1. Post Operative Arterial Hypoxemia
Oren Erlichman, M.D
UCLA Department of Anesthesiology

2. PACU Patient
73 yo female with hx of depression and chronic cholesthiasis underwent GA for biliary duct leak repair.
Presented to PACU in respiratory distress.
Noted to be weak, altered, unable to talk, with poor inspiratory effort.
VS: 142/83, 114, 15 and shallow, 91-93% on FM.

3. PACU Patient – Continued
Review of Anesthesia chart:
GA, sevo, nitrous, ETT, 3hrs.
150mcg of fentanyl at beginning of case, 0.4 of dilaudid at the end of case after spontaneous breathing.
50mg of rocuronium at beginning of case, then vecuronium titrated with nerve stimulator, then fully reversed to sustained tetanus.
Extubated once followed command to eye opening.

4. PACU Patient Studies ABG – 7.20/83/81/25/93.2
Other labs normal except for increase in Crt from 0.9 to 1.5.
CXR, EKG – normal.
Rechecked twitches with nerve stimulator – 2mg of Neo/0.4 of Glyco given in PACU.

5. Causes of Arterial Hypoxemia in the PACU
Hypoventilation
Residual narcotics
Residual benzos
Residual inhaled anesthetics
Residual muscle relaxants
Pain, splinting
Restrictive Conditions, abdominal wall binding, abdominal distension
Airway obstruction
Bronchospasm
V/Q mismatch and Shunt
Atelectasis
Inhibition of Hypoxic Pulmonary Vasoconstriction.
Pulmonary edema
Aspiration, Pneumonitis
Increased Venous Admixture

6. How Does Hypoventilation Cause Hypoxemia?
The alveolar gas equation
PaO2= FIO2 (Patm-PH2O) – PCO2/R
If PaCO2=40
PaO2= 0.21(760-47) – 40/0.8 = 100
If PaCO2=80
PaO2= 0.21(760-47) – 80/0.8= 50

7. How Does Hypoventilation cause Hypoxemia?
Normally there is a linear increase in minute ventilation for increase in CO2.
This linear ventilatory response is blunted in the post operative period by the effects of drugs.

8. How does V/Q mismatch and shunt cause arterial hypoxemia?
Alveoli that are either not getting perfused or not getting ventilated affect the transport of oxygen.
The diffusion capacity of oxygen is limited compared to that of carbon dioxide.

9. Treatment Identify the Underlying Cause
Hypoventilation
Reversal of drugs
Decrease dead space ventilation
Supplemental O2
Mechanical ventilation
V/Q Mismatch and Shunt
Sitting position
Incentive Spirometry
Encourage deep breathing.
Positive airway pressure
Supplemental O2, although not effective in true shunt.
Mechanical Ventilation

10. PACU Patient - Course
Patient was assisted with AMBU bag intermittently for 2hrs, with some improvement in mental status and saturation.
Eventually patient was intubated, transferred to ICU and extubated the next day.