4D-Micro: a tiered, testable framework for hemodynamic-tissue perfusion mismatch in cardiac surgery

Organ dysfunction can develop after cardiac surgery even when mean arterial pressure, cardiac output, hemoglobin, temperature, and pump flow meet conventional targets. These variables remain the safety foundation, but they do not directly establish exchange-capable capillary flow or cellular oxygen use. We propose 4D-Micro, an unvalidated conceptual framework organized around four necessary functions: barrier and conduit integrity, perfusion driving, hemorheology, and cellular oxygen use. The framework was formalized from a recurrent clinical reasoning problem through targeted evidence mapping and explicit construction rules; it was not derived from a new patient dataset or statistical latent-variable analysis. 4D-Micro separates where recovery is discordant from the provisional mechanism that might explain it, then uses a prespecified proximal response and stopping boundary to update that explanation. It is not a substitute for established cardiac surgical monitoring or a claim that all four domains can be measured directly at the bedside. A tiered implementation distinguishes a core mode based on routine variables, an enhanced mode using regional and congestion signals, and a research mode using direct microvascular or biomarker measurements. Insufficient or conflicting data remain indeterminate rather than being forced into a phenotype. We specify a staged validation pathway: content and feasibility testing, prospective assessment of classification reliability and construct validity, and only then a pragmatic comparison with protocolized usual hemodynamic care. The framework should be narrowed or rejected if it cannot be applied reliably, its predicted responses are not observed, or it fails to improve decision processes without added harm.