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
