The telemetry unit nurse is reviewing laboratory results for a client who is scheduled for an operative procedure later in the day. The nurse notes on the laboratory report that the client has a serum potassium level of 6.5 mEq/L (6.5 mmol/L), indicative of hyperkalemia. The nurse informs the health care provider of this laboratory result because the nurse recognizes hyperkalemia increases the client's operative risk for: