Post Operative Fever is extremely common, and with the increase in same day surgery this is a common complaint presenting to the ED. The mnemonic "5Ws" are often taught to remember the causes. They are:
Wind - Pneumonia, aspiration, pulmonary embolism, and atelectasis
Water - urinary tract infection
Walking - Deep Venous Thrombosis or pulmonary embolism
Wound - surgical wound infection
Wonder drugs - Drug fever, or infection due to indwelling lines, or a reaction to blood products
Though many surgical textbooks report that atelectasis is the most common cause of early post-operative fever, some even claiming that it is responsible for over 90% of febrile episodes in the first 48 hours after surgery; a recent review in CHEST (reference below) showed that there is no evidence to support this. We often see atelectasis in medical patients too, and few if any of them have fever. The CHEST review found that there was no clear evidence that atelectasis causes fever at all.
Pearl: Temperature >38.9C should raise concern for a true infection, where lower temperatures can be due to pulmonary embolism, DVT, drug fever, etc….
References
Mavros MN, Velmahos GC, Falagas ME.Atelectasis as a cause of postoperative fever: where is the clinical evidence? Chest. 2011 Aug;140(2):418-24. doi: 10.1378/chest.11-0127. Epub 2011 Apr 28. Review. PMID: 21527508
