Every year, hospital errors kill 210,000 to 440,000 patients, making it the third leading cause of death in the United States, after heart disease and cancer. Short staffing at hospitals is one of the primary causes of errors.

But there is a way to avoid understaffed hospitals — by knowing when staff will be thin. Here’s how to avoid this predictable danger:

• Schedule your procedure early in the week. Mondays and Tuesdays are best. Avoid Thursdays, Fridays, and weekends.

• Ask to have your surgery scheduled for early in the morning. Outcomes are usually better for morning procedures.

• Don’t schedule on a major holiday. Avoid especially the week between Christmas and New Year’s, when surgeons are apt to be on vacation. Also avoid the first week of January, which is a very busy time in most hospitals. Delay the procedure until mid-January, when staffing levels and patient loads are back to normal.

• Ask information about the nurse-to-patient ratio for the time you are thinking of scheduling it. There should be one nurse for every four patients in a surgical unit.

• Make sure you will be assigned to a room in the correct unit after surgery. If you had cardiac surgery, for instance, make sure you will be assigned to that ward and not to a urology unit or some other area of the hospital. You may not receive appropriate care in the wrong unit, and that could lead to serious medical problems.