REN and Nephropathy: Fluid and electrolyte imbalance has previously been reported as a putative driver of adverse effects in critically ill patients submitted to ICU, and three underpinning mechanisms have been suggested: (1) reduced perfusion to the kidney owing to hypotension or hypovolemia, (2) tubular damage caused by ischemic or nephrotoxic kidney damage, and (3) inappropriate activation of kidney-regulating hormones such as those in the renin–angiotensin–aldosterone system32.