SESSION 3 Flashcards
What is the maximum rate of K+ infusion
20mmol/hour
How do we manage an anaphylactoid-like reaction from acetyl cysteine?
generally treated by stopping the infusion and restarting at a slower rate
Common SE from IV sodium bicarbonate?
Skin exfoliation; soft tissue necrosis; ulcer
• 0.3% sodium chloride… what does this mean?
means 0.3G of sodium chloride per 100ml
What is the formula for calculating molecular weight?
Mass (g) / moles (mol) = molecular weight (g/mol)
How is adenosine administered?
• Adenosine must be given over 2 seconds into central or large peripheral vein followed by rapid sodium chloride 0.9% flush for rapid IV injection
• When giving GTN IV infusion what must you monitor?
you must monitor BP and HR
What is linezolid?
What monitoring does it need and why?
Llinezolid is an oxazolidinone antibacterial active against gram positive bacteria including MRSA. Resistance can develop with prolonged treatment.
It requires weekly FBC due to risk of myelosuppression
Side effect of IV sodium fusidate (a type of fusidic acid)
IV sodium fusidate can cause dizziness, drowsiness with pain and irritation at the point of administration
What is 1 mole?
The number of atoms in 12g of carbon
What is 1 osmole?
The number of moles of solute particles (ions, molecules) that influence the movement of water across a semi-permeable membrane.
For example:
1 mole of glucose (a non-ionizing substance) equals 1 osmole, because it doesn’t dissociate in water.
1 mole of NaCl (which dissociates into Na⁺ and Cl⁻) equals 2 osmoles, because it splits into two particles.
What is osmotic pressure?
The ability of a solute to attract water over a semipermeable membrane
What is osmolarity?
number of osmoles of solute particles per unit volume of a solution (osmol/L)
What is osmolality?
number of osmoles of solute particles per unit weight of a solution (osmol/Kg)
What is tonicity?
The relative solute concentrations of 2 solutions separated by a semi-permeable membrane - the ability of a solution to cause water to move in or out of a cell through the process of osmosis, depending on the concentration of solutes outside the cell compared to inside.
Importantly: it is influenced by non-penetrating solutes—those that cannot cross the cell membrane. Unlike osmolality or osmolarity, which measure total solute concentration, tonicity specifically affects water movement and cell volume
What is an isotonic solution?
The solute concentration outside the cell is equal to that inside the cell. No net movement of water occurs, and the cell’s volume remains unchanged.
Example: 0.9% saline solution (used in IV fluids) is isotonic to human cells.
What is a hypotonic solution?
The solute concentration outside the cell is lower than inside the cell.
Water moves into the cell, causing the cell to swell and possibly burst (lysis).
Example: Pure water or very dilute solutions are hypotonic to cells.
What is a hypertonic solution?
The solute concentration outside the cell is higher than inside the cell.
Water moves out of the cell, causing the cell to shrink (crenation in red blood cells).
Example: A strong saline or sugar solution is hypertonic to cells.
What % of body weight is water in women and men?
Men ~60%
Women ~50%
Why do men have more water volume on average compared to women?
As on average men have more muscle and women have more fat
Adipose tissue is relatively lower in water % than skeletal muscle
(This means very obese pts and elderly have less water per kg)
Outline the proportions of total body water in compartments?
2/3rds intracellular
1/3rd extracellular - 3/4 of this is interstitial and 1/4 is plasma (a very very small amount is transcellular fluids)
What is transcellular fluid?
the portion of total body water contained within the epithelial-lined spaces.
E.g. pericardial fluid, CSF, ocular fluid etc
Main cations and anions intracellular?
K+
Phosphates
Proteins
Main cations and anions extracellular?
Na+
CL-
Explain briefly why the main cation intracellular is K+ and extracellular its Na+?
As ions cannot move freely between intracellular and extracellular space.. they require pumps e.g. ATPase pump which exchanges 3 Na+ out of the cell for 2 K+ in to the cell
What is hydrostatic pressure?
