acid base disturbances smythe

brownsted lowry definition of acid

acid HA donates proton to a solution when it dissociates into H and conjugate anion A-

the amount of acidity (H+) in the blood can be expressed by which equation

henderson hasselbach equation

ph = pka + log (A/HA)

alter the henderson hasselbach equation in terms of CO2 and HCO3

ph = pka + log HCO3/CO2

CO2 is the acid and HCO3 is the base

what is the equation for the carbonic acid and bicarb buffer system

H2O + CO2 <--(carbonic anhydrase)---> H2Co3 <----> H+ + HCO3-

the buffer system in our body involves which 2 compounds

carbonic acid and bicarbonate

the conversion of CO2 to H2CO3 is slowly catalyzed by

carbonic anhydrase

when an acid is added to the system, it combines with _______ to form CO2 and be eliminated via lungs

HCO3- (forms H2CO3 and dissociates to H2O and Co2)

when a base is added to the system, it combines with _____ to form HCO3- which is eliminated via kidneys

H2CO3

what depends on acid base balance in our bodies

-pH dependant enzymes, transport proteins

-arterial muscle tone

- glycemic control and insulin

- immune system fxns

- neurotransmission, CNS function

-myocardial fxn

sources of acid in body

MAJORITY= carbon dioxide (15k mmol/day)

beta-hydroxybutyrate

phopshoric acid

fatty acids

sulfuric acid

lactic acid

acetoacetate

which organs modulate CO2 and HCO3

lungs= CO2

kidneys= HCO3

how much H+ is produced via diet and metabolism

40-70meq/h

the __________ is the specific site where respiratory control of CO2 occurs based on blood pH

alveoli

describe process of respiratory control of pCO2

1. chemoreceptors in CNS detect increase in blood acidity-> alert resp center

2. respiratory center INCREASES ventilation rate

3. more CO2 exhaled to offset extra acid

describe renal control of HCO3/ pH balance (what is absorbed/ eliminated)

1. reabsorbs filtered HCO3

2. eliminates acid via NH4+ elimination

pCO2= _____ regulation

HCO3-= ______ regulation

pCo2= respiratory regulation

HCO3= metabolic regulation (kidney)

what is the primary reabsorption site of bicarb?

proximal tubule (but reabsorbed at diff locations in glomerulus)

acid secretion is considered _________ to HCO3 production

equivalent

in what form is acid removed from the kidneys

NH4+ (ammonium)

describe the steps in the kidney that allows H+ to become HCO3 for reabsorption

1. H+ secreted into lumen-> reacts with HCO3 via carbonic anhydrase

H⁺ + HCO₃⁻ → CO₂ + H₂O

2. Co2 and H2O are formed in the lumen-> diffuse back into renal cell

3. Co2 and h2o undergo another carbonic anhydrase rxn

CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻

4. HCO3- enters sodium cotransporter and enters back into blood

is arterial or venous blood gas used for determining acid-base status

arterial bc it hasnt picked up tissue metabolic byproducts (unlike venous blood)

which pH range is considered incompatible with life

ph< 6.8

pH>7.8

normal arterial pH?

pCO2?

PO2?

HCO3-?

pH= 7.35-7.45

pCO2= 35-45 mmHg

pO2= 80-100mmHg

HCO3= 22-26 meq/L

which pH is considered acidemia? alkalemia?

acidemia: pH<7.35

alkalemia: pH >7.45

why must plasma be electrically neutral

net charge imbalance in solution is physically impossible. charges will always redistribute until balance is restored

what is the anion gap?

normal range?

equation?

major blood cations - major blood anions

usually, AG is 8-12 since there are more unmeasured anions than cations. anions can be protein, sulfates, ketones,etc. cations are calcium, Mg, K, etc.

anion gap= [Na] - [Cl- + HCO3-]

why is the anion gap only calculated in acidosis?

