Cervical effacement or cervical ripening refers to a thinning of the cervix. Background
Cervical effacement is a component of the Bishop score and can be expressed as a percentage.Prior to effacement, the cervix is like a long bottleneck, usually about four centimeters in length. Throughout pregnancy, the cervix is tightly closed and protected by a plug of mucus. When the cervix effaces, the mucus plug is loosened and passes out of the vagina. The mucus may be tinged with blood and the passage of the mucus plug is called bloody show (or simply "show"). As effacement takes place, the cervix then shortens, or effaces, pulling up into the uterus and becoming part of the lower uterine wall. Effacement may be measured in percentages, from zero percent (not effaced at all) to 100 percent, which indicates a paper-thin cervix. Results from a systematic review of the literature found no differences in cesarean delivery nor neonatal outcomes in women with low-risk pregnancies between inpatient or outpatient cervical ripening.Effacement is accompanied by cervical dilation. == References ==
Even when only one side of the chest is injured, inflammation may also affect the other lung. Uninjured lung tissue may develop edema, thickening of the septa of the alveoli, and other changes. If this inflammation is severe enough, it can lead to dysfunction of the lungs like that seen in acute respiratory distress syndrome. Ventilation/perfusion mismatch
Normally, the ratio of ventilation to perfusion is about one-to-one; the volume of air entering the alveoli (ventilation) is about equal to that of blood in the capillaries around them (perfusion). This ratio is reduced in pulmonary contusion; fluid-filled alveoli cannot fill with air, oxygen does not fully saturate the hemoglobin, and the blood leaves the lung without being fully oxygenated. Insufficient inflation of the lungs, which can result from inadequate mechanical ventilation or an associated injury such as flail chest, can also contribute to the ventilation/perfusion mismatch. As the mismatch between ventilation and perfusion grows, blood oxygen saturation is reduced. Pulmonary hypoxic vasoconstriction, in which blood vessels near the hypoxic alveoli constrict (narrow their diameter) in response to the lowered oxygen levels, can occur in pulmonary contusion. The vascular resistance increases in the contused part of the lung, leading to a decrease in the amount of blood that flows into it,  directing blood to better-ventilated areas. Although reducing blood flow to the unventilated alveoli is a way to compensate for the fact that blood passing unventilated alveoli is not oxygenated, the oxygenation of the blood remains lower than normal.