A 43-year-old woman develops acute renal failure following an emergency resection of a leaking abdominal aortic aneurysm.Three days after surgery, the following laboratory values are obtained:* Serum electrolytes (mEq/L): Na+:127;K+:5.9;Cl-:92;HCO3-:15* Blood urea nitrogen: 82 mg/dL* Serum creatinine: 6.7 mg/dLThe patient has gained 4 kg since surgery and is mildly dyspneic at rest. Eight hours after these values are reported, the electrocardiogram shown below is obtained. The initial treatment for this patient should be