Unit 9 Fluid Electrolytes / Acid-base Balance Flashcards
What hormones act on the kidneys?
Antidiurectic Hormone (ADH), also known as vasopressin, functions include:
- water balance; acts on aquaporines in kidney (closes them to decrease loss of H2)
- decrease urine production (act on kidneys)
- decrease sweating (sudiferous, sweat, glands)
- increase BP (arterioles)
Aldosterone (mineralocorticoid) functions include:
- Sodium balance
- increase reabsorption of Na+ with Cl- , bicarbonate and water following it
- promotes excretion of K+ and H+
ANP
- Sodium balance
- produced from specialized atrial myocardial cells
- inhibits Na+ reabsorption
- promotes natriuresis and accompanying diuresis
How is aldosterone regulated by the body?
Aldosterone production is regulated by the Renin-Angiotensinogen-Aldosterone System (RAA)
1) dehydration, Na+ deficiency, or hemorrhage reduces BP (sensed by juxtaglomerular cells in kidneys)
2) humoral effects
- kidney produces renin
- liver produces angiotensinogen
- renin and angiotensinogen = angiotensinogen I
- lungs + ACE = angiotensinogen II
3) Adrenal cortex increases production of aldosterone
- angiotensinogen II = vasoconstriction of arterioles
- aldostertone = kidney effects include increased NA+ absorption and water reabsorption; increased K+secretion into urine; results increased blood volume
4) Increases the BP!
What are the two actions of angiotensinogen II?
- stimulates adrenal gland to produce aldosterone
- alters blood pressure by causing vasoconstriction
Describe the bodies general responses during periods of dehydration.
1) Trigger hypothalamus
- stimulates thirst centre
- hormone production (post. pituitary) - kidney to decrease urine volume, and increase its concentration
2) Other
- sweat glands
- blood vessels
What are the general responses of the body to overhydration?
Increased fluid results in increased blood volume this triggers the hypothalamus to produce hormones resulting in:
- ANP production (produce by atria in response to the distended wall of atria), results in Na and water elimination
- kidney which increases urine volume producing diluted urine
What is the relationship between acidosis and hyperkalemia?
Why does hyperaldosteronism result in hypernaturiemia and hypokalemia?
What conditions result in activation of the RAA system?
- decreased arterial pressure
- decreased Na
- decreased ECF volume
- increased K in plasma
What is hyperkalemia?
Hyperkalemia refers to the condition in which the concentration of the electrolyte potassium (K+) in the blood is elevated. Extreme hyperkalemia is a medical emergency due to the risk of potentially fatal abnormal heart rhythms (arrhythmia).
Potassium is the most abundant intracellular cation. It is critically important for many physiological processes, including maintenance of cellular membrane potential, homeostasis of cell volume, and transmission of action potentials in nerve cells. Its main dietary sources are vegetables (tomato and potato), fruits (orange and banana) and meat. Elimination is through the gastrointestinal tract and the kidney.
The renal elimination of potassium is passive (through the glomeruli), and reabsorption is active in the proximal tubule and the ascending limb of the loop of Henle. There is active excretion of potassium in the distal tubule and the collecting duct; both are controlled by aldosterone.
Hyperkalemia develops when there is excessive production (oral intake, tissue breakdown) or ineffective elimination of potassium. Ineffective elimination can be hormonal (in aldosterone deficiency) or due to causes in the renal parenchyma that impair excretion.
Increased extracellular potassium levels result in depolarization of the membrane potentials of cells. This depolarization opens some voltage-gated sodium channels, but not enough to generate an action potential. After a short while, the open sodium channels inactivate and become refractory. It raises the charge closer to the action potential threshold, thus less sodium entry is needed to produce an action potential. This leads to the impairment of neuromuscular, cardiac, and gastrointestinal organ systems. Of most concern is the impairment of cardiac conduction which can result in ventricular fibrillation or asystole.
During extreme exercise, potassium is released from active muscle, and the serum potassium rises to a point that would be dangerous at rest. High levels of adrenaline and noradrenaline have a protective effect on the cardiac electrophysiology because they bind to beta 2 adrenergic receptors, which, when activated, extracellularly decrease potassium concentration.[8]
Patients with the rare hereditary condition of hyperkalemic periodic paralysis appear to have a heightened muscular sensitivity that is associated with transient elevation of potassium levels. Episodes of muscle weakness and spasms can be precipitated by exercise or fasting in these subjects.
Decribe the situations that result in secretion of ANP.
- high NaCl
- high ECF volume
- high arterial BP
Describe how ANP corrects high NaCl concentration, ECF volume and arterial blood pressure.
