Hemodialysis Modality in Critically Ill Patients
RRT Modality
The superiority of any particular extracorporeal modality of RRT for the treatment of patients who are critically ill with respect to survival or kidney recovery after AKI has not been established and remains a matter of debate: 1. Intermittent HD (IHD) 2. Continuous RRT (CRRT) 3. Prolonged intermittent RRT (PIRRT)
IHD in Critically Ill Patients
Basic Considerations
- Hemodynamic instability is the major issue with IHD in ICU patients. Results from myocardial stunning, fluid and osmotic shifts.
- IHD has worse hemodynamic effects, but more rapidly fixes toxin and electrolyte issues, is more accessibly. Risk of DDS is higher as well.
Prescription
| Parameter | Usual Prescription | Comments |
|---|---|---|
| Duration | 3–6 h, or as tolerated | Longer duration of treatment may reduce hemodynamic instability |
| Frequency | Minimum 3×/wk ensuring minimum dose is met (i.e., URR ≥67%) | Extra treatments often required to ensure adequacy, electrolyte, acid-base, and volume status control achieved |
| Blood flow | 200–500 ml/min | Lower rates used to reduce efficiency for patients at high risk of dialysis disequilibrium syndrome (e.g., first treatment for AKI superimposed on advanced CKD with very high urea) |
| Dialysate flow | 500–800 ml/min | |
| Temperature | 35°C–37°C | Lower temperature (i.e., 35°C–35.5°C) preferred to potentially mitigate hemodynamic instability |
| Filter size | 1.5–2.5 m2 | Primarily diffusive clearance occurs across the filter |
| Ultrafiltration rate | 0–5000 ml/3–4 h | Consider use of isolated ultrafiltration for a portion of treatment if primary indication for intermittent hemodialysis is volume overload |
| Timing of delivery | Usually during daytime hours | Usually requires hemodialysis nurse and/or hemodialysis technician and portable reverse osmosis machine |
| Anticoagulation | Not usually required | If anticoagulation is required, unfractionated heparin is preferred |
| Dialysate [Na+] | Approximately 140–150 mmol/L | Higher dialysate [Na+] may mitigate hemodynamic instability; avoid in patients with hyponatremia |
| Dialysate [Ca++] | 1.25–1.75 mmol/L | Higher dialysate [Ca++] may mitigate hemodynamic instability; avoid in patients with hypercalcemia, hyperphosphatemia |
Vascular Access
- Preferred, in descending order, of temporary nontunnled HD lines: right IJV, femorals, left IJV, subclavian
- Cathedia trial showed that bed-bound ICU patients had similar rates of catheter colonization at femoral and IJV sites, but more catheter dysfunction at the left IJV.
- Obese --> IJV better
- Not obese --> Femoral better
- Subclavian vein --> central vein stenosis is highest risk
- predict a long duration of need for RRT? --> tunneled HD line
Hemodynamic Instability during IHD
- independent risk factors for its occurrence: lower systolic BP before intermittent HD, any vasopressor use, shorter treatment time, and higher ultrafiltration volumes. This strongly suggests that, for patients receiving CKRT with ongoing hypotension or vasopressor dependence, transition to intermittent HD from CKRT should be deferred.
- mechanisms: myocardial stunning, ultrafiltration, rapid osmotic shifts
- associated with higher risk of death and impaired renal function
Mitigation Strategies
| Mechanism | Strategy |
|---|---|
| Hypovolemia | reduced UF goal, longer duration, lower blood flow rate, isolated UF, hypertonic solutions (albumin, mannitol, hypertonic saline), Na profiling |
| Myocardial stunning | Cooler dialysate temperature, higher dialysate [Ca++] |
| Decreased SVR | Cooler dialysate temperature, higher dialysate [Ca++], midodrine |
Overall, the best-supported practice for mitigating hemodynamic instability related to intermittent HD in patients who are critically ill are the routine use of low-temperature dialysate and increased dialysate sodium concentration/sodium profiling. The effect of these and any of the other strategies used to mitigate hemodynamic instability during intermittent HD on clinically relevant outcomes remains unknown. If other parameters have been optimized and hemodynamic instability continues to limit achievement of ultrafiltration goals, initiation or uptitration of agents such as the oral α-1 agonist midodrine or intravenous Vasopressors are pharmacologic options that can mitigate hemodynamic instability. A transition to PIKRT or CKRT could also be considered.
CRRT in Critically Ill Patients
Although CKRT is often considered standard of care for patients who are hemodynamically unstable and requiring KRT, data to prove superiority of CKRT over intermittent HD or PIKRT have been elusive
Outcomes/Trials for CRRT vs IHD
CKRT has been compared with intermittent HD in observational studies, randomized controlled trials (RCTs), and meta-analyses with largely equivalent outcomes, including mortality and kidney recovery. 1. VA ATN study used a strategy where patients on Vasopressors did not receive IHD, but patients with hypotension or on Inotropes could still receive IHD. 2. SHARF RCT
Advantages of CRRT
- Preventing or treating volume overload - can gradually remove volume, mitigating the risk of hypotension associated with aggressive ultrafiltration. Address thes intra-dialytic volume rebound with IHD. CRRT achieves superior volume control than IHD in patients with critical illness.
- Less risk of cerebral edema/DDS in patients at risk of intracranial hypertension (brain inury, acute liver injury, dialysis naive)
Indications for CRRT
- Essentially, same as indications for general RRT plus:
- hemodynamic instability
- continuous solute control (severe rhabdo, TLS)
- severe dysnatremia at risk for overcorrection (osmotic demyelination or cerebral edema)
- acute brain injury, acute liver failure, ECMO
- bridge to organ transplantation and who cannot tolerate IHD
CRRT Modalities
No convincing evidence exists to suggest that a specific CKRT modality influences clinical outcomes: - CVVHD (diffusive clearance) - CVVH (convective clearance) - CVVHDF (both)
PIRRT in Critically Ill Patients
References
- Chan RJ, Helmeczi W, Canney M, Clark EG. Management of Intermittent Hemodialysis in the Critically Ill Patient. CJASN [Internet]. 2022 Jul 15 [cited 2022 Oct 8]; Available from: https://cjasn.asnjournals.org/content/early/2022/07/15/CJN.04000422
- Ostermann M, Bagshaw SM, Lumlertgul N, Wald R. Indications for and Timing of Initiation of KRT. CJASN [Internet]. 2022 Sep 13 [cited 2022 Oct 8]; Available from: https://cjasn.asnjournals.org/content/early/2022/09/12/CJN.05450522
- Levine Z, Vijayan A. Prolonged Intermittent Kidney Replacement Therapy. CJASN [Internet]. 2022 Aug 29 [cited 2022 Oct 8]; Available from: https://cjasn.asnjournals.org/content/early/2022/08/29/CJN.04310422
- Teixeira JP, Neyra JA, Tolwani A. Continuous KRT: A Contemporary Review. CJASN [Internet]. 2022 Aug 18 [cited 2022 Oct 8]; Available from: https://cjasn.asnjournals.org/content/early/2022/08/18/CJN.04350422
Tags: