Lec 48-49 Acid Base Flashcards
What is equation for pH?
pH = -log[H]
What is pH of stomach acid?
2
What is pH of urine?
6
what is pH of saliva?
6
What is normal blood pH?
7.4
What are the two types of acid you make?
- non-carbonic/non-volatile/fixed [from protein digestion]
- carbonic/volatile [from cell respiration]
What are some non-volatice acids from protein metabolism?
- cycstein
- H2S
- SO4
How are carbonic acids excreted?
via lungs
How are non-carbonic acids eliminated?
via kidney
What is plasma conc HCO3?
24 mEq/L = 24 mmol/L
What is plasma pCO2?
40 mmHg
What happens if we eat excess H?
- more glutamine comes into PT cell –> more NH4 into lumen and more HCO3 into blood
- in alpha intercalated: can excrete more H since it can bind NH3 and won’t affect urine pH , create more HCO3 that goes into blood
Will you get alkaline blood if you eat too much HCO3?
No - because there is a threshold in PT for how much HCO3 the transporter can reabsorb
- if you eat too much HCO3 it will get excreted and not reabsorbed
What happens if you exercise heavily and generate lactic acid?
- lactic acid –> lactate + H
- the H then: H + HCO3 -> H2CO3
- H2CO3 –> H2O + CO2 and breathed off
What is function of kidney in high H handling?
- reabsorption and generation of HCO3
- excretion of H
What is function of lungs in high H handling?
regulation pCO2
What is relationship [H] to pCO2 and [HCO3]
[H] is proportional to pCO2/[HCO3]
What is definition acidemia?
blood pH < 7.4
what is definition alkalemia?
blood pH > 7.4
what is definition acidosis?
a process that increases the [H]
what is definition alkalosis?
a process that decreases the [H]
Can you have acidemia and alkalemia at the same time?
No
Can you have alkalosis and acidosis at the same time?
yes
What does it mean if an acidosis/alkalosis is respiratory? [ie what value is changing]
- primary change in pCO2 –> problem caused by lungs
What does it mean if an acidosis/alkalosis is metabolic? [ie what value is changing]
- primary change in HCO3
What is a compensation?
predictable response by body to change in pCO2 or HCO3
in the equation H ~ pCO2/[HCO3] which part do lungs compensate with? which part does kidney compensate with?
- lungs compensate by altering pCO2
- kidney compensates by altering HCO3
What is cause of respiratory acidosis?
not breathing too much – accumulate pCO2
what is cause of respiratory alkalosis?
breathing too much - loss of pCO2
What is path of respiratory disorder [initial change, acute, chronic]?
initial: change in pCO2
acute: compensate by intracellular buffering
chronic: compensation by kidney HCO3 handling
What is path of changes [initial and compensation] from hypoventilation?
initial: respiratory acidosis
- low pH/ high H
- high pCO2
- normal HCO3
compensation by kidneys
- slightly less low pH
- still high pCO2
- high HCO3
What are lab pH, CO2, and HCO3 values from respiratory acidosis?
- low pH
- high pCO2
- high HCO3
two in same direction = respiratory
What are some acute causes of respiratory acidosis?
- upper airway obstrcution
- respiratory center inhibition
- exacerbation of chronic lung disease
- mechanical ventilation
What are some chronic causes of respiratory acidosis?
- mechanical ventilation
- COPD
- extreme obesity
What is path of changes [initial and compensation] from hyerventilation?
initial: respiratory alkalosis
- high pH/ low H
- low pCO2
- normal HCO3
compensation by kidneys
- slightly less high pH
- still low pCO2
- low HCO3
What is kidney compensation for respiratory acidosis?
- increased regeneration of HCO3 in alpha intercalated cells
What is kidney compensation for respiratory alkalosis?
- decreased HCO3 reabsorption in PT
- decreased regenration HCO3 in alpha intercalated
What are some causes of respiratory alkalosis
hypoxemia - from anemia, high altitutide, fibrosis/edema, CHF
- direct stimulation of medullary respiratory center
- mechanical ventilation
What are lab pH, CO2, and HCO3 values from respiratory alkalosis?
- high pH
- low pCO2
- low HCO3
2 in same direction = respiratory
Case: 54 M, COPD, hip fracture
Na = 138, K = 3.9, CL = 103, HCO3 = 29, pH = 7.35, pCO2 = 55
acidemia or alkalemia?
metabolic or respiratory?
is compensation appropriate?
respiratory acidemia
What rise in HCO3 do you expect from 15 mmHg rise pCO2 in respiratory acidosis if acute? if chronic?
acute: 1.5 mEq/L rise
chronic: 5.25 mEq/L rise
What is initial change in metabolic disorder? compensation?
