Fluid and Electrolyte Balance Flashcards
Describe the different body fluid compartments and the approximate proportion of fluid inside each one
Intracellular – 60% - Inside of cells
Extracellular – 40% - Interstitial compartment (fluid surrounding cells), Intravascular component (blood)
Discuss the pressures involved in the movement of water between the plasma, interstitial fluid, lymphatic vessels and intracellular fluid.
Hydrostatic Pressure (push) and Oncotic Pressure (pull).
Hydrostatic pressure (‘pushing force’), pushing the fluid out of the capillaries (pressure of the fluid on the capillary walls)
Oncotic pressure (‘pulling force’), pulling fluids from the surrounding tissue into the capillaries. It’s the result of a difference in the concentration of solutes in the fluid inside the capillaries as opposed to outside them, because water will naturally seek a state of balance in the concentration of solute (particles).
As fluid leaves the capillaries as a result of hydrostatic pressure, albumin and other large proteins cannot pass through the capilary walls. This results in a greater concentration of solutes inside the capillaries as opposed to outside of them, and the oncotic pressure rises, pulling more water into the capillaries in order to balance the solute concentration.
Whenever hydrostatic pressure is greater than oncotic pressure, fluid will leave the capillaries, whenever the onctoic pressure is greater than the hydrostatic pressure fluid will enter the capillaries.
Explain how an increase in capillary hydrostatic pressure causes oedema, and how a decrease in capillary oncotic pressure causes oedema.
Hydrostatic - fluid is pushed from the capillaries into the surrounding tissue. Hydrostatic pressure pushes fluid out of the capillaries and into the tissue causing a build up of fluid resulting in swelling/oedema.
Oncotic - pressure decreases, less fluid is pulled from the surrounding tissue into the capillaries resulting in an excess of fluid in the tissue which causes oedema.
Describe what is meant by fluid being in the third space
Third spacing is when body fluids collect somewhere that is not in one of the two compartments where your body can use it. Fluid in third spaces is outside of the circulatory system and cannot be used by the body.
Briefly describe how sodium, chloride and potassium are normally kept in balance
If serum sodium levels are decreased (leading to a shift in fluid balance so that blood also decreases) or potassium levels are too high, the renin-angiotensin-aldosterone system is activated and the body secretes aldosterone, which causes the kidneys to reabsorb sodium and secrete potassium into the filtrate, adjusting the balance back to normal. Aldosterone also causes more potassium to be excreted in sweat. Chloride has a negative charge that allows it to interact with sodium so the passive transport of chloride follows the active transport of sodium, with levels rising and falling in concert.
Briefly list some common causes of water deficit
Insufficient fluid intake, haemorrhage, severe wound drainage, excessive diaphoresis (sweating), vomiting, diarrhoea, diuretic medications.
List some causes of water excess
caused by compulsory water drinking, decreased urine formation, the syndrome of inappropriate secretion of antidiuretic hormone
Why is the healthy body unable to remain in a state of water excess?
water excess = hypervolemia = diluting effect of excess plasma volume leads to decreased haematocrit + decreased plasma protein concentration = increased BP = increased capillary hydrostatic pressure = oedema leading to pulmonary oedema and heart failure
Discuss what metabolic dysfunctions occur in potassium deficiency and in potassium excess
Potassium deficiency:
- Carbohydrate metabolism is affected because insulin secretion is depressed and muscle and liver glycogen synthesis is reduced
- Metabolic alkalosis can occur because, as potassium moves from the intracellular fluid (ICF) to the ECF, hydrogen ions move into the cells to maintain cation balance
- Polyuria and volume depletion can occur because decreased potassium levels impair renal function, resulting in a decreased ability of the kidneys to respond to ADH and to concentrate urine
- Skeletal, smooth, and cardiac muscle weakness and cardiac dysrhythmias can occur because low potassium levels decrease neuromuscular and cardiac excitability.
Potassium excess:
• Skeletal, smooth, and cardiac muscle excitability is increased
• Cardiac dysrhythmias such as heart block and cardiac arrest can occur
• Metabolic acidosis can occur as potassium moves from the ECF into the cells and intracellular hydrogen ions move out of the cells and into the ECF
• Renal function is affected, resulting in fluid retention and oliguria.
