Effect of atelectasis and embolization on extravascular thermal volume of the lung

Abstract

The extravascular volume of distribution for heat in the lung has been advocated for the measurement of lung water. The purpose of these experiments was to investigate how extremes of ventilation-perfusion mismatch influence this measurement. Twenty-six dogs were studied with right and left atrium-to-aorta thermal and dye-dilution curves before and 60 min after total right main-stem bronchial obstruction or microembolization of the pulmonary circulation with 0.275-mm glass beads. Whereas atelectasis had no influence on our measurements, embolization with 0.32 g/kg of beads decreased the detected pulmonary blood volume from 10.63 to 8.55 ml/kg and increased the extravascular thermal volume (ETV) from 9.89 to 10.99 ml/kg. Embolization with 0.65 g/kg decreased the detected ETV from 9.29 to 8.38 ml/kg, while the extravascular wet-to-dry weight ratio was increased, and the regression of postmortem extravascular mass on ETV differed from control. We conclude that microembolization but not atelectasis causes errors in the measurement of lung fluid when the thermodye technique is used. The errors are variable and depend on the degree of embolization.

Extravascular lung water measurements and hemodynamic monitoring in the critically ill: bedside alternatives to the pulmonary artery catheter

“…The thermal indicator, being blood borne, gains access to the extravascular compartment of ITTV via the diffusion of heat. The exact distance over which such diffusion can take place during a typical measurement period is not clear [the diffusion coefficient of heat in water is estimated at 1.5 ϫ 10 Ϫ3 cm 2 /s (55)], but factors such as vascular obstruction caused by embolism (2,6) or by physiological hypoperfusion [from positive end-expiratory pressure (PEEP) (1,17), hypovolemia, or hypoxic vasoconstriction (16,44)] result in an underestimation of EVLW as measured by gold standard gravimetric methods. The underestimates due to PEEP are less likely to occur if pulmonary artery pressures are significantly higher than PEEP levels (11), which clinically is almost always the case.…”

“…The underestimates due to PEEP are less likely to occur if pulmonary artery pressures are significantly higher than PEEP levels (11), which clinically is almost always the case. Despite the hypoxic vasoconstriction associated with atelectasis, this type of lung pathology has not been shown to cause underestimates of ITTV, at least at the level of whole lung atelectasis (6). Theoretically, high flows (high CO, reducing the time for diffusion) could cause the extravascular component of lung water to be underestimated, but in general this has not been observed experimentally with the thermodilution method (1,44).…”

A new experimental model of ARDS and pulmonary hypertension in the dog

“…1a, b). Concomitantly, PVR rose from 115 to 622 dyn· slem 5 ( Fig. 1e) and RVSW increased from 57 to 149 Nm .10-3 (Table J).…”

“…This is in accordance with Becketl el al. , who failed to detect a substantial impairment of oxygenation after GB (5]. O n the other hand , GS and additional applicalion of more than 0.025-0.05 mVkg OA resulted in severe and progressive hypoxemia with p.0 2 levels 100 low « 50 rum Hg; authors' unpublished data) to bc acceptable for a model designcd to investigate cardiac function.…”

“…Most of them , however, mimic only single aspects of ARDS or PAH . The techniques used indude pulmonary microembolization (e.g., g1ass beads (5,22,26,28], fat emboli [4] , oleie acid [3 , 12, 19, 40] , stareh granules [9J, alpha-naphthyl-thiourea (ANTU) [21], blood dots {39] , air [40], barium sulfate [25]) and the intraveflous (thrombin [1 , 27], bacteria [8 , 38], endotoxin [7 , 15], lycopodium spores [13], heroin , alloxan , pyrroles [21]) , intratracheal (ozone [34] , Hel [16] , papain [30]) or intraperitoneal (ammonium sulfate [21]) administration of agents. Most oCten PAH was induced by constriction or OCclflSioli of the pulmonary artery (10,32].…”