ABG INTERPRETATION

STEPWISE APPROACH Obtain clues from the clinical setting Determine primary disorder Check the compensatory response Calculate the anion gap Calculate the delta/deltas Identify specific etiologies for the acid-

base disorder Prescribe treatment

DETERMINE CLUES FROM THE

CLINICAL SETTING

CLUES FROM CLINICAL SETTING

HIGH ANION GAP METABOLIC ACIDOSIS

Ketoacidosis – dm, alcohol, starvation

INH, methanol, lactic acid

Renal failure

Hypotension

CLUES FROM CLINICAL SETTING

NORMAL ANION GAP METABOLIC ACIDOSIS

Diarrhea

RTA

Interstitial nephritis

Early renal failure

Urinary tract obstruction

CLUES FROM CLINICAL SETTING

METABOLIC ALKALOSIS

(urine Cl < 10 mEq/d)

Vomiting

Remote diuretic use

Post hypercapnea

Chronic diarrhea

Cystic fibrosis

CLUES FROM CLINICAL SETTING

METABOLIC ALKALOSIS(urine Cl > 10 mEq/d)

Bartter’s syndromeSevere potassium depletion

Current diuretic useHypercalcemia

HyperaldosteronismCushing’s syndrome

CLUES FROM CLINICAL SETTING

RESPIRATORY ACIDOSIS

CHRONIC: COPD

ACUTE: pneumonia

RESPIRATORY ALKALOSIS

Hyperventilation

DETERMINE THE

PRIMARY DISORDER

DETERMINE PRIMARY DISORDER

Check the trend of the pH, HCO3, pCO2

The change that produces the pH is the primary disorder

pH = 7.25 HCO3 = 12 pCO2 = 30

ACIDOSIS ACIDOSIS ALKALOSIS

METABOLIC ACIDOSIS

DETERMINE PRIMARY DISORDER

Check the trend of the pH, HCO3, pCO2

The change that produces the pH is the primary disorder

pH = 7.25 HCO3 = 28 pCO2 = 60

ACIDOSIS ALKALOSIS ACIDOSIS

RESPIRATORY ACIDOSIS

DETERMINE PRIMARY DISORDER

Check the trend of the pH, HCO3, pCO2

The change that produces the pH is the primary disorder

pH = 7.55 HCO3 = 19 pCO2 = 20

ALKALOSIS ACIDOSIS ALKALOSIS

RESPIRATORY ALKALOSIS

DETERMINE PRIMARY DISORDER

If the trend is the same, check the percent difference

The bigger %difference is the 10 disorder

pH = 7.25 HCO3 = 16 pCO2 = 60

ACIDOSIS ACIDOSIS ACIDOSIS

RESPIRATORY ACIDOSIS

(16-24)/24 = 0.33 (60-40)/40 = 0.5

DETERMINE PRIMARY DISORDER

If the trend is the same, check the percent difference

The bigger %difference is the 10 disorder

pH = 7.55 HCO3 = 38 pCO2 = 30

ALKALOSIS ALKALOSIS ALKALOSIS

METABOLIC ALKALOSIS

(38-24)/24 = 0.58 (30-40)/40 = 0.25

CHECK THECOMPENSATORY RESPONSE

COMPENSATORY RESPONSE

HENDERSEN-HASSELBACH EQUATION

24 x pCO2

H = ----------------

HCO3

Metabolic or Respiratory Acidosis

COMPENSATORYRESPONSE

HENDERSEN-HASSELBACH EQUATION

24 x pCO2

H = ----------------

HCO3

Metabolic or Respiratory Alkalosis

COMPENSATORY RESPONSE

METABOLIC ACIDOSIS

pCO2 = HCO3 x 1.2 + 2

