Hypernatremia in Hyperglycemia: Clinical Features and Relationship to Fractional Changes in Body Water and Monovalent Cations during Its Development

In hyperglycemia, the serum sodium concentration ([Na]S) receives influences from (a) the fluid exit from the intracellular compartment and thirst, which cause [Na]S decreases; (b) osmotic diuresis with sums of the urinary sodium plus potassium concentration lower than the baseline euglycemic [Na]S, which results in a [Na]S increase; and (c), in some cases, gains or losses of fluid, sodium, and potassium through the gastrointestinal tract, the respiratory tract, and the skin. Hyperglycemic patients with hypernatremia have large deficits of body water and usually hypovolemia and develop severe clinical manifestations and significant mortality. To assist with the correction of both the severe dehydration and the hypovolemia, we developed formulas computing the fractional losses of the body water and monovalent cations in hyperglycemia. The formulas estimate varying losses between patients with the same serum glucose concentration ([Glu]S) and [Na]S but with different sums of monovalent cation concentrations in the lost fluids. Among subjects with the same [Glu]S and [Na]S, those with higher monovalent cation concentrations in the fluids lost have higher fractional losses of body water. The sum of the monovalent cation concentrations in the lost fluids should be considered when computing the volume and composition of the fluid replacement for hyperglycemic syndromes.

The role of intra- and interdialytic sodium balance and restriction in dialysis therapies

The relationship between sodium, blood pressure and extracellular volume could not be more pronounced or complex than in a dialysis patient. We review the patients' sources of sodium exposure in the form of dietary salt intake, medication administration, and the dialysis treatment itself. In addition, the roles dialysis modalities, hemodialysis types, and dialysis fluid sodium concentration have on blood pressure, intradialytic symptoms, and interdialytic weight gain affect patient outcomes are discussed. We review whether sodium restriction (reduced salt intake), alteration in dialysis fluid sodium concentration and the different dialysis types have any impact on blood pressure, intradialytic symptoms, and interdialytic weight gain.

Pseudohyponatremia: Mechanism, Diagnosis, Clinical Associations and Management

Pseudohyponatremia remains a problem for clinical laboratories. In this study, we analyzed the mechanisms, diagnosis, clinical consequences, and conditions associated with pseudohyponatremia, and future developments for its elimination. The two methods involved assess the serum sodium concentration ([Na]_S) using sodium ion-specific electrodes: (a) a direct ion-specific electrode (ISE), and (b) an indirect ISE. A direct ISE does not require dilution of a sample prior to its measurement, whereas an indirect ISE needs pre-measurement sample dilution. [Na]_S measurements using an indirect ISE are influenced by abnormal concentrations of serum proteins or lipids. Pseudohyponatremia occurs when the [Na]_S is measured with an indirect ISE and the serum solid content concentrations are elevated, resulting in reciprocal depressions in serum water and [Na]_S values. Pseudonormonatremia or pseudohypernatremia are encountered in hypoproteinemic patients who have a decreased plasma solids content. Three mechanisms are responsible for pseudohyponatremia: (a) a reduction in the [Na]_S due to lower serum water and sodium concentrations, the electrolyte exclusion effect; (b) an increase in the measured sample's water concentration post-dilution to a greater extent when compared to normal serum, lowering the [Na] in this sample; (c) when serum hyperviscosity reduces serum delivery to the device that apportions serum and diluent. Patients with pseudohyponatremia and a normal [Na]_S do not develop water movement across cell membranes and clinical manifestations of hypotonic hyponatremia. Pseudohyponatremia does not require treatment to address the [Na]_S, making any inadvertent correction treatment potentially detrimental.

Hypertonic Saline Infusion for Hyponatremia: Limitations of the Adrogué-Madias and Other Formulas

Hypertonic saline infusion is used to correct hyponatremia with severe symptoms. The selection of the volume of infused hypertonic saline ( VInf ) should address prevention of overcorrection or undercorrection. Several formulas computing this VInf have been proposed. The limitations common to these formulas consist of (1) failure to include potential determinants of change in serum sodium concentration ([ Na ]) including exchanges between osmotically active and inactive sodium compartments, changes in hydrogen binding of body water to hydrophilic compounds, and genetic influences and (2) inaccurate estimates of baseline body water entered in any formula and of gains or losses of water, sodium, and potassium during treatment entered in formulas that account for such gains or losses. In addition, computing VInf from the Adrogué-Madias formula by a calculation assuming a linear relation between VInf and increase in [ Na ] is a source of errors because the relation between these two variables was proven to be curvilinear. However, these errors were shown to be negligible by a comparison of estimates of VInf by the Adrogué-Madias formula and by a formula using the same determinants of the change in [ Na ] and the curvilinear relation between this change and VInf . Regardless of the method used to correct hyponatremia, monitoring [ Na ] and changes in external balances of water, sodium, and potassium during treatment remain imperative.

Using herbs medically without knowing their composition: are we playing Russian roulette?

Herbal medicine, a form of complementary and alternative medicine (CAM), is used throughout the world, in both developing and developed countries. The ingredients in herbal medicines are not standardized by any regulatory agency. Variability exists in the ingredients as well as in their concentrations. Plant products may become contaminated with bacteria and fungi during storage. Therefore, harm can occur to the kidney, liver, and blood components after ingestion. We encourage scientific studies to identify the active ingredients in herbs and to standardize their concentrations in all herbal preparations. Rigorous studies need to be performed in order to understand the effect of herbal ingredients on different organ systems as well as these substances' interaction with other medications.

Edelman Revisited: Concepts, Achievements, and Challenges

The key message from the 1958 Edelman study states that combinations of external gains or losses of sodium, potassium and water leading to an increase of the fraction (total body sodium plus total body potassium) over total body water will raise the serum sodium concentration ([Na]_S), while external gains or losses leading to a decrease in this fraction will lower [Na]_S. A variety of studies have supported this concept and current quantitative methods for correcting dysnatremias, including formulas calculating the volume of saline needed for a change in [Na]_S are based on it. Not accounting for external losses of sodium, potassium and water during treatment and faulty values for body water inserted in the formulas predicting the change in [Na]_S affect the accuracy of these formulas. Newly described factors potentially affecting the change in [Na]_S during treatment of dysnatremias include the following: (a) exchanges during development or correction of dysnatremias between osmotically inactive sodium stored in tissues and osmotically active sodium in solution in body fluids; (b) chemical binding of part of body water to macromolecules which would decrease the amount of body water available for osmotic exchanges; and (c) genetic influences on the determination of sodium concentration in body fluids. The effects of these newer developments on the methods of treatment of dysnatremias are not well-established and will need extensive studying. Currently, monitoring of serum sodium concentration remains a critical step during treatment of dysnatremias.

Dysnatremias in Chronic Kidney Disease: Pathophysiology, Manifestations, and Treatment

The decreased ability of the kidney to regulate water and monovalent cation excretion predisposes patients with chronic kidney disease (CKD) to dysnatremias. In this report, we describe the clinical associations and methods of management of dysnatremias in this patient population by reviewing publications on hyponatremia and hypernatremia in patients with CKD not on dialysis, and those on maintenance hemodialysis or peritoneal dialysis. The prevalence of both hyponatremia and hypernatremia has been reported to be higher in patients with CKD than in the general population. Certain features of the studies analyzed, such as variation in the cut-off values of serum sodium concentration ([Na]) that define hyponatremia or hypernatremia, create comparison difficulties. Dysnatremias in patients with CKD are associated with adverse clinical conditions and mortality. Currently, investigation and treatment of dysnatremias in patients with CKD should follow clinical judgment and the guidelines for the general population. Whether azotemia allows different rates of correction of [Na] in patients with hyponatremic CKD and the methodology and outcomes of treatment of dysnatremias by renal replacement methods require further investigation. In conclusion, dysnatremias occur frequently and are associated with various comorbidities and mortality in patients with CKD. Knowledge gaps in their treatment and prevention call for further studies.

Development of Lupus Erythematosus Tumidus During the Course of Systemic Sclerosis

A man with systemic sclerosis (SS), manifested by characteristic skin lesions, gastro-esophageal reflux disease, and pulmonary fibrosis producing progressive respiratory failure, and a positive antinuclear antibody consistent with reactivity to fibrillarin, developed skin lesions with the clinical and histological characteristics of lupus erythematosus tumidus (LET) 10 years after the diagnosis of SS. His respiratory failure progressed and he expired from sepsis after tracheal intubation and mechanical ventilation two years after developing LET. The association of SS and LET, not described until now, raises questions about its pathogenesis and its prognostic significance.

A four-stream method for providing variable dialysis fluid bicarbonate concentrations for bicarbonate-based dialysis fluid delivery systems

BACKGROUND

Hemodialysis corrects metabolic acidosis by transferring bicarbonate or bicarbonate equivalents across the dialysis membrane from the dialysis fluid to the plasma. With the conventional three-stream bicarbonate-based dialysis fluid delivery system, a change in the bicarbonate concentration results in changes in the other electrolytes. In practice, the dialysis machine draws either a little less or more from the bicarbonate concentrate and a little more or less from the acid concentrate, respectively in a three-stream delivery system. The result not only changes the bicarbonate concentration of the final dialysis fluid but also causes a minor change in the other ingredients.

METHODS

We propose a four-stream bicarbonate-based dialysis fluid delivery system consisting of an acid concentrate, a base concentrate, a product water, and a new sodium chloride concentrate.

RESULTS

By adjusting the flow rate ratio between the sodium chloride and sodium bicarbonate concentrates, one can achieve the desired bicarbonate concentration in the dialysis fluid without changing the concentration of sodium or ingredients in the acid concentrate. The chloride concentration mirrors the change in bicarbonate but in the opposite direction.

CONCLUSION

A four-stream, bicarbonate-based dialysis fluid delivery system allows the bicarbonate concentration to be changed without changing the other constituents of the final dialysis fluid.

A new approach to individualize dialysis fluid sodium concentration using a four-stream, bicarbonate-based fluid delivery system

We propose a new 45X, four-stream, triple-concentrate, bicarbonate-based dialysis fluid delivery system, allowing a wide range of dialysis fluid sodium concentrations\\ (DF_Na ) without affecting the concentrations of other crucial solutes. The four streams consist of product water (W), and concentrates with sodium chloride (S), acid (A), and sodium bicarbonate (B). An adjustment in the DF_Na in this new system requires changes only in the W and S concentrate streams. The ingredients in A and B concentrates do not change.

Blood pressure control and kidney damage in hypertension: Results of a three-center cross-sectional study in North Central Nigeria

Background

Hypertension is one of the commonest cause of chronic kidney disease (CKD) in Nigerians. We describe blood pressure (BP) control and kidney disease markers in patients with hypertension as part of measures to curb the burden of this chronic debilitating disease.

Methods

Patients with hypertension in the main tertiary hospitals in three states in north central Nigeria were evaluated for indicators of CKD, including proteinuria and estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m². Patients had their early morning first void urine tested for proteinuria using Combi-10 test strips. eGFR was estimated using the MDRD equation.

Results

A total of 1063 subjects (63.1% females and 36.8% males) with a mean age of 55 ± 11 years were studied. Diabetes mellitus (DM) was present in 214 (20.6%) and 422 (39.7%) had optimal BP control. The median duration of hypertension was 6 years (range 1-44 years). Proteinuria occurred in 130 (12.2%), while 212 (19.9%) had reduced eGFR and 46 (4.3%) had proteinuria and reduced eGFR. The use of calcium channel blockers [adjusted odds ratio (AOR): 0.70, 95% Confidence Interval (CI) 0.50-0.99] and the use of more than two antihypertensive medications (AOR: 0.62, 95% CI 0.40-0.96) were associated with reduced odds of optimal BP control. Male sex (AOR: 1.75, 95% CI 1.14-2.70) and the use of renin-angiotensin-aldosterone system blocking medications (AOR: 2.07, 95% CI 1.18-3.64) were independently associated with proteinuria while DM (AOR: 1.69, 95% CI 1.06-2.55) and treatment with more than two medications (AOR: 1.86, 95% CI 1.09-3.17) were more likely to have reduced eGFR.

Conclusion

A large proportion of hypertensive patients in north-central Nigeria have poorly controlled BP. Kidney damage is common among these patients.

