Measurements of extravascular lung water in vivo by external counting

Techniques for estimating pulmonary oedema in vivo require extensive arterial sampling and do not provide regional information. In order to estimate extravascular lung water (idQwl) by external counting the authors used gamma emitting cyclotron produced radioisotopes: H 215O as diffusible indicator and red blood cells labelled with 11C monoxide as intravascular tracer. The authors injected these tracers in the superior vena cava of supine anaesthetized dogs recording externally by means of probes collimated over the chest and obtaining, at the same time, the arterial dilution curves. They showed a very good correlation between idQwl as measured by arterial sampling and by external counting. It is concluded that an external counting technique can be used to detect and to follow changes of idQwl in patients with pulmonary oedema and, in turn, to assess its regional distribution.