Intravenous fluids Flashcards
What are the daily requirements for Water, Na and K for a normal adult?
Water: 2.5 - 3 Litres
Na+: 140 - 160 mmol (~3.5 grams)
K+: 80 - 100 mmol (~3.5 grams)
Classify intravenous fluid
Crystalloids
Colloids
What is the difference between crystalloids and colloids
Crystalloids contain water and small particles (ions±glucose) which can readily move between fluid compartments.
Colloids contain larger molecules which move more slowly out of the intravascular compartment hence they are also known as ‘plasma expanders’
What is the difference between ECF and ICF Na
ECF: 145 mmol/L
ICF: 12 mmol/L
What is the difference between ECF and ICF K
ECF: 5 mmol/L
ICF: 150
What is the difference between ECF and ICF Ca2+
ECF: 2.5 mmol/L
ICF: 0.001 mmol/L
What is the difference between ECF and ICF Cl-
ECF: 105 mmol/L
ICF: 5 mmol/L
What is the difference between ECF and ICF HCO3-
ECF: 25 mmol/L
ICF: 12 mmol/L
What is the difference between ECF and ICF pH
ECF: 7.4
ICF: 7.1
For a fit patient having elective surgery not involving the abdomen, what fluid losses do you expect before and during surgery of less than an hour?
does this patient need intraoperative fluid?
Pre-operative: Normal losses during starvation time (6 - 12 hours) –> 500 to 800 mls.
Intra-operative losses depend on blood loss. If minimal and surgery is less than an hour then fluid loss is ~ 150 mL
No. But on a hot day when insensible losses are increased –> Hartmann’s solution 500ml might make patient feel more comfortable in postoperative period
In the setting of history of vomiting and surgery involving the abdomen, why should the patient be resuscitated with fluid preoperatively, rather than just performing surgery as quickly as possible?
Induction of anaesthesia drops the blood pressure and impairs the myocardium much more in a hypovolaemic patient, and this could be fatal.
Define an osmole
An osmole is a unit of measurement that describes the number of moles of a compound that contribute to the osmotic pressure of a chemical solution.
The osmole is related to osmosis and is used in reference to a solution where osmotic pressure is important, such as blood and urine.
Define osmolarity
Osmolarity is defined as the number of osmoles of solute per liter (L) of a solution. It is expressed in terms of osmol/L or Osm/L. Osmolarity depends on the number of particles in a chemical solution, but not on the identity of those molecules or ions.
Define osmolality
Osmolality is defined as the number of osmoles of solute per kilogram of solvent. It is expressed in terms of osmol/kg or Osm/kg.
When the solvent is water, osmolarity and osmolality may be nearly the same under ordinary conditions, since the approximate density of water is 1 g/ml or 1 kg/L. The value changes as the temperature changes (e.g., the density of water at 100 C is 0.9974 kg/L).
Describe the contents, ion concentration, osmolarity, pH of 0.9% NaCl
Contents: 9g NaCl/L water
Na+ 154 mmol/L
Cl- 154 mmol/L
Osmolarity: 308 mOsm/L
pH = 5 - 6.5
What are the potential problems with 0.9% NaCl
If used exclusively for fluid maintenance –>
- Hyperchloraemic metabolic acidosis may develop (especially in renal failure)
- Hypokalaemia
Compelling indication for 0.9% NaCl
Vomiting (must add potassium)
Name the three other saline solutions available for specific purposes
FIFTH normal saline (0.18%)
HALF normal saline (0.45%)
TWICE normal saline (1.8%)
NB –> the names of these solutions refer to their tonicity relative to normal saline and hence their tonicity relative to plasma
What are the indications for hypotonic saline: 0.18% NaCl + 4% glucose
In which scenario is this fluid not suitable
Used to replace INTRACELLULAR fluid loss in severe dehydration because it distributes throughout total body water
NOT SUITABLE for use alone to provide maintenance because it does not contain sufficient sodium to replace daily losses and hyponatraemia can occur
Describe the contents, ion concentration, osmolarity, pH of 0.18% NaCl + 4% Glucose
Content: 1.8 g NaCl with 40g glucose per litre of water
Ion concentration:
Na: 31 mmol/L
Cl: 31 mmol/L
Osmolarity:
277mOsm/L
What percentage of the body is composed of water
What is total body water
60% –> 70kg man: 42 kg is water and since 1L water weighs 1 kg –> 42 liters of total body water
How is total body water distributed in the body
Intracellular fluid: 28 L
Extracellular fluid: 14 L
- Interstitial fluid - 10L
- plasma volume - 3L
- trans-cellular fluid - 1L
What is trans-cellular fluid
The portion of total body water contained within epithelial-lined spaces, such as the cerebrospinal fluid, and the fluid of the eyes and joints.
