Fluid and Electrolyte Prescribing Flashcards
Identify the main kinds of IV fluids.
1) Glucose 5%
2) Sodium Chloride 0.18% and glucose 4%
3) Saline 0.9%
4) Balanced crystalloids
5) Colloids
How well does colloid fluid pass through semi-permeable membrane ? 5% dextrose ? Saline ? Crystalloids ? NaCl 0.18% and glucose 4% ?
-Colloid- large proteins in it, will not pass (in intravascular space, stays there)
-Dextrose 5%- passes through (Initially distributes through ISF and plasma; glucose
metabolised so effectively adding just water. Further distributes into cells as well as ISF and plasma)
-Saline and crystalloids- Similar to extracellular fluid, passes through and disperse into other extracellular compartments
-Sodium 0.18% and dextrose 4%- passes through (disperses into other compartments including both extra and intracellular)
Identify the major fluid divisions. State the Volumes ff each.
INTRACELLULAR (28)
EXTRACELLULAR (14)
- Plasma (3)
- Interstitial (11)
Total (for an average 70 kg male)= 42 L
Why are UandE results always good indicators of K+ levels ?
Intracellular potassium acts as a reservoir (attenuates change, so low K+ may not appear in plasma).
HENCE, low K+ reflects VERY significant loss of total body K+
What is the barrier between plasma and interstitial fluid ? To what extent can ions, water, and proteins pass freely ?
Capillary wall (water and ions can pass freely, but not proteins)
What is the barrier between extracellular and intracellular fluid ? To what extent can ions, water, and proteins pass freely ?
Plasma membrane (water can pass freely, ions have to pass through channels, proteins cannot pass)
Describe exchange of fluid across the capillary membrane.
Arterial end: hydrostatic force larger, will push fluid out
Venous end: Oncotic force will force fluid back into plasma from interstitial space
State the following for the intracellular compartment:
K+ Na+ Mg2+ Cl- pH
INTRACELLULAR K+: 150 mM Na+: 10 mM Mg2+: 2.5 mM Cl-: 10 mM pH: around 7.0
EXTRACELLULAR Interstitial K+: 4.5 mM Na+: 130 mM Mg2+: 0.85 mM Cl-: 110 mM pH: 7.4
Plasma K+: 4.5 mM Na+: 130 mM Mg2+: 0.85 mM Cl-: 110 mM pH: 7.4
What is the main difference between plasma and ISF in terms of composition ?
Proteins (oncotic P higher in plasma)
Intracellularly, where does most of the negative charge come from ? Extracellularly ?
INTRA
Negatively charged proteins
Phosphate
EXTRA
Chloride
Identify the main gains, and losses of total body fluid, and the V of fluid lost through each of these on average per day.
GAINS
Food and water intake; oxidation of food
LOSSES
- Urine(variable; average 1500ml)
- Faeces (variable; average 100 ml)
- Sweat (variable; average 50mls)
- Insensible losses (variable; average 900ml)
How much fluid do we lose on average per day ?
2250 mmL
Identify examples of insensible water losses.
- Transepidermal diffusion: water that passes through the skin and is lost by evaporation
- Evaporation loss from the respiratory tract
Insensible losses are solute free
What is the difference between the role of sweat and insensible fluid loss.
SWEAT
Body temperature regulation
INSENSIBLE FLUID
Cannot be prevented
Evaporation of insensible fluid is a major source of heat loss from body but is NOT under regulatory control
Identify respiratory disease processes, and iatrogenic processes which can result in increased fluid loss.
RESPIRATORY
Disease process: anything which increases respiratory rate, will increase insensible losses via respiratory route (e.g. asthma, pneumonia)
Iatrogenic: Oxygen mask (dry air, takes up more humidity, increases sensible losses)
Identify GI disease processes, and iatrogenic processes which can result in increased fluid loss.
