Hyponatremia, a frequent electrolyte imbalance, occurs when serum sodium levels drop below 135 mmol/L. It is commonly encountered in hospitalized patients, particularly those admitted to intensive care units (ICUs). It reflects an imbalance in water and sodium homeostasis and is often a marker of underlying disease severity rather than an isolated abnormality.

In critically ill patients, hyponatremia may develop due to multiple factors such as syndrome of inappropriate antidiuretic hormone secretion (SIADH), cardiac failure, liver cirrhosis, impaired kidney function, and administration of diuretics or intravenous fluid therapy.

The clinical manifestations of hyponatremia range from mild symptoms like nausea and malaise to severe neurologic deficits such as confusion, seizures, coma, and death, depending on the severity and rapidity of sodium decline. Furthermore, several studies have shown that hyponatremia is associated with increased morbidity, prolonged ICU stay, and higher mortality rates, especially in cases of acute or severe hyponatremia. However, whether hyponatremia is an independent prognostic marker or a surrogate for severe underlying illness remains under investigation.

Despite its clinical significance, hyponatremia remains under-recognized and under-treated in many intensive care settings, particularly in resource-limited environments. Timely identification and appropriate management of hyponatremia can help reduce complications and improve outcomes in critically ill patients. In India, there is a paucity of regional data exploring the prognostic implications of hyponatremia in ICU populations, especially in tertiary care settings of the Northeast region.

This study was undertaken to assess the prevalence of hyponatremia in ICU patients at Assam Medical College and Hospital and to evaluate its association with various clinical parameters and outcomes such as duration of ICU stay, mechanical ventilation requirement, presence of comorbidities, and mortality. Understanding these associations may aid in early risk stratification and better clinical decision-making in the management of critically ill patients with hyponatremia.

This observational study with a prospective design was conducted in the ICUs of Assam Medical College and Hospital, located in Northeast India. Conducted over a 12-month period from March 2023 to February 2024, the study aimed to assess the prognostic significance of hyponatremia in patients admitted to the ICU with critical illness.

The study population comprised adult individuals admitted to the ICU and diagnosed with hyponatremia, characterized by a serum sodium level below 135 mmol/L. Patients who were admitted to the ICU for more than 24 hours and had at least one recorded episode of hyponatremia either at admission or during their ICU stay were considered for inclusion.

Patients with hyperglycemia (blood glucose >300 mg/dL), those receiving mannitol or contrast agents, and cases of pseudohyponatremia due to hyperlipidemia or hyperproteinemia were excluded. Additionally, patients with terminal illness and expected survival less than 24 hours, as well as those unwilling to provide informed consent, were excluded from the study.

A total of 90 patients who met the inclusion criteria were enrolled. A structured case record form was used to collect data on demographics, clinical features, comorbidities, biochemical parameters, and outcomes. Parameters such as age, sex, primary diagnosis, presenting symptoms, comorbid conditions, serum sodium and potassium levels, blood urea, serum creatinine, and random blood sugar levels were documented.

The volume status of patients was clinically assessed and categorized as hypovolemic, euvolemic, or hypervolemic hyponatremia based on history, physical examination, and fluid balance. Hyponatremia was further classified based on severity into mild (130–134 mmol/L), moderate (125–129 mmol/L), and severe (<125 mmol/L). Patient outcomes, including ICU length of stay, need for mechanical ventilation, and in-hospital mortality, were documented.

Data were analyzed using Microsoft Excel and SPSS version 26.0. Descriptive statistics such as mean, standard deviation, frequencies, and percentages were used. Associations between categorical variables were tested using Chi-square or Fisher’s exact test. A p-value < 0.05 was considered significant. Ethical approval was obtained from the institutional Ethics Committee, and informed consent was taken from all participants or their legal guardians.

The study enrolled 90 critically ill patients with hyponatremia, most of whom were aged 61-0 years (34%), followed by those aged 4-60 years (20%) Males constituted the majority (74.4%). Among them, 43.3% had mild hyponatremia, 35.6%. had moderate, and 21.) had severe hyponatremia, Clinically, nausea and vomiting were the most common symptoms (32.2%), followed by irritability (28.9%), confusion (18.9%), seizures (17.8%), and coma (8.9%), while 16 patients (17.8%) were asymptomatic. Most patients (93.3%) had an ICL stay of less than 10 days. Mechanical ventilation was required in 69 patients (76.7%). Euvolemic hyponatremia was the most frequent (54.4%), with hypervolemic and hypovolemic types comprising 26.7% and [8%, respectively. The most common comorbidities were hypertension (25.6%) and diabetes mellitus (16.7%), with smaller proportions having chronic kidney disease, liver disease. or hypothyroidism. Among the study participants, 47 (52.2%) expired, while 43 (47.8%) survived. (Table 1)

Table 1. Demographic, Clinical, Hyponatremia-Related, and Outcome Characteristics of study participants (n=90)

Figure 1 illustrates the distribution of various comorbidities among survivors (n = 22) and non-survivors (n = 44). Hypertension (8 vs. 15) and diabetes mellitus (3 vs. 12) were more frequently observed among non-survivors. Chronic kidney disease and ‘other’ comorbidities also showed slightly higher prevalence in the non-survivor group. Although the differences were observed, they were not statistically significant, with the exception of diabetes mellitus, which showed a significant association (p= 0.018).