The Corrected Serum Sodium Concentration in Hyperglycemic Crises: Computation and Clinical Applications

In hyperglycemia, hypertonicity results from solute (glucose) gain and loss of water in excess of sodium plus potassium through osmotic diuresis. Patients with stage 5 chronic kidney disease (CKD) and hyperglycemia have minimal or no osmotic diuresis; patients with preserved renal function and diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS) have often large osmotic diuresis. Hypertonicity from glucose gain is reversed with normalization of serum glucose ([Glu]); hypertonicity due to osmotic diuresis requires infusion of hypotonic solutions. Prediction of the serum sodium after [Glu] normalization (the corrected [Na]) estimates the part of hypertonicity caused by osmotic diuresis. Theoretical methods calculating the corrected [Na] and clinical reports allowing its calculation were reviewed. Corrected [Na] was computed separately in reports of DKA, HHS and hyperglycemia in CKD stage 5. The theoretical prediction of [Na] increase by 1.6 mmol/L per 5.6 mmol/L decrease in [Glu] in most clinical settings, except in extreme hyperglycemia or profound hypervolemia, was supported by studies of hyperglycemia in CKD stage 5 treated only with insulin. Mean corrected [Na] was 139.0 mmol/L in 772 hyperglycemic episodes in CKD stage 5 patients. In patients with preserved renal function, mean corrected [Na] was within the eunatremic range (141.1 mmol/L) in 7,812 DKA cases, and in the range of severe hypernatremia (160.8 mmol/L) in 755 cases of HHS. However, in DKA corrected [Na] was in the hypernatremic range in several reports and rose during treatment with adverse neurological consequences in other reports. The corrected [Na], computed as [Na] increase by 1.6 mmol/L per 5.6 mmol/L decrease in [Glu], provides a reasonable estimate of the degree of hypertonicity due to losses of hypotonic fluids through osmotic diuresis at presentation of DKH or HHS and should guide the tonicity of replacement solutions. However, the corrected [Na] may change during treatment because of ongoing fluid losses and should be monitored during treatment.

Relationship between dietary sodium and sugar intake: A cross-sectional study of the National Health and Nutrition Examination Survey 2001-2016

Dietary sodium intake and cardiovascular outcomes have a reported J-shaped curve relationship. This study analyzes the relationship between dietary sodium and sugar intake as a potential mechanism to explain this association. The authors examined cross-sectional data from the National Health and Nutrition Examination Survey (NHANES) 2001-2016 where dietary sodium, carbohydrate, fat, cholesterol, and sugar intakes were assessed by 24-hour dietary recall and were standardized to a total daily intake of 2000 calories. Sodium intake was categorized into sodium quintiles (SQ) as follows: SQ1(0.06-2.6 g/d); SQ2(2.6-3.0 g/d); SQ3(3.0-3.4 g/d); SQ4(3.4-4.0 g/d); and SQ5(4.0-29.3 g/d). Simple and multivariate linear regression using SQ3 as reference were used to assess associations between daily sodium intake and the other nutrients. Our results showed that among 38 722 participants that met our study criteria, the mean age was 43.6 years (SD 16.8 years) and sex was equally distributed (48.8% male vs 51.2% female). Sugar intake went down across increasing SQs and was significantly higher in SQ1 (141.2 g/d) and SQ2 (118.6 g/d) and significantly lower in SQ4 (97.9 g/d) and SQ5 (85.6 g/d) compared to SQ3 (108.6 g/d; all P < .01). These same trends remained unchanged and significant in the fully adjusted multivariate model. In conclusion, NHANES study participants reporting low sodium intake on 24-hour dietary recall have a higher consumption of sugar. The negative impact of low sodium diet on cardiovascular health may be explained at least partially by the associated high sugar intake.

Management of extracellular volume in patients with end-stage kidney disease and severe hyperglycemia

This commentary addresses volume replacement in hyperglycemic crises in patients with end-stage kidney disease (ESKD). The management of volume issues in this group of patients should not be based on guidelines for management of hyperglycemic crises, but should be individualized and based on directed patient medical history, physical examination, and imaging of the heart and lungs. A scheme for combining information from these three sources is provided.

Continuous Peritoneal Dialysis in Heavyweight Individuals: Urea and Creatinine Clearances

Objective

To study whether or not continuous peritoneal dialysis (CPD) can provide acceptable levels of normalized urea and creatinine clearance in heavyweight individuals.

Design

Retrospective analysis of urea and creatinine clearance studies.

Setting

CPD patients followed in four dialysis units in Albuquerque, two dialysis units in Thessaloniki, and two dialysis units in Athens.

Participants

One hundred and ninety-nine patients on CPD with 266 clearance determinations between 1991 and 1995.

Interventions

The heavyweight group consisted of 22 patients (24 clearance studies) weighing 100 kg or more (109.0±8.7 kg) at the time of the clearance study. All subjects were obese. The reference group consisted of 177 CPD subjects (242 clearance studies)ofnormal weight (68.7±12.2 kg). Urea fractional clearance (KT/V) and normalized creatinine clearance (Ccr) were compared between the heavyweight and the reference groups.

Main Outcome Measures

The lowest acceptable weekly levels were set at 1.70 for KT/V and 54.4 L/1. 73 m2 for Ccr.

Results

Weekly KT/V was 1.75±0.41 in the heavyweight group and 1.94±0.52 in the reference group (p = 0.047). Corresponding weekly Ccr levels were 64.0±24.3 and 77.6±40.3 L/1.73 m2, respectively (p = 0.021). In the heavyweight group, 13 studies (54.2%) had acceptable KT/V values compared to 160 studies (66.1 %) in the reference group (NS). Corresponding values for acceptable Ccr were 17 (70.8%) and 165 (68.2%), respectively (NS). Drain volume was 12.96±4.40 L/24 hours in the heavyweight group and 9.63±2.58 L/24 hours in the reference group (p = 0.001). High daily exchange volume was delivered by a combination of daily continuous ambulatory peritoneal dialysis (CAPD) and nocturnal automated peritoneal dialysis (APD) in 13116 heavyweight studies. This combination was tolerated better than any other method of delivering a large daily exchange volume.

Conclusion

Although normalized urea and creatinine clearances are lower in obese, heavyweight individuals than in lean CPD subjects with lower weight, approximately equal percentages of these two groups achieve acceptable clearance levels. However, heavyweight individuals require larger-than-usual daily exchange volumes. The preferred way to deliver these large dialysate volumes is a combination of daily CAPD and nocturnal APD.

Normalization of Clearances in Peritoneal Dialysis Using a Formula for Body Water Derived from an End-Stage Renal Disease Population

Objective

To compare body water (V) estimates from the Chertow formula (VC), which was derived in an end-stage renal disease population, to V estimates from the Watson formulas (VW) in continuous ambulatory peritoneal dialysis (CAPD) patients. To identify CAPD patients in whom VC is preferred to VW for clearance studies.

Design

Retrospective analysis of clearance studies.

Setting

Dialysis units of four academic medical centers.

Participants

302 subjects on CAPD.

Intervention

613 clearance studies by standard methods.

Main Outcome Measures

Comparisons between VC and VW, and between urea clearance normalized by VC [(Kt/VC)ur] and VW [(Kt/VW)ur].

