Electrolytes and acid base balance

THE EXPECTED BLOOD GAS RESULTS FOR A PATIENT IN CHRONIC RENAL FAILURE WOULD MATCH THE PATTERN OF:

METABOLIC ACIDOSIS (REDUCED EXCRETION OF ACIDS)

SEVERE DIARRHEA CAUSES:

METABOLIC ACIDOSIS (EXCESSIVE LOSS OF BICARBONATE)

PH 7.18

PO2 86MM HG

PC02 60MM HG

02 SAT 92%

HCO3 7921 MEQ/L

TCO2 23MEQ/L

BASE EXCESS: -8.0

THESE RESULTS ARE MOST COMPATIBLE WITH?

EMPHYSEMA; RESPIRATORY ACIDOSIS

A FACTOR THAT CONTRIBUTES TO A PC02 ELECTRODE REQURING 60-120S TO REACH EQUILIBRIUM INCLUDE THE:

DIFFUSION CHARACTERISTICS OF THE MEMBRANE.

AN EMPHYSEMA PATIENT SUFFERING FROM FLUID ACCUMULATION IN THE ALVEOLAR SPACES IS LIKELY TO BE IN WHAT METABOLIC STATE?

RESPIRATORY ACIDOSIS

AT BLOOD PH 7.4, WHAT IS THE RATIO OF BICORBONATE TO CARBONIC ACID?

20:1

THE REFERENCE RANGE FOR THE PH OF ATERIAL BLOOD AT 37C IS?

7.35-7.45

A 68 YEAR OLD MAN ARRIVES IN THE EMERGENCY ROOM WITH A GLUCOSE LEVEL OF 722 MG/DL AND SERUM ACETONE OF 4+ UNDILUTED. AN ARTERIAL BLOOD GAS pH FROM THIS PATIENT IS LIKELY TO BE:

LOW PH WHICH IS CONSISTENT WITH DIABETIC KETOACIDOSIS

A PATIENT IS ADMITTED TO THE EMERGENCY ROOM IN A STATE OF METABOLIC ALKALOSIS. WHAT WOULD BE CONSISTENT WITH THIS DIAGNOSIS?

HIGH TC02, INCREASE HC03

A PERSON SUSPECTED OF HAVING METABOLIC ALKALOSIS WOULD HAVE WHICH OF THE FOLLOWING LABORATORY FINDINGS?

C02 CONTENT AND PH ELEVATED.

METABOLIC ACIDOSIS IS DESCRIBED AS AN:

DECREASE IN C02 CONTENT AND PC02 WITH A DECREASED PH.

RESPIRATORY ACIDOSIS IS DESCRIBED AS AN:

INCREASE IN C02 CONTENT AND PC02 WITH A DECREASED PH.

A COMMON CAUSE OF RESPIRATORY ALKALOSIS IS:

HYPERVENTILATION

ACIDOSIS AND ALKALOSIS ARE BEST DEFINED AS FLUCTUATIONS IN BLOOD PH AND C02 CONTENT DUE TO CHANGES IN:

BICARBONATE BUFFER

A BLOOD GAS SAMPLE WAS SENT TO THE LAB ON ICE, AND A BUBBLE WAS PRESENT IN THE SYRINGE. THE BLOOD HAD BEEN EXPOSED TO ROOM AIR FOR AT LEAST 30 MINS. THE FOLLOWING CHANGES IN BLOOD GAS WILL OCCUR:

PO2 INCREASED HC03 DECREASED

SODIUM 136 MEQU/L

POTASSIUM 4.4 MEQ/L

CHLORIDE 92MEQ/L

BICARBONATE 40 MEQ/L

ARTERIAL BLOOD PH 7.32

PC02 79 MM HG

RESULTS MOST COMPATIBLE WITH?

RESPIRATORY ACIDOSIS

WHICH TEST EVALUATES RENAL TUBULAR FUNCTION?

OSMOLARITY

SODIUM 140MEQ/L

POTASSIUM 4.0MEQ/L

GLUCOSE 95MG/DL

BUN 10MG/DL (BLOOD UREA NITROGEN)

WHICH OSMOLALITY IS CONSISTENT WITH THESE RESULTS?

270

THE DEGREE TO WHICH THE KIDNEY CONCENTRATES THE GLOMERULAR FILTRATE CAN BE DETERMINED BY:

URINE TO SERUM OSMOLALITY RATIO

OSMOLAL GAP IS THE DIFFERENCE BETWEEN:

CALCULATED AND MEASURED OSMOLALITY VALUES.

What is the major cation of extracellular fluid?

