As we have passed the upper blade behind the right acetabulum or foramen ovale, so now we must introduce the other in the opposite direction, viz. before the left sacro-iliac synchondrosis: and, as the blades being exactly opposite to each other is essential to the easy locking of the instrument, it will be necessary to guide the course of the second blade, not so much by the form of the pelvis, as by the direction of the first blade. It must, therefore, pass up, so that when introduced to its full extent, the inner surface of its handle shall correspond precisely to that of the first blade. The easy or difficult locking of the blades is a proof of their having been correctly or incorrectly introduced. If, therefore, on bringing the locks together we find that they do not correspond, that the inner surfaces of the handles are not parallel, but form an angle with each other, we must endeavour to rectify this, by withdrawing, to a short extent, that blade which deviates most from the proper direction, and pass it up again more correctly. All attempts to twist the handles so as to correspond with each other, are bad and cannot fail to put the patient to much suffering.
When we are about to lock the blades, we cannot be too careful in preventing the soft parts from being pinched between them, for it causes most intolerable pain, and frequently makes the patient give such an involuntary start, as to run the risk of altering the position of the instrument.
The whole process of introducing and fixing the forceps should be conducted in as gentle and gradual a manner as possible: no attempt should be made to proceed with the operation during a pain; and in no case is force either necessary or justifiable.
Every thing being now prepared for the extraction, we must endeavour to make this resemble as far as possible the natural expulsion. When a pain, therefore, comes on, we should grasp the handle firmly, and pull gently, at the same time giving them a rotatory motion. The direction of the handles, as before said, will depend upon the situation of the head in the pelvis: if it be at the outlet, it will point downwards and forwards; if in the cavity, nearly directly downwards. If the head makes but little or no advance with one or two efforts, it will be advisable to tie the handles firmly together, and thus keep up a continued pressure upon it, and dispose it the more to elongate and adapt itself to the passages. As it advances and begins to press upon the perineum, we must be more than ever cautious not to hurry the expulsion, and give the soft parts time to dilate sufficiently. At this period it is desirable to make the extractive effort not so much forwards as the direction of the handles would seem to indicate: we thus avoid pressing too severely upon the urethra and neck of the bladder, which might otherwise suffer, and assist the dilatation of the perineum. When the head is on the point of passing the os externum, all farther extractive efforts should cease; the perineum must be supported in the usual manner, and the head should be expelled if possible by the patient herself.[87]