The influence of fentanyl injection followed by infusion on the intraocular pressure, pupil size and aqueous tear production in healthy non-painful dogs

Abstract

The goal of the presented research was to assess the influence of continuously administered fentanyl on the intraocular pressure, pupil size and aqueous tear production in dogs. A prospective, randomised, double “blind” clinical study was performed. Twenty-five non-painful dogs, 13 breeds, a body weight of 10.0 ± 5.4 kg (mean ± SD) and age of 6.5 ± 3.3 years, 12 males and 13 females with no ocular abnormalities were randomly allocated into two groups receiving an intravenous injection of saline (SAL) 0.3 ml/kg followed by an infusion 2 ml/kg/h or an intravenous injection of fentanyl (FEN) 0.005 mg/kg (diluted in 0.3 ml/kg) followed by an infusion 0.005 mg/kg/h (diluted in 2 ml/kg/h). The intraocular pressure (IOP), pupil size (PS), pulse rate (PR), respiratory frequency (f<sub>R</sub>) and systolic and diastolic arterial pressures (SAP, DAP) were measured before (baseline) and at 2, 5, 10, 20 and 30 minutes after the premedication. The Schirmer Tear Test I (STT-I) was measured prior to and at 30 min after the premedication. The data were analysed by Bartlett’s, Anderson-Darling and Dunnett’s tests, the t-test and an analysis of variance (ANOVA) (P < 0.05). Relative to the baseline, in the fentanyl group, the PS was significantly decreased at all time points, the PR was significantly decreased at T<sub>30</sub> and the f<sub>R</sub> was significantly decreased at T<sub>5</sub>, T<sub>10</sub>, T<sub>20</sub> and T<sub>30</sub>. There were no other significant changes in the IOP, STT-I, SAP and DAP relative to the baseline. Compared to the control group, in the fentanyl group, the PS was significantly smaller at T<sub>2</sub>, T<sub>5</sub>, T<sub>10</sub>, T<sub>20</sub> and T<sub>30</sub>, the PR was significantly lower at T<sub>2</sub>, T<sub>20</sub> and T<sub>30</sub> and the f<sub>R</sub> was significantly higher at T<sub>20</sub>. Within thirty minutes of a constant rate infusion of fentanyl in the healthy non-painful dogs, the intraocular pressure and aqueous tear production were not affected. However, the fentanyl significantly decreased pupil size. This fact should be considered, when planning analgesia where miosis is undesirable.

Effects of fentanyl on intraocular pressure and pupil size in medetomidine‐methadone premedicated dogs: a pilot study

“…This finding matches the results in a previous study where the effect of fentanyl (10 µg/kg) on IOP was described as a unique agent 10. In contrast, a different study found that the administration of a lower dose of fentanyl (5 µg/kg) intravenously followed by an infusion resulted in no change in IOP 11. The increase in IOP observed could be due to a state of dysphoria as a result of adverse effects following fentanyl administration.…”

“… 10 In contrast, a different study found that the administration of a lower dose of fentanyl (5 µg/kg) intravenously followed by an infusion resulted in no change in IOP. 11 The increase in IOP observed could be due to a state of dysphoria as a result of adverse effects following fentanyl administration. This is a possibility because fentanyl has a high affinity for μ-receptors, but it also affects kappa and sigma receptors which can cause a state of dysphoria.…”

“…A significant increase in IOP was found after administration of a bolus of fentanyl 10. In contrast, a recent study found that the administration of a lower dose of fentanyl followed by an infusion resulted in no change in IOP 11. The effects on IOP might be inconsistent when a combination of α 2 adrenergic agonists and opioids is used 12 13…”

Influence of fentanyl, ketamine or lidocaine infusion on the intraocular pressure and pupil size in conscious dogs

“…The animal owners provided informed consent to have their animals participate in the study. The study protocol was adopted from our previous study (Rauser et al 2019), to which it directly follows, complements and extends.…”