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.