Learning Objectives
By the end of this section, you will be able to:
- Discuss the pathophysiological changes to the patient’s renal system when in the intensive care unit
- Describe the medical assessments and therapies that apply to the critical care patient’s renal system
- Apply nursing concepts and plan associated nursing care for the critical care patient’s renal system
The kidneys play many major roles in the body, most notably the filtration of toxins and control of blood pressure and hydration status. Without optimal kidney functioning, perfusion to body organs will be decreased and there will be a resulting buildup of toxins and electrolytes that can result in life-threatening systemic complications. For that reason, it is imperative to prioritize care of the renal system for all critically ill patients.
Pathophysiological Insult to the Critical Care Patient’s Renal System
Although some patients may be admitted to the ICU for a primary kidney issue, most often, patients are admitted for an issue within another body system but then experience acute kidney injury due to the nature of their illness or from medical interventions. Certain medications administered in critical care settings are nephrotoxic, or capable of causing renal damage, and some procedures also pose the risk of causing acute kidney injury. Therefore, it is important to closely monitor renal function and intervene as soon as the patient is at risk of injury.
Exemplar: Acute Kidney Injury
We define acute kidney injury (AKI) as a sudden reduction in kidney function. It is caused by an insult to the nephron unit that manifests with alteration in laboratory values and decreased urine output. There are many etiologies for the development of AKI (Goyal et al., 2022), several of which are listed in Table 35.11.
| Etiology | Causes |
|---|---|
| Hypovolemia |
|
| Severe hypotension from decreased CO |
|
| Severe hypotension from widespread vasodilation |
|
| Renal vasoconstriction |
|
AKI can be classified into one of three categories on the basis of its etiology. These three classifications are defined and described in Table 35.12.
| Classification Category | Definition | Clinical Examples |
|---|---|---|
| Prerenal causes | Conditions that result in decreased perfusion to the kidneys |
|
| Intrarenal causes | Conditions that result in direct damage to kidney tissue itself |
|
| Postrenal causes | Conditions that block the outflow of urine |
|
Medical Assessments and Therapies
Diagnosing AKI involves close evaluation of serum laboratory values, especially creatinine and BUN. Serum creatinine is a breakdown product of skeletal muscle. It is made at a relatively stable rate and so is a good laboratory value to use for the diagnosis of AKI when alterations are noted. An increase in serum creatinine level may indicate an early sign of AKI: as renal function decreases, the kidneys are unable to filter out the excess creatinine at the same rate as when they are optimally functioning. Blood urea nitrogen is a breakdown product of protein metabolism, so elevations in this value may indicate the kidneys are unable to effectively excrete the excess protein byproducts. However, there are other conditions beyond AKI that can increase BUN level, such as dehydration or GI bleeding; therefore, although important, it is not the most reliable indicator of AKI on its own.
Trends in glomerular filtration rate (GFR) should also be monitored closely to determine the level of functioning of the kidneys. Glomerular filtration rate is a measurement of how quickly the kidneys can filter out toxins and other waste products. A decrease in GFR indicates the kidneys are unable to filter as quickly as they could when functioning at an optimal level. The trend of the GFR will also influence medication therapy selection and dosing to avoid toxic level accumulation.
Beyond laboratory values, several imaging procedures may be used to diagnose kidney injury. These include renal ultrasound, CT scans, and renal angiography. The main concern with these procedures is that they often necessitate the use of nephrotoxic contrast media for better visualization. It is important to weigh the risks versus benefits of performing these procedures with contrast, depending on the patient’s current renal status (Davenport et al., 2020).
Pharmacological Supports
Most of the pharmacological interventions for AKI are focused on maintaining optimal fluid and electrolyte balance. Patients experiencing prerenal causes of AKI may require IV fluid replacement to restore renal perfusion. For patients experiencing intra- or postrenal causes of AKI, use of diuretics to remove excess fluid and toxins may be indicated. It is important to note that diuretics have some nephrotoxic qualities; they should be used cautiously, with the lowest dose, to avert further damage. The decision to give IV fluids or diuretics is based on the specific cause of the AKI and the patient’s current renal status.
When the kidneys are not functioning at their highest level, they are often unable to excrete electrolytes effectively. This can result in a buildup of some electrolytes in the body, with hyperkalemia being a significant resulting electrolyte imbalance. Elevated levels of potassium can result in life-threatening cardiac dysrhythmias. Patients with hyperkalemia will require continuous telemetry to monitor for dysrhythmias. Often, these patients will require the administration of sodium polystyrene (e.g., Kayexalate) to help the body excrete potassium and maintain a normal electrolyte balance. Administration of dextrose with insulin assists with mobilization of excess potassium into the intracellular fluids. Another therapy, calcium gluconate, has been used emergently by stabilizing hyperexcitability of myocardial cells, which is caused by excess potassium. In some cases, emergency dialysis may be required to remove the potassium more quickly.
Another important consideration when caring for patients with AKI is limiting the use of medications that may further harm the kidneys. Many medications, most notably antibiotics, are nephrotoxic. The nurse should work closely with the pharmacist to ensure that patients with or at risk for AKI are receiving the lowest doses possible of these medications to prevent worsening of the kidney injury.
Nursing Care
Because of the kidney’s role in the maintenance of fluid balance, a priority aspect of nursing care for patients with AKI is measuring and recording strict intake and output data. A decrease in urine output can be one of the first signs of AKI; hence, it is vital that the nurse be attentive to any changes in urination, even subtle ones. Additionally, weighing the patient at the same time daily and comparing measurements is important. Every pound of weight gain is associated with a liter of fluid accumulation; therefore, these measurements can show fluid retention that may indicate AKI. Other deviations the nurse may observe are hypertensive blood pressures, due to fluid volume excess, and irregular heart rates and alteration of mentation, due to electrolyte disturbance. Lastly, appropriate use of medications is essential. There are many nephrotoxic medications whose risks and benefits must be determined before administration. Some of these medications are:
- aminoglycoside antibiotics (e.g., gentamicin, tobramycin)
- antivirals (e.g., acyclovir, nirmatrelvir co-packaged with ritonavir [brand name, Paxlovid])
- diuretics (e.g., furosemide)
- NSAIDs (e.g., ibuprofen, naproxen)
- vancomycin
Cultural Context
AKI and Ethnicity
Nurses must be aware that certain ethnic groups and patients with chronic comorbidities are at risk for AKI. Black, Hispanic, American Indian, and Alaskan Native people carry the highest risk for kidney failure (National Institutes of Health, 2023). Comorbid conditions, such as uncontrolled diabetes, hypertension, and hyperlipidemia, and risk factors, such as smoking, obesity, and use of certain recreational drugs, also place patients at risk. Nurses must reconcile all active medications against the EHR to spot patterns for potential new nephrotoxic agents. If identified early, and with the proper assessment and implementation of treatment, AKI can be reversed.