The three main findings of this study of serum albumin level in 7,121 intensive care unit patients with chronic heart failure were: 1) Higher albumin levels were found to be independently associated with a higher risk of 14th-, 28th- and 90th day all-cause mortality in HF patients through the continuous follow-up. Especially when the albumin level is above 3.56mg/dl, the risk of death on 14th day is lower. 2) The negative association between albumin (as a continuous variable) and all-cause mortality at the 14th- and 28th day is mixed by ARDS. 3) With the passage of time, the increase of albumin conveyed a higher reduction of all-cause mortality on the 14th-, 28th- and 90th days, which have a significant negative impact on clinical results.
In the case of acute HF, albumin has been proved to have an important influence on survival 17,18,19. Although multiple risk grading models and HF prognostic scores have been proposed and validated, the role of SA has not been investigated 20, 21. In a recent meta-analysis, Peng et al 22 investigated HA and mortality in HF and found that HA was associated with increased mortality in heart failure. In addition, Mahmoud et al 23 found that in-hospital mortality in HF was inversely associated with SA. SA showed a decreasing trend and was associated with worse prognosis in acute and chronic HF 24, 25. Jabbour et al 26 followed 212 patients with chronic systolic HF for more than 2 years and found that SA reduction from baseline was associated with higher mortality compared with retention of baseline SA. A study by Biegus et al 24 showed that a decreasing trend in SA during the first 4 days of hospitalization was associated with increased mortality at 6 months, and the risk was proportional to the degree of albumin reduction. Interestingly, studies have found that serum albumin levels < 3 g/dL are associated with decreased renal function during treatment in patients with acute HF 27. Similarly, our study is the first to find a linear association between serum albumin and all-cause mortality on days 14, 28, and 90 in patients with chronic heart failure. In addition, the risk of all-cause mortality on day 14 was significantly reduced when albumin was increased above 3.56 mg/dl. However, the pathophysiology behind this association is unclear.
Low albumin in patients with heart failure is mainly manifested by reduced albumin synthesis and protein loss, which may be caused by hemodilution, chronic inflammatory states, hepatic congestion, malnutrition, cachexia due to volume overload, and proteinuria or intestinal disease. Albumin is associated with numerous detrimental biological processes which are present in HF and pertain to a worse outcome 28. Low albumin in heart failure promotes and aggravates congestion due to the decrease of intravascular colloidal osmotic pressure 29, increases oxidative stress 30, inflammation 31, and susceptibility to infection. The mechanism may be that supposed that S-thiolation of albumin is increased in the plasma of HF patients and induced changes in the structure and antioxidant function of human serum albumin, and provide a new paradigm of the proinflammatory effect of S-thiolation HAS 32. Therefore, low albumin is the sum of many harmful factors in patients with heart failure, which is expected to provide important prognostic information for patients with heart failure.
Our research results suggest that ARDS and albumin interact in the prediction of results. Previous studies have found that hypoproteinemia (< 5.9 g/dl) and hypoproteinemia level < 2.4 g/dl are considered as signs of increased lung permeability in patients with sepsis and acute respiratory distress syndrome. The lung leakage index would decrease with the rise of serum protein 33. In-depth analysis of the results shows that the decrease of colloidal osmotic pressure under normal permeability of vascular endothelium will not cause edema. On the contrary, it is the increased permeability caused by endothelial damage that leads to hypoproteinemia 33. The increase of systemic permeability caused by low albumin can’t be equated with similar pulmonary vascular permeability. Besides, on the day of admission to ICU, serum albumin has nothing to do with the degree of pulmonary degassing described by LUSS in ARDS patients. Serum albumin level < 3.25g/dL increases the chances of prolonging ICU stay (≥10 days), but it cannot predict the mortality rate 34. This is also consistent with our conclusion, suggesting that ARDS may be the main risk of all-cause death on the 28th day. Therefore, albumin reduction in patients with initial heart failure may be largely influenced by other factors such as inflammation.
An interesting finding in this study is the extent to which albumin level change over time to the recent death of chronic HF. The all-cause mortality on the 90th day predicted better clinical results with the all-cause mortality on the 14th day. A significantly different finding is reported in the case of chronic HF 35, 36. This finding seems to be biologically unreasonable, as the decline of albumin over time is the characteristic of the degradation state of HF patients. However, the condition of patients tends to be stable after staying in ICU for 14 days, and the mortality is obviously decreasing due to the different death time ranges of our follow-up. This means that in acute cases, these changes are related to the severity, sequelae and progress of acute events. In the chronic environment, these changes may reflect the progress of chronic diseases of albumin, the harmful biological process related to low albumin and its significance to prognosis 36.
Whether high albumin can effectively reduce the all-cause mortality of chronic HF requires a sufficiently powerful placebo-controlled randomized controlled trial, but there are few studies on whether albumin supplementation can reduce the all-cause death of chronic heart failure patients in intensive care unit, most of them are only observational studies. Experiments show that administration of albumin will not change the length of stay or mortality of patients in intensive care unit 37, 38. It seems unreasonable that exogenous albumin is expensive to treat hypoalbuminemia. But maybe exogenous albumin can't stay in the body for a long time.
The most important limitation of our study is related to observation design, which makes it impossible to infer the causal relationship between the observed association between serum albumin and all-cause mortality. Even after multivariable adjustment, residual confusion remains an issue. In addition, there is a lack of treatment in the course of the disease, and the stage of heart failure has not been assessed, and the mechanism of death has not been assessed. Nevertheless, our advantage lies in the discussion of short-term all-cause mortality, and the serum albumin level has no obvious change with time. We also believe that it is the first time that we have continuously followed up all-cause mortality for 14th-, 28th- and 90th days.
In conclusion, hypoproteinemia in patients with chronic heart failure in intensive care unit has a linear relationship with the 14th-, 28th- and 90th day mortality rate, and the recommended range exceeds 3.56g/dl. ARDS strongly confuses the association between albumin and the 14th- and 28th day all-cause mortality. Meanwhile, With the passage of time, the all-cause mortality on the 90th day predicted better clinical results with the all-cause mortality on the 14th day. Sufficient and powerful randomized, placebo-controlled trials are needed in chronic heart failure of intensive care unit to test whether supplementing endogenous albumin may prove to be an effective method to reduce short-term all-cause mortality.