Results

VC exceeded VW by 3.5 ± 1.6 L ( p < 0.001), or 9.6% on average. This degree of overestimation of VW is in the range of body water estimates found in CAPD subjects with severe volume overload (> 5% of body weight) in previous studies. Total (Kt/VW)ur exceeded total (Kt/VC)ur by 8.6%. By linear regression, VC = –0.589 + (1.112 x VW), r = 0.983. VW exceeded VC in only 12 studies. Young age, short height, low body weight, and low prevalence of diabetes characterized the studies with VW > VC. Total (Kt/VW)ur was adequate (≥ 2.0 weekly) in 276 studies. Among these, 74 studies had inadequate total (Kt/VC)ur (< 2.0 weekly). By logistic regression, the predictors of inadequate (Kt/VC)ur, when (Kt/VW)ur was adequate, included the presence of diabetes, great height, and long duration of CAPD.

Conclusions

VC provides estimates of body water exceeding those provided by VW in a great majority of CAPD patients. Consequently, approximately 25% of the clearance studies that are adequate when VW is used as the normalizing parameter may be inadequate when VC is used. VC may provide a more appropriate estimate of body water than VW in CAPD patients with volume overload.

Dialysis Dose Required for a Minimal Acceptable Level

Objectives

To identify the most advantageous formula for estimating creatinine clearance (CCr) and to establish a dose of dialysis that will ensure minimal acceptable levels of creatinine clearance in patients on continuous peritoneal dialysis (CPD).

Design

Analysis of all CCr studies performed in CPD patients over 40 months.

Setting

All four dialysis units following CPD patients in one city. One dialysis unit is government-owned, one is university-affiliated, and two are community-based.

Participants

One hundred and ninety-four patients representing almost the entire CPD population in Albuquerque.

Interventions

Creatinine and urea clearance studies were performed in 24-hour urine and drained dialysate samples. Creatinine clearance (peritoneal plus urinary) was normalized to either 1.73 m2 body surface area (CCr) or body water estimated by the Watson formulas (KT/V Cr). CCr and KT/Vcr were either corrected by averaging urinary creatinine and urea clearances or were not corrected. Two dialysis units were designated as the training set (92 patients, 143 clearance studies) and the other two units as the validation set (102 patients, 181 clearance studies).

Main Outcome Measures

Minimal acceptable creatinine clearance levels were determined in the training set by computing the creatinine clearance value corresponding to 1.70 weekly KTN urea by linear regression. Logistic regression models predicting low creatinine clearance were developed in the training set and were tested in the validation set.

Results

The following weekly creatinine clearance values corresponded to 1.70 KTN urea: corrected CCr 52.0 L/1. 73 m2, uncorrected CCr 54.4 L/1.73 m2, corrected KT/Vcr 1.46, uncorrected KT/Vcr 1.53. Logistic regression identified as predictors of low creatinine clearance low daily urine volume (UV) and low daily dialysate drain volume/body water (DV/V) for all four creatinine clearance formulas, plus low/low-average peritoneal solute transport (only for uncorrected CCr) and serum creatinine (for both KT/Vcr formulas). In the validation set, the predictive models produced an area under the receiver operating characteristic (ROC) curve between 0.835 and 0.919 indicating very good predictive accuracy. For corrected CCr and anuria, the regression model produced a minimal normalized drain volume (DV/V) value consistent with minimal acceptable CCr equal to 0.305 L/L per 24 hours. This DV/V cutoff detected low corrected CCr in validation set anuric subjects (n = 55) with a sensitivity of 85% and a specificity of 71 %. For uncorrected CCr and anuria, DV/V cutoffs were 0.273 L/L per 24 hours (high/ high-average peritoneal solute transport) and 0.420 L/L per 24 hours (low/low-average transport). Sensitivity and specificity of these cutoffs in validation set anuric subjects were 87% and 85%, plus 86% and 33%, respectively.

Conclusions

The uncorrected CCr appears to be the most advantageous creatinine clearance formula in CPD, because it allows the use of peritoneal solute transport type in the calculation of the minimal required normalized drain volume. The minimal acceptable uncorrected CCr is 54.4 L/1. 73 m2weekly. To achieve this uncorrected CCr in anuria, the required minimal normalized drain volume is 0.273 L per liter of body water daily if peritoneal solute transport is high or high-average and around 0.420 L per liter of body water daily if peritoneal solute transport is low or low-average. The required total daily drain volume is computed by multiplying the required normalized drain volume by body water.

Effect of Preventing Staphylococcus Aureus Carriage on Rates of Peritoneal Catheter-Related Staphylococcal Infections. Literature Synthesis

Objective

To determine whether specific preventive measures reduce the rate of peritoneal catheter-related infections and peritoneal catheter loss due to Staphylococcus aureus.

Design

Structured literature synthesis.

Methods

Relevant studies were identified by medline search, from personal files, and from the reference lists of retrieved articles. We analyzed English-language studies on treatment targeted at S. aureus, with at least 10 subjects and at least 3 months of follow-up, and data on staphylococcal peritoneal dialysis catheter infections. We excluded noncontrolled studies. Two investigators abstracted data using a structured form.

Results

W e evaluated six studies with concurrent controls and eight studies with historical controls. In one randomized, placebo-controlled, blinded study, periodic nasal mupirocin ointment reduced the rate of staphylococcal exit-site infection from 0.42 to 0.12 episodes/patient-year ( p = 0.006), but had no effect on the rates of staphylococcal tunnel infection, peritonitis, or catheter loss. In one randomized study without placebo control, periodic oral rifampin reduced the rate of staphylococcal exit-site infection from 0.65 to 0.22 epi/pt-yr ( p = 0.011), but had no effect on the rate of staphylococcal peritonitis. In another nonblinded, randomized, controlled study, the use of either rifampin or mupirocin was associated with low rates of staphylococcal catheter infections and catheter loss. In one study with historical controls, the rate of staphylococcal exit-site infection and peritonitis was lower after oral rifampin prophylaxis. In seven other studies comparing nasal or exit-site mupirocin to historical controls, the rate of staphylococcal exit-site infection decreased from 0.17 to 0.05 epi/pt-yr, the rate of staphylococcal peritonitis decreased from 0.18 to 0.06 epi/pt-yr, and the rate of catheter loss decreased from 0.09 to 0.05 epi/pt-yr during the mupirocin period.

