Hemodynamic Determinants of Urine Output During Spinal Anesthesia

The proposed clinical trial aims to explore the relationship between urine output and mean arterial pressure (MAP) during spinal anesthesia, a subject that has not been thoroughly studied in humans despite previous research under general anesthesia. Studies have demonstrated that the diuretic response to intravenous volume loading, using Ringer's solution or 20% albumin, varies with MAP levels. Specifically, Ringer's solution shows a greater diuretic effect when MAP exceeds 70 mmHg, whereas 20% albumin is more effective at lower pressures. This differential response highlights the importance of considering MAP in the choice of fluid for managing hypovolemia and oliguria.

The study's relevance is highlighted by the physiological dynamics at play, particularly how high levels of anesthesia, which influence the sympathetic nervous system from the mid-thoracic region, might reduce MAP and consequently decrease urine output. While this hypothesis has been examined in animal studies, its validity in humans remains unconfirmed.

To address this, the trial will measure hemoglobin levels, MAP, and urine output simultaneously, aiming to establish a clear correlation among these variables during spinal anesthesia. This methodical approach seeks to yield significant insights with minimal additional effort, contrasting with the complexities inherent in more elaborate study designs.

Inclusion criteria

• Written informed consent provided by patients or their legally authorized representatives.
• Adults aged 18 years and older.

Exclusion criteria

• Contraindications to Spinal Anesthesia:

• Patient refusal
• Presence of coagulopathy.
• Current use of anticoagulant or antiplatelet medications.
• Critical or severe aortic stenosis or other fixed cardiac output states.
• High risk of infection at the spinal needle insertion site.
• Elevated intracranial pressure.
• Allergy
• Sepsis
• Procedures Not Amenable to Spinal Anesthesia:

• Planned concurrent procedures that cannot be performed under spinal anesthesia.