ACID-BASE DISTURBANCES

CLINICAL CASES
Marwa Adel, PhD
Lecturer of Clinical Pharmacy
Faculty of Pharmacy, Ain Shams University
Acid–base disorders should be evaluated using a
stepwise approach
1. Obtain a detailed patient history and clinical
assessment.
2. Check the arterial blood gas, sodium, chloride, and
HCO−3 and identify all abnormalities in pH, Paco2, and
HCO−3
3. Determine which abnormalities are primary and which
are compensatory based on pH.
A. If the pH is less than 7.35, then a respiratory or metabolic
acidosis is primary.
B. If the pH is greater than 7.45, then a respiratory or metabolic
alkalosis is primary.
4. If Paco2 changes in the same direction as the pH then
the disorder is metabolic, if in the opposite direction,
then the disorder is respiratory
Acid–base disorders should be evaluated using a
stepwise approach
5. If metabolic acidosis is present, calculate the anion gap.
If equals to or more than 12 an elevated anion gap
metabolic acidosis is present, if less than 12 a normal or
non-anion gap metabolic acidosis is present
6. If the anion gap is increased, calculate the delta-gap

a. If > 1, a metabolic alkalosis is also present.

b. If < 1, a non anion gap metabolic acidosis is also
present.
Acid–base disorders should be evaluated using a
stepwise approach
7. Consider other laboratory tests to further differentiate
the cause of the disorder.
A. If the anion gap is high and a toxic ingestion is expected,
calculate an osmolal gap.
B. If the anion gap is high, measure serum ketones and lactate.
C. If the anion gap is normal, consider calculating the urine anion
gap.
Acid–base disorders should be evaluated using a
stepwise approach
8. If Metabolic Alkalosis, measure urine chloride to be sure from
the cause.
9. Respiratory Acidosis is due to CO2 excess because of
depressed respiration.
10. Respiratory Alkalosis is very commonly induced by what the
body or patient perceives as a stressor. The stressor which is
often associated with anxiety, pain, and infection stimulates
the CNS leading to hyperventilation.
11. If the pH is normal (7.40) and there are abnormalities in
PaCO2 and HCO3- , a mixed disorder is probably present
because metabolic and respiratory compensations rarely
return the pH to normal.
12. Compare the identified disorders to the patient history and
begin patient-specific therapy.
Case study
1. A 55-year-old woman is admitted to the hospital after
several days of worsening shortness of breath. Recently,
she was discharged from the hospital after a similar
episode and was doing fine until 3 days before admission,
when she developed a productive cough, necessitating an
increase in her home oxygen and more frequent use of her
metered dose inhalers. On admission to the medical ICU,
she was anxious and markedly distressed, with rapid,
shallow breaths. She was hypertensive (160/80 mm Hg),
tachycardic (140 beats/minute), and tachypneic (respiratory
rate 28 breaths/minute)
Case study
Her ABG showed a pH of 7.30, PaCO2 59 mmHg, PaO2 50
mmHg, HCO3− 28 mEq/L, and SaO2 83% on 6 L/minute of
oxygen by face mask, and she was immediately intubated.
• Which primary acid-base disturbance is most consistent
with this patient’s presentation and laboratory data?
• A. Metabolic acidosis.
• B. Metabolic alkalosis.
• C. Respiratory acidosis.
• D. Respiratory alkalosis.
Case study
Her ABG showed a pH of 7.30, PaCO2 59 mmHg, PaO2 50
mmHg, HCO3− 28 mEq/L, and SaO2 83% on 6 L/minute of
oxygen by face mask, and she was immediately intubated.
• Which primary acid-base disturbance is most consistent
with this patient’s presentation and laboratory data?
• A. Metabolic acidosis.
• B. Metabolic alkalosis.
• C. Respiratory acidosis.
• D. Respiratory alkalosis.
Case study
2. A 62-year-old woman has been hospitalized in the ICU
for several weeks. Her hospital stay has been complicated
by aspiration pneumonia and sepsis, necessitating
prolonged courses of antibiotics. For the past few days, she
has been having high temperatures again, and her stool
output has increased dramatically.
• Her most recent stool samples have tested positive for
Clostridium difficile toxin, and her laboratory tests reveal
serum sodium 138 mEq/L, potassium (K) 3.5 mEq/L, Cl
115 mEq/L, HCO3− 15 mEq/L, albumin 4.4 g/dL, pH 7.32,
Paco2 30 mm Hg, and HCO3− 15 mEq/L. Which is most
consistent with this patient’s primary acid-base
disturbance?
• A. AG metabolic acidosis.
• B. Non-AG metabolic acidosis.
• C. Chloride-responsive metabolic alkalosis.
• D. Acute respiratory acidosis.
Case study
3. A 58-year-old woman remains intubated in the intensive
care unit (ICU) after a recent abdominal operation. In the
operating room, she receives more than 10 L of fluid and
blood products but has received aggressive diuresis with
furosemide postoperatively. In the past 3 days, she has
generated 12 L of urine output, and her blood urea nitrogen
(BUN) and serum creatinine (SCr) have steadily increased
to 40 and 1.5 mg/dL, respectively. Her urine chloride (Cl)
concentration was 9 mEq/L (24 hours after her last dose of
furosemide).
This morning, her arterial blood gas (ABG) reveals pH 7.50,
Paco2 46 mm Hg, and bicarbonate (HCO3−) 34 mEq/L.
Her vital signs include a blood pressure (BP) of 85/40 mm
Hg and a heart rate (HR) of 110 beats/minute. Which action
is best to improve her acid-base status?

