What is the role of peritoneal dialysis in critically ill patients with impaired renal function in the Intensive Care Unit (ICU)?

Peritoneal Dialysis in the ICU: A Comprehensive Overview

Current Role and Practice Patterns

Peritoneal dialysis (PD) is rarely used for critically ill adult patients in Western ICUs, where extracorporeal kidney replacement therapy (KRT) represents the gold standard, but it remains a viable and underutilized option that offers distinct advantages in specific clinical scenarios. 1

Geographic and Practice Variations

• In Western countries and the United States, PD is not routinely utilized for critically ill adult patients in the ICU setting 1
• PD is more frequently used in developing countries due to lower cost and minimal infrastructural requirements 2
• The modality is more commonly continued in hospitalized patients previously on continuous ambulatory peritoneal dialysis (CAPD) or automated peritoneal dialysis (APD) 1

Physiological Mechanism and Principles

Core Operational Characteristics

• The peritoneum serves as a natural semipermeable membrane, with blood flow provided by peritoneal microcirculation rather than an artificial extracorporeal circuit 3
• Dialysate solution instilled into the peritoneal cavity removes uremic toxins through diffusion and convection, while ultrafiltration is achieved by creating an osmotic gradient using hypertonic glucose or icodextrin solutions 3

Solute Clearance Mechanisms

• Diffusion is the primary mechanism for small molecule clearance (creatinine, urea, electrolytes), where solutes move from high to low concentration across the peritoneal membrane 3
• Convection provides additional clearance through solvent drag, where water carries dissolved solutes across the membrane during ultrafiltration 3
• Middle molecule clearance is maximized by continuous 24-hour PD without dry periods, as it depends more on total dialysis time than dialysate flow rate 3

Specific Indications in the ICU

Absolute Indication

• The absolute indication for acute PD is the need for dialysis when unable to perform any other renal replacement technique 4

Relative Indications for Critically Ill Patients

• Hemodynamically unstable patients who cannot tolerate rapid fluid and solute shifts 1, 4
• Presence of bleeding or hemorrhagic conditions where systemic anticoagulation is contraindicated 4, 5
• Difficulty obtaining or maintaining vascular access 4, 5
• Patients requiring removal of high molecular weight toxins 4
• Heart failure refractory to medical treatment 4

Special Population: LVAD Patients

• For patients with left ventricular assist devices (LVADs), peritoneal dialysis represents an attractive alternative to hemodialysis given smaller hemodynamic shifts, lack of need for venous catheters, more patient-centric approach, and potentially better chance at renal recovery 1
• Earlier LVAD models had compatibility issues, but current generation devices with intrapericardial placement have much lower risk of direct device infection 1

Contraindications

Absolute Contraindications

• Recent abdominal or cardiothoracic surgery 6
• Diaphragmatic peritoneal-pleural connections 6
• Fecal or fungal peritonitis 6

Relative Contraindications

• All other contraindications are considered relative and must be weighed against clinical circumstances 4

Technical Aspects and Prescription

Catheter Selection and Insertion

• Flexible peritoneal catheters should be used where resources and expertise exist (optimal standard) 6
• Rigid catheters and improvised catheters may be used in resource-poor environments where they may still be life-saving (minimum standard) 6
• Catheters should be tunneled to reduce peritonitis and peri-catheter leak 6
• Insertion should take place under complete aseptic conditions using sterile technique 6
• Prophylactic antibiotics should be administered prior to PD catheter implantation 6

Dialysate Solutions

• In critically ill patients, especially those with significant liver dysfunction and marked lactate elevation, bicarbonate-containing solutions should be used (optimal) 6
• Where bicarbonate solutions are unavailable, lactate-containing solutions are an acceptable alternative (minimum standard) 6
• Commercially prepared solutions should be used when available (optimal), though locally prepared fluids may be life-saving in resource-limited settings 6

Potassium Management

• Once serum potassium falls below 4 mmol/L, potassium should be added to dialysate or given orally/intravenously to maintain levels at 4 mmol/L or above 6
• Potassium levels should be measured daily (optimal) 6
• After 24 hours of successful dialysis, consider adding potassium chloride to achieve 4 mmol/L concentration in dialysate when frequent monitoring unavailable (minimum standard) 6

Dialysis Prescription and Adequacy

• Targeting a weekly Kt/V urea of 2.2 has been shown equivalent to higher doses for most AKI patients 6
• Targeting weekly Kt/V of 3.5 provides outcomes comparable to daily hemodialysis in critically ill patients, though higher doses do not improve outcomes 6
• Tidal automated PD using 25L with 70% tidal volume per 24 hours shows equivalent survival to continuous venovenous hemodiafiltration 6

Cycle Time Adjustments

• Short cycle times (1-2 hours) should be used to rapidly correct uremia, hyperkalemia, fluid overload, and/or metabolic acidosis 6
• Cycle times may be increased to 4-6 hours once acute issues are controlled to reduce costs and facilitate clearance of larger solutes 6
• For fluid overload, increase dextrose concentration and reduce cycle time to 2 hours 6
• Once euvolemic, adjust dextrose concentration and cycle time to maintain neutral fluid balance 6

Advantages in the ICU Setting

Hemodynamic Benefits

• More prolonged KRT modalities like PD offer better hemodynamic stability, slower and reduced solute shifts, and better tolerance of fluid removal compared to intermittent hemodialysis 1
• PD avoids episodes of hypotension common in hemodialysis patients 4
• Continuous therapy allows gradual correction of acid-base and electrolyte imbalances 4

Practical Advantages

• Does not require vascular access or arterial/venous puncture 4, 5
• Systemic anticoagulation is not necessary 4, 5
• Widely available and easy to perform 4
• Does not require special staff or expensive equipment 4
• No interaction between blood and dialyzer 4
• Large amounts of fluid can be removed in hemodynamically unstable patients, allowing parenteral nutrition 4

Limitations and Disadvantages

Clearance Limitations

• PD achieves only 10-20% of normal kidney clearance for index substances like urea and creatinine, with even lower clearance for higher molecular weight solutes 3
• PD is less efficient than hemodialysis for acute complications (pulmonary edema, intoxication, hyperkalemia) 4
• Not the therapy of choice in patients with extreme catabolism requiring daily hemodialysis or continuous renal replacement therapy 4

Functional Limitations

• Critical kidney functions not replaced by PD include tubular secretive and reabsorptive function, and endocrine function 3
• Continuous protein loss can contribute to malnutrition 3
• Nutrient losses occur during treatment, including low molecular weight macronutrients and micronutrients 3

Monitoring and Discontinuation

Laboratory Monitoring

• Creatinine, urea, potassium, and bicarbonate levels should be measured daily where resources permit 6
• 24-hour Kt/V urea and creatinine clearance measurement is recommended to assess adequacy when clinically indicated 6
• Regular assessment of residual renal function is crucial 7

Discontinuation Criteria

• Interruption of dialysis should be considered once the patient is passing >1L of urine per 24 hours and there is spontaneous reduction in creatinine 6

Outcomes and Evidence

Comparative Effectiveness

• Studies have shown that with careful planning, critically ill patients can be successfully treated using PD 2
• Survival of ARF patients is similar between PD and hemodialysis patients 4
• Recent evidence demonstrates similar outcomes when PD is compared with other extracorporeal therapies 6

Common Pitfalls

• Classic limitations such as infectious and mechanical complications and poor metabolic control have been decreased with use of cyclers, flexible catheters, and high volume of dialysate 2
• The perception that PD is inadequate for ICU patients is outdated and not supported by current evidence when appropriate techniques are employed 2, 6