How does the composition of stomach secretions differ at low and high secretion rates?
During high secretion rate the contents of stomach secretion differs in that the levels oh H, Cl, K are significantly increased and Na decreased
During low secretion rate - Na is significantly higher in the stomach
What is the fundamental difference between the secretion content of the stomach and the small bowel
NaHCO3 and K in Small bowel secretions
HCl and K in stomach secretions
How does the capillary membrane differ from the cell membrane in terms of movement of glucose, ions and water across it?
Since Na is the major determinant of fluid distribution across membranes and the fact that the cell membrane is impermeable to sodium, how is water absorbed into this intracellular space?
Capillary membrane - permeable to Na, K, Glucose, Water
Cell membrane - permeable to K, Water and glucose by facilitated diffusion (swopped for an IC Na ion)
Glucose moves by facilitated diffusion into the IC space. i.e. it is exchanged for a Na ion (one osmole) inside the cell the glucose is metabolized into 2 3 Carbon containing sugars = 2 osmoles. This increases the number of osmotically active particles inside the cell and draws water into the intracellular space
Which fluids allow water to move from the ECF into the ICF, and so distribute through the entire volume of body water?
Of the isotonic fluids:
0.18% NaCl + 4% Glucose
5% Glucose
All hypotonic fluids allow movement from ECF to ICF
Where does 0.9% NaCl allow water to distribute?
Only in the ECF. The lactate in Hartmann’s solution enter’s the cell taking a small proportion of water with it - but not as much as for the glucose containing fluids
Where do glucose containing isotonic fluids distribute?
Throughout the total body water
If a litre of 5% glucose is given, how much is found in:
Plasma
Interstitial fluid
Intracellular fluid
The distribution is in the same ratio as for the volumes of these three compartments. Plasma: interstitial fluid volume ratio is 1:3 and extracellular: intracellular fluid volume ratio is 1:2.
Thus, 333 ml is in the ECF and 667 ml is in the ICF. Of the 333 ml in the ECF, 83 ml is in the plasma and 250 ml in the interstitial fluid.
0.9% NaCl distributes through the ECF.
Question: If you give 1 litre of 0.9% NaCl, how much remains in the intravascular compartment?
The distribution ratio is the same as for the plasma; interstitial fluid ratio, which is 1:3. 250 ml remains in the intravascular space and 750 ml in the interstitial fluid compartment.
Why might 0.9% NaCl be preferred to Hartmann’s solution during surgery or during resuscitation when there has been significant haemorrhage?
The calcium in Hartmann’s solution can cause clotting of administered blood, so should not be in the giving set either just before or just after blood has been given.
Explain why sodium is the key determinant of the proportion of fluid that distributes to each compartment
For isotonic solutions, which contain a mixture of ions and/or glucose, sodium content is the key determinant of the proportion of fluid that distributes to each compartment. If there is no sodium, the fluid distributes evenly throughout total body water, as with 5% glucose. If there is only sodium, plus its anion, fluid distributes only through the ECF.
How does 0.18% NaCl + 4% glucose distribute into each compartment
In 0.18% NaCl + 4% glucose, the glucose part distributes through total body water, whereas the NaCl part is entirely limited to the ECF.
1/5 is effectively 0.9% NaCl, and 4/5 5% glucose.
For every litre given, 200 ml stays in the ECF and 800 ml distributes evenly throughout total body water, i.e. 1/3 in ECF and 2/3 in ICF.
So 533 ml is in the ICF and 467 ml in the ECF, of which a quarter remains intravascular, i.e. 107 ml.
