chem solo 4

primary cationic electrolytes

Na, K, Ca, and Mg

Primary anionic electrolytes

Cl, HCO3, HPO4, SO4, organic ions, and negatively charged proteins

Electrolytes, four major electrolytes included in an electrolytes panel include

Na, K, Cl, Co2 (HCO3)

Electrolyte functions

water homeostasis, acid-base balance, muscle function, co-facters for enzymes

Hypervolemia

increased fluid volume in the blood; symptoms include swelling (edema), discomfort, cramping, headache, stomach bloating, high blood pressure

Hypovolemia

decreased fluid volume in the blood; symptoms include orthostatic hypotension, tachycardia, decreased skin turgor

Euvolemia

normal fluid volume in the blood

osmolality

expresses concentrations related to the mass of solvent

Osmolarity

expresses concentration per volume of solution

Even though these electrolytes have different molecular weights, they contribute equally to osmo because osmo is not affected by density only the

number of particles present (higher # = more osmo)

Major osmotic substances in normal plasma

sodium, chloride, glucose, urea (BUN: blood urea nitrogen)

Osmolality formula

mOsm/kg = 2[Na(mmol/L)] + glucose[mg/dL]/18 + urea[mg/dL]/2.8

causes of hypovolemia

vomiting, diarrhea, and excessive bleeding

Glomerulus in renal function

acts as a filter, retaining large proteins and protein-bound constituents while most other plasma constituents pass into the filtrate

sources of error for electrolytes

prolonged storage of whole blood at 4C causes a falsely increased K result, prolonged storage of whole blood at 37C causes a falsely decreased K result

Na/K ATPase pump

diffusion of K+ out of the cell into ECF occurs when pump activity is decreased

Sodium (Na) is the major

cation of extracellular fluid, the high extracellular concentration of sodium contributes the most to the osmotic strength of extracellular fluid; it is responsible for almost half of the osmotic strength of the plasma

average daily requirement of Na vs US diet

1-2 mmol/day or 23-46 mg/day vs 90-250 mmol/day or 3000-6000 mg/day

Reference range for adults of sodium

136-145 mmol/L

Sodium is regulated by

RAAS of the kidneys

RAAS (renin-angiotensin-aldosterone system)

regulates blood flow to and within the glomerulus and responds to changes in blood pressure and plasma sodium content (of the kidney)

Aldosterone

a sodium-retaining hormone produced in the adrenal gland in response to renin, it regulates reabsorption of sodium in the distal convoluted tubule and is essential for sodium conservation in the kidneys

Increased sodium loss is a cause of Hyponatremia that can occur with:

Hypoadrenalism: leads to decreased aldosterone, Diuretics: such as thiazides, Ketonuria: Na is lost with ketones, Salt-losing nephropathies: due to renal tubular dysfunction, Potassium deficiency causes sodium loss because it trades off with K, prolonged vomiting/diarrhea or severe burns can result in Na loss.

Increased water retention causes of Hyponatremia

Renal failure: causes dilution of plasma sodium while urine sodium levels are increased, nephrotic syndrome and hepatic cirrhosis, congestive heart failure

water imbalance causes of Hyponatremia

excess water intake, Syndrome of inappropriate anti-diuretic hormone (SIADH), Pseudohyponatremia can occur in ISE and in vitro hemolysis

LOW osmolality classification of Hyponatremia

caused by increased sodium loss or increased water retention; most instances of hyponatremia occur with decreased osmolality

Normal osmolality classification of Hyponatrema

may be the result of a high increase in non-sodium cations and multiple myeloma

High osmolality classifications of Osmolality

associated with hyperglycemia

Hypernaternia due to excess water loss (relative to sodium)

diabetes insipidus is caused by low ADH production, secretion, or response, renal tubular disease, any condition that increases water loss such as prolonged diarrhea, exposure to heat (profuse sweating), or severe burns

Hypernatermia due to decreased water intake

seen with older persons, infants ,and mental impairment

Hypernatremia due to increased sodium intake or retention

Hyperaldosteronism: excess aldosterone inhibits ADH release, Hypernatremia may be from excess ingestion of salt as with sodium bicarbonate from excess dialysis fluids

