A child undergoes in-patient treatment for acute staphylococcal destruction of the right lung. Unexpectedly he develped acute chest pain on the right, dyspnea, cyanosis. The right side of chest lags behind in the respiratory act. Percussion reveals dullness in the lower parts on the right, bandbox resonance in the upper parts. Borders of the relative cardiac dullness are shifted to the left. What complication has most likely developed?