Diagnosis of metabolic acid-base disturbances in critically ill patients.

We compare two commonly used diagnostic approaches, one relying on plasma bicarbonate concentration and "anion gap," the other on "base excess," with a third method based on physicochemical principles, for their value in detecting complex metabolic acid-base disturbances. We analyzed arterial blood samples from 152 patients and nine normal subjects for pH, PCO(2), and concentrations of plasma electrolytes and proteins. Ninety-six percent of the patients had serum albumin concentration < or = 3 SD below the mean of the control subjects. In about one-sixth of the patients, base excess and plasma bicarbonate were normal. In a great majority of these apparently normal samples, the third method detected simultaneous presence of acidifying and alkalinizing disturbances, many of them grave. The almost ubiquitous hypoalbuminemia confounded the interpretation of acid-base data when the customary approaches were applied. Base excess missed serious acid-base abnormalities in about one-sixth of the patients; this method fails when the plasma concentrations of the nonbicarbonate buffers (mainly albumin) are abnormal. Anion gap detected a hidden "gap acidosis" in only 31% of those samples with normal plasma bicarbonate in which such acidosis was diagnosed by the third method; when adjusted for hypoalbuminemia, it reliably detected the hidden abnormal anions. The proposed third method identifies and quantifies individual components of complex acid-base abnormalities and provides insights in their pathogenesis.

Anion gap and hypoalbuminemia.

OBJECTIVES: To show how hypoalbuminemia lowers the anion gap, which can mask a significant gap acidosis; and to derive a correction factor for it. DESIGN: Observational study. SETTING: Intensive care unit in a university-affiliated hospital. SUBJECTS: Nine normal subjects and 152 critically ill patients (265 measurements). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Arterial blood samples analyzed for pH, PCO2, and concentrations of plasma electrolytes and proteins. Marked hypoalbuminemia was common among the critically ill patients: 49% of them had serum albumin concentration of <20 g/L. Each g/L decrease in serum albumin caused the observed anion gap to underestimate the total concentration of gap anions by 0.25 mEq/L (r2 = .94). CONCLUSIONS: The observed anion gap can be adjusted for the effect of abnormal serum albumin concentrations as follows: adjusted anion gap = observed anion gap + 0.25 x ([normal albumin] [observed albumin]), where albumin concentrations are in g/L; if given in g/dL, the factor is 2.5. This adjustment returns the anion gap to the familiar scale of values that apply when albumin concentration is normal.

[Case reports of disturbances of effective osmolality regulation in disorders of the central nervous system]. / Kasuistiky poruch regulace efektivní osmolality pri postizení centrálního nervového systému.

The topic of the effective osmolality disorder in the patients with the central nervous system injury is documented with the four selected cases from the case collection monitored in the Department of Anesthesia and Intensive Care. The syndroms were diagnosed using the computer programme evaluating renal functions in relation to homeostasis. Authors present two case reports of the Inappropriate ADH Secretion Syndrome (IADHS), one of the Cerebral Salt Wasting Syndrome (CSWS) and one of Diabetes Insipidus (DI). The cases were recorded with the aid of the computer programme working with the 13 routinely monitored values and 12 output parameters. Two case studies were retrospective. Mentioned four cases are the example of the effective use of the currently monitor values in the intensive care setting. According to the incidence of the effective osmolality disorders, inputing quickness and programme simplicity authors reccomend the routine use of the programme in the central nervous system damaged patients.

[Disturbances of effective osmolality regulation in disorders of the central nervous system and possible methods of monitoring]. / Poruchy regulace efektivní osmolality u postizení centrálního nervového systému a moznosti jejich monitorování.

Authors deal in detail with the pathophysiology of the osmolal regulation. Besides hyperosmolality the secretion of antidiuretic hormone (ADH) in increased by hypovolemia and hypotension. Secretion of ADH is lowered in hypoosmolal states. All other mechanisms are preferebly volume regulating and they influence mainly retention and excretion of sodium. Authors discuss homeostatic effects of the renin-angiotensin-aldosteron system, effects of renal failure with prevailing glomerular or tubular function disorder, impact of diuretics, natriuretic peptides, digitalis-like hormone, urodilantin and influence of the other solutes. Disorders of the effective osmolality regulation are frequent in the cerebral affections that originate from trauma, vascular disease, inflammation or tumors. Hypoosmolality and hyponatremia are presented in two different conditions: Inappropriate Vasopressin Secretion Syndrome (IADHS) and Cerebral Salt Wasting Syndrome (CSWS). Quick differential diagnose is important because the treatment of both syndromes is essentially different. Typical cause of hypernatremia is central diabetes insipidus (DI). The group of available calculated renal function parameters is applied in the differential diagnosis of these syndromes. They are creatinin clearance, excretion fraction of water and sodium, electrolyte clearance and electrolyte free water clearance. Investigation of ADH and natriuretic peptide could be even misleading. Pathophysiologic consequence of the state given by inappropriate elevation of one hormone can be the elevation of the second one.

Modelling of acid-base equilibria.

A quantitative evaluation of metabolic acid-base component is described. The model is based on Stewart's analysis of acid-base chemistry. The metabolic component of acid-base disturbances is divided into four partial metabolic disorders; they can result from abnormal concentrations of chloride, albumin and phosphate disturbances, or from appearance of abnormal unidentified strong anions. The efficiency of the model is sufficient, quantitative partial results are given in the same units as base excess. In complex acid-base disturbances, such as are seen in critically ill patients, a detailed analysis of the specific components of the metabolic acid-base status allows one to plan specific therapeutic interventions.

