Acid – Base Disorders1

7/27/2019 Acid Base Disorders1

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Acid Base Disorders

Viyeka Sethi

PGY 4

Med-Peds


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Four Main Acid-Base Disorders

Suppression of acid

excretion; decrease in

reabsorption of HCO3

in plasmaHCO3

in plasmapCO2

Respiratory

Alkalosis

Increase in acid

excretion; increase in

reabsorption of HCO3

in plasma

HCO3

in plasma

pCO2

Respiratory

Acidosis

Hypoventilationincrease in

pCO2 in plasma

HCO3

Metabolic

Alkalosis

Hyperventilationin plasma

pCO2

in plasmaHCO3

Metabolic

Acidosis

Mechanism of

Response

Secondary

Response

Primary

Alteration

Disorder


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Normal Values

70pO2

>4040pCO2

2424HCO3


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Step by Step

1. Determine the primary disturbance:

Acidemia or Alkalemia: look at the pH

< 7.40 = acidemia> 7.40 = alkalemia

Respiratory or Metabolic: look at HCO3 and CO2

HCO3 = primary metabolic acidosis

pCO2 = primary respiratory acidosis

and vice versa for alkalosis


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2. Determine acute or chronic for Respiratory

Disturbance:

o Compensation attempts to normalize pH but canbe present with an abnormal pH

o Expected change in pCO2 best used for primary

metabolic disturbance and expected change in

HCO3 for primary respiratory disturbance


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Respiratory Disturbance

Compensation

30.0310Chronic Resp.Acidosis

10.0810Acute Resp.

Acidosis

in HCO3in pHpCO2

50.0310Chronic Resp.Alkalosis

20.0810Acute Resp.Alkalosis

in HCO3in pHpCO2


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3. Primary Metabolic Disturbance:

o Calculate anion gap : Na (Cl + HCO3)

o Normal = 12 +/- 2o If gap is >20 then there is primary metabolic

acidosis regardless of pH or bicarb.

o Helps narrow differential with a anion gap ornon-anion gap metabolic acidosis


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4. Assess appropriate respiratorycompensation for metabolic disorder:

o Respiratory compensation is fasto Winters formula:

Expected pCO2 = (1.5 * HCO3) + 8 (+/-2)

o If measured pCO2 is

< expected then co-existing resp. alkalosis

> expected then co-existing resp. acidosis


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5. Determine if other metabolic disturbances

co-exist with AG metabolic acidosis:

o Delta gap accounts for increase in anion gapand shows any variation in HCO3

o If no other disorder is present then the

calculation should be 24


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Delta Gap

Corrected HCO3 = measured HCO3 + (AG - 12)

o So if corrected HCO3

>24 then metabolic alkalosis co-exists


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Hints

Simple acid base compensatory response

always in direction of primary variable

Compensation is more pronounced withchronic disorders

Normal pH indicates two or more acid-base

disorders

If given electrolytes, use them!!!


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Pneumonics for pnuemonic lovers

CNS disease

Hypocapnia

Anxiety

Mech. Ventilation

Progesterone

Salicylates

Sepsis

Contraction

Licorice

Endocrine

(Conn/Cushing

/Bartters)

Vomiting

Excess alkali

Refeeding

Post-

hypercapnia

Diuretics

CNS depression

Airway

obstruction

Pulmonary

edema

Pneumonia

Hemo/Pneumo

thorax

Neuromuscular

Hyperalimentation

Acetazolamide

Renal Tubular

Acidosis

Diarrhea

Uretero-Pelvic

shunt

Post-hypocapnia

Spironolactone

Methanol

Uremia

DKA/Alcoholic

ketoacidosis

Paraldehyde

Isoniazid

Lactic acidosis

Ethanol

Renal

failure/Rhabdo

Salicylates

Respiratory

Alkalosis

CHAMPS

Metabolic

Alkalosis

CLEVERPD

Acute Resp.

Acidosis

anything

causing

hypoventilation

Metabolic

Acidosis Non-

Gap

HARDUPS

Metabolic

Acidosis Anion

Gap

MUDPILERS


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Case 1

3 yo boy with diarrhea is evaluated in the

ER. Initial ABG shows:

ph 7.23

HCO3 10

pCO2 23

AG - 13

Alkalemia or acidemia?Low pH = acidemia

Primary disturbance resp. or metabolic?

Low HCO3 = metabolic acidosis

Normal AG so no need for Delta gap equationBUT

Is there adequate respiratory compensation?

(Use Winters formula)

Expected pCO2 = (1.5 * HCO3) + 8 +/-2

So,Expected pCO2 = (1.5 * 10) + 8 +/-2

=(15) + 8 +/-2

=23 +/- 2

So, we have a metabolic acidosis with

respiratory compensation


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Case 2

5 yo boy presents to ED with dyspnea for 3

days. ABG shows the following:

pH 7.35

paCO2 60

paO2 57

HCO3 - 31

Acidemia or alkalemia?Low pH = Acidemia

Primary Resp. or Metabolic disturbance?

Respiratory

Check yourself.using rules for Primary Resp

disturbance

For every 10 increase in pCO2 -

pH decreases by .08 acutely or .03 chronically

HCO3 increases by 1 acutely or 3 chronically

So, this is a chronic resp. acidosis


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Case 3

15 yo with 4 days of vomiting and fever.

pH- 7.50 Na- 138

pCO2- 42 Cl- 80

pO2- 80 HCO3- 34

Acidemia or alkalemia?

High ph = alkalemia

Respiratory or Metabolic?

High HCO3 = metabolic

Is Resp. compensation appropriate?

Exp. pCO2 = (1.5 * HCO3) + 8 +/-2=(51) + 8 +/-2

=59 +/- 2

So, NO the CO2 is lower so we have a

Co-existent resp.alkalosis

Anion Gap?

138 (80 + 34) = 24

Checking the Delta gap only usefulin a primary metabolic acidosis.


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Case 4

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Acid – Base Disorders1