curs acid base balance 2015 nov

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Focus onFocus onAcid-Base BalanceAcid-Base Balance


PurposePurpose

• Maintain a steady balance between acids Maintain a steady balance between acids and bases to achieve homeostasisand bases to achieve homeostasis

• Health problems lead to imbalanceHealth problems lead to imbalance Diabetes mellitusDiabetes mellitus Vomiting and diarrhea Vomiting and diarrhea Respiratory conditionsRespiratory conditions Shock Shock


• Acid Substance that contains H+ ions

that can be released H2CO3-Carbonic acid releases H+

• BaseSubstance that can accept H+ ionsHCO3-Bicarbonate accepts H+


pHpH

• Measure of HMeasure of H++ ion concentration ion concentration

H+ = 40 nmol/l

pH = NEGATIVE LOGARITHM OF H+


pHpH

•Blood is slightly alkaline pH 7.35 to 7.45Blood is slightly alkaline pH 7.35 to 7.45 Below 7.35 is acidemiaBelow 7.35 is acidemia Above 7.45 is alkalemiaAbove 7.45 is alkalemia


Regulators of Acid/BaseRegulators of Acid/Base

• Metabolic processes produce acids that Metabolic processes produce acids that must be neutralized and excreted must be neutralized and excreted

• Regulatory mechanismsRegulatory mechanisms BuffersBuffers Respiratory systemRespiratory system Renal systemRenal system


Buffer Systems

• Combination of a weak acid with the respective salt

• Acts as a base or an acid depending of the environment

• Prevent major changes in pH• Act as sponges… • 3 main systems

Bicarbonate-carbonic acid bufferPhosphate bufferProtein buffer

H+H+

H+


Henderson equation

• Key conceptH+ = Ka x (HA/A-)H+ = 24 x (PCO2/HCO3) = 40 nmol/l

CO2 +H2O H2CO3 H+ + HCO3Carbon Carbonic Bicarbonate

Dioxide Acid

(ACID) (BASE)


Henderson-Hasselback equation

pH = pKa x log (A-/HA)pH = pK x log(HCO3/paCO2) x 0.03 = 7.4

7.4 = 6.1 + log 20/1



• Buffers: act chemically to neutralize acids Buffers: act chemically to neutralize acids or change strong acids to weak acidsor change strong acids to weak acids Primary regulatorsPrimary regulators React immediatelyReact immediately Cannot maintain pH without adequate Cannot maintain pH without adequate

respiratory and renal functionrespiratory and renal function



• Respiratory system:Respiratory system: eliminates CO eliminates CO22

Respiratory center controls breathingRespiratory center controls breathing Responds within minutes/hours to changes in Responds within minutes/hours to changes in

acid/baseacid/base Increased respirations lead to Increased respirations lead to increasedincreased CO CO22

elimination and elimination and decreased COdecreased CO22 in blood in blood



• Renal system:Renal system: eliminate H eliminate H++ and reabsorb and reabsorb HCOHCO33

Regeneration of HCORegeneration of HCO33

Reabsorption and secretion of electrolytes Reabsorption and secretion of electrolytes

(e.g., Na(e.g., Na++, Cl, Cl)) Responds within hours to daysResponds within hours to days



• Kidneys usually secrete acidic urine (pH 6)Kidneys usually secrete acidic urine (pH 6)• Kidneys can increase or decrease pH as a Kidneys can increase or decrease pH as a

compensatory mechanism compensatory mechanism


Blood Gas ValuesBlood Gas Values

• Arterial blood gas (ABG) values provide Arterial blood gas (ABG) values provide information about information about Acid-base statusAcid-base status Underlying cause of imbalance Underlying cause of imbalance Body’s ability to regulate pHBody’s ability to regulate pH Overall oxygen statusOverall oxygen status


Interpretation of ABGsInterpretation of ABGs


Acid-Base Imbalances

• Acidemia• pH falls below 7.35• Increase in blood carbonic acid

or • Decrease in bicarbonate



• Alkalemia• pH greater than 7.45• Increase in bicarbonate

or • Decrease in carbonic acid



Primary cause or origin:• Metabolic

Changes brought about by systemicalterations (cellular level)

• RespiratoryChanges brought about by respiratory alterations


Acid-Base Imbalances (cont'd)Acid-Base Imbalances (cont'd)

• Alterations in acid-base balanceAlterations in acid-base balance Respiratory acidosisRespiratory acidosis Respiratory alkalosisRespiratory alkalosis Metabolic acidosisMetabolic acidosis Metabolic alkalosisMetabolic alkalosis Mixed acid-base disordersMixed acid-base disorders


Modificări primare ale EAB şi mecanismul compensator corespunzător

Modificare primarăParametru modificat

Mecanism compensator

Acidoza metabolică HCO3- ↓ pCO2 ↓

Alcaloza metabolică HCO3- ↑ pCO2 ↑

Acidoza respiratorie pCO2 ↑ HCO3- ↑

Alcaloza respiratorie pCO2 ↓ HCO3- ↓



• Diagnosis in six stepsDiagnosis in six steps Evaluate pH Evaluate pH Analyze PaCOAnalyze PaCO22

