Fluid Prescribing and electrolyte abnormalities Flashcards
What it the average total body water of humans?
Males = 60%
Females = 50%
Infant = 75%
How is total body water divided between intracellular and extracellular?
2/3 - intracellular
1/3 - extracellular
How is water distributed in the extracellular fluid?
Interstitial fluid - 3/4
Plasma - 1/4
What is meant by obilagated and free water in the body?
Obligated - follows electrolytes gradients typically Na+
Free water - created by loop of Henle left in ascending limb LOH, contains no electrolytes, used to concentrate urine, influenced by ADH.
What is a transcellular fluid?
Fluid in epithelial lined spaced e.g fluids of the gut, synovial fluid, cerebrospinal fluid,
Give an overview of the intra-cellular fluid compartment.
Stable compartment
Do not adjust to rapid changes
Maintains osmolarity for chemical reactions
What is meant by third spacing in fluid regulation?
When fluid moves from the intra-vascular compartment (where it contributes to cardiac output) to a compartment where it does not (ascities, burn sites and pleural effusion)
The fluid is essentially lost -> hypovolemic/hypotensive.
What are the main fluid balance abnormalities?
Fluid overload = oedema
Decrease in effective fluid = dehydration
What are the different factors that control the direction of flow of interstitial fluid?
Hydrostatic pressure
Oncotic pressure
Endothelial integrity
Lymphatic systems.
(Relates to Starling law)
What are the key forces at play in Starling forces?
Capillary and interstitium hydrostatic pressure
Capillary and interstitium oncotic pressures.
What makes up microcirculation in the body?
Capillaries (connection between venules and metaarterioles)
And lymphatic vessels.
What are the common modes of transport at microcirculations?
Simple diffusion
Vesicular transport
Osmosis.
What are the common causes of oedema?
Heart Failure
Renal Failure
Liver disease
How does heart failure lead to oedema?
Decreased cardiac efficienct and capacity of left side of heart creates back pressure in pulmonary veins/systemic veins -> increasing hydrostatic pressure.
How does renal failure lead to oedema?
Failure to remove fluids and osmotic componenets from the body results in increased osmotic pull into tissues and increased hydrostatic push out of capillaries.
How does liver disease lead to oedema?
Failure to produce osmotically active proteins (albumin) decreases the osmotic pull into the capillaries.
What is the average required water intake of an adult?
1600 to 2500ml of water per day
What are the different primary sources of fluid loss?
Insensible losses
urine, stool, respiration and sweat.
What are the common pathological causes of fluid loss?
Diarrhoea
Vomiting
infection
Polyuria
Burns
What is the common presentation of dehydration?
Decreased urine output
Dizziness
Fatigue
Tachycardia
Increased skin turgidity
Tachycardia
Low BP
Dry mucosal membranes.
How do we calculate fluid deficit?
Use following calculation for both pre-dehydration and post-dehydration weight
0.6*weight (kg) * [1-(140/sodium)]
When should IV fluids be prescribed for dehydration?
When needs cannot be met by oral intake or enteral routes
e.g NBM, vomiting, severe diarrhoea, acute blood loss
What should be included ina fluid prescription?
Type, volume and rate of fluid
What is included in an IV fluid management plan?
Regular monitoring
Re-assessment of clinical volumes status
U+Es
Fluid input/output balancing
Fasting weight measurements.
What is meant by a crystalloid fluids?
Small molecules in water - e.g NaCl, Hartmanss, dextrose
Low cost
Small molecules move around easily within the body
Superior in initial fluid resus
What is meant by colloid fluids?
Solution of larger organic molecules e.g albumin, gelofusin
More expensive
Bigger molecules remain in blood for longer
Increased risk of anaphylaxis.
IV fluid composition chart for reference
What is important to know about the tonicity of different IV fluids that can be given?
Isotonic = 0.9% sodium chloride and Hartmans solution
Hypotonic = 0.18% NaCl and 4% glucose, 5% dextrose.
What is important to know about the Na+ content of IV fluids?
0.9% chloride is slightly higher
Hartmans solution - slightly lower
0.18% NaCl and 4% glucose and 5% dextrose - significantly lower.
How can potassium be added into IV fluids?
Pre-mixed 20mmmol or 40mmol additives in bags that do not already contains potassium e.g 0.9% NaCl, Hartmans, dextrose.
What should be monitored when patients are on IV fluids in relation to their sodium levels?
BP
Urine output
U&Es
If decrease in either should increase fluid input.
What is a patients history can indicate fluid imbalance?
Age
Reason for admission
Past medical history
Medications
Input/output inc fluid
Symptoms of overload
Fluid restrictions.
What on general inspection can indicate a fluid imbalance in a patient?
Cynosis
SOB
Pallor
Mallor flush
Odema
Vital signs
Fluid balance chart
Daily weights
Access to fluids.
What in the bedside assessment of the body can indicate fluid imbalance?
Hands - colour, leukonychia, temp, CRT, skin turgor
Pulses/BP
JVP
Face - sunken eyes, pallor, mucous membranes
Chest - RR, central CRT, Heart sounds, Lung fields
Oedema - sacral or peripheral
Abdomen - distention, striate, shifting dullness.