The force exerted by a liquid in a close system e.g. force of blood against the vessel wall
What is the oncotic pressure?
a form of osmotic pressure exerted by proteins, particularly albumin, in the blood plasma. These large molecules draw water toward them due to their inability to pass through the capillary walls
What is starlings forces concept?
In the capillary bed, the movement of fluid is determined by the balance between hydrostatic and oncotic pressures:
At the arterial end of the capillary, hydrostatic pressure is higher, so fluid is pushed out into tissues (filtration).
At the venous end, oncotic pressure is higher, so fluid is pulled back into the capillary (reabsorption).
Explain what happens when you give 1000ml of 5% glucose IV?
5% glucose is 50g of glucose dissolved in 1000mL of water.
The glucose in the solution will be rapidly taken into the cells and metabolised under the influence of insulin. This will leave pure water which will distribute equally across compartments i.e. 2/3rds go to the intracellular compartment and 1/3rd to the extraclelular fluid compartment.
In regards to the extracellular fluid compartment, 1/4 of the volume will go to the plasma and 3/4 will go to the interstitium. This will only increase the blood volume by less than 2% and this volume increase will not even be sensed by the volume receptors (note that volume receptors sense volume increases at 7-10%).
Once the glucose is metabolized, the remaining water is hypotonic, meaning it lowers plasma osmolality. This decrease in osmolality is sensed by osmoreceptors, particularly in the hypothalamus, leading to inhibition of vasopressin (ADH) release. With less ADH, the kidneys will excrete more water to normalize plasma osmolality, leading to an increase in urine output.
Explain what happens when you give 1000ml of 0.9% sodium chloride IV?
0.9% is simply 9g of NaCl dissolved in 1000ml of water.
Because there’s practically no Na+ and Cl- in the intracellular fluid compartment, distribution of solution is limited to the extracellular fluid compartments. 1/4 will distribute to the plasma and 3/4 to the interstitial fluid. Therefore the plasma volume will be expanded by 250ml.
As 0.9% NaCl is isotonic it will not significantly alter plasma osmolality and this means the osmoreceptors will have no involvement in excretion of excess fluid.
Assuming a blood volume of ~5L, 1L of fluid will increase plasma volume by about 5% which is below the sensitivity of the volume receptors.
0.9% NaCl will lower oncotic pressure by diluting the proteins present in plasma, this promotes fluid movement into the interstitium from the plasma. This leads to an increase in GFR and reduced water reabsorption of water in the proximal tube. This fluid in the interstitium will slowly move back into the intravascular compartment as urine flow continued until all transfused fluid is excreted.
As this takes quite a while this 0.9% NaCl can be used for fluid resuscitation as it expands plasma volume without causing rapid shifts in osmolality
Types of IV fluids?
Crystalloids
Glucose solutions
Mixed solutions
Colloid solutions
What are unbuffered and buffered Crystalloids?
The main difference is that buffered crystalloids, contain substances that act as buffers to help maintain a more physiological pH, reducing the risk of acid-base imbalances.
Unbuffered examples e.g. 0.9% sodium chloride which if given very quickly may cause hyperchloraemic metabolic acidosis
Buffered examples include hartmanns, lactated ringers solution
How is 0.9% sodium chloride different to plasma?
It contains significantly more chloride ions than plasma
it has slightly more sodium ions.
its relatively hypertonic compared to plasma but once given it actually acts as isotonic
It does not have K+, HCO3-, Ca2+, MG2+, glucose etc
Explain why 0.9% sodium chloride is considered isotonic?
0.9% Sodium Chloride has an osmolality of about 308 mOsm/L, which is slightly higher than the osmolality of plasma which is around 275–295 mOsm/L
Sodium chloride dissociates into sodium (Na⁺) and chloride (Cl⁻) ions, both of which are non-penetrating solutes. Therefore, these ions remain in the extracellular space, and water movement across cell membranes is determined by their concentration.
The concentration of sodium (Na⁺) and chloride (Cl⁻) ions in 0.9% sodium chloride is similar to the concentration of these ions in extracellular fluid (ECF). This means that, when infused into the body, it does not cause a significant shift of water into or out of cells.
Since sodium and chloride are non-penetrating solutes, they remain in the extracellular space which prevents water from moving out of the intracellular space, which would otherwise cause cells to shrink or swell.
