Fluid and ion redistribution in skeletal muscle in an animal sepsis model

Effects of small-volume hypertonic saline on acid-base and electrolytes balance in rats with peritonitis-induced sepsis

Our previous study has demonstrated that hypertonic saline (HS) given at 3 h after cecal ligation and puncture (CLP) surgery alleviates circulatory failure, multiple organ dysfunction syndrome, and mortality rate in rats. However, only few data exist on the application of HS in acid-base and electrolyte imbalance of sepsis. In addition, early one-dose HS administration seems to have only modest improvement on mortality rate. Thus, we evaluated the effects of HS on acid-base equilibrium and electrolyte balance in CLP-induced sepsis model and further compared with the effects of two- and one-dose HS administration. Male Wistar rats received CLP or sham operation followed by the administration of saline or HS (7.5% NaCl, 4 mL/kg, intravenously at 3 and 9 h after laparotomy or CLP). The changes in hemodynamics, biochemical variables, blood gas, electrolytes, organ histology, and plasma levels of nitric oxide (NO) and interleukin 1β (IL-1β) were examined during the 18-h observation. Hypertonic saline given either at 3 h (one-dose administration) or at 3 and 9 h (two-dose administration) after CLP attenuated circulatory failure, multiple organ dysfunction syndrome, metabolic acidosis, hyperkalemia, neutrophil infiltration, and 18-h mortality. Moreover, both one- and two-dose HS administrations significantly diminished plasma NO and IL-1β levels in CLP rats. However, only the two-dose HS administration significantly improved hyponatremia and hypocalcemia in septic rats. Beneficial effects of HS in septic rats may be attributed to not only reducing plasma levels of NO and IL-1β, but also improving metabolic acidosis and electrolyte imbalance. In addition, two-dose HS administration could reverse electrolyte imbalance caused by CLP.

Temporal changes in the involvement of pyruvate dehydrogenase complex in muscle lactate accumulation during lipopolysaccharide infusion in rats

A characteristic manifestation of sepsis is muscle lactate accumulation. This study examined any putative (causative) association between pyruvate dehydrogenase complex (PDC) inhibition and lactate accumulation in the extensor digitorum longus (EDL) muscle of rats infused with lipopolysaccharide (LPS), and explored the involvement of increased transcription of muscle-specific pyruvate dehydrogenase kinase (PDK) isoenzymes. Conscious, male Sprague-Dawley rats were infused i.v. with saline (0.4 ml h(-1), control) or LPS (150 mug kg(-1) h(-1)) for 2 h, 6 h or 24 h (n = 6-8). Muscle lactate concentration was elevated after 2, 6 and 24 h LPS infusion. Muscle PDC activity was the same at 2 h and 6 h, but was 65% lower after 24 h of LPS infusion (P < 0.01), when there was a 47% decrease in acetylcarnitine concentration (P < 0.05), and a 24-fold increase in PDK4 mRNA expression (P < 0.001). These changes were preceded by marked increases in tumour necrosis factor-alpha and interleukin-6 mRNA expression at 2 h. The findings indicate that the early (2 and 6 h) elevation in muscle lactate concentration during LPS infusion was not attributable to limited muscle oxygen availability or ATP production (evidenced by unchanged ATP and phosphocreatine (PCr) concentrations) or to PDC inhibition, whereas after 24 h, muscle lactate accumulation appears to have resulted from PDC activation status limiting pyruvate flux, most probably due to cytokine-mediated up-regulation of PDK4 transcription.

Body water and plasma volume in severe community-acquired pneumonia: implications for fluid therapy

OBJECTIVES

To determine changes in total and extracellular body water, plasma volume and sodium in children with severe and very severe pneumonia, and examine the association between these changes and oxygenation.

DESIGN

Prospective, observational.

SUBJECTS

Fifty children aged 2-59 mths with severe and very severe pneumonia.

METHODS

Serum sodium (SNa), plasma osmolality (Posm), urinary sodium (UNa) and osmolality, total body water (TBW), extracellular water (ECW) and plasma volume (PV) were estimated during the acute phase of pneumonia (within 3-6 hrs of presentation) and after recovery. These were correlated with oxygen saturation (SpO(2)) recorded on presentation.