What is the most prominent ECG change associated with hyperkalaemia?
Peaked T waves, small or indiscernible P waves. Shorter QT interval.
What is the most prominent ECG change associated with hypokalaemia?
flattened T wave, with a larger U wave, and ST segment depression (as it progresses inverted T waves can be seen with slightly prolonged PR interval)
Identify four clinical manifestations associated with respiratory alkalosis
- Dizziness
- Numbness and tingling - the mouth, hands and feet
- Dyspnoea
- Chest tightness
- Seizures
- Loss of consciousness
Explain how hyperglycaemia contributes to dehydration and metabolic acidosis.
With regard to renal tubular reabsorption: glucose is an example of a substance for which there is a threshold to reabsorption. That is, beyond a certain concentration in the tubular filtrate any excess glucose will not be reabsorbed. As glucose is filtratable at the glomerulus so the initial filtrate glucose concentration will reflect blood glucose level. Thus in the hyperglycaemia: the filtrate will also have an elevated glucose concentration. Under these circumstances the concentration of glucose in the filtrate exceeds the threshold (thus glycosuria). There will be excess glucose in the filtrate which will increase filtrate osmotic pressure and so reduce water reabsorption (thus osmotic diuresis).
Type 1 diabetes mellitus represents an insulin deficiency. The reduction in insulin will lead to reduced cellular uptake of glucose and also reduced triglyceride synthesis. Under these circumstances there will be elevated fatty acid breakdown. With reduced glucose consumption, acetyl-CoA will accumulate and lead to increased ketone/ketone body formation. Blood levels of ketone bodies will rise: these ionise to hydrogen ions and the paired base. The elevated hydrogen ions will react with bicarbonate leading to a decrease in blood bicarbonate levels which is clinically a metabolic acidosis.
Identify five risk factors associated with the development of fluid, electrolyte and acid-base imbalances.
- age
- gender
- environment
- chronic diseases
- trauma
- therapies
- gastrointestinal losses
Explain the clinical implications of hypovolaemia
can lead to insufficient vascular volume, tachycardia, hypotension and, if severe, to hypovolaemic shock. Other manifestations include rapid weight loss, dry skin and mucous membranes, and a decreased urine output.
Explain the clinical implications of hypervolaemia
causes the blood volume and blood pressure to increase, and leads to oedema and heart failure.
Discuss the role of Antidiuretic hormone in maintaining homeostasis of body fluids
When fluid volume decreases, the concentration of sodium in the blood will increase (increased osmolarity), which in turn stimulates the hypothalamus. The hypothalamus is an osmoreceptor - a sensory end organ that reacts to changes in osmotic pressure and has an effect on the pituitary gland.
In response, the posterior pituitary gland releases antidiuretic hormone (ADH) into the bloodstream, resulting in the kidneys retaining water. This in turn results in more concentrated urine and an increase in water returned to the ECF, thus correcting the volume depletion.
When sodium concentration in the blood decreases the adrenal cortex is stimulated into secreting the hormone aldosterone, which instructs the distal nephrons of the kidney to retain more sodium. Normal levels of sodium in the ECF will attract and maintain the optimum amount of water.
Definition Arterial Blood Gases (ABGs)
The sampling of the blood levels of oxygen and carbon dioxide within the arteries, as opposed to the levels of oxygen and carbon dioxide in venous blood. Typically the acidity, or pH, of the blood is measured simultaneously with the gas levels in ABG sampling.
Definition of PaO2
The partial pressure of oxygen, also known as PaO2, is a measurement of oxygen in arterial blood
Definition of PaCO2
Partial pressure of carbon dioxide in arterial blood. It evaluates how well carbon dioxide (CO2) moves from the lungs into the blood
Definition of Base Excess
The base excess is defined as the amount of H+ ions that would be required to return the pH of the blood to 7.35 if the pCO2 were adjusted to normal.
Definition of Haematocrit
The ratio of the volume of red blood cells to the total volume of blood.
Definition of Difussion
The passive movement of molecules or particles along a concentration gradient, or from regions of higher to regions of lower concentration.
Definition of Osmosis
Diffusion of a solvent (usually water molecules) through a semipermeable membrane from an area of low solute concentration to an area of high solute concentration
