Читать книгу Obstetrics for Nurses - Charles B. Reed - Страница 6

Table of Contents

The study of obstetrics is an investigation of the passage, the passenger, and the driving powers of labor, as well as of the various complications and anomalies that may attend the process of reproduction.

The passage is composed of a bony canal, called the pelvis, and the soft tissues which line and almost close its outlet.

The pelvis is made up of four bones; the sacrum, the coccyx, and two other large structures of irregular shape, called the hip, or innominate bones. Joined by cartilage and held in place by ligaments, they form a cavity or basin which, in the male is deep, narrow, small and funnel-shaped, while in the female, slighter bones, expanded openings and wider arches make a broad, shallow channel, through which the child is born.

The bony pelvis is divided for description into two parts, the upper or false pelvis, and the lower or true pelvis. The upper pelvis is formed by the wings of the innominate bones and has but two functions of importance to child-bearing. It acts as a guide to direct the child into the true passage, and when measured by the pelvimeter, it gives information as to the shape and size of the inlet to the true pelvis. The true pelvis is of most concern to the obstetrician, because anomalies in its size or shape may impede the progress of labor or render it impossible. The pelvis is divided conveniently into three parts: the brim, the outlet, and the cavity.

The brim, inlet, or upper pelvic strait, is the boundary line between the false and true pelvis. It is traced from the upper border of the symphysis along the iliopectineal line on both sides to the promontory of the sacrum. The shape and size of this opening varies much in different races and individuals, both normally and through disease; and when pathologically altered, both shape and size may exercise a marked influence on the course of labor. In American women, the outline of the brim is roughly heart-shaped, like an ovoid with an indentation where the promontory of the sacrum impinges upon the opening.

Fig. 1.—The normal female pelvis. (Eden.) The lines ab and cd divide the pelvis into the right and left anterior and the right and left posterior quadrants. ab indicates the anteroposterior diameter of the brim, cd shows the transverse diameter while gh and ef represent, respectively, the right and left oblique diameters.

The brim or inlet has four important diameters to be remembered; important because the hard, round head of the child must pass through them by accommodating its diameters as favorably as possible to those of this opening. These diameters are named respectively the anteroposterior or conjugate diameter, the transverse, and the right and left oblique diameters. The two oblique diameters attain their greatest importance when the pelvis is irregularly distorted, but the others are essential in every case where labor impends. It is to secure an estimate of these latter diameters that the bony prominences are measured. This upper opening lies not horizontally, but in oblique relation to the body in standing position, and the weight of the abdominal viscera rests largely upon the bones and in consequence does not crowd into the inlet unless forced in by corsets or faulty habits.

Fig. 2.—The planes of (a) the brim, (b) the cavity and (c) the outlet. (Eden.)

Passing through the brim, a cavity is found below it, midway between the inlet and outlet, which is nearly round in shape. This is the “excavation,” or the true pelvis. Then comes the outlet, bounded in front by the pubic arch and soft parts, and behind by the coccyx pushed back as far as it can go. It is ovoid in shape, but the long axis of this ovoid lies at right angles with the axis of the ovoid inlet.

We find, therefore, a succession of three geometric figures or planes through which the head must pass by means of a spiral motion called rotation. These figures are inclined to one another so markedly in front that a line drawn through the center of each will curve forward at both ends, one end passing out near the umbilicus, the other through the vulva. This is known as the axis of the pelvis or the curve of Carus.

Fig. 3.—Visceral relations. (Redrawn from Gray.)