Overview
Definition:
Continuous Renal Replacement Therapy (CRRT) is a slow, continuous extracorporeal blood purification process used to treat critically ill patients, including children, with acute kidney injury (AKI) and fluid overload
In pediatrics, CRRT aims to mimic the kidney's physiological functions more closely than intermittent hemodialysis, providing gradual fluid removal and solute clearance, which is better tolerated by hemodynamically unstable children
Fluid balance targets in pediatric CRRT are critical to prevent both under-resuscitation and over-resuscitation, optimizing hemodynamic stability and organ perfusion.
Epidemiology:
Pediatric AKI affects approximately 10-30% of critically ill children in PICUs
CRRT is employed in a significant proportion of these children, particularly those with severe AKI, fluid overload, and hemodynamic instability
The incidence of CRRT use varies widely by institution and patient population, but it is a cornerstone therapy for severe pediatric renal failure in intensive care settings.
Clinical Significance:
Accurate fluid management is paramount in pediatric CRRT
Inadequate fluid removal can lead to pulmonary edema, worsening acidosis, and increased intracranial pressure
Conversely, excessive fluid removal can precipitate hypovolemia, hypotension, and impaired organ perfusion, potentially leading to further organ dysfunction and increased mortality
Establishing and adhering to precise fluid balance targets is therefore essential for successful CRRT management in children and a key learning objective for DNB and NEET SS examinations.
Indications For Crrt In Pediatrics
Fluid Overload:
Significant fluid overload unresponsive to diuretics
pulmonary edema
cerebral edema.
Electrolyte Imbalances:
Severe hyperkalemia refractory to medical management
symptomatic hyponatremia.
Acidosis:
Severe metabolic acidosis (pH < 7.15) with inadequate clearance, especially if associated with hemodynamic instability.
Uremic Syndromes:
Uremic pericarditis
uremic encephalopathy
intractable nausea and vomiting due to uremia.
Other Indications:
Sepsis-induced AKI
drug intoxication requiring extracorporeal removal
multiple organ dysfunction syndrome (MODS).
Fluid Balance Targets And Monitoring
Initial Assessment:
Baseline assessment of fluid status is crucial
This includes: clinical signs of fluid overload (edema, rales, ascites, weight gain)
hemodynamic parameters (mean arterial pressure, heart rate, urine output)
central venous pressure (if available)
and imaging (e.g., chest X-ray for pulmonary edema).
Hourly Fluid Balance:
The primary target in CRRT is to achieve a negative fluid balance or maintain euvolemia, depending on the clinical scenario
Typically, a negative fluid balance of 1-3 mL/kg/hr is targeted initially, adjusted based on patient response
This involves meticulous tracking of all fluid inputs (IV fluids, medications, feeds) and outputs (ultrafiltration, urine output, drains, gastrointestinal losses).
Weight Based Targets:
Fluid targets are often expressed as a percentage of body weight or as a net fluid removal rate
For example, a target of removing 5-10% of body weight in fluid over 24 hours might be set, or a continuous removal rate of 1-3 mL/kg/hr
These targets require continuous adjustment.
Hemodynamic Parameters:
Monitoring for signs of hypovolemia (hypotension, tachycardia, decreased urine output, decreased capillary refill) or fluid overload (hypertension, increased work of breathing, edema) is essential
Central venous pressure or other invasive monitoring may be necessary in unstable patients.
Laboratory Monitoring:
Regular monitoring of electrolytes (Na+, K+, Cl-, HCO3-), BUN, creatinine, acid-base status (pH, pCO2, HCO3-), and hematocrit is vital to guide CRRT efficacy and fluid balance adjustments.
Ultrafiltration Strategies
Convective Vs Diffusive:
Ultrafiltration (UF) is the process of removing fluid across a semipermeable membrane
In CRRT, UF can be achieved via continuous venovenous hemodialysis (CVVHD), continuous venovenous hemofiltration (CVVH), or a combination (CVVHDF)
The choice impacts solute removal and fluid balance.
Setting Uf Rate:
The UF rate is the primary knob to control fluid balance
It is initiated based on the targeted fluid removal rate (e.g., 1-3 mL/kg/hr) and adjusted based on hourly fluid balance and hemodynamic response
Higher UF rates may be needed for severe overload, but must be done cautiously to avoid hypovolemia.
Fluid Management In Sepsis:
In septic patients with AKI, initial resuscitation often involves fluid boluses
Once stable or if fluid overload develops, CRRT with a negative balance becomes crucial
Targets may be more aggressive in this setting if significant overload is present, but careful hemodynamic monitoring is paramount.
Management Of Edema:
Pulmonary and peripheral edema are key indicators of fluid overload
CRRT UF aims to gradually reduce this
Achieving negative fluid balance will directly address edema and improve respiratory status
Close correlation between weight changes, UF, and clinical signs is vital.
Challenges And Considerations In Pediatric Crrt
Pediatric Access Challenges:
Achieving adequate vascular access in small infants and children can be challenging, often requiring specialized catheters and experienced operators
Access size impacts blood flow rates, affecting CRRT efficacy.
Pediatric Anticoagulation:
Anticoagulation strategies in pediatric CRRT are complex and vary
Regional anticoagulation (e.g., citrate) is often preferred to minimize systemic bleeding risk
Adequacy of anticoagulation affects circuit life and UF efficiency.
Pediatric Dosing And Fluids:
Accurate calculation of fluid inputs and outputs is complicated by small volumes and frequent medication administrations in neonates and infants
Diluted solutions and specialized pediatric CRRT machines may be used.
Thermoregulation:
Heat loss can occur during CRRT, especially in neonates and infants
Warming of replacement fluids and blood is essential to maintain normothermia and prevent complications.
Monitoring Complexity:
Continuous monitoring of hemodynamic parameters, fluid balance, and laboratory values in critically ill pediatric patients requires a multidisciplinary team approach
DNB and NEET SS exam questions often test this comprehensive monitoring aspect.
Key Points
Exam Focus:
DNB and NEET SS questions frequently assess the ability to calculate hourly fluid balance, set appropriate UF rates, and interpret the impact of CRRT on hemodynamic stability and organ perfusion in critically ill children
Understanding the interplay between fluid removal, solute clearance, and vital signs is crucial.
Clinical Pearls:
Always start CRRT with a conservative UF rate (1-2 mL/kg/hr) and titrate upwards based on response and fluid status
Monitor for hypovolemia before increasing UF
Document every mL of fluid input and output meticulously
Weight changes are the most reliable indicator of fluid status over time.
Common Mistakes:
Failing to account for all fluid inputs (including IV medications, feeds, and insensible losses)
Overly aggressive UF rates leading to hypovolemia and hypotension
Underestimating the fluid requirements for critically ill children who may still need maintenance IV fluids
Inadequate monitoring leading to delayed recognition of complications.