensive treatment protocols suggest that resuscitation to a target mean arterial pressure of 65 mm Hg may be too low.

Influence of resuscitation volume on blood cells TNF production in a murine model of haemorrhage

The influence of haemorrhage and resuscitation on Tumour Necrosis Factor (TNF) production by whole blood cultures under endotoxin (Escherichia coli LPS) stimulation was investigated in male BALB/c mice. Haemorrhagic shock was induced by removing 0.026 +/- 0.003 mL of blood/g via a cardiac puncture, resulting in a 50% decrease in arterial pressure and a metabolic adidosis. Animals were resuscitated successfully (normotensive) despite a residual base deficit and hyperlactatemia, 60 min after the haemorrhage by the restitution of shed blood volume (SBV) with or without an additional volume of crystalloid (Lactated Ringer's solution) equal to 50, 100 (isovolumetric resuscitation) or 200% of SBV. Pulmonary failure (hypoxia-hypercarbia) and myocardial injury (troponin I release) was observed in this last group. TNF production by whole blood cultures stimulated ex vivo by LPS was estimated 60 min after the end of resuscitation. Haemorrhage resulted in a 48-60% decrease in TNF production. This decrease so-called 'leukocyte deactivation' was not modified by the restitution of SBV with or without crystalloid except for isovolumetric resuscitation which resulted in the cytokine level returning to control in the absence of clear cardiopulmonary dysfunction. In the present murine model of haemorrhage, modifying resuscitation volume influences in vitro TNF production in whole blood cultures challenged by LPS.

Beneficial effects of hypertonic saline/dextran on early survival in porcine endotoxin shock

BACKGROUND

Hypertonic saline/dextran (HSD) has been shown to have beneficial effects in haemorrhagic shock. These effects, with improved haemodynamics and organ perfusion, would in theory also be of benefit in septic shock. However, this is less studied. We have therefore further evaluated the effect of additional treatment with HSD in a porcine endotoxin shock model.

METHODS

Sixteen anaesthetized pigs were used. A continuous infusion of endotoxin (LPS EC) was increased stepwise during 30 min to a rate of 5 microg/kg/h. The infusion was discontinued after 3 h and the animals were observed for another 2 h. The animals received continuous basal fluid resuscitation with isotonic Ringer's glucose 2.5% at a rate of 20 ml/kg/h throughout the experiment. After 1 h of endotoxin infusion, the animals were randomized to additional treatment with HSD, 4 ml/kg over 5 min, or the same volume of isotonic saline. Every 30 min, haemodynamics and mixed venous saturation (SvO2) were measured via a pulmonary artery catheter. Regional blood flow rates were measured continuously by perivascular ultrasonic flow probes. The metabolic response was measured by arterial blood gas analysis.

RESULTS

The endotoxin put all animals into a progressive hypodynamic circulatory shock during the experiment. Treatment with HSD improved survival rate to 8/8 compared with controls 3/8. There was a transient circulatory recovery with improved central and regional haemodynamics, accompanied by stabilized metabolic response.

CONCLUSION

Treatment with additional HSD improves survival in an early phase of endotoxin shock. Generally improved haemodynamics and oxygenation of peripheral tissues are suggested as possible mechanisms.

Diverse dextranase genes from Paenibacillus species

Genes encoding dextranolytic enzymes were isolated from Paenibacillus strains Dex40-8 and Dex50-2. Single, similar but non-identical dex1 genes were isolated from each strain, and a more divergent dex2 gene was isolated from strain Dex50-2. The protein deduced from the Dex40-8 dex1 gene sequence had 716 amino acids, with a predicted M(r) of 80.8 kDa. The proteins deduced from the Dex50-2 dex1 and dex2 gene sequences had 905 and 596 amino acids, with predicted M(r) of 100.1 kDa and 68.3 kDa, respectively. The deduced amino acid sequences of all three dextranolytic proteins had similarity to family 66 glycosyl hydrolases and were predicted to possess cleavable N-terminal signal peptides. Homology searches suggest that the Dex40-8 and Dex50-2 Dex1 proteins have one and two copies, respectively, of a carbohydrate-binding module similar to CBM_4_9 (pfam02018.11). The Dex50-2 Dex2 deduced amino acid sequence had highest sequence similarity to thermotolerant dextranases from thermophilic Paenibacillus strains, while the Dex40-8 and Dex50-2 Dex1 deduced protein sequences formed a distinct sequence clade among the family 66 proteins. Examination of seven Paenibacillus strains, using a polymerase chain reaction-based assay, indicated that multiple family 66 genes are common within this genus. The three recombinant proteins expressed in Escherichia coli possessed dextranolytic activity and were able to convert ethanol-insoluble blue dextran into an ethanol-soluble product, indicating they are endodextranases (EC 3.2.1.11). The reaction catalysed by each enzyme had a distinct temperature and pH dependence.

