Chapter 17 — Limb Ischaemia and Vascular Complications

Built on two reviews retrieved in full: the 2019 Critical Care narrative review (DOI 10.1186/s13054-019-2541-3) and the 2024 Perfusion review of distal limb perfusion (DOI 10.1177/02676591241236650), plus five meta-analyses and eight cohorts read as abstracts. Organising idea: SIX mechanisms threaten the limb (arterial obstruction, cannulation injury, loss of pulsatile flow, thromboembolism, venous stasis, systemic vasoconstriction) and a distal perfusion cannula addresses only two. Owns: the definition problem behind the 10-70% incidence range; limb ischaemia as a mortality marker across five cohorts, persisting to four years (HR 1.80); the risk-factor set, whose dominant MODIFIABLE factor is vasopressor dose (aOR 6.8) rather than cannula size; why Doppler fails as circuit flow rises - distal peak systolic velocity tracks pulse pressure, the exact analogue of Chapter 16's pulse-oximetry failure; NIRS thresholds and the bilateral probe that separates a cannula problem from a vasopressor problem; the Rutherford-style staging (arterial signal lost = threatened, both lost = non-salvageable) and the fact that sedation hides when the clock started; distal perfusion routes, sizes and the three silent failure modes; VENOUS congestion, which the arterial-focused literature ignores; the six-step conservative ladder; upper-limb hyperperfusion; dissection, pseudoaneurysm, retroperitoneal haemorrhage and LATE arterial stenosis; and two devices in one limb. CONTROVERSY: prophylactic versus selective distal perfusion - every meta-analysis favours prophylactic (RR 0.41-0.49; prophylactic beats reactive RR 0.41) while the largest and longest cohorts find no protection against ischaemia, only against needing an intervention. Resolved as this book's reasoning: the meta-analyses compare cannula against NO PROTOCOL, not against surveillance. NUMERICAL AUDIT found three published-source problems, all flagged and none silently corrected: an artery diameter in impossible units, an odds ratio whose direction contradicts its own conclusion, and a NIRS between-legs threshold with an inconsistent direction. First authorship of the 2019 review is disputed between sources and no author list is asserted. Publication defects caught in the post-publication check and fixed: twelve HTML entities and one bold-italic asterisk collision.