Pericardial effusion causes interstitial pulmonary edema in dogs

The pulmonary effects of pericardial effusion were studied in eight anesthetized dogs, with emphasis on lung mechanics, O₂ exchange, and extravascular thermal lung volume (ETV) accumulation, while warm saline was instilled into the pericardium to elevate pericardial pressure. The results were compared with those from four time-controlled and sham-operated dogs. ETV, as measured by a double-indicator technique, increased from 8.1 ± 0.8 ml/kg at a pericardial pressure of 0 mm Hg to 12.9 ± 2.1 ml/kg at 11.0 mm Hg (p < .01). In the control group, ETV increased from 6.5 ± 0.7 to 8.2 ± 0.5 ml/kg over an equal time span. This increase in ETV in the experimental dogs was inversely related to pulmonary compliance, which decreased by 29% as ETV increased (p < .05), whereas in the time-controlled group of animals it decreased by 8.8%. Arterial PO₂ did not deteriorate during the protocol in either group. Histologic examination showed increased interstitial fluid, but neither alveolar fluid nor septal edema, and gravimetric measurements of lung liquid were also consistent with interstitial fluid accumulation in experimental but not control animals. These findings are concordant with the clinical observation that alveolar edema is rarely seen in the presence of pericardial tamponade. Conceivably, progression from interstitial to alveolar edema did not occur both because of the low pulmonary blood flow that occurs as part of pericardial tamponade physiology and/or because the hydrostatic pressures were not elevated enough to produce higher rates of fluid transudation.