Does preoperative hyponatremia potentiate the effects of left ventricular dysfunction on mortality after cardiac surgery?

Association of preoperative hyponatremia with surgical outcomes: a systematic review and meta-analysis of 32 observational studies

BACKGROUND

Preoperative hyponatremia is prevalent in patients undergoing surgical procedures, but it is uncertain if hyponatremia will lead to increased risk of surgical mortality and morbidity.

METHODS

A systematic search of Medline (PubMed), Embase and Cochrane Library from inception till 2 July 2021 was performed. Full length articles that reported on the association between surgical outcomes among adults ≥18 years with documented preoperative hyponatremia were included.

FINDINGS

We identified 32 observational studies comprising 1,301,346 participants. All studies had low risk of bias. When adjusted for covariates, patients with hyponatremia had significantly higher odds of developing major complications (defined as a composite measure of 9 major complications) compared to patients with normal sodium concentrations (aOR =  1.37, 95%CI = 1.23-1.53, I2 = 78%. N = 10). Additionally, patients with preoperative hyponatremia also significantly higher hazards of early mortality (<90 days) compared to patients with normonatremia (aHR = 1.27, 95%CI = 1.13-1.43, I2 = 97%. N = 10) after adjustment for covariates. Preoperative hyponatremia also had significant associations with respiratory, renal and septic complications. In terms of prognostic performance, preoperative hyponatremia performed adequately in predicting major complications in surgical patients (AUC = 0.70, LR- 0.90) with a specificity of 88% and a sensitivity of 25%.

INTERPRETATION

Our meta-analysis suggests that preoperative hyponatremia is associated with poorer early mortality and major morbidity outcomes in surgical patients. Hyponatremia is also a specific prognosticator for major complications in surgical patients, reiterating its potential use as a clinical indicator of poor outcomes.

Preoperative hyponatremia and survival after left ventricular assist device implantation

BACKGROUND

Hyponatremia is associated with adverse outcomes in heart failure and after cardiac surgery. We hypothesized that hyponatremia is associated with poorer short-term and longer-term survival in patients after continuous-flow left ventricular assist device (CF-LVAD) placement.

METHODS

We reviewed a single-center database of patients who received a CF-LVAD during 2012-2017. Sodium (Na) values obtained within 14 days before CF-LVAD insertion were averaged; patients (n=332) were divided into hyponatremia (mean Na <135 mEq/L; n=160; 48.2%) and normonatremia groups (mean Na 135-145 mEq/L; n=172; 51.8%). Patients requiring preoperative dialysis or pump exchanged were excluded. We compared outcomes between preoperative hyponatremia and normonatremia groups.

RESULTS

The two groups' baseline characteristics were similar, although hyponatremia patients more often had preoperative mechanical circulatory support (44.4% vs 31.4%, p=0.002). Although hyponatremic and normonatremic patients did not differ in 30-day mortality (7.5% vs 6.5%, p=0.7), preoperative hyponatremia was associated with greater 5-year mortality (61% vs 44%, p=0.03). On binary logistic regression analysis, the strongest independent predictors of late mortality were hyponatremia (odds ratio [OR] 1.88, 95% CI [1.07-3.31], p=0.02), older age (OR 1.03, 95% CI [1.01-1.05], p=0.01), and elevated mean right atrial pressure/pulmonary capillary wedge pressure ratio (OR 4.69, 95% CI [1.76-12.47], p=0.002).

CONCLUSIONS

Hyponatremia was not associated with greater early mortality but was associated with poorer late survival. Optimal timing of LVAD implantation in relation to hyponatremia, and whether correcting hyponatremia perioperatively improves long-term survival, should be investigated.