GASTROINTESTINAL
Disease process: Chorea, other causes of vomiting and diarrhea
Iatrogenic: Industrial strength laxative given before bowel surgery will cause marked fluid depletion
Identify urinary disease processes, and iatrogenic processes which can result in increased fluid loss.
URINARY
Disease process: Uncontrolled diabetes (glucose is osmotic diuretic, will be lost in urine and pull water with it)
Iatrogenic: Diuretic
Identify skin disease processes, and iatrogenic processes which can result in increased fluid loss.
SKIN
Disease process: Fever (insensible losses), burns
Iatrogenic: Surgery on abdomen with large SA of bowel exposed, moisture evaporates
How is total body fluid controlled ?
Sensors/ Central controller/ Effectors
Changes to gains/ losses result in a change in osmolality
and/or volume
Identify the main sensors of the body.
SENSORS
- osmoreceptors in the hypothalamus (daily housekeeping, sense osmolality in blood)
- low pressure baroreceptors in right atria and great veins (when dramatic event occurs e.g. shock)
- high pressure sensors (carotid sinus / aorta)
How do osmoreceptors respond to water shortages (i.e. effectors).
In times of water shortage, blood osmolality increases, sensed by osmoreceptors resulting in:
- Increased thirst (for increased water input)
- ADH secretion (for decreased water output)
What is the key driver of total volume ? How so ?
Total sodium
- If total sodium drops and osmolality (tightly regulated) stays the same, the total volume falls (including plasma volume)
- If total sodium rises and osmolality stays the same, the total volume will rise
Identify the compensatory mechanisms linked to low V and high V.
Compensatory mechanisms are really linked to low volume (low GFR, stimulation of JGA ) or high volume (increased GFR and release of ANP)
Identify the main gains and losses of NaCl.
- Gains: food and drink
- Losses: sweat (0.25g), faeces (0.25g), urine (10g)
How may your body compensate for too much/too little Sodium ?
- If you eat too much/ too little salt, the only controllable route of loss is via urine: hormonal control
- May increase losses via the other routes in a non- hormonally controlled way (exercise/heat etc causing increased sweating; diarrhoea causing increased loss via faeces)
Why is intake of sodium in excess of need ?
Hedonistic
Describe hormonal control of urine output in the context of too high/low Sodium.
- DCT is the area of control in the nephron
- No receptors detecting Na+, controlled indirectly via volume sensors (changes in Na+ lead to changes in BV)
- Net Sodium excretion = Na+ filtered (changed via GFR) - Na+ reabsorbed (changed via rate of flow, aldosterone, ANP)
Describe responses if osmolality rises, and falls.
IF OSMOLALITY RISES (Na+ increase):
- Increase in thirst
- Increase in release of ADH
- Increase in water intake/retention (take in more water, retain more water)
- Increase in V
IF OSMOLALITY FALLS (Na+ falls):
- Decrease in thirst
- Decrease in release of ADH
- Decrease in water intake/retention
- Decrease in V
Describe responses if volume increases. When might this occur ?
Increase in V may occur when heading towards Heart Failure
Increase in stretch of vascular system
- Baroreceptors (high pressure areas; low pressure areas)
- Decrease in renin release
- Decrease in aldosterone release (aldosterone normally retains sodium so if not released, lose sodium and water)
- Increased release of ANP (cardiac myocytes)
- Decreased sodium and water retention
Describe responses if volume decreases. When might this occur ?
Decrease in V may occur when heading towards shock (e.g. hypoV due to loss in GI, or trauma)
Decrease in stretch of vascular system
- Baroreceptors (high pressure areas; low pressure areas)
- If pressure (from decreased volume) falls, also influences ADH release and thirst centres
- Increase in renin release
- Increased levels of AII
- Increase in aldosterone release
- Decreased release of ANP
- Increased sodium and water retention
What are the main gains and losses of K+ ?
Gains via food/drink
Losses: predominantly via urine, little is lost in sweat or
faeces in normal conditions
How may your body compensate for too much Potassium ?