The american heart association recommends a daily intake of sodium of

less then 2300 mg

the enzyme renin is produced by the kidney in

response to low plasma sodium levels

Hyponatremia with high urine Na is likely due to

renal loss

Hyponatremia due to loss of Na in the urine can occur with

salt-losing nephropathies

Hypernatremia occurs with

decreased synthesis of ADH due to hyperaldosteronism

Excess plasma sodium with a high blood volume often occurs

in hospital patients receiving hypertonic saline

Potassium is the major

intracellular cation, high intracellular concentrations are maintained by the Na/K ATpase pump

Potassium reference ranges for serum

3.5 - 5.1 mmol/L

Hypokalemia causes

Gastrointestinal loss: occurs most commonly with diarrhea, renal loss: indicated by increased urine potassium, cellular shift: a feature of alkalosis, also occurs after insulin therapy, hydration: decreased K intake may occur

Hyperkalemia due to decreased renal excretion

the most common causes of prolonged hyperkalemia are decreased excretion of K in renal disease/failure, Na depletion in hypoaldosteronism due to adrenocortical insufficiency such as Addisons disease

Hyperkalemia due to cellular shift

Metabolic acidosis, latrogenic: relating to illness caused by medication or treatment (digoxin or beta blockers)

Hypokalemia (<3) is considered a serious health threat because

the heart rate increases, leading to weakness, difficulty in breathing, and eventual cardiac arrest

The high extracellular concentration of which cation contributes the most to the osmotic strength of extracellular fluid

sodium

Chloride is the

major extracellular anion

Chloride reference range in serum or plasma

98-107 mmol/L

Chloride is not

significantly affected by hemolysis

sweat chloride is elevated in

cystic fibrosis

Silver ion (Ag+) are generated by a

silver electrode

The start to stop time is proportionate to the amount of

Cl- present in solution

Ion selective electrodes (ISE) measures the

electrical potential formed when an ion-exchange membrane is used to selectively bind chloride ions

Cystic clinical features of cystic fibrosis

Chronic obstructive pulmonary disease (COPD), pancreatic insufficiency

Most newborn screening protocols being with immunoreactive trypsinogen assay (IRT), infants born with a positive newborn screen are referred for a quantitative

sweat chloride test, the gold standard for diagnosis of cystic fibrosis

special considerations for sweat testing

individuals should be at least 48 hours old, physiologically and nutritionally stable, thoroughly hydrated, free of acute illness, skin free of cuts rashes and inflammation to avoid contamination

Sweat testing three phases

1. sweat stimulation by pilocarpine iontophoresis

2. Collection of the sweat is onto gauze pads or filter paper

3. qualitative or quantitative analysis of chloride

reference ranges for sweat chloride testing

infants: normal intermediate, cystic fibrosis indicated <30, 30-59, >60, beyond infancy: <40, 40-59, >60

Quality assurance can be maintained for the sweat chloride test by

having sufficient testing volumes to ensure familiarity with the test, limiting testing to a small number of well trained individuals, monitoring accuracy and precision by running at least two quality controls (high and low)

Historically, chloride was measured in blood by spectrophotometry, now the methods of choice for chloride measurement include ion-selective electrodes and

coulometric amperometric titration

clinical significance of Bicarbonate

Bicarbonate accounts for 90% of total carbon dioxide, alterations in bicarbonate and Co2 dissolved in plasma are characters of acid-base imbalances (higher ratio indicates alkalosis, decreased ratio indicates acidosis)

Buffer

mixture of a weak acid and salt of its conjugate base that resists changes in pH when a strong acid or base is added to the solution

most important buffer of plasma

Bicarbonate/carbonic acid buffer system, also major component for the buffering system in blood

whenever there is an accumulation of metabolically produced acids, the body attempts to neutralize those acids to maintain a constant

acid-base balance

Buffering systems, if concentrations of a buffer are equal the

pH will equal the pk, buffers work best when the acid:base ratio is within the range 10:1 to 1:10

