Water/Electrolyte Balance and Diarrhoea Flashcards
In a healthy person how much water is absorbed through the GI tract every day?
9L
In a healthy person how much water is expelled in faeces every day?
100-200ml
What is the approximate value of daily insensible loss?
800ml
2L of the 9L of fluid that are absorbed every day by the GI tract are from dietary intake. Where does the remaining 7L come from?
Salivary, gastric, pancreatic, biliary and intestinal secretions
How does increase fluid lead to a self perpetuating cycle that presents as diarrhoea?
Increased fluid causes more rapid propulsion of the intestine which decreases the amount of absorption which can take place and leads to further fluid accumulation. This is a self perpetuating cycle which results in diarrhoea
Give example of drugs and conditions which can lead to osmotic diarrhoea?
Laxatives Antacids Acarbkse Orlistat Digestive enzyme deficiencies Pancreatic insufficiency Inflammatory disease Short bowel syndrome
What is osmotic diarrhoea?
Diarrhoea which results from either the accumulation of non absorbable solutes or a failure to digest or absorb nutrients
What molecules are absorbed in the large intestine?
Water
Electrolytes
Short chain fatty acids
Which transporter protein is responsible for the cotransport of sodium and glucose?
SGLT1
Once sodium and glucose have been absorbed into the enterocyte, how do they e it the enterocyte?
Glucose moves out via facilitated diffusion with a GLUT2 transporter in the basolateral membrane
Sodium is actively pumped out of the cell at the basolateral membrane via the sodium potassium pump
Why are low osmolality oral rehydration salts preferable than isoosmotc ORS in the treatment of diarrhoea?
These further reduce the need for IV fluid use as the low osmolality prevents any unwanted secretion of water into the intestinal lumen
List some of the causes of secretory diarrhoea?
Infections such as rotavirus, e.coli, shigella, campylobacter, salmonella and v cholerae
Carcinoid syndrome
Zollinger ellison syndrome
How can inflammation cause diarrhoea?
This can damage the epithelium and impair its ability to absorb water and electrolytes
Infection with which bacterium commonly causes bloody diarrhoea?
Shigella
Describe how diarrhoeal disease might be prevented
Vaccinations against organisms such as rotavirus and measles which can cause diarrhoea
Good hand washing
Improved sanitation
What are the differences between colloid and crystalloid IV fluids?
Colloids are large molecular weight molecules which act to increase blood volume
Crystalloids contain water and electrolytes and restore water homeostasis in tissues - these include saline and dextrose solutions
What percentage of saline solution will remain intravascular after infusion?
25%
What percentage of dextrose solution will remain intravascular after infusion?
10%
Describe the situations in which you would choose to use IV saline or IV dextrose solutions to treat diarrhoea
Saline is used when the patient has lost both water and electrolytes
Dextrose is used when the patient has only lost water
0.9% saline is most commonly used, why is this?
Because this is closest to the physiological level of sodium
Which IV fluid may be used to treat metabolic acidosis and why?
Ringer lactate solution as the lactate in this solution is readily metabolised and will produce bicarbonate ions
What ratio of saline:dextrose is most commonly given as a postoperative regimen?
2:1
What patient factors will influence the rate of fluid replacement?
Age Cardiovascular status Renal function Severity of dehydration Length of time it took to become rehydrated
What volume of fluid is contained in a standard IV fluid bag?
500ml
