In estimating the value of the substitution of aspiration for the trocar-and-canula method, we must bear in mind that with the latter there was danger of the introduction of air into the thoracic cavity, of the production of fistulous orifices, and the too rapid, and therefore dangerous, evacuation of the fluid. Moreover, there are cases where the trocar and canula is not effectual, although the quantity effused be considerable—where, indeed, the fluid cannot flow out, although the canula be pushed in actual contact with the fluid. The explanation of this is now understood. The fluid is kept in the pleural sac by a negative pressure of from 4 to 5 inches of water (Stone), 6 millimeters mercury (Donders), 5 millimeters mercury (M. Foster), exercised by the lung in its elastic contraction, and by the passive tension of the arched diaphragm. The fluid has no tendency to flow out, and this suctional pulmonary force must be antagonized by an external suctional force, that of aspiration, before the fluid can be withdrawn.
The invention can best be appreciated from the standpoint reached by modern investigations of the physics of the living mechanism of the chest. The principle of applying suctional force in pleurisy is in imitation of nature's gentle methods in connection with respiration. We have shown that most of the dangers connected with aspiration are caused by not taking into consideration the adjustment of lung-tension with thoracic resilience, and consequently of using too great negative force and withdrawing the fluid too rapidly and in too great quantity.
Thoracentesis by aspiration, with greater or less force as may be necessary, is now placed upon a scientific basis. We claim that this modern method is an American invention—that Morrill Wyman was the discoverer and H. I. Bowditch the utilizer of the discovery. As such they may be regarded as benefactors of the human race.
It is extraordinary that Trousseau never alluded to Bowditch's operations, and that Dieulafoy should never have heard of them. Fraentzel acknowledges that Bowditch was the first to introduce aspiration into practice. The Germans have been very slow in appreciating its value. Fraentzel states that he did not use it until 1871, and that it was not until 1879 that it had in Germany any ardent supporters. Bowditch315 has now operated 387 times upon 246 patients without any unpleasant result.316 The distinctive points in Dieulafoy's ingenious modification of the aspirator are that the needles are very fine, even one-half of a millimeter in diameter; that the barrel of the exhausting pump is of glass; that there is a pre-existing vacuum; that we are not compelled to jar the side of the patient by the process of pumping, and moreover by turning the cock we produce at once a vacuum in the needle itself, and know with certainty the moment the fluid is reached, and can see it flow through the glass index in the tubing, even if it be in drops. We can judge of the nature of the fluid, whether it be serum, pus, or blood. The minuteness of the needle is a great cause of safety, because it allows the fluid to flow so gradually that the lung has time to expand slowly. We can in an instant arrest the flow of the fluid by turning the stopcock, and if necessary by drawing out the needle. By giving the needle a downward direction after it enters the cavity, we prevent the point from pricking the lung. So small an orifice is made that even if the needle does touch the lung, there is no danger, for the orifice closes over at once. As Dieulafoy claims, "the fineness of the needle guarantees the harmlessness of the puncture." Castraux's concealed point (invented in 1873), and Fitch's (of Nova Scotia) protected canula (invented in 1873), are valuable additions to the aspirator-needle. These dome-trocars, as they are called, prevent the possibility of injuring the lung, for the sharp-pointed needle, after it has penetrated the pleural cavity, is at once, by a slight movement, converted into a blunt-pointed needle with an orifice near the end. With these very fine needles the force is sufficient to draw up the thickest fluids. We are compelled to admit that Dieulafoy's instrument is a great advance on any other that has been invented. Its simplicity, its easy application, its safety, have rendered paracentesis a harmless operation and one of great value in serous effusions. While Guérin and Wyman may both claim priority of invention, all must admit that Dieulafoy has improved upon their ideas and given us a beautiful and effective instrument. There have been proposed, since Dieulafoy showed his instrument in 1869, no less than forty other aspirators, modifications in form or dimensions of his apparatus. Of these, to us the most valuable is Potain's bottle aspirator, with which aspiration can be so easily and effectually employed. It is simple and cheap. An india-rubber cork accurately fitting a strong bottle is perforated for two tubes each having a stopcock. One of the tubes fits on the end at the exit in the basin, and the other is adapted to an aspirating syringe.
315 London Lancet, vol. ii., 1879.
316 Letter to author, 1883.
One of the most important of the improvements to the aspirator-canula is the addition—first suggested in 1858 by Charles Thompson,317 and afterward adopted by Potain, Powell, and Fraentzel—of a lateral tube for the outflow connected with the main canula through which the trocar passes. By this improvement, in case the canula is clogged up, the trocar can be pushed down to remove the obstruction without danger.
317 Med. Times and Gazette, 1858.
The principle of aspiration is now well established, and the indications for its use are becoming more defined and more accurate. New applications as a means of diagnosis, as well as of treatment, daily render it more valuable.
To guard against the dangers shown by modern experience to be sometimes attendant upon the operation of aspirating the pleura (see [Dangers of Thoracentesis]), it is now generally admitted that the removal of the contents of the chest should be slow and gradual; and that, ordinarily, it is safest at one operation to remove only a portion of the effused liquid. Our object should be to remove pressure and allow nature by absorption to take away the remainder, for positive pressure is an urgent indication for thoracentesis. It is therefore of primary importance to properly estimate the quantity present, and thus to test the intra-thoracic pressure. Great care and caution must be used, because if we extract too much the operation may be followed by serious results.318 Large-sized canulæ should never be used, for fear of too rapid withdrawal of fluid. It has been demonstrated that even with a capillary perforated needle we can exercise more negative pressure than is safe, especially toward the close of the operation, when there supervenes a negative pressure exerted by the fluid remaining in the pleural cavity. It is from these well-known facts that we recognize the great value of Potain's ingenious addition to the aspirator of a manometer of extreme simplicity, a kind of barometer or cuvette, which is placed along the tube which withdraws the fluid. If we are not satisfied with this new safety improvement of the aspirator, we may adopt Douglass Powell's suggestion (On Consumption, etc.) of fitting into the bottle a pressure-gauge, so as to know at any moment what degree of aspiration is being used.