Analyze HCOAnalyze HCO33

Determine if CODetermine if CO22 or HCO or HCO33 matches the matches the

alterationalteration Decide if the body is attempting to Decide if the body is attempting to

compensatecompensate


Interpreting ABGsDetermine level of compensationHas the body tried to readjust the pH?• Uncompensated• Partly compensated• Compensated


Interpreting ABGsUncompensated• pH abnormal (high or low)• One component abnormal (high or low

CO2 or HCO3)• The other component is normal(The component not causing the acid-base

imbalance is still normal)Example: pH 7.2; pCO2 65; HCO3 24


Partly compensated• pH not normal (but moving toward

normal)• Both CO2 and HCO3 are outside normal

range• The component that was normal is

changing in order to compensate• Example: pH 7.30; pCO2 65; HCO3 30


Interpreting ABGsCompensated• pH almost normal• Other values abnormal in

opposite directions• One is acidotic the other alkaline• Example: pH 7.35; pCO2 65; HCO3 39


pH = 0,017 x (40 – PCO2) Alcaloza respiratorie cronica

pH = 0,008 x (40 – PCO2) Alcaloza respiratorie acuta

pH = 0,003 x (PCO2 – 40)Acidoza respiratorie cronica

pH = 0,008 x (PCO2 – 40)Acidoza respiratorie acuta

PCO2 = 0,7 x HCO3 + (21 2)Alcaloza metabolica

PCO2 = 1,5 x HCO3 + (8 2)Acidoza metabolica

Variatie asteptataModificari primare

pH = 0,017 x (40 – PCO2) Alcaloza respiratorie cronica

pH = 0,008 x (40 – PCO2) Alcaloza respiratorie acuta

pH = 0,003 x (PCO2 – 40)Acidoza respiratorie cronica

pH = 0,008 x (PCO2 – 40)Acidoza respiratorie acuta

PCO2 = 0,7 x HCO3 + (21 2)Alcaloza metabolica

PCO2 = 1,5 x HCO3 + (8 2)Acidoza metabolica

Variatie asteptataModificari primare

Modificari in tulburarile acido-bazice primare


Practice Problem

• 80 year old female with severe pneumonia, fever

• pH = 7.25• PaCO2 = 55 mm Hg• HCO3 = 24 mEq/L• PaO2 = 65 mm Hg• O2 sat = 80%


Practice Problems

What is the problem?Acidosis or alkalosis?Respiratory or metabolic?Compensated or not?Level of hypoxemia?Diagnoses?Interventions?



• pH 7.18pH 7.18• PaCOPaCO22 38 mm Hg 38 mm Hg• PaOPaO22 70 mm Hg 70 mm Hg• HCOHCO33

15 mEq/L 15 mEq/L• What is this?What is this?




22 mEq/L 22 mEq/L• What is this?What is this?



• pH 7.36pH 7.36• PaCOPaCO22 67 mm Hg 67 mm Hg• PaOPaO22 47 mm Hg 47 mm Hg• HCOHCO33 37 mEq/L 37 mEq/L• What is this?What is this?




18 mEq/L 18 mEq/L• What is this ?What is this ?


pH 7,47paCO2 45 mmHgHCO3 32 mEq/lCl 97 mEq/lNa 140 mEq/lK 2,8 mEq/l



Management - Respiratory Acidosis

• Maintain patent airway• Oxygen support, ventilation• Positioning/turning q 2 hrs• Pulmonary hygiene (postural drainage, chest

clapping)• Noninasive ventilation• Mechanical ventilation


Management - Respiratory Alkalosis

• Teach how to relieve/ prevent anxiety• Calm environment• Positioning for comfort


Management - Metabolic Alkalosis• Monitor serum electrolytes, ABG’s• Antiemetics to relieve vomiting• Administer K and Cl replacement as ordered• Monitoring of diuretic therapy


Management - Metabolic Acidosis

• Frequent assessment of vital signs esp respiratory rate and rhythm (compensatory mechanisms)

• Treat diabetes, shock….• Sodium bicarbonate IV ?


1. What are the deleterious effects of 1. What are the deleterious effects of acidemia and when are they acidemia and when are they manifest? manifest?

2. When is acidemia severe enough to 2. When is acidemia severe enough to warrant therapy? warrant therapy?

In considering acute bicarbonate replacement four In considering acute bicarbonate replacement four questions should be consideredquestions should be considered


3. How much bicarbonate should be given 3. How much bicarbonate should be given and how is that amount calculated? and how is that amount calculated?

