Overview
Definition:
Continuous Renal Replacement Therapy (CRRT) is a slow, continuous form of extracorporeal blood purification, typically used in hemodynamically unstable patients
Surgical Acute Kidney Injury (AKI) is a common and severe complication following major surgical procedures, often driven by factors like hypoperfusion, sepsis, nephrotoxic agents, and direct surgical insult.
Epidemiology:
Surgical patients, particularly those undergoing major abdominal, cardiac, or trauma surgery, have a significantly higher incidence of AKI, ranging from 20-60%
CRRT is indicated in a subset of these patients who develop severe AKI with fluid overload or metabolic derangements unresponsive to conventional management.
Clinical Significance:
Prompt and appropriate initiation of CRRT in surgical AKI is critical for hemodynamic stabilization, correction of fluid overload and electrolyte imbalances, and removal of inflammatory mediators
It can improve outcomes in critically ill surgical patients by providing a more physiological solute and fluid removal compared to intermittent therapies, thus sparing the cardiovascular system.
Indications In Surgical Aki
Fluid Overload:
Persistent fluid overload despite diuretic therapy and fluid restriction, leading to pulmonary edema or worsening hemodynamics
This is common in the post-operative period due to aggressive fluid resuscitation or impaired renal function.
Refractory Hypertension:
Severe uncontrolled hypertension refractory to pharmacological management, especially in the context of impaired fluid excretion.
Metabolic Derangements:
Severe metabolic acidosis (pH < 7.2) unresponsive to medical management, or severe hyperkalemia (serum K+ > 6.5 mEq/L) with ECG changes, or severe hyponatremia/hypernatremia.
Uremic Symptoms:
Development of uremic symptoms such as encephalopathy, pericarditis, or coagulopathy, indicating significant accumulation of uremic toxins.
Sepsis And Inflammation:
In septic surgical patients with AKI, CRRT may assist in clearing inflammatory mediators and endotoxins, although its role in sepsis-induced AKI is still debated and primarily supportive.
Abdominal Hypertension:
Patients with intra-abdominal hypertension or abdominal compartment syndrome where fluid management is precarious and impaired renal function exacerbates the situation
CRRT can help manage fluid balance without causing significant hemodynamic shifts.
Preoperative Considerations For Crrt
Hemodynamic Assessment:
Thorough assessment of the patient's hemodynamic status is crucial
Surgical patients requiring CRRT are often unstable, necessitating careful titration of vasopressors and inotropes during initiation.
Fluid Status Evaluation:
Accurate assessment of fluid overload is paramount
This involves clinical examination, daily weights, intake-output balance, and sometimes advanced monitoring like lung ultrasound or cardiac output monitoring.
Coagulopathy Assessment:
Many surgical patients have pre-existing coagulopathy or are on anticoagulation
Assessment and correction of coagulopathy are vital before initiating CRRT to minimize bleeding risks, especially at vascular access sites.
Vascular Access Planning:
Appropriate vascular access is essential for CRRT
Central venous catheters (e.g., internal jugular, subclavian) are typically used, with preferred diameters (e.g., 13-15 French) to ensure adequate blood flow
Site selection should consider prior surgeries or anatomical limitations.
Involvement Of Multidisciplinary Team:
Initiation and management of CRRT in surgical AKI requires close collaboration between surgeons, intensivists, nephrologists, and nurses
Communication regarding fluid goals, hemodynamic targets, and potential surgical interventions is key.
Initiation And Surgical Implications
Access Site Management:
The choice of vascular access site must consider potential future surgical interventions
For example, avoiding the internal jugular vein on the side of a planned neck dissection or an axillary artery cannulation if future thoracic surgery is anticipated.
Hemodynamic Tolerance:
CRRT is generally better tolerated hemodynamically than intermittent therapies
However, initiation should be slow and gradual, with close monitoring of blood pressure, heart rate, and central venous pressure
Anticoagulation for the circuit requires careful consideration in patients with bleeding risks.
