Continuous is not continuous: the incidence and impact of circuit down-time on uraemic control during continuous veno-venous haemofiltration

Objective: There is little information on the duration of time that patients spend off therapy (down-time) during continuous veno-venous haemofiltration (CVVH) and the effect of this treatment free time on azotaemic control. Design and setting: Prospective observational study in the ICU of tertiary hospital. Patients and participants: 48 critically ill patients treated with CVVH at 2 1/h of ultrafiltration. Interventions: Prospective collection of demographic and biochemical data. Measurements and results: Two hundred and sixty-six filters were observed. Start and end times were collected for each filter. Creatinine and urea were measured daily and percentage of reduction of these two solutes was calculated (%Delta creatinine and urea). The median period when CVVH was not applied to a patient (down-time) was 3 h per day. There was a significant inverse correlation between down-time and %Delta creatinine and urea over each 24-h time cycle. On average at least 16 h per day of CVVH was required to maintain creatinine and urea concentration for each 24-h cycle. Conclusions: Continuous therapy is not truly continuous. Down-time adversely affects azotaemic control. Physicians prescribing CRRT should be aware of the consequences of such down-time on the quality and quantity of renal replacement therapy delivered.