ABG INTERPRETATION Teaching file. STEPWISE APPROACH Obtain clues from the clinical setting Determine...
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Transcript of 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
CLUES FROM CLINICAL SETTING
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
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
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
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
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
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 0.4 x kg BW
How will you correct the acid base disorder?
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