Fluid Management Goals:
CRRT allows for precise and continuous fluid removal
Surgeons must communicate their fluid goals and targets to the critical care team to ensure alignment with surgical recovery and prevent complications like anastomotic leaks or wound dehiscence due to fluid shifts.
Drug Clearance Considerations:
Many antibiotics, sedatives, and analgesics are cleared by the kidneys and/or by CRRT
Surgeons need to be aware of altered pharmacokinetics and pharmacodynamics and collaborate with the medical team for appropriate drug dosing adjustments to maintain therapeutic levels.
Abdominal Compartment Syndrome Monitoring:
In surgical patients with intra-abdominal hypertension, CRRT initiation does not negate the need for ongoing monitoring of intra-abdominal pressure
Significant fluid shifts during CRRT could potentially impact abdominal pressure, requiring vigilant assessment.
Postoperative Care And Monitoring
Circuit Anticoagulation Strategy:
The choice of anticoagulation (e.g., citrate, heparin, no anticoagulation) depends on the patient's coagulopathy, contraindications, and institutional protocols
Surgeons must be aware of the bleeding risks associated with different anticoagulation strategies.
Fluid And Electrolyte Balance:
Continuous monitoring of fluid balance, electrolytes (especially potassium and calcium), and acid-base status is essential
Surgeons should communicate any concerns related to fluid status or electrolyte imbalances that could impact surgical recovery.
Monitoring For Surgical Complications:
While on CRRT, patients are closely monitored
Surgeons must remain vigilant for signs of surgical complications such as bleeding at the access site, anastomotic leak, wound infection, or intra-abdominal hypertension, independent of renal function.
Weaning From Crrt:
Weaning from CRRT is typically guided by improvement in renal function, resolution of fluid overload, and hemodynamic stability
Surgeons should be involved in discussions regarding the patient's readiness for CRRT cessation as it relates to their surgical recovery trajectory.
Nutrition And Metabolic Support:
Adequate nutritional support is critical for surgical patients
CRRT can lead to the loss of amino acids and other nutrients, necessitating adjustments in nutritional regimens
Collaboration with dietitians is crucial.
Complications And Prevention
Vascular Access Complications:
Bleeding, infection, thrombosis, and pneumothorax (if subclavian/internal jugular)
Prevention involves meticulous sterile technique, proper catheter care, and careful site selection.
Circuit Related Complications:
Clotting of the circuit, hypotension due to excessive fluid removal, electrolyte abnormalities, and air embolism
Prevention includes adequate anticoagulation, appropriate flow rates, air detection devices, and careful monitoring.
Surgical Site Complications:
In surgical AKI patients, CRRT initiation might indirectly influence surgical site healing if fluid management is not optimal
Vigilant wound care and early detection of dehiscence or infection are paramount.
Sepsis And Infection:
Patients on CRRT are at increased risk of infection
Strict adherence to aseptic techniques for access care and timely identification and management of potential surgical site infections or catheter-related bloodstream infections are crucial.
Hemodynamic Instability:
Can occur during initiation or rapid fluid removal
Close collaboration and staged initiation of CRRT, coupled with vasopressor support, can mitigate this risk.
Key Points
Exam Focus:
CRRT offers continuous, gentle solute and fluid removal suitable for hemodynamically unstable surgical patients with AKI
Vascular access is critical
site selection must account for surgical plans
Coagulopathy assessment is vital for safe anticoagulation.
Clinical Pearls:
Always assess hemodynamic status and fluid overload meticulously before CRRT initiation
Communicate fluid goals with the critical care team
Remember that CRRT does not replace the need for surgical intervention or management of the underlying surgical condition.
Common Mistakes:
Initiating CRRT without adequate vascular access planning
Underestimating the impact of fluid shifts on surgical site integrity
Inadequate consideration of drug clearance by CRRT
Failing to involve the surgical team in decisions regarding fluid management and CRRT weaning.