Figure 1. Distribution of Corrorbidities Among Survivors and Non-Survivers in Hyponatraemic ICL) Patients

Among the 90 critically ill patients with hyponatremia, a comparison between survivors and non-survivors revealed that input-output balance, hyponatremia severity, volume status, age, and gender did not show statistically significant associations with outcomes. Positive fluid balance was equally distributed in both survivors and non-survivors (40% each), while a slightly higher percentage of non-survivors had negative fluid balance (17.22%) compared to survivors (7.78%) (p = 0.3994). Although severe hyponatremia (<125 mEq/L) was more common in non-survivors (14.44%) than survivors (6.67%), the association between hyponatremia severity and outcome was not statistically significant (p = 0.1243). Similarly, volume status showed no significant difference between the groups (p = 0.4382), with euvolemia being the most common state among both survivors (28.89%) and non-survivors (25.56%).

However, the presence of comorbidities was significantly associated with outcome (p = 0.0379); 34.44% of non-survivors had comorbidities compared to only 21.11% of survivors. The most striking difference was observed in mechanical ventilator use, which was significantly higher among non-survivors (50%) than survivors (26.67%) (p < 0.0001), indicating a strong association with poor outcomes. Age distribution and gender did not show any significant correlation with survival. Most patients in both groups were in the 41–80 years age range (p = 0.4281 for age, p = 0.6315 for gender). These findings suggest that comorbidities and the need for mechanical ventilation are important prognostic indicators in critically ill hyponatremic patients.

Table 2. Clinical and Demographic Characteristics of Survivors and Non-Survivors in Critically III Hyponatraemic Patients (n = 90) Survivor Non-Survivor

Table 3 presents a comparison of the average vital parameters between survivors and non-survivors among critically ill hyponatraemic patients. Non-survivors exhibited a significantly higher mean systolic blood pressure (SBP) (135.38 23.33 mmHg) compared to survivors (124.42 +21.36 mmHg), with a p-value of 0.0227. Similarly. SpOs levels were lower in non-survivors (98.68±1.42%) than in survivors (99.33 1.02%), showing a significant difference (p=0.0158). The temperature was slightly higher in non-survivors (99.911.60°F) than in survivors (99.28 1.06°F), with a significant p-value of 0.0306. Although mean arterial pressure (MAP) and diastolic blood pressure (DBP) were higher in non-survivors, the differences were not statistically significant (p = 0.0535 and (0.1428, respectively). Other parameters, such as heart rate (HR) and respiratory rate (RR), did not show significant differences between the two groups. In conclusion, elevated SBP, temperature, and decreased SpO: were significantly associated with higher mortality in hyponatraemic ICU patients.

Table 4 presents the association of diagnosis, age, and mechanical ventilator use with the severity of hyponatremia in critically ill patients. Among various diagnoses, head injury was the most common across all severity levels, especially in mild (21.11%) and moderate (18.89%) cases, followed by respiratory causes and gastrointestinal losses. However, the association between diagnosis and severity of hyponatremia was not statistically significant (p = (0.6541).

In contrast, age showed a significant association with hyponatremia severity (p = 0.0417) Severe hyponatremia was more common in older patients, particularly those aged 161-80 years (8.89%), while milder forms were predominant in younger age groups (21-40 years). Use of mechanical ventilation increased with hyponatremia severity-26.67% of patients with mild, 31.11% with moderate, and 18.89% with severe hyponatrenia required ventilatory support. Although this trend was suggestive, it did not reach statistical significance (\mathfrak{p} = 0.0728) Overall, age emerged as a significant factor influencing hyponatremia severity, whereas diagnosis and ventilator use showed trends but were not statistically significant.

Table 3. Comparison of Key Vital Parameters in Survivors and Non-Survivors of Critically III Hypenatraemic Patients

Table 4. Relationship Between Diagnosis, Age, Mechanical Ventilator Use, and Hyponatremia Severity in Critically III Patients (n=90)

Patients with moderate hyponatremia had the longest mean ICU stay (5.34 4.25 days), followed by mild (4.97 ± 3.47 days), while those with severe hyponatremia had the shortest stay (2.89 1.94 days), though this difference was not statistically significant (p = 0.0586) significant association was observed between age and use of mechanical ventilation (p (0.0345), with higher ventilator use noted in patients aged 41-80 years.

