Question

Arterial Blood Gas Patient Normal pH 7.1 7.35- 7.45 pCO2 40 mmHg 35-45 mmHg p02 95 mmHg 90-100 mm Hg HCO3 Concentration 6 mEq/liter 22-26 mEq/liter Hemoglobin 02 Saturation 95% 94-100%

Uncompensated Acid/Base Imbalance

Case 1

Mrs. Benette, a 71 year old woman, is brought in by ambulance to the ED. She is very tired and lethargic but can communicate. She is complaining of tinnitus (ringing in her ears) that she describes as a freight train driving by her head and severe dyspepsia (upset stomach). She has a medical history of rheumatoid arthritis. Upon questioning of the patient, she tells you she is taking pain medication for her arthritis but can’t remember which one she took today.

Vitals are as follows:

HR: 80 bpm
RR: 17 breaths/min
BP: 100/70 mmHg
Weight:150 lbs
Multiple Tests were ordered and the results can be found HERE.

Question 1: How would you classify her acid-base disturbance? What lead you to this conclusion? Justify your answers with normal and abnormal test results.

Question 2: Based on the patients case history and test results what might have caused her particular acid-base disturbance? Why? Justify your answers with relevant test results.

Question 3: How would the respiratory and urinary systems compensate for this acid-base disturbance? Be specific in your answer.

Question 4a: Based on your knowledge of this type of acid/base imbalance what would you administer to this patient to treat this imbalance?

Question 4b: What dose of the drug in mEq would you use?

Dosage Calculation:

Medication dosage: 3 mEq per kg of body weight;
Weight conversion: 1 kg = 2.2 lbs or 1 lb = 0.453 kg

Question 4c: This medication needs to be administered over a 6 hour period. What would the dose be per hour?

Note : pictures above are the tests and results.

Answer 1

1.Mrs. Benette is having

PH - 7.1 (acidic) normal range 7.35-7.45

HCO3 - 6 new/L (very low)

PCo2 - 40 mm (Normal)

Since both PH and bicarbonate is low and PCO2 is normal it is a case of uncompensated metabolic acidosis

2. She is a known case of rheumatoid arthritis,

Work up for infective pathology complete blood count, blood cultures‌, CSF culture, stool culture, and urine analysis is normal, substance abuse has also been ruled out.

Aspirin level is 100 mg/dl i.e. in the range of toxicity and BUN/Creatinine Ratio is 20:1 which is suggestive of border line dehydration, so diagnosis is Salicylic acid toxicity.

3.acid base, fluid and electrolyte abnormality due to acetyl salicylic acid poisioning occurs in 3 stages

Stage 1 - Acetyl salicylic acid is a direct stimulation of respiratory centre which causes hyperventilation and it leads to respiratory alkalosis (Co2 washout) and to compensate loss of HCO3 and K+ occurs through kidney (Compensatory alkaluria)

Stage 2 - in this stage "Paradoxical aciduria" occurs even in the presence of respiratory alkalosis due to sufficient loss of K+ from the kidney.

Stage 3 - it is characterised by hypokalemia and metabolic acidosis

salicylates also causes inhibiton of citric acid cycle and uncoupling of oxidative phosphorylation that causes accumulation of phosphoric and sulfuric acid and these process also contribute for metabolic acidosis

4. Since patient is having severe metabolic acidosis we have to give soda bicarbonate which is a systemic, and urinary alkalinizer. It also increases renal clearance of acidic drugs. Alkalization of the urine enhances elimination of salicylates through ion trapping in the renal tubules.

Dosage is 3 meq/kg

Weight is 150 lbs = 68 kg,

Dosage - 3 x 68 = 204 meq

Since it has to be given over 6 hrs, Per hour dose will be 36 meq/hour