Effect of Hypertension on Hemodynamics in the Prone Position

The number of spine surgeries has increased in recent years due to degenerative diseases of the spine and age. Lumbar spine surgery is a surgery performed in the prone position. Changing the patient's position from supine to prone may cause a decrease in cardiac output, arterial pressure and tissue perfusion due to the decrease in the preload of the heart. In addition to the decrease in venous return due to increased intra-abdominal pressure, left ventricular compliance may be impaired due to increased thoracic pressure. All these changes may cause decreased cardiac output and systemic hypotension. These changes may be more pronounced especially with the prone position accompanied by anesthesia. This situation is thought to be due to the fact that anesthetic drugs cause direct hypotension as well as impairing reflex responses to hypotension such as the sympathetic system. Perioperative cardiac complications are the main causes of mortality after non-cardiac surgery. Intraoperative hypotension, especially in patients in the prone position, has been shown to be significantly associated with clinical outcomes such as spinal cord ischemia and postoperative vision loss and may lead to serious complications. Therefore, optimization of hemodynamic variables is an integral part of perioperative care to reduce postoperative mortality and morbidity during surgeries that require patients to be placed in the prone position, such as vertebral surgery. More than 280 million surgeries are performed worldwide each year, and approximately one-third of these patients use antihypertensive agents before surgery. It has been reported that hypertension is associated with hypotension, especially after induction, in patients receiving general anesthesia. Therefore, it has been stated that perioperative management of patients receiving antihypertensive drugs is especially important. Patients diagnosed with preoperative hypertension have been associated with increased risk of surgical bleeding, stroke, and cardiovascular complications. Long-term use of antihypertensive drugs in hypertensive patients may cause autonomic nerve dysfunction, leading to perioperative hypovolemia, decreased tolerance to postural changes, and sharp fluctuations in circulation. Therefore, maintaining hemodynamic stability in hypertensive patients receiving general anesthesia may be difficult. The change in prone position required for vertebral surgery may be associated with a high risk of developing hypotension due to decreased venous return from inferior vena cava compression and increased intrathoracic pressure. In awake patients, hypotension caused by changes in position is prevented by baroreceptor reflex and sympathetic activation, whereas in anesthetized patients, anesthetic drugs may block these compensatory mechanisms, potentially increasing the incidence of hypotension associated with postural change. It has been reported that the incidence of hypotension associated with the change from supine to prone position under general anesthesia is approximately three times higher than in awake patients. However, there are also studies reporting that perioperative hemodynamic changes in patients with hypertension are similar to those without additional comorbidities. MostCare (Vytech Health™, Vygon, Padova, Italy) is a self-calibrating device based on continuous analysis of the systolic and diastolic phases of the arterial waveform via an intraarterial catheter. In short, this monitoring method provides valuable information in terms of cardiac and vascular functions and intravascular volume, as well as close monitoring of blood pressure. It is an important guide in the rapid recognition of etiology and treatment of hemodynamic changes. Spine surgery is mostly performed in the prone position and under general anesthesia. Both general anesthesia and prone position can cause significant changes in the patient's hemodynamics. However, there are limited studies on hemodynamic changes during anesthesia of patients diagnosed with hypertension, and their results are contradictory. In this study, researchers aimed to investigate the effect of hypertension on cardiovascular and hemodynamic changes in the prone position.