INCREASED K+ IN PLASMA
-Increases activity of basolateral sodium pump (i.e. more K+ enters the cell)
- Increased secretion of K+ across simple diffusion channels on apical membrane
-Increased secretions of aldosterone (NOT driven by AII, but by direct detection of raised K+ levels by the aldosterone-secreting cells of the adrenal cortex), which does the following:
• Increases activity of sodium pump (basolateral)
• Increases the number of sodium pumps (basolateral)
• Increases the number of sodium and potassium channels in apical membrane
• Result: increased reabsorption of sodium and increased secretion of potassium
Describe normal excretion of K+ at the kidney.
K+ is freely filtered, then predominantly reabsorbed again in the PCT with controlled secretion at the DCT. This secretion is linked to Na+ reabsorption (sodium pump).
What is Conn’s syndrome ?
Hyperaldosteronism leading to a) hypertension from increased
fluid volume, and b) hypokalaemia
What are the main risks with IV fluids ?
- Peripheral Vascular Catheter (PVC) required
- Easy to give too much fluid (especially in sick people)
- Errors in prescribing
Should you encourage patients to take oral fluids rather than IV fluids if possible ?
YES
How may history help determine fluid status of a patient ?
- Limited intake?
- Abnormal losses?
- How much?
- What kind of fluid?
- Ongoing? Can you treat the cause? - Comorbidities?
- Current illness?
- Symptomatic?
- Fluid balance charts?
Identify signs and symptoms of hyperV.
- Shortness of breath when lying flat
- Peripheral oedema
- Orthopnea
- PND
- History of cardiac or renal problems
- Raised JVP
- Inspiratory crackles at lung bases (e.g. pulmonary edema)
- HyperT
Identify signs and symptoms of hypoV.
- Dry mouth, dry eyes
- Postural hypoT (sensitive marker of HypoV)
- Systolic BP: <100 mmHg
- HR: >90 bpm
- Capillary refill: >2 secs
- Respiratory rate: 20 breaths/min
- Urine output/color: <0.5 mLs/kg/hr
- Decreased skin turgor
- Responsive to passive leg raising (HR decreases and BP increases as a result of lifting legs)
Identify investigations which may be helpful in assessing volume status of a patient (after history and examination).
Full Blood Count Urea and Electrolytes Chest x-ray Lactate Urine biochemistry
What are the daily electrolyte requirements of Sodium, Potassium and calories in IV fluids ?
Sodium: 1mmol/kg/24hours
Potassium: 1mmol/kg/24hours
Calories: minimum of 400kcal/24hours
ALSO keep an eye on Magnesium, Calcium and Phosphate
Identify the main kinds of fluids given for different kinds of fluid losses.
Maintenance fluids: Patient does not have excess losses (may be supplementing oral intake)
Replacement fluid: of previous and/or current abnormal losses (in addition to maintenance fluid)
Resuscitation fluid: the patient is hypovolaemic and requires urgent correction of intravascular depletion (with BOLUS)
How much maintenance fluids are needed if no other intake ? If there are oral intakes ?
If no other intake approximately 30mls / kg/ 24hours. May only need part of this IV if some oral intake
In the case where abnormal losses have taken place, what factor determines the replacement fluid used ?
Use fluid which mirrors ion content of abnormal losses
How often should peripheral venous catheters be changed ?
Every 72 hours
Identify examples of cystalloid IV fluids. When is each of these used ?
- 5% dextrose
- 0.18% NaCl 4%dextrose: used as maintenance fluid
- 0.9% NaCl (isotonic saline): used when losing ion rich fluid, including as bolus as resuscitation fluid
- Plasmalyte: used when losing ion rich fluid, or as resuscitation fluids (as bolus)
0.9% NaCl and Plasmalyte mirror contents of ECF so when given into intravascular space, expand ECF
How well does Plasmalyte distribute in different compartments ?
Distributes through ISF and plasma; does not enter cells
Identify examples of colloid IV fluid. How good is each of these at distributing around different compartments ?