Conclusion

The literature provides strong evidence that staphylococcal carriage prophylaxis using either oral rifampin or mupirocin ointment in the nares or exit site reduces significantly the rate of exit-site infection due to Staphylococcus aureus. Weaker evidence based on studies with historical controls suggests that rifampin or mupirocin prophylaxis also reduces the rate of staphylococcal peritonitis and peritoneal catheter loss. Studies with a stronger level of evidence are needed to verify this last point.

In Search of the Ideal V

The ideal normalization parameter for urea and creatinine clearance is not yet known. The best current practices are to normalize urea clearance by anthropometric V, corrected for certain conditions such as edema, and creatinine clearance by BSA. Normalization parameters should be calculated using the actual weight. In addition, the ideal weight also should be used in underweight individuals.

Mechanical Cardiopulmonary Resuscitation Choice of Patients on Chronic Peritoneal Dialysis

Fifty-five adult patients (5 women, 50 men) on chronic peritoneal dialysis, mostly continuous ambulatory peritoneal dialysis (CAPD), for 2 to 155 mon were asked whether or not they wanted to have mechanical cardiopulmonary resuscitation (CPR) in case of sudden death. Thirty-five patients (65%) opted for CPR and 20 (36%) declined. Statistically, sex (although the number of women interviewed was too small for a valid sample) and duration of dialysis had no effect on choice of CPR, whereas older age, the presence of diabetes, advanced medical disability, and advanced socioeconomic disability were associated with a tendency to decline CPR. Among the 10 patients who had CPR, 5 developed flail chest, 4 had multiple rib fractures, and only 1 had no chest wall trauma from CPR. Two patients left the hospital alive. One third of the patients on chronic peritoneal dialysis do not want CPR. Advanced age, diabetes, and poor medical and socioeconomic states predispose peritoneal dialysis patients to decline CPR.

A Population-Specific Formula Predicting Creatinine Excretion in Continuous Peritoneal Dialysis

Objective

The Cockroft–Gault formula was shown to systematically overestimate the decline in creatinine excretion with age in continuous peritoneal dialysis (CPD) patients and is, therefore, not suitable for studying creatinine excretion. The purpose of the present study was to develop and test a population-specific formula predicting average creatinine excretion in CPD.

Methods

Creatinine excretion in urine plus dialysate was measured in 925 CPD patients. Forty patients were excluded because of evidence of noncompliance. The remaining 885 subjects were randomly grouped into a derivation group ( n = 432) and a validation group ( n = 453). Stepwise multiple linear regression models were used to predict creatinine excretion in the derivation group. The candidate variables, chosen because they were previously shown to be predictors of creatinine excretion in CPD, included weight (W), age (A), gender (G), diabetes (D), and interaction terms between these four variables. Estimates of creatinine excretion from the best-fit regression formula (CrExcr1) and from the Cockroft–Gault formula (CrExcr2) were compared to creatinine excretion (CrExcr) in the validation group.

Results

The best-fit regression model in the derivation group included all four candidate variables (W, A, G, D), but no interaction terms. This model was as follows: CrExcr1 = 302.150 – 4.380A + 171.234G – 39.041D + 11.730W ( r 2 = 0.477, p < 0.001). In the validation set, CrExcr = –15.795 + 0.988CrExcr1 ( r2 = 0.447, p < 0.001), and CrExcr = –303.823 + 0.732CrExcr2 ( r2 = 0.340, p < 0.001). When the differences between measured and predicted creatinine excretion did not take into account the sign of each individual difference, CrExcr – CrExcr1 = 201 ± 156 mg/24 hours, and CrExcr – CrExcr2 = 235 ± 174 mg/24 hr ( p < 0.001) in the validation group. When the sign of the difference was taken into account, CrExcr – CrExcr1 = –28 ± 149 mg/24 hr, and CrExcr – CrExcr2 = 63 ± 295 mg/24 hr ( p < 0.001).

Conclusions

A population-specific formula predicting creatinine excretion in CPD was derived. This formula has greater accuracy than the Cockroft–Gault formula and can be used in studies of creatinine excretion in CPD.

Volume of Distribution and Fractional Clearance of Urea in Amputees on Continuous Ambulatory Peritoneal Dialysis

Objectives

To demonstrate the effects of amputation on the estimates of urea volume of distribution (V) and KTN urea in continuous ambulatory peritoneal dialysis (CAPD) patients and to present a method for correcting the errors created by the uncorrected anthropometric formulas estimating V.

Design

(1) A mathematical analysis of the error and the correction proposed was performed. (2) Urea kinetic modeling with uncorrected and corrected estimates utilizing both the Watson and the Hume anthropometric formulas was performed in amputees on CAPD.

Setting

Subjects were recruited from four dialysis units in one city: one Veterans Affairs unit, one university-affiliated unit, and two community units.

Patients

Fourteen amputees on CAPD: 12 with unilateralleg amputation and 2 with bilateral leg amputation, at the same length of the leg, were studied.

Interventions

Urea kinetic studies were performed in 24-hour drained dialysate and urine specimens.

Main Outcome Measures

Uncorrected and corrected estimates of V and KTN urea were compared to each other and to the predictions of the mathematical model. Body weights corresponding to uncorrected and correct ed V estimates were compared to the actual body weights.

Results

(1) The mathematical model predicts that uncorrected estimates by the anthropometric formulas will falsely characterize unilateral amputees as leaner than they are and bilateral amputees as more obese than they are. (2) In unilateral amputees studied with the Watson formulas, uncorrected V was 0.546±0.023 L/kg and corrected V was 0.520±0.023 L/kg (p < 0.001). Corresponding weekly KTN urea values were 1.97±0.14 and 2.07±0.14, respectively (p < 0.001). Similar results were obtained with the Humeformulas. In bilateral leg amputees studied with the Watson formulas, uncorrected V was 0.479±0.022 L/kg and corrected V was 0.514±0.023 L/kg. Corresponding KT N estimates were 2.11 ±0.45 and 1.96±0. 14, respectively. The differences were even greater with the Hume formulas. Estimates of body weight calculated from corrected V values were equal to actual weight measurements, whereas those calculated from uncorrected V values were lower than actual body weight measurements in unilateral amputees, and much higher than actual body weight measurements in bilateral amputees.

Conclusion

Uncorrected anthropometric estimates falsely characterize unilateral amputees as leaner than they actually are and bilateral amputees, amputated at the same leg length, as more obese than they actually are. Uncorrected KTN estimates are, therefore, falsely low in unilateral amputees, and falsely high in bilateral amputees. The proposed correction of the anthropometric formulas provides estimates agreeing closely with dietary estimates of body composition. Further studies are needed to define the accuracy of the corrected formulas.