Bicarbonate/carbonic acid buffer system Co2 is a

volatile acidic gas that is soluble in water, CO2 is produced as a major product of energy metabolism

Bicarbonate/Carbonic acid buffer system acid formation

a process that acidifies blood will be neutralized by the bicarbonate ions thus minimizing the change in pH

Bicarbonate/carbonic acid buffer system alkaline formation

a process that alkalizes blood will be neutralized by the equailbrium concentration of carbonic acid

Indirect ISE measurement of bicarbonate

acidification of a serum, or plasma sample occurs;

Enzymatic methods measurement of bicarbonate

alkalization converts all CO2 and carbonic acid to HCO3

most of the total CO2 present in the blood is in what form

bicarbonate ion

Anion gap two formulas

Na - (Cl +HCO3) reference range 7-16, (Na + K) - (Cl + HCO3) reference range 10 -20, the gap is due to unmeasured anions such as proteins

Causes of decreased AG (rare)

unmeasured cations such as Ca, Mg, or IgG

causes of increased AG

unmeasured anions, increased in many patients with metabolic acidosis due to the presence of organic acid

MUDPILES: increased anion gap

Methanol, uremia of renal failure, diabetes or ketoacidosis, paraldehyde toxicity, isoniazed, iron, ischemia, Lactic acidosis, Ethylene glycol, Salicylate intoxication

Diabetic ketoacidosis

increase of intermediate organic acids such as beta-hydroxybutrate (BHB), blood and urine glucose will be increased, pH will be decreased, pCO2 will be increased, HCO3 will be decreased

Causes of a decreased anion gap include

increased immunoglobins

Acids

chemical substances that donate protons (H+ ions) in solution, strong acids readily give up H+

Bases

chemical substances that accept protons in solution, strong bases readily accept H+

Acidosis

increased addition of acid, decreased elimination fo acid, increased loss of base

Alkalosis

increased addition of base, decreased elimination of base, increased loss of acid

purpose of blood gases and pH

detects respiratory and metabolic disorders, detect acid-base imbalances

behavior of gases

partial pressure (P) or tension: the substance function of gas times the total pressure, lowercase p in pH stands for negative log, uppercase in PCO2 stands for the partical pressure

pH is defined as

-log[H+], a decrease in one pH unit represents a tenfold increase in H activity

Acidemia

arterial blood < 7.35

Alkalemia

arterial blood > 7.45

pK

measure of acid strength

HCO3

Bicarbonate is considered the metabolic (renal) component, can be calculated using the Henderson-Hasselbalch equation pH - pK + log[A-]/[HA]

PO2

relates to ability of the lungs to oxygenate blood from alveolar air

clinical signficance of increased PO2

acidosis

clinical significance of decreased PO2

decreased pulmonary ventilation (airway obstruction)

Instrumentation of SO2

pulse oximetry

Patient temperature below 37 degrees would cause the

pH to be higher, PCO3 to be lower, PO2 to be lower

patient temperature above 37 degrees would cause the

pH to be lower, PCO3 to be higher, PO3 to be higher

Acidosis

increased addition of acids, decreased elimination, increased loss of base

Alkalosis

increased addition of base, decreased elimination of base, increased loss of acid

Acid-base balance

the homeostatic maintenance of acids and bases within the body to achieve a physiological pH of approximately 7.40

pH of plasma is function of two independent variables

1. PCO3 regulated by the lungs, represents the acid component of the carbonic acid/bicarbonate buffer system

2. HCO3: regulated by the kidneys, represents the base component of the carbonic acid/bicarbonate buffer system

Acid/base status of the blood, indicated by the pH, is affected by changes in bicarbonate to dCO2 ratio, which is normally

20:1

Respiratory components of acid-base regulation

clinical conditiosn characterized as respiratory disturbances of acid-base balance are classifed as primary disturbances in dissolved CO3 (PCO2), will change pH in minutes

Metabolic (renal) components of acid-base regulation

disturbances in HCO3, which will change pH in hours to days

Respiration

the respiratory system contributes to maintenace of typical body pH through elimination of rentention of CO2