RESULTS

All children had cough, fever, tachypnoea and chest-wall indrawing; 70% had inability to feed and 90% were hypoxaemic (SpO(2) < or = 90%). During the acute phase of illness, among the survivors (n=46), mean (SD) ECW and PV were significantly higher than that after recovery [ECW 318 (45) vs 308 (49) ml/kg, PV 53.2 (2.3) vs 52.1 (2.3) ml/kg, p<0.05]. SNa < or = 135 mmol/L was significantly correlated with ECW and PV excess. SpO(2) showed a significant linear relationship with TBW, ECW and PV (r=0.43, 0.46 and 0.42, respectively, p<0.005) and SNa (r= or <0.33, p=0.02). On multiple regression analysis, ECW, blood urea and PV were significant predictors of SpO(2) (combined r=0.63). The four patients who died had significantly higher Posm and blood urea and lower SpO(2) but in a logistic regression model SpO(2) was the only significant predictor of death (odds ratio 0.54, 95% CI 0.32-0.9, p=0.02).

CONCLUSION

ECW and PV were moderately increased in severe and very severe pneumonia and the increase correlated with better oxygenation. These findings suggest that fluid retention in response to hypoxaemia is directed towards improving circulating volume. The current practice of fluid restriction in hypoxaemic patients with severe pneumonia might be logical only after correction of hypoxaemia.

Sugar Solutions Used In Resuscitation

Although recent studies have shown that the timing of volume replacement deserves careful consideration (56), which fluid to use is less clear, with the perennial debate of crystalloid v colloid and now colloid v colloid still unresolved. This review has examined three sugar solutions, two colloids and one crystalloid. In general, all three agents are unhelpful in the immediate resuscitation of hypovolaemic trauma by virtue of a combination of pathophysiology and side effects. Dextran solutions and mannitol are useful in specific situations.

Hyponatremia in hospitalized critically ill children: current concepts

Hyponatremia (serum sodium to < 136 mEq/l) is the most common electrolyte abnormality in critically ill children. It could result from a deficit of sodium, or surplus of water. Impaired water excretion, 'inappropriate' release of vasopressin, use of hypotonic fluids, redistribution of sodium and water, sick cell syndrome, several drugs and primary illness all may contribute to hyponatremia. Acute hyponatremia, defined as a fall in serum sodium to ~ 120 mEq/l within 48 hours may result in acute cerebral edema and brain stem herniation particularly in children. However, there is paucity of data on hyponatremia in hospitalized critically ill patients. Studies addressing incidence, cause and outcome of hyponatremia in critically ill patients are needed to plan rational fluid therapy protocols, and resolve the current debate, which calls for abandonment of N/5 saline in 5% dextrose solution as maintenance intravenous fluid in favour of normal saline to prevent hyponatremia. At present it is not fully correct to assume that isotonic maintenance fluids would be superior to current maintenance fluids. Reducing the volume of maintenance fluid to about 75% of normal maintenance volume may be more appropriate way to prevent hyponatremia in view of water retaining effect of high ADH and reduced renal free water clearance in critically ill children.

Salt of the earth or a drop in the ocean? A pathophysiological approach to fluid resuscitation

The evolved endocrine response after injury leads to sodium, chloride, and water retention at a time when large volumes of sodium containing fluids are given to maintain the circulation and preserve tissue oxygenation. Sodium, chloride, and water are also retained because of increased systemic vascular permeability to plasma proteins, especially albumin, which sequesters fluid in the interstitial space and causes oedema. Excessive fluid and electrolyte retention and interstitial oedema are associated with the systemic inflammatory response syndrome and multiple organ dysfunction, and failure. This review attempts an overview of these processes and addresses the question, "Can manipulation of fluid resuscitation influence the inflammatory response to injury and organ function". Results of randomised controlled prospective clinical studies suggest that limiting the sodium and chloride input and optimal use of synthetic colloids, which are well retained in the vascular space, can reduce the inflammatory response to injury and improve organ function.

