abg ppt -metabolic alkalosis

1. “Life is a struggle, not against sin, not
against the Money Power, not against
malicious animal magnetism, but against
hydrogen ions.”
H.L. MENCKEN
ABG IN ICU

2. METABOLIC
ALKALOSIS

3. Etiology of Metabolic Alkalosis

4. Etiology of Metabolic Alkalosis

5. Pathways Leading to Metabolic
Alkalosis

6. Maintenance Factors for Metabolic Alkalosis

7. compensation
 Predicted PCO2 = (0.7 × HCO3–) + 21
 Lower PCO2 values than predicted indicate the
presence of a coexisting respiratory alkalosis.
Higher CO2 values than predicted indicate a
coexisting respiratory acidosis.

8. Chloride-depletion alkalosis
 “saline responsive”. It is the most common type of
metabolic alkalosis.
 Hypokalemia and/or hypochloremia may be present.
 Urinary Cl– <20 mEq/L (Often, urine Cl– is<10
mEq/L).
 Chloride depletion states:
 GI tract: Vomiting or nasogastric aspiration, villous
adenoma, chloridorrhea, gastrocystoplasty Kidney:
Chloruretic diuretics, severe K+ depletion,
posthypercapnia; Skin: Cystic fibrosis.

9. Potassium-depletion alkalosis
 Also known as chloride-resistant alkalosis: it is actually
exacerbated when Cl– is administered without K+ (e.g., NaCl
infusion: “saline unresponsive”).
 Urinary Cl– >20 mEq/L.
 A high urinary chloride suggests:
 Ongoing diuretic therapy: Decreased chloride absorption
 Bartter’s or Gitelman’s syndrome Severe hypokalemia (<2
mEq/L) in potassium depletion states:
 Gut: laxative abuse
 Kidney: hyperaldosteronism, primary and secondary, other
hypokalemic hypertensive syndrome, Bartter and Gitelman
syndrome.

19. Diagnostic Utility of Urinary Chloride

20. Effects of metabolic alkalosis

21.  salicylate intoxication - metabolic acidosis and respiratory
alkalosis
 renal failure and vomiting – metabolic acidosis and
metabolic alkalosis
 hyperemesis during pregnancy – metabolic alkalosis and
respiratory alkalosis
 COPD and vomiting – metabolic alkalosis and respiratory
acidosis
 respiratory acidosis and respiratory alkalosis cannot co-
exist

22. Case 1
 A 72 year old COPD patient was brought to the EMD.
During transport, Mr. G had been given oxygen
supplementation by a partial rebreathing mask at 12 l/min.
 At reception, Mr. G was drowsy and was breathing at only
5–6 breaths/min.
 An ABG performed on arrival showed
pH 7.19,
PaO2 66 mmHg,
PaCO2 92 mmHg

23.  Treatment options would include:
 (a) Administering FIO2 at 0.28 by ventimask
 (b)Making the patient breathe room air to augment the
his hypoxic ventilatory drive
 (c)Increasing FIO2 by administering O2 through a
non-rebreathing mask

24. PAO2 ={(Patm -Pw )*FIO2}- {(PaCO2 /RQ)}
PAO2 ={(760-47)́*0.6-(92/0.8)=312.8mmHg
PAO2 =(760-47)* 0.21-(92/0.8)=34mmHg

25. Case 2
 A 20 year old woman is under evaluation in the ER for
acute shortness of breath. Her chest X-ray is interpreted as
normal:
 pH: 7.55,
 HCO −: 22 mEq/L,
 PCO : 27 mmHg,
 PO : 93 mmHg on room air.
 Anion gap is normal.

26.  PAO2 = FiO2 (Pb – Pw) – PaCO2/R
 Assuming a barometric pressure of 760 mmHg (sea
level), and a respiratory quotient of 0.8:
 PAO2 = [0.21(760 − 47)] − (27/0.8) = 116
 PAO −PaO = 116 − 93 = 23.22
 A-aDO2 = 23 (normally 7 − 14 on room air): The A-
aDO2 is widened.

