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In order to maintain a constant internal environment, the body has a unique ability to respond to changes that would alter the normal state of homeostasis. A wide range of regulatory processes maintains the fluid, electrolyte, and acid-base balance crucial for normal cellular function. An understanding of these processes allows the nurse to identify problems and anticipate various treatment modalities in certain disease states.
M.T. battled SLE for 9 years before renal failure occurred. She is now free of extrarenal symptoms of lupus, as has been described elsewhere (Ziff & Hilderman, 1983). The patient has regained here appetite, lost 13 pounds, recovered some strength and reestablished her social network. Without the severe proteinuria, M.T. has a chance to improve her nutritional status and increase her albumin. Her pulmonary status may also improve if she can refrain from smoking. Although fatigue is a debilitating feature of lupus, M.T. has increased stamina and is learning energy conservation techniques. Immediately after surgery, she did experience problems with bleeding, pneumonia, and pleural effusions, but the medical and nursing management prevented serious adverse outcomes. Fluid balance is no longer problematic, and M.T. is approaching her ideal body weight as her nutritional status improves. Her serum albumin has increased to about 2.6 gm/dl with some decrease in her proteinuria.
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An automated servo-control system to maintain total body weight constant was used to investigate the role of fluid volume expansion in the development of salt-dependent hypertension in dogs continuously infused with subpressor doses of angiotensin II. Dogs maintained on a fixed salt and water intake were studied in metabolic scale cages, which enabled continuous 24 h/day monitoring of changes in body weight as an index of changes in total body water. Beat-by-beat hemodynamics were determined 24 h/day. Daily fluid and electrolyte balances and hormonal profile were determined. Blood volume was periodically measured by injection of 51Cr red blood cells. After a 3-day control period, salt intake was increased from 8 to 120 meq/day. In contrast to the rise of arterial pressure that was observed in our previous nonservo-controlled volume studies, average 24-h mean arterial pressure, cardiac output, and total peripheral resistance remained unchanged during a 4-day high-salt period. Total body weight was maintained within 7 +/- 17 g of the original weight. Blood volume was unchanged by day 2 as indicated by direct measurement (51Cr red blood cells) or by analysis of plasma protein concentration. There was a retention of 82 +/- 5 meq (P less than 0.05) of sodium on day 1 of high-salt period. Plasma sodium concentration increased approximately 7 meq/l (P less than 0.05) above control levels. Plasma renin activity and aldosterone decreased to undetectable values, whereas vasopressin and atrial natriuretic peptide increased significantly. These results confirm that elevations of blood volume and cardiac output normally observed when salt intake was increased in dogs infused with angiotensin II are secondary to water retention and that this salt-dependent model of hypertension is dependent on fluid volume expansion.
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Four adolescents or young adults with the Prader-Willi syndrome (hypotonia, mental retardation, hypogonadism and obesity) received a protein-sparing modified fast consisting of 1.5 g of meat protein per kilogram of ideal body weight and meeting vitamin, mineral and fluid requirements. Evaluation of nitrogen and energy metabolism revealed the development of starvation ketosis and a positive nitrogen balance. Serial whole-body potassium measurements in two patients confirmed preservation of lean tissue despite continuing loss of weight. Clinical diabetes mellitus in two subjects was rapidly ameliorated by the regimen. Short-term weight loss greater than 18 kg occurred in three of the four subjects, and reduced weight persisted during observation periods of 26 to 44 months. This degree of outpatient diet adherence by mentally deficient subjects, who do not normally experience satiety, suggests that hunger is eliminated or at least reduced by modified, protein-sparing fasting.
Changes in body composition were studied in 13 girls with anorexia nervosa before and during 2 months of refeeding. Fat body mass and fat-free body mass were derived from skin-fold measurements. Total body potassium was measured by whole body counter, and intracellular water was calculated from it. Extracellular water was measured as the bromide space after oral bromide administration. A gradual increase was noted in weight, fat body mass, fat-free body mass, and total body potassium during refeeding. Extracellular water was expanded on admission and increased in all patients in the first weeks of treatment; later it fell to normal. Most of the changes in fat-free body mass over the first weeks of refeeding could be accounted for by an expansion in extracellular water. Particular care must therefore be taken with fluid balance during the first few weeks of refeeding.
Evidence exists of the important role of sodium balance and extracellular fluid volume in the genesis of hypertension in chronic renal failure (CRF). Several studies have shown that patients with advanced CRF have an increased, interstitial and intravascular, extracellular water volume (ECW). The relationship between the increase in ECW and high blood pressure has also been reported. Using electric bioimpedance, body water distribution was studied in 32 patients from our dialysis unit. Twelve of these patients were hypertensive and 20 had normal blood pressure. Hypertensive patients had a significantly greater total body water volume and ECW than the normotensive patients. Given the importance of ECW in controlling blood pressure, one of the main aims of haemodialysis is a suitable extraction of sodium and water during the treatment. Despite technological advances in dialysis therapy, cardiovascular instability during treatment is still a clinical problem. In recent years, new strategies to control ECW, with good haemodynamic tolerance, have been developed. These strategies include haemofiltration, haemodiafiltration and sodium and ultrafiltration profiles.
