27, 3
Twelve healthy pigs, mechanically ventilated, connected to a low-flow carbon dioxide removal circuit on a renal replacement platform (membrane surface area 1.8 m²). Two degrees of induced hypercapnia (PaCO2 50–69 and 70–89 mmHg), blood flows of 200 and 350 mL/min, gas flows of 4, 6 and 10 L/min.
The finding Chapter 27 uses: at the low blood flows characteristic of carbon dioxide removal, the sweep stops being the sovereign lever.
- In severe hypercapnia, raising the sweep from 4 to 10 L/min increased removal from 86.38 ± 7.08 to 96.50 ± 8.71 mL/min at a blood flow of 350 mL/min, and was ineffective at 200 mL/min.
- Removal rose with the degree of hypercapnia at 350 mL/min but not at 200 mL/min — interpreted as maximal removal already reached at the lower flow.
- Post-membrane PCO2 was similar regardless of pre-membrane PCO2 (p = 0.08), demonstrating that the membrane strips what reaches it nearly completely, so the limit is delivery rather than exchange.
Certainty: low. Twelve animals, one device, one surface area, an experimental model rather than disease. The authors record that device-specific plateaus beyond which more sweep achieves nothing differ widely across the literature — above 2 L/min in one device, no effect above 4 L/min in another, and 4–5 L/min in COPD exacerbations. No transferable threshold is asserted, only the principle: a sweep increase that achieves nothing means the blood flow is the limit.
Read as indexed full-text passages. DOI not independently resolved.