Interpret · Respiratory
Blood Gas Lab
Acid-base is arithmetic wearing a stethoscope. Every case here shows the working: Winter's formula, the corrected gap, the delta ratio, so 'compensated' becomes a checked calculation, never an impression.
The workflow
- 1pH
- 2Acidemia or alkalemia
- 3Primary process
- 4Compensation (do the math)
- 5Anion gap (correct for albumin)
- 6Delta ratio
- 7Mixed disorder?
- 8Oxygenation
- 9Clinical integration
The gases
The sighing teenager
coreThe 19-year-old from the DKA lab case, breathing deeply at 28 per minute.
pH 7.12 · PaCO2 22 · HCO3 9
Three days of vomiting, one blood gas
coreThe 45-year-old with gastric outlet obstruction from the lab module.
pH 7.50 · PaCO2 47 · HCO3 36
The blue-lipped regular
coreA 71-year-old with severe COPD attends clinic feeling his usual self.
pH 7.36 · PaCO2 62 · HCO3 34
Found drowsy with pinpoint pupils
introA 33-year-old is found unresponsive on the ward two hours after a dose escalation of hydromorphone. Respiratory rate 6.
pH 7.21 · PaCO2 68 · HCO3 27
Septic and breathing hard
advancedA 66-year-old with pyelonephritis, BP 84/50, lactate 4.8.
pH 7.32 · PaCO2 26 · HCO3 13
Ringing ears and a strange gas
advancedA 26-year-old presents six hours after a large aspirin ingestion, hyperventilating with tinnitus.
pH 7.42 · PaCO2 21 · HCO3 13
A week of diarrhea
coreA 52-year-old returns from travel with a week of profuse watery diarrhea.
pH 7.28 · PaCO2 30 · HCO3 14
Tingling fingers in the waiting room
introA 22-year-old with acute anxiety, perioral tingling, and carpal spasm. Breathing 32 times a minute.
pH 7.54 · PaCO2 24 · HCO3 21
The asthmatic whose gas 'normalized'
advancedA 24-year-old in a severe asthma attack, two hours in. The repeat gas is 'better than the last one', says the night resident.
pH 7.38 · PaCO2 41 · HCO3 24
The retainer who got worse
coreA 70-year-old with severe COPD, drowsy on arrival with a chest infection. His clinic letters mention 'chronic CO2 retention'.
pH 7.26 · PaCO2 78 · HCO3 34
The cold, quiet abdomen
coreA 76-year-old with atrial fibrillation, sudden severe abdominal pain out of proportion to a soft exam, and a blood pressure drifting down.
pH 7.24 · PaCO2 24 · HCO3 10
The water tablet's chemistry
coreAn 81-year-old on escalating furosemide doses for leg swelling, admitted with weakness and cramps. She is thirsty and her mouth is dry.
pH 7.50 · PaCO2 49 · HCO3 37
Breathless and thirty-two weeks
advancedA 29-year-old at 32 weeks gestation, referred for breathlessness on stairs. The gas is drawn to 'rule things out'.
pH 7.45 · PaCO2 31 · HCO3 21
A normal pH, and nothing else normal
advancedA 44-year-old with alcohol use disorder, three days of vomiting, now febrile and unwell with epigastric pain. The resident notes with relief that the pH is normal.
pH 7.40 · PaCO2 30 · HCO3 18