Relative contributions of macrovascular and microvascular dysfunction to disease severity in falciparum malaria

Sequestration of parasitized erythrocytes in the microcirculation is considered the central pathophysiological process in severe falciparum malaria. Hypovolemia with reduced oxygen delivery and microvascular obstruction have different implications for patient management; however, their relative contributions to disease severity are uncertain.

Adult patients (n = 28) with severe Plasmodium falciparum malaria were enrolled in a prospective hemodynamic study. Volume status and oxygen delivery were assessed using transpulmonary thermodilution. Microvascular sequestration was measured using orthogonal polarized spectroscopy.

Duration of therapy before study enrollment was correlated with the amount of directly visualized and quantitated microvascular sequestration (P = .03). The amount of sequestration correlated with plasma lactate (r(s )= 0.55; P = .003) and disease severity (r(s )= 0.41; P = .04). In patients who had received artesunate for <10 hours, sequestration was higher in fatal cases than in survivors: median (range) 45% (32-50) vs 15% (0-40); P = .03). Parasite biomass estimated from plasma P. falciparum histidine-rich protein 2 correlated positively with disease severity (r(s )= 0.48; P = .01) and was significantly higher in patients who died (P = .046). There was no relationship between oxygen delivery and disease severity (P = .64) or outcome (P = .74).

Vital organ dysfunction in severe malaria results primarily from sequestration of parasitized erythrocytes in the microvasculature rather than reduction in circulating blood volume and oxygen delivery.