Often when effusion is undoubtedly present the introduction of the exploring needle is followed by no appearance of fluid; or although pus has been withdrawn by the test puncture the aspirator needle is intro duced without any result. The instrument may have entered the chest cavity at a spot where the lung is adherent to the parietes, or the layer of false membrane lining the pleura may be so thick that the needle fails to penetrate into the sac. In choosing a place for the puncture it is advisable to select one where the dulness is complete ; and it is well, as Dr. Allbutt has suggested, to look for a spot where there is bulging of the intercostal space, as here the false membranes are scanty and thin. Often it is necessary to Puncture several times, on each oc casion selecting a fresh spot, before we succeed in obtaining evidence of fluid.
In some cases the difficulty met with in withdrawing the fluid is due to rigidity of the chest-walls. If the walls of the empyema cavity cannot collapse, there is no expolsive force to drive out the fluid. As Mr. R. W. Parker has pointed out, the pleural cavity is emptied by the pressure of the atmosphere acting in three different ways. It acts on the condensed lung causing it to re-expand, on the diaphragm causing it to ascend, and on the thoracic wall causing it to fall in. If for any reason pressure can not be brought to bear on the confined fluid, no amount of suction force will have any power of withdrawing the liquid contents of the chest. In not a few cases, the aspirator being found to be useless and no fluid ap pearing after repeated punctures, we are forced to incise the chest and insert a drainage-tube in order to evacuate the pleural cavity. Mr. Parker has devised an apparatus to meet this difficulty, by means of which filtered, warmed, and carbolised air can be pumped into the upper part of the chest while fluid passes out through the aspirator needle introduced into the lower part.
The above are not the only causes by which thoracentesis is rendered difficult. Large thick flakes of lymph may be present and obstruct the opening of the needle or drainage-tube. A child, aged one year and eight months, was admitted under my care into the East London Children's Hospital, with the physical signs of a large effusion on the left side of the chest. An exploratory puncture showed pus to be present. Many attempts were made to aspirate the chest, but only small quantities of pus could be withdrawn. After repeated failures it was determined, in consultation with my colleague Mr. Parker, to incise the wall and put in a drainage-tube. This was done, but even then pus did not flow freely. Mr. Parker then put in his finger through the opening in the chest-wall and found large flakes of thick membraniform lymph which had to be removed by the for ceps. A large quantity of pus was then expelled, containing smaller flakes
of lymph, besides pultaceous matter. Listerian precautions were observed and the case did well.
the effusion of fluid has accumulated to such a degree as seriously to hamper the circulation and produce a cyanotic tint of the skin, the aspirator should be used at once, as instant relief is required to avert death. If, however, the effusion be more moderate and no danger be anticipated, the question of operative interference will depend upon the nature of the pleural contents, and the presence or absence of signs of absorption. If the fluid be purulent there is no likelihood of a spontaneous cure by ab sorption. Therefore retention of the purulent contents can in any case only do harm ; and in children with tubercular or scrofulous tendencies a collection of pus should not be allowed to remain in the chest a day longer than is necessary. Even if the fluid be still serous, it is well to remove it if after three weeks no sign of absorption has been noticed. In many of these cases the serous fluid is not renewed after emptying the chest ; and often if only a portion of the contents be evacuated the remainder is rapidly taken up by the absorbent vessels.
In cases of empyema it is best in the first instance to employ the aspi rator, as sometimes after the chest-cavity has been evacuated by this means the fluid is not reproduced. During the operation the child should be in a semi-recumbent position, supported by the nurse, and the needle should be introduced, as recommended by Bowditch, in an interspace immediately below the inferior angle of the scapula, unless the empyema be loculated. The operation often provokes cough ; but this may be disregarded unless it grow excessive, in which case the needle may be withdrawn. If there be any sign of faintness, we should at once remove the aspirator and close the wound.
Sudden death, although fortunately a very uncommon catastrophe, is sometimes a consequence of the rapid withdrawal of fluid from the chest. The accident may arise from syncope, from rapid interference with the function of the healthy lung, or from cerebral embolism. If the effusion have been copious enough to produce marked cardiac displacement and interfere with the circulation through the large vessels, the muscular sub stance of the heart may be in a state of temporary malnutrition from having been supplied for some time with imperfectly purified blood. The sudden withdrawal of the pressure, combined with the slight shock of the opera tion, may so impress the weakened organ as completely to paralyse its action ; or if this be borne without result, a sudden movement of the pa tient which throws extra work upon the circulatory centre may prove fatal.