HCO3 =12 pCO2 =14.4 – 40 = 25.6

pCO2 =20.4 – 40 = 19.6HCO3 =7

COMPENSATORY RESPONSE

HCO3 =35 pCO2 =7.7 + 40 = 47.7

pCO2 =11.2 + 40 = 51.2HCO3 =40

METABOLIC ALKALOSIS

pCO2 = HCO3 x 0.7 + 2

COMPENSATORY RESPONSE

pCO3 =55 HCO3 =1.5 + 24 = 25.5

HCO3 =4 + 24 = 28pCO3 =80

ACUTE RESPIRATORY ACIDOSIS

HCO3 = pCO2 x 0.1

COMPENSATORY RESPONSE

pCO3 =55 HCO3 =5.25 + 24 = 29.25

HCO3 =14 + 24 = 38pCO3 =80

CHRONIC RESPIRATORY ACIDOSIS

HCO3 = pCO2 x 0.35

COMPENSATORY RESPONSE

pCO3 =25 HCO3 =3 - 24 = 21

HCO3 =1.6 - 24 = 22.4pCO3 =32

RESPIRATORY ALKALOSIS

HCO3 = pCO2 x 0.2

CALCULATE THE ANION GAP

ANION GAP

Na – (HCO3 + Cl) = 12 + 4

Na = 135 HCO3 = 15 Cl = 97 RBS = 100 mg%

AG = 135 – 112 = 23

ANION GAP

Na – (HCO3 + Cl) = 12 + 4

Na = 135 HCO3 = 15 Cl = 97 RBS = 500 mg%

Corrected Na = Na + RBS mg% -100 x 1.6

100

AG = 135 + 6.4 – 112 = 29.4

CHECK THE DELTA / DELTA

DELTA - DELTA If with high AG metabolic acidosis

AG

HCO3

If with normal AG metabolic acidosis

Cl

HCO3

A high AG always indicates the presence of a HAG metabolic acidosis

DELTA - DELTA

/ = 1

/ > 1

/ < 1

Simple NAG metabolic acidosis

HAGMA/NAGMA + meta alk

HAGMA+NAGMA

CASE 1

56F with vomiting and diarrhea 3 days ago despite intake of loperamide. Her last

urine output was 12 hours ago.

PE showed BP = 80/60, HR = 110, RR = 28. There is poor skin turgor.

CASE 1

serum Na = 130 pH = 7.30

K = 2.5 pCO2 = 30

Cl = 105 HCO3 = 15

BUN = 15 pO2 = 90

crea = 177

RBS = 100

BCR = BUN / crea x 247.6 = 21 PRE-RENAL

CASE 1

serum Na = 130 pH = 7.30

K = 2.5 pCO2 = 30

Cl = 105 HCO3 = 15

BUN = 15 pO2 = 90

crea = 177

RBS = 100

pH = acidosis, pCO2 =alk, HCO3 = acidosis

Metabolic Acidosis

CASE 1

serum Na = 130 pH = 7.30

K = 2.5 pCO2 = 30

Cl = 105 HCO3 = 15

BUN = 15 pO2 = 90

crea = 177

RBS = 100

pCO2 = 9 x 1.2 = 10.8Compensated

Metabolic Acidosis

CASE 1

serum Na = 130 pH = 7.30

K = 2.5 pCO2 = 30

Cl = 105 HCO3 = 15

BUN = 15 pO2 = 90

crea = 177

RBS = 100

AG= 130 – (105+15) = 10 NAGMA

CASE 1

serum Na = 130 pH = 7.30

K = 2.5 pCO2 = 30

Cl = 105 HCO3 = 15

BUN = 15 pO2 = 90

crea = 177

RBS = 100

/= (105-100)/(24-15) = 0.56 NAGMA + HAGMA

CASE 1

56F with vomiting and diarrhea 3 days ago despite intake of loperamide. Her last urine

output was 12 hours ago.

PE showed BP = 80/60, HR = 110, RR = 28. There is poor skin turgor.

pH 7.30, HCO3=15, pCO2=30, Na=130 K=2.5

How will you correct the acid base disorder?

CASE 1

1) Hydrate

2) Hydrate + IV NaHCO3

3) Hydrate + oral NaHCO3

4) Hydrate + correct hypokalemia

How will you correct the acid base disorder?

