Comparing Two Different Norepinephrine Infusion Rates for Prophylaxis Against Spinal-induced Hypotension in Elderly

Baseline preoperative blood pressure will be recorded in the supine position as average of 3 reading with difference less than 5 mmHg in the mean arterial pressure.

Inferior vena cava collapsibility will be used to assess the patient's intravascular volume status.

After induction of spinal anesthesia, patients will receive the vasopressor infusion according to the previous randomization All drug preparations will be done by a research assistant who will be responsible for opening the envelope and group assignment with no further involvement in the study.

Any episode of hypotension (defined as mean arterial pressure (MAP) < 70% of the baseline or MAP<65mmHg) will be managed by 5 mcg norepinephrine.

If bradycardia (defined as heart rate less than 50 bpm) with hypotension occurred, it will be manged with 9 mg ephedrine. If bradycardia occurred with hypertension (MAP increase 20% over the baseline) and persisted for more than one reading, the vasopressor infusion will be stopped.

If hypertension occurred (defined as increased mean arterial pressure by > 20% of the baseline reading), vasopressor infusion will be decreased by 50%. If hypertension persisted 2 minutes after reduction of the infusion, the vasopressor infusion will be stopped. The vasopressor will be returned to 50% of the starting dose if there was further decline in blood pressure.

The infusion will continue for 45 minutes after spinal anesthesia.

Inclusion criteria

• Elderly patients (>65)
• ASA I-II-III
• scheduled for hip surgery under spinal anesthesia

Exclusion criteria

• Contraindication of spinal anesthesia
• history of allergy to any of the study's drugs,
• Patients with cardiac morbidities (impaired contractility with ejection fraction < 50%, heart block, arrhythmias)
• patients with uncontrolled hypertension