Effect of Different Positive End-Expiratory Pressure (PEEP) Levels on Optic Nerve Sheath Diameter

Optic Nerve Sheath Diameter

Optic nerve sheath diameter, Intracranial Pressure Increase, spinal surgery

The goal of this prospective observational study is to evaluate the effects of different PEEP values on the optic nerve sheath diameter (ONSD), a noninvasive indicator of intracranial pressure (ICP), in patients undergoing vertebral surgery. The main question it aims to answer is how mechanical ventilation setting of 5 and 10 cmH2O PEEP effect optic nerve sheath diameter after surgery at extubation.

During general anesthesia, endotracheal intubation can cause varying degrees of alveolar collapse, particularly in the lower lung regions, in 15-20% of cases. Postoperative atelectasis and pulmonary infections are responsible for both prolonged hospital stays and increased mortality and morbidity. Positive end-expiratory pressure (PEEP) combined with low tidal volume, defined as lung-protective ventilation strategies, is used in anesthesia practice because it prevents pulmonary barotrauma, improves pulmonary function, and reduces postoperative pulmonary complications. PEEP can prevent atelectasis and reduce the risk of ventilator-associated lung injury. PEEP at 10 cmH2O or less can be used without causing a significant increase in intracranial pressure or a significant decrease in cerebral perfusion pressure. For years, low PEEP was used in neurosurgery and neurosurgical intensive care patients, considering that PEEP could increase ICP. However, recent studies in normovolemic patients without hypotension have shown that even with increased PEEP, no clinically significant increase in ICP was observed. The optic nerve is anatomically an extension of the central nervous system. Cerebrospinal fluid (CSF) circulates within this extension, which is surrounded by dura mater. Therefore, noninvasive ultrasonographic measurement of optic nerve sheath diameter (ONSD) has been shown to be effective in detecting increased intracranial pressure (ICP) due to the reflection of changes in subarachnoid space pressure and CSF on the optic nerve sheath. An optic nerve sheath diameter greater than 6 mm is a noninvasive indicator of increased intracranial pressure. The effect of positive end-expiratory pressure (PEEP) on optic nerve sheath diameter in patients undergoing vertebral surgery will be evaluated. Optic nerve sheath diameter measurements will be taken twice with ultrasound, once before surgery in the preoperative waiting room and once after surgery in the postoperative recovery unit. Hemodynamic data (systolic blood pressure, diastolic blood pressure, mean blood pressure, heart rate, peripheral oxygen saturation), and PEEP values during anesthesia will be recorded on the anesthesia observation form.

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