abg interpretation teaching file. stepwise approach obtain clues from the clinical setting determine...

ABG INTERPRETATION

Teaching file

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:

AG, normal Cl

Lactic acidosis Ketoacidosis Ingestions; alcohol, INH, methanol, ethylene

glycol Renal failure Massive rhabdomyolysis


NORMAL ANION GAP METABOLIC ACIDOSIS

Normal AG, Cl

Diarrhea- GI loss of HCO3 RTA- renal loss of HCO3 Ingestion of ammonium chloride or hyperalimentation

fluids Acetazolamide therapy


METABOLIC ALKALOSIS

(urine Cl < 10 mEq/d)

Vomiting

Remote diuretic use

Post hypercapnea

Chronic diarrhea

Cystic fibrosis


METABOLIC ALKALOSIS(urine Cl > 10 mEq/d)

Bartter’s syndromeSevere potassium depletion

Current diuretic useHypercalcemia

HyperaldosteronismCushing’s syndrome


RESPIRATORY ACIDOSIS

CHRONIC: COPD

ACUTE: pneumonia

RESPIRATORY ALKALOSIS

Hyperventilation

DETERMINE THE

PRIMARY DISORDER

Important values at normal physiologic state

pH= 7.4 (7.35-7.45) HCO3= 24 mmol/L (18-26 mmol/L) pCO2= 40 mmHg ( 35-45 mmHg)

Characteristics of primary acid base disturbances

disorder pH (H+) Primary

disturb

Compensa-tory

response

Met Acidosis

Dec inc Dec (HCO3)

Dec PCO2

Met Alkalosis

inc dec Inc (HCO3) Inc PCO2

Resp acid dec inc Inc (PCO2) Inc HCO3

Resp alkalosis

inc dec Dec (PCO2)

Dec HCO3

Moving on…

disorder Primary abnormality

Secondary response

Resp acidosis hypoventilation HCO3 generation- kidneys

Resp alkalosis hyperventilation HCO3 consumption

Metabolic acidosis Loss of HCO3 or gain H+

Hyperventilation

Metabolic alkalosis Gain of HCO3 or lose H+

hypoventilation

Moving on…

Metabolic acidosis Dec HCO3 1.2 mmHg dec in PCO2 foe every 1 meq/L fall

in HCO3

Metabolic alkalosis Inc HCO3 0.7 mmHg inc in CO2 for every 1 meq/L rise

in HCO3

Respiratory acidosis Inc PCO2 1 meq/L inc in HCO3 for every 10 mmHg rise

in PCO2

Respiratory alkalosis Dec PCO2 2 meq/L dec in HCO3 for every 10 mmHg fall

in PCO2

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




pH = 7.25 HCO3 = 28 pCO2 = 60

ACIDOSIS ALKALOSIS ACIDOSIS





pH = 7.55 HCO3 = 19 pCO2 = 20

ALKALOSIS ACIDOSIS ALKALOSIS

RESPIRATORY ALKALOSIS


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


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


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

Examples: in simple metabolic acidosis

If patient presents with pH=7.2 and HCO3=16, what is the normal compensated value for

pCO2? 24-16= 8 meq/L 8 x 1.2 = 9.6 mmHg fall in

PCO2 40 mmHg-9.6 mmHg = 30.4 mmHg

Normal compensation PCO2 = 30.4 mmHg

Example 2

If patient presents with pH= 7.23. HCO3= 22 meq/L, and pCO2= 9, what is your

interpretation?

Note the pH and tell whether it is acidosis or alkalosis? Note the HCO3 and pCO2 values to determine which causes the primary

disturbance? Determine the compensatory response

What is our diagnosis?

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

Cl

HCO3

NAGMA

Delta-delta

HCO3

AG

HAGMA

Delta values

HCO3 = HCO3 patient – HCO3 normal

HCO3 patient – 24 mmol/L AG = AG patient – AG normal

AG patient – 12 meq/L Cl= Cl patient – Cl normal

Cl patient – 105 mmol/L

NAGMA

HCO3 = Cl

HCO3< Cl

HCO3 > Cl

Pure NAGMA

NAGMA with metabolic alkalosis

NAGMA plus HAGMA

HAGMA

HCO3 = AG

HCO3< AG

HCO3 > AG

Pure HAGMA

HAGMA with metabolic alkalosis

HAGMA plus NAGMA

Confused?... Sample problems

Problem #1 ABG: HCO3 = 15 mmol/L AG= 21 meq/L

What type of metabolic acidosis are we dealing? Calculate your delta values Determine any underlying metabolic disorder based on the

comparison of delta values?

Solution

Step 1 The anion gap is elevated ( N value is 12),

chloride values are not given so we assume them to be normal. Therefore we have HAGMA

Step 2 HCO3 = 24 mmol/L – 15 mmol/L = 9 mmol/L

AG = 21 meq/L – 12 meq/L = 9 mmol/L

solution

Step 3: Compare your delta values

HCO3 AG

9 mmol/L 9mmol/L

The values are equal Diagnosis: Pure HAGMA

Isa pa…

Problem No 2 ABG: HCO3 = 15 mmol/L AG = 30 meq/L Step 1: what type of metabolic acidosis Step 2: calculate your delta waves Step 3: compare your delta values Step 4: diagnosis

Problem 3

ABG: HCO3 = 15 mmol/L Cl = 114 meq/L Step 1: we have a Cl elevation instead of an

anion gap elevation therefore we have a NAGMA

Step 2: HCO3: 24-15= 9 mmol/L

Cl: 114-105 meq/L = 9 mmol/L Step 3: Compare 9 mmol/L 9 mmol/L Step 4: Pure 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 + metabolic alkalosis

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


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


pH = 7.14 Na = 140

pCO2= 45 K = 4

HCO3 = 17 Cl = 98

pCO2 =7 x 1.2 = 8.4Metabolic & Respiratory

Acidosis

CASE 2


pH = 7.14 Na = 140

pCO2= 45 K = 4

HCO3 = 17 Cl = 98

AG = 140 – (98+17) = 25 HAGMA + RAc

CASE 2


pH = 7.14 Na = 140

pCO2= 45 K = 4

HCO3 = 17 Cl = 98

HAGMA + MAlk + RAc

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

CASE 2


pH = 7.14 Na = 140

pCO2= 45 K = 4

HCO3 = 17 Cl = 98


CASE 2

1) IV NaHCO3 using HCO3 deficit

2) oral NaHCO3 at 1 mEq/kg/day

3) intubate

4) no treatment


CASE 2

HCO3 DEFICIT = (D –A) x 0.4 x kg BW


HCO3 deficit = (18 – 17) x 0.4 x 60 = 24

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

use 0.7 to 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 NaHCO3 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 Acidifying 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=39°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

The anion gap

QUESTIONS?

Thank You

abg interpretation teaching file. stepwise approach obtain clues from the clinical setting determine...

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