Radiosulphate as a measure of the extracellular fluid in acute hemorrhagic shock

[Pharmacokinetics characteristics of dexamethasone in Crush syndrome model rats]

Crush syndrome (CS) is characterized by ischemia/reperfusion-induced rhabdomyolysis and subsequent systemic inflammation and has a high mortality rate, even when treated with conventional therapy. In previous studies, we demonstrated that treatment of rats with acute lethal CS using dexamethasone (DEX) had therapeutic effects in laboratory findings and improved the clinical course of CS. However, because the application of DEX in CS therapy is unknown, evaluation of the pharmacokinetic parameters of DEX was considered essential to support its clinical use. Here, we investigated the pharmacokinetic characteristics of DEX in a rat model of CS. Anesthetized rats were subjected to bilateral hind limb compression using rubber tourniquets for 5 h, followed by reperfusion for 0 to 24 h. Rats were divided randomly into 4 groups: saline-treated sham (S) and CS groups and 5.0 mg/kg DEX-treated S (S-DEX) and CS (CS-DEX) groups. Blood and tissue samples were collected for HPLC analysis. In the CS-DEX group, the pharmacokinetic parameters of the area under the concentration-time curve, mean residence time, and distribution volume levels increased significantly compared to the S-DEX group, whereas total body clearance, elimination rate constant, and renal clearance levels decreased significantly. Moreover, decrease of muscle tissue DEX concentration and of CYP3A activity were observed in the CS-DEX group. These results show the pharmacokinetic characteristics of DEX in the rat CS model and support the potential use of DEX in disaster medical care.

Fluid therapy for the surgical patient

Perioperative fluid therapy is the subject of much controversy, and the results of the clinical trials investigating the effect of fluid therapy on outcome of surgery seem contradictory. The aim of this chapter is to review the evidence behind current standard fluid therapy, and to critically analyse the trials examining the effect of fluid therapy on outcome of surgery. The following conclusions are reached: current standard fluid therapy is not at all evidence-based; the evaporative loss from the abdominal cavity is highly overestimated; the non-anatomical third space loss is based on flawed methodology and most probably does not exist; the fluid volume accumulated in traumatized tissue is very small; and volume preloading of neuroaxial blockade is not effective and may cause postoperative fluid overload. The trials of 'goal-directed fluid therapy' aiming at maximal stroke volume and the trials of 'restricted intravenous fluid therapy' are also critically evaluated. The difference in results may be caused by a lax attitude towards 'standard fluid therapy' in the trials of goal-directed fluid therapy, resulting in the testing of various 'standard fluid regimens' versus 'even more fluid'. Without evidence of the existence of a non-anatomical third space loss and ineffectiveness of preloading of neuroaxial blockade, 'restricted intravenous fluid therapy' is not 'restricted', but rather avoids fluid overload by replacing only the fluid actually lost during surgery. The trials of different fluid volumes administered during outpatient surgery confirm that replacement of fluid lost improves outcome. Based on current evidence, the principles of 'restricted intravenous fluid therapy' are recommended: fluid lost should be replaced and fluid overload should be avoided.

Hemorrhage and operation cause a contraction of the extracellular space needing replacement—evidence and implications? A systematic review

BACKGROUND

Hemorrhagic hypotension or operative trauma is believed to cause a contraction of the extracellular fluid volume (ECV) beyond the measured fluid losses. The aim of this review was to explore the evidence and implications of ECV loss.

METHODS

We performed a systematic review of original trials measuring ECV changes during hemorrhage or operation. PubMed, relevant periodicals, and reference lists were searched until no further original articles appeared. The quality of both the scientific and the technical methods of the trials were evaluated.

RESULTS

A total of 61 original articles were found. The pattern appeared that all investigators reporting shock or operation to cause a disparate reduction of the ECV had measured the ECV with the same method. The ECV was calculated from very few blood samples that were withdrawn after 20 to 30 minutes of equilibration of a tracer (the (35)SO(4)-tracer). Trials calculating ECV from multiple blood samples, after longer equilibration times, or using other tracers did not find a contraction of the ECV. On the contrary, trials using a bromide tracer found the ECV to be expanded after operation.

CONCLUSIONS

The evidence supporting the idea that hemorrhage or operation cause a contraction of the ECV is weak, and probably a result of flawed methodology.

Hematocrit and metabolic changes caused by varied resuscitation strategies in a canine model of hemorrhagic shock

The effect of acute hemorrhage on hematocrit is controversial. Our aims were to (1) define hematocrit (Hct) changes caused by acute hemorrhage and (2) to compare Hct, hemodynamic, and metabolic responses to varied resuscitation strategies. Twenty-five dogs were instrumented for hemodynamic monitoring and randomized to 4 groups: control (n = 4), large volume (n = 7), small volume (n = 7), and no fluid resuscitation (n = 7). Dogs were hemorrhaged 30% of blood volume. Large- and small-volume groups received 3 mL or 1 mL lactated ringers (LR) for every mL hemorrhaged, respectively. Data were collected over 6 hours. Mean Hct dropped by 17% in all groups posthemorrhage (P <.002) and further decreased to 50% and 24% of baseline in the large- and small-volume groups postresuscitation (P <.001). Hct changes stabilized within 1 hour. No prolonged differences in hemodynamics or metabolic parameters were observed between groups. Acute hemorrhage caused a rapid, moderate drop in Hct, which quickly stabilized. Larger decreases in Hct were caused by fluid resuscitation. Large-volume resuscitation had no advantage over small volume in this hemorrhagic shock model.