[Energy expenditures in patients with acute and chronic catabolic conditions]. / Energetický výdej u pacientu ve stavu akutního a chronického katabolismu.

The authors investigated the energy expenditure and utilization of different nutrients by indirect calorimetry. They examined three groups of subjects: patients with acute febrile diarrhoeal diseases (n = 36), patients with subacute to chronic severe febrile diseases (n = 10) and healthy subjects (n = 21). The measurements were made three times a day. In all groups the energy requirements of the organism were met in the morning above all by fats, in the course of the day the ration of utilized carbohydrates increased markedly. The authors discuss the problem of optimal nutrition of patients in a critical condition from the quantitative and qualitative aspect.

[Suitable variables for the evaluation of combined acid-base disorders: residual anions, buffer base sera, proteins and delta bases]. / Vhodné veliciny pri hodnocení kombinovaných acidobazických poruch; reziduální anionty, nárazníkové báze séra, proteiny a delta báze.

In 254 findings of the acid-base balance ions and proteins, the authors evaluated mutual relations between the acid-base balance and calculation from the anion column. Contrary to the commonly used anion gap value, the authors used concurrently for evaluation buffer base sera, serum protein values and residual anions. The logical result of summarization of these three parameters is the creation of a new term, delta bases, which correlates closely with the resulting metabolic acid-base situation. The optimal relationship of the mentioned parameters to the value of base excess is described by the following equation: BE = 0.805*BBS--0.852*RA--0.204*SProt--15.8 which is consistent with the theoretical value of delta bases.

[Prognosis in patients in intensive care from the aspect of renal function]. / Prognóza nemocných v intenzívní péci z hlediska funkce ledvin.

The authors evaluated in 82 patients 228 findings of renal functions. Twenty-nine patients with a total number of 113 findings died. In those who died frequently the values of renal functional parameters were beyond the reference limits, indicating various failures (high serum creatinine, high serum urea, elevated fractional osmolal and water excretion, reduced creatinine clearance). In those who died tubular osmotic diuresis was more frequent, while overflow osmotic diuresis was found mostly in the surviving patients. By means of linear discrimination analysis vectors of parameters were assessed suitable for evaluation of the relationship of renal functions and the prognosis and functional shapes of so-called renal prognostic indicators. In the calculation of renal prognostic parameters the following ones prove useful: serum creatinine (SKrea), creatinine clearance (CKrea), serum osmolality (SOsm), osmolality of urine (UOsm), sodium cation in serum (SNa), fractional excretion of water (FeH2o), of potassium (FeK), osmolal (FeOsm), urinary excretion per 24 hours of creatinine (DuKrea), sodium (DuNa) and potassium (DuK). The best prognostic effectiveness was obtained from the calculation of the renal prognostic indicator (RPU) according to the following equation: RPU = SOsm.0.0178--CKrea.0.944 + FeK.0.854 + + DuKrea.0.0665--DuNa.0.0022 + DuK.0.0047--4.931. The RPU value rises with the deteriorating prognosis of the patients; in those who died it reaches more frequently positive values, in surviving patients the values are negative. By reclassification, using this prognostic index, 82% of the patients with a favourable prognosis and 68% with a poor prognosis (those who died) were correctly classified, i. e. a total of 74% patients.

Evaluation of renal functions--a computer programme.

The authors describe the operational characteristics of a computer programme, which they developed and routinely use, to facilitate the evaluation of renal function tests data. Upon input of the necessary biochemical parameters the values of the various clearances, fractional excretions and other indices and ratios obtained from renal function tests are calculated. The computer programme provides an output of diagnostic commentaries in text format for further evaluation by the attending physician. The programme is written in FORTRAN IV language.

[Renal function parameters in patients in intensive care]. / Renální funkcní parametry u nemocných v intenzívní péci.

82 patients treated at a ward of anaesthesiology and resuscitation had 330 renal function tests performed using a computerized programme. While glomerular functions were often preserve or even increased, tubular functions displayed a broad spectrum of disorders. --Nosocomial effects may have a significant role to play there. Extreme changes in regulation as regards impaired ADH involvement are nothing exceptional. Tubular osmotic diuresis and overflow osmotic diuresis are the most frequent types of diuresis, while lower frequency is seen in water diuresis, mixed water and tubular osmotic diuresis, and mixed overflow and tubular osmotic diuresis. The therapeutical effects of the incidence of overflow osmotic diuresis and wider use of aldosterone antagonists are discussed.

Meeting the energy requirements in sepsis.

Sepsis is associated with severe metabolic disturbances and progressive failure of utilization of carbohydrates, lipids and proteins to meet the energy requirements of peripheral tissue. The causes of this condition are analysed. The interrelation between malnutrition and sepsis is discussed. Current concepts regarding the meeting of water and ion requirements, indications for administration of colloid solutions and infusion of glucose, lipid emulsions and amino acid solutions in each stage of sepsis are presented. Various views on the amount and quality of necessary nutrients are discussed providing evidence that a number of problems have to be solved yet.

Sepsis--metabolic changes and their development.

As sepsis develops, the patient passes through four stages of haemodynamic and metabolic disturbances. The stages are compensated sepsis, metabolic insufficiency, respiratory insufficiency and cardiac insufficiency. Once the septic process has become uncontrollable, the patient dies in septic shock. On the contrary, all the above stages are potentially reversible if appropriate therapy is instituted. Typical development of the haemodynamic and endocrinologic changes, values of blood gases including metabolites affecting acid base balance as well as changes in the metabolism of carbohydrates, lipids and proteins are described. The article points to aspects that still make accurate sepsis staging difficult.