Ch.3 Fluids, Electrolytes and Acid-Base Therapy Flashcards
The volume of total body water (TBW) represents what % of body weight in adults?
60%
The volume of total body water (TBW) represents what % of body weight in neonates?
Up to 70%
ECF Extracellular fluid represents what % of total body water (TBW) in adults?
33% of TBW (20% of body weight)
ECF Extracellular fluid represents what
% of total body water (TBW) in neonates?
40% of TBW decreases to 30% by week 24
ICF Intracellular fluid represents what % of total body water (TBW) in adults?
66% of TBW (40% of body weight)
What is the ECF composed of?
75% interstitial fluid
25% plasma
<1% lymph, transcellular fluids - synovial, pleural, abdominal, cerebrospinal
What is the normal volume of gastrointestinal secretion in horses per 24hr
100L/24Hr in a 500kg
Blood volume represents what % of body weight
8% in sedentary horses up to 14% in fit horses
Blood volume represents what % of body weight in neonates
15% decreases to 8% by 12 weeks
What are the significant components of interstitial fluid
Sodium
Bicarbonate
Chloride
Interstitial fluid makes up what % of the ECF?
75%
What are the main cations and anions in plasma?
Cation - Sodium
Anions - Bicarbonate and Chloride
Plasma has more protein than interstitial fluid and these act as anions, how is this compensation for in the interstitial fluid
Increased chloride
What are the important cations and anions of ICF?
Cations - Potassium, Magnesium
Anions - Phosphates and proteins
Define Osmolality
The concentration of osmotically active particles in solution per kg of solvent (mOsm/kg)
Define osmolarity
The number of particles of solute per litre of solvent (mOsm/L)
What is normal plasma Osmolality for adult horses
275-313 mOsm/kg
What is starlings equation and what does it describe
Net filtration = Kf<(Pcap - Pint) - delta(Pie p - Pie int)>
extracellular fluid movements between blood and tissues are determined by differences in hydrostatic pressure and colloid osmotic pressure between plasma inside microvessels and interstitial fluid outside them
What does COP (Colloid osmotic pressure) represent
The osmotic pressure generated by proteins mainly albumin
What are normal COP readings for adult horses and foals
19.2 - 31.3mmHg Adult
15 - 22.6mmHg Foal
Describe the endothelial glycolax layer
1 - Space between the plasma volume and endothelial cells lining the capillaries
2 - Contains no proteins
3 - Prevents movement of fluid from interstitial compartment to the capillaries
Forces that retain fluid in vascular space
1- Plasma oncotic pressure
2 - Tissue hydrostatic pressure
Forces that favour filtration
1 - Capillary hydrostatic pressure
2 - Tissue oncotic pressure
How is fluid transferred back into the capillaries from the interstitial space?
Fluid cannot be absorbed back into the capillaries from the interstitial space, instead it returns to circulation via the lymph
What is the ECF osmolarity formula?
Used to estimate serum osmolarity
2<(Na+(mmol/L)> + glucose(mmol/L)/18 + urea(mmol/L)/2.8
Exchanges between the extra and intracellular compartments are fast or slow? How long do they take to reach equilibrium
Slow
Up to 24 hours
Normal Cation values in an adult horse
1) Sodium 132 - 146 mmol/L
2) Potassium 2.4 - 4.7 mmol/L
3) Calcium 2.8 - 3.4 mmol/L
a- Ionized Ca 1.0 - 1.3 mmol/L
4) Magnesium 0.9 - 1.15 mmol/L
a- Ionized Magnesium 0.4 - 0.55 mmol/L
Normal Anion values in an adult horse
1) Chloride 99 - 109 mmol/L
2) Lactate 1.11 - 1.78 mmol/L
3) Total CO2 24 - 32 mmol/L
4) Plasma protein 58-87 g/L
a) Albumin 29 - 38 g/L
Normal venous blood gas values in adult horses
1) pH 7.32 - 7.44
2) pCO2 38 - 46 mmHg
3) pO2 37 - 56 mmHg
a- arterial 80 - 100 mmHg
4) HCO3- 20 -28 mmol/L
5) Base excess -2 to +2 mmol/L
Stewart’s definition of acids and bases
Acids increase H+ in fluid
Bases decrease H+ ih fluid
Describe the traditional approach to determine the acid-base and electrolyte status of a patient
Henderson-Hasselbach
1) Centered on pH, bicarb, hydrogen ions
2) HCO3- and H+ are independent
3) pH is maintained within narrow margins in health
4) Buffering of acids and bases
Describe the quantitative strong ion approach to determine the acid-base and electrolyte status of a patient
1) Centred on strong ions, weak acids and bases
2) HCO3- and H+ are dependent on strong ions and weak acids and bases
3) Concentration of strong ions are maintained within narrow margins in health
4) Change in the dissociative state of weak acids to satisfy rule of electroneutrality, conservation of mass and dissociation equilibrium
How many mmol/L of H+ is present in the body?