What are the 5 Rs of IV fluids?
Resuscitation
Routine maintenance
Replacement
Redistribution
Re-assessment
How does resuscitation often occur in IV fluids process?
Hypovoaemic
1. initial 250-500ml bolus IV crystalloid STAT
2. Re-assess ABCDE
3. If hypo persisted repeat bolus and re-asses
4. Can repeat until 2000ml fluid has been given
5. Contact senior
If complex risk of overload give smaller boluses and get help earlier.
What is meant by routine maintenance of IV fluids?
Given when haemodynamically stable but unable to meet daily needs
Daytime house
Water = 25-30ml/kg/day
K+/Na+/Cl- = 1mmol/kg/day
Glucose - 50-100g/day
Norm 1 salty and 2 sweet bags of fluid.
What is meant by replacement and redistribution in IV fluid management?
Some patients require different management
Existing fluid or electrolyte abnormalities
Ongoing abnormal fluid or electrolyte losses
Re-distribution and other complex issues - oedema, sepsis, liver impairment etc
How is ADH produced?
Baroreceptors - stretch with high BV inhibit ADH release
Osmorecepotrs - shrink during dehydration, trigger ADH release
ADH is produced by the hypothalamus and secreted by the posterior pituitary gland.
What is the main action of ADH?
Acts of collecting ducts and DCT of the nephron to stimulate water re-absorption from the urine into the blood.
Also acts on V1 receptors to cause vasoconstriction of vascular smooth muscle
Increase ACTH release from anterior pituitary
Overall effect is to reduce diuresis (dec urine output and increase fluid retention)
What specifically does ADH do at the nephron?
Acts on vasopressin (V2) receptors on the basal epithelial DCT and CD - resulting in signalling cascade that insertrs aquaporin 3 channels into the apical membrane
This allows water to pass from the filtrate into the cell, then into the interstitial fluid through aquaporin 3 and 4 channels.
What factors affect ADH production in the hypothalamus?
Stimulated by: inc plasma osmolarity, inc angiotensin 2, dec BP, dec BV
Inhibited by ethanol.
Define hyponatremia
Less than <135mmol?L
What are the different severities of hyponatremia?
Mild 130-135 mmol/L
Moderate 125-129mmol/L
Severe <125mmol/L
What is the difference between acute and chronic hyponatreaemia?
48 hours onset
What is the basic physiology underpinning sodium concentration in the body?
Determined by total body water
Major determinant of effective osmolarity in the ECF - regulates pressure gradient
ADH controls osmoregulation
What is osmolarity?
The concentration of a solute dissolved in a solution
What is the human body responses at different osmolarities?
Norm - 275-295mOsm/L
ADH released at 280mOsm/L
Thrist at 290mOsm/L
What are some causes of hypovolemia hyponatremia?
GI losses
Skin losses
Renal losses
Other
What can cause euvolaemia hyponatremia?
SIADH
Abnormal ADH release (hypothyroidism and Addisons)
Psychogenic polydipsia
What are some causes of hypervolaemia hyponatremia?
Failure - heart, liver, renal
Nephrotic syndrome
What causes pseudo-hyponatremia?
Artefact when serum protein or serum lipids rise.
What are some common symptoms of hyponatremia?
Asymptomatic or vague
Headache, confusion, nausea, elthargy
Severe - seizures and loss of consciousness
What drugs can cause hyponatremia?
ACEi and ARBs
Proton pump inhibitors
Anti-epiletpci drugs
Amiodarone
Thiazide and loop diuretics
Temazepam
Sulphonylureas
SSRIs
Ecstasy.
What investigations are often done for hyponatremia?
Bloods: U&Es, glucose, lipids, TFT, LFTs, 9am cortisol, plasma osmolarity
Urine: osmolarity and sodium
What are some complications of hyponatremia?
Severe - seizures, loss of consciousness and coma
Cerebral oedema - raised ICP, large fluid shift due to changes in osmolarity -> concentration, cognitive deficits, gait distrubances and falls.
Osmotic demyelination syndrome - central pontine demyelination, rapid correction of hypoNa+, rapid shift of water in pons
How fast should sodium levels rise?
Not more than 10mmol/L in 24hrs.
Define hypernatremia
Acute v chronc
Plasma sodium conc >145mmol/L
Acute <24hrs
Chronic >48 hrs
What are the common causes of hypernatremia?
- Unreplaced water loss
- Sodium overload - hypertonic saline, salt ingestion
- Water loss into cells - extreme excersie or seizures
How to calculate plasma Na?
TBW
What are the symptoms of hypernateraemia?
Thirst and dehydration
Lethargy
Fever
Nausea, vomiting and diarrhoea
Confusion and abnormal speech
What are the clinical signs of hypernatremia?
Dry mucous membranes
Hypotension (postural) tachycardia
Altered mental status
Oliguria (dehydrated) or polyuria (diabetes inspidus)
What blood tests should be done for hypernatremia?
U&Es
FBC
Glucose
LFTs
Bone profile
Plasma osmolarity
CRP (infection)
Creatine kinase