INDICATIONS FOR HCO3 THERAPY

pH < 7.2 and HCO3 < 5 – 10 mmHg When there is inadequate ventilatory

compensation Elderly on beta blockers in severe acidosis with

compromised cardiac function Concurrent severe AG and NAGMA Severe acidosis with renal failure or intoxication

COMPLICATIONS OF HCO3 THERAPY

Volume overload Hypernatremia Hyperosmolarity Hypokalemia Intracellular acidosis Causes overshoot alkalosis Stimulates organic acid production tissue O2 delivery

NaHCO3 50 ml = 45 mEq Na

NaHCO3 gr X tab = 7 mEq Na

POTASSIUM CORRECTION

K deficit = (3.5 – K)/0.27 x 100 Give ½ of the deficit in 24 hours

1 cc oral KCL = 1.33 mEq K1 potassium durule = 10 mEq K

K deficit = (3.5 – 2.5)/0.27 x 100 = 370

CASE 2

30M with epilepsy has a grand mal seizure. Labs showed:

pH = 7.14 Na = 140

pCO2= 45 K = 4

HCO3 = 17 Cl = 98

%pCO2 =13, %HCO3 = 29 Metabolic Acidosis

CASE 2

30M with epilepsy has a grand mal seizure. Labs showed:

pH = 7.14 Na = 140

pCO2= 45 K = 4

HCO3 = 17 Cl = 98

pCO2 =7 x 1.2 = 8.4Metabolic & Respiratory

Acidosis

CASE 2

30M with epilepsy has a grand mal seizure. Labs showed:

pH = 7.14 Na = 140

pCO2= 45 K = 4

HCO3 = 17 Cl = 98

AG = 140 – (98+17) = 25 HAGMA + RAc

CASE 2

30M with epilepsy has a grand mal seizure. Labs showed:

pH = 7.14 Na = 140

pCO2= 45 K = 4

HCO3 = 17 Cl = 98

HAGMA + MAlk + RAc

/= (25-12)/(24-17) = 1.9

CASE 2

30M with epilepsy has a grand mal seizure. Labs showed:

pH = 7.14 Na = 140

pCO2= 45 K = 4

HCO3 = 17 Cl = 98

How will you correct the acid base disorder?

CASE 2

1) IV NaHCO3 using HCO3 deficit

2) oral NaHCO3 at 1 mEq/kg/day

3) intubate

4) no treatment

How will you correct the acid base disorder?

CASE 2

HCO3 DEFICIT = (D –A) x 0.5 x kg BW

How will you correct the acid base disorder?

HCO3 deficit = (18 – 17) x 0.5 x 60 = 30

As HCO3 < 5-10, the Vd increases; hence

use 0.7 to 0.1

dHCO3 = 15 - 18

Maintenance 1 mEq/day

Give ½ as bolus and the other ½ as drip in 24 hrs

PRINCIPLES OF HCO3 THERAPY

LACTIC ACIDOSIS

Primary effort should be improving O2 delivery Use NaCO3 only when HCO3 < 5 mmol/L In states of CO, raising the CO will have more

impact on the pH In cases of low alveolar ventilation, ventilation

to lower the tissue pCO2

PRINCIPLES OF HCO3 THERAPY

KETOACIDOSIS

Rate of H+ production is slow; NaHCO3 tx may just provoke severe hypokalemia

Should be given if…1) severe hyperkalemia despite insulin

2) HCO3 < 5 mmol/L3) worsening acidemia inspite of insulin

CASE 3

19F, fashion model, is surprised to find her K=2.7 mmol/L because she was

normokalemic 6 months ago. She admits to being on a diet of fruit and vegetables

but denies vomiting and the use of diuretics or laxatives. She is

asymptomatic. BP = 90/55 with subtle signs of volume contraction.

CASE 3

serum Na 138 63

K 2.7 34

Cl 96 0

HCO3 30 0

pH 7.45 5.6

pCO2 45

Metabolic Alkalosis

Plasma Urine

pH = alk, pCO2 =acidosis HCO3 = alkalosis

CASE 3

pCO2 = 6 x 0.7 = 4.2Compensated

Metabolic Alkalosis

serum Na 138 63

K 2.7 34

Cl 96 0

HCO3 30 0

pH 7.45 5.6

pCO2 45

Plasma Urine

CASE 3

AG= 138 – (96+30) = 12 NAG

Plasma Urine

serum Na 138 63

K 2.7 34

Cl 96 0

HCO3 30 0

pH 7.45 5.6

pCO2 45

CASE 3Plasma Urine

serum Na 138 63

K 2.7 34

Cl 96 0

HCO3 30 0

pH 7.45 5.6

pCO2 45

What is the cause of the acid base disorder?