Immune effect of hypertonic saline: fact or fiction?

Hypertonicity affects many parts of the immune system. Animal studies and experiments in isolated cell cultures show that hypertonicity reversibly suppresses several neutrophil functions and at the same time up-regulates T-lymphocyte function. Infusion of hypertonic saline with or without colloids may thus, besides providing efficient plasma volume expansion, ameliorate the detrimental consequences on the immune function of trauma, shock, reperfusion, and major surgery. However, the few clinical studies conducted to date, specifically addressing the immune effect of hypertonic saline infusion, have shown little, if any, effect on markers of immune function, and larger clinical trials have not demonstrated benefit in terms of morbidity or mortality. Thus, as opposed to animal and cell-culture studies, the immune-modulating properties of hypertonic saline infusion would appear to be of limited value in clinical practice. This review presents in vitro studies, animal experiments, and clinical trials which investigated the consequences of hypertonic saline on markers of immune function.

Fluid and electrolyte therapy in ruminants

Five important questions always must be asked and answered regarding fluid and electrolyte therapy in ruminants: (1) Is therapy needed? (2) What type of therapy? (3) What route of administration? (4) How much should be administered? and (5) How fast should the solution be administered? Food animal veterinarians routinely should carry the following commercially available crystalloid solutions and have the knowledge of how to use the products appropriately: Ringer's solution, 1.3% NaHCO3, acetated Ringer's solution, HS (7.2% NaCl), 8% NaHCO3, 23% calcium gluconate, calcium-magnesium solutions, and 50% dextrose. Ruminants with a blood pH less than 7.20 should be treated intravenously with 1.3% or 8.0% NaHCO3, and those animals with a blood pH greater than 7.45 should be treated intravenously with Ringer's solution. Oral electrolyte solutions or intravenous acetated Ringer's solution should be administered to ruminants with a blood pH greater than 7.20 but less than 7.45, and acetated Ringer's solution is preferred to lactated Ringer's solution. HS solution should be administered whenever rapid resuscitation is required. Oral administration of electrolyte solutions is underused in neonatal and adult ruminants. The optimal solution for oral administration to neonatal ruminants has a sodium concentration between 90 and 130 mmol/L; a potassium concentration between 10 and 20 mmol/L; a chloride concentration between 40 and 80 mmol/L; 40 to 80 mmol/L of metabolizable (nonbicarbonate) base, such as acetate or propionate; and glucose as an energy source. The optimal formulation for adult ruminants is unknown, but such a solution should contain sodium, potassium, calcium, magnesium, phosphate, and propionate to facilitate sodium absorption and to provide an additional source of energy to the animal. Acidemia is treated best by intravenous or oral administration of NaHCO3. Alkalemia is treated best by intravenous administration of Ringer's solution and oral administration of chloride-rich electrolytes such as KCl; the latter provides a physiologically more appropriate treatment than oral administration of vinegar or acetic acid solutions. Hypocalcemia is treated best by administering intravenous calcium borogluconate solutions or oral CaCl2 gels. Hypomagnesemia is treated best by intravenous or subcutaneous administration of combined calcium and magnesium solutions. Hypophosphatemia is treated best by oral administration of feed-grade monosodium phosphate. Hypokalemia is treated best by oral administration of feed-grade KCl; hyperkalemia is treated best by intravenous administration of 8.0% NaHCO3 or HS. The major challenges in treating fluid and electrolyte disorders in ruminants are making treatment protocols more practical and less expensive and formulating an optimal electrolyte solution for oral administration to adult ruminants.

