Clinical validity of pre-bypass filters in standard extracorporeal circulation

Introduction

Microembolism of silicone particles from the extracorporeal circuit (ECC) may cause organ dysfunction after open heart surgery. To evaluate a possible clinical effect of reducing the number of particles by pre-bypass filtering, we performed a prospective randomized clinical study with a 0.2 μm pre-bypass filter (PBF).

Methods

336 consecutive patients undergoing all kinds of open heart operation were randomized into two groups (A and B). In group A the heart-lung machine (HLM) was prepared with a PBF, in group B it was not. The filter strains the priming volume for 10min by flow rates of 4 l/min. Primary excluded were patients younger than 18 years and patients who needed blood priming of the HLM. In case of emergency cannulation patients were secondary excluded. The average age was 61 ± 8.5 years (mean ± SEM) in both groups. 66% of patients were male. Coronary artery bypass grafting (CABG) was performed at 229 (68%) patients, aortic valve replacements at 54 (16%) patients, mitral valve replacements at 23 (7%) patients and other including complicated operations were done in 30 (9%) of patients. Both groups were similar in distribution of the different operations and their duration, gender and average age. Preoperatively and postoperatively (1, 2, 3 and 6 days) liver enzymes (GOT, GPT, γ-GT, GLDH, Bilirubin), pancreatic enzymes (amylase, lipase), renal function (urea, creatine, urinary volume/24 h) and general inflammatory parameter (leucocytes, c-reactive protein) were measured. Also drug demand of ecatecholamines and furosemide and frequency of rhythm disturbances were registered. For evaluation each parameter was compared with the students t test for each day on statistical differences between the groups.

Results

Both groups showed no differences in any parameter. The mean demand of catecholamines (suprarenin/dopamine) has its maximum value at the first postoperative day and then fall contiguously to the sixth postoperative day in both groups. Mechanical ventilation time was 16.2 ± 1.3 h in group A and 17.8 ± 1.3 h in group B. The maximum demand of furosemide is found on the second postoperative day in both groups, on day 6 only a few patients needed furosemide. Urea and creatine remained nearly constant for both groups at each day. In group A urea levels range between 6.7 mmol/l (preoperative) and 8.8 mmol/l (third postoperative day), and group B levels were between 6.7 mmol/l (preoperative) and 8.9 mmol/l (third postoperative day) and showed no significant difference between the groups. The highest urinary flow/24h was noticed at the first postoperative day in both groups (4676 ± 176 ml/24 h Group A/4368 ± 150 ml/24 h Group B), than it fell significantly to preoperative values at the third and sixth postoperative days. Pancreatic enzymes showed maximum values at the first postoperative day. While Amylase fall to normal lipase has a second maximum on the 6th postoperative day. Liver enzymes remain inconstant the following maximum values are reached [U/l] Group A/Group B: GOT 35 ± 4/32 ± 2; GPT 25 ± 2/31 ± 4; γ -GT 38 ± 4/45 ± 5; GLDH 8 ± 2/10 ± 2; LDH 420 ± 35/404 ± 15; Bilirubin 17 ± 1/17 ± 1. The maximum response of leucocytes and CRP appeared at the second postoperative day without reaching reference scope at the sixth postoperative day also showing no significant difference between the groups.

Conclusion

We conclude that use of 0.2 μm pre-bypass filters in ECC for removal of microparticles does not prevent organ dysfunction after open heart surgery. Possible effects seem to be of less clinical importance or appear elsewhere.