Continuous Renal Replacement Therapy during Extracorporeal Membrane Oxygenation: Circuit Haemodynamics and Circuit Failure.

INTRODUCTION: Treatment with continuous renal replacement therapy (CRRT) is common during extracorporeal membrane oxygenation (ECMO). Such ECMO-CRRT has specific technical characteristics, which may affect circuit life. Accordingly, we studied CRRT haemodynamics and circuit life during ECMO. METHODS: ECMO and non-ECMO-CRRT treatments in two adult intensive care units were compared using data collected over a 3-year period. A potential predictor of circuit survival identified in a 60% training data subset as a time-varying covariate within a Cox proportional hazard model was subsequently assessed in the complementary remaining data (40%). RESULTS: Median [interquartile range] CRRT circuit life was greater when associated with ECMO (28.8 [14.0-65.2] vs. 20.2 [9.8-40.2] h, p < 0.0001). Access, return, prefilter, and effluent pressures were also greater during ECMO. Higher ECMO flows were associated with higher access and return pressures. Classification and regression tree analysis identified an association between high access pressures and accelerated circuit failure, while both first access pressures ≥190 mm Hg (HR 1.58 [1.09-2.30]) and patient weight (HR 1.85 [1.15-2.97] third tertile vs. first tertile) were independently associated with circuit failure in a multivariable Cox model. Access dysfunction was associated with a stepwise increase in transfilter pressure, suggesting a potential mechanism of membrane injury. CONCLUSION: CRRT circuits used in conjunction with ECMO have a longer circuit life than usual CRRT despite exposure to higher circuit pressures. Markedly elevated access pressures, however, may predict early CRRT circuit failure during ECMO, possibly via progressive membrane thrombosis as evidenced by increased transfilter pressure gradients.

Circuit haemodynamics during non-citrate and regional citrate continuous renal replacement, and impact of blood flow on filter life.

BACKGROUND: During continuous renal replacement therapy (CRRT) with regional citrate anticoagulation (RCA), blood flow (Qb) might affect vascular access dysfunction (AD) and, thereby, circuit life. METHODS: Circuit life and circuit haemodynamics were studied in three intensive care units (ICUs) by analysing hemofilter device data (Prismaflex®, Baxter, Chicago, IL). The three sites shared similar RCA protocols but differed in Qb (120-130 vs 150-200 mL/h). Non-RCA circuits were compared with RCA circuits in which the impact of Qb was also assessed. RESULTS: About 3,981,906 min of circuit pressures were analysed in 2568 circuits in 567 patients. High-Qb RCA was associated with more extreme pressures, and greater AD (IRR 3.7 (1.93-7.08) as well as reduced filter life 21.1 (10.2-42.6) vs 27.0 (14.8-41.6) h). AD in high-Qb RCA circuits was associated with a 49% reduction in filter life, versus 24% reduction in low-Qb RCA, associated with a rise in the rate of increase in transfilter pressure. CONCLUSIONS: High-Qb RCA-CRRT was associated with greater access dysfunction, earlier filter loss and increased haemodynamic impacts of access dysfunction, suggesting low-Qb RCA-CRRT may improve circuit mechanics, function and longevity.

Low Blood Flow Continuous Veno-Venous Haemodialysis Compared with Higher Blood Flow Continuous Veno-Venous Haemodiafiltration: Effect on Alarm Rates, Filter Life, and Azotaemic Control.

