Doxapram is licensed for drug-induced post-anesthesia respiratory depression , arousal effect and return airway protective reflexes caused by barbiturates, volatile anesthetics, nitrous oxide or benzodiazepines over dosage.

Value of theophylline to stimulate the respiratory neuronal network has been examined by previous studies and increases the activity of respiratory muscles, including the intercostal , transversus abdominis muscles and the diaphragm, it also has bronchodilator and anti-inflammatory effects.

This randomized comparative study will be conducted in the post-surgical cardio-thoracic intensive care unit in Beni -Suef University Hospital after approval of the department of anesthesiology, surgical ICU and pain management , and cardio thoracic department and the local ethics and research committee, and obtaining written informed consents from the patients to compare the effect of doxapram versus theophylline on diaphragmatic function using ultrasonography parameter: thickening fraction of the diaphragmatic muscle during respiration which defined as [(thickness at end-inspiration - thickness at end-expiration)/thickness at end-expiration] during spontaneous breathing trial as a primary outcome and its effect on weaning time and weaning success rate as secondary outcomes.

Inclusion Criteria: Patients (males and females) in the age group 20 -60 scheduled for elective open heart surgery ( e.g. coronary artery bypass grafting, valve replacement ) under cardiopulmonary bypass .

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Exclusion Criteria:The preoperative exclusion criteria:

1. Age older than 60 years
2. Preoperative left ventricular ejection fraction less than 30%
3. Chronic obstructive pulmonary disease
4. Significant hepatic disease (alanine aminotransferase or aspartate aminotransferase >150 U/l).
5. Renal failure (creatinine >200 μm).
6. History of seizure, or stroke.
7. History of diaphragmatic palsy, cervical spine injury, or neuromuscular disease (eg, myasthenia gravis, Guillain-Barré syndrome).
8. Lesion adjacent to the diaphragm
9. Intra-abdominal hypertension (intra-abdominal pressure ≥12 mm Hg )
10. Known allergy to the study drugs.

The Post enrollment exclusion criteria:

1. Postoperative hemorrhage (chest tube drainage ≥ 200 ml/h).

2. Surgical complications necessitating reoperation.

3. Postoperative cardiac failure necessitating high-dose inotropes or intra -aortic balloon pump.

4. Refractory hypoxemia (ratio of arterial oxygen tension [PaO2] to fraction of inspired oxygen [FIO2] <150 mmHg).

5. Occurrence of neurologic deficit.

6. -Myocardial ischemia (ST-segment depression) lasting more than 30 min

7. Failure of spontaneous breathing trial.

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