differentiates btwn AGMA (rise in acids consumes bicarb= rise) and NAGMA (Cl rises and compensates for bicarb loss)

more unmeasured anions is represented by an anion gap > ____

AG>12

if an acid base disturbance occurs, what does the body do

1. buffer system

2. respiratory compensation (lungs within hours)

3. metabolic compensation (kidneys within 3 days)

how is arterial blood gas obtained? what values does it provide?

obtained via percutaneous needle puncture

gives pH, pCO2, pO2, HCO3-

what are the 5 steps used after obtaining arterial blood gas (summary)

1. evaluate the pH and categorize it as acidosis or alkalosis

norm: 7.35-7.45

acidosis: <7.35

alkalosis: >7.45

2. evaluate pCO2

norm: 35-45mmHg

saME direction as pH is metabolic

opposite is respiratory

3. categorize metabolic or respiratory

(saME or opposite=resp)

4. if metabolic acidosis, calculate anion gap

if AG>12 then AGMA

5. evaluate for compensation. Winter's for acidosis, alkalosis equation if alkalosis

pH

norm:

acidosis:

alkalosis:

norm: 7.35-7.45

acidosis: <7.35

alkalosis: >7.45

how to evaluate pCo2 and categorize metabolic or respiratory

normal pCO2: 35-45mmHg

-if abnormal, look at direction of change

- if saME direction as pH, then metabolic

if opposite than respiratory

classify the following as alkalosis or acidosis and as metabolic or respiratory disturbance

pH= 7.32

pCo2= 55

pH=7.32 is less than 7.35-7.45 range-> acidosis

pCO2= 55 (norm 35-45). so pH lowers but pCO2 increases so that is OPPOSITE direction= respiratory disturbance

this is primary respiratory acidosis

classify the following as alkalosis or acidosis and as metabolic or respiratory disturbance

pH= 7.51

pCo2= 49

pH is above 7.45-> alkalosis

pCO2=49 is above 35-35 range

both above= saME direction= metabolic

this is metabolic alkalosis

classify the following as alkalosis or acidosis and as metabolic or respiratory disturbance

pH= 7.25

pCo2= 51

7.25-> below, acidosis

51-> above

opposite= respiratory

this is respiratory acidosis

if __________ acidosis exists, calculate the anion gap

metabolic

(respiratory changes CO2, not plasma anions so they dont affect AG)

if anion gap is ____, then AG metabolic acidosis can be present

>12

what is the compensatory change for metabolic acidosis? alkalosis?

metabolic acidosis: decrease PCO2

metabolic alkalosis: increase PCO2

what is the compensatory change for respiratory acidosis? alkalosis?

resp acidosis: increase HCO3-

resp alkalosis: decrease HCO3-

(issue is with CO2, need metabolic compensation)

what is winters formula and why is it used?

used to predict respiratory compensation (PCO2) for metabolic acidosis

acidosis: pCO₂= 1.5×[HCO₃⁻] + 8 ±2

what is alkalosis compensation equation

alkalosis: pCO2= 0.7×[HCO₃] + 21 ±2

compensation is considered appropriate if ___________

calculated value and measured value are within 10% of each other

what is the acid-base disorder and is it compensated

pH= 7.22

pCO2= 29

HCo3= 10

pH is below= acidosis

CO2 is below

SAME= metabolic acidosis

pCO₂= 1.5×[HCO₃⁻] + 8 ±2

pCO2= 1.5(10) + 8+-2

= 21-25

calc= 21-25

actual= 29

not fully compensated. PCO2 needs to be lower

AGMA vs NAGMA

AGMA= anion gap metabolic acidosis (>12)

- extra acids consume HCO3 so AG widens (Cl doesnt rise here since we have neg charge from acids)

NAGMA= non anion gap MA (normal 8-12 AG)

-HCO3 loss causes Cl to rise and AG is maintained (or Cl loss causes HCO3 rise)

anion gap acidosis- MUDPILES

Methanol (toxic ingestions)

Uremia (renal failure)

Diabetic Ketoacidosis

Propylene glycol (drug diluent toxicity)

Isoniazid/ iron (toxic drug exposure)