Sodium

What percent of sodium is reabsorbed in the kidney tubules?

85%

What is the function of sodium?

Maintains osmotic pressure

Normal distribution of water

50% plasma osmolality

What are sodium levels regulated by?

Aldosterone: increases renal reabsorption

What is the typical Na+/K+ ratio in serum?

30:1

What conditions could cause depletional hyponatremia (completely absent of Na+)?

Diabetic acidosis

Diarrhea/Vomiting

Addison's disease (hypoaldosteronism)

Renal tubular disease

Diuretics

What conditions could cause dilutional hyponatremia (excess body water causes diluted/decreased concentration of sodium)?

Overhydration

SIADH

CHF

Cirrhosis

Nephrotic syndrome

What symptoms are associated with hyponatremia?

Weakness

Nausea

Altered mental status

What conditions could cause hypernatremia?

Cushing's syndrome

Dehydration

Hyperaldosteronism

Insulin treatment

What symptoms are associated with hypernatremia?

Tremors

Irritability

Confusion

Coma

How is sodium measured?

ISE

Glass electrode selective for Na+

How does direct compare to indirect ISE testing?

Indirect requires sample be diluted (direct does not)

What describes the phenomenon of pseudohyponatremia?

Sample with increased triglycerides or protein is measured with indirect ISE

Sodium appears falsely elevated

What is the major cation of intracellular fluid?

Potassium

How much more abundant is potassium intracellularly compared to extracellularly?

23x higher in cells

What specimen collection and handling techniques may cause false increase in potassium?

Hemolysis

IV fluid contamination

EDTA contamination

Prolonged tourniquet application

Excessive squeezing for capillary specimens

Excessive fist clenching prior to venipuncture

Delay in separation of serum from cells

Leukocytosis (> 500,000 WBC)

Thrombocytosis (> 700,000 platelets)

How could falsely elevated potassium from a high platelet count be resolved? Why?

Retest with heparinized plasma; When blood clots into serum, platelets and cells break down and release intracellular potassium and magnesium into the liquid portion, so lithium heparin keeps blood unclotted to prevent release

How are potassium values different between serum, plasma, and whole blood?

Plasma and WB: 0.1-0.7 mmol/L lower than serum

Why is potassium lower in plasma and whole blood compared to serum?

Presence of platelets; clotting causes them to release potassium (serum has no plt)

What conditions could cause hypokalemia?

Insulin injection

Alkalosis

Diarrhea/vomiting

Hyperaldosteronism

Cushing's syndrome

Diuretics

What symptoms are associated with hypokalemia?

Muscle weakness

Paralysis

Breathing problems

Cardiac arrhythmia

Death

What conditions could cause hyperkalemia?

Conditions causing increased K+

Diabetic/metabolic acidosis

Intravascular hemolysis, Severe burns

Renal failure, Addison's disease (hypoaldosteronism)

What symptoms are associated with hyperkalemia?

high potassium: Muscle weakness, Nausea, and Altered mental status

What method is used to measure potassium?

ISE

Valinomycin membrane selectively binds K+

What is the major anion of extracellular fluid?

Chloride

What is the function of chloride?

Maintain hydration, osmotic pressure, and normal cation-anion balance

How are sodium and chloride levels related?

Directly; as one increases/decreases, as does the other

What conditions may cause hypochloremia?

Diabetic ketoacidosis

Chronic pyelonephritis

Vomiting (lose gastric HCl)

Hypoaldosteronism

Diuretics

What conditions may cause hyperchloremia?

Diarrhea

Renal tubular acidosis

Dehydration

Adrenocortical hyperfunction (Cushing's or hyperaldosteronism)

What methods are used to measure chloride?

ISE

Amperometric-coulometric titration

Colorimetry

How is chloride measured in ISE?

Uses sensor with solid state electrodes containing AgCl

How is chloride measured in amperometric-coulometric titration?

Silver (Ag) ions are generated (automated method)

How is chloride measured in colorimetric methods?

Cl + Hg(SCN)2 -> red color

What conditions shows an increase in sweat chloride?

Cystic fibrosis

How is sweat chloride collected?

Iontophoresis using pilocarpine (to induce sweating)

What value of sweat chloride is indicative of cystic fibrosis?

> 60 mmol/L

What is the reaction taking place in the chloride shift?

HCO3 is pulled out of RBC and replaced with Cl

Result is a decreased serum Cl

What is the purpose of the chloride shift?

Buffering system of the blood

What does the anion gap represent?

Difference between measured and unmeasured cations and anions

What are the primary unmeasured cations?

K, Mg, Ca

What are the major unmeasured anions?

