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Roles of the kidneys and fluid volumes in arterial pressure regulation and hypertension.

The goal of this paper has been to show that the renal-fluid volume mechanism for control of the arterial pressure is an extremely powerful one, so powerful that it is either impossible or almost impossible for the arterial pressure ever to be adjusted to any other value besides the level dictated by this mechanism. The reason for the extreme potency of this mechanism for pressure control is that it never stops working until the intake and output of salt and fluid volume come to an exact state of equilibration. This occurs where the salt and water intake line, as illustrated in Figure 3, crosses the renal function curve which expresses the relationship between arterial pressure and fluid output by the kidneys. Some of the factors that make this renal-fluid volume mechanism such an excellent pressure regulator are the following: First, once the baroreceptor mechanism for pressure control has adapted, the systemic arterial pressure is affected greatly by the levels of extracellular fluid volume and blood volume. Second, the blood flow autoregulation mechanism further enhances the effect of slight changes in fluid volume on pressure, increasing the effectiveness of the pressure control system at least five times additional. Third, the renin-angiotensin system also plays a major role in increasing the sensitivity of this pressure control system. When salt intake becomes very great, renal output of renin and subsequent formation of angiotensin both decrease drastically. This shifts the renal function curve back toward a lower pressure level, thus compensating for most of the increase in pressure that would otherwise occur as a result of the increased salt intake. Putting all the above factors together, one finds that very slight changes in the fluid volume level in the body can have drastic effects on pressure. And, conversely, very slight changes in arterial pressure above or below the normal level can initiate large changes in urinary output of salt and water, thus rapidly returning the pressure back to that level at which intake and output of water and salt are in balance.

Adaptation, Physiological↗

Low-volume peritoneal dialysis in 116 neonatal and paediatric critical care patients.

UNLABELLED: Acute renal insufficiency accounts for high mortality in paediatric intensive care patients, particularly in infants. Peritoneal dialysis, usually carried out with dialysate volumes of >20 ml/kg body weight, increases pulmonary artery pressure, which may compromise myocardial function in critical illness. In this paper we report our experiences with the use of lower dialysate volumes in the treatment of critically ill children with renal impairments. We suggest that low-volume peritoneal dialysis is able to achieve adequate ultrafiltration, which relieves overhydration in ventilated and haemodynamically compromised children. A total of 116 paediatric intensive care patients treated between 1992 and 2000 was the subject of this investigation. Diagnosis, indication for dialysis, arterial and central venous pressure, blood gases, creatinine, blood urea nitrogen, urinary output at installation, ultrafiltration, fluid balance, duration and complications during dialysis as well as survival were investigated. The overall mortality was 53%. The respective diagnoses and mortality rates were as follows: 65% of the patients suffered from cardiac diseases (54% mortality), 7% from renal diseases (13%) and 28% from multi-organ system failure (62%). Low-volume peritoneal dialysis was started at evidence of total body fluid overload with inadequate urinary output and resulted in a mean ultrafiltration of 2.8 ml/kg body weight per h. A negative fluid balance was achieved in 53% of patients, mainly in those suffering from hypervolaemia and minor oliguria. None of the complications resulted in death. CONCLUSION: early installation of low-volume peritoneal dialysis offers a safe and adequate ultrafiltration procedure for paediatric critical care patients suffering from minor oliguria and fluid overload.

Acute Kidney Injury↗

Influence of body water distribution on skin thickness: measurements using high-frequency ultrasound.

BACKGROUND: Although it is known that the skin acts as a water reservoir and participates in the fluid content of the whole body, no method has been established to quantify the fluid shifts in superficial tissue. OBJECTIVES: The aim of this study was to investigate changes in dermal and subcutis thickness and echodensity at the forehead and lower leg by high-frequency (20 MHz) ultrasound under various physiological conditions influencing water balance. METHODS: These parameters were measured in the skin of 20 healthy male volunteers at baseline and successively at 30 min after lying down, in a head-down position, after physical activity and after infusion of 10 mL kg-1 body weight of Ringer's solution. RESULTS: Dermal thickness at the forehead showed a significant increase from baseline to a horizontal position and a further increase in the head-down position. Physical activity did not lead to further changes, whereas after fluid infusion the dermal thickness also increased markedly. The echodensity showed inverse changes, with decreasing values. The thickness of the subcutis increased slightly from baseline to a lying position and decreased in the head-down position and after fluid infusion. At the lower leg, skin thickness decreased slightly in the head-down position with elevated legs, and increased after fluid infusion. CONCLUSIONS: Our results show that slight changes in the water distribution of the body influence the thickness and the echodensity of the dermis. Changes are more pronounced at the forehead than on the lower legs. Further, the fluid storage takes place mainly in the dermis and not in the subcutis. High-frequency ultrasound is able to quantify these effects and is a sensitive method for measuring fluid intake and balance during anaesthesia and therapy.

Adult↗

Effect of carnitine on liver fat and nitrogen balance in intravenously fed growing rats.

Carnitine is an essential metabolite whose function is to transport activated long-chain fatty acids across the mitochondrial membrane. It is consumed in the diet and is synthesized from lysine and methionine to meet body needs. Hepatic fat deposition has been reported in experimental animals and patients receiving total parenteral nutrition (TPN) fluids devoid of preformed carnitine. In the present experiment, nitrogen balance, hepatic fat deposition and serum and tissue carnitine were determined in rats receiving a hypercaloric TPN regimen containing 0, 10, 50, and 100 mg DL-carnitine per 100 g body weight for 14 days. Rats fed a stock diet served as controls. Increased nitrogen balance was observed in TPN rats receiving the highest dose of carnitine supplementation. Hepatic fat deposition induced by the hypercaloric infusion was ameliorated but not eliminated by infusing carnitine. Serum, liver and skeletal muscle carnitine concentrations were maintained, whereas that of heart decreased in TPN rats without carnitine supplementation. Between 90 and 100% of the administered L-carnitine was excreted. It is suggested that the observed effects of carnitine on nitrogen balance and hepatic fat deposition are due to as yet undefined pharmacological properties. The significant decrease of carnitine in cardiac muscle resulting from TPN in a patient population already stressed and traumatized and the metabolic and physiological effects of this decrease deserve further exploration.

Animals↗

Burn resuscitation: crystalloid versus colloid versus hypertonic saline hyperoncotic colloid in sheep.

OBJECTIVES: The present study was undertaken to assess the fluid balance and hemodynamic effects during the first 8 hrs of resuscitation in animals with a large body surface area burn, using lactated Ringer's solution, 6% hetastarch, and hypertonic saline dextran. DESIGN: A prospective, blinded, controlled, terminal study, using anesthetized animals. The initial baseline period was followed by scald injury, and three different treatment regimens were administered from coded bags to achieve a physiologic end point. SETTING: University laboratory. SUBJECTS: Eighteen female sheep (35 to 45 kg) were anesthetized with isoflurane. INTERVENTIONS: Test solutions (10 mL/kg of either lactated Ringer's solution, hetastarch, or hypertonic saline dextran) were infused 30 mins after the scald injury at a rate to restore and maintain the baseline oxygen delivery (DO2) value. MEASUREMENTS AND MAIN RESULTS: Cardiovascular hemodynamics, plasma sodium concentration, plasma colloid osmotic pressure, and fluid balance were measured before and after scalding and resuscitation. After the initial 10-mL/kg test solution dose was given, lactated Ringer's solution was infused to achieve the same end point of baseline DO2 for the remainder of the 8 hrs. The scald caused an initial 30% reduction in cardiac output, a 20% reduction in mean arterial pressure, and 10% to 15% increase in hematocrit. All three test solutions restored and maintained baseline DO2 within 1 hr. However, hetastarch and hypertonic saline dextran reduced the net fluid volume over 8 hrs by 48% and 74%, respectively, compared with lactated Ringer's solution. Edema in the burn wound was not affected by treatment, while hypertonic saline dextran reduced edema in nonburned skin compared with both lactated Ringer's solution and hypertonic saline dextran. Plasma colloid osmotic pressure was significantly higher in the hetastarch and hypertonic saline dextran groups. A continuous decrease in plasma sodium concentrations from baseline values (140 to 145 mmol/L) was measured in the lactated Ringer's solution and hetastarch groups (130 to 133 mmol/L) over 8 hrs. Plasma sodium concentrations in the group receiving hypertonic saline dextran were increased (150 to 155 mmol/L) at 4 hrs, but returned toward baseline by 8 hrs. CONCLUSIONS: Net volume loading can be reduced markedly by initial resuscitation of large body surface area burn injury using a colloid (hetastarch), and can be further reduced by use of hypertonic saline colloid. Hyponatremia was apparent in the isotonic crystalloid- and colloid-treated animals, but not in those animals treated with hypertonic saline colloid.

