Effect of edema and hemodynamic changes on extravascular thermal volume of the lung

Abstract

The extravascular thermal volume of the lung (ETV) has been measured in dogs as the difference between mean transit time (t) volumes for heat and indocyanine green dye across the pulmonary circulation, calculated as the product of thermal dilution cardiac output (CO) and the difference in t for aortic indicator-dilution curves generated by right and left atrial injections. ETV measurements were compared with the extravascular lung mass (ELM): in 21 normal dogs, ETV/ELM = 1.11 +/- 0.14 (SD); in 17 dogs with hydrostatic pulmonary edema (up to 21 g/kg), ETV/ELM = 0.90 +/- 0.11; and in 27 dogs with alloxan pulmonary edema (up to 51 g/kg); ETV/ELM = 0.93 +/- 0.13. For all 65 dogs the mean ETVELM was 0.98 +/- 0.15, and the liner regression was ETV (ml/kg) = 0.90 ELM (g/kg) + 0.86 +/- 2.25 (SEE; r = 0.96). Calculations based on measurements of lung specific heat predict that ETV/ELM should equal 0.984. With acute changes in pulmonary hemodynamics, ETV was reduced by reductions in pulmonary arterial pressure (Ppa) sufficient to produce zone 1 conditions at the top of the lung. However, ETV was not affected by increases in CO (mean = 50%) produced by nitroprusside or by increases in Ppa and pulmonary blood volume (mean = 27%) produced by partial mitral valve obstruction. Distortion of the thermal dilution curve due to position of the arterial thermistor appears to be the greatest source of variability and overestimation. Simultaneous measurements from pairs of thermistors differed by 14% (range 0.4-50%).

Evaluation of noninvasive determinants for capillary leakage syndrome in septic shock patients

“…There was no clinical evidence on chest radiographs, and respiratory function was found to be normal as indicated by PaO 2 /FIO 2 ratio. Multiple gravimetric studies [21,22] have demonstrated that the thermal-dye method slightly overestimates extravascular lung water at normal levels of water content. This may explain the EVLWI value in the control group.…”

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.…”

“…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). [Reports that EVLW measurements are dependent on CO appear to be related more to previous instrumentation than to the method itself (11).…”

“…In experimental animal studies, the double-indicator dilution method can detect changes of as little as 20 -33% increases in EVLW (11,44), significantly below the level usually associated with alveolar flooding (ϳ100% increase) (12). The coefficient of variation for repeat measurements is Ͻ10% (11).…”

Extravascular lung water measured with99mTc-RBC and99mTc-DTPA is increased in left-sided heart failure

“…10 We performed first pass radionuclide (RN)-angiocardiography using 99 mTc-RBC (technetium99m labeled autologous red blood cells) to measure the pulmonary blood volume (PBV) by a method developed by our laboratory." Simultaneously, extravascular lung water (EVLW) was determined using 99 mTc-RBC and 99 mTc-DTPA (diethylene triamine pentaacetate).…”