Chronic Obstructive Pulmonary Disease [COPD] is a major cause of chronic morbidity and mortality worldwide. COPD is characterized by persistent progressive airflow limitation that adversely affects the ventilation/perfusion (V/Q) matching and mechanics of the respiratory muscles and leads to hypoventilation and reduced gas transfer. COPD was identified as a significant comorbidity associated with increased incidences of postoperative pulmonary complications and prolonged hospital stay. MgSO4 either intravenous or inhalational has been shown to promote bronchodilation and to improve lung function in asthmatic patients. MgSO4 either intravenous or inhalational has been shown to promote bronchodilation and to improve lung function in asthmatic patients. Administration of MgSO4 in patients with stable COPD was associated with reduced lung hyperinflation and improvement of respiratory muscle strength. This randomized control trial is designed to assess the effect of intravenous MgSO4 infusion on oxygenation and pulmonary mechanics and incidence of postoperative pulmonary complications and length of hospital stay in patients with COPD undergoing cancer larynx surgery.

Inclusion Criteria:

• Patients undergoing cancer larynx surgery (partial laryngectomy, total laryngectomy with or without neck dissection).
• Age more than 40 years old
• ASA physical status II and III.
• Diagnosed as having COPD by preoperative spirometry. The classification is bases on the post-bronchodilators forced expiratory volume in the first second (FEV1). Mild COPD is diagnosed when FEV1 is > 80% of predicted while moderate COPD is diagnosed when FEV1 is < 80% and > 50% of predicted and sever COPD is diagnosed when FEV1 is < 50% and > 30% of predicted

Exclusion Criteria:

• o Patients with heart failure.

  • History with arrhythmias or treatment with antiarrhythmic drugs.
  • Patient with heart block or on beta blockers or calcium channel blockers.
  • Patients with impaired renal function (creatinine > 2)
  • Patients with impaired liver function (ALT more than 2 folds).
  • Patient with combined restrictive and obstructive pulmonary disease.
  • Patients with preoperative tracheostomy.
  • Patients with huge mass obstructing > 50% of the view. (due to its influence on the spirometry measurements).