Role of skeletal muscle Na+-K+ ATPase activity in increased lactate production in sub-acute sepsis

Bacterial sepsis is frequently accompanied by increased blood concentration of lactic acid, which traditionally is attributed to poor tissue perfusion, hypoxia and anaerobic glycolysis. Therapy aimed at improving oxygen delivery to tissues often does not correct the hyperlactatemia, suggesting that high blood lactate in sepsis is not due to hypoxia. Various tissues, including skeletal muscle, demonstrate increased lactate production under well-oxygenated conditions when the activity of the Na+-K+ ATPase is stimulated. Although both muscle Na+-K+ ATPase activity and muscle plasma membrane content of Na+, K+-ATPase subunits are increased in sepsis, no studies in vivo have demonstrated correlation between lactate production and changes in intracellular Na+ and K+ resulting from increased Na+-K+ pump activity in sepsis. Plasma concentrations of lactate and epinephrine, a known stimulator of the Na+-K+ pump, were increased in rats made septic by E. coli injection. Muscle lactate content was significantly increased in septic rats, although muscle ATP and phosphocreatine remained normal, suggesting oxygen delivery remained adequate for mitochondrial energy metabolism. In septic rats, muscle intracellular ratio of Na+:K+ was significantly reduced, indicating increased Na+-K+ pump activity. These data thus demonstrate that increased muscle lactate during sepsis correlates with evidence of elevated muscle Na+-K+ ATPase activity, but not with evidence of impaired oxidative metabolism. This study also further supports a role for epinephrine in this process.

Linkage of aerobic glycolysis to sodium-potassium transport in rat skeletal muscle. Implications for increased muscle lactate production in sepsis

Although a linkage between aerobic glycolysis and sodium-potassium transport has been demonstrated in diaphragm, vascular smooth muscle, and other cells, it is not known whether this linkage occurs in skeletal muscle generally. Metabolism of intact hind-leg muscles from young rats was studied in vitro under aerobic incubation conditions. When sodium influx into rat extensor digitorum longus (EDL) and soleus muscles was facilitated by the sodium ionophore monensin, muscle weight gain and production of lactate and alanine were markedly stimulated in a dose-dependent manner. Although lactate production rose in both muscles, it was more pronounced in EDL than in soleus. Monensin-induced lactate production was inhibited by ouabain or by incubation in sodium-free medium. Preincubation in potassium-free medium followed by potassium re-addition also stimulated ouabain-inhibitable lactate release. Replacement of glucose in the incubation medium with pyruvate abolished monensin-induced lactate production but exacerbated monensin-induced weight gain. Muscles from septic or endotoxin-treated rats exhibited an increased rate of lactate production in vitro that was partially inhibited by ouabain. Increases muscle lactate production in sepsis may reflect linked increases in activity of the Na+, K+-ATPase, consumption of ATP and stimulation of aerobic glycolysis.

Pentoxifylline improves intracellular electrolytes in sepsis

Sepsis is associated with a generalised membrane dysfunction leading to an increase in intracellular sodium, chloride, and water. The decrease in extracellular water is thought to act as a nonosmotic stimulus to the secretion of antidiuretic hormone. The resultant hyponatraemia is associated with increased surgical morbidity and mortality. Treatment aimed at improving intracellular electrolytes may improve surgical morbidity and mortality. An animal model of peritonitis was used to evaluate the effect of pentoxifylline. Previously, this dimethyl xanthine derivative was shown to stabilise the cell membrane. Administration of pentoxifylline significantly lowered intracellular sodium and chloride, particularly when given after caecal ligation and puncture. This may have clinical implications in the treatment and prevention of hyponatraemia.

Pentoxifylline improves resting membrane potential in sepsis

The resting membrane potential (RMP) of skeletal muscle cells was investigated in a hyperdynamic animal model of sepsis. Reduced membrane potential is known to parallel the clinical course of sepsis and hemorrhagic shock in animal models. Pentoxifylline (PTF), a dimethyl xanthine derivative of the theophylline family, may improve the metabolic effects of sepsis. A cecal ligation and puncture (CL&P) sepsis model in Wistar rats was used in which RMP was measured with differing administration regimes of PTF. The RMP decreased less rapidly in our study when PTF was administered after CL&P and this effect was most noticeable after 18 hours. Administration of PTF before CL&P had little effect on membrane potential fall-off. These results suggest a potential role for PTF in the management of sepsis.