Unmeasured anions in critically ill patients: Can they predict mortality?

Jens Rocktaeschel, Hiroshi Morimatsu, Shigehiko Uchino, Rinaldo Bellomo

Research output: Contribution to journalArticle

108 Citations (Scopus)

Abstract

Objective: To determine whether base excess, base excess caused by unmeasured anions, and anion gap can predict lactate in adult critically ill patients, and also to determine whether acid-base variables can predict mortality in these patients. Design: Retrospective study. Setting: Adult intensive care unit of tertiary hospital. Patients: Three hundred adult critically ill patients admitted to the intensive care unit. Interventions: Retrieval of admission biochemical data from computerized records, quantitative biophysical analysis of data with the Stewart-Figge methodology, and statistical analysis. Measurements and Main Results: We measured plasma Na +, K+, Mg2+, Cl-, HCO 3-, phosphate, ionized Ca2+, albumin, lactate, and arterial pH and Paco2. All three variables (base excess, base excess caused by unmeasured anions, anion gap) were significantly correlated with lactate (r2 = .21, p <.0001; r2 = .30, p <.0001; and r2 = .31. p <.0001, respectively). Logistic regression analysis showed that the area under the receiver operating characteristic (AUROC) curves had moderate to high accuracy for the prediction of a lactate concentration >5 mmol/L: AUROC curves, 0.86 (95% confidence interval [Cl], 0.78-0.94), 0.86 (95% Cl, 0.78-0.93), and 0.85 (95% Cl, 0.77-0.92), respectively. Logistic regression analysis showed that hospital mortality rate correlated significantly with Acute Physiology and Chronic Health Evaluation (APACHE) II score, anion gap corrected (anion gap corrected by albumin), age, lactate, anion gap, chloride, base excess caused by unmeasured anions, strong ion gap, sodium, bicarbonate, strong ion difference effective, and base excess. However, except for APACHE II score, AUROC curves for mortality prediction were relatively small: 0.78 (95% CI, 0.72-0.84) for APACHE II, 0.66 (95% CI, 0.59-0.73) for lactate, 0.64 (95% CI, 0.57-0.71) for base excess caused by unmeasured anions, and 0.63 (95% CI, 0.56-0.70) for strong ion gap. Conclusions: Base excess, base excess caused by unmeasured anions, and anion gap are good predictors of hyperlactatemia (>5 mmol/L). Acid-base variables and, specifically, "unmeasured anions" (anion gap, anion gap corrected, base excess caused by unmeasured anions, strong ion gap), irrespective of the methods used to calculate them, are not accurate predictors of hospital mortality rate in critically ill patients.

Original languageEnglish
Pages (from-to)2131-2136
Number of pages6
JournalCritical Care Medicine
Volume31
Issue number8
DOIs
Publication statusPublished - Aug 1 2003
Externally publishedYes

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Acid-Base Equilibrium
Critical Illness
Anions
Mortality
Lactic Acid
APACHE
Ions
Hospital Mortality
Intensive Care Units
Albumins
Sodium Bicarbonate
Acids
Bicarbonates
Tertiary Care Centers
Chlorides
Retrospective Studies
Logistic Models
Phosphates
Regression Analysis
Confidence Intervals

ASJC Scopus subject areas

  • Critical Care and Intensive Care Medicine

Cite this

Unmeasured anions in critically ill patients : Can they predict mortality? / Rocktaeschel, Jens; Morimatsu, Hiroshi; Uchino, Shigehiko; Bellomo, Rinaldo.

In: Critical Care Medicine, Vol. 31, No. 8, 01.08.2003, p. 2131-2136.

Research output: Contribution to journalArticle

Rocktaeschel, Jens ; Morimatsu, Hiroshi ; Uchino, Shigehiko ; Bellomo, Rinaldo. / Unmeasured anions in critically ill patients : Can they predict mortality?. In: Critical Care Medicine. 2003 ; Vol. 31, No. 8. pp. 2131-2136.
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title = "Unmeasured anions in critically ill patients: Can they predict mortality?",
abstract = "Objective: To determine whether base excess, base excess caused by unmeasured anions, and anion gap can predict lactate in adult critically ill patients, and also to determine whether acid-base variables can predict mortality in these patients. Design: Retrospective study. Setting: Adult intensive care unit of tertiary hospital. Patients: Three hundred adult critically ill patients admitted to the intensive care unit. Interventions: Retrieval of admission biochemical data from computerized records, quantitative biophysical analysis of data with the Stewart-Figge methodology, and statistical analysis. Measurements and Main Results: We measured plasma Na +, K+, Mg2+, Cl-, HCO 3-, phosphate, ionized Ca2+, albumin, lactate, and arterial pH and Paco2. All three variables (base excess, base excess caused by unmeasured anions, anion gap) were significantly correlated with lactate (r2 = .21, p <.0001; r2 = .30, p <.0001; and r2 = .31. p <.0001, respectively). Logistic regression analysis showed that the area under the receiver operating characteristic (AUROC) curves had moderate to high accuracy for the prediction of a lactate concentration >5 mmol/L: AUROC curves, 0.86 (95{\%} confidence interval [Cl], 0.78-0.94), 0.86 (95{\%} Cl, 0.78-0.93), and 0.85 (95{\%} Cl, 0.77-0.92), respectively. Logistic regression analysis showed that hospital mortality rate correlated significantly with Acute Physiology and Chronic Health Evaluation (APACHE) II score, anion gap corrected (anion gap corrected by albumin), age, lactate, anion gap, chloride, base excess caused by unmeasured anions, strong ion gap, sodium, bicarbonate, strong ion difference effective, and base excess. However, except for APACHE II score, AUROC curves for mortality prediction were relatively small: 0.78 (95{\%} CI, 0.72-0.84) for APACHE II, 0.66 (95{\%} CI, 0.59-0.73) for lactate, 0.64 (95{\%} CI, 0.57-0.71) for base excess caused by unmeasured anions, and 0.63 (95{\%} CI, 0.56-0.70) for strong ion gap. Conclusions: Base excess, base excess caused by unmeasured anions, and anion gap are good predictors of hyperlactatemia (>5 mmol/L). Acid-base variables and, specifically, {"}unmeasured anions{"} (anion gap, anion gap corrected, base excess caused by unmeasured anions, strong ion gap), irrespective of the methods used to calculate them, are not accurate predictors of hospital mortality rate in critically ill patients.",
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T1 - Unmeasured anions in critically ill patients

T2 - Can they predict mortality?

AU - Rocktaeschel, Jens

AU - Morimatsu, Hiroshi

AU - Uchino, Shigehiko

AU - Bellomo, Rinaldo

PY - 2003/8/1

Y1 - 2003/8/1

N2 - Objective: To determine whether base excess, base excess caused by unmeasured anions, and anion gap can predict lactate in adult critically ill patients, and also to determine whether acid-base variables can predict mortality in these patients. Design: Retrospective study. Setting: Adult intensive care unit of tertiary hospital. Patients: Three hundred adult critically ill patients admitted to the intensive care unit. Interventions: Retrieval of admission biochemical data from computerized records, quantitative biophysical analysis of data with the Stewart-Figge methodology, and statistical analysis. Measurements and Main Results: We measured plasma Na +, K+, Mg2+, Cl-, HCO 3-, phosphate, ionized Ca2+, albumin, lactate, and arterial pH and Paco2. All three variables (base excess, base excess caused by unmeasured anions, anion gap) were significantly correlated with lactate (r2 = .21, p <.0001; r2 = .30, p <.0001; and r2 = .31. p <.0001, respectively). Logistic regression analysis showed that the area under the receiver operating characteristic (AUROC) curves had moderate to high accuracy for the prediction of a lactate concentration >5 mmol/L: AUROC curves, 0.86 (95% confidence interval [Cl], 0.78-0.94), 0.86 (95% Cl, 0.78-0.93), and 0.85 (95% Cl, 0.77-0.92), respectively. Logistic regression analysis showed that hospital mortality rate correlated significantly with Acute Physiology and Chronic Health Evaluation (APACHE) II score, anion gap corrected (anion gap corrected by albumin), age, lactate, anion gap, chloride, base excess caused by unmeasured anions, strong ion gap, sodium, bicarbonate, strong ion difference effective, and base excess. However, except for APACHE II score, AUROC curves for mortality prediction were relatively small: 0.78 (95% CI, 0.72-0.84) for APACHE II, 0.66 (95% CI, 0.59-0.73) for lactate, 0.64 (95% CI, 0.57-0.71) for base excess caused by unmeasured anions, and 0.63 (95% CI, 0.56-0.70) for strong ion gap. Conclusions: Base excess, base excess caused by unmeasured anions, and anion gap are good predictors of hyperlactatemia (>5 mmol/L). Acid-base variables and, specifically, "unmeasured anions" (anion gap, anion gap corrected, base excess caused by unmeasured anions, strong ion gap), irrespective of the methods used to calculate them, are not accurate predictors of hospital mortality rate in critically ill patients.

AB - Objective: To determine whether base excess, base excess caused by unmeasured anions, and anion gap can predict lactate in adult critically ill patients, and also to determine whether acid-base variables can predict mortality in these patients. Design: Retrospective study. Setting: Adult intensive care unit of tertiary hospital. Patients: Three hundred adult critically ill patients admitted to the intensive care unit. Interventions: Retrieval of admission biochemical data from computerized records, quantitative biophysical analysis of data with the Stewart-Figge methodology, and statistical analysis. Measurements and Main Results: We measured plasma Na +, K+, Mg2+, Cl-, HCO 3-, phosphate, ionized Ca2+, albumin, lactate, and arterial pH and Paco2. All three variables (base excess, base excess caused by unmeasured anions, anion gap) were significantly correlated with lactate (r2 = .21, p <.0001; r2 = .30, p <.0001; and r2 = .31. p <.0001, respectively). Logistic regression analysis showed that the area under the receiver operating characteristic (AUROC) curves had moderate to high accuracy for the prediction of a lactate concentration >5 mmol/L: AUROC curves, 0.86 (95% confidence interval [Cl], 0.78-0.94), 0.86 (95% Cl, 0.78-0.93), and 0.85 (95% Cl, 0.77-0.92), respectively. Logistic regression analysis showed that hospital mortality rate correlated significantly with Acute Physiology and Chronic Health Evaluation (APACHE) II score, anion gap corrected (anion gap corrected by albumin), age, lactate, anion gap, chloride, base excess caused by unmeasured anions, strong ion gap, sodium, bicarbonate, strong ion difference effective, and base excess. However, except for APACHE II score, AUROC curves for mortality prediction were relatively small: 0.78 (95% CI, 0.72-0.84) for APACHE II, 0.66 (95% CI, 0.59-0.73) for lactate, 0.64 (95% CI, 0.57-0.71) for base excess caused by unmeasured anions, and 0.63 (95% CI, 0.56-0.70) for strong ion gap. Conclusions: Base excess, base excess caused by unmeasured anions, and anion gap are good predictors of hyperlactatemia (>5 mmol/L). Acid-base variables and, specifically, "unmeasured anions" (anion gap, anion gap corrected, base excess caused by unmeasured anions, strong ion gap), irrespective of the methods used to calculate them, are not accurate predictors of hospital mortality rate in critically ill patients.

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