The Accuracy of Peripheral Perfusion Index and Inferior Vena Cava Collapsibility Index for Predicting Hypotension in Patients Undergoing Shoulder Arthroscopy in Beach Chair Position:

Shoulder arthroscopy is a minimally invasive surgical procedure widely utilized for the diagnosis and treatment of various shoulder joint pathologies, it is commonly performed with patients positioned in the beach chair position , which enhances access to the shoulder joint.

In the beach chair position, the patient is placed in in a semi-sitting position with an angle ranging from 30-60 degrees, depending on surgeon preference and procedure requirements. The lower extremities are typically slightly flexed. Patient's head is securely supported using a specialized head rest or padding while the operative arm draped freely or positioned using a mechanical arm holder for optimal access to the shoulder joint.

Nonetheless, the beach chair position has unique physiological challenges including reduced venous return, decreased cardiac output which eventually results in an increased risk of hypotension. Hypotension during surgery can compromise organ perfusion, potentially leading to cerebral ischemia, myocardial dysfunction, and delayed recovery, thus blood pressure monitoring across the procedure is crucial for optimizing patient safety, outcomes and to prevent potential complications.

Various parameters have been implemented to predict hypotension in beach chair position including; pre-induction values of mean arterial pressure , stroke volume variation , cardiac index and stroke volume index but the inconsistent sensitivity and specificity, together with the necessity for invasive monitoring, may limit their routine use.

Ultrasound measurement of the inferior vena cava collapsibility index and inferior vena cava diameter has the advantages of easy performance, repeatability and low cost and has often been used to predict fluid responsiveness in emergency and critical care settings. Recently, this noninvasive hemodynamic assessment method was introduced to predict post induction hypotension in the operating room . However, its utility remains controversial across different population settings and different types of anaesthesia.

Peripheral Perfusion Index is a non-invasive measure of peripheral perfusion. It is derived from the ratio of pulsatile to non-pulsatile blood flow as measured by photoplethysmography, it measures the central hemodynamics reflecting both vascular tone and cardiac output in patients undergoing general anesthesia, and a correlation between low PPI and low blood volume has been reported. As an emerging clinical tool it helps in early detection of hemodynamic instability.

This study will assess the accuracy of Peripheral Perfusion Index and inferior vena cava collapsibility index as predictive tools for predicting hypotension in patients undergoing shoulder arthroscopy in the beach chair position under general anesthesia, contributing to the broader understanding of its role in perioperative hemodynamic management.

Primary outcome The accuracy of Peripheral Perfusion Index for predicting hypotension in patients undergoing shoulder arthroscopy in the beach chair position

Inclusion criteria

• Adult patients of both sexes (aged 21- 65 years)
• patients with American Society of Anesthesiologists physical status I or II scheduled for elective shoulder arthroscopy in beach chair position under general anesthesia.

Exclusion criteria

• Patient's refusal
• Patients with suspected difficult airway
• Patients with preexisting hypertension, diabetes mellitus, cardiovascular, cerebrovascular and peripheral vascular diseases
• Patients with preoperative hypotension (mean arterial blood pressure < 65 mmHg).
• Patients with preexisting renal or hepatic impairment.
• Pregnancy 8. Patients with increased intra-abdominal pressure 9. Patients with post induction hypotension