Hyperosmolarity enhances the lung capillary barrier

Although capillary barrier deterioration underlies major inflammatory lung pathology, barrier-enhancing strategies are not available. To consider hyperosmolar therapy as a possible strategy, we gave 15-minute infusions of hyperosmolar sucrose in lung venular capillaries imaged in real time. Surprisingly, this treatment enhanced the capillary barrier, as indicated by quantification of the capillary hydraulic conductivity. The barrier enhancement was sufficient to block the injurious effects of thrombin, TNF-alpha, and H2O2 in single capillaries, and of intratracheal acid instillation in the whole lung. Capillary immunofluorescence indicated that the hyperosmolar infusion markedly augmented actin filament formation and E-cadherin expression at the endothelial cell periphery. The actin-depolymerizing agent latrunculin B abrogated the hyperosmolar barrier enhancement as well as the actin filament formation, suggesting a role for actin in the barrier response. Furthermore, hyperosmolar infusion blocked TNF-alpha-induced P-selectin expression in an actin-dependent manner. Our results provide the first evidence to our knowledge that in lung capillaries, hyperosmolarity remodels the endothelial barrier and the actin cytoskeleton to enhance barrier properties and block proinflammatory secretory processes. Hyperosmolar therapy may be beneficial in lung inflammatory disease.

Resuscitation from hemorrhagic shock: experimental model comparing normal saline, dextran, and hypertonic saline solutions

OBJECTIVE

To compare the effectiveness of normal saline, dextran, hypertonic, and hypertonic-hyperoncotic solutions in hemorrhagic shock.

DESIGN

Laboratory investigation.

SETTING

University hospital, Emergency Surgery and Intensive Care staff.

SUBJECTS

Thirty-two large white female pigs.

INTERVENTIONS

Routine care included: anesthesia and sedation (ketamine 10 mg/kg, droperidol 0.25 mg/kg, diazepam 0.7 mg/kg, fentanyl 0.006 mg/kg, 2% enflurane, 20% nitrous oxide, pancuronium bromide 0.13 mg/kg); volume-controlled ventilation (Paco(2) 35-40 torr; 4.7-5.4 kPa); cannulation of right carotid artery and pulmonary artery. Three flow probes (subdiaphragmatic aorta, superior mesenteric artery, right renal artery) and regional venous catheters (superior mesenteric vein, right renal vein) were positioned. Animals were bled to 45 mm Hg for 1 hr and resuscitated with four different fluids and blood to normal aortic blood flow and hemoglobin.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure and blood flow through abdominal aorta ([OV0312](aor)), mesenteric artery ([OV0312](mes)), and renal artery ([OV0312](ren)) were continuously monitored. Cardiac output, systemic and regional oxygen delivery ([U1E0A]o(2), [U1E0A]o(2mes), [U1E0A]o(2ren)), and consumption ([OV0312]o(2), [OV0312]o(2mes), [OV0312]o(2ren)) were recorded every 30 mins. Baseline [OV0312](aor) was restored with different amounts of fluids in the four groups: normal saline (91.35 +/- 22.18 mL/kg); dextran (16.24 +/- 4.42 mL/kg); hypertonic (13.70 +/- 1.44 mL/kg); and hypertonic-hyperoncotic (9.11 +/- 1.20 mL/kg). The amount of sodium load was less using dextran and hypertonic-hyperoncotic and sodium levels were only transiently increased after hypertonic infusion. Mean arterial pressure and cardiac output were normalized in all groups. Animals resuscitated with normal saline and dextran showed increased pulmonary artery pressures. [U1E0A]o(2) was significantly higher after hypertonic-hyperoncotic infusion, because of reduced hemodilution. Hypertonic and hypertonic-hyperoncotic normalized [OV0312](mes), [U1E0A]o(2mes), [OV0312]o(2mes), [OV0312](ren), and [U1E0A]o(2ren), whereas normal saline and dextran did not achieve this result. At the end of the experiment, hypertonic-hyperoncotic maintained mean arterial pressure, cardiac output, and [U1E0A]o(2) until the end of observation in contrast to normal saline, dextran, and hypertonic.