Figure 1. Distribution of Corrorbidities Among Survivors and Non-Survivers in Hyponatraemic ICL) Patients

Among the 90 critically ill patients with hyponatremia, a comparison between survivors and non-survivors revealed that input-output balance, hyponatremia severity, volume status, age, and gender did not show statistically significant associations with outcomes. Positive fluid balance was equally distributed in both survivors and non-survivors (40% each), while a slightly higher percentage of non-survivors had negative fluid balance (17.22%) compared to survivors (7.78%) (p = 0.3994). Although severe hyponatremia (<125 mEq/L) was more common in non-survivors (14.44%) than survivors (6.67%), the association between hyponatremia severity and outcome was not statistically significant (p = 0.1243). Similarly, volume status showed no significant difference between the groups (p = 0.4382), with euvolemia being the most common state among both survivors (28.89%) and non-survivors (25.56%).

However, the presence of comorbidities was significantly associated with outcome (p = 0.0379); 34.44% of non-survivors had comorbidities compared to only 21.11% of survivors. The most striking difference was observed in mechanical ventilator use, which was significantly higher among non-survivors (50%) than survivors (26.67%) (p < 0.0001), indicating a strong association with poor outcomes. Age distribution and gender did not show any significant correlation with survival. Most patients in both groups were in the 41–80 years age range (p = 0.4281 for age, p = 0.6315 for gender). These findings suggest that comorbidities and the need for mechanical ventilation are important prognostic indicators in critically ill hyponatremic patients.

Table 2. Clinical and Demographic Characteristics of Survivors and Non-Survivors in Critically III Hyponatraemic Patients (n = 90) Survivor Non-Survivor

Table 3 presents a comparison of the average vital parameters between survivors and non-survivors among critically ill hyponatraemic patients. Non-survivors exhibited a significantly higher mean systolic blood pressure (SBP) (135.38 23.33 mmHg) compared to survivors (124.42 +21.36 mmHg), with a p-value of 0.0227. Similarly. SpOs levels were lower in non-survivors (98.68±1.42%) than in survivors (99.33 1.02%), showing a significant difference (p=0.0158). The temperature was slightly higher in non-survivors (99.911.60°F) than in survivors (99.28 1.06°F), with a significant p-value of 0.0306. Although mean arterial pressure (MAP) and diastolic blood pressure (DBP) were higher in non-survivors, the differences were not statistically significant (p = 0.0535 and (0.1428, respectively). Other parameters, such as heart rate (HR) and respiratory rate (RR), did not show significant differences between the two groups. In conclusion, elevated SBP, temperature, and decreased SpO: were significantly associated with higher mortality in hyponatraemic ICU patients.

Table 4 presents the association of diagnosis, age, and mechanical ventilator use with the severity of hyponatremia in critically ill patients. Among various diagnoses, head injury was the most common across all severity levels, especially in mild (21.11%) and moderate (18.89%) cases, followed by respiratory causes and gastrointestinal losses. However, the association between diagnosis and severity of hyponatremia was not statistically significant (p = (0.6541).

In contrast, age showed a significant association with hyponatremia severity (p = 0.0417) Severe hyponatremia was more common in older patients, particularly those aged 161-80 years (8.89%), while milder forms were predominant in younger age groups (21-40 years). Use of mechanical ventilation increased with hyponatremia severity-26.67% of patients with mild, 31.11% with moderate, and 18.89% with severe hyponatrenia required ventilatory support. Although this trend was suggestive, it did not reach statistical significance (\mathfrak{p} = 0.0728) Overall, age emerged as a significant factor influencing hyponatremia severity, whereas diagnosis and ventilator use showed trends but were not statistically significant.

Table 3. Comparison of Key Vital Parameters in Survivors and Non-Survivors of Critically III Hypenatraemic Patients

Table 4. Relationship Between Diagnosis, Age, Mechanical Ventilator Use, and Hyponatremia Severity in Critically III Patients (n=90)

Patients with moderate hyponatremia had the longest mean ICU stay (5.34 4.25 days), followed by mild (4.97 ± 3.47 days), while those with severe hyponatremia had the shortest stay (2.89 1.94 days), though this difference was not statistically significant (p = 0.0586) significant association was observed between age and use of mechanical ventilation (p (0.0345), with higher ventilator use noted in patients aged 41-80 years.

