5- Fluid replacement and renal response Flashcards
What is osmolality
Number of particles of solute per Kg of solvent mOsm/g
What is osmolarity
Solute per litre of solution mOsm/L
What is tonicity
Effective osmotic pressure gradient of two solutions separated by semipermeable membrane
Where does water move when hypotonic
Into cells = swells
Distribution of water in Male
60% 2/3 ICF 1/3 ECF 25% plasma 75% interstitial
Why do women have less fluid
More fluid in muscle then in fat
55% in women 60% men
Total body water of baby
75%
Total body water of elderly
45%
Main intracellular cation and anion
K and PO4
Main extracellular cation and anion
Na and Cl-
What happens to water in hypernatremia
Water drawn out of cell
Shrinks
Confusion/ seizures
What happens to water in hyponatremia
Water moves into cells
Swells
Cerebral oedema
Headache/ seizures
Where does 5% dextrose distribute
Glucose taken up by cell H2O reduces osmolarity of all compartments 2/3 rd to intracellular 1/3 to interstitial 1/12 to intravascular
Where does NaCl 0.9% go
Remains in ECF
3/4 interstitial
1/4 intravascular
Where does Hartmanns go
Majority retained in ECF
3/4 and 1/4
Composition of Hartmanns
Na, K, Ca, Lactate (metabolised into HCO3)
Where does 4% dextrose, 0.18% saline go
Effectively 200ml NaCl and 800ml dextrose
200ml remains in ECF
Then 800 ml distributes 2/3, 1/4, 1/12
Why do patients need fluid
NBM GI malfunction Fluid loss Dehydration Electrolyte imbalance
How are hospitalised patients requirements different
Do not sweat excessively
Stress response- RAAS - Na reabsorbed = retention
ADH- pain, nausea, drugs
NICE guidelines- maintenance
25-30ml/kg/day water
1mmol kg/day K,Na,Cl
50-100g/day glucose
NICE guidelines- resus
500ml bolus
Up to 2L
How do we lose Na
Vomiting
NG tube
Biliary drainage lost
Pancreatic drain, colostomy, ileostomy
How do we lose K
Vomiting
Diarrhoea
When does congestive cardiac failure occur
When heart muscle pump cannot cope with workload
Output falls
Fails to perfuse tissues
What does hypoperfusion in CCF lead to
Renal hypoperfusion sensed by kidneys as hypovolemia which results in compensation and retention in NaCl and water to increase circulating volume.
Edema
How does pulmonary oedema come around
Increased pulmonary venous pressure = transudate from capillaries in lungs
How do you manage pulmonary oedema
ACEI
Diuretics
Vasodilators
Causes of fluid overload
Excess of body salt and water Retention by kidneys Reduced effective arterial volume Decreased effective circulating volume- CCF Cirrhosis- protein in plasma Hyperaldosteronism
How does hypovolemia lead to shock
Inadequate perfusion
Hypoxic state leading to anaerobic metabolism and inefficient clearance of metabolites
Tired, dizzy, thirst
Vasodilation occurs to maintain blood supply = acute tubular necrosis = AK
Severe decrease in circulating volume leads to
Stimulation of sympathetic activity by increases HR, peripheral vasoconstriction and increased contractility of heart.
How to kidneys react to systemic vasoconstriction
Prostaglandins released to maintain GFR by dilating afferent
Acid base disturbances in hypovolemic shock
Na involved in co-transport of H, K, Cl
as Na is retained this disturbs H distribution
Initially increase in H and K secretion = met alkalosis and hypokalemia
Then shift to anaerobic metabolism as a result of hypoxia = metabolic acidosis
As hypovolemia worsens less urine and less H secretion = more acidosis.
Changes seen in hypertensive renal disease
Arteriosclerosis of renal arteries
Hyalinization of small vessels with intimal thickening- respond to myogenic feedback
Can lead to reduced kidney size and chronic renal damage (hypertensive nephrosclerosis)
Secondary hypertension
- Impaired excretion
- Stenosis
- Renal causes
Impaired Na and water excretion = increase blood volume
Renin release - Renal artery stenosis = reduced perfusion = excessive activation of RAAS
