A woman with mitral stenosis but no pulmonary hypertension is in labor at 39 weeks of gestation. She has dyspnea on exertion. Her pulse rate is 80 bpm. There are no basal creps in lungs.The cervix is 4 cm dilated. She is having 1-2 uterine contractions in 10 minutes. Which of the following steps is best avoided in her?