A system for hypobaric oxygenation, the system comprising: a fluid source; an inflow flow controller fluidly connected to the fluid source, wherein the inflow flow controller is configured to control the flow rate of the fluid from the fluid source; an inflow sensor configured to measure a flow rate, a fluid composition, a pressure, a temperature, an oxygen fraction, a carbon dioxide fraction, a chemical composition, an anesthetic concentration, an anesthetic partial pressure, or a combination comprising at least one of the foregoing from the fluid source; an oxygenator fluidly connected to the fluid source, wherein the oxygenator is configured to have a subatmospheric pressure, and wherein the oxygenator is configured to oxygenate blood and/or other fluids from a separate fluid source; an optional sweep gas reservoir fluidly connected to the fluid source and the oxygenator; an oxygenator inflow sensor fluidly connected to the oxygenator, the oxygenator inflow sensor configured to measure one or more of a flow rate, a fluid composition, a pressure, a temperature, an oxygen fraction, a carbon dioxide fraction, a chemical composition, an anesthetic concentration, an anesthetic partial pressure, or a combination comprising at least one of the foregoing from the sweep gas reservoir when present or from an anesthetic vaporizer or from the fluid source; an oxygenator inflow flow controller fluidly connected to the sweep gas reservoir when present or to the anesthetic vaporizer or to the fluid source, wherein the oxygenator inflow flow controller 9 is configured to control the flow rate of fluid from the sweep gas reservoir when present or the anesthetic vaporizer or the fluid source, wherein the oxygenator inflow sensor is between the oxygenator and the oxygenator inflow flow controller; an optional outflow sensor fluidly connected to the oxygenator, the outflow sensor configured to measure a flow rate, a fluid composition, a pressure, a temperature, an oxygen fraction, a carbon dioxide fraction, a chemical composition, an anesthetic concentration, an anesthetic partial pressure, or a combination comprising at least one of the foregoing from the oxygenated fluid; an outflow flow controller fluidly connected to the oxygenator, wherein the outflow flow controller is configured to control the flow rate of fluid from the oxygenator; a controller configured to control the inflow flow controller (2,) the oxygenator inflow flow controller, or the outflow flow controller, or a combination comprising at least one of the foregoing, in response to a measurement from the inflow sensor, the oxygenator inflow sensor, the outflow sensor when present, or a combination comprising at least one of the foregoing; and a vacuum source downstream of the oxygenator. a fluid source; an inflow flow controller fluidly connected to the fluid source, wherein the inflow flow controller is configured to control the flow rate of the fluid from the fluid source; an inflow sensor configured to measure a flow rate, a fluid composition, a pressure, a