Thus, even though the osmolality of 0.9% sodium chloride is slightly higher than plasma, its tonicity is similar to that of plasma because it does not disrupt the balance of water between intracellular and extracellular compartments.
Whats the only disadvantage of 0.9% sodium chloride as a fluid option?
Risk of hyperchloraemic metabolic acidosis when used in aggressive fluid resuscitation but there has not been any study evidence on this significantly impacting pt outcomes
What is the buffer in hartmanns solution?
It contains 29mmol/L lactate
How is hartmanns different from 0.9% sodium chloride?
Has a more similar osmolality to plasma
Lower chloride and sodium and is more similar to plasma
Contains 5mmol of K+
Contains lactate as a buffer
Why is hartmanns solution not suitable for K+ replacement therapy?
As infusing 1 L will only cause a rise of serum K+ by about 0.035 which is a negligible amount
This also means its very unlikely to result in clinically significant K+ rises even in renal impairment
Can hartmanns fluid cause lactic acidosis?
No in normal circumstances lactate is metabolized by the liver into bicarbonate, which helps buffer acids in the body
Therefore this actually helps to correct the acidosis!
Not ethere may be a transient rise in serum lactate immediately after administration on bloods
Explain the distribution of hartmanns solution when administered?
Like 0.9% sodium chloride, Hartmann’s solution is primarily distributed in the extracellular fluid compartment, which includes both intravascular (1/4) and interstitial spaces (3/4). This is because the ions in both solutions (Na⁺, Cl⁻, etc.) are unable to penetrate cell membranes significantly.
It’s also isotonic with respect to plasma, which means it does not cause significant shifts of water into or out of cells when administered.
Upon infusion, lactate is metabolized in the liver to bicarbonate, which can help maintain pH balance and counteract acidosis. Hartmann’s solution also contains potassium and calcium, which are not present in 0.9% sodium chloride. This composition can make Hartmann’s more physiologically appropriate for certain conditions, as it helps replenish not just sodium and chloride but also other essential electrolytes.
While both Hartmann’s solution and Normal Saline can effectively expand intravascular volume, Hartmann’s may provide better overall fluid balance due to its additional electrolytes and the bicarbonate-forming effect of lactate.
Just like 0.9% sodium chloride… if we infuse 1L we expand plasma volume by 250ml
Cons of using hartmanns?
Expensive!
Why do we never use glucose solutions for acute fluid resuscitation?
As glucose solutions are distributed equally across all compartments i..e 2/3rds intracellular and 1/3rd extracellular. Within the extracellular only 1/4 of that 1/3rd goes to plasma i.e. if you give 1L plasma is only expanded by 83ml. = very little expansion!
When should you definitely not give glucose solutions?
When a pt has or is at risk of hypokalaemia
The glucose stimulates insulin release which favours potassium shift intracellular which will induce or worsen hypokalaemia
Note it may also lead to hyponatraemia if given alone
Examples of mixed solutions?
0.18% sodium chloride and 4% glucose
0.45% sodium chloride and 4% glucose
What are colloids?
Solutions with large molecular weight particles present in a solution that does not cross the semipermeable membrane
What are the 2 types of colloids?
blood-derived products and semisynthetic colloids
Example of blood derived products used as colloid fluids?
Packed red cells
Platelets
Albumin
FFP
Examples of semisynthetic colloids?
Gelatins
Hydroxyethyl starches
Dextrans
(Note you should never be prescribing these as an F1 doctor!!)
Possible adverse events of IV fluid therapy?
Hypovolaemia
Peripheral oedema
Dehydration
Pulmonary oedema
Hyponatraemia
Hypernatraemia
Hypokalaemia
Hyperkalaemia
Infiltration
Extravasation
Air embolism
Phlebitis
Infection
Hypersensitivity reactions
Hypovolaemia vs dehydration?
Dehydration is a loss of total body water
Hypovolaemia is a loss of the extracellular fluid
Normal human fluid intake?
Water - 1500ml
Water from food - 750ml
Metabolism byproduct - 250ml
Normal human fluid output daily?
