This is a very good question to be asking. Actually, Norma M. Metheny addresses this subject in the first pages of her book Fluid & Electrolyte Balance: Nursing Considerations
. The answer to your question "should intake & output totals equal each other" is both yes and no. Strictly speaking, in theory, yes, the intake should equal the output. However, it is almost nearly impossible to be able to accurately measure all the output from a person's body. This is because of insensible
fluid losses through the skin and the lungs. This is water that evaporates and cannot be seen or detected with the naked eye. According to Metheny this amounts to approximately 900mL/day (600mL through the skin and 300mL through the lungs). Because we have no accurate way to measure it, we can't include it in our I&O measurements, but we do need to be aware of it.
So, in a more real sense the answer to your question is no. Intake should be more than the output. Theoretically, if you included the insensible fluid loss, your intake should equal your output. But, we do not do that
. Keep in mind that we only report the facts. So you only record the fluid that you have measured and that you know for sure have gone into the patient and come out of the patient.
In general, you contact the doctor when there is fluid retention (too little urine coming out compared to the fluids being taken in). Keep in mind that you are going to notify the doctor when you expect the doctor to order some sort of intervention. You need to assess not only the I&O but it would also be a good idea to have a baseline body weight to compare a current weight to. One pound of weight gain is generally thought to be equivalent to one liter (1000mL) of fluid. You should also assess the situation before calling the doctor and look for symptoms of fluid volume excess:
- elevated B/P
- distended neck veins and bounding pulse
- crackles auscultated in the lungs
- the development of edema, anasarca or ascites
- electrolyte imbalances in the labwork
The lower limit of normal urine output is considered to be 30mL of urine per hour. This can be sustained for some days until the kidneys will begin to react. I'm also finding references saying that oliguria is defined as producing less than 500mL of urine in a 24 hour period. That is about 20mL per hour of urine.
If the patient is putting out way more urine than the fluid being taken in, assess the situation and check to see if diuretics are being given. When there is diabetes insipidus, the huge urine outputs are usually quite astounding and difficult to miss because these patients put out a whopping 8 to 10 liters of urine a day! Besides losing the water, they are also losing electrolytes. Without equivalent fluid and electrolyte replacement they become dehydrated very rapidly. Symptoms will be nearly the opposite of fluid overload:
- change in mental status
- flat neck veins and thready pulse
- decreased B/P
- dry mouth and mucous membranes
- poor skin turgor
One of the reasons for doing I&O measurements is to compare the results you are getting over time. You are looking for trends, or patterns. When you begin to see widening variances showing up, remember to also assess your patient and don't base a call to a physician merely on the results of I&O alone.