1. Acute Respiratory Failure: 5 types of Hypoxemia
John Heisler, PA-C

2. Forms of Respiratory Failure
Acute Hypoxemic Respiratory Failure
Acute Hypercapnic Respiratory Failure
Difference between hypoxemia “blood” and hypoxia “cell”
PaO2: ABG
SpO2: O2 monitor

3. Types of Oxygen

4. 5 types of hypoxemia

5. THE 5 CAUSES OF HYPOXIA #1 – High Altitude #2 – Hypoventilation
#3 – Diffusion Disorder
#4 – Shunt
#5 – VQ Mismatch
(Normal A-a gradient)
(High A-a gradient)

6. Case 1
You are a medical volunteer at Everest Base camp clinic (~16,900 ft). A 27 year old man with no significant PMH, new climber presents with complaints of throbbing headache and shortness of breath x 1 day. On exam patient is tachypneic with bibasilar crackles. Tachycardic, SpO2 85%. Remainder of exam normal.

8. s/p O2

9. Diagnosis?
Altitude Sickness!

10. A-a gradient aka the difference between alveolar and arterial oxygen
𝑨𝒂 𝒈𝒓𝒂𝒅𝒊𝒆𝒏𝒕=𝑷𝑨𝑶𝟐 −𝑷𝒂𝑶𝟐
𝐴𝑎 𝑔𝑟𝑎𝑑𝑖𝑒𝑛𝑡=[ 𝑚𝑚𝐻𝑔 −47𝑚𝑚𝐻𝑔 − 𝑃𝑎𝐶𝑂 −𝑃𝑎𝑂2
150

12. All about the alveolus!
High A-a gradient: Lots of O2 in Alveolus, not a lot in artery
Low/Normal A-a gradient: Little O2 in Alveolus thus little in artery

13. Why is this patient hypoxemic?
Case Study 2
Young woman overdosed on antidepressants and alcohol
Respiratory rate 8 breaths/min
Arterial blood gas: pH 7.15, Paco mm Hg (9.5 kPa), Pao2 56 mm Hg (7.5 kPa) in room air
Copyright 2016 Society of Critical Care Medicine
Why is this patient hypoxemic?

14. Which of the following is the most likely cause of hypoxemia in this patient?
Hypoventilation
Acidemia
Alveolar hyperventilation
Auto-positive end-expiratory pressure
Copyright 2016 Society of Critical Care Medicine 14 14

16. Select all of the interventions that would be helpful in treating this patient’s hypoxemia.
Administer supplemental oxygen.
Prepare to initiate mechanical ventilation.
Treat the patient’s overdose.
Encourage the patient to breathe deeply.
Copyright 2016 Society of Critical Care Medicine 16 16

17. THE 5 CAUSES OF HYPOXIA #1 – Low Patm #2 – Hypoventilation
#3 – Diffusion Disorder
#4 – Shunt
#5 – VQ Mismatch
(Normal A-a gradient)
(High A-a gradient)

18. #3: Diffusion Responds to Oxygen O2 CO2 Impaired diffusion
interstitium
1 cell layer thick
Responds to Oxygen

19. The pearl of clinical truth: Diffusion Dz
VERY wide differential for ILD:
Environmental
Drug-induced
Autoimmune dz
Infection
Idiopathic
Malignancy
Your job? GOOD H&P

20. #4: Shunt SYSTEM 82.5% What’s the A-a gradient? What happens with O2?
70%
SYSTEM
82.5%
95%
What’s the A-a gradient?
What happens with O2?

21. #4 Shunt Two types of shunt: Does not correct with O2!
Anatomic “cardiac”
Congenital Heart Defects
ASD
VSD
PDA
Physiologic “intrapulmonary”
ARDS
Does not correct with O2!

22. #5 CASE STUDY
A 31 year old smoker presents to the ED with acute onset shortness of breath. Symptoms began ~2 hours prior to arrival. Syncopal event en route. She also endorses chest pain. T98.0 HR 125 BP 90/55 SpO2 85% on 6L NC.

23. A R L B

24. ABG
7.56/20/56/24
pH/CO2/O2/HCO3

26. Diagnosis?
Massive PE!

27. #5 VQ Mismatch Normal Dead Space Most common cause of hypoxemia
Pulmonary Embolism
Pneumonia
Pulmonary Edema
COPD
Normal
Dead Space

30. Summary Cause of Hypoxia Remember! A-a gradient. Altitude / low Patm
Low alveolar oxygen
↓A-a. Fully corrects w/ O2
Hypoventilation
Hypercapnia comes first
Diffusion disorder
Diffusion distance limited
↑A-a. Partially corrects w/ O2
VQ mismatch
MCC of hypoxia
Shunt
Anatomic or physiologic
↑A-a. O2 WON’T CORRECT

31. Summary Cause of Hypoxia Disease states Altitude / low Patm
Altitude sickness
Hypoventilation
OSA/OHS
Opioid/drug overdose
Encephalopathy (all comers)
Neuromuscular weakness
Diffusion disorder
Interstitial lung disease (many types)
VQ mismatch
COPD/asthma
PNA PE
Pulmonary Fibrosis
Pulmonary Edema
Shunt
Anatomic: ASD, VSD, PDA
Physiologic: SCAPE, ARDS
OSA – obstructive sleep apnea
OHS – obesity hypoventilation syndrome
ASD – atrial septal defect
VSD – ventricular septal defect
PDA – patent ductus arteriosus
SCAPE – sympathetic acute crashing pulmonary edema
ARDS – acute respiratory distress syndrome