Comparison of Pleth Variability Index vs. Diastolic Shock Index for Predicting Hypotension During Anesthesia Induction

Comparison of the Effectiveness of Pleth Variability Index and Diastolic Shock Index in Predicting Hypotension During Anesthesia Induction

This study aims to explore the frequent occurrence of hypotension during anesthesia induction due to anesthetic drugs or fasting. Predicting this condition is important for patient safety and anesthesia management. The study examines two indices: the Pleth Variability Index (PVI), derived from pulse oximeter readings, and the Diastolic Shock Index (DSI), calculated using heart rate and diastolic blood pressure. While PVI is a well-known method, DSI has been less explored in predicting anesthesia-related hypotension. The study aims to compare the effectiveness of these two indices in forecasting hypotension during anesthesia induction.

Hypotension is frequently observed during anesthesia induction due to the effects of anesthetic drugs on hemodynamics and the requirement of a specific fasting period before surgery. Induction-related hypotension can lead to decreased tissue perfusion and, consequently, secondary organ damage. Predicting anesthesia-induced hypotension in advance contributes to better anesthesia management and patient safety (1). Induction-related hypotension is defined as arterial hypotension occurring within the first 20 minutes after anesthesia induction or until the start of the surgery. Arterial hypotension is identified when mean systolic arterial pressure (MAP) decrease > 20% or MAP <65 mmHg or when norepinephrine is administered at a dose >;6 mcg/min at least once during this period (2).

The peripheral perfusion index (PI) is a simple, cost-effective monitoring method derived from non-invasive plethysmographic data using pulse oximetry. It provides an assessment of fluid status based on respiratory changes in pulse oximeter waves, with higher PI values indicating lower arterial tone. Changes in PI are interpreted as signs of vascular tone or fluid deficit issues in patients. The ratio of the highest and lowest PI values yields the Pleth Variability Index (PVI) (3,4). PVI can be used to predict hypotension during anesthesia induction (5).

Cardiac output (CO) is calculated by multiplying systemic vascular resistance (SVR) and heart rate (HR). In septic and shock patients, CO may be low, often due to decreased SVR. The autonomic system tries to maintain CO by increasing HR in response to the reduced SVR (6). Systolic and diastolic shock indices are obtained by dividing the HR by systolic and diastolic blood pressures, respectively. The diastolic shock index has been evaluated in studies to predict vasopressor response in septic patients (7). A high shock index has been associated with early vasopressor initiation and better prognosis. However, no study has yet examined the predictive power of the diastolic shock index, which is related to sympathetic response and systemic vascular resistance, for hypotension following anesthesia induction.

Moreover, the diastolic shock index has not been compared with the more commonly used PVI in terms of their ability to predict hypotension. Therefore, our study aims to test the success of diastolic shock index and PVI measurements in predicting anesthesia-induced hypotension

Inclusion Criteria:

1. Patients with a preoperative fasting period of at least 6 hours
2. Patients scheduled for elective surgery under general anesthesia
3. Patients aged 18-65 with ASA classification I-III
4. Patients undergoing lumbar spinal surgery

Exclusion Criteria:

1. Patients who do not agree to participate in the study
2. Emergency surgeries
3. Patients who will undergo surgery under spinal anesthesia
4. Patients diagnosed with autonomic neuropathy
5. Patients undergoing surgery with inotropic support