Fractional Urea Clearance Estimates Using Two Anthropometric Formulas in Continuous Peritoneal Dialysis: Sex, Height, and Body Composition Differences

Objective

To compare estimates of urea volume (V) and KT/V obtained by the Watson and Hume anthropometric formulas, and to identify the similarities and differences between these estimates.

Design

Theoretical analysis applying wide variations in the determinants of anthropometric V (age, height, weight) in hypothetical women and men. Analysis of urea kinetic studies performed in patients on continuous peritoneal dialysis (CPD).

Setting

Four dialysis units in Albuquerque, two in Athens, and two in Thessaloniki.

Participants

Three hundred and two CPD patients who had 440 urea kinetic studies.

Intervention

Standard urea clearance was performed by 24-hour collections of urine and drained dialysate followed by blood sampling. V was estimated by both the Watson and Hume formulas.

Main Outcome Measures

Estimates of V and KT/V were compared separately in women and men by Student's t-test, linear regression, and limits of agreement (mean difference±2 SD). The agreement of the KT/V estimates was also tested by the kappa ratio using a value of 1.70 weekly as the lowest acceptable KT/V.

Results

The theoretical analysis indicated important disagreement only in extreme variations from the ordinary in height and, to a lesser extent, weight. Differences due to height variation were pronounced only in hypothetical women. CPD patient findings were as follows: in women, Watson V and weekly KT/V were 30.4±4.4 L and 2.10±0.61, respectively. Corresponding Hume estimates were 30.3±5.4 L and 2.12±0.66, respectively. Corresponding estimates for men were 40.5±5.7 L and 1.92±0.57 (Watson) plus 41.4±5.6 L and 1.88±0.57 (Hume), respectively. By linear regression, KT/VHume = -0.083 + 1.052 (KT/Vw8tson), r = 0.961 (women); and KT/VHume = -0.026 + 0.992 (KT/Vwatson), r = 0.985 (men). Limits of agreement were -1.41 L and 2.10 L for V, and -0.15 and 0.14 weekly for KT/V. In 94.3% of the cases, KT/Vw8tson and KT/VHume agreed (both >1.70 or both <1.70 weekly). Kappa ratio was 0.875 (excellent agreement). The concordant and discordant groups differed in height and degree of obesity, in agreement with the theoretical analysis.

Conclusion

The Watson and Hume formulas provide similar estimates of V and KT/V in CPD patients. Differences may be noted only if women's height or, to a lesser extent, both sexes’ weight is at a great variance with the ordinary values.

Nutrition Indices in Obese Continuous Peritoneal Dialysis Patients with Inadequate and Adequate Urea Clearance

♦ Objective

To test whether better nutrition is associated more with adequate urea clearance than with inadequate urea clearance in obese patients on continuous peritoneal dialysis (CPD).

♦ Design

Retrospective analysis of clearance and nutrition indices in obese CPD patients. Only obese patients were analyzed. Obesity was defined as a ratio of actual weight to desired weight (W/DW) ≥ 1.2. The dose of dialysis was considered adequate at weekly Kt/V urea ≥ 2.0. Small solute clearances and nutrition indices were compared between patients with weekly Kt/V urea < 2.0 and patients with weekly Kt/V urea ≥ 2.0 at the first clearance study.

♦ Setting

Four university-affiliated and two private dialysis units in Canada and the United States.

♦ Patients

A total of 270 CPD patients with W/DW ≥ 1.2 at the first clearance study.

♦ Results

Among the 270 obese CPD patients, 157 (58.1%) were underdialyzed (weekly Kt/V urea 1.66 ± 0.22) and 113 (41.9%) had adequate dialysis (weekly Kt/V urea 2.51 ± 0.47) at the first clearance study. Creatinine clearance values also differed between the underdialyzed and adequately dialyzed obese groups (55.6 ± 15.2 vs 87.6 ± 29.8 L/1.73 m2 weekly, respectively, p < 0.001). The underdialyzed group contained fewer women (39.5% vs 60.2%, p < 0.001) and more patients with anuria (35.0% vs 8.8%, p < 0.001), and had higher serum urea (20.7 ± 6.9 vs 18.2 ± 5.3 mmol/L, p = 0.001) and serum creatinine (974 ± 283 vs 734 ± 275 μmol/L, p < 0.001), marginally lower serum albumin (35.8 ± 5.2 vs 37.2 ± 6.4 g/L, p = 0.082), lower urea nitrogen excretion (5778 ± 2290 vs 7085 ± 2238 mg/24 hr, p < 0.001) and indices derived from urea nitrogen excretion (protein nitrogen appearance and normalized protein nitrogen appearance), and lower creatinine excretion (1034 ± 349 vs 1217 ± 432 mg/24 hr, p < 0.001) and indices derived from creatinine excretion (lean body mass normalized to actual or desired weight) than the adequately dialyzed group.

♦ Conclusion

Nutrition indices derived from urea nitrogen and creatinine excretion are worse in underdialyzed than in adequately dialyzed obese CPD patients. This finding may have clinical importance, despite the mathematical coupling between small solute clearances and excretion rates in cross-sectional studies, because of evidence from other studies that small solute excretion rate in cross-sectional studies is a robust independent predictor of outcome in CPD.

Peritoneal Catheter Loss and Death in Continuous Ambulatory Peritoneal Dialysis Peritonitis: Correlation with Clinical and Biochemical Parameters

Clinical and biochemical parameters associated with the removal of the peritoneal catheter and death following continuous ambulatory peritoneal dialysis (CAPD) peritonitis were analyzed In 120 episodes of peritonitis. Episodes resulting In catheter removal (n=24, 20%) and those ending in patient death (n=12, 10%) were respectively compared with episodes in which peritoneal catheters were saved and from which the patients survived. Variables associated with catheter removal included advanced age, long duration of peritonitis, coexisting exit-site/tunnelinfection, Infection caused by pseudomonas or fungi, elevated aspartate aminotransferase (AST) and malnutrition at presentation with peritonitis (serum albumin 29.5±7.6 g/L vs 33.8±4.8 glL In episodes In which the catheters were saved, p=0.014), and worsening malnutrition during peritonitis. Variables associated with death from peritonitis included diabetes mellitus, persistence of the infection, removal of the peritoneal catheter, Infection with pseudomonas, malnutrition prior to the infection (serum albumin 29.5±3.2 glL vs 34.7±4.2 glL In survivors, p<0.001), presentation with elevated AST and worsening malnutrition, and the development of pronounced malnutrition during infection (serum albumin 18.1:t4. 1 g/L vs 28.9±5.8 glL in survivors, p<0.001). Deaths were caused primarily by cardiovascular events. Both removal of the peritoneal catheter and death as consequences of CAPD peritonitis are associated with malnutrition and pseudomonas Infection. In addition, death is more frequent in diabetic patients.

