The Impact of Steep Trendelenburg Position on Intraocular Pressure

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Abstract

Intraocular pressure occurring during the Trendelenburg position may be a risk for postoperative visual loss and other ocular complications. Intraocular pressure (IOP) higher than 21 mmHg poses a risk for ocular impairment causing several conditions such as glaucoma, detached retina, and postoperative vision loss. Many factors might play a role in IOP increase, like peak expiratory pressure (PIP), mean arterial blood pressure (MAP), end-tidal CO2 (ETCO2) and surgical duration and some others (anaesthetic and neuromuscular blockade depth) contribute by reducing IOP during procedures requiring both pneumoperitoneum and steep Trendelenburg position (25–45° head-down tilt). Despite transient visual field loss after surgery, no signs of ischemia or changes to the retinal nerve fibre layer (RNFL) have been shown after surgery. Over the years, several studies have been conducted to control and prevent IOPs intraoperative increase. Multiple strategies have been proposed by different authors over the years to reduce IOP during laparoscopic procedures, especially those involving steep Trendelenburg positions such as robot-assisted laparoscopic prostatectomy (RALP), and abdominal and pelvic procedures. These strategies included both positional and pharmacological strategies.

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Primary open-angle glaucoma.

Robert N. Weinreb, Peng Khaw (2004)

Primary open-angle glaucoma is a progressive optic neuropathy and, perhaps, the most common form of glaucoma. Because the disease is treatable, and because the visual impairment caused by glaucoma is irreversible, early detection is essential. Early diagnosis depends on examination of the optic disc, retinal nerve fibre layer, and visual field. New imaging and psychophysical tests can improve both detection and monitoring of the progression of the disease. Recently completed long-term clinical trials provide convincing evidence that lowering intraocular pressure prevents progression at both the early and late stages of the disease. The degree of protection is related to the degree to which intraocular pressure is lowered. Improvements in therapy consist of more effective and better-tolerated drugs to lower intraocular pressure, and more effective surgical procedures. New treatments to directly treat and protect the retinal ganglion cells that are damaged in glaucoma are also in development.

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Retrograde axonal transport of BDNF in retinal ganglion cells is blocked by acute IOP elevation in rats.

Jeffrey McKinnon, D Zack, K Pease … (2000)

To determine whether acute experimental glaucoma in rats obstructs retrograde transport of brain-derived neurotrophic factor (BDNF) to retinal ganglion cells (RGCs). Forty rats had unilateral injection of either (125)I-BDNF (20 animals) or a mixture of (125)I-BDNF and 100-fold excess nonradiolabeled BDNF (20 animals). In each group of 20 animals, eyes contralateral to injection had either normal intraocular pressure (IOP; 10 animals) or IOP elevated to 25 mm Hg below the systolic blood pressure of the eye (10 animals). In each group of 20 rats, ipsilateral eyes had IOP set at systolic blood pressure (4 eyes), had optic nerve transection (10 eyes), or had normal IOP (6 eyes). Six hours after injection, animals were killed and tissues were fixed, embedded, and sectioned for autoradiography. Grain counts were performed over retina and optic nerve using automated image analysis. IOP elevation to 25 mm Hg below systolic blood pressure (perfusion pressure [PP] 25) decreased median retinal nerve fiber layer (NFL) grains by 38% compared with controls (P: < 0.001). Competition by cold BDNF reduced NFL grains by 28% (P: = 0.013). Considering only the radioactivity representing specific retrograde transport of BDNF, IOP elevation to PP25 reduced transport by 74%, whereas elevation to PP0 (equaling systolic blood pressure) reduced specific transport by 83%. BDNF is transported retrogradely from the superior colliculus in adult rats, and this transport is substantially inhibited by acute IOP elevation. Deprivation of BDNF among RGCs may contribute to neuron loss in glaucoma.

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The effects of steep trendelenburg positioning on intraocular pressure during robotic radical prostatectomy.

Andrew Roth, Hamdy Awad, Soledad Fernandez … (2009)

Intraocular pressure (IOP) increases in steep Trendelenburg positioning, but the magnitude of the increase has not been quantified. In addition, the factors contributing to this increase have not been studied in robot-assisted prostatectomy cases. In this study, we sought to quantify the changes in IOP and examine perioperative factors responsible for these changes while patients are in the steep Trendelenburg position during robotic prostatectomy. In this prospective study, we measured IOP using a Tono-pen XL in 33 patients undergoing robot-assisted prostatectomy. The IOP was measured before anesthesia while supine and awake (baseline T1), anesthetized and supine (T2), anesthetized after insufflation of the abdomen with carbon dioxide (CO(2)) (T3), anesthetized in steep Trendelenburg (T4), anesthetized in steep Trendelenburg at the end of the procedure (T5), anesthetized supine before awakening (T6), and 1 hr after awakening in the supine position (T7). On average, IOP was 13.3 +/- 0.58 (mean +/- SE) mm Hg higher at the end of the period of steep Trendelenburg position (T5) compared with supine position T1 (P < 0.0001). The least square estimates for each time point in mm Hg were as follows: T1 = 15.7, T2 = 10.7, T3 = 14.6, T4 = 25.2, T5 = 29.0, T6 = 22.2, T7 = 17.0. Using univariate mixed effects models for the T1-T5 time periods, peak airway pressure, mean arterial blood pressure, ETco(2), and time were significant predictors of the IOP increase, whereas age, body mass index, blood loss, volume of IV fluid administered, mean airway pressure, and desflurane concentration were not predictive. In T4-T5, which involved no significant positional or perioperative interventions, we performed a multivariate analysis to evaluate predictors of IOP increases. Surgical duration (in minutes) and ETco(2) were the only significant variables predicting changes in IOP during stable and prolonged Trendelenburg positioning. On average, IOP increased 0.21 mm Hg per mm Hg increase in ETco(2) after adjusting for time. An increase of 0.05 mm Hg in IOP per minute of surgery on average was observed during this period in the Trendelenburg position after adjusting for ETco(2). IOP reached peak levels at the end of steep Trendelenburg position (T5), on average 13 mm Hg higher than the preanesthesia induction (T1) value. Surgical duration and ETco(2) were the only significant predictors of IOP increase in the Trendelenburg position (T4-T5).