Postoperative nausea and vomiting (PONV) is considered one of the most unpleasant postoperative discomforts and lead to serious complications of aspiration of gastric contents, suture dehiscence, esophageal rupture, subcutaneous emphysema, or pneumothorax. The incidence of PONV is 30-40% in normal population and touches a peak of 75-80% in certain high-risk groups. PONV is associated with delayed recovery and prolonged hospital stay and is associated with significant morbidity. It may also result in delayed discharge, which is particularly significant after potentially ambulatory surgery. Women are 2 to 3 times more susceptible to PONV than men and breast surgery, which is primarily done in an outpatient setting, is associated with high incidence of PONV, ranging between 15% and 84% in the absence of prophylactic treatment.

Nitrous oxide (N2O) has analgesic and sedative properties but may potentially increase the incidence of PONV. N2O might increase the incidence of PONV by several potential mechanisms: (1) increase in middle ear pressure (2) bowel distension, (3) activation of the dopaminergic system in the chemoreceptor trigger zone and (4) interaction with opioid receptors. N2O has been demonstrated to increase the incidence of PONV in some studies but not in others. The present study is undertaken to evaluate the effect of nitrous oxide- free general anesthesia on the undesirable clinical outcome of PONV.

Inclusion Criteria:

1. ASA I and II female patients aged 18 years or over posted for Breast Surgeries under General Anesthesia in the main operating rooms

Exclusion Criteria:

1. ASA III, IV, V female patients
2. Age less than 18 years
3. Patients undergoing Breast Reconstructive Surgery
4. Patients with contraindications to Fentanyl, Diclofenac, Paracetamol, Atracurium
5. Chronic pain patients on long-term opioid medication
6. Use of regional anesthetic technique (e.g. Paravertebral Block)