CONCLUSIONS

Resuscitation with a small volume of hypertonic-hyperoncotic solution allows systemic and splanchnic hemodynamic and oxygen transport recovery, without an increase in pulmonary artery pressure. It only transiently increased sodium concentration.

Acute intravascular volume expansion with rapidly administered crystalloid or colloid in the setting of moderate hypovolemia

Although the distribution of various crystalloid and colloid solutions at equilibrium has been well established, the acute peak expansion of intravascular volume that can be achieved with the rapid administration of crystalloid or colloid is unknown. We studied eight healthy male subjects in a two-part crossover trial designed to assess the maximal increase in intravascular volume achieved with 1000 mL of lactated Ringer's solution compared with the same volume of 6% Hetastarch. Subjects were made moderately hypovolemic by the withdrawal of 900 mL of blood, and then the crystalloid or colloid solution was rapidly infused over 5-7 min. Serial dilution of hematocrit was measured every 5 min for 30 min to determine changes in blood volume. Peak expansion of intravascular volume with lactated Ringer's solution was 630 +/- 127 mL, occurring immediately the rapid infusion was complete, whereas the peak expansion of intravascular volume with 6% Hetastarch was 1123 +/- 116 mL and occurred 5 min after the completion of the fluid infusion. The results were significantly different (P < 0.001). These results would suggest that even for very short periods of time, rapid infusion of colloid significantly more effectively increases blood volume and, by inference, cardiac output than the same volume of crystalloid, even if the crystalloid is administered very rapidly.

IMPLICATIONS

Under conditions of moderate hypovolemia, the maximal acute intravascular volume expansion with the rapid infusion of 1000 mL of lactated Ringer's solution is slightly more than half that achieved with the same volume of 6% Hetastarch.

Blood mercury following DMPS administration to subjects with and without dental amalgam

The use of DMPS as a diagnostic tool in patients with symptoms allegedly caused by mercury from dental amalgam fillings is disputed. We have previously shown that the mercury concentrations in urine cannot be used in such a way. In the present study, we wished to evaluate the effect on blood mercury levels (B-Hg) following intravenously injected DMPS in four groups of subjects: 19 controls without amalgam experience; 21 healthy controls with amalgam fillings; 20 patients with self-reported symptoms from existing dental amalgams; and 20 patients who had removed amalgam fillings. A single dose of DMPS (2 mg/kg) was injected. Blood samples were collected prior to the injection and after 15, 30, 120 min, and after 24 h, and mercury was analyzed by cold vapor atomic absorption spectrophotometry. All groups showed an initial drop of 24 to 30% in the blood levels, approaching baseline values (2.5-5.5 microg/l) after 2 h. The subjects with no amalgam experience had the lowest mercury values. There was no significant difference between the three groups with such experience. There were no significant differences between the two groups with amalgam fillings present. Patients with symptoms allegedly caused by amalgam were not different from the control groups. There were indications that part of the urinary mercury excreted during the first 30 min originated from blood.

Burns: military options and tactical solutions

Burn injury remains a constant source of morbidity and mortality in the military environment. The logistic constraints of combat casualty care can make it impossible to provide the large volumes of crystalloid typically used for burn resuscitation. Unlike penetrating trauma, the immediate and sustained fluid requirements necessary for resuscitation of thermal injury preclude the use of limited or hypotensive resuscitation. We examine the physiology, traditional resuscitation strategies, and rationales for the use of novel regimens in the resuscitation of thermal injury. Although strategies such as early use of colloids or hypertonic saline may not reduce morbidity or mortality when compared with large-volume infusions of lactated Ringer's, they can be volume sparing for some hours and sustain life until more definitive therapy is initiated. An intriguing hypothesis is that oral resuscitation can effectively restore plasma volume after thermal injury. We present data from recent experiments of gastric and intestinal infusions of an oral rehydration solution in a porcine burn model that demonstrates restoration of plasma volumes and improvement in hemodynamic parameters associated with significant gastric emptying and intestinal absorption.

