Fluid challenge ◦ Fluid management ◦ Fluid overload

Overview

Fluid challenge can be viewed as the initial phase of fluid resuscitation/replacement of a patient with suspected hypovolaemia. During a challenge, fluid is administered fairly rapidly and the patient is closely monitored to determine what effect the challenge has on haemodynamic parameters. Subsequent fluid maintenance is performed based on the result of the challenge. Fluid responsiveness is an increase in stroke volume after a fluid challenge and is generally a good sign. The risk of fluid challenge is fluid overload, in which the blood volume is increased excessively, leading to oedema.

Fluid challenge

A fluid challenge is an administration of an intravenous bolus of fluid over a short time period and observation of the cardiovascular response in order to determine how to proceed with fluid management. In hypovolaemic patients, this should improve cardiac output and blood pressure. A fluid challenge may also have diagnostic value. For example, a patient with sepsis may not respond to a fluid challenge, indicating septic shock.

Fluid management

Managing fluids and electrolytes is a complex task that is sadly often left to inexperienced junior medical staff. In UK hospitals, inappropriate fluid therapy is estimated to contribute to the morbidity of an estimated 1 in 5 patients so treated. Prescribing fluids should be considered as seriously as prescribing drugs and requires careful assessment of the patient. The National Institute for health and Clinical Excellence (NICE) fluid therapy guidelines recommend that healthcare practitioners remember the 5 Rs:

Resuscitation
When an assessment suggests it is require, give 500 ml of crystalloids over 15 minutes. This is a fluid challenge by another name. Once these patients are fixed their further needs can be assessed for one of the Rs below.

Routine maintenance
These patients don’t have unusual replacement or redistribution issues and doesn’t require resuscitation. Keep the fluids going at a rate and via a route appropriate to the case at hand.

Replacement
Replacement of what with what? Exactly! Consider what is missing in terms of fluids or electrolytes (especially potassium). Consider ongoing problems such as drainage losses, diarrhoea or polyuria and the specific effect they have on fluids and electrolytes.

Redistribution
Is fluid being redistributed in the body? Check for gross oedema, sodium imbalances, organ impairment (eg liver or heart). Sepsis?

Reassessment
Assess patients at least daily by someone with experience and expertise. Stable patients on routine maintenance may require less frequent reassessment.

The NICE algorithm to follow for the 5Rs is available here.

Fluid overload

The risk of administering fluids is that the increased blood volume might exceed the capacity of the heart to deliver enough cardiac output. This situation has similarities with heart failure. For example, the blood volume returning from the lungs might be in excess of what the heart can pump to the body, leading to back pressure in the pulmonary bed and oedema in the lungs. You’d see the same problem if the blood volume was “normal” but the heart was failing (for whatever reason), limiting cardiac output.