Animals↗

Theophylline toxicity.

The adverse effects of theophylline were recognized soon after its introduction into clinical medicine. Reports of major toxic reactions to theophylline, particularly in children, discouraged its use and led to homeopathic dosing recommendations that had little therapeutic effect. Concomitant with the renaissance in theophylline use during the past decade, reports of theophylline toxicity have increased. The epidemiology of theophylline intoxication has changed in recent years, and today most instances of serious toxicity are due to intentional overdosage, as in a suicide attempt. The adverse effects of theophylline involve the gastrointestinal, nervous, cardiovascular, and urinary systems. In addition, significant metabolic derangements are noted in patients with severe intoxication. Treatment of theophylline intoxication involves attention to fluid and electrolyte balance and initiation of measures to remove theophylline from the body (gastric lavage or emesis, repeated charcoal administration by mouth, and charcoal hemoperfusion in serious cases).

Asthma↗

Exercise-associated hyponatremia: role of cytokines.

Exercise-associated hyponatremia (EAH) has emerged in recent years as a life-threatening complication of endurance sports that may lead to fatal cerebral and pulmonary edema. Defined as a serum sodium concentration <135 mEq/L (1 mEq/L = 1 mmol/L), symptomatic EAH is a dilutional hyponatremia with abnormal fluid retention mediated by decreased urine production, which is a variant of the syndrome of inappropriate antidiuretic hormone secretion. Strategies for prevention and treatment must take into account the pathophysiology underlying this dominant clinical paradigm. Beyond educating runners to drink moderately, monitoring changes in body weight during endurance sports may facilitate the early detection of positive fluid balance characteristic of symptomatic cases. Rapid diagnosis by point-of-care testing indicates the need for fluid restriction in mild cases and emergent treatment with hypertonic (3%) NaCl to reverse acute hypotonic encephalopathy. The efficacy of arginine vasopressin V(2) receptor antagonists warrants study as an alternative treatment to loop diuretics for volume overload in these patients. Nonosmotic stimulation of arginine vasopressin secretion may be mediated in part by enhanced release of muscle-derived interleukin-6 during glycogen depletion, linking exertional rhabdomyolysis to the pathogenesis of EAH.

Arginine Vasopressin↗

Race specific altitude effects on blood pressure.

Altitude affects blood pressure (BP) depending on duration and absolute altitude of exposure. Until now changes in BP during exposure to altitude were studied only in Caucasians. It is not known whether BP is affected differently in black and white people in response to altitude. During a 6-day climb on Kilimanjaro, BP was measured in five white and four black people. All participants (mean +/- s.d.: age 31 +/- 8 years, body mass index 22 +/- 2 kg/m2, BP 125 +/- 11/84 +/- 9 mm Hg) had previous similar experience of high-altitude mountaineering. In the base camp (3040 m) systolic BP (SBP) was similar in both groups (131 +/- 9 vs 119 +/- 8 mm Hg). During ascent until 4600 m SBP increased in all whites (6.5 +/- 2.2 mm Hg) and decreased in all blacks (-7.3 +/- 4.6 mm Hg; P = 0.02, blacks vs whites). During descent SBP returned to initial values in whites, whereas it decreased further in blacks. Diastolic BP (DBP) and heart rate remained constant in all participants. During ascent body weight increased in all whites (1.0 +/- 0.8 kg) and decreased in all blacks (-1.9 +/- 1.4 kg; P = 0.02, blacks vs whites) whereas it returned approximately to initial levels during descent: +0.8 +/- 0.4 kg in blacks and -1.0 +/- 1.3 kg in whites (P = 0.03, blacks vs whites). In this study changes in SBP and body weight during exposure to high altitudes varied between whites and blacks. Fluid balance, acclimatisation, physical fitness or genetics could explain these findings.

Adult↗

Hormonal and metabolic changes during a strenuous tennis match. Effect of ageing.