4. What are the deleterious effects of 4. What are the deleterious effects of bicarbonate therapy? bicarbonate therapy?


• Decreased myocardial contractility Decreased myocardial contractility • Fall in cardiac output Fall in cardiac output • Fall in BPFall in BP• Pulmonary venoconstriction Pulmonary venoconstriction • Sensitizes the myocardium to arrhythmias Sensitizes the myocardium to arrhythmias

Deleterious effects of Deleterious effects of acidemiaacidemia


• Decreased binding of norepinephrine to its Decreased binding of norepinephrine to its receptors receptors

• Acidemia may adversely affect cell Acidemia may adversely affect cell functions such as enzymatic reactions, functions such as enzymatic reactions, ATP generation, fatty acid biosynthesis, ATP generation, fatty acid biosynthesis, and bone formation/resorption and bone formation/resorption

Deleterious effects of Deleterious effects of acidemiaacidemia


• Extracellular pH is a surrogate for intracellular Extracellular pH is a surrogate for intracellular pH pH

• Optimal extracelluar pH 7.4Optimal extracelluar pH 7.4

• Optimal intracellular pH 7.1Optimal intracellular pH 7.1

• Deviations from normal pH will obviously Deviations from normal pH will obviously decrease the efficiency of all reactionsdecrease the efficiency of all reactions


• Acidemia protects the central nervous Acidemia protects the central nervous system against seizuressystem against seizures

• Acidemia favours oxygen release to tissuesAcidemia favours oxygen release to tissues


• Give bicarbonate to a patient with an Give bicarbonate to a patient with an arterial pH < 7.1 arterial pH < 7.1

• Not a hard and fast ruleNot a hard and fast rule

When is acidemia severe enough to warrant therapy?When is acidemia severe enough to warrant therapy?


• The volume of distribution of The volume of distribution of bicarbonate is approximately that of bicarbonate is approximately that of total body water total body water

How much bicarbonate should be given and How much bicarbonate should be given and how is that amount calculatedhow is that amount calculated??


• Any calculated amount is approximate Any calculated amount is approximate

• 0,6 x G x (15 - HCO3 actual):20,6 x G x (15 - HCO3 actual):2

How much bicarbonate should be given and how is How much bicarbonate should be given and how is that amount calculated?that amount calculated?


• Reevaluate in two hoursReevaluate in two hours

• Make new plan based on the new dataMake new plan based on the new data

• Correct the underlying cause(s)Correct the underlying cause(s)


• Bicarbonate therapy is associated with an Bicarbonate therapy is associated with an increase in mortality increase in mortality

• Fall in blood pressure and cardiac outputFall in blood pressure and cardiac output

• Sensitizes the heart to abnormal electrical Sensitizes the heart to abnormal electrical activity and subsequent arrhythmiasactivity and subsequent arrhythmias

What are the deleterious effects of bicarbonate What are the deleterious effects of bicarbonate therapy?therapy?


• ““Paradoxical” intracellular acidosis – COParadoxical” intracellular acidosis – CO22 shifts into cellsshifts into cells

• Both volume expansion and hypernatremia Both volume expansion and hypernatremia can occur can occur

• Fulminate congestive heart failure with flash Fulminate congestive heart failure with flash pulmonary edema may result pulmonary edema may result

What are the deleterious effects of bicarbonate What are the deleterious effects of bicarbonate therapy?therapy?


Anionic gap

• AG = (Na+ + K+) - (Cl- + HCO3-) Acidoza metabolica cu AG crescut• acumulare H+ -> +HCO3 -> H2CO3 =>

scadere bicarbonat• acidoza lactica• ketoacidoza• insuficienta renala


Acidoza metabolica cu AG normal

• pierdere de bicarbonat din SEC => acumulare de clor pentru mentinerea electroneutralitatii

• diaree• IR precoce


Metabolic acidosisAnion-Gap:• Acids associated with an

unmeasured anion are produced or exogenously gained

• Treatment: Correct underlying

cause (Bicarbonate: severe

acidemia)

Non-anion gap: Bicarbonate, chloride• “Hyperchloremic” acidosis• Renal vs. GI loss of HCO3-

• Treatment: Bicarbonate therapy


Indicaţiile terapiei cu soluţii alcaline

Indicaţii ferme Indicatii posibile Indicatii abandonate

Acidoză metabolicăhipercloremică(pH 7,20)

Acidoza metabolică severăcu AG crescut

Stopul cardio-respirator(în faza iniţială aresuscitării cardio-pulmonare

Pierderi de HCO3

- Agravarea rapidă a acidozei metabolice cuAG crescut

Acidoza metabolicămoderată cu AG normalpH 7,20


ExempluAcidoza hipercloremica in diaree severapH 7,29paCo2 29 mmHgHCO3 14 mEq/lNa 138 mEq/lCl 116 mEq/lAG 11 mEq/llactat 1.5 mEq/lK 3,0 mEq/l

ExempluAcidoza lacticapH 7,29paCo2 29 mmHgHCO3 14 mEq/lNa 136 mEq/lCl 105 mEq/lAG 21 mEq/llactat 10 mEq/lK 4.0 mEk/l

curs acid base balance 2015 nov

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