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