Ethanol induced negative water balance has been previously inferred from fluid turnover rates upon initial exposure followed by restored normal fluid balance with prolonged exposure. The first two experiments of the present investigation noted hypovolemia and carcass dehydration during the initial few days of forced choice maintenance on 10% ethanol with recovery to near normal levels of intravascular volume and carcass water after 2 months of forced consumption. A third experiment attempted to test whether the alcohol induced dehydration could be corrected with the administration of exogenous ADH.
This study was done to determine how differences in dietary NaCl influence water and electrolyte balance during gestation. Eighteen adult female rats were fed diets containing either 0.12 (low), 1.0 (mid, control), or 3.0% (high) NaCl throughout gestation. On gestation days 1-19, body weight, water and food intakes, urine volume and electrolyte levels were measured. On gestation day 20, amniotic fluid electrolyte levels were determined; litter sizes were assessed 24-hr after birth. Because food intakes were similar throughout gestation, the dams of the three groups ingested different amounts of NaCl. Differences in dietary NaCl were accompanied by large differences in the daily patterns of urine sodium, urine sodium/potassium ratios, water intake, and urine volume. Despite these differences in intake and output, water and electrolyte balance (intake minus output) was the same for the three groups. There were no differences in the dams' body weights, amniotic fluid electrolyte levels, or litter sizes. The long-term consequences of perinatal dietary NaCl for the developing pups are discussed.
UNLABELLED: During acute febrile diseases mild disturbances of water and electrolyte balance occur frequently. It has been suggested that changes in electrolyte balance, in particular hyponatraemia, might predispose a child to convulsions during febrile illness; however, the changes of electrolytes in the CSF are not known. We have studied the effects of fever and convulsions on water and electrolyte balance in CSF and serum by measuring osmolality and electrolyte concentrations in children. The febrile population consisted of 60 children, 36 of whom had seizures during fever. Twenty-one children without convulsions and nine children with epileptic symptoms were nonfebrile controls. We noticed that CSF is subject to changes in osmolality and electrolyte concentration during fever, while convulsions do not exhibit such changes. CSF osmolality and sodium concentrations were lower in febrile children than in nonfebrile controls. The osmolality in febrile children with convulsions was 3.8% (P < 0.01) and without seizures 3.5% (P < 0.01) lower than in nonfebrile nonconvulsive children. The changes in CSF sodium concentration, and to a lesser extent potassium and chloride concentrations, paralleled those of CSF osmolality. A positive correlation was observed between the CSF and serum osmolatities (r = 0.73, P < 0.0001), and sodium concentrations (r = 0.63, P < 0.0001). A negative correlation between the body temperature and both CSF osmolality (r = -0.66, P < 0.0001) and sodium concentration (r = -0.59, P < 0.0001) exhibits also the important regulative role of increased body temperature. CONCLUSION: Fever is an important factor for disturbances in fluid and electrolyte balance. The alterations in CSF osmolality and sodium concentration do not, however, give an unambiguous explanation for the susceptibility to simple febrile seizures.
These experiments were performed to determine the role of fluid volume contraction in the compensatory cardiovascular response to an abrupt neurogenically mediated increase in systemic arterial blood pressure. Acute neurogenic hypertension was produced by selective aortic baroreceptor deafferentation (ABD) in the rat. Salt and water balance, fluid compartment volumes, and arterial pressure were measured before and for 5 days after the induction of hypertension by ABD. In rats with ABD, arterial pressure was increased approximately 30 mmHg 1 day after deafferentation and declined 15-20 mmHg over the next 4 days. Plasma volume and extracellular fluid volume were decreased 5 days after ABD. Urine output did not increase after ABD, and the fluid volume contraction was instead the result of a significant decrease in water intake. Sham-operated rats did not exhibit significant changes in any of these parameters. Sodium balance decreased slightly in both sham-operated and ABD rats postsurgery. These results confirm that fluid volume contraction is a prominent compensatory response to an abrupt rise in arterial pressure, but suggest that this compensation is not necessarily mediated through alterations in renal salt and water excretion.
Body water compartment changes were assessed during postnatal weight loss in 14 infants with respiratory distress syndrome. Total body water and extracellular volume were measured by dilution methods on the first day of life and again between the third and sixth days of life. Extracellular volume changes were calculated between the first and second determinations by measurement of chloride balance. Fluid therapy was prescribed to allow negative net water balance and a 1% to 3% reduction in body weight per day. All infants had concurrent reductions in body weight, total body water, and extracellular volume. Progressive daily extracellular volume reduction concurrent with weight loss was also apparent from chloride balance data. The correlation of changes in body weight with extracellular volume in individual subjects was poor (r = 0.05). We speculate that variations between sodium and free water balance in the sick preterm infant may be responsible for variability in the distribution of postnatal body water losses. Assessment of hydration in the newborn infant should include consideration of sodium balance and alterations of serum osmolality, and changes in body weight.