Elevated serum sodium in recipients of liver transplantation has a substantial impact on outcomes

Dysnatremias are a rare but significant event in liver transplantation. While recipient pre-transplant hypernatremia has been demonstrated to increase post-transplant mortality, the degree of hypernatremia and the impact of its resolution have been less well characterized. Here, we used multivariate Cox regression with a comprehensive list of donor and recipient factors in order to conduct a robust multivariate retrospective database study of 54,311 United Network for Organ Sharing (UNOS) liver transplant patients to analyze the effect of pre-transplant serum sodium on post-transplant mortality, post-transplant length of hospitalization, and post-transplant graft survival. Mortality and graft failure increased in a stepwise fashion with increasing pre-transplant hypernatremia: 145 -150 mEq/L (HR = 1.118 and HR = 1.113), 150-155 mEq/L (HR = 1.324 and HR = 1.306), and > 155 mEq/L (HR = 1.623 and HR = 1.661). Pre-transplant hypo- and hypernatremia also increased length of post-transplant hospitalization: < 125 mEq/L (HR = 1.098), 125-130 mEq/L (HR = 1.060), 145 -150 mEq/L (HR = 1.140), and 150-155 mEq/L (HR = 1.358). Resolution of hypernatremia showed no significant difference in mortality compared with normonatremia, while unresolved hypernatremia significantly increased mortality (HR = 1.254), including a durable long-term increased mortality risk for patients with creatinine < 2 mg/dL and MELD < 25. Pre-transplant hypernatremia serves as a morbid prognostic indicator for post-transplant morbidity and mortality.

Sodium Abnormalities in Cardiac Surgery With Cardiopulmonary Bypass in Adults: A Narrative Review

Perioperative sodium abnormalities or dysnatremia is not uncommon in patients presenting for cardiac surgery and is associated with increased morbidity and mortality. Both the disease process of heart failure and its treatment may contribute to abnormalities in serum sodium concentration. Serum sodium is the main determinant of serum osmolality, which in turn affects cell volume. Brain cells are particularly vulnerable to changes in serum osmolality because of the nondistensible cranium. The potentially catastrophic neurologic sequelae of rapidly correcting chronic dysnatremia and the time-sensitive nature of cardiac surgery can make the management of these patients challenging. The use of cardiopulmonary bypass to facilitate surgery adds another layer of complexity in the intraoperative management of sodium and water balance. This narrative review examines the definition and classification of dysnatremia. It also covers the etiology and pathophysiology of dysnatremia, implications during cardiac surgery requiring cardiopulmonary bypass, and the perioperative management of dysnatremia.

Hyponatremia associated with long-term medication use in the elderly: an analysis in general practice

INTRODUCTION The aim of this study is to determine the prevalence of hyponatremia, its association with long-term medication use and underlying chronic conditions, the rate of hospitalisation and death within 3 months from its discovery and its management in community-dwelling older people. METHODS One year of data for ~5635 patients aged >65 years was extracted from the databases of 19 general practitioners (GPs); 2569 (45.6%) were checked for hyponatremia. RESULTS Hyponatremia occurred in 205 (8.0%) of 2569 checked individuals: 78.5% (161/205) had hypertension, 31.2% (64/205) diabetes, 23.9% (49/205) chronic renal failure; 38.0% (78/205) received diuretics, 36.6% (75/205) renin-angiotensin system antagonists (ACE-I/ARB) and 9.8% (20/205) serotonin reuptake inhibitors. Drug consumption was higher in hyponatremic patients, although only diuretics, ACE-I/ARB, anti-arrhythmics and opioids were significantly associated with hyponatremia. The likelihood of hyponatremia trebled when four drugs were taken, and it was seven-fold higher with the use of six drugs. Hyponatremia was associated with a higher prevalence of chronic illnesses and higher rate of hospitalisation (13.7% vs 7.7%, P = 0.005) and death (3.9% vs 1.8%, P < 0.035). The use of at least one long-term medication was associated with hospitalisation or death in hyponatremic patients (10% vs 6.3%, P = 0.010). Less than 20% of hyponatremic patients had their sodium level checked again after 1 month. DISCUSSION Hyponatremia is not uncommon among community-living older patients, especially in patients taking medications potentially causing hyponatremia. Hyponatremic patients are likely to encounter more serious events, including hospitalisation and death. Targeted training of GPs is desirable to improve their practice.

Hyponatremia Predicts Poor Outcomes in Patients With Chronic Kidney Disease Undergoing Heart Operation

BACKGROUND

Preoperative hyponatremia adversely affects outcomes of cardiothoracic operation. However, in patients with chronic kidney disease, the association of sodium levels on postoperative events has never been evaluated. We investigated the impact of preoperative hyponatremia on outcomes after cardiac operation in patients with non-dialysis-dependent chronic kidney disease. Primary end points were operative mortality and acute kidney injury that required dialysis. Secondary end points were major infection and long-term survival.