- initial change [HCO3]
- compensate by change in ventilation of pCO2
What are the four ways you can get metabolic acidosis?
- increased acid production
- decreased acid excretion
- decreased HCO3 production
- increased HCO3 excretion
What is path of changes in metabolic acidosis? Initial and compensation?
initial:
- low pH/ high H
- normal pCO2
- low HCO3
compensation by lungs:
- slightly less low pH
- low pCO2
- still low HCO3
What are lab pH, CO2, and HCO3 values from metabolic acidosis?
- low pH
- low pCO2
- low HCO3
all in same direction = metabolic
What could cause metabolic acidosis from under excretion of acid?
acute or chronic renal failure
What could cause metabolic acidosis from over-secretion of HCO3?
GI loss
renal loss
What could cause metabolic acidosis from under-production of HCO3?
renal defect
What could cause metabolic acidosis from over-production of acid? Exogenous? endogenous?
endogenous
- lactic, ketone, amino, phosphoric
exogenous
- salicylate, methanol, HCl, ethylene glycol, toluene
What is the equation for anion gap?
AG = Na - (HCO3 + Cl)
What is normal anion gap? range?
11 ‘unmeasured anions’
8-12 mEq/L
What is explanation of anion gap idea?
- blood must be electrically neutral
- [Na] = 140 is main cation so there must be equivalent anion conc in blood
- main anions are:
- – [HCO3] = 24
- – [Cl] = 105
the anion gap = whatever leftover anions unmeasured
Why is it normal to have an anion gap?
because there are anions present that aren’t measured like albumin, phosphaste etc
When do you have low Cl?
hyponatremia –> Na and Cl travel together
Why might you have low bicarb in metabolic acidosis?
bicarb is buffering the H+ from whatever extra acid acumulated
What are the causes of high anion gap acidosis? [mnemonic]
MUDPILES
- Methanol
- Uremia = kidny failure
- Diabetic, alcoholic, or starvation ketoacidosis
- Propylene glycol, pyroglutamic acid
- INH or Iron
- Lactic Acidosis
- Ethylene glycol
- Salicylates
Methanol is associated with what metabolic state?
high anion gap acidosis
[due to exogenous acid acumulation]
Uremia [kidney disease] is associated with what metabolic state?
high anion gap acidosis
[due to failure to excrete acid]
ketoacidosis [from diabetes, alcohol, or starvation] is associated with what metabolic state?
high anion gap acidosis
[due to endogenous acid build up]
propylene glycol is associated with what metabolic state?
high anion gap acidosis
[due to exogenous acid]
Iron is associated with what metabolic state?
high anion gap acidosis
[due to exogenous acid]
Lacid Acidosis is associated with what metabolic state?
high anion gap acidosis
[due to endogenous acid]
Ethylene glycol is associated with what metabolic state?
high anion gap acidosis
[due to exogenous acid]
Salicylates are associated with what metabolic state?
high anion gap acidosis
[due to exogenous acid]
What causes non-anion gap acidosis?
- due to loss of bicarbonate in diarrhea or renal
What happens to Na/HCO3/Cl/unmeasured levels in non anion-gap acidosis?
- normal Na
- low HCo3
- high Cl
Why do you get high Cl in non anion-gap acidosis?
You don’t have as much HCO3 around to use to reabsorb Na
you start increasing Cl reabsorption to help with Na reabsorption
Case:
- 25F 3 days diarrhea
Bp 100/60 HR 110 RR 20
Na = 143, K = 3.3, Cl = 117, HCO3 = 16, Alb = 3.7 pH = 7.25, pCO2 = 34
acidemia or alkalemia?
met or resp?
anion gap or none?
appropriate compensation?
- metabolic acidemia
- no anion gap and high Cl
What is winter’s formula? what do you use it for
expected pCO2 = 1.5 (HCO3) + 8 +/- 2
determining expected respiratory compensation in metabolic acidosis
What is path of changes in metabolic alkalosis? Initial and compensation?
initial
- high pH/low H
- normal pCO2
- high HCO3
compensation:
- less high pH/ less low H
- high pCO2
- still high HCO3
What are two causes of metabolic alkalosis?
- loss of H via GI [vomit] or kidney [diuretics]
- loss of ECF [contraction alkalosis]
- less volume with same HCO3 so HCO3 conc rises
What are 3 reasons you might get HCO3 reabsorption increases even when you have high HCO3?
- decreased GFR: get decreased filtered load
- decreased effective circulation volume: promotes Na/HCO3 reabsorption in PT
- hypokalemia: promotes H secretion / K reabsorption in a-intercalated cell
What are lab pH, CO2, and HCO3 values from metabolic alkalosis?
- high pH
- high HCO3
- high pCO2
