Acute Kidney Injury and Chronic Kidney Disease

Acute kidney injury (AKI) is an abrupt fall in kidney function over hours to days, while chronic kidney disease (CKD) is a sustained reduction in kidney function or structural damage lasting three months or more. Together they describe the loss of the kidney's filtering and regulatory roles, and they are central to renal nursing because they generate the fluid, electrolyte, and uremic problems that nurses monitor and help manage.

Definition

Acute kidney injury is a rapid decline in glomerular filtration, marked by rising serum creatinine and/or falling urine output; chronic kidney disease is a persistent abnormality of kidney structure or function (for example, reduced glomerular filtration rate or albuminuria) present for at least three months, classified by GFR and albuminuria category (KDIGO, 2013).

Scope

This topic covers how AKI and CKD are defined and staged, why they are now understood as interconnected rather than separate conditions, the disturbances they produce, and the nursing-relevant aspects of assessment and supportive care. It is reference material on the conditions and their monitoring, not a treatment protocol.

Key concepts

• Glomerular filtration rate (GFR)
• Serum creatinine and urine output criteria
• AKI staging
• CKD GFR and albuminuria categories
• AKI-to-CKD transition
• Uremia and accumulation of nitrogenous waste
• Volume overload and electrolyte derangement
• Disease progression and risk-factor modification

Mechanisms

In AKI, an abrupt drop in glomerular filtration — from reduced perfusion, intrinsic kidney injury, or obstruction — causes retention of waste, fluid, potassium, and acid (Bellomo et al., 2012). In CKD, progressive and largely irreversible loss of functioning nephrons produces a sustained reduction in filtration, with anaemia, mineral-bone disturbance, and cardiovascular risk accumulating as function declines (Webster et al., 2017). AKI and CKD share risk factors and reinforce each other: an episode of AKI raises the risk of subsequent CKD, and CKD predisposes to AKI, so the two are best viewed as parts of a continuum rather than discrete states (Chawla et al., 2014).

Clinical relevance

Recognising AKI early and tracking CKD over time underpin much renal and general adult nursing, because both drive the fluid, electrolyte, and symptom problems that prompt nursing assessment and patient education. This entry describes how the conditions are defined, staged, and monitored as reference knowledge; it does not specify diagnostic thresholds, drug choices, or dialysis decisions for any individual, which rest with the treating service.

Epidemiology

Acute kidney injury is common in hospitalised and especially critically ill patients, with a pooled world incidence in the order of one in five hospital admissions in adults (Susantitaphong et al., 2013). Chronic kidney disease affects a large share of adults globally, rising with age and with diabetes and hypertension, and is a major contributor to cardiovascular morbidity and to progression to kidney failure (Webster et al., 2017).

History

For much of the twentieth century acute and chronic kidney failure were described in clinical but non-standardised terms. Consensus definitions and staging systems — culminating in the KDIGO framework that defines and classifies CKD by GFR and albuminuria and AKI by changes in creatinine and urine output (KDIGO, 2013) — gave clinicians and nurses a shared language, and the recognition of the AKI-CKD continuum (Chawla et al., 2014) reframed the two as linked syndromes.

Debates

Are AKI and CKD distinct conditions or a continuum?

Evidence that an episode of AKI raises the long-term risk of CKD, and that CKD predisposes to AKI, has shifted understanding toward viewing them as interconnected syndromes sharing risk factors and mechanisms rather than wholly separate diseases.

Seminal works

• bellomo-2012
• webster-2017
• kdigo-ckd-2013
• chawla-2014

Frequently asked questions

What is the difference between acute kidney injury and chronic kidney disease?

AKI is an abrupt loss of kidney function over hours to days and is often partly reversible; CKD is a sustained reduction in kidney function or structural damage lasting at least three months and is generally progressive.

Why are AKI and CKD discussed together?

Because they are interconnected: an episode of AKI increases the risk of later developing CKD, and existing CKD increases vulnerability to AKI, so they are understood as parts of a continuum.