0.0004 mmol/L
What is the primary buffer system of the extracellular fluid
Bicarbonate
What are the primary buffers of the intracellular fluid
Protein and inorganic and organic phosphates
In body fluids pH is a function of what ratio
HCO3- : pCO2
20 : 1
What do metabolic (acid-base) disorders refer to
Net excess or deficit of nonvolatile or fixed acid
(lactate, acetate, pyruvate, citrate)
What do respiratory (acid-base) disturbances refer to
Net deficit or excess of volatile acid (dissolved CO2)
What is metabolic acidosis and what is a common cause of it in horses
Decrease in HCO3- due to loss or buffering nonvolatile acids (lactate, pyruvate, citrate, acetate)
Accumulation of lactate due to poor perfusion and HCO3- losses in the GI tract from diarrhoea
What is metabolic alkalosis and what is a common cause in horses
Increased conc of HCO3-
Loss of chloride through sweating or reflux
Tachypnea may cause respiratory acidosis or alkalosis?
Alkalosis
How does the body compensate for respiratory disorders
Initial titration by nonbicarb buffers
Chronic response mediated by the kidney - net acid secretion and bicarbonate resorption - 2-5 days to be complete
What are the strong ions?
Exist completely dissociated in solution
Cations: Na+, K+, Mg++, Ca++
Anions: Cl-, Lactate
Cl-, K+ and Na+ are present in high concentrations
How is SID strong ion difference calculated
(Na+ + K+) - (Cl- + lactate) = 38 - 42
What causes an increased SID
Metabolic alkalosis
What causes a decreased SID
Metabolic acidosis
What does Atot represent
Total mass of nonvolatile weak acids mainly comprised of proteins and in ruminants phosphate
Are total proteins weak acids or weak bases
Weak acids
How is blood collected for blood gas analysis?
Anaerobically
Anticoagulant - lithium heparin
Introduction of room air will falsely increase the pO2
How does temp affect the pO2 and pCo2
Increased temp gas is less soluble - increases pO2 and pCO2
decreased temp gas is more soluble - decreases in pO2 and pCO2
What are the measured values and calculated values provided by the gas analysers
Measured - pO2, pCO2, pH
Calculated - Total CO2, HCO3- and Base Excess
What does the AG anion gap measure?
AG = (Na+ + K+) - (Cl- + HCO3-)
The difference between the sum of the commonly measured cations and anions
The negatively charged plasma proteins are responsible for what % of the normal AG
90%
What is a normal AG
10.4 +/- 1.2mmol/L
SIG (strong ion gap) measures what?