The effect of a strenuous tennis match was studied in 9 young (21.2 +/- 1.9 yr) and 10 veteran women players (46.5 +/- 1.3 yr) of equivalent skill. Each match was carried out during the summer (ambient temperature 27 +/- 1 degree C), as an official competition, under conditions as similar as possible. Heart rate (HR) was monitored throughout the match, weight loss was evaluated and pre- and post-match values of haematocrit, plasma lactate, free fatty acid (FFA), glycemia, ionogram, norepinephrine (NOR), epinephrine, arginine vasopressin (AV) concentrations and plasma renin activity (PRA) were measured. Plasma volume was calculated. While mean HR remained steady in young players, it increased progressively in veteran players as the match went on and reached a very high level towards the end of the match. When post-match values were compared to pre-match values, the mean results were: no substantial changes in plasma lactate and electrolyte concentrations, a large increase in FFA, no increase in epinephrine, a moderate rise in NOR and a large increase in PRA and AV. Despite a similar weight loss, a large drop in plasma volume occurred only in veteran players, who also showed FFA and AV values greater than in young players. During these strenuous matches the large response of hormones which control body fluid probably contributed to the limiting of changes in water and electrolyte balances. However, under similar conditions marked differences occurred as a function of ageing concerning the control of plasma volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

Nutritional assessment and treatment of chronic renal failure.

The experience with chronic renal failure in two institutions, a tertiary care referral hospital with a high prevalence of diabetes mellitus and a Veterans Administration Hospital, was utilized to formulate guidelines for the nutritional assessment and therapy of chronic renal failure. For optimal nutritional support of patients with renal failure, it is important to characterize objectively nutritional deficiencies. Thus, dietary history, anthropometric measurements (weight/height ratio, arm muscle circumference, and triceps skinfold), and serum protein measurements (total protein, albumin, and transferrin, in particular) provide valuable data concerning the nutritional status of the patient. The serum urea nitrogen to serum creatinine ratio and urea nitrogen appearance are useful for selecting optimal protein intake. The serum urea nitrogen/creatinine ratio must be interpreted with respect to the factors which influence it; i.e., the urea clearance and the urea nitrogen appearance. The goal of nutritional therapy is the preservation of body cell mass and function, fluid, electrolyte, and acid-base homeostasis, mineral balances, and with early use of dialysis, the avoidance of uremic toxicity. Nutritional therapy, especially in patients with superimposed illnesses and associated anorexia, may be enhanced by the use of formula feedings, tube feedings, and, if necessary, total parenteral nutrition.

Blood Urea Nitrogen↗

Oral mannitol in control of fluid balance.

Oral mannitol 40 g/m2 was given as 5.5% and 20% solutions to six dialysed children. Both solutions caused diarrhoea. Body weight showed no significant change after the 5.5% solution, which may be used as 'free drink', but fell by 19.8 g/g mannitol after the 20% solution.

Administration, Oral↗

Restoration of fluid balance after exercise-induced dehydration: effects of alcohol consumption.

The effect of alcohol consumption on the restoration of fluid and electrolyte balance after exercise-induced dehydration [2.01 +/- 0.10% (SD) of body mass] was investigated. Drinks containing 0, 1, 2, and 4% alcohol were consumed over 60 min beginning 30 min after the end of exercise; a different beverage was consumed in each of four trials. The volume consumed (2,212 +/- 153 ml) was equivalent to 150% of body mass loss. Peak urine flow rate occurred later (P = 0.024) with the 4% beverage. The total volume of urine produced over the 6 h after rehydration, although not different between trials (P = 0.307), tended to increase as the quantity of alcohol ingested increased. The increase in blood (P = 0.013) and plasma (P = 0.050) volume with rehydration was slower when the 4% beverage was consumed and did not increase to values significantly greater than the dehydrated level (P = 0.013 and P = 0.050 for blood volume and plasma volume, respectively); generally, the increase was an inverse function of the quantity of alcohol consumed. These results suggest that alcohol has a negligible diuretic effect when consumed in dilute solution after a moderate level of hypohydration induced by exercise in the heat. There appears to be no difference in recovery from dehydration whether the rehydration beverage is alcohol free or contains up to 2% alcohol, but drinks containing 4% alcohol tend to delay the recovery process.

Adult↗

Anthrax toxin characterization.

The anthrax toxin comprises three proteins. When they work together, they can kill humans, especially after spores of the bacteria have been inhaled. One anthrax protein, called protective antigen (PA), chaperones the two other toxins into human or animal cells and shields them from the body's immune system. The second, lethal factor (LF), destroys the white blood cells that hosts send in defence. The third toxin molecule, edema factor (EF), hijacks the signaling system in the body. This disrupts the energy balance of cells and leads to them accumulating fluid and complete destroy of cells.

Animals↗