Pyelonephritis is upper UTI with renal parenchymal infection — fever, chills, flank/CVA pain, and systemic illness. Nurses monitor for sepsis, ensure culture before antibiotics when possible, and differentiate from simple cystitis. Connect Pyelonephritis to bedside cues you will reassess first: vitals trends, work of breathing, perfusion, mentation, and pain or ischemic equivalents when relevant. NCLEX items often reward recognizing when subtle instability outweighs reassurance, then selecting nursing actions that protect airway, circulation, and neurologic status before routine tasks.