Unmeasured anions
How to avoid in vitro lactate production by erythrocytes in a sample
Analyze immediately
Use a fluoride containing tube
Store on ice
Separate plasma
What is the difference between replacement fluids and maintenance fluids
Maintenance - lower Na+ and Cl-
- higher Ca++, K+ and Mg++
What is the maintenance fluid requirement for a horse
60 ml/kg/day (2.5ml/kg/hr)
Variables used to determine degree of dehydration
1) HR Ranges 40 - >100
2) CRT 2 - >4
3) PCV/TP 40/70 - >50/>80
4) Creatinine 132 - >350
When lack of water intake is prolonged what steps should be taken in replenishing
Slowly to allow time for slow fluid shifts to occur
When is the use of IV Saline indicated
If acute hyponatremia is present
Na+ <125 mmol/L for 24 hours or less
or
If there is severe hypochloremia relative to hyponatremia
Why should IV saline not be used in cases of metabolic acidosis
It has a pH of 5
Longterm fluid maintenance with BES will result in?
Hyperchloremia
Hypernatremia
Hypocalcema
Hypokalemia
Hypomagnesemai
Low concentrations of serum ionized Ca and Mg are more prevalent in what colic cases
Surgical GI disease
Esp SI or large and small colon non strangulating infarction or strangulation
and in post op ileus
Enterocolitis
How much 23% Calcium gluconate is usually sufficiency to maintain normocalcemia
50-100ml per 5L bag
Hypocalcemia which is refractory to calcium therapy may indicate what
Hypomagnesemia
What is the maintenance req of Mg2+
13mg/kg/day
When Mg2+ is provided by MgO, MgCO3 or MgSO4 what are their respective doses?
MgO - 31 mg/kg/day
MgCO3 - 64 mg/kg/day
MgSO4 - 93 mg/kg/day
At what rate should K+ be administered
No faster than 0.5 mmol/kg/hr
Rules of thumb fro choosing NaHCO3 supplementation in acute severe metabolic disorders
- Horse should have normal respiratory function
- Hyponatremia in relation to Cl- conc should be present
- Blood pH should be less than 7.2
- Half of the calculated amount should be administered rapidly, the remainder over 12-14 hrs
- IV Na bicarb should not be given with Ca+ containing sols
What concentrations in NaHCO3- injectable available in
5% - contains 0.59 mmol/ml of HCO3- and 0.59 mmol/ml of Na+
8.4% - contains 1 mmol/ml of each
How many mmol of HCO3- in 1gram of baking soda?
12
As a source of energy dextrose can be administered at what dose
1-4 mg/kg/min
Hypertonic saline is what conc
7.2% NaCl
How does the tonicity of Hypertomic crystalloids compare to plasma
Hypertonic saline has 9 times the tonicity of plasma and ECF (Na+ 1232 mOsm/L, Cl- 1232 mOsm/L)
How many litres does hypertonic saline expand blood vol by
2L
What is the duration of effect of hypertonic saline
45mins
What is the recommended dosage of hypertonic saline
4ml/kg or 2L/500kg
When is Collodi use indicated
TP <40g/L (4g/dl)
Albumin <20g/L (2g/dl)
Oncotic pressure <12 mmHg
Clinical signs of hypo proteinemia
Calculating plasma dose
Plasma to be delivered (L) =
(TPdes - TPpt) x 0.05BWkg / TP don
What molecular weight colloids are advised
Low molecular weight and molar substitution 130kDa/0.4
Dose of HES
10ml/kg/day
What dose of HES has been associated with coagulopathies
20ml/kg/day
What effect do HES have on protein
Dilutes it due to its oncotic effects decreasing the measured TP
Dose of crystalloids for dehydration or shock
20ml/kg bolus over 30-60mins followed by another 10-20ml/kg if required
Maintenance crystalloid fluid rate following bolus in dehydrated horse who is stabilising
2-4ml/kg/hr
How would you prepared an isotonic electrolyte solution for oral fluids
Per 1L of tap water add
5.27g of NaCl
0.37g of KCl
3.78f of NaHCO3-
135 mmol/L Na+
95 mmol/L Cl-
5 mmol/L K+
45 mmol/L HCO3-
Osmolarity - 255mOsm/L
What is the least thrombogenic catheter material
Silastic
What is the most thrombogenic catheter material
Polypropylene, polyethylene
How often should teflon and polyurethane catheters be replaced
Teflon - 3 days
Polyurethane - 2 weeks