Proteins (albumin), sulfate, phosphate, organic acids

What is the second largest anion fraction of extracellular fluid?

Bicarbonate (HCO3)

What is the calculation for anion gap?

(Na + K) - (Cl + HCO3)

K is optional if not provided

What is the reference range for anion gap (including potassium)?

10-20 mmol/L

What is the reference range for anion gap (wihtout potassium)?

7-16 mmol/L

What does an increased anion gap indicate?

Increased concentration of unmeasured anions

Decreased concentration in unmeasured cations

What could result in an increased anion gap?

Low serum Ca or Mg

Salicylate poisoning

Lactic acidosis

Methanol

Polyethylene glycol

Ethanol

Ketoacidosis

What does a decreased anion gap indicate?

Decreased concentration of unmeasured anions

Increased concentration of unmeasured cations

What could cause a decrease in anion gap?

Albumin loss

High serum Mg or Ca

Lithium therapy

Hemodilution

What analytes are measured in a typical electrolyte test?

Serum sodium, potassium, chloride and bicarbonate (total CO2)

What is osmolality?

Measure of total number of dissolved particles in a solution

What does not affect osmolality?

Molecular weight

Size

Density

Type of particle

What method is used to measure osmolality?

Freezing point depression

Vapor pressure depression

What equation can be used to calculate osmolality?

2(Na) + (Glucose/20) + (BUN/3)

What does the osmolar gap represent?

Compares calculated serum osmolality to measured serum osmolality

What does an osmolar gap of > 10 indicate?

Exogenous unmeasured anions (methanol, ethanol, ketone bodies)

What test is used to evaluate renal tubular function?

Urine osmolality

What is the urine to serum osmolality ratio used for?

Determines the degree to which the kidney concentrates urine

What is the function of magnesium?

Calcium channel blocking agent (affects the heart)

Cofactor for many enzymes

What condition could cause increased magnesium?

Renal failure

Excess antacids

Hypothyroidism

Hypoaldosteronism

Bone cancer

How is magnesium regulated?

Kidney reabsorption & excretion

PTH enhances renal reabsorption and intestinal absorption

What conditions could cause decreased magnesium?

Diabetes mellitus (glycosuria)

Diuretics, alcohol and other drugs (cardiac disorders)

Gastrointestinal disorders

Renal disease

Pancreatitis

What methods are used to measure magnesium? Which is the reference method?

Atomic absorption - reference

Colorimetric methods (calmagite, methylthymol blue)

ISE (free magnesium)

What may interfere with magnesium measurement?

Hemolysis

Any anticoagulant other than heparin (others bind Mg)

What is the reference range for magnesium?

1.7-2.4 mg/dL

What ion would you suspect to be deficient in tetany?

Calcium

If not calcium, possibly magnesium or potassium

What is the distribution of protein bound, ionized and complexed calcium in the plasma?

45-50% Ionized (free)

40-45% Protein bound (albumin)

10% Complexed (anions)

What percent of calcium is in the bones?

99%

What hormones control calcium levels? How do each affect calcium?

PTH: increases

Calcitonin: decreases (inhibits bone reabsorption)

Vitamin D: increases (increases absorption in intestines)

What conditions could cause hypercalcemia?

Hyperparathyroidism

Cancer with bone metastasis

Multiple myeloma

Renal failure

What conditions could cause hypocalcemia?

Hypoparathyroidism

Hypoalbuminemia

Vitamin D deficiency

What methods are used to measure calcium? Which one is the reference method?

Atomic absorption spectroscopy - reference

Colorimetric method

ISE

What takes place in colorimetric measurement of calcium?

Calcium + o-cresophthalein -> red complex

8-hydroxyquinoline is added to remove Mg

What takes place in ISE measurement of calcium?

Acidified to convert protein bound and complexed calcium into free calcium

Ca binds reversibly to membrane

Measured at 37 C

What could interfere with calcium measurement?

Collection in any anticoagulant besides heparin

Spectrophotometric: hemolysis, lipemia, icterus, increased protein

ISE: aerobic collection (loss of CO2 = pH change in vitro), affected by pH and temp

What is the reference range of total calcium in adults?

8.6-10.3 mg/dL

What is the reference range of free calcium in adults?

4.6-5.3 mg/dL

Which form of calcium is active? Which form is typically measured with most methods?

Active: free/ionized calcium

Measured: total calcium

What form of phosphate is measured with most methods?

Inorganic phosphorous (PO4) only

What is the function of phosphate?

Component of nucleic acids & coenzymes

Reservoir of energy (ATP)