Describe the interaction between Na and water.
- Because water follows the osmotic gradients, sodium balance and water balance are intimately related
- Chloride is the major anion in the ECF, and provides electrical neutrality to sodium
- The transport of chloride is passive and follows the active transport of sodium
Describe the fluid distribution in the body.
Body fluid contain water and electrolytes
Body fluid -60% of body weight
ICF – 40% (2/3)
ECF – 20% (1/3)
- 20% - intravascular (plasma)
- 80% - interstitial fluid including small amount of transcellular fluid
- Transcellular fluids (3 types): fluid in body cavities, cerebrospinal fluid, fluid in joint spaces
What is the difference between osmotic pressure and tonicity?
The tension or effect that the effective osmotic pressure of a solution with impermeable solutes exerts on cell size because of water movement across the cell membrane
Solutions can be classified according to whether or not they cause cells to shrink.
- Isotonic: neither shrink nor swell
- Hypotonic: swell
- Hypertonic: shrink
Tonicity is commonly used when describing the response of cells immersed in an external solution. Like osmotic pressure, tonicity is influenced only by solutes that cannot cross the membrane, as only these exert an osmotic pressure. Solutes able to freely cross the membrane do not affect tonicity because they will always be in equal concentrations on both sides of the membrane.
OP is directly related to tonicity.
Not that there are penetrating and non-penetrating solutes.
What forces favour filtration and what forces favour reabsorption?
A. Forces favoring filtration (from capillaries to the interstitial space)
- Capillary hydrostatic pressure (blood pressure)
- Interstitial oncotic pressure (water-pulling)
B. Forces favoring reabsorption (from interstitial space to the capillaries) with some fluid remaining (this drains to the lymph)
- Plasma oncotic pressure (water-pulling)
- Interstitial hydrostatic pressure
Final outcome – A greater or B greater = net filtration
**proteins are the primary contributor to osmostic pressure**
What are three alterations in fluid distribution?
What physiolgoical mechanisms contribute to edema formation?
- Increase the capillary filtration pressure
- Decrease the capillary colloidal osmotic pressure
- Increase capillary permeability
- Produce obstruction to lymph flow
What are major causes of edema according to the following categories:
- hypoprotemia - causes water retention in ISF
- hypertension
- capillary damage
- blockage of lymphatic system
What is dependent edema?
Dependent edema is a condition in which there is an accumulation of fluid underneath the skin that causes abnormal swelling. This usually happens in areas of the body that are lower than the heart. The most common sites for dependent edema are the arms, legs, and ankles. There are several health factors that can cause this type of swelling.
The most common cause of dependent edema is a condition called congestive heart failure. This is a condition in which the muscles of the heart become too weak to effectively pump blood throughout the body. A symptom of congestive heart failure is swelling of the lower legs and ankles. If an individual with congestive heart failure does not get treatment for this condition it could produce more serious symptoms.
Another cause of dependent edema can be damage to the kidneys. The kidneys are responsible for removing excess waste and fluid from the body. When the kidneys become damaged, this can cause swelling as the fluid builds up in the body. High blood pressure and diabetes are both chronic conditions that can damage the kidneys.
Describe how the following conditions contribute to the formation of edema:
- burns, allergic inflammation reactions
- cirrhosis, malnutrition
- lymph obstruction
- venous obstruction, salt/water retention, heart failure
How is pitting edema graded?
Grading edema
1+: slight pitting/2 mm, disappears rapidly,
2+: somwehat deeper pit/4 mm, disappears in 10-15 sec
3+: deep pit/6 mm, may last > 1 minute; dep extremity swollen
4+: very deep pit/8 mm, lasts 2-5 min, dep extremity grossly distorted
What is third spacing?
The third space is space in the body where fluid does not normally collect in larger amounts,[5][6] or where any significant fluid collection is physiologically nonfunctional.[7]
Major examples of third spaces include the peritoneal cavity and pleural cavity. Still, small amount of fluid does exist normally in such spaces, and function for example as lubricant in the case of pleural fluid. Also, the lumen of the gastrointestinal tract is often classified as belonging to the third space, although it has substantial fluid content physiologically. In this classification system, the first and second space generally refer to the intravascular space (within vessels) and the extravascular space (the interstitial and intracellular spaces), respectively.
Fluid which collects in the second space (i.e. the combined interstitial and intracellular space) is more readily available for the body to use (such as for the correction of ionic imbalances in other compartments) than fluid in the third space, because fluid in the second space is physiologically more active with the intravascular (“first”) space than third space fluid is.
