A 17-year-old patient presents to the ED complaining of a tight feeling in their chest, shortness of breath as well as some tingling in their fingers and around their mouth. They have no significant past medical history and are not on any regular medication. An ABG is performed on the patient while they’re breathing room air and the results are shown below:

PaO2: 105 mmHg

pH: 7.49

PaCO2: 24 mmHg

HCO3–: 22 mEq/L

A 48-year-old male has been admitted with a 24 hour history of abdominal distention and profuse vomiting. A CT scan reveals a large mass causing bowel obstruction. As part of the patient’s assessment, the surgical resident requests that you check his blood gas (on air), with the results shown below:

PaO2: 95.2 mmHg

pH: 7.50

PaCO2: 41 mmHg

HCO3-: 29 mEq/L

You’re asked to review a 59-year-old female who has been admitted the acute medical ward of your hospital. The nurse tells you that she appears short of breath despite currently receiving 3 liters of oxygen via nasal cannula.

You take an arterial blood gas which reveals the following results:

PaO2: 68.2 mmHg

pH: 7.30

PaCO2: 63 mmHg

HCO3-: 29 mEq/L

An 89-year-old patient presents with fever, rigors, hypotension and reduced urine output. They appear confused and are unable to provide any meaningful history. The care home that the patient came from has provided some basic documentation. You look through the information available and note that the nurse changed this patient’s catheter 24 hours ago. The medical doctor initiates antibiotics, aggressive fluid resuscitation and asks you to perform an arterial blood gas, with the results shown below. The patient was not on oxygen at the time of the ABG.

PaO2: 93 mmHg

pH: 7.29

PaCO2: 41.2 mmHg

HCO3-: 15 mEq/L

A 22-year-old female is brought into the ED by ambulance with a 5-day history of vomiting and lethargy. When you begin to talk with the patient you note that she appears disorientated and looks clinically dehydrated. At present, you are unable to gain any further details, but the patient looks very unwell from the end of the bed. You gain IV access, send off a routine panel of bloods and commence some fluids. You ask the nurse to check the patient’s observations and she notes an increased respiratory rate, low blood pressure and tachycardia. You perform an ABG on the advice of your registrar. The results of the ABG are shown below (the patient was not on oxygen when this was taken).

PaO2: 97.5 mmHg

pH: 7.3

PaCO2: 30.7 mmHg

HCO3-: 13 mEq/L

A 56-year-old man was found unconscious at home with a respiratory rate of 6 breaths per minute and pinpoint pupils. An ambulance was called and the paramedics administered some naloxone. On arrival to ED his ABG showed the following (not on oxygen at the time of the ABG):

PaO2: 59 mmHg

pH: 7.31

PaCO2: 53 mmHg

HCO3-: 22 mEq/L

A 77-year-old lady was admitted to hospital 10 days ago with a fractured neck of femur. The orthopedic team repaired the fracture and she has been an inpatient on the orthopedic ward recovering ever since. The patient’s nurse is becoming increasingly concerned as the patient’s oxygen requirements are increasing (she is now on 3L) and the patient is now tachypneic (respiratory rate 35). In addition, the patient has recently started complaining of calf pain.

You review the patient and perform an ABG which reveals the following:

PaO2: 45 mmHg

pH: 7.51

PaCO2: 23.2 mmHg

HCO3-: 22 mEq/L

A 24-year-old medical student has just returned from his elective in Ghana. In the last few days, he has developed severe diarrhea and has now presented to ED. On assessment, he is very dehydrated and tachypneic.

An ABG is performed and reveals the following:

PaO2: 109.5 mmHg

pH: 7.32

PaCO2: 30 mmHg

HCO3-: 13 mEq/L

A 64-year-old man is admitted to ED with central crushing chest pain. As the nurses are getting him attached to the ECG he has a cardiac arrest. Thankfully CPR was commenced immediately and after 6 minutes he regained spontaneous circulation and began breathing again.

An ABG (on 15L O2) performed following this sequence of events reveals the following:

PaO2: 71.3 mmHg

pH: 7.14

PaCO2: 60.8 mmHg

HCO3-: 15.2 mEq/L