Peritonitis Associated with Intra-Abdominal Pathology in Continuous Ambulatory Peritoneal Dialysis Patients

Features helpful in diagnosis and associated with death were evaluated In 26 episodes of peritonitis associated with intra-abdominal pathology (IAP) In continuous ambulatory peritoneal dialysis (CAPD) patients. Culture of multiple enteric pathogens, or of a single unusual enteric pathogen, from the dialysate was useful for diagnosis in 22/26 instances. Other diagnostic features (fecal material in dialysate, diarrhea containing dialysate, Increasing free air in the abdominal cavity) were infrequently found. A comparison of patients who died (n=11, 42%) and those who survived revealed that death was associated with bowel gangrene (5/6 died), recovery of bacteroides from the dialysate, more frequent and severe comorbid conditions (bacteremia, pneumonia, intra-abdominaland intracerebral bleeding, septic shock, hepatic failure), the development of severe malnutrition and thrombocytopenia during infection, and multiple surgical procedures until the diagnosis was established. Peritonitis associated with intra-abdominal pathology In CAPD patients is a severe infection with considerable diagnostic difficulty and high mortality. Early exploratory laparotomy upon suspicion of the nature of the peritonitis, usually raised by the recovery of enteric pathogens from the dialysate, may improve mortality.

Gender Differences in Normalized Clearances in Capd: Role of Body Size and Normalizing Parameters

Objective

To compare raw (not normalized) and normalized urea and creatinine clearances between women and men on continuous ambulatory peritoneal dialysis (CAPD). To study whether potential gender differences are due to the normalization process.

Design

Retrospective analysis of clearance studies.

Setting

Dialysis units of four academic medical centers.

Participants

The study included 302 subjects (135 women and 167 men) on CAPD with four daily exchanges and a 2-L exchange volume.

Intervention

Measurement of urea and creatinine clearances (261 in women, 352 in men) by standard methods. Body water (the volume of distribution, V, for both urea and creatinine) was estimated by the Watson anthropometric formulas.

Main Outcome Measures

Comparison of raw and normalized clearances between women and men. Urea clearance was normalized by V (Kt/Vur), while creatinine clearances was normalized by both V (Kt/Vcr) and body surface area (BSA) (Ccr).

Results

Mean values of weekly total (peritoneal plus renal) raw clearances were higher in men (urea clearance: women 67.1 L, men 77.4 L; Ccr: women 61.7 L, men 78.3 L). Raw renal clearances were higher in men, while raw peritoneal clearances were comparable. Mean weekly total Kt/Vur was higher in women (2.19 vs 1.94 in men), mean weekly total Kt/Vcr did not differ between the genders (women 2.01, men 1.95), while mean weekly Ccr was higher in men (73.0 vs 64.7 L/1.73 m2 in women). When clearances differed, the differences were significant at p < 0.001. Men had greater height and weight, while women had greater body mass index. On the average, V in men exceeded V in women by 31%, while BSA in men exceeded BSA in women by only 12%.

Conclusions

Normalization of clearances by V creates relatively higher clearance values in women, while normalization by BSA creates relatively higher clearance values in men. Thus the normalization process may create artificial differences in the normalized clearances between genders.

Symptomatic Ascites after Discontinuation of Continuous Peritoneal Dialysis

Objective

To analyze pathogenetic associations, clinical features, management, and outcome of ascites following discontinuation of continuous peritoneal dialysis (CPD).

Design

Retrospective analysis of symptomatic ascites, defined as ascites requiring at least one therapeutic paracentesis, developing in patients who discontinued CPD.

Setting

Dialysis unit of one tertiary care center.

Participants

Twelve patients with 13 episodes of symptomatic ascites diagnosed soon after (a few days to 2 months) discontinuation of CPD.

Interventions

Diagnostic tests to characterize the pathogenesis of ascites; management of ascites by hemodialysis or CPD.

Main Outcome Measures

Evolution of clinical features and nutritional parameters, survival.

Results

Ascites was infectious in 3 episodes (nontuberculous mycobacterial peritonitis) and noninfectious in the remaining 10 episodes. Serum-to-ascites albumin concentration gradient (AG) was 6.3 ± 1.5 g/L in infectious ascites and 17.3 ± 2.7 g/L (>11 g/L in every episode) in noninfectious ascites. Infectious ascites was managed with hemodialysis, prolonged courses of antimicrobial agents, and repeated paracentesis. Paracentesis ceased after 3 9 months. The patients were alive after 52 ± 19 months. Seven episodes of noninfectious ascites were managed by hemodialysis and repeated paracentesis. Five patients died within 6 months from cardiac causes or sepsis. The remaining 2 patients died after 14 and 16 months from cardiac causes. Three episodes of noninfectious ascites in 2 patients were treated by restarting CPD within 2 -5 months. Patients were alive at 16.9 ± 13.2 months. They were asymptomatic and achieved fluid control. On the same CPD schedule, peritoneal clearances of urea and creatinine and normalized protein nitrogen appearance were unchanged between the initial and restarted CPD. Serum albumin was 33.3 ± 2.5 g/L at the end of the first CPD period, 23.6 ± 2.5 g/L soon after restarting CPD, and 31.3 ± 5.5 g/L 4 months after restarting CPD.

Conclusions

Noninfectious ascites after discontinuation of CPD is often characterized by an AG > 11 g/L, suggesting portal hypertension. Restarting CPD in noninfectious ascites may be associated with improvement in ascites symptomatology and nutritional parameters and with satisfactory survival.

Symptomatic Hyperglycemia in a Patient with Dialysis Ascites

An anuric woman with ascites rapidly developed extreme hyperglycemia and seizures after hemodialysis. During development of hyperglycemia, the decrease in serum sodium concentration (Δ[Na]) was nearly twice the value predicted by a formula accounting for the degree of hyperglycemia and the intracellular-to-extracellular volume ratio. The prediction assumed that ascitic fluid is part of the extracellular volume. Potential contributors to the development of seizures include the rapid development of severe hypertonicity, a remote history of seizure disorder and development of dialysis disequilibrium syndrome. Observations in peritoneal dialysis suggest that fluid with sodium concentration lower than in the ascitic fluid is transferred from the abdominal cavity into the blood during rapid development of hyperglycemia. In this case, Δ[Na], which determines the tonicity level expected after correction of hyperglycemia, resulted from exit of both intracellular and ascitic fluid into the extracellular compartment and, therefore, ascitic fluid functions as an extension of the intracellular fluid.

