This chapter begins by discussing the basic principles of fluid and electrolyte homeostasis, fluid therapy, healthcare-associated infection, microorganisms and antimicrobials, preoperative assessment, and acute pain, before focusing on the key areas of knowledge, namely deep venous thrombosis, pulmonary embolism, respiratory tract infection, asthma, chronic obstructive pulmonary disease, acute respiratory failure, ischaemic heart disease, heart failure, cardiac arrhythmias, hypertension, diabetes mellitus, acute renal failure, stroke, acute confusional state, and haematological conditions. The chapter concludes with relevant case-based discussions.