1) bowel obstruction: fluid moves out of gut into peritoneal cavity (hydrostatic)
2) peritonitis: inflammatory process causing fluid to build up in peritoneum
3) ascites: large accumulation of fluid in peritoneal space
What are the normal osmotic pressure and tonicity of homeostasis?
- osmotic pressure (300 mOsm)
- isotonic
What conditions result in proportionate and disproportionate change in sodium and water
Proportionate changes in sodium and water
- Isotonic alterations
- Total body water change with proportional electrolyte and water change
Disproportionate changes in sodium and water
- Hyponatremia (hypotonic) (i.e., overhydration)
- Hypernatremia (hypertonic) (ie., dehydration)
What is Isotonic Fluid Volume Excess?
Isotonic Fluid Volume Excess
- Isotonic expansion of the ECF compartment with increases in both interstitial and vascular volumes
- Increase in total body sodium that is accompanied by a proportionate increase in body water
Causes (http://postimg.org/image/fzc80llg3/)
- Excess intake of Na containing IV fluids
- -Excess of intake of Na in diet or medications like antacids hypertonic enema
- -impaired fluid balance regulation related to heart failure, renal failure or cirrhosis of the liver
Clinical Manifestations
- Weight gain
- fluid intake greater than output
- FULL POUNDING PULSE; increased BP and tachycardia
- distended neck veins
- moist crackles in the lungs; dyspnea
- mental confusion
What is Isotonic Fluid Volume Defecit?
Causes (http://postimg.org/image/5g90vzjid/)
- Inadequate intake
- Coma
- Impaired thirst center
- Therapeutic withholding
- Excessive losses
- Excessive GI losses
- Excessive Renal losses
- Excessive Skin Losses
Clinical Manifestations
- signs of dehydration
- decreased skin tugor
- weight loss
- sucken eyeballs
- dry mucous membrains
- weak pulse; tachcardia
- decreased BP
- orthostatic hypotension
- decreased capillary refill
- collapsed jugular veins
- less than 30mL/hr urine volume
- increased Specific gravity >1.030
- increased hematocrit
- increased BUN
Hypotonic alterations
Develops when osmolality (concentration) of the ECF is less than normal. Most common causes:
- Sodium deficit in ECF (hyponatremia)
- Water excess in ECF (water excess)
- Hypertonic hyponatremia, caused by resorption of water drawn by molecules such as glucose (hyperglycemia or diabetes) or mannitol (hypertonic infusion)
CAUSES (http://postimg.org/image/9qvy44u6r/)
Hyponatremia
- GI
- excessive sweating
Water excess
- sodium free solutions (GI irrigation, tap water enema)
- SIADH
- compulsive water drinking
CLINICAL MANIFESTATIONS
If hyponatremia:
- water moves into the cell
- plasma volume decreases
- symptoms of hypovolemia*
- movement of water into brain cells – depression, lethargy, stupor, coma
if water excess
- symptoms of hypervolemia*
*The excess fluid, primarily salt and water, builds up in various locations in the body and leads to an increase in weight, swelling in the legs and arms (peripheral edema), and/or fluid in the abdomen (ascites). Eventually, the fluid enters the air spaces in the lungs, reduces the amount of oxygen that can enter the blood, and causes shortness of breath (dyspnea), which is the best indicator of estimating central venous pressure is increased. Fluid can also collect in the lungs when lying down at night, possibly making nighttime breathing and sleeping difficult (paroxysmal nocturnal dyspnea).
Hypertonic alterations
Osmolarity of the ECF is elevated above normal
CAUSES (http://postimg.org/image/w5n9v7snn/)
hypernatremia or a deficit of ECF free water, causing ICF dehydration
1) Hypernatremia:
* Excessive administration of sodium containing parenteral solutions
2) Deficit of ECF free water
- Watery diarrhea
- Diabetes Insipidus
CLINICAL MANIFESTATIONS
1) Hypernatremia
- osmotic attraction of water from ICF – symptoms of hypervolemia
- movement of water out of brain cells – agitation, restlessness, seizures
2) Free water loss
- extracellular dehydration and decreased plasma volume
dehydration and stimulation of thirst center
What is the role of Potassium in the body?
Major intracellular cation
- Concentration maintained by the Na+/K+ pump
- Regulates intracellular electrical neutrality in relation to Na+ and H+
- Essential for transmission and conduction of nerve impulses, normal cardiac rhythms, and skeletal and smooth muscle contraction
What is hypokalemia?
