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 l/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.