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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.
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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.
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 Causes of Arterial Hypoxemia in the PACU
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.
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 TreatmentIdentify the Underlying Cause
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.