Acid Base Biochemistry Flashcards
Acid base balance seeks to?
Maintain normal hydrogen ion balance in the body.
Acid base balance achieves this by?
Buffers in ecf and icf
Respiratory mechanisms- removal of CO2
Renal mechanisms- reabsorb bicarbonate, secrete H+ ions
Normal range of arterial ph?
7.35-7.45
Ph range compatible with life.
6.8-8.0
Which mechanisms of blance occur rapidly?
Buffering
Respiratory
Which mechanism of balance occur slowly?
Renal
CO2 mechanism.
- CO2 end product of aerobic metabolism
- Found in venous blood
- RBC in venous blood react CO2 +H2O—H2CO3—>H+ +HCO3–>lungs. In lungs reverse reactions occur and CO2 expelled.
- H+ generated must be buffered.
Fixed acids
•Proteins within body end up producing acid.
• phospholipids-phosphoric acid
•proteins containing sulfur-sulphiric acid.
• When the above are in excess, they tend to accumulat since they are not volatile., hence fixed acids.
• They need to be buffered by intracellular protein buffers till they are excreted by kidney.
I.e phosphate buffers locates in bone.
Acid base balance is disrupted by?
Vomiting Diarrhoea Respiratory failuire Kidny failuire Infections Ingestions
What ratio determines blood pH?
[HCO3]/Pa(CO2)
What mechanisms alter [hco3]
Metabolic acid base disorders(kidneys)
Secondary metabolic compensation.-increased excretion of h+
What mechanisms alter Pa(CO2)
Respiratory acid base disorders
Secondary respiratory compensation
Why does acid base balance need to be in a certain range?
- Acid base pairs which buffer the system will become unbalanced under subtle changea in ph.
- affects drug delivery and enzymatic action
- Proteins function within a certain optimum ph
What is acidemia?
Serum pH <7.36
What is alkalemia?
Serum pH > 7.44
Acidosis.
Pathologic process that lowers [HCO3] or increases PaCO2
Alkalosis
Pathologic process that raises [HCO3] or lowers PaCO2
How does pulmonary compensation work?
•peripheral chemoreceptors in carotid body and central chemoreceptors in medulla change minute ventilation upon decreased ph.
Decreased ph—>increased minute ventilation —> decreased PaCO2
As it is increasingly being expelled.
What is anion gap?
Estimates unmeasured anions in plasma.
•Usually hco3 accounts for measured anions
• Proteins end up not measured.
• increased proteins,(acid anions) from metabolic acidosis ie phosphates will release h+ released which reacta with hco3 reducing anions accounted for and increasing acid anions and hence the anion gap.
Formula for anion gap.
AG= Na-(hco3+cl)
Causes of respiratory acidosis.
Anything thay reduces minute ventilation.
•Airway obstruction
•Aspiration
•drug induced cns depression
•Neuromascular dx ie MG,guillian barre
• Pulmonary dx ie pneumonia edema emphysema
• Thoracic cage damage ie pneumothorax, flail chest
What are the respiratory acidosis compensations?
Acute- increased hco3 production from intracellular proteins to combine with h+ produced. Inc by 1meq/l for every 10mmhg rise of PaCO2
Chronic- renal retention of hco3. Increases by 3.5 meq/l for every 10mmhg rise in paCO2
How to manage respiratory acidosis?
Manage airway problem to increase minute ventilation.
•bronchodilators, antibiotics, clear airway, re expand lung, correction of cns dx
Normal bicarbonate level?
23-29mmol/l
Would you expect conc of hco3 to increase with increasing Paco3?
Yes.
H+ +hco3 —-> h2co3—>co2 +h2o
How do you know it is an acute respiratory acidosis?
Hco3 remains unchanged. If it ila chronic it goes up.
What causes respiratory alkalosis?
Anything that increases minute ventilation.
•hypoxia mediated hyperventilation. Ie high altitude, severe anemia,ventilation perfusion mismatch
• cns mediated ie psychogenic(anxiety, nervousness, etc: cva, increased intracranial pressure .
•pharmacologic ie salicylates, caffeine, vasoprssors,thyroxine
Pulmonary ie pneumonia , pulmonary edema, atelectasis
Hepatic encephalopathy ie damage to brain bc liver didnt remove toxins
Would you expect hco3 to decrease or increase with decreases paco2?
Decrease.
Eqn : co2+h2o—>h2co3–>h+hco3
The relationship between hco3 and paco2 is directly proportional.
Hco3 level in acute r. Alkalosis?
Normal
Hco3 level in chronic r alkalosis?
Reduced.
Acute R. Alkalosis compensation ?
Plasma hco3 lowered by 2meq/l for every 10mmhg of decreases paco2
Chronic r alkalosis compensation?
Decrease of 5meq/l of hco3 for every 10mmhg decrease in paco2
What is metabolic acidosis?
Increased h+ conc
Or decreased hco3 conc
Conditions that cause anion gap metabolic acidosis?
M-Methanol U-ureamia D-DKA P-propylene glycol, paraldehyde I-infection, iron, isoniazid L- lactic acidosis E-Ethylene glycol,ethanol S- salicylates
Non anion gap metabolic acidosis causes?
•GI losses of hco3. Diarrhea, ileostomy, colostomy •renal losses of hco3 Hyperparathyroidism Renal tubular acidosis • ingestion Acetaxolamide, cacl,mgso4
Compensation for metabolic acidosis?
Winters formula
1.5*[HCO3-]+6 or 10
Treatment for metabolic acidosis
Treat underlying condition
What is metabolic alkalosis?
Decrease in h+
Increase in hco3
Compensated for by hypo ventilation
Causes of metabolic alkalosis
• Reduced volume
Due to vomiting
Or diuretics (increased urination)
•Normal /increased volume
Due to cusions syndrome
Hyperaldosteronism
Severe pottasium depletion.
Treatment of metabolic alkalosis
Treat underlying disorder
Correct pottasium levels
Give fluids if urine cl is less than 10 meq/l
Acetazolamide if edematous to increase hco3 secretion.
Compensation for metabolic alkalosis?
Paco2= 0.9*[HCO3]+15
Mixed disorders can exist. Possible mixed disorders include?
Metabolic* respiratory processes
Metabolic acidosis and alkalosis
Respiratory acidosis and alkalosis cannot coexist
When to consider mixed disorder?
Ph = normal
Paco2 and or hco3 conc is abnormal
What is the delta ratio?
Used when high anion gap has been detected to check if a mixed disorder is present.
Delta ratio formula?
Change in AG/change in hco3 =(AG-12)/(24-HcO3)
Value less than 2/1 suggests hco3 disnt fall as would be expected of metabolic acidosis. Hence a metabolic alkalosis.