CASE 3

What is the cause of the acid base disorder?

1) diuretic intake

2) surreptitious vomiting

3) diuretic intake

4) Bartter’s syndrome

5) Adrenal tumor

6) nonreabsorbable anionHow should her acid-base disorder be managed?

CASE 3

How should her acid-base disorder be managed?

1) correct hypokalemia

2) hydrate with NSS

3) administer acidyfing agent

4) give carbonic anhydrase inhibitor

MANAGEMENT OF METABOLIC ALKALOSIS

Chloride repletion Potassium repletion Tx hypermineralocorticoidism Dialysis Carbonic anhydrase inhibitors Acidyfing agents

HCl, NH4Cl

INDICATIONS OF HCl

pH > 7.55 and HCO3 > 35 with contraindications for NaCl or KCl use

Immediate correction of metabolic alkalosis in the presence of hepatic encephalopathy, cardiac arrhythmias, digitalis intoxication

When initial response to NaCl, KCl, or acetalozamide is too slow or too little

USE OF HCl

HCL requirement = (A – D) x 0.5 x kg BW 0.1 – 0.2 N HCl solution = 100 – 200 mEq Do not exceed 0.2 mEq/kg/hour of HCl

HCO3 = 70 wt = 60 kg

HCl = 1,380 mEq

CASE 4

73M with long standing COPD (pCO2 stable at 52-58 mmHg), cor pulmonale, and

peripheral edema had been taking furosemide for 6 months. Five days ago, he had anorexia, malaise, and productive cough. He continued his medications until he developed nausea. Later he was found

disoriented and somnolent

CASE 4

PE: BP 110/70, HR 110, RR 24, T=40respiratory distressprolonged expiratory phasepostural drop in BPdrowsy, disorientedscattered rhonchi and rales BLFsdistant heart soundstrace pitting edema

CASE 4admission after 48 hrs

pH = acidosis pCO2 =acidosis, HCO3 = alk

Respiratory Acidosis

serum Na 136 139

K 3.2 3.9

Cl 78 86

HCO3 40 38

pH 7.33 7.42

pCO2 78 61

pO2 43 56

serum Na 136 139

K 3.2 3.9

Cl 78 86

HCO3 40 38

pH 7.33 7.42

pCO2 78 61

pO2 43 56

CASE 4admission after 48 hrs

HCO3 = (55-40) x 0.35 = 5.25 HCO3 = (78-55) x 0.1 = 2.3

HCO3 = 24 + 5.25 + 2.3 =

31.55

Respiratory Acidosis & M. Alkalosis

serum Na 136 139

K 3.2 3.9

Cl 78 86

HCO3 40 38

pH 7.33 7.42

pCO2 78 61

pO2 43 56

CASE 4

How should this patient be managed?

admission after 48 hrs

1) intubation and mechanical ventilation

2) low flow oxygenation by nasal prong

3) oxygen by face mask

4) sodium bicarbonate infusion with KCl

CASE 4

How should this patient be managed?

MANAGEMENT OF RESPIRATORY ACIDOSIS

Correct underlying cause for hypoventilation

effective alveolar ventilation intubate, mechanically ventilate

Antagonize sedative drugs Stimulate respiration (e.g. progesterone) Correct metabolic alkalosis

CASE 5

42M, alcoholic, brought to the ER intoxicated. He was found at Rizal park in a pool of vomitus. PE showed unkempt and incoherent patient with a markedly contracted ECF volume. T=390 C with

crackles on the RULF.

