Final answer:
The nurse should monitor the client's fundal consistency to evaluate the effectiveness of oxytocin following a vaginal birth, as it indicates effective uterine contractions and the process of involution.
Step-by-step explanation:
To evaluate the effectiveness of the medication oxytocin following a vaginal birth, the nurse should monitor the client's fundal consistency. Oxytocin is administered to induce labor or strengthen labor contractions, and after birth, it helps contracting the uterus to prevent postpartum hemorrhage. The fundal height provides information on whether the uterus is contracting properly, thereby aiding in preventing postpartum bleeding.
The nurse should assess whether the uterus is firm (indicating effective uterine contractions) and returning to the pre-pregnancy size at a normal rate, a process known as involution. While other parameters like pulse rate, blood pressure, and output are important for overall patient monitoring, they are not specifically indicative of the effectiveness of oxytocin in achieving its intended purpose of uterine contraction post-birth.