IS IT RELIABLE ТО REFRESH A REVERSED CIRCUIT WITH MINIMAL FLOW FOR STABLE OXYGENATION?

ანოტაცია

 Minimal flow anesthesia (MFA) is associated with better preservation of airway moisture and less  heat loss. Decreased gas waste also reduces costs. The total amount of vaporized anesthetics is reduced and the risk for unnecessary work place contamination is decreased as well as the amount released into the atmosphere and subsequent impact on the global ecosystem. But low fresh gas flow (FGF) means increased rebreathing of exhaled gases. Thus, some risk of hypoxic gas mixture formation appears. Carrier gas composition acquires high importance. If pure oxygen is used as a carrier gas, adequate oxygenation for patient must be ensured. However pure oxygen delivering rises arterial oxygen partial pressure. So, we have to consider the degree of hyperoxemia Using oxygen and air mixture as a carrier gas gives us possibility of maintaining blood oxygen level in more physiologic range, but in case of MFA, steady oxygen concentration in breathing circuit is not guaranteed, especially with fixed flow. The aim of present review is to update information about safety of MFA as a method ensuring stable oxygenation. Not using nitrous oxide accelerates the process of shortening high flow phases. Ensuring sufficient denitrogenation and the avoidance of volume imbalances are only of secondary importance. As a result of rapid reduction to a low fresh gas flow, considerable cost saving can be expected. Using fixed minimal flow gives us the possibility to take the advantages of rebreathing systems right from the start. Minimal fixed FGF needs high _FiO2 of the carrier gas to ensure steady inhaled oxygen concentration (FinspO₂) during long term anaesthesia. Effect of high FiO₂ on respiratory system and clinical outcome is being debated. Finding appropriate balance between the FiO₂ of the carrier gas and the FinspO2 is challenging. Minimal fixed flow anesthesia (0.5 L/min) is safe if pure oxygen is used as a carrier gas. Using oxygen/air mixture as a carrier gas includes some risks of  FinspO₂ dropping. Patients' age and body size can be used as the prognostic factors to prevent significant decreasing of PinspO₂. Fixed MFA needs more time for inhala-tional agent to achieve desired alveolar concentration. Less soluble agents are more suitable for MFA.