Low calcium dialysate associated with sudden cardiac arrest

From Medscape Medical News
Low Calcium Dialysate During Hemodialysis and Sudden Cardiac Arrest

Rod Franklin

November 24, 2010 (Denver, Colorado) — Sudden cardiac arrest (SCA) is the most common cause of death among patients with end-stage renal disease (ESRD) on hemodialysis; it occurs at a rate 30 times greater than in the general population. But research presented here at Renal Week 2010: American Society of Nephrology 43rd Annual Meeting suggests that modifications of dialysate prescriptions, particularly with regard to calcium levels, can help mitigate SCA risk.

The results of the study were also published online September 1 in Kidney International.

In an abstract presented as a follow-up to their 2009 study on alterations of dialysate prescriptions for ESRD patients, researchers from the Duke University Medical Center Division of Nephrology in Durham, North Carolina, reported that reduced calcium dialysate levels are associated with increased risk for SCA, despite published guidelines suggesting that calcium dialysate concentrations be lowered as a means of controlling vascular complications and soft tissue calcification.

Recommendations promulgated by the National Kidney Foundation Kidney Disease Outcome Quality Initiative in 2000 suggested a reduction of calcium dialysate levels to 2.5 mEq/L. The recent Duke University study, led by Patrick H. Pun, MD, showed, however, that such adjustments are likely to worsen the prolongation of QT intervals, which has been acknowledged as a source of increased risk for ventricular tachyarrhythmias and sudden death.

Secondarily, their clinical trial showed that low calcium concentrations in dialysate can be a promoter of arrhythmias.

The researchers suggest that inherent or acquired cardiac disturbances, along with low potassium dialysates (odds ratio [OR], 2.9; 95% confidence interval [CI], 1.9 - 4.3), exposure to medications aimed at mitigating QT prolongation, and calcium absorption related to bone remodeling, should be considered when attempting to determine an optimal dialysate calcium prescription.

A weighing of these considerations against each other as causal SCA factors was not included in the study protocol. For instance, the research did not indicate whether bone turnover is considered a less significant initiator of SCA than other identified SCA promoters.

"Proponents of using lower calcium dialysate often cite concerns about low-turnover bone disease or soft tissue calcification," coinvestigator John Middleton, MD, associate professor in the Division of Nephrology, told Medscape Medical News in written correspondence. "Our study did not directly address bone turnover."

Moreover, the study did not assess whether adjusting coincident medications mitigated risk for SCA by reducing QT prolongation. "Our study only addressed cardiac arrests that occurred within dialysis clinics; thus, the risk factors we identified only apply to a fraction of clinical events," Dr. Middleton said. "However, they are variables that are potentially modifiable by clinicians."

The Duke researchers previously reported that in approximately 800 patients who experienced SCA while under observation in outpatient hemodialysis clinics, the 30-day survival rate was 19% and the 1-year survival rate was 9%.

SCA risk was assessed after adjustment for patient variabilities in demographics, comorbidity, serum calcium levels, and other baseline characteristics. The Duke team compared clinical and dialysis-specific data for 502 patients who experienced SCA with 1632 age- and dialysis-vintage-matched control patients.

They identified a rate of 4.5 SCA events per 100,000 dialysis treatments during the 3-year study period. They also noted other factors that look to be strongly associated with SCA in multivariable analyses, including increased ultrafiltration volumes and predialysis serum creatinine levels.

The scientists were particularly interested in modifiable elements of the hemodialysis procedure, such as rapid fluid and electrolyte shifts, which they suspect might play a larger role in peridialytic SCA risk than preexisting risk factors.

The principal findings of the original Duke study include the following:

* There was no evidence of a strong relation between traditional cardiac arrest risk factors, such as congestive heart failure, coronary heart disease, and a history of cardiac arrhythmia, and the occurrence of peridialytic SCA.
* The composition of dialysate, specifically with regard to potassium or calcium concentrations, was influential in predicting SCA risk. These relations persisted even after adjustment for preexisting cardiac comorbidities and predialysis serum electrolyte levels.
* Ultrafiltration of consistently large volumes during hemodialysis was an important risk factor for peridialytic cardiac arrest.
* Lower serum creatinine levels were a strong predictor of SCA.
* There were significant relations between oral and injectable medications and SCA.

Taken together, these observations suggest that modifications of hemodialysis procedures can improve the cardiovascular risk profile of patients with ESRD, the researchers report. Traditional factors, such as history of coronary heart disease and congestive heart failure, were not shown to be significantly influential.

The researchers have disclosed no relevant financial relationships.

Renal Week 2010: American Society of Nephrology 43rd Annual Meeting: Abstract TH-FC035. Presented November 20, 2010.

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