Extracorporeal circuit pressure profiles during continuous venovenous haemofiltration

Continuous renal replacement therapy machines are capable of providing continuous pressure measurements at different points of the extracorporeal circuit. This study investigates the pattern of circuit pressure changes during high-volume continuous venovenous haemofiltration (CVVH) with regional anticoagulation with anticoagulant citrate dextrose in formula A. Extracorporeal circuit pressures during 91 treatments of CVVH were analysed. Distinct patterns of extracorporeal circuit pressures were observed: (a) the extracorporeal circuit pressures during a routine uncomplicated CVVH treatment remained close to initial values. The interquartile range (IQR) of pressures during the treatments were as follows: PA (arterial pressure) -3.5 to -10 mmHg, PV (venous pressure) 51 to 41.5 mmHg, PBE (prefilter pressure) 120.5 to 104 mmHg, PD2 (fluid outlet pressure) -23 to -70 mmHg, TMP (transmembrane pressure) 142.75 to 102.75 mmHg and PFD (pressure filter difference) 70 to 62 mmHg. (b) PD2 and TMP showed early separation from baseline values in CVVH treatment compromised by haemofilter clot. Haemofilter clotting problems were associated with median PD2 of -164 mmHg (IQR: -66.2 to -228.7), a fourfold increase from baseline. (c) PA and PV values changed abruptly in catheter-malfunction-related circuit disruption. Poorly functioning catheters tended to have a higher baseline PA (median: -33 versus -25.5) than in those without catheter problems; however, the difference was not statistically significant (p= 0.13). (d) A rise in PBE and PFD followed by changes in PD2 and TMP were noted in a treatment disrupted because of air detection chamber clotting. Distinct patterns of extracorporeal circuit pressures were present in patent and disrupted CVVH circuits. We suggest that the pattern of pressure profiles, not absolute values, may be more relevant in clinical practice.