ACID BASE BALANCE

n General Principles –Dynamic relationship which reflects the concentration of hydrogen (H+) ions –Hydrogen ions are acids which must be maintained within strict limits »Any deviation from norm affects biochemical events –Measured in a negative log (pH) which is inversely proportional to the hydrogen ion concentration »High H+ ion concentration = Low pH »Low H+ ion concentration = High pH

THE pH SCALE n Most frequently used measure of acid base balance n Ranges from 1-14 –1 means only hydrogen ions present –14 means no hydrogen ions present –pH of water is 7.0 (neutral) n pH of human body is n pH compatible with life = –pH of < 7.35 indicates a state of acidosis –pH of > 7.45 indicates a state of alkalosis –Variation of 0.4 in either direction can be fatal

Acid-Base Balance n A pH below 7.35 is referred to as acidosis n A pH above 7.45 is referred to as alkalosis

n Body constantly produces acids through metabolism –Carbon dioxide –Metabolic acids (lactic and pyruvic acid) n Acids must be constantly eliminated from the body –As acids increase, bodily functions decrease –Example »Diminishes myocardial contractility »Reduces vascular response to catecholamines »Interferes with the actions of pharmacological agents

BUFFER SYSTEM n Fastest acting defense mechanism (seconds) n Chief buffer is bicarbonate –Bicarbonate combines with excess hydrogen ions to form carbonic acid in a dynamic relationship: HCO3 + H+ H2CO3 HCO3 + H+ H2CO3 –For every molecule of carbonic acid, there are 20 molecules of bicarbonate –Any change in 20:1 ratio is immediately corrected to maintain pH »An increase in H+ causes an increase in H2CO3 »A decrease in H+ causes a decrease in H2CO3

Bicarbonate Buffer System n Fastest mechanism n Hydrogen will bind with bicarbonate n Results in formation of carbonic acid

Carbonate Buffer System n An increase in hydrogen ions leads to an increase in carbonic acid. n A deficit in hydrogen ions (alkalosis); carbonic acid will dissociate into bicarbonate ion and hydrogen ion

BUFFER SYSTEM (CONT.) n Carbonic acid is a weak, volatile acid which must be eliminated n Enzyme carbonic anhydrase catalyzes the carbonic acid to convert to carbon dioxide and water: H2CO >CO2 + H2O n CO2 and H2O are easily eliminated by the lungs and kidneys

n Functions within minutes (1-3) n Lungs eliminate excess CO2 by increasing respirations, causing a decrease in H+ ion and an increase in pH n Lungs can retain more CO2 by decreasing respirations, causing an increase in H+ ions and a decrease in pH

Respiratory Mechanisms n Increased respirations cause increased elimination of CO 2 and H 2 O. –An increase in pH n Decreased respirations cause retention of CO 2 and H 2 O. –Decreasing pH

n Slowest onset and generally important in long term maintenance of acid-base balance (hours to days) n Function –Kidneys retain bicarbonate, causing a decrease in H+ ions and an increase in pH –Kidneys excrete bicarbonate, causing an increase in H+ ions and a decrease in pH

Respiratory Acidosis n Caused by abnormal retention of CO 2 from impaired ventilation due to problems occurring in the lungs or respiratory center of the brain Respiration = CO 2 + H 2 O H 2 CO 3 H + + HCO 3 -

Caused by increased respiration and excessive elimination of CO 2 The CO 2 level is decreased and the pH is increased. Respiratory Alkalosis Respiration = CO 2 + H 2 O H 2 CO 3 H + + HCO 3 -

ACID-BASE DERANGEMENTS (CONT.) n Metabolic acidosis –Increased production of acids (lactic and pyruvic) –Can also result from diarrhea, vomiting, diabetes and medications (ASA) –pH is decreased and CO2 level is normal –Treatment is aimed at improving ventilations to eliminate CO2 –Sodium bicarbonate with documented metabolic acidosis »Rarely administered during initial resuscitative strategies

ACID-BASE DERANGEMENTS (CONT.) n Metabolic alkalosis –Caused by increased vomiting, overdosing on antiacids, diuretics –pH is increased and CO2 remains normal –Treatment is aimed at underlying cause n Combinations –Any combination of acid-base derangements –Only ABG can accurately diagnose problem

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