Urine 1.5L
Resp 400ml
Skin 400ml
Faeces 200ml
Total =2.5L
Normal adult daily fluid and electrolyte requirements?
25-30ml/kg/day water
1mmol/kg/day of Na+, K+ and Cl-
50-100g glucose
If a pt is likely to need maintenance fluids for >3 days would should you consider?
NG tube or enteral feeding
For how many hours a day should a pt be getting Iv fluids when indicated?
About 16 hours as you want to be giving fluids in the daytime to allow pt to sleep!
How should you calculate maintenance fluids for an obese pt?
you should adjust the prescription to their ideal body weight rather than their actual body weight!! Otherwise you will overprescribe
You should use the lower range for volume per kg (e.g. 25 ml/kg rather than 30 ml/kg) as patients rarely need more than 3 litres of fluid per day.
How do we calculate ideal body weight for fluids?
Using the Devine formula
What is the Devine formula?
Men - 50kg + (2.3kg for each inch over 5ft)
Women - 45.5kg + (2.3kg for each inch over 5 foot)
In which pts should you have a cautious approach to prescribing fluids i.e. probably give 20-25ml per kg per day?
Elderly patients
Patients with renal impairment or cardiac failure
Malnourished patients at risk of refeeding syndrome
What should you do before prescribing fluids for resuscitation?
Assess pts volume status
BP, HR, CRT, periphery temperature, RR, NEWS score, passive leg raising
Why do we do a passive leg raise to assess pts volume status?
As this allows about 300ml of fluid to move back to the right side of the heart - it acts as a fluid challenge by increasing preload
It indicates pt needs a fluid bolus
What should you give for fluid resuscitation?
500ml of a Crystalloid given over 15 minutes or less
Either 0.9% sodium chloride or hartmanns solution
What should you do after a fluid bolus is given?
Reassess pts A-E ans volume status
If appropriate give another bolus
At what point does a pt who’s requiring fluid resuscitation likely need ICU support?
If you are getting anywhere close to giving 2000ml fluid
Do resuscitation fluids count towards maintenance fluid calculations?
NO
Why should potassium never be added to resuscitation fluids e.g. 0.9% sodium chloride + 20mmol glucose?
As it shouldn’t be given a faster than 10mmol per hour due to risk of local irritation of the vein and precipitating cardiac arrhythmias
In which pts should you be cautious about giving fluid resuscitation?
What should you give them?
Elderly, renal impairment, cardiac impairment, malnourished pts at risk of refeeding syndrome
Give 250ml bolus over 15 minutes
When might you need replacement and redistribution fluids?
If there’s existing fluid or electrolyte deficits/ecxess e.g. in dehydration, fluid overload
If ongoing abnormal fluid or electrolyte losses e.g. vomiting, ileal stoma losses, blood loss, sweating, urine
If redistribution or other complex issues e.g. oedema, severe sepsis, renal/liver/cardiac impairment, malnourished etc
How do you work out how much fluid to give when there is replacement and redistribution issues?
Prescribe by adding to/subtrating from routine maintenance
Adjust for all other sources of fluid and electrolytes e.g. oral, enteral, drug prescriptions etc
Work out routine maintenance
Calculate losses or excesses
Add or subtract this
How can you check the drop rate on a giving set?
20 drops = 1 ml
Drip rate is drops per second = 1 drop per second = 180ml in an hour (3600seconds / 20 drops)
This means 1 L bag will be delivered over 5.5. Hours
What is hypokalaemia defined as?
K+ serum level <3.5
How to estimate the K+ deficit?
{normal potassium value (typically 4) - the serum potassium} x body weight (kg) x 0.4
Note you should replace this AND give maintenance K+
What should you always check when you have hypokalaemia?
The serum magnesium as hypomagnaesaemia induces potassium wasting in the kidneys so often Mg needs to be replaced before the K will improve
Considerations for fluid prescribing immediately in the post-operative period?
Sodium and water retention occur due to stress response and around 60% of sodium load is retained for up to 48 hours
This effect is mediated by renin and activation of RAAS leafing to water retention
Consider monitoring urine output closely instead of jumping in with further IV fluid therapy. Post-operative oliguria is a normal physiological response to surgery
What other factors can affect fluid distribution?
