Our results indicate the existence of a deficiency in the diagnostic and therapeutic approach of the hyponatremia made by non-endocrinologist nor nephrologist clinicians in hospitalized patients.
The lack of description/identification of the volemic state made by IS physicians, observed in almost 82% of our cases, is very striking. We observed that the measurement of HIJBP in the physical examination was apparently not carried out by any IS clinician, which guides us to hypothesize the existence of a scarce knowledge of this exploration or an underestimation of its usefulness. Our results coincide with others described in previous retrospective [12–14] and prospective [3,15] studies, which have shown the poor performance of a complete and accurate diagnostic study of hyponatraemia, including volemia assessment.
Because the clinical classification of volemia could be difficult [5–8], other test have been recommend to assay for this purpose. A value of UNa < 30 mmol/L has been found as a useful indicator of hypovolemia [5,7,21,22]; nevertheless, disorders that cause urinary sodium losses or states of urinary dilution will hinder its interpretation for this purpose. Some authors have proposed using UOsm as an unique criterion for classifying hyponatremia and to direct the initial treatment [23,24]. Our results regarding the UOsm and UNa measurements are similar to those observed in the Hyponatremia Registry, where only in 68% and 63% of the patients diagnosed with syndrome of inappropriate secretion of antidiuretic hormone, the UOsm and UNa measurements were performed , respectively . These results suggest that many clinicians might not know the recommendations about using urine tests for initial diagnostic or therapeutic support in the hyponatremia management.
Although the main clinical guidelines not include a routine acid-base status assessment in their recommendations [1,2], there is a close pathophysiological relationship between acid-base status, sodium homeostasis and effective circulating volume (ECV) . Sahay M. and Sahay R. included the blood gas assessment within the diagnostic algorithm of hyponatremia . Low ECV, when the integrity of the renin-angiotensin-aldosterone system is maintained, is usually accompanied by metabolic alkalosis as a consequence of hyperaldosteronism secondary to low ECV . On the other hand, when hyponatremia appears in context of hypoaldosteronism, hyperchloremic metabolic acidosis could be observed [27,28]. Therefore, the study of the acid-base status would help in the diagnosis of hyponatremia. In our study, patients handled in ER had a higher rate of blood gas measurements than those in IF. It is probably explained by the accessibility for performing this test in the ER of the hospital. Another explanation might be that this test is included in a “basic” profile assessment of the patients admitted to the ER. Anyway, this is a good practice that should be enhanced.
In the current study there was an incongruity between the volemic classification - when it was developed - and the treatment prescribed by the IS physicians. Furthermore, the most patients received treatment with isotonic saline infusion despite the lack of volemic status description in the clinical records. Although that treatment was correct, as all patients of this series were hypovolemic, we have to hypothesize that it was a coincidence. Additionally, we observed that IS clinicians treated severe hyponatremia with HSS, according to the guidelines , in only 40% of patients. Whether clinicians truly know the importance of the relation between a correct initial classification of the hyponatremia and its treatment, remains to elucidate.
Monitoring of SNa every 4-8 hours during the first 48 hours after starting treatment is a recommended approach to avoid overcorrection of SNa [1,2,30,31]. In the most patients of our series, the first SNa control was carried out after 6 hours post-treatment. But we observed a significantly higher percentage of SNa controls before 6 hours in patients placed in the ER (Table 2). It might be explained by the perennial presence of physicians in the ER, a rapid access to a blood-gas machine, or the use of HSS in 2 of the 8 patients of this group. Both human and logistical resources as well as the use of HSS could be factors associated with the frequency and intervals of the post-treatment SNa controls.
Our results suggest us that the training and knowledge about Hyponatremia approach should probably be improved in non-endocrinologist nor nephrologist clinicians. It has been found that when hyponatremia in hospitalized patients is managed from the beginning by well-trained practitioners, hospitalization time decrease  and approximately 80% of patients could receive a complete diagnostic assessment, as compared to 5% when the physicians are not well-trained . Furthermore, a complete and correct diagnostic of hyponatremia from the beginning allows a better treatment , with up to 8-fold more probabilities of achieving a NaS > 130 mmol/L at discharge , as well as a reduction of the hospital mortality . Therefore, we believe that, in level-3 hospitals, there should be multidisciplinary teams for the management of hyponatremia, and thus guarantee the best care for these patients in all services.
Our study has some limitations. Its retrospective design leads to the existence of biases despite our attempt to avoid them. The results come from a small number of cases and from a unique hospital center. The medical specialty and the degree of training/experience of the IS physicians were not collected, which could be a factor that interfered with the results.
The main strength of our research is the selectivity and correct volemic classification of patients, based on various known scientific parameters [2,11,17,18] and a concise methodology. The exposed results are relevant and show the probable reality about hyponatremia approach by the physicians of a high-resolution hospital. Nevertheless, this situation is likely to occur in other hospitals in our region. Therefore, more studies, preferably multicenter and prospective, should be carried out.
In conclusion, we evidenced the existence of deficiencies in the management of patients with hyponatremia by non-endocrinologists nor nephrologists in our series, a situation similarly observed in other studies. The likelihood of this happening in other hospitals could be high. Therefore, we believe it is prudent to reinforce training in matters of hyponatremia already from medical schools, as well as during formation in medical specialties.