32, 31, 33, 37, 89
Expect an oxygenator exchange in roughly four in ten venovenous runs and expect about a third of them to fall outside working hours — which is the entire argument for surveillance, since the swap itself takes under two minutes but its preparation takes 15 to 30 minutes or more. The carbon dioxide channel carries independent information about membrane decline, so record the sweep, the blood flow and the arterial carbon dioxide on the same line. Do NOT expect the pressure drop to give a day's notice: the one study that tested the short window found nothing. And treat every operating characteristic quoted for these parameters as partly a description of local practice until a study evaluates them against an outcome determined independently of them.
Patients with no oxygenator exchange; and elective versus emergency exchanges
DOI 10.1177/02676591231168642; PMID 36995209; PMC11191661
Oxygenator exchange, classified as elective or emergency by TIMING (outside the 10 a.m. to 5 p.m. window) rather than by indication
Forty-five patients and 29 events; retrospective and single centre; a single oxygenator brand throughout, so results may not transfer to other devices; over half the cohort had COVID-19 ARDS with its own prothrombotic phenotype. THE AUTHORS' OWN CENTRAL LIMITATION: the variables tested were the same variables clinicians used to decide on an exchange, so there is a risk of a self-fulfilling prophecy; they note there were no emergency exchanges due to an acute shutdown of the system, and that the indication for exchange was not generally recorded so emergency exchanges during office hours could be missed. The emergency-exchange finding rests on 10 events with a confidence interval touching 1.00. No threshold is offered for any parameter and the authors explicitly call for research to define cut-off values.
19 of 45 patients (42 percent) had at least one oxygenator exchange, on median day 12; 10 (22 percent) had a second on median day 9 of that circuit; 29 exchanges in total. 10 of 29 (34 percent) were emergency exchanges. THE MOST PREVALENT INDICATION FOR BOTH EMERGENCY AND ELECTIVE EXCHANGE WAS A RISING TRANSMEMBRANE PRESSURE DROP. Independent risk factors for exchange (backward stepwise Cox regression): higher arterial carbon dioxide tension with correspondingly lower pH, higher transmembrane pressure drop, and higher haemoglobin; Harrell c-statistic 0.77 for the combined linear predictor. Univariately associated: higher Hb, plasma free haemoglobin, platelets, pressure drop, PaCO2, lower pH, SOFA score and COVID-19 as indication. EMERGENCY EXCHANGE: lower lactate dehydrogenase was the only independent risk factor, OR 0.90 (0.82-1.00), borderline, on 10 events; both LDH and CRP were LOWER before emergency than before elective exchanges. NEGATIVE FINDINGS THAT MATTER: the percentage change in pressure drop adjusted for blood flow over the 12 and 24 hours before the exchange showed NO correlation with the exchange, and a sensitivity analysis substituting the pressure-drop-to-blood-flow ratio for the raw pressure drop gave similar results throughout. D-dimer was higher in the exchange group but was not associated with exchange in the regression. Plasma free haemoglobin was associated univariately but did not survive, and the authors attribute haemolysis more plausibly to the pump than to the membrane. Oxygenator exchange had no impact on ICU survival. The authors describe deteriorating gas exchange as a LATE marker of functional decline, and cite an in-vitro study finding alteration of the carbon dioxide concentration at the oxygenator OUTLET to be an early indicator, a measurement they note is not generally performed.
All 45 consecutive adults supported with venovenous ECMO for at least 48 hours, single Dutch tertiary centre, October 2018 to March 2022. Median ECMO duration 16 days; 28 of 45 (62 percent) discharged alive; 23 of 45 (51 percent) COVID-19 ARDS. Cardiohelp with the HLS advanced 7.0 set throughout; unfractionated heparin to aPTT 50-70 s; oxygenator inspected twice daily by a perfusionist and an intensivist; weaning by lowering the sweep rather than the blood flow; no strict exchange protocol.