Hypertonic resuscitation: physiologic mechanisms and recommendations for trauma care

Hypertonic saline solutions, with or without added colloid, have received extensive evaluation as volume expanders in both animal studies and clinical trials. Most studies have used 7.5% NaCl/6% dextran 70 (HSD). HSD's primary mechanism of action is rapid osmotic mobilization of cellular water into the blood volume. The measured volume expansion efficiency of HSD is equal to 10 times that of lactated Ringer's solution. Part of HSD's effectiveness is because of the hyperosmotic vasodilation of both systemic and pulmonary vessels. Increased cardiac effectiveness occurs because of the combination of increased preload (venous return) and reduced afterload (vasodilation). Increased cardiac contractility also has been reported in several studies and may play a role, but other studies refute a direct effect on contractility. HSD has been shown to be effective and safe with preexisting dehydration. Animal studies of immune function suggest that increased osmolarity prevents T-cell depression and decreases neutrophil activation. Several perioperative and eight randomized, blinded trauma trials have shown safety and reduced volume needs and suggest increased survival, particularly in head- and penetrating-injury patients. Infusion rates for HSD of 10 to 20 minutes may be recommended for the initial resuscitation of hypotensive trauma.

Hemodilution does not alter arterial baroreflex control of heart rate in anesthetized dogs

The cardiovascular effects of acute normovolemic hemodilution (ANH) are characterized by increased cardiac output and decreased systemic vascular resistance. However, whether arterial baroreflex function is altered by ANH remains undetermined. We assigned 23 anesthetized, mechanically ventilated dogs to mild ANH (hemoglobin, 7-8 g/dL; n = 11) or profound ANH (hemoglobin, 4-5 g/dL; n = 12) achieved by phlebotomy and simultaneous exchange with lactated Ringer's solution at 1:3 ratio to maintain constant central venous pressure and pulmonary artery occluded pressure. Baroreflex sensitivity was assessed by measurements of RR intervals of the electrocardiogram and mean arterial blood pressure (MAP) through a femoral artery catheter. Baroreflex responses were triggered by bolus IV injections of phenylephrine (25-75 micro g) and nitroprusside (50-100 micro g). The linear portion of the baroreflex curves relating RR intervals and MAP were used to determine baroreflex sensitivities. Compared with the predilution period, both ANH groups had significant increases in cardiac output and decreases in systemic vascular resistance (P < 0.01), whereas MAP and heart rate (HR) remained unchanged. However, no significant difference was detected between pre-ANH and post-ANH baroreflex sensitivities in either group. Our results indicate that arterial baroreflex control of HR is preserved during ANH to a hemoglobin concentration of 4-5 g/dL in anesthetized dogs.

IMPLICATIONS

Acute normovolemic hemodilution may be preoperatively used to minimize the requirement of allogeneic blood products during major surgery. We found that baroreflex function is preserved during mild (hemoglobin concentration, 7-8 g/dL) and profound hemodilution (hemoglobin concentration, 4-5 g/dL) in pentobarbital-anesthetized dogs.

Influence of rate and volume of infusion on the kinetics of 0.9% saline and 7.5% saline/6.0% dextran 70 in sheep

We examined whether volume kinetic variables obtained during infusion of a short bolus of 0.9% saline (NS) or 7.5% saline/6.0% dextran 70 (HSD) predict the dilution-time curve resulting from a 20-min infusion of the same fluid. Each of six conscious, splenectomized sheep (mean body weight, 36 +/- 3 kg), on 4 different days, in a random order, received each of 4 IV boluses: NS at a rate of 1.2 mL. kg(-1). min(-1) over 5 min or 20 min or 4.0 mL/kg of HSD over 2 min or 20 min. One, 2, and 3-volume kinetic models were fitted to the dilution of the arterial hemoglobin concentration and the urinary excretion as sampled during 180 min. The maximum dilution of arterial plasma at the end of the 5-min and 20-min infusions of NS was approximately 10% and 22%, respectively, and after the 2-min and 20-min infusions of HSD, maximum dilution was 24% and 21%, respectively. The median absolute performance error was virtually identical when the mean variable estimates from the 5-min infusion of NS were used to predict the individual dilution-time curves of the 5-min (mean, 0.027 dilution units) and 20-min (mean, 0.027) infusions and when the 2-min infusion of HSD was used to predict the dilution during the individual 2-min (mean, 0.050) and 20-min infusions (mean, 0.047). Computer simulations indicated that the difference at the end of infusion between the volume effects of NS and HSD is larger after longer infusions. We concluded that the volume kinetic variables obtained during a short infusion can be used to predict the outcome of a longer one, even if the longer infusion also delivers a larger volume.

