Fluid Balance, Assessment, and Prescribing Flashcards
Describe the distribution of water in body compartments
Adults= 45-60% water • Intracellular 66% (25L) • Extracellular 34% Interstitial (12L) Plasma (3L) Lymph Transcellular (CSF, joints, vitreous of the eye)
Compare salt distribution between extracellular, intracellular and plasma compartments
- Extracellular= much more sodium but same amount of potassium than intracellular
- Plasma= much higher protein content than extracellular
What are the 4 regulatory mechanisms?
- Antidiuretic hormone
- Thirst
- Renin-angiotensin-aldosterone mechanism
- Vasomotor regulation
What is serum osmolality and what is the normal range?
- Measure of total solid content in serum
- Tightly regulated at 278-300 mmol (normal= 285-295)
How does loss of water stimulate thirst?
• Loss of water= increase in serum osmolality= activates osmo receptors in roof of ventricle= stimulate thirst
How does ADH affect water balance?
• Osmoreceptors stimulate ADH= stimulates thirst and reabsorption of water in the collecting duct of the kidney by transferring aquaporins / vasoconstrictor
How does the renin-angiotensin-aldosterone system affect water balance?
- Fluid loss= reduced renal perfusion= renin secretion
- Angiotensinogen to angiotensin 1 by renin, angiotensin 2 by ACE (pulmonary endothelium)
- A2= vasoconstrictor so raises blood pressure; adrenal cortex stimulates aldosterone secretion to increase sodium and water reabsorption
Where in the brain signals fluid loss?
• Fluid loss= low blood pressure= reduced baroreceptor activation (aortic arch and carotid area) = signals to medulla
What action does the medulla have on water balance?
- Medulla= increased sympathetic activity= vasoconstriction, increased stroke volume, increased heart rate/ recued parasympathetic activity increases heart rate
- Increased heart rate and stroke volume= increased cardiac output
- Vasoconstriction increases blood pressure
Compare fluid input and output
- Water input: water, liquids, tissue catabolism (carbohydrates= CO2 and water)
- Food: 700ml, drink 1500ml, 200ml catabolism
- Output: expiration (250), sweat (100) and diffusion (350), faeces (200), excreted through kidneys (1400)
What are the causes of fluid loss?
- Diarrhoea, vomiting, other GI losses
- Bleeding e.g., GI haemorrhage, trauma, surgical
- Diuresis e.g., medication, diabetes
- Sepsis (multifactorial as fever and hypotension/ hypovolaemia contribute to fluid state)
Describe causes of reduced fluid intake
- Reduced oral intake-thirst is powerful driver of behaviour- reduced conscious level? Unable to reach in environment?
- Inadequate fluid supplementation-intravenous or enteral
Examples of fluid overload states
- Heart failure
- Liver cirrhosis and liver failure
- Nephrotic syndrome
- Renal failure
- Excess fluid administration
What factors in the NEWS chart show trends in fluid imbalance?
Temperature (fever) Pulse (tachycardia) Blood pressure (falling) Respiratory rate Oxygen saturation
What factors in physical examination would indicate fluid imbalance?
• Feel hands (temperature, cold= vasoconstriction), capillary refill time (normal <2 secs)
• Peripheral cyanosis NB harder to see on black and brown skins
• Skin turgor on skin on back of hands and over sternum (loss of elastic tissue in older patients)
• Pulse: radial and brachial–rate and volume
• Repeat BP
Postural hypotension often useful indicator of hypovolaemia
• JVP-normal is 2-3 cm above sternal angle (vertical height)
• Check mucous membranes
• Heart sounds-third heart sound may indicate fluid overload (3rd sound)
• Chest examination-pleural effusions, pulmonary oedema
• Ascites (abdominal distention, fluid thrill, shifting dullness)
• Oedema-sacral and ankle
-Sunken eyes
What in the fluid chart needs to be checked?
Input and output
Daily fluid balance
Daily weight (reduction= loss)
What drugs affect fluid balance?
Diuretics
Anti-hypertensives
Opioids (reduces blood pressure)
Drugs affecting kidney function e.g., Non-steroidal anti-inflammatory drugs
What further investigations would be required to assess fluid balance?