(K+<3.5 mmol/L)
CAUSES (http://postimg.org/image/89awulb1t/)
Nutritional deficit
- Renal loss
- excessive diuresis (non K+ sparing)
- hyperaldosteronism
GI loss
- vomiting, diarrhea
- excessive enemas, laxatives
- GI drainage, suction
Alkalosis
CLINICAL MANIFESTATIONS
GI
- paralytic ileus, vomiting
- abdominal distension
Nervous system
- lethargy, fatigue, paresthesia
- skeletal muscle
- weakness, paralysis, shallow respiration
What is hyperkalemia?
(K+>5.0 mmol/L)
CAUSES (http://postimg.org/image/59zgb37jl/)
excessive intake
- parenteral potassium
- whole blood transfusion (especially old blood)
Renal
- renal failure
- adrenal insufficiency (Addison’s disease)
Shift of K+ from ICF
- acidosis
- burns
- tissue injury
CLINICAL MANIFESTATIONS
Mild attacks
- Hypopolarized membrane, causing neuromuscular irritability
- Tingling of lips and fingers, restlessness, intestinal cramping, and diarrhea
Severe attacks
- The cell is not able to repolarize, resulting in muscle weakness, loss or muscle tone, and flaccid paralysis
SYSTEMS AFFECTED
Neuromuscular
- Weakness, muscle cramps
Cardiovascular
- Changes in ECG
- Risk of ventricular fibrillation and cardiac arres
How does one assess a patient for fluid therapy?
History taking
Clinical examination
- indication of plasma volume: BP, JVP, CVP
- interstitial volume: edema
- others: high fever, nasogastric tubes, surgical drains, fistula, ventilator
Fluid balance charts
Lab data
What to give?
Calculate how much to give
Monitor
What is Acid-Base Balance?
- Refers to precise regulation of free H+ concentration in body fluids
- Acids: Group of H+ containing substances that dissociate in solution to release free H+ and anions
- Bases: Substance that can combine with free H+ and remove it from solution
pH
- Designation used to express the concentration of H+
- pH 7 – neutral
- pH less than 7 → acidic
- pH greater than 7 → basic
- Normal blood pH – 7.35 – 7.45
What is a buffer system?
defense against changes in H+ concentration to maintain homeostasis
- chemical buffer system
- the respiratory system
- the renal system
Describe the chemical buffer systems in the body.
Minimize changes in pH by binding with or yielding free H+, First line of defense, Body has four buffer systems
H2CO3-, HCO3- buffer system
- Primary ECF buffer for noncarbonic acids
Protein buffer system
- Primary ICF buffer; also buffers ECF
Hemoglobin buffer system
- Primary buffer against carbonic acid changes
Phosphate buffer system
- Important urinary buffer; also buffers ICF
Describe the respiratory buffer system.
- second line of defense after buffers
- by controlling the rate of CO2 removal from the plasma
- through adjustments in pulmonary ventilation
Describe the renal buffer system.
- third line of defense
- each H+ excreted adds one HCO3 to plasma
What mechanisms contribute to controlling the rate of H+ secretion?
Explain how various mechanisms contribute to the maintain of pH.
How can pH imbalances arise in the body?
Respiratory dysfunction
- respiratory acidosis
- respiratory alkalosis
Metabolic disturbances
- metabolic acidosis
- metabolic alkalosis
What are respiratory acidosis and alkalosis and what are their causes?
Respiratory acidosis (pCO2 > 45 mmHg)
Causes
- respiratory center depression
- respiratory muscle paralysis
- chest wall deformities
- lung diseases (COPD/cancer lung)
Respiratory alkalosis (pCO2 < 35 mmHg)
Causes
- hyperventilation caused by
- high fever
- salicylate intoxication
- thyrotoxicosis
- hysteria
- poorly adjusted mechanical ventilator
What is Metabolic acidosis and Metabolic alkalosis?
Metabolic acidosis
- arterial plasma HCO3 < 22 mmol/L
- causes
- loss of HCO3 – diarrhea
- accumulation of acid – ketosis
- failure of kidney to excrete H+ - renal failure
Metabolic alkalosis
- arterial plasma HCO3 > 26 mmol/L
- causes
- vomiting, gastric suctioning
- ingestion of alkaline drugs eg. diuretics
- endocrine disorders
- eg. hyperaldosteronism
A reduction in circulating HCO3- due to kidney dysfunction would result in ______________.
- Metabolic compensation
- Respiratory compensation
- Respiratory alkalosis
- Respiratory alkalemia
A decrease in PCO2 is a manifestation of ______________.
- Metabolic compensation
- Respiratory compensation
- Respiratory alkalosis
- Respiratory alkalemia
How does one interpret a patient’s acid-base status?
