IOP Clinical Trial
Official title:
A Pilot Crossover Study in Healthy Volunteers to Assess the Effect of Acetazolamide on Intraocular Pressure After Being in the Trendelenburg Position.
Perioperative vision loss following laparoscopic colorectal surgery is rare but has been
reported. Studies show Trendelenburg positioning during surgery can produce a significant
rise in the IOP, and this rise is thought to be a possible factor. Acetazolamide decreases
IOP by reducing the formation of aqueous humour.
Aims:
To investigate if acetazolamide reduces the IOP rise resulting from Trendelenburg
positioning.
Methods:
A randomised cross-over blinded pilot study. Nine healthy volunteers were randomised to
start with the placebo or Acetazolamide with a 5 days' washout period. Baseline IOP was
measured on both days. After 1.5 hours of taking the medication, volunteers lay head-down at
17 degrees' for 4 hours and IOP measurements repeated. This reading was subtracted from the
baseline to give a 'change in IOP'.
Background:
Laparoscopic (keyhole) bowel surgery often requires positioning patients on the operating
table in very steeply angled positions for up to four or more hours. There have been case
reports of patients suffering cognitive impairment after surgery with long periods of
Trendelenburg (person is lying flat at an incline where their head lies lower than their
feet) positioning.
Evidence from other fields of surgery suggests that "head-down" positions can produce a
significant rise in the intraocular pressure. Transient vision problems and loss of sight
has been reported following surgery is rare instances, including one case after laparoscopic
colorectal resection. The cause of this is not fully understood, but rises in intraocular
pressure (IOP) has been suggested as a possible factor. This may be particularly relevant in
patients who have pre-existing high baseline IOP as a result of glaucoma. Studies looking at
the effect of Trendelenburg positioning have shown that there is an increase in IOP. This
study is to assess the effect of acetazolamide on the IOP rise after being placed in the
Trendelenburg position. Acetazolamide is a carbonic anhydrase inhibitor which is used to
treat glaucoma. The drug works by decreasing aqueous humour formation. It can be given as
eye drops (but the absorption of this is variable and therefore so is the effect), orally
and intravenously. The oral dose can be given as a one off dose or a divided dose. Maximum
onset of IOP reduction occurs 2 to 5 hours after taking an oral dose and duration is 6-8
hours.
Aims:
This study aims to investigate the effect of acetazolamide on the IOP rise whilst in the
Trendelenburg position.
Experimental protocol and methods:
This will be a pilot randomised crossover study with 9 healthy volunteers recruited and
randomised to either Group 1 or Group 2. Group 1 will start with the Control Day; Group 2
will start with the Intervention Day. On the Control Day, a baseline IOP using a Tonopen XL
will be taken. They will then be placed in 17 degrees head-down position 2.5hours after a
placebo is administered for a minimum of 1 hour and a maximum of 4 hours. Repeat IOP measure
will be taken whilst in the Trendelenburg position after 5 minutes, and then every 30
minutes from the start of Trendelenburg position. On the Intervention Day, baseline IOP will
be taken, they will then be 500mgs of acetazolamide. After 2.5 hours, the volunteers will
then be placed in the Trendelenburg position at 17 degrees for position for a minimum of
1hour and a maximum of 4 hours. Repeat IOP measure will be taken whilst in the Trendelenburg
position after 5 minutes, and then every 30 minutes from the start of Trendelenburg
position.
Inclusion criteria:
Healthy volunteers, aged 18 and over
Exclusions criteria
Pregnancy Breast Feeding Hepatic impairment Patients with pre-existing conditions affecting
IOP regulation eg Glaucoma, previous eye surgery Regular medication affecting IOP Under the
age of 18 Refusal to give written informed consent
Measurable endpoints/ statistical power
Primary endpoint: Comparison of IOP pressure before and after being placed in the
Trendelenburg position between the two days - Day 1 volunteers will be administered with a
placebo before being placed in the Trendelenburg position and Day 2 after acetazolamide has
been administered.
Power: Bucci et al compared the effect of oral acetazolamide on IOP on 22 patients. They
detected a 3.7mmHg decrease in IOP after 2 hours. Using this study, we powered our study to
require 18 patients.
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