METHODS

The study is observational and includes all patients with stage III to IV chronic kidney disease (non-dialysis) undergoing cardiac operation between February 2000 and January 2016. Patients were stratified into two groups by preoperative sodium levels: sodium less than 135 mEq/L and sodium of 135 mEq/L or more.

RESULTS

There were 1,008 patients (mean estimated glomerular filtration rate [GFR]: 43 ± 14 mL • min^-1 • 1.73 m^-2) with 92 patients (9%) in the low-sodium group. Patients with low sodium had higher operative mortality (p = 0.0004), need for new dialysis (p = 0.0008), and infection (p = 0.002). Predictors of operative mortality were European System for Cardiac Operative Risk Evaluation (EuroSCORE) (hazard ratio [HR] 1.03. 95% confidence interval [CI]: 1.02 to 1.05, p < 0.0001), decreasing values of sodium (HR 1.14. 95% CI: 1.07 to 1.2, p = 0.0002), and decreasing values of GFR (HR 1.01, 95% CI: 1.003 to 1.03, p = 0.007). Sodium less than 135 mEq/L was independently associated with increased need for dialysis (HR 1.3, 95% CI: 1.1 to 1.7, p = 0.0008). By linear regression, decreasing values of preoperative sodium were proportionate to the incidence of operative mortality (p < 0.0001) and need for dialysis (p < 0.0001).

CONCLUSIONS

Preoperative hyponatremia is a predictor of increased mortality and other adverse events in patients with non-dialysis-dependent chronic kidney disease undergoing cardiac operation. These findings are similar to those in hyponatremic patients without kidney disease.

The Economic Burden of Hyponatremia: Systematic Review and Meta-Analysis

BACKGROUND

Hyponatremia is the most common electrolyte abnormality observed in clinical practice. Several studies have demonstrated that hyponatremia is associated with an increased length of hospital stay and of hospital resource utilization. To clarify the impact of hyponatremia on the length of hospitalization and costs, we performed a meta-analysis based on published studies that compared hospital length of stay and cost between patients with and without hyponatremia.

METHODS

An extensive Medline, Embase, and Cochrane search was performed to retrieve all studies published up to April 1, 2015 using the following words: "hyponatremia" or "hyponatraemia" AND "hospitalization" or "hospitalisation." A meta-analysis was performed including all studies comparing duration of hospitalization and hospital readmission rate in subjects with and without hyponatremia.

RESULTS

Of 444 retrieved articles, 46 studies satisfied the inclusion criteria, encompassing a total of 3,940,042 patients; among these, 757,763 (19.2%) were hyponatremic. Across all studies, hyponatremia was associated with a significantly longer duration of hospitalization (3.30 [2.90-3.71; 95% CIs] mean days; P < .000). Similar results were obtained when patients with associated morbidities were analyzed separately. Furthermore, hyponatremic patients had a higher risk of readmission after the first hospitalization (odds ratio 1.32 [1.18-1.48; 95% CIs]; P < .000). A meta-regression analysis showed that the hyponatremia-related length of hospital stay was higher in males (Slope = 0.09 [0.05-0.12; 95% CIs]; P = .000 and Intercept = -1.36 [-3.03-0.32; 95% CIs]; P = .11) and in elderly patients (Slope = 0.002 [0.001-0.003; 95% CIs]; P < .000 and Intercept = 0.89 [0.83-0.97; 95% CIs]; P < .001). A negative association between serum [Na(+)] cutoff and duration of hospitalization was detected. No association between duration of hospitalization, serum [Na(+)], and associated morbidities was observed. Finally, when only US studies (n = 8) were considered, hyponatremia was associated with up to around $3000 higher hospital costs/patient when compared with the cost of normonatremic subjects.

CONCLUSIONS

This meta-analysis confirms that hyponatremia is associated with a prolonged hospital length of stay and higher risk of readmission. These observations suggest that hyponatremia may represent one important determinant of the hospitalization costs.