Increased vascular permeability e.g. in severe sepsis there is vasodilation and leaky capillary beds which cause a relative hypovolaemia
Increased cardiac filling pressures e..g in pulmonary hypertension
Reduced plasma oncotic pressures e.g. in hypoalbuminaemia in liver cirrhosis pts this can cause fluid losses from the plasma to the interstitial spaces causes oedema
Pt advice for any antimuscarinics eye drops?
They may not be able to undertake skilled tasks until vision clears from Mydriasis
SE of prostaglandins eye drops?
Thickened eye lashes and increased brown pigment in iris
Thiazide diuretics effects on calcium?
They can reduce urine Ca levels and increase serum levels
This is because they increase calcium reabsorption from the kidneys in exchange for sodium
What do you do to the dose when changing from IV to oral digoxin?
Increase by 20-33% to maintain the same plasma-digoxin concentration.
What to do if you suspect digoxin toxicity?
Measure digoxin concentrations 8-12 hours a after last dose
Remember the plasma concentration alone does not determine the toxicity - toxicity can ccur when plasma concentration is in therapeutic levels
Features of digoxin toxicity?
GIT: Nausea, vomiting, anorexia, diarrhoea
Visual: Blurred vision, yellow/green discolouration, haloes
CVS: Palpitations, syncope, dyspnoea
CNS: Confusion, dizziness, delirium, fatigue
ECG features of digoxin toxicity?
down-sloping ST depression (‘reverse tick’, ‘scooped out’)
flattened/inverted T waves
short QT interval
arrhythmias e.g. AV block, bradycardia
Which parkinsons drugs can cause impulse control behaviours e.g. gambling?
Dopamine receptor agonists
Moa of quinagolide?
Indication?
A dopamine 2 receptor agonist
Indicated for hyperprolactinaemia
Patient information for dopamine agonists?
Excessive daytime sleepiness and sudden onset of sleep - warn pts about driving and operating heavy machinery
Monitor BP for a few days after starting Tx and dose changes
Most important SE to remember for Ciclosporin?
Gingival hyperplasia and bleeding gums
Monitoring required when on bupropion hydrochloride?
Monitoring of bp before and during Tx
MOA of bupropion for smoking cessation?
a norepinephrine and dopamine reuptake inhibitor, and nicotinic antagonist
When should you not give potassium with glucose solutions?
If any hypokalaemia!!
The insulin used to move glucose will shift K+ intracelluarly which will worsen low K+
If chloride increases what happens to bicarbonate?
Goes down as compensation
Anion gap calculation?
(Na+ + K+) - (Cl- + HCO3-)
Normal is 10-18 - this really varies depending on resource!!
Causes of metabolic acidosis with a normal anion gap (i..e hyperchloraemic metabolic acidosis)?
Loss of HCO3- from GIT e.g. diarrhoea, ileostomy fluid loss, fistula
Recovery from DKA
Carbonic anhydrase inhibitor use e.g. acetazolamide
Addison’s is disease
Ammonium chloride injection
Renal tubular acidosis
Causes of metabolic acidosis with a raised anion gap?
Lactate e.g. shock, sepsis, hypoxia, burns, metformin use
Ketones e.g. DKA, alcoholic ketoacidosis
Urate e.g. renal failure
Acid poisoning e.g. methanol or salicylates
Hyponatraemia mild, moderate and severe levels?
Mild 130-135
Mod 125-129
Sev <125
Hypokalaemia mild, moderate and severe levels?
3-3.4 mild
2.5-3 mod
<2.5 sev
If a pt has a metabolic acidosis and you start correcting it with fluids why should you be aware of potassium?
Acidosis often causes a shirt of K+ into extracellular space so when this is corrected it’s likely to shift back causing a drop.
Administering large volumes of fluids can also dilute K+ causing a drop
If a pt has renal function issues and you correct this the kidneys will then increase K+ excretion
All of this is important as you mist be aware that when you correct a metabolic acidosis the K+ will drop!! Important for cardiac issues!!
