Viva 5

You are caring for a previously well 60-year-old male after a motorcycle accident yesterday. He has isolated chest injuries (bilateral rib fractures and pulmonary contusions).

He has been stable in the ICU overnight receiving High Flow Nasal O2 (HFNO) with multimodal analgesia including Patient Controlled Analgesia. The anaesthetic registrar has just left after inserting a thoracic epidural, when the bedside nurse calls for assistance.
The patient has become disoriented and agitated with the following vital signs: Heart rate = 55 beats/minute, sinus rhythm
Blood pressure = 78/38 mmHg
SaO2 = 88% (on 40% FiO2 HFNO) with a poor trace

Explain the likely causes for the patient’s deterioration.
 

(This viva dealt with hyperthermia.)

Disclaimer: the viva stem above may be an original CICM stem, acquired from their publicly available past papers. Or, perhaps it is a slightly altered version of the original CICM stem. Or, it is a completely original viva stem, concocted by the monstrously amoral author of Deranged Physiology for nothing more than his own personal amusement. In either case, because the college do not make the main viva text or marking criteria available, almost everything here has been confabulated. It might sound like a plausible viva and it could be used for the purpose of practice, but all should be aware that it does not represent the "true" canonical CICM viva station.