Lactic acidosis (hypoperfusion)

Ethylene glycol (toxic ingestion)

Salicylates (toxic ingestion)

drugs with propylene glycol diluents that could cause metabolic acidosis

can be continuous infusion/ greater implications: "el pen"

esmolol

lorazepam

pentobarbital

etomidate

nitroglycerin

other:

phenobarbital

phenytoin

digoxin

drug induced AG metabolic acidosis

beta agonists

metformin

propofol

linezolid

nucleoside reverse transcriptase inhibitors

propylene glycol

what is non-anion gap acidosis

results from issues with measured ions (Na, Cl, HCo3)

- usually from loss of bicarb via GI

- sometimes bc of exogenous Cl intake (ex NS)

compare to AG acidosis-> which is from anions that are NOT measured (AG>12)

non anion gap acidosis- ACCRUED

Acetazolamide

Chloride administration (NS)

Cholestyramine

Renal tubular acidosis

Ureteral diversion

Endocrinopathies

Diarrhea

metabolic alkalosis results from gain of _____ or loss of ______

pH _______

HCO3 _______

gain of HCO3 or loss of H

pH increase

HCO3 increase

chloride responsive vs non responsive metabolic alkalosis

chloride responsive (low urine Cl <10)

- vomiting

-NG suctioning

-loop or thiazides

=== there is depletion of Cl; replace it w NaCl or KCl

chloride NON-responsive (norm or high >10)

- excess mineralocorticoids

-cushing syndrome

hypokalemia and mineralocorticoids cause HCO3 reabsorption

== must correct hypokalemia or remove mineralocorticoid to tx

scenarios that ________ the respiratory rate and/or tidal volume will cause respiratory acidosis

decrease

-bc CO2 is building up which is causing acidosis

hypercapnia

elevated CO2 in blood

decrease in respiratory rate causes CO2 buildup and respiratory acidosis

tidal volume

how much air you exhale or inhale in single normal breath

_______ the respiratory rate and _____ tidal volume will eliminate more CO2

increasing; increasing

causes of respiratory acidosis vs alkalosis

acidosis:

-meds: opioids, sedatives, alcohol

-pneumonia

-COPD

alkalosis:

- mechanical ventilation, ANXIETY

summarize how lungs and kidneys work to maintain acid homeostasis

1st: lungs

- HCO3 moved to lungs and exhaled as CO2

- increase or decrease respiratory rate as response

2nd: kidneys

- retain (in acidosis) or excrete (in alkalosis) HCO3-

- generates ammonia NH3 which secretes H and makes new HCO3

renal compensation begins ________ after acid-base derangement but can take ____________ for full compensation

6-12hrs

3-5 days

this is why this second line of defense and lungs are first

hypoventilation results in _______ CO2

hyperventilation results in _______ Co2

Hypoventilation → ↑ CO₂ (hypercapnia)

Hyperventilation → ↓ CO₂ (hypocapnia) bc breathing more off

compensation can be classified as

uncompensated, partially compensated, fully compensated (pH is near normal)

in low albumin states, add ____ to the calculated AG for every 1g/dL of albumin <4

2

normal AG range? metabolic acidosis can be present if AG___

normal: 8-12

metabolic acidosis if AG>12

an AG > _______meq indicates a primary metabolic acidosis regardless of pH or serum HCO3

>20 (if >12 metabolic acidosis might be present but not guaranteed)

acidosis occurring from toxic metabolites of methanol and ethylene glycol can be managed by _______, an alcohol dehydrogenase inhibitor

fomepizole

how is chloride responsive and non responsive metabolic alkalosis corrected

chloride responsive: replace Cl loss with NaCl or KCl

non responsive: correct low K or remove the mineralocorticoid

t/f: on a daily basis, we generate a daily base load that must be excreted

false. we generate daily acid load

which 2 acids are generated in DKA

beta-hydroxybutyrate

acetoacetate

hypoperfusion can cause which acid base disturbances and which

hypoperfusion causes lactic acidosis-> metabolic acidosis