• A. 0.9% sodium chloride (NaCl) bolus.

• B. 5% dextrose (D5W) bolus.
• C. Hydrochloric acid infusion.
• D. Acetazolamide intravenously
Case study
4. A 27-year-old man with no medical history is admitted to
the hospital after being “found down” at a party, where he
reportedly ingested a handle of whiskey during a 60-min
period. On arrival at the emergency department, he was
neurologically unresponsive, with the following ABG values:
pH 7.23, Paco2 58 mm Hg, Pao2 111 mm Hg, HCO3− 24
mEq/L, and Sao2 96% on 2 L/minute of oxygen by nasal
cannula. Which action is most appropriate?
• A. Administer tromethamine 500 mL over 30 minutes
• B. Administer 100% oxygen by face mask
• C. Give NaHCO3− 100 mEq intravenous push
• D. Urgent intubation
Case study
5. A 50 year old female is brought to the emergency
department in a semi-comatose state by her neighbor. Her
neighbor reports that she had complained of stomach pain in
the morning that day and then began vomiting and urinating
frequently for several hours prior to bringing her in. Her
toxicology screen is negative but her urine test is positive for
ketones. Labs: Serum chemistry: Na 135 (nl: 135-145mEq/l),
K 4.5 (3.5-5 mEq/l), Cl 105 (nl: 95-105 mEq/l), Blood
Glucose 675 mg/dL (nl: 70-110 mg/dL), ABG: pH 7.29, PCO2
28, HCO3-18, Serum albumin: 2.4 (nl: 4.4 g/dl)
A. Based on the clinical presentation of this female and her
ABG, what acid-base disturbance is present? Mention the
type and the subtype
Case study
5. A 50 year old female is brought to the emergency
department in a semi-comatose state by her neighbor. Her
neighbor reports that she had complained of stomach pain in
the morning that day and then began vomiting and urinating
frequently for several hours prior to bringing her in. Her
toxicology screen is negative but her urine test is positive for
ketones. Labs: Serum chemistry: Na 135 (nl: 135-145mEq/l),
K 4.5 (3.5-5 mEq/l), Cl 105 (nl: 95-105 mEq/l), Blood
Glucose 675 mg/dL (nl: 70-110 mg/dL), ABG: pH 7.29, PCO2
28, HCO3-18, Serum albumin: 2.4 (nl: 4.4 g/dl)
A. Based on the clinical presentation of this female and her
ABG, what acid-base disturbance is present? Mention the
type and the subtype
Case study
B. Is there a second acid base disorder?
C. What is the likely cause of her acid-base disturbance?
 Case study
6. An 18 years old female was brought to the Faculty Health Center by her friends
who noticed that she seemed very confused. She is a first year faculty student and
she was preparing for final exams. She has a past medical history of anxiety disorder.
Vital signs: HR 115, BP 150/90, RR 39. Her ABG shows pH 7.49, PaCO2 25, HCO3-
21.
What primary acid-base disorder is present?
A. Metabolic acidosis
B. Metabolic alkalosis
C. Respiratory acidosis
D. Respiratory alkalosis
What should be the initial management for her case?
A. Treatment may be unnecessary because most patients have few symptoms and
only mild pH alterations (i.e., pH <7.50).
B. Reassuring the student, try to calm her and ask her to slow her respiration.
C. A rebreathing device (e.g., paper bag) can help control her hyperventilation
D. Any of the above
• Supplement:

Primary disorder Expected level of compensation

Metabolic Acidosis ↓PCO2 = 1.2×∆ [HCO3−]
Metabolic Alkalosis ↑PCO2 = 0.7 ×∆ [HCO3−]
Respiratory Acidosis
• Acute ↑[HCO3-] = 0.1 x ∆PCO2
• Chronic ↑[HCO3-] = 0.35 x ∆PCO2
Respiratory Alkalosis
• Acute ↓[HCO3-] = 0.2 x ∆PCO2
• Chronic ↓[HCO3-] = 0.4 x ∆PCO2