A comparison of the response of near-fatal acute hemorrhage models with and without a vascular injury to rapid volume expansion

Recent studies in which animals were bled from a vascular injury rather than an intravascular catheter demonstrate increased blood loss and mortality with rapid volume expansion. The purpose of this study was to better define the importance of incorporating a vascular injury in animal models of acute hemorrhage. We directly compared the response to resuscitation from hemorrhage of comparable severity in animals with and without a vascular injury. Thirty-four immature swine (14.6 to 23.2 kg) were instrumented and subjected to severe blood loss (40 to 46 mL/kg). Groups I and II were hemorrhaged from a femoral artery catheter only. Groups III and IV were initially bled in the same manner; however, when the mean arterial pressure (MAP) decreased to 30 mm Hg, a 4-mm tear was created in the infrarenal aorta, allowing free intraperitoneal hemorrhage. In all groups, the catheter hemorrhage was discontinued once the pulse pressure reached 5 mm Hg. Groups II and IV were resuscitated with normal saline (NS) infused at a rate of 6 mL/kg/min followed by shed blood at a rate of 2 mL/kg/min. The resuscitation fluids were infused as needed to maintain a MAP of 80 mm Hg. Groups I and III served as controls and were not resuscitated. All animals were observed for 60 minutes or until death. The data were compared using repeated measures analysis of variance with a post hoc Tukey Kramer and the Fisher's exact test. Mortality was 100%, 0%, 88%, and 78% for groups I, II, III, and IV, respectively (P < .05 for group II vs groups I, III, and IV).(ABSTRACT TRUNCATED AT 250 WORDS)

Post-traumatic changes in, and effect of colloid osmotic pressure on the distribution of body water

The aim of this study was to define the post-traumatic changes in body fluid compartments and to evaluate the effect of plasma colloid osmotic pressure (COP) on the partitioning of body fluid between these compartments. Forty-two measurements of plasma volume (green dye), extracellular volume (bromine), and total body water (deuterium) were done in ten traumatized patients (mean Injury Severity Score, ISS, = 34) and 23 similar control studies were done in eight healthy volunteers who were in stable fluid balance. Interstitial volume, intracellular volume, and blood volume were calculated from measured fluid spaces and hematocrit; COP was directly measured. Studies in volunteers on consecutive days indicated good reproducibility, with coefficients of variation equal to 3.5% for COP, 6.3% for plasma volume, 4.5% for extracellular volume, and 4.9% for total body water. COP values extended over the entire range seen clinically, from 10 to 30 mmHg. Interstitial volume was increased by 55% in patients, but intracellular volume was decreased by 10%. We conclude (1) that posttraumatic peripheral edema resulting from hemodilution is located in the interstitial compartment, with no intracellular space expansion; and (2) that interstitial volume, but not intracellular volume, is closely related to plasma COP.

Microcirculation and hemorrhagic shock

Blood loss is followed by compensatory cardiovascular readjustments that favor the maintenance of blood flow to central vital organs rather than to peripheral tissues. The microcirculatory changes that occur in skeletal muscle in shock states are of major importance, since skeletal muscle is not only the largest cell mass of the body but also one of the major target organs for neurohumorally mediated compensatory vascular readjustments. Intravital microscopic studies show that the microvascular blood flow in skeletal muscle is intermittent in the early posthemorrhagic period. This probably reflects an interplay between alpha-adrenergic vasoconstrictor and beta-adrenergic vasodilator activities, which serves to enhance a compensatory mobilization of interstitial fluid into the vascular compartment. A period of complete microcirculatory arrest is then seen, followed by reperfusion engaging only 30% to 50% of the capillaries that were seen perfused in resting skeletal muscle. The microvascular blood flow in shock is further characterized by a pronounced heterogeneity in distribution. Many capillaries remain constantly unperfused, while in others a slow, intermittent blood flow is seen. Obstruction of many capillaries by white blood cells and their slow passage through other capillaries seem to be the main reasons for the maldistribution of capillary blood flow in shock. Red blood cell aggregates obstructing capillary blood flow are not seen. The heterogeneous tissue perfusion is accompanied by local variations in cellular hypoxic injury, as is evidenced by multifocal measurements of tissue oxygen tension and by cellular transmembrane potential registrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaesthesia and the kidney

Applied anatomy and physiology of the kidney are briefly reviewed. This includes an account of renal blood flow, glomerular filtration rate, juxtaglomerular apparatus, renal autoregulation and intra-renal blood flow distribution, tubular transport mechanisms, solute handling in proximal tubule, function of loop of Henle and distal tubule system. This section concludes with a summary of changes in tubule fluid along the length of the nephron. Acute effects of anaesthesia are reviewed in detail. Indirect effects include those on circulatory and sympathetic nervous systems, autoregulation, endocrine systems such as those involving anti-diuretic hormone, adrenaline and noradrenaline, renin-angiotensin and aldosterone. Direct effects of anaesthesia on renal function have now been confirmed both in vitro and in vivo. Delayed direct nephrotoxicity of anaesthetics relates predominantly to methoxyflurane (MOF) and its metabolism to inorganic fluoride. Other factors are MOF dose, genetics, age, enzyme induction, obesity, other nephrotoxic drugs. Clinical implications are presented. Enflurane nephrotoxicity is rare but aetiologic factors are similar to the foregoing. Isoflurane and halothane are not nephrotoxic. A consideration of the influence of anaesthetic management on the incidence and severity of postoperative acute renal failure concludes the review.

Alterations in cellular membrane function during hemorrhagic shock in primates

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