Tumoral Calcinosis of the Neck in a Patient with Systemic Sclerosis

Tumoral calcinosis (TC) is rare in patients with systemic sclerosis but is associated with morbidity. Paraspinal TC may cause severe pain and potentially devastating neurological deficits. Surgical decompression by removing the TC masses and applying surgical techniques to support the spine have provided substantial relief of the symptoms in the majority of cases. However, death has occurred in the immediate postoperative period and can even occur after several months. Current indications for surgery include intractable neck pain and, most importantly, the development of neurological deficits. We present a patient with systemic sclerosis and symptomatic paraspinal TC in the neck treated conservatively for two years. This case report illustrates conditions permitting the sustained conservative treatment of paraspinal TC in systemic sclerosis patients.

Noninfectious Cloudy Peritoneal Effluent in a Peritoneal Dialysis Patient with Mantle Cell Lymphoma

A 77-year-old man on peritoneal dialysis (PD) presented repeatedly with cloudy spent dialysate containing an elevated mononuclear cell count. He had mantle cell lymphoma diagnosed by colonic polyp biopsy two years before the start of PD. The first episode of cloudy dialysate was treated for peritonitis. However, the culture of the peritoneal fluid was negative and the mononuclear cells were proven to be atypical lymphocytes of the mantle cell lymphoma variety. In addition to the peritoneal effluent, atypical lymphocytes were also found consistently in the patient’s blood samples and once in his right pleural effusion. The patient exhibited high peritoneal transport status and clinical features of volume overload raising the question of alterations in the peritoneal transport processes in PD patients with malignancies involving the peritoneal membrane. Distinction between infectious and noninfectious cloudy dialysate and the potential of changes in the peritoneal membrane transport mechanisms are issues that should concern the care of PD patients with cloudy dialysate containing malignant cells.

Hyperglycemic Crisis in an Anuric Peritoneal Dialysis Patient with Profound and Symptomatic Hypertonicity

An anuric peritoneal dialysis patient with diabetes mellitus, congestive heart failure, and anasarca developed severe hyperglycemia with hypertonicity causing profound neurological manifestations after prolonged and continuous use of hypertonic (4.25%) dextrose dialysate. She expired with hypotensive shock from a new myocardial infarction soon after completion of treatment with insulin infusion. The degree of the presenting hypertonicity far exceeded the value expected from the degree of hyperglycemia. We identified prolonged peritoneal dialysis with hypertonic solutions and profound extracellular volume expansion as the causes of the excessive hypertonicity. Hyperglycemia developing in diabetic patients treated for anasarca by peritoneal dialysis after continuous use of hypertonic dextrose dialysate is associated with the risk of excessive hypertonicity with severe clinical manifestations.

Inadequacy of Dialysis, Chronic Inflammation and Malnutrition in Nigerian Patients on Chronic Hemodialysis

Purpose

To identify the extent of underdialysis, chronic inflammation and malnutrition and their interrelationships in Nigerian hemodialysis patients.

Methods

In a prospective study including 10 adult patients, (6 men, 4 women) on hemodialysis in North Central Nigeria, malnutrition was assessed by body mass index (BMI), serum albumin and prealbumin, and bioimpedance (BIA) pre-and post dialysis, inflammation was evaluated by C-reactive protein (CRP) and adequacy of dialysis was judged by frequency of the hemodialysis sessions and Kt/V urea.

Results

Post-dialysis BMI was 21.3 (19.9, 24.3) kg/m2 (< 20 kg/m2 in 4 patients), serum albumin 31.5 (24.0, 32.0) g/L (< 30.0 g/L in 5), serum pre-albumin 25.2 (15.3, 31.1) mg/dL (< 18.0 mg/dL in 4), serum CRP 4.8 (1.2, 11.5) mg/dL (> 1.0 mg/dL in 8), phase angle 4.2 (3.7, 5.1)° (< 3° in 3) and body fat deficit was diagnosed by BIA in 4 patients. Weekly frequency of dialysis was 3 times in 2 patients, twice in 1 and ≤1 time in 7. Single-pool Kt/V urea was 0.81 (0.68, 0.95, <1.2 in 9 patients and > 1.2 in one patient receiving dialysis only twice weekly). By combined frequency of dialysis and Kt/V urea values, no patient received an adequate dose of dialysis and, indeed, all patients had overt symptoms of uremia. Low body weight, low serological and BIA nutrition indices, and high CRP levels occurred in the same patients. Patients on dialysis for > 1 year had worse nutrition indices than those on dialysis for < 1 year.

Conclusions

Underdialysis was universal, while poor nutrition and chronic malnutrition were found in the majority of the small number of patients studied. These three adverse conditions, which were interlinked, may be common in Nigerian hemodialysis patients, because their underlying socioeconomic causes are widespread. (Int J Artif Organs 2006; 29: 1067–73)

Fluid balance concepts in medicine: Principles and practice

The regulation of body fluid balance is a key concern in health and disease and comprises three concepts. The first concept pertains to the relationship between total body water (TBW) and total effective solute and is expressed in terms of the tonicity of the body fluids. Disturbances in tonicity are the main factor responsible for changes in cell volume, which can critically affect brain cell function and survival. Solutes distributed almost exclusively in the extracellular compartment (mainly sodium salts) and in the intracellular compartment (mainly potassium salts) contribute to tonicity, while solutes distributed in TBW have no effect on tonicity. The second body fluid balance concept relates to the regulation and measurement of abnormalities of sodium salt balance and extracellular volume. Estimation of extracellular volume is more complex and error prone than measurement of TBW. A key function of extracellular volume, which is defined as the effective arterial blood volume (EABV), is to ensure adequate perfusion of cells and organs. Other factors, including cardiac output, total and regional capacity of both arteries and veins, Starling forces in the capillaries, and gravity also affect the EABV. Collectively, these factors interact closely with extracellular volume and some of them undergo substantial changes in certain acute and chronic severe illnesses. Their changes result not only in extracellular volume expansion, but in the need for a larger extracellular volume compared with that of healthy individuals. Assessing extracellular volume in severe illness is challenging because the estimates of this volume by commonly used methods are prone to large errors in many illnesses. In addition, the optimal extracellular volume may vary from illness to illness, is only partially based on volume measurements by traditional methods, and has not been determined for each illness. Further research is needed to determine optimal extracellular volume levels in several illnesses. For these reasons, extracellular volume in severe illness merits a separate third concept of body fluid balance.