TITLE: Low blood flow continuous veno-venous haemodialysis (CVVHD) compared with higher blood flow continuous veno-venous haemodiafiltration (CVVHDF): effect on alarm rates, filter life, and azotaemic control. INTRODUCTION: Continuous renal replacement therapy (CRRT) can be delivered via convective, diffusive, or mixed approaches. Higher blood flows have been advocated for convective clearance efficiency and promotion of filter life. It is unclear whether a lower blood flow predominantly diffusive approach may benefit filter life and alarm rates. MATERIALS AND METHODS: Sequential cohort study of 284 patients undergoing 874 CRRT circuits from January 2015 to August 2018 in a single university-associated tertiary referral hospital in Australia. Patients underwent a protocol of either CVVHDF at blood flow 200-250 mL/min or CVVHD at blood flow 100-130 mL/min. Machine and patient data were analysed. Outcomes of azotaemic control, filter life, and warning alarm rates were log transformed and analysed with mixed linear modelling with patient as a random effect. RESULTS: Both groups had similar azotaemic control (effect estimate on log creatinine CVVHD vs. CVVHDF 1.04 [0.87-1.25], p = 0.68) and median filter life (CVVHDF 16.8 [8.4-90.5] h and CVVHD 16.4 [9.4-82.3] h, p = 0.97). However, circuit pressures were less extreme with a narrower distribution during CVVHD. Multivariate analysis showed CVVHD had a reduced risk of warning alarms (incidence risk ratio [IRR] 0.51 [0.38-0.70]) and femoral access placement also had a reduced risk of alarms (IRR 0.55 [0.41-0.73]). CONCLUSION: Low blood flow CVVHD and femoral vascular access reduce alarms while maintaining azotaemic control and circuit patency thus minimizing bedside clinician workload.

A pilot study of high frequency accelerometry-based sedation and agitation monitoring in critically ill patients.

OBJECTIVE: The degree of sedation or agitation in critically ill patients is typically assessed with the Richmond Agitation and Sedation Scale (RASS). However, this approach is intermittent and subject to unrecognised variation between assessments. High frequency accelerometry may assist in achieving a quantitative and continuous assessment of sedation while heralding imminent agitation. DESIGN: We undertook a prospective, observational pilot study. SETTING: An adult tertiary intensive care unit in Melbourne, Australia. PARTICIPANTS: 20 patients with an admission diagnosis of trauma. MAIN OUTCOME MEASURES: Accelerometers were applied to patients' wrists and used to continuously record patient movement. Video data of patient behaviour were simultaneously collected, and observers blinded to accelerometry data were adjudicated the RASS score every 30 seconds. Exploratory analyses were undertaken. RESULTS: Patients were enrolled for a median duration of 9.7 hours (interquartile range [IQR], 0-22.8) and a total of 160 hours. These patients had a median RASS score of 0 (IQR, -4 to 0). A 2-minute moving window of amplitude variance was seen to reflect contemporaneous fluctuations in motor activity and was proportional to the RASS score. Furthermore, the moving window of amplitude variance was observed to spike immediately before ≥ 2 point increases in the RASS score. CONCLUSIONS: We describe a novel approach to the analysis of wrist accelerometry data in critically ill patients. This technique not only appears to provide novel and continuous information about the depth of sedation or degree of agitation, it is also notable in its aptitude to anticipate impending transitions to higher RASS values.

Circuit Hemodynamics and Circuit Failure During Continuous Renal Replacement Therapy.

OBJECTIVES: To study hemodynamic changes within continuous renal replacement therapy circuits and evaluate their relationship with continuous renal replacement therapy longevity. DESIGN: Analysis of downloaded variables recorded by continuous renal replacement therapy machines during multiple episodes of clinical care. SETTING: Tertiary ICU in Melbourne, Australia. PATIENTS: Cohort of 149 ICU patients: 428 episodes of continuous renal replacement therapy. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Indices of continuous renal replacement therapy function representing 554,991 minutes were assessed including blood flow, access pressure, effluent pressure, prefilter pressure, and return pressure. We defined three patterns of artificial kidney failure: early (≤ 12 hr), intermediate (> 12-24 hr), and late (> 24 hr) in 35%, 31%, and 34% of circuits, respectively. Mean access pressure in late artificial kidney failure was 7.5 mm Hg (7.1-7.9 mm Hg) less negative than early failing circuits and pressures demonstrated lower variability in such late failing circuits. Access dysfunction, defined as access pressure less than or equal to -200 mm Hg occurred in the first 4 hours in 118 circuits (27%) which had a shorter (median [interquartile range]) life at 12.9 hr [5.5-21.3 hr]) hours than access dysfunction-free circuits (18.8 hr [10.1-33.4 hr]; p < 0.0001). Multivariate analysis found the first occurrence of access dysfunction (as a time-varying covariate) was independently associated with increased hazard of subsequent failure (hazard ratio, 1.75; 1.36-2.26). Classification and regression tree analysis of summary pressure indices in the first 2 hours confirmed minimum access pressure to be a significant predictor, as well as indices of transmembrane pressure and return pressure. A pressure-based predictor correctly identified early and late failing circuits (86.2% and 93.6% specificity, respectively). CONCLUSIONS: Access dysfunction is a predictor of continuous renal replacement therapy circuit failure. Future monitoring of continuous renal replacement therapy hemodynamics may facilitate remedial actions to improve circuit function.

