Almost every patient admitted to hospital receives IV fluids at some point in their journey. However, the body manages this, without the need for careful medical assessment and adjustment, as fluid balance is one of its core functions. Despite this, there are many situations where we need careful and controlled management. These include:
- Electrolyte disturbance (hypernatraemia, hyponatraemia, hypercalcaemia) or hyperglycaemia (particularly DKA or HHS)
- Fluid overload (e.g. in AKI, CKD, heart failure or pulmonary oedema)
- Dehydration or shock
- Any other situation where a patient cannot control their input (e.g. nil my mouth or reduced GCS) or output (diuretics)
What is fluid balance?
Fluid balance is the measuring of a patient’s fluid input and output and calculating the net difference or balance. Depending on your patient’s fluid status, you will have set a 24-hour goal for their fluid balance – positive, negative, neutral.
The main reasons to record fluid balance is to prevent or correct dehydration and fluid overload.
In ITU, patients will have their input and output carefully monitored due to one-to-one nursing. Fluid balance targets can be prescribed e.g. “Mr Jones should be +500ml over the next 24 hours”. Thus, careful manipulation of the rate of IV fluids and/or furosemide can allow this to be closely achieved. Even in ITU however, it is very difficult to measure this accurately and fluid balance charts are prone to error.
The important thing to recognise is whilst we don’t have great tools to accurately assess a patient’s fluid balance, a comprehensive history and examination can give us some idea. Observing for changes in these parameters can give us an idea where the patient is heading and then we can make adjustments accordingly. Therefore monitoring a response to interventions that affect fluid balance is vital.
Fluid balance assessment
- Oral intake of food and fluids. Are they thirsty? Don’t forget about soups & hot drinks particularly if a patient is on a fluid restriction
- Insensible losses e.g. fever, sweats, burns, trauma, tachypnoea
- Output including vomiting/diarrhoea/stoma output, bleeding & for urine the amount and colour. It is often more helpful to ask if they’ve noticed a change in colour or amount
- Features of dehydration (syncope or pre-syncope) or overload (shortness of breath, leg swelling, paroxysmal nocturnal dyspnoea or orthopnoea)
- Dry weight (sometimes known to dialysis or heart failure patients)
|– Impaired perfusion will lead to cool peripheries e.g. hypovolaemic shock or cardiogenic shock
– Warm peripheries can be found in a hypervolaemic patient or in vasodilatory shock e.g. sepsis
|Capillary refill time
|– Ensure you apply at least 5 seconds of pressure
– If > 2 seconds, check if they are centrally deplete with a sternal capillary refill time
|– Generally less helpful in the elderly
– More helpful in younger patients in whom you expect quite elastic skin
|Peripheral & Central pulse
|– Usually very helpful
– A normal HR is reassuring that a patient isn’t significantly deplete (in an otherwise well patient)
– Beware of b-blockers that’ll blunt the compensatory tachycardia
– A weak volume pulse occurs in the later stages of shock & may suggest an emergency
|Jugular venous pressure
|– Assessment of overload, approximates the CVP or right atrial pressure
– Difficult to assess (even for registrars). Looking for the JVP regularly can boost confidence
|– Usually unhelpful unless the patient is obviously dry
– They may appear wet if the patient has just had a few sips of water
|– Usually unhelpful
– A gallop rhythm or third heart sound can sometimes occur in overload (but usually is missed)
|– Very helpful to judge the presence & extent of pulmonary oedema
– Don’t forget percussion for pleural effusions
|– Consider whether there is any ascites
|– Assess how far up it extends (it can be as far as abdominal wall oedema)
– Don’t forget sacral oedema. This can be extensive and is frequently missed!
– Documenting this allows each new assessor to know whether things are improving
|(Passive leg raise)
|– Consider this if you want to assess whether a patient is fluid responsive
– You raise a patient’s leg for 5 minutes and repeat the observations
– It is, in effect, a fluid bolus of around 250-500 ml (without actually giving the fluid)
– A response means that fluid will increase the cardiac output (Starling’s law)
Review the charts
- Observations (high respiratory rate and tachycardia. Hypotension occurs later when the body can no longer compensate). Note a normal blood pressure in a patient that is usually hypertensive may be low for them.
- Lying and standing blood pressure can help differentiate hypovolaemia from euvolaemia
- Review the fluid balance chart (see below)
- Check their weight (really helpful to see whether diuresis is effective)
- Review any confounding medications (antihypertensives or b-blockers) and whether the patient is on diuretics
- Don’t assume an AKI means a patient is dehydrated. An AKI must be reviewed in context – it could be cardiogenic, hypovolaemic or a renal/post-renal AKI
Fluid Balance Chart
Nursing staff will normally document the patient’s fluid input and output on a fluid balance chart. The template may vary between trusts but the aim is the same:
- Input will be all the fluid intake a patient is having during the day including orally, via nasogastric or PEG and intravenously.
- Output will include the patient’s urine output (helpful if you are concerned about acute kidney injury), vomiting, stomas, NG tubes – any obvious loss of fluid
- A running total for both input and output may also be documented (up to hourly) to aid quick calculation of the balance with 24-hour totals and balance recorded at the bottom of the chart
- Urine output can be really helpful to judge your interventions over a few hours e.g. the effects of diuretics
- Accuracy of fluid balance depends on staffing levels, expertise of the nursing team, patient’s concordance to having their input/output measured e.g. catheter vs using the toilet and whether they will stick to a fluid restriction
There are a lot of things to cover in a comprehensive fluid balance assessment, and it can be hard to remember them all. Fortunately, there is a useful memory aid that can be used to structure examination: The A-M approach
The A-M Approach for Assessing Fluid Balance
|A: Ask the Patient
|Do they feel thirsty, dizzy or short of breath?
|B: Blood Pressure
|Lying, sitting and/or standing as appropriate
|Refill time, and peripheral temperature
|D: Dry Mucous Membranes
|Does the patient’s mouth look moist or dry?
|E: Elastic Skin Turgor
|Is the patient’s skin bouncy, or thin and friable?
|F: Fluid intake and output
|Review the charts, being sure to consider insensible losses
|G: Glasgow Coma Score
|Assess consciousness level
|Auscultate and Palpate for character and rate
|I: Interstitial Fluid
|Consider the 3 A’s – Ankle oedema, Alveolar (pulmonary) oedema, and Ascites
|J: Jugular Venous Pressure
|A raised JVP could indicate fluid overload
|Inspect the Blood Tests for Renal Impairment and/or Electrolyte Disturbance
|L: Look at the Prescription
|How appropriate is the volume and content of the IV Fluids prescribed?
|Does the patient need regular weight monitoring?
References & Useful Resources
- Fluid balance poster
- Fluid overload by Patient.info
- Hydration status exam by GeekyMedics
- Fluid status exam by Oxford Medical Education
- Hydration examination by OSCEStop
Written by Dr Sophie Legg (F3) & Dr Akash Doshi (ST3 in Endocrinology & Diabetes)
Contributions by Glen Davies (F1)
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