27. Case 3
 A 45-year-old woman is S/P thyroid surgery 2 weeks
ago. She presents with painful spasms of her legs and
arms. She has a positive Chvostek’s sign on exam.
 Na+ = 142
 K+ = 4.0
 Cl- = 100 HCO3 = 24 Glu = 100 BUN= 10
 Why is her Anion Gap 18?

28.  This is an unusual cause of an elevated anion gap.
Because this patient just had neck surgery, the natural
worry is the function of her parathyroid glands, which
leaves her at risk for hypocalcemia and
hypomagnesemia. There is no evidence of an ongoing
metabolic acidosis, so one must consider a decrease
in unmeasured cations. She can have severe hypo-
calcemia and magnesemia, and her gap normalized
with cation replacement.

29. Case 4
 An elderly woman CHF on diuretics with severe
arthritis is found in her apartment lethargic and
confused.
 Na+ = 137 K+=3.6
 Cl-=95 HCO3 = 20
 Glu = 126 BUN= 9
 pH = 7.60 pCO2 = 25 pO2=80 HCO3 = 20

30.  metabolic acidosis due to lactate, respiratory alkalosis
due to sepsis, and the metabolic alkalosis secondary
to the diuretics.

31. Case 5
 An alcoholic presents with vomiting.
 pH 7.20;
 pCO2 25
Na 130;
 Cl 80;
 HCO3 10

32.  Primary AGMA (alcoholic ketoacidosis), metabolic
alkalosis (vomiting)

33. Case 6
 A man with arthritis presents with confusion, shortness
of breath, and diaphoresis.
 pH 7.30;
 pCO2 18
 Na 147;
 Cl 108;
 HCO3 16

34.  Primary AGMA and respiratory alkalosis (Salicylate
toxicity)

35. Case 7
 A patient with COPD presents with shortness of
breath.
 pH 7.18;
 pCO2 80
 Na 135;
 Cl 93;
 HCO3 30

37. Case 8
 A woman with Crohn’s disease presents with fever,
vomiting, and diarrhea.
 pH 7.36;
 pCO2 22
 Na 147;
 Cl 121;
 HCO3 14

38.  Primary NAGMA (diarrhea), respiratory alkalosis (fever), metabolic
alkalosis (vomiting)
 If metabolic acidosis, is there another concomitant metabolic
disturbance?
If AGMA, then calculate ∆Gap = ∆AG – ∆ HCO3 = (AG -12) – (24 –
HCO3)
 If the ∆Gap is > 6, there is a combined AGMA and metabolic
alkalosis.
 If the ∆Gap is < -6, there is a combined AGMA and NAGMA.
If NAGMA, for every 1 mEq/L ↑Cl, there should be a 1 mEq/L ↓
HCO3 (±5).
 If HCO3 decrease is less than predicted, then NAGMA and
metabolic alkalosis

39. Corrected bicarbonate
 If anion gap is increased, assess the corrected
bicarbonate
 Hco3 + (measured anion gap -12)
 If it is < 24 –hidden non anion gap met acidosis
 If it is >24 – hidden metabolic alkalosis

40. Case 9
 A 58-year-old man (heavy smoker) admitted to the
ICU with sepsis.
 He is not intubated yet but has an NG tube.
 His ABG showed pH (6.88), PaCO2 (40), HCO3 (7), Na+
(142), Cl− 100.
 What type of acid–base disturbance does this patient
have?

41.  Combined AGMA, metabolic alkalosis, and respiratory
acidosis. This patient’s metabolic acidosis is most
likely related to sepsis. His respiratory acidosis is
likely due to respiratory failure (COPD ± aspiration)
and the metabolic alkalosis is due to gastric suction.

42. Case 10
 A noncompliant patient with diabetes and cirrhosis
presents with vomiting.
 pH 7.46;
 pCO2 17
Na 133
 Cl 84
 HCO3 15

43.  Primary chronic respiratory alkalosis (cirrhosis), AGMA
(DKA), metabolic alkalosis (vomiting)