Filter lifespan in critically ill adults receiving continuous renal replacement therapy: the effect of patient and treatment-related variables.

OBJECTIVE: To examine the effects of patient and treatment-related variables on filter lifespan in critically ill adults receiving continuous renal replacement therapy (CRRT). DESIGN AND SETTING: This was a single-centre, retrospective, observational study conducted in a tertiary referral centre in metropolitan Melbourne, Australia. All CRRT filters used over a 44-month period from 1 January 2008 to 31 August 2011 were assessed for their hours of function before being stopped non-electively (due to clotting) or electively. Analyses were performed primarily for all CRRT filters and secondarily for those ceased non-electively during the study period. To assess for any relationship with filter life, we performed multivariable regression analyses for blood flow rate, anticoagulation type, vascular access site, vascular catheter type, reason for stopping the filter circuit, platelet count and activated partial prothrombin time. RESULTS: A total of 1332 treatments in 355 patients were assessed for filter life. Of these, 474 were electively ceased, leaving 858 filter circuits for secondary analysis. In both analyses, higher blood flow rate predicted longer filter lifespan (P=0.03 for all filters and P=0.04 for non-electively ceased filters). Vascular catheter type was predictive of increased filter lifespan in the non-electively ceased filters (P=0.002) but not on analysis of all filters. Type of anticoagulation and vascular access site were not predictive of filter lifespan in either analysis. Of the patient haematological variables, only platelet count was predictive of increased filter lifespan (P=0.003 for all filters and P< 0.001 for non-electively ceased filters). CONCLUSIONS: Our study found that an increased CRRT filter lifespan is associated with higher blood flow rates and lower platelet count. Vascular catheter design may also be a factor.

Critically ill obstetric patients in Australia: a retrospective audit of 8 years' experience in a tertiary intensive care unit.

OBJECTIVE: To review the indications for admission, demographics, clinically relevant aspects of medical care and outcomes of critically ill obstetric patients admitted to a tertiary hospital intensive care unit. DESIGN: Retrospective review. SETTING AND PARTICIPANTS: General medical and surgical ICU of a tertiary university-affiliated hospital in central Melbourne, Victoria, Australia. Medical records were reviewed for all women who were admitted to the ICU between January 1998 and June 2006 and were pregnant or within the 6-week postpartum period. All were transferred from other hospitals. MAIN OUTCOME MEASURES: Primary diagnoses, clinical indications for ICU admission, ICU interventions, and maternal and fetal outcomes. RESULTS: Over the 102-month period, 56 obstetric patients were admitted to the ICU (0.38% of all ICU admissions). Their mean (+/-SD) age was 31.8 (+/-5.76) years. All but two admissions were postpartum. The most common indications for ICU admission were haemodynamic instability (38%), respiratory complications (29%) and neurological complications (27%). Mechanical ventilatory support was required by 61% (34/56) of the patients, and blood transfusion by 48%. The median length of ICU stay was 45.75 hours (range, 8-281 hours). There were no maternal deaths, but residual functional or physical disability was noted in eight patients. There were four perinatal deaths. CONCLUSIONS: This audit is a reminder that continued vigilance is required to ensure maternal safety. It also emphasises the need to integrate free-standing maternity units with hospital intensive care services.