IMPLICATIONS

Kinetic analysis of a short infusion of 7.5% saline/6% dextran or 0.9% saline accurately predicts the effects of a longer infusion of the same volume (7.5% saline/6% dextran) or of a larger volume (0.9% saline).

Early postoperative respiratory acidosis after large intravascular volume infusion of lactated ringer's solution during major spine surgery

In this study, we compared the effects of large intravascular volume infusion of 0.9% saline (NS) or lactated Ringer's (LR) solution on electrolytes and acid base balance during major spine surgery and evaluated the postoperative effects. Thirty patients aged 18-70 yr were included in the study. General anesthesia was induced with 5 mg/kg thiopental and 0.1 mg/kg vecuronium IV. Anesthesia was maintained with oxygen in 70% nitrous oxide and 1.5%-2% sevoflurane. In Group I, the NS solution, and in Group II, the LR solution were infused 20 mL. kg(-1). h(-1) during the operation and 2.5 mL. kg(-1). h(-1), postoperatively. Electrolytes (Na+, K+, Cl-) and arterial blood gases were measured preoperatively, every hour intraoperatively and at the 1st, 2nd, 4th, 6th, and 12th hours postoperatively. In the NS group, pHa, HCO3 and base excess decreased, and Cl- values increased significantly at the 2nd hour and Na+ values increased at the 4th hour intraoperatively (P < 0.001). The values returned to normal ranges at the 12th hour postoperatively. In the LR group, blood gas analysis and electrolyte values did not show any significant difference intraoperatively, but the increase in PaCO2 and the decrease in pHa and serum Na+ was significant at the 1st hour postoperatively. Although intraoperative 20 mL. kg(-1). h(-1) LR infusion does not cause hyperchloremic metabolic acidosis as does NS infusion, it leads to postoperative respiratory acidosis and mild hyponatremia.

IMPLICATIONS

The infusion of large-volume lactated Ringer's solution does not cause hyperchloremic metabolic acidosis as does 0.9% saline during major surgery, but leads to postoperative mild hyponatremia and respiratory acidosis.

Early postoperative respiratory acidosis after large intravascular volume infusion of lactated ringer's solution during major spine surgery

In this study, we compared the effects of large intravascular volume infusion of 0.9% saline (NS) or lactated Ringer's (LR) solution on electrolytes and acid base balance during major spine surgery and evaluated the postoperative effects. Thirty patients aged 18-70 yr were included in the study. General anesthesia was induced with 5 mg/kg thiopental and 0.1 mg/kg vecuronium IV. Anesthesia was maintained with oxygen in 70% nitrous oxide and 1.5%-2% sevoflurane. In Group I, the NS solution, and in Group II, the LR solution were infused 20 mL. kg(-1). h(-1) during the operation and 2.5 mL. kg(-1). h(-1), postoperatively. Electrolytes (Na+, K+, Cl-) and arterial blood gases were measured preoperatively, every hour intraoperatively and at the 1st, 2nd, 4th, 6th, and 12th hours postoperatively. In the NS group, pHa, HCO3 and base excess decreased, and Cl- values increased significantly at the 2nd hour and Na+ values increased at the 4th hour intraoperatively (P < 0.001). The values returned to normal ranges at the 12th hour postoperatively. In the LR group, blood gas analysis and electrolyte values did not show any significant difference intraoperatively, but the increase in PaCO2 and the decrease in pHa and serum Na+ was significant at the 1st hour postoperatively. Although intraoperative 20 mL. kg(-1). h(-1) LR infusion does not cause hyperchloremic metabolic acidosis as does NS infusion, it leads to postoperative respiratory acidosis and mild hyponatremia.

IMPLICATIONS

The infusion of large-volume lactated Ringer's solution does not cause hyperchloremic metabolic acidosis as does 0.9% saline during major surgery, but leads to postoperative mild hyponatremia and respiratory acidosis.