- Urea and electrolytes: Elevation in urea and creatinine, estimated glomerular filtration rate
- Full blood count: Blood loss or haemoconcentration
- Albumin: Hypoalbuminaemic states e.g., nephrotic syndrome and liver disease
- Chest X-ray (fluid overload)
- Infection screen (sepsis)
Describe a fluid balance assessment examination
- Check respiratory rate and effort (accessory muscles)
- Check for oxygen presence, obs chart, fluid balance chart and weight chart
- Hands: assess for peripheral cyanosis and pallor (poor circulation), temperature, skin turgor, capillary refill time, pulse, blood pressure (erect and supine)
- JVP check
- Face: eyes for periorbital oedema, mouth for central cyanosis, drawing mucous membranes
- Auscultate heart for cardiac failure (gallop 3rd sound)
- Check lungs for evidence of fluid- percuss to both base (stony dullness for pleural effusion), auscultate for dine inspiratory crepitations (pulmonary oedema), sacral oedema
- Peripheral oedema in ankles
- Ascites with shifting dullness, fluid thrill
What is the daily salt, glucose, and water requirement?
• Fluid requirement= 25-30mL/kg per day
• Kidneys can excrete/retain sodium
• Requirements are Sodium 1 mmol/kg/24 hours, Potassium 1 mmol/kg/24 hour (95% intracellular)
-50-100g/day glucose to limit starvation ketosis
When should you prescribe fluids?
- Patient is fluid deplete/hypovolaemic (resuscitation fluids)
- Patient is unable to take adequate amounts of fluid orally (maintenance fluids)
- Maintenance fluids also require sodium, potassium (& glucose for calories)
What factors of a patient history may indicate fluid imbalance?
- Fluid loss
- Light headedness
- Inadequate fluid intake
- Thirst
- Fluid accumulation (abdominal/ ankle swelling)
What are the symptoms of hypovolaemia?
- Thirst, dizziness
- Tachycardia
- Low BP, postural drop
- Prolonged CRT (capillary refill time)
- Reduced skin turgor
- Dry mucous membranes
- JVP not visible
- Oliguria
- Weight loss
- Elevated urea and creatinine
What are the symptoms of hypervolaemia?
- Ankle swelling
- Breathlessness
- Abdominal swelling
- Hypertension
- Raised JVP
- Inspiratory crepitations (pulmonary oedema)
- Pleural effusion
- Ascites
- Weight gain
What are the types of IV fluids?
• Crystalloids +/- potassium Plasmalyte 0.9% Sodium chloride 5% glucose 0.18% sodium chloride/ 4% glucose • Blood and blood products • Colloids
How are crystalloids used?
- Resuscitation fluids= 0.9% sodium chloride OR Plasmalyte
* Maintenance fluids= 0.18% sodium chloride/4% glucose OR 5% glucose OR 0.9% sodium chloride (will need added potassium)
What is the sequence for resuscitation fluid?
- Hypovolaemic= 500mL plasmalyte/ 0.9% sodium chloride bolus over 15 mins
- Assess response: BP rises, pulse falls, CRT shortens, urine output
- 2000mL IV fluids if inadequate (up to)
What needs to be considered for maintenance fluids?
• Can the patient manage oral or enteral fluids for some or all of their requirements?
Patient fasting pre-operation
Failed swallow assessment (neurological)
Unable to meet normal intake (profound diuresis)
• Are there ongoing additional losses?
Temperature
Diarrhoea, vomiting
Diuresis
What is the maintenance fluid regimen?
• A simple place to start
1000ml 0.18% NaCl/4% glucose with 40mmol/L K+ alternating with
1000ml 0.18% NaCl/4% glucose with 20mmol/L K+
Run at 1.25 mL/kg/hour and not more than 100 mL/hour
• Check urea and electrolytes, creatinine at least daily if giving IV fluids
What are the caveats to maintenance fluids?
• 0.18% sodium chloride/4% glucose is hypotonic once glucose metabolized
Risk of hyponatraemia especially in the elderly
Do not use as sole replacement therapy if sodium <132 mmol/L (use 0.9% sodium chloride instead)
• Potassium replacement
Normal serum potassium does not mean there is not potassium deficiency (intracellular)
Do not add potassium if serum potassium >5.0 mmol/L (recheck)
