EFFECT OF CHANGES IN PC0₂ AND BODY POSITIONS ON INTRAOCULAR PRESSURE DURING GENERAL ANAESTHESIA

Abstract

Elevated arterial carbon dioxide tension, induced by the administration of CO2 via the respiratory air or by hypoventilation, entailed a gradual increase in the IOP in patients without eye diseases under general anaesthesia. A sudden cessation of CO2 administration or hyperventilation caused such a rapid, simultaneous fall in IOP to values below the initial level that the pressure variations must be of vascular nature, presumably related to changes in choroidal blood volume. The above-mentioned procedures always cause a change in the central venous pressure (CVP) simultaneously with the IOP changes. Alterations of the CVP induced by hydrostatic factors in postural changes, placing the head 15 degrees above or below the horizontal level while keeping the PaCO2 constant, caused IOP changes of the same configuration and magnitude as described above. It is concluded, therefore, that presumably the CO2-conditioned IOP changes are due predominantly to changes in central venous pressure, being one link in a CO2-conditioned action upon the general circulation, entailing passive secondary changes in the choroidal venous blood volume and thereby an influence upon the IOP. On the basis of the present results it appears rational to recommend hyperventilation to keep the PaCO2 between 25 and 30 mm and a 15 degree anti-Trendelenburg position in operations on the eye under general anaesthesia, since both procedures afford a low central venous pressure and consequently a low pressure in the posterior segment of the eye, with its attendant advantages as regards vitreous complications and the insertion of intraocular lenses. Owing to the risk of an unacceptable fall in BP in the combined procedure, a frequent checking of the BP is needed.

Influence of dexmedetomidine-propofol-isoflurane and medetomidine-propofol-isoflurane on intraocular pressure and pupil size in healthy dogs

“…However, in that study we used an alpha-2 adrenoceptor agonist in combination with butorphanol and the patient was positioned in ventral recumbency. It is possible that patient positioning could cause these differences, as the ventral position can significantly increase IOP (Hvidberg et al 1981). Supine body position has been shown to increase IOP in humans, but Broadwater et al (2008) showed that this was not the case in conscious dogs in sternal recumbency.…”

“…Intraocular pressure can be influenced by patient recumbency (Hvidberg et al 1981;Broadwater et al 2008). All of the patients in the current study were positioned in lateral recumbency.…”

“…These drugs can influence ocular blood inflow and outflow and intraocular vascular tonus, which can affect IOP (Murphy 1985). The intraocular vascular tonus is regulated by the partial arterial pressure of carbon dioxide (PaCO 2 ) that influences ocular blood flow (Hvidberg et al 1981). Additionally, changes in arterial blood pressure (systolic arterial pressure) can induce alteration of the IOP (Cunningham and Barry 1986).…”

Intraocular pressure and its correlation with blood gas parameters in crested caracaras (Caracara plancus) anesthetized with isoflurane and sevoflurane

“…Gelatt and Gelatt (2001) informed that some anesthetic drugs that are to produce ocular hypotension can also produce ocular hypertension, secondary to respiratory depression and acidosis that sometimes occurs with prolonged general anesthesia. Hypoventilation contributes to the increase in venous blood pressure, with choroidal vasodilatation, causing an elevation in IOP (Duncalf and Weitzner, 1963;Hvidberg et al, 1981). In respiratory alkalosis, diminution of IOP occurs as a consequence of the reduction in the choroidal blood volume, diminution of blood flow to the ciliary body, inhibition of carbonic anhydrase enzyme, and decrease of filtration of the aqueous humor (Smith et al, 1981;Cunningham and Barry, 1986).…”

Positioning patients for spine surgery: Avoiding uncommon position-related complications

“…Most of the blood volume of the choroid is in the venules of the choroid. Venular filling of choroid depends on the pressure in the orbital veins [117] . Pressure in the orbital veins can be affected by body position [117,124,125] .…”