What is the composition of compounded sodium lactate (Hartmann’s solution)?
Na 131 Cl 111 K 5.4 Ca 2.0 (Undesirable as can cause transfused blood to clot) Lactate 29
What constituent of Hartmann’s solution has be removed from more modern balanced salt solution resuscitation fluids such as plasmalyte
Calcium is not included in Plasmolyte to prevent the risk associated with co-administration of blood transfusion and risk of clotting of transfused blood
How many grams of potassium constitute 20 mmol of KCl
1.5 gram per 20 mmol
What is the daily potassium requirement and how can this be accomplished
80 mmol = 6 g of potassium
2 L of solution containing 3g/L potassium should provide sufficient daily potassium
Does Hartmann’s solution alone adequately replace potassium loss
1L of Hartmann’s contains 5.4 mmol of potassium which is 5% of daily requirement meaning that 20 bags of Hartmann’s would provide enough potassium for the day
What defines colloid solution
The colloids all contain large molecules that do not easily cross the capillary membrane and so remain in the intravascular compartment. This increases the colloid oncotic pressure in the capillary.
What is oncotic pressure
Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure induced by proteins, notably albumin, in a blood vessel’s plasma (blood/liquid) that displaces water molecules, thus creating a relative water molecule deficit and creates an oncotic force which is opposite to the hydrostatic forces present in the capillary
Intra-operatively, what are colloids used for?
- Replace blood loss that does not trigger transfusion requirements
OR
- To buy time until blood products are available following significant haemorrhage
What are the three important groups of colloids
Modified Gelatins
Dextrans
Etherified starches
How are gelatins produced?
Hydrolysis of bovine collagen followed by modification of the resulting fragments
Name the two modified gelatins available, describe how their synthesis and constituents differ
Gelofuscin 3.5% is a succinylated modified fluid gelatin
- Mean molecular mass = 35 000
- Na 154
- Cl 120
Haemaccel 4% contains urea-linked gelatin polypeptides
- Mean molecular mass = 30 000
- Na 145 mmol/L
- Cl 145 mmol/L
- K 5.1 mmol/L
- Ca 6.25 mmol/L
What are the main disadvantages for Haemaccel 4% and for Gelafusine 3.5%
Haemaccel - Contains calcium which can lead to clotting of blood administered through the same giving set
Gelofusine 3.5% - Do not interfere with cross-matching but have the HIGHEST ANAPHYLACTOID HYPERSENSITIVITY reactions of all the colloids
What are dextrans?
Branched polysaccharides
What are the two available dextransand what is their use
Dextran 40 (mean molecular mass = 40 000) - NOT used as a plasma expander --> It improves blood flow and is used in the treatment of peripheral vascular disease
Dextran 70 (mean molecular mass = 70 000) - Plasma expander
What are the major problems with dextrans
Interfere with cross matching and laboratory tests of coagulation (although not with more modern techniques)
Hypersensitivity reactions: 1 in 3000
What is an etherified starch
Glucose polymers containing mainly amylopectin (branched glucose chains) that has been etherified (the process of converting a substance - as an alcohol or phenol - into an ether.) with hydroxyethyl groups (R-C-O-C2H3)
Name the Hydroxyethyl Starches (HES) / Etherified Starches and give an explaination of the prefix in each name
There are several starches available and they differ in the degree of etherification. Hexastarch is more etherified than pentastarch, which is more etherified than tetrastarch.
Hexastarch
Pentastarch
Tetrastarch
Hetastarch
How are the Starches removed from the body
Very slowly by the reticulo-endothelial system
What is the reticulo-endothelial system (RES)
The reticuloendothelial system (RES) removes immune complexes from the circulation in healthy persons, and is formed of phagocytic cells that are found in the circulation and in tissues. The RES encompasses monocytes of the blood, macrophages in connective tissue, lymphoid organs, bone marrow, bone, liver, and lung.
What is the maximum recommended daily volume for Etherified Starches
2500mL
Which cause a longer plasma expansion HES versus Dextrans versus gelatins
HES - longest duration plasma expansion
What is the osmolarity of gelatins compared to plasma
Gelatins are isosmotic with plasma (approximately 300 mOsm/kg).
