The WHO defines a fall as the consequence of an involuntary event resulting in the person coming inadvertently to the ground.1

Falling is one of the risks patients have during their hospital stay. Even when falls do not cause injury, they may have a negative effect in elderly adults: restricting their physical activity and increasing the risk of another fall.2 Twenty-seven per cent (27%) of adults over the age of 65 fall once a year and 15% fall more than once a year.3

Falls are an important cause of morbidity and mortality, especially in people over the age of 65.1,4–7 There is evidence that 3.7% of hospitalised patients in Spain experience a fall,8 and intrinsic and extrinsic factors are involved in its aetiology.9 In a controlled hospital environment, accidental falls attributable to an extrinsic factor are much less common than non-accidental falls attributable to an intrinsic factor.2 The intrinsic factors include age-related physiological alterations, acute or chronic diseases, altered consciousness, difficulty walking and medication.10 Implementing and evaluating fall prevention protocols forms part of the safety strategy in the care of hospitalised patients.8

As there are multiple, predisposing physical risk factors for falls, it is essential to evaluate the risk of patients who have a fall to thus ensure that all the possible factors have been assessed.2 This risk is currently measured according to different scales in the hospitals in our setting. The scale used most often is the Downton Fall Risk Index,11 which does not include acute hyponatraemia among the items assessed. The manifestations of acute hyponatraemia include lethargy, confusion, gait instability, cognitive impairment and loss of consciousness.5,12,13 New evidence also associates hyponatraemia with bone demineralisation, recurrent falls and fractures; thus it should be considered an important independent risk factor for falls.5,6,14

Therefore, it must be determined whether hyponatraemia may be a risk factor to be systematically assessed and included in fall prevention protocols. Thus, the objective of this study is to determine whether hyponatraemia is a risk factor for falls in the hospitalised population over the age of 65.

During the study period 4415 patients were admitted and 135 falls occurred. Table 1 describes the sociodemographic and clinical variables of the groups of cases and controls, and shows that there were no statistically significant differences between the two groups with regard to these variables, so the groups were homogenous.

In terms of the fall results, Table 2 shows that more than half of the falls had no consequences and only one resulted in a wound that needed to be sutured. The rest of the environmental characteristics and the time of the fall suggest that the greatest number of falls occurred in the patient's room, when he or she was walking around and the most typical safety devices were in place.

Tables 3 and 4 show the results of the bivariate analysis. Table 3 shows the values of the factors that did not have statistical significance, and Table 4 shows those that did obtain a statistically significant relationship and were subsequently included in the regression model.

Once the data had been analysed with the logistic regression model and any possible confounding factors had been removed, we found an association between falls and the following variables: sensory impairment in extremities and hyponatraemia (Table 5).

In this study we found an association between hyponatraemia and falls. We also showed the relationship between falls and sensory impairment in the extremities. This association was independent from other factors, such as: medications, auditory impairment in communication or visual impairment and continence problems. Therefore, it can be concluded that hyponatraemia is a risk factor for falls.

The manifestations of acute hyponatraemia include lethargy, confusion, gait instability and loss of consciousness. These are all symptoms that are assessed using the Downton fall risk index, but they are not identified as symptoms of a disease requiring early treatment, such as hyponatraemia; rather, they are considered to be symptoms related to patient's age and physical status that lead to the application of restrictive measures and adapting the environment to prevent falls. Additionally, hyponatraemia has traditionally been considered asymptomatic and its treatment, unnecessary.5,12,13

In view of our results, patients should be evaluated clinically including in the differential diagnosis whether the symptoms and risk factors presented are due to a state of hyponatraemia or other reasons.

Until 2006, only one study had investigated the association between falls and the presence of hyponatraemia.5,6,15 In recent years, studies have emerged demonstrating that hyponatraemia is an important independent risk factor for falls and is related to fractures.5,6,16 The results obtained are consistent with these conclusions, considering hyponatraemia and sensory impairment to be risk factors that directly impact falls.

In Spain, approximately 30% of people over the age of 65 fall once a year, and, of these, 50% fall again in the same year.2,3 Given this high prevalence and considering that falls are more common in institutionalised elderly patients,2 the conclusions of this study take on special clinical relevance: there are great repercussions in the safety of the most vulnerable patients, as falls are an important source of comorbidity and deterioration in quality of life.3

Certain physical conditions and environmental situations have been described in the literature which are predisposing factors for falls and can be modified, such as the intake of some drugs, activity level and the environment.2 Therefore, while elderly patients are hospitalised they should be routinely asked about falls, the risk should be evaluated and the underlying factors susceptible to change should be approached.

According to the Pharmacovigilance centre of the Community of Madrid, since the year 1992 there has been a 70% increase in the cases of hyponatraemia attributable to drugs, and half of these cases occurred in patients over the age of 75. The most related drugs are antidepressants (33%), diuretics (35%), desmopressin (28%) and antiepileptic drugs (26%). However, in our study we did not find a direct relationship between taking drugs and falls.

The need and importance of implementing programmes that guarantee patient safety is incontestable, including fall prevention.8,17 To this end, effective tools must be created to assess the risks factors for falls in hospitalised patients.

In view of the above, and as a result of the data provided by this study, we believe that hyponatraemia is a risk factor for falls and serum sodium should be determined and included in the falls risk assessment scales, and be part of the fall prevention strategies in the elderly.

Lastly, it should be highlighted that efficiency has become one of the main concerns of healthcare managers, which has led to a major upsurge in financial assessment analyses in the last decade. Therefore, since healthcare costs must be considered among the reasons for implementing the measures proposed, we believe that cost studies should be conducted, enabling us to evaluate the efficiency of including serum sodium measurements in fall risk scales.

The authors have no conflicts of interest to declare.