ReviewThe relevance of hyponatraemia to perioperative care of surgical patients
Introduction
Hyponatraemia is usually defined as a serum sodium level below-135 mmol/l and it is the most common electrolyte disturbance found in clinical practice.1 The prevalence of hyponatraemia at the time of hospital admission varies between 2 and 5%, but in some series, up to 30% of in patients have been reported to be affected.2 In comparison with patients with normal serum sodium levels, patients who develop hyponatraemia have been reported to have an increase in mortality rate,3, 4, 5 longer duration of hospital stay,4, 6 higher readmission rate and increased direct and indirect costs associated with their care.6
Although hyponatraemia has traditionally been viewed as a condition relevant to internal medicine, and managed principally by endocrinologists, nephrologists and geriatricians, there is an increasing evidence base which documents the relevance of hyponatraemia to the perioperative management of surgical patients. Firstly, hyponatraemia is common in the peri-operative period. In a recent observational study of over a million patients undergoing major surgery, 7.8% of patients presented with preoperative hyponatraemia. Hyponatraemia in this large cohort was particularly common in patients undergoing cardiac surgery (11.8%), perhaps because of the high rate of diuretic therapy in cardiac patients. However, hyponatraemia was also common in patients presenting for vascular surgery (11.2%), with lower rates in patients admitted for general surgical procedures (7.5%), orthopaedic operations (7.1%), and other (6.1%) procedures. Patients with hyponatraemia tended to be older, male and with higher rates of comorbid conditions; hyponatraemia was also commoner in patients admitted for urgent surgery. The authors concluded that hyponatraemia was associated with increased morbidity, including increased risk of coronary events, pneumonia and wound infection, and higher mortality and prolonged length of stay.7 It was not clear whether the increased morbidity was related to the hyponatraemia per se, or whether hyponatraemia was simply a marker for patients with complex co-morbidities which predisposed them to worse outcomes. The results of this study have been reproduced in other small surgical studies and subgroup analyses,4, 8 which emphasizes the risk of perioperative complications associated with preoperative hyponatraemia. Hyponatraemia is also common in a variety of neurosurgical conditions such as traumatic brain injury (20%), subarachnoid haemorrhage (50%) and transsphenoidal hypophysectomy (10%).9 There is also evidence that patients admitted to surgical-ICUs are at high risk of developing hyponatraemia, with higher prevalence rates following organ transplantation, cardiovascular procedures and surgery for trauma or gastroenterological conditions.10
The second issue with hyponatraemia is the poorer outcome when plasma sodium concentration drops perioperatively. Studies in surgical patients entering intensive care units have demonstrated a clear association of worse surgical outcomes, including excess mortality, with post-operative hyponatraemia.11 Furthermore, symptomatic hyponatraemia predisposes the patient to gait instability,12 frequent falls12 and increased fracture rate,13 complications which compromise post-operative rehabilitation, particularly in the elderly. Preoperative evaluation and appropriate management of hyponatraemia offers the opportunity to improve perioperative care,14 to assess surgical risk and to individualize the treatment including type and amount of fluids used for each patient.15
For these reasons, hyponatraemia is relevant to surgical patients, and therefore to surgeons. In this review we will discuss the differential diagnosis of hyponatraemia, and explain the specific relevance of hyponatraemia to pre-, peri- and post-operative care.