In order to prevent and correct hypohydration and negative electrolyte balance, the effects of exercises, lower body negative pressure (LBNP) and water-salt supplements (WSS) were investigated in more than 100 test subjects during 14-, 49- and 182-d headdown tilt tests (-4 degrees). A combined use of WSS and LBNP during regular exercises led to a distinct water and sodium retention. These changes were mainly determined by the stimulation of the renin-angiotension-aldosterone and antidiuretic systems. After these countermeasures were tested in simulation studies, they were used by 12 cosmonauts during the 63- and 185-d space flights. The detailed analysis of the postflight examinations of the crewmembers suggests that these countermeasures may exert a beneficial effect on fluid-electrolyte balance.
Ultrafiltration is an extracorporeal technique that employs the principle of convective solute transport across a semipermeable membrane and by which plasma water is removed from blood. Ultrafiltration has been employed in 74 cardiac surgical patients intraoperatively, preoperatively, and postoperatively. In 55 patients with clinical evidence of excess body water, the ultrafilter was employed at the start of cardiopulmonary bypass. The amount of ultrafiltrate removed was 2,914 +/- 1,662 ml (SD), and the fluid balance was -219 +/- 1,298 ml (SD). In 17 patients the ultrafilter was inserted during bypass because of excess reservoir volumes, low hematocrit, or prolonged bypass time. The amount of ultrafiltrate removed was 1,450 +/- 898 ml (SD), and the fluid balance was 1,296 +/- 2,161 ml (SD). One patient with cardiopulmonary failure and nutritional depletion underwent slow continuous ultrafiltration preoperatively along with intravenous alimentation, producing a positive nitrogen balance and improvement in cardiorespiratory failure. One patient underwent slow continuous ultrafiltration for severe, diuretic-resistant congestive heart failure postoperatively. After 9 days of ultrafiltration, there was an 8 kg weight loss, an improvement in congestive heart failure, and a return of the response to diuretics. From this experience my colleagues and I have developed the following indications for ultrafiltration in the cardiac surgical patient: during cardiopulmonary bypass to prevent further fluid accumulation in the patient with clinical evidence of excess body water; during bypass to prevent excess fluid balance in a patient whose bypass time will be greater than 2 hours; during bypass when the pump reservoir volumes are excessive and/or the hematocrit is less than 18%; preoperatively or postoperatively to increase caloric intake in the fluid-overloaded patient; and preoperatively or postoperatively to reverse severe congestive heart failure in the diuretic-resistant patient.
Rates of weight and fat loss in sixteen female and nine male obese patients during calorie restriction (655-789 kcal/day) for up to 120 days were studied by a method for estimating daily changes in body composition. Fat mass is calculated by subtracting daily fluid (calculated from sodium and potassium balances) and protein mass changes from daily weight changes. After the natriuresis of the first 4 days, there was a slower rate of weight loss between days 5 and 28 due largely to a decreasing contribution from fluid and protein losses. No significant change in the rate of weight loss could be shown after the first 28 days. The rate of fat loss did not change significantly from day 5 onwards suggesting no significant change in total energy expenditure during the study period. After 68 days, 93.4% of the weight loss was fat.
The sequential hemodynamics, fluid and electrolyte balances, and the hormonal responses to a 7-day high-salt (NaCl) intake were investigated in sodium-depleted conscious dogs (n = 6). Studies were carried out in metabolic cages mounted on sensitive load cells, which enabled continuous 24 h/day monitoring of total body weight (TBW) as an index of changes in body water. Beat-by-beat hemodynamics were determined 24 h/day. Water (700 ml/day iv) intake was maintained constant. Daily fluid and electrolyte balances and hormonal analyses were performed. An increase of daily salt intake from 8 to 120 meq increased TBW 251 +/- 44 g (P less than 0.05), which was sustained thereafter. Average 24-h mean arterial pressure (MAP) and heart rate (HR) remained unchanged. Average cardiac output (CO) increased 11% (P less than 0.05) above control values by day 2, while total peripheral resistance (TPR) decreased proportionally. CO and TPR returned to control values only when low salt was resumed. Blood volume (BV) was unchanged on day 2 as indicated by direct measurement of BV (51Cr-labeled red blood cells) or by analysis of plasma protein concentration. A 92-meq (P less than 0.05) sodium retention was observed initially, and plasma sodium concentration increased slightly. Plasma renin activity, angiotensin II, and aldosterone levels decreased significantly, whereas vasopressin and atrial natriuretic peptide levels remained unchanged. In summary, chronic high-salt intake resulted in a net retention of water and sodium with no changes in MAP, HR, or BV. The rise in CO was offset by a reduction in TPR, which appeared at least in part related to angiotensin II suppression.