serum Na = 130 pH = 7.53

K = 2.9 pCO2 = 25

Cl = 80 HCO3 = 20

BUN = 12 pO2 = 60

crea = 120 alb = 38

RBS = 15 mmol/L

CASE 5

PRE-RENALBCR = (12/120) x 247.6 = 24.76

serum Na = 130 pH = 7.53

K = 2.9 pCO2 = 25

Cl = 80 HCO3 = 20

BUN = 12 pO2 = 60

crea = 120 alb = 38

RBS = 15 mmol/L

CASE 5

Respiratory Alkalosis

%pCO2 =38, %HCO3 = 18

serum Na = 130 pH = 7.53

K = 2.9 pCO2 = 25

Cl = 80 HCO3 = 20

BUN = 12 pO2 = 60

crea = 120 alb = 38

RBS = 15 mmol/L

CASE 5

Compensated Respiratory

Alkalosis

HCO3 = (40-25) x 0.2 = 3

serum Na = 130 pH = 7.53

K = 2.9 pCO2 = 25

Cl = 80 HCO3 = 20

BUN = 12 pO2 = 60

crea = 120 alb = 38

RBS = 15 mmol/L

CASE 5

HAGMA + RAlkAG = 130 – (80 + 20) = 30

serum Na = 130 pH = 7.53

K = 2.9 pCO2 = 25

Cl = 80 HCO3 = 20

BUN = 12 pO2 = 60

crea = 120 alb = 38

RBS = 15 mmol/L

CASE 5

What are the causes of his acid base disturbance?

1) aspiration pneumonia

2) alcohol ketoacidosis

3) vomiting

CASE 5

What are the causes of his acid base disturbance?

MANAGEMENT OF RESPIRATORY ALKALOSIS Correct underlying cause of

hyperventilation Rebreathe carbon dioxide Mechanical control of ventilation

increase dead space

decrease back up rate

decrease tidal volume

paralyze respiratory muscles

QUESTIONS?

Thank You

ACID BASE PHYSIOLOGY

by:

ROMMEL S. GAMBOA, M.D.

ACID BASE PHYSIOLOGY

maintenance of constant blood pH physiologic buffers renal system respiratory system

BUFFERS 1. Extracellular buffers a. HCO3- major extracellular buffer b. PO4- minor extracellular buffer2. Intracellular buffers a. Organic phosphates (AMP. ADP, ATP, 2,3DPG) b. Proteins (hemoglobin [major intracellular], DeoxyHgb, oxyHgb, imidazole and α-amino groups.

HENDERSON-HASSELBALCH EQUATION

is used to calculate pH pH = pK + log [A-]/[HA-]

pH = log of 10 [H]

pK = log 10 equilibrium constant

[A-] = base form of the buffer

[HA] = acid form of the buffer

Techniques of obtaining a sample Materials The patient is seated or lying down The wrist should be extended

approximately30 degrees A definite pulse should be palpated The site should be cleansed with 70%

isopropyl alcohol The radial artery should again be palpated

while holding the heparinized syringe much like a pencil or dart with the opposite hand.

Techniques of obtaining a sample The needle is then inserted opposite the

blood flow at 45-degree angle or less with the bevel turned upward.

After a 3-4 ml of sample is withdrawn, a sterile cotton is applied over the puncture site. Digital pressure should be applied for at least 5 minutes.

The specimen must be placed on ice and transported within 15 minutes at 4ºC and tested immediately

NORMAL BLOOD GAS VALUES

pH pCO2 pO2 HCO3 BE Hgb O2Sat

Hi 7.45 45 100 26 +2 18 100

Lo 7.35 35 80 22 -2 12 90

TWO ORGAN SYSTEM INVOLED IN ACID-BASE PHYSIOLOGY

1. Respiratory System

2. Renal System

BLOOD GAS ANALYZERS

determine acid-base balance through the measurement of partial pressure of oxygen, carbon dioxide and pH.

Bicarbonate and other parameters are calculated from previously mentioned measurements

METABOLIC ACIDOSIS

increase in arterial [H+] decrease in arterial [HCO3] respiratory compensation –

hyperventilation (Kussmaul breathing) renal compensation - ↑ excretion of H+ as

titratable acid and NH4; ↑ reabsorption of HCO3

METABOLIC ALKALOSIS

decrease in arterial H+ ↑ HCO3 because of loss of H+ e.g.

vomiting when H+ is lost from the stomach respiratory compensation: hypoventilation renal compensation: ↑ excretion of HCO3

RESPIRATORY ACIDOSIS

caused by primary decrease in respiratory rate and retention of CO2

↑ in H+ and HCO3 by mass action no respiratory compensation renal compensation: ↑ excretion of H+ and

NH4 ↑ reabsorption of HCO3

RESPIRATORY ALKALOSIS

caused by primary increase in respiratory rate and loss of CO2

↓ H+ and HCO3 by mass action no respiratory compensation renal compensation: ↓ excretion of H+ and

NH4 ↓ reabsorption of HCO3