Macromolecular capillary leakage is involved in the onset of anaphylactic hypotension

The role of the hypovolemic component secondary to the microcirculatory changes in the onset of inaugural anaphylactic hypotension remains debated. We investigated the microcirculatory permeability in a model of anaphylactic shock using a fluorescence confocal microscopy imaging system.

Ovalbumin-sensitized anesthetized Brown Norway rats were randomly allocated into two groups (n = 6/group): control and anaphylaxis, respectively induced by intravenous saline or ovalbumin at time 0 (T0). The mesentery was surgically exposed. Macromolecular fluorescein isothiocyanate-dextran was intravenously injected (T0-5min) allowing in vivo visualization of the mesenteric microvascular network by fluorescence microscopy. After a period of stabilization of the contrast agent concentration, a 5-s movie was recorded to obtain baseline signal intensity. Following T0, 5-s movies were recorded every 30 s for 30 min. Capillary leakage of fluorescein isothiocyanate-dextran was assessed in interstitium and compared between groups. Data are expressed as mean ± SD.

Following anaphylactic shock onset, an early, progressive, and global signal intensity increase over time was detected in the interstitium. Mean index leakage differed between control and anaphylaxis (respectively 20 ± 11 vs. 170 ± 127%; P < 0.0001), starting at 2 min after shock onset and progressively increasing. Index leakage correlated with the drop in arterial blood pressure until T0 + 10 min (r = -0.75, P = 0.0001).

During anaphylaxis, interstitial capillary leakage occurs within minutes after shock onset. Compared with controls, the mesenteric microcirculation showed at least 8-fold-increased macromolecular capillary leakage. The inflammation-induced microcirculatory changes with subsequent intravascular fluid transfer might be involved in the onset of the inaugural hypotension during anaphylactic shock.