Chapter 26 — Echocardiography During ECMO

Second chapter of Part V. ORGANISING INSIGHT: on ECMO there is no ejection fraction, only an ejection fraction at a stated circuit flow — the ELSO Red Book Ch 48 instructs that all parameters be reported with the ECMO flows at the time of assessment, and almost nobody does it. Consequence: the CHANGE in a measurement across a deliberate change in flow carries more information than the measurement, and the magnitude of that swing is itself a variable (Ng 2022, 46 patients at 100/120/50% of target flow: GLS sensitivity 72.7% acute phase vs 22.5% delayed). SECOND STRUCTURAL CLAIM: cannula position is a variable, not a fact — the distal cannula end is radiolucent so the chest film physically cannot do the job; loss of lung volume on a rest strategy raises the diaphragm and moves the heart relative to a skin-fixed cannula (Red Book intrahepatic-reinjection case); Tabak 2012 found at least one port misplaced in 5 of 11 dual-lumen studies. CENTRAL CONTROVERSY: the three standard weaning criteria (LVEF over 20-25%, LVOT VTI 10 cm or more, mitral S' 6 cm/s or more) have been reported with three incompatible performances — Aarhus 96% weaned among criteria-met (verification bias: the criteria selected who was tested); Ng AUC 0.86 for weanability but 0.68 for decannulation in the same 46 patients; and a cohort summarised in the 2022 review in which 30% of UNWEANABLE and only 16% of successfully weaned patients met all three (labelled VERIFICATION REQUIRED). Also owns: the low-pulsatility differential that Ch 25 deferred (two chambers, ten seconds); tamponade on a circuit where every physical sign is abolished (a rising CVP is the sign — one case went 9-11 to 35 mmHg over ten hours); the LVOT VTI cross-check obligation; the three turndown techniques and which chamber each can assess (simple flow reduction cannot assess the RV — full RV loading is not achieved); the 1.5 L/min imaging-turndown floor; a two-tier model for who holds the probe. FOUR PROBLEMS FLAGGED UNCORRECTED: the Kim reversal figures; two different mitral S' thresholds in the literature (6 vs 8 cm/s); a date discrepancy in the Yastrebov reference; and the fact that the ELSO ultrasound guidance expired in May 2018 by its own text and is used throughout.