Abstract
Background: Oxygen is a commonly administered drug which if given for long periods at high doses can have detrimental effects to a patient's health. Critically ill patients in the ICU often receive oxygen administration as part of their treatment plan, many of whom are mechanically ventilated. There are recommendations around safe oxygen administration but no clear protocols on reducing oxygen administration which allows for a sustained high dose over long periods. Treating patients with liberal oxygen therapy increases the patient's risk of hyperoxia and oxidative stress. As reactive oxygen species themselves cannot be measured other biomarkers left behind are measured. Plasma ascorbate acts as an antioxidant in the body so may be measured as a marker of oxidative stress with the expectation that as oxidative stress increases, plasma ascorbate concentrations should decrease.
Aim: The aim of this research project was to assess the effect that two different oxygen regimes had on plasma ascorbate concentrations as a marker of oxidative stress in critically unwell adults receiving treatment in the ICU.
Methods: This research project was a sub study of the Intensive Care Unit Randomised trial of two approaches to giving Oxygen (ICU-ROX trial). A quantitative, prospective, randomised controlled trial methodology was used to collect blood samples from 60 ICU patients for up to three days. Patients were randomised into either the conservative or liberal oxygen treatment groups and treated with oxygen at differing levels with different target SpO2 ranges. Plasma ascorbate concentrations were measured in the laboratory using high performance liquid chromatography. Data was collated and analysed to determine statistical significance.
Results: Most participants had inadequate vitamin C concentrations throughout all measurements taken with only two participants testing within the adequate range at baseline (i.e. >50 ?mol/L). There was a significant difference in plasma ascorbate concentrations over time, but no significance was seen between the treatment groups. A significant difference was seen in some of the FiO2 and PaO2 measurements with the standard treatment group having higher recordings than the conservative treatment group.No difference was seen between the cardiac or infection disease categories, nor when comparing plasma ascorbate concentrations against 90-day mortality, age, or gender.
Conclusion: Plasma ascorbate deficiency is common in critically ill patients, whether receiving conservative or liberal oxygen therapy. With the risks of oxidative stress being known to cause worsened morbidity and mortality, new interventions are required to reduce the risks to the patients. The role of nurses in ICU is to treat these critically ill patients, commonly with oxygen, so nurses must understand the risk of oxidative stress and the need for antioxidant testing and supplementation to inform best practice in the future.