In this study involving 90 critically ill hyponatraemic patients, the mortality rate was found to be 52.2%, underscoring the clinical importance of this prevalent electrolyte disturbance in ICU environments. Although the severity of hyponatremia did not show a statistically significant association with mortality (p = 0.1243) , a trend toward poorer outcomes was observed in those with severe hyponatremia t < 125mEc / L * lambda which is consistent with findings from previous studies that reported increased morbidity and mortality in such cases [1.8] Waikar et al. found that both mild and severe hyponatremia were independently associated with higher in-hospital mortality, reinforcing the idea that even modest sodium deficits may worsen outcomes in hospitalized patients [5], la our study, patients with severe hyponatremia also had shorter ICU stays, possibly due to early deterioration or death, a pattern similarly reported by Mohan et al. [9]

Systolic blood pressure and oxygen saturation (SpO:) were significantly associated with survival outcomes tp = 0.0227 and p = 0.0158 respectively), highlighting the importance of hemodynamic and respiratory parameters as key prognostic indicators in hyponatracic patients. This indicates that hemodynamic and respiratory status play crucial roles as prognostic markers in hyponatraemic patients. Similar associations have been demonstrated in earlier studies, which identified hypotension, hypoxia, and altered mental status as indicators of worse outcomes in ICU patients with electrolyte disturbances [4]. Additionally, a statistically significant association was observed between comorbidities and mortality (p = 0.0379) Comorosities, including diabetes mellitus, hypertension, and chronic kidney disease, were more prevalent in non-survivors, emphasizing the increased risk these conditions contribute in the context of hyponatremia [10]. These findings are in Ene with other observational studies that have reported higher mortality in hyponatraemic patients with underlying chronic illnesses [6]

Mechanical ventilation was required significantly more often in nan-survivors (p < 0.0001) highlighting its strong correlation with a poor prognosis. This indicates that hyponatremia in critically ill patients may either reflect or exacerbate the decline in respiratory function. A multicenter study by Funk et al. also exhibited that the need for ventilatory support in hyponatraemic patients was a strong predictor of mortality [11]. Interestingly, while severity of hyponatremia did not significantly correlate with ventilator use (p=0.0728), age showed a significant association with both ventilator use (p=0.0345) and severity of hyponatremia ip 0.0417), suggesting that elderly patients may be more vulnerable to both sodium imbalance and associated complications [2]. This is consistent with the findings of Renneboog et al., who reported that elderly patients with mild hyponatremia face a higher risk of falls, cognitive impairment, and increased hospitalizations [12].

Although diagnosis (eg, head injury, sepsis, cardiac and renal causes) was not statistically associated with hyponatremia severity (p=0.6541), head injury remained the most frequent diagnosis across all severities. This could be due to SLADH and cerebral salt wasting, common in neurocritical care patients [13]. Overall, our study supports the role of age, comorbidities, and respiratory deterioration as key prognostic factors in hyponatraemic ICU patients However, due to the study's single-center design and small sample size, additioned multicentric studies are needed to confirm these findings and provide more robust data for refining management protocols.

Hyponatremia is a prevalent electrolyte imbalance in critically ill patients and is closely linked to high mortality rates. Although the severity of hyponatremia alone may not predict outcome, factors like older age, presence of comorbidities, and need for mechanical ventilation are strongly associated with poor prognosis. Early recognition and comprehensive management of these high-risk patients are essential to improve clinical outcomes in ICU settings.

Conflict of Interest: None declared.

Funding: No external funding received.

1. Adrogué HJ, Madias NE. Hyponatremia. N Engl J Med. 2000;342:1581–9.
2. Hoorn EJ, Zietse R. Hyponatremia and the brain. JASN. 2017;28:1340–9.
3. Liamis G, Milionis HJ, Elisaf M. Hyponatremia in patients with infectious diseases. J Infect. 2011;63:327–35.
4. Spasovski G et al. Clinical Practice Guideline on diagnosis and treatment of hyponatremia. Nephrol Dial Transplant. 2014;29(Suppl 2):i1–39.
5. Waikar SS et al. Mortality after hospitalization with hyponatremia. Am J Med. 2007;122:357–65.
6. Corona G et al. The economic burden of hyponatremia. Am J Med. 2016;129:823–35.e4.
7. Rafat C et al. Hyponatremia in ICU: how to avoid Zugzwang. Ann Intensive Care. 2015;5:39.
8. Upadhyay A et al. Incidence and prevalence of hyponatremia. Am J Med. 2006;119:S30–35.
9. Mohan S et al. Hyponatremia and ICU outcomes. Crit Care Med. 2013;41:1621–7.
10. Verbalis JG et al. Expert panel recommendations on hyponatremia. Am J Med. 2013;126:31–42.
11. Funk GC et al. Dysnatremias on ICU admission. Intensive Care Med. 2010;36:304–11.
12. Renneboog B et al. Mild chronic hyponatremia and falls. Am J Med. 2006;119:71.e1–8.
13. Sherlock M et al. Hyponatremia after subarachnoid hemorrhage. Clin Endocrinol (Oxf). 2006;64:250–4.