The Effect of Thyroid Lobe Volume on the Common Carotid Artery Blood Flow

This observational study investigates how the size of the thyroid gland affects blood flow in the common carotid artery during thyroidectomy, a surgical procedure to remove part or all of the thyroid gland. The thyroid gland is anatomically close to the carotid artery, a major blood vessel supplying blood to the brain. Enlarged thyroid lobes may compress the artery, potentially altering blood flow dynamics, particularly during the semi-Fowler's position required for the surgery. By examining these effects, this study aims to provide insights into the interplay between thyroid anatomy and carotid blood flow, which could have implications for surgical and anesthetic management.

Study Objectives

The primary objective is to determine the relationship between thyroid lobe volume and carotid artery blood flow during thyroidectomy. Specifically, the study seeks to:

• Evaluate how thyroid lobe volume influences systolic and diastolic blood flow in the carotid artery.
• Identify a thyroid lobe volume cutoff associated with significant alterations in systolic/diastolic flow time ratios (<0.3).

Study Population

The study includes adult patients aged 18 years and older scheduled for elective thyroidectomy. Participants must be in a euthyroid state, as thyroid hormone abnormalities may influence recovery and perioperative outcomes. Patients with conditions such as anemia, labile hypertension, or prior thyroid surgeries, as well as pregnant or emergency cases, are excluded.

Study Design

This is a prospective observational study conducted at a tertiary academic hospital. Measurements are obtained from each participant at three critical time points:

• Baseline (T0): Before anesthesia induction.
• After anesthesia induction (T1).
• After surgical positioning (T2): In the semi-Fowler's position with head extension.

Doppler ultrasound is used to assess carotid artery diameters and flow velocities. Regional cerebral oxygenation is also measured using a cerebral oximeter to evaluate the impact of altered blood flow on brain perfusion.

Study Methods

Participants undergo the following procedures during the study:

• Ultrasound Measurements: The diameters of the common carotid artery at systole and diastole are measured, and Doppler flow velocities (peak systolic velocity, end-diastolic velocity) are recorded. These values are used to calculate mean velocity, Gosling pulsatility index, and Pourcelot resistance index.
• Manual Tracing of VTI: In cases with altered systolic/diastolic flow ratios, manual tracing is used to ensure accuracy.

Inclusion criteria

• Adult patients (≥18 years old) scheduled for elective thyroidectomy.
• Patients in a euthyroid state as confirmed by recent laboratory tests.
• Ability to provide written informed consent.

Exclusion criteria

• Pregnant patients.
• Emergency thyroidectomy cases.
• History of subtotal thyroidectomy.
• History of allergic reaction to anesthetic agents.
• Presence of anemia (hemoglobin levels below local institutional thresholds).
• Presence of labile hypertension (documented by repeated measurements on the surgical ward)
• Presence of abnormal thyroid hormone levels.