Oxygen is not toxic under usual conditions and is required to support life. Liquid oxygen or cold gas will freeze tissues leading to severe burns. Proper personal protective equipment should be used when necessary, and all safety protocols are to be followed. Some clients however, may suffer from hypoxic drive due to too much oxygen. Normally, our body tends to respond to high levels of carbon dioxide (CO²) in the blood by breathing. Excess CO² is then removed through exhalation. In other words, your body is usually stimulated to breathe when the levels of CO² increase or are too high. In some clients with chronic conditions such as Chronic Obstructive Pulmonary Disease (COPD), their body builds up a tolerance and no longer responds to the high blood carbon dioxide level. With this adjustment made by the body, it now uses low blood oxygen levels to help stimulate it to breathe instead of the high CO². Oxygen users who suffer from chronic CO² levels (CO² retention) may risk suffering from inadequate breathing patterns or rates (also known as oxygen-induced hypoventilation) caused by too much oxygen. Since the body no longer responds to high levels of CO² and prefers to be stimulated to breathe by lower oxygen levels, you won’t have the urge to breathe if you are receiving too much oxygen. Ideally, the PaO² or arterial blood oxygen levels should be 50-60mmHg (SaO² at 88-92%). These levels will allow for the maintenance of adequate tissue oxygenation while minimizing the chances of oxygen-induced hypoventilation. The most accurate method of determining if a client is retaining CO² is by obtaining arterial blood gases. Blood gases are generally drawn prior to initiation of oxygen therapy to determine if the client meets the Home Oxygen Program (HOP) criteria and qualifies for funding. Oxygen-induced hypoventilation may be monitored by routine oximetry testing during monthly or weekly visits. Further blood gases may be required to determine accurate levels of CO² and O².