Section snippets
Differential diagnosis of hyponatraemia
There are a large number of different syndromes which may lead to the development of hyponatraemia. The treatment of hyponatraemia depends on the underlying aetiology so it is of paramount importance to be accurate in diagnosing the cause of the biochemical abnormality; inaccurate diagnosis leads to inappropriate and potentially damaging treatment. There are a number of clinical algorithms available to aid the approach to the patient with hyponatraemia, some of which give simple guidelines,
Symptoms and morbidity associated with hyponatraemia
Although symptoms are related to the severity of hyponatraemia, itself, the rapidity of the fall in plasma sodium concentration is far more important in determining the likelihood of neurological symptoms Chronic hyponatraemia, which is seen in many elderly patients, may have relatively few symptoms, as the brain adapts to hyponatraemia over time. In contrast, acute hyponatraemia, occurring over <48 h, is much more likely to develop neurological symptoms, due to osmotic movement of water from
Hyponatraemia in the preoperative evaluation
Plasma sodium concentrations between 130 and 135 mmol/l are unlikely to be associated with serious perioperative sequelae, unless they are a mild biochemical manifestation of a more serious problem such as undiagnosed hypopituitarism. However, lower plasma sodium concentrations (<130 mmol/l) should prompt clinical questions regarding the safe management of the patient around surgery.
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Is the patient symptomatic? If the patient has symptoms of cerebral irritation, such as diminished conscious
Postoperative management
Post-operative hyponatraemia is common and the pathophysiology is often multifactorial and complex. Surgery is associated with non-osmotic release of the anti-diuretic hormone, vasopressin, and in conjunction with intravenous hypotonic fluid administration or excess isotonic fluids, this can cause dilutional hyponatraemia. Potent non-osmotic stimuli, like positive pressure ventilation, stress, nausea and vomiting, hypoglycemia, fever, or a decrease in intravascular volume are commonly found in
Summary
Hyponatraemia has been underestimated as a cause of morbidity and mortality in surgical patients. We believe that improved surgical outcomes will arise from appropriate peri-operative management of hyponatraemia, though there is a paucity of intervention data to confirm this statistically. Management of hyponatraemia in surgical wards needs good collaboration between surgical teams and anaesthetists, endocrinologists and nephrologists. Greater understanding of the relevance of hyponatraemia to
Case 1
A 70 year old man with stable mild hyponatraemia due to idiopathic SIADH was admitted for TURP. The anaesthetist cancelled surgery because of concerns that intravenous fluids perioperatively would worsen hyponatreamia and risk seizures. They recommended discharge and readmission after two months of fluid deprivation. Endocrine consultation recommended Tolvaptan therapy; administration of 15 mg day caused a steady rise in plasma sodium from 124 to 133 mmol/l over two days; Tolvaptan therapy was
Case 2
A 28 year old man underwent coiling for an anterior communicating artery aneurysm which had ruptured, causing subarachnoid haermorrhage. On day three post-procedure his GCS had fallen to 9/15 and the patient could not engage with physiotherapy. Plasma sodium had fallen acutely from 142 mmol/l on admission to 121 mmol/l three days post-op. The neurosurgeons were unsure whether the diminished conscious level was attributable to hyponatraemia or further subarachnoid bleed. Tolvaptan, 30 mg daily
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Impact of hyponatremia on mortality and morbidity in patients with COPD exacerbations
2016, Respiratory MedicineCitation Excerpt :Hyponatremia is the most common electrolyte disorder in hospitalized patients, with a prevalence ranging between 15% and 37% depending on the definition, population and healthcare system [1–5]. However, the most accepted lower limit of normality for serum sodium is 135 mEq/L. Below this value there is growing evidence that hyponatremia associates with increased morbidity, mortality and health costs in different clinical scenarios and diseases, including heart failure, myocardial infarction, lung diseases, stroke, cancer, cirrhosis, pulmonary embolism and hypertension, chronic renal failure and the postoperative period [6–25]. The initial symptoms of acute hyponatremia include nausea, vomiting and headaches.
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2016, Endocrinologia y NutricionCitation Excerpt :However, data supporting the use of tolvaptan for SIADH in neurosurgical patients is scarce. We have used oral tolvaptan in a patient with SAH complicated by symptomatic SIADH, and reduced Glasgow Coma Score (9/15); steady improvement in plasma sodium concentration over 48 h was associated with improved cognition, such that the patient was able to engage with rehabilitation and be discharged from hospital.59 Nevertheless, there is need for new prospective studies with oral tolvaptan compared to other established therapies for SIADH in the neurosurgical setting.