•4.5% albumin:
Tends to stay in plasma; does not enter cells (expands intravascular space)
•Hydrolysed gelatin:
Initially tends to stay in plasma; does not enter cells. Protein metabolised over time so then equivalent to 0.9% NaCl
•Blood:
Stays in the vasculature and increases blood volume
How are 4.5M albumin and hydrolysed gelatin infused as fluids ?
Both supplied in 0.9% NaCl
How are maintenance fluid prescribed ?
Prescribed in mls/hour
True or False: Maintenance Fluid are available with additional K+ (10 or 20mmol/500mls) if required
TRUE
What is a possible side effect of colloid IV fluids ?
May expose patients to anaphylaxis
When should resuscitation fluids be given ? How are they given ?
Fluid challenge:
- Oligouria or hypotension and no sign of overload
- Given in 500 mLs balanced salt solution, QUICKLY (<15 mns), then re-assess and can repeat up to 2000 mLs
Explain what happens when a fluid challenge is given to a hypotensive patient.
Underfilled patient will be both tachycardic and hypotensive.
By infusing 500 mL into intravascular space, increase CO, so increase BP and decreased HR
(refer to slide 47)
Identify cautions of fluid challenges.
- Obese patients (used ideal body weight)
- Elderly or frail
- Renal impairment
- Cardiac failure (may want to cut down to 250 mL bolus)
- Malnourished or at risk of refeeding syndrome
Identify monitoring techniques when the heart is not working adequately despite IV fluids.
1) CVP line (measures R atrial P, target is 8-12 mmHg)
2) Point of care USS (look at IVC to see how full venous compartment is) or ECHO (determine ejection fraction of heart)
Describe the principles involved in managing a patient with DKA.
ACTRAPID
-Airway, breathing, circulation
-Commence fluid resuscitation
-Treat K+
-Replace insulin
-Acidosis management
-Prevent complications
Information for patients
-Discharge
What is the effect of DKA on K+ ? Effect of insulin treatment ?
OVERALL TOTAL POTASSIUM LOSS
-Because since Potassium is present in the blood it may be excreted by kidneys, and may be additional losses if vomiting
But serum K+ may be normal or even high (because shifted out of cells, into plasma) can be excreted by kidneys and possible addition losses if vomitting)
HOWEVER, INSULIN INFUSION
Plasma K+ will fall and will have to start supplementing K+
Identify the main clinical features of DKA.
Hyperglycaemia
- Dehydration (i.e insignificant urine output)
- Tachycardia
- Hypotension
- Clouding of conciousness
Acidosis
- Air hunger (Kussmaul’s respiration)
- Acetone on breath
- Abdominal pain
- Vomiting
- May be present with Gastroparesis
+ features related to precipitating factors (e.g. sepsis)
Why are DKA patients dehydrated ?
- Hyperglycaemia
- Vomiting
- Kaussmaul respiration
- Altered conscious level (reduced intake)
What is the total body deficit of water in DKA ?
Up to 7 liters in 70 kg adult
What hormones may be produced in DKA ?
Stress response hormones: glucagon, cortisol, growth hormone, adrenaline
Describe the IV fluids given to a patient in DKA.
In an adult start by giving 1000mls 0.9% saline over first hour (may require 4-6 L over 24 hrs), and subsequently Dextrose 5% (to replace water losses)
+
IV Insulin infusion 6 units/hour (for hyperG)
+
Possible IV K+ (slowly)
At which ranges of K+ should K+ be infused IV ?
If K+ is high (i.e. above 5.3 mmol/L), do not give K+ but monitor it every 2 hrs (anticipating that it will be driven into cells by insulin and will drop)
If K+ is within normal (3.3-5.3 mmol/L), give 20-30 mmol K+/hr in each L of IV fluid to keep K+ between 4 and 5 mmol/L
If K+ is low (i.e. below 3.3 mmol/L), hold insulin (don’t want to push more K+ into cells) and give 20-30 mmol K+/hr until K+ > 3.3 mmol/L
