How continuous is continuous veno-venous haemofiltration?

Introduction

Data exist from centres in the United States and Australia demonstrating that only 67–85% of the planned cycle time of CVVH could be delivered due to unplanned interruptions. As there is some evidence that higher CVVH doses may improve outcome, interruptions may adversely affect the outcome of critically ill patients with acute renal failure.

Methods

We undertook an audit of CVVH in two tertiary adult ICUs (total of 15 beds) in the United Kingdom. Patients requiring CVVH were audited, and data on length and causes of any interruptions were collected.

Results

Over a 4-month period 34 patients received CVVH, ranging from a total of 10 hours to 40 days. Two hundred and thirty CVVH cycles were run, comprising 4511 hours (∼ 75 days) of CVVH. Only six out of 34 patients (17.6%) received CVVH without any interruptions, seven patients had one interruption, but two patients had at least one interruption during each cycle of their CVVH treatment. A total 351 hours (7.7%) of CVVH time were lost due to interruptions. The length of interruptions for individual patients, however, varied from 0% to 34% of their total CVVH time. The longest period of continuous CVVH lasted 17 cycles (each 24 hours), and the shortest period was 50 min until the first interruption. Table 1 presents the causes of interruptions and their duration.

Table 1

Discussion

This audit demonstrates that filter clotting is by far the most common cause for interruption of CVVH and is responsible for 70.7% of lost CVVH time. Planned interruptions represent a small minority (10%). The total time lost from CVVH was only 7.7%, considerably less than previously reported. This may well be due to the closed organisation of our units and increased awareness of the important role of CVVH among staff. However, time lost from CVVH varied widely (0–34%) and one patient illustrates the persisting problem: repeated prescription of an erroneously low CVVH dose of 28 ml/kg/hour (instead of 35 ml/kg/hour) and multiple unplanned interruptions led to an average dose of only 18 ml/kg/hour, approximately one-half of the intended dose.

Conclusion

Multiple unplanned interruptions occur frequently during CVVH treatment in intensive care and can have considerable negative impact on the total delivered dose of CVVH.