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Communications to the Editor |

Negative Fluid Balance as Predictor of Mortality Negative Fluid Balance as Predictor of Mortality FREE TO VIEW

Tara Quasim; Donald C. McMillan, PhD; John Kinsella
Author and Funding Information

Affiliations: Royal Infirmary Glasgow, United Kingdom,  Yale University School of Medicine New Haven, CT

Correspondence to: John Kinsella, FRCA, Department of Anesthesia, Royal Infirmary, 10 Alexandria Parade, Glasgow G-31 2 ER, United Kingdom; e-mail: j.kinsella@clinmed.gla.ac.uk



Chest. 2001;120(4):1424-1425. doi:10.1378/chest.120.4.1424
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Alsous and coworkers (June 2000)1 reported that, in a study of 36 patients in a medical ICU, a negative fluid balance of > 500 mL on any of the first 3 days of hospital admission was associated with better survival.

In a retrospective analysis, we examined 80 critically ill surgical patients who were admitted to an intensive therapy unit (ITU) for mechanical ventilation and who had survived at least 3 days. There were 30 female and 50 male patients, and they had a median APACHE (acute physiology and chronic health evaluation) II score of 21 (range, 10 to 43) and a predicted percentage mortality of 40.8% (range, 10.1 to 90.5). Twenty-nine patients died within 30 days. There was no significant difference in APACHE II scores or predicted mortality rates between those patients who died compared with those who lived. In those patients who survived, there was a nonsignificant trend toward a higher proportion of patients who had a negative fluid balance > 500 mL on any of the first 3 days (12 of 51 patients), compared with those who died (2 of 29 patients; p = 0.072, two tailed).

These results, in an unselected cohort of critically ill surgical patients, do not confirm the strong prognostic value of a negative fluid balance > 500 mL on any of the first 3 days of hospital admission. The reasons for the conflicting results are unclear, as the mean APACHE II scores in the previous and present study (25 vs 22, respectively) and the percentage of patients who died (56% vs 36%, respectively) were similar.

In the present study, there were approximately twice the number of patients and twice the number of deaths. All the patients were either postoperative or had severe pancreatitis. This would have a major influence on the fluid requirements of the patients. Also, the normal stress response to surgery involves alterations in circulating hormone concentrations, with an antidiuretic response and water retention for the first 48 h after surgery. Therefore, it may be that, in the critically ill, postoperative surgical patient, the mobilization of excess fluid occurs at a later period of time than in medical patients.

We conclude that a negative fluid balance, achieved by the third day after admission to the ITU, is not a significant predictor of death in the critically ill surgical patient, and therefore, it is not generally applicable to critically ill patients.

Alsous, F, Khamiees, M, DeGirolamo, A, et al (2000) Negative fluid balance predicts survival in patients with septic shock: a retrospective pilot study.Chest117,1749-1754. [PubMed] [CrossRef]
 

Negative Fluid Balance as Predictor of Mortality

To the Editor:

We appreciate the opportunity to respond to the interesting letter of Drs. Quasim, McMillan, and Kinsella. We are very pleased that these physicians took the time to interrogate our hypothesis.1We published our observation because we are convinced that fluid fluxes are common in critically ill patients and that vascular leak and dilatation and the need for refilling are followed by a diuretic phase in those patients with sepsis who recover (it is inevitable). In our original report, we did not imply that these findings were conclusive, nor did we assert that they were applicable to any other than septic patients with sepsis. Nevertheless, a reanalysis of the data provided by Quasim et al demonstrates that there was a survival advantage for their postoperative patients who achieved a negative fluid balance in the first 3 days (relative risk = 1.45; 95% confidence interval = 1.08 to 1.94).2 The two studies differ merely in the magnitude of the observed survival advantage. This is to be expected for a number of reasons.

The average amount of fluid administered to our patients with septic shock in the first day was 5.5 L. We have not been given the average amount of fluid administered to their patients on the first day but we doubt that the magnitude was similar. Another possibility is that different surgeries have variable rates of recovery based upon the gravity of the initial injury and factors pertaining to the procedure (eg, duration of anesthesia, size of the wound, site of the operation). Insofar as the dispersion of vascular recovery times is greater in a heterogenous group of postoperative patients, the dispersion of transition points from positive to negative balance would also be greater. The difference in observed death rate (56% in our study versus 21% in their cohort) may reflect differences in the severity of the systemic inflammatory response in the two patient groups—a factor that may impact the magnitude of vascular dilatation and/or leak and, therefore, outcomes. We are not provided with significant information about the characteristics of their patients. Differences in age, severity of illness, and baseline creatinine levels are bound to effect the magnitude of survival advantage, as demonstrated in Table 3 of our report.1 For instance, whereas patients with sepsis with negative fluid balance and APACHE II score < 20 were 1.3 times more likely to survive, those with negative balance and APACHE II score ≥ 20 were 6 times more likely to survive. Thus, any meaningful differences in the proportional representation of the groups with APACHE II scores < 20 and ≥ 20 would result in significant variations in the reported unadjusted risk ratios.

Accordingly, we are delighted that our findings have been replicated in studies with postoperative patients. We hope that larger cohort studies will further validate these findings and will provide more precise estimates of the true magnitude of survival advantage in various populations of critically ill patients.

References
Alsous, F, Khamiees, M, DeGirolamo, A, et al Negative fluid balance predicts survival in patients with septic shock: a retrospective pilot study.Chest2000;117,1749-1754. [PubMed] [CrossRef]
 
Greenland, S, Robbin, JM Estimation of common effect parameter from sparse follow-up data.Biometrics1985;41,55-68. [PubMed]
 

Figures

Tables

References

Alsous, F, Khamiees, M, DeGirolamo, A, et al (2000) Negative fluid balance predicts survival in patients with septic shock: a retrospective pilot study.Chest117,1749-1754. [PubMed] [CrossRef]
 
Alsous, F, Khamiees, M, DeGirolamo, A, et al Negative fluid balance predicts survival in patients with septic shock: a retrospective pilot study.Chest2000;117,1749-1754. [PubMed] [CrossRef]
 
Greenland, S, Robbin, JM Estimation of common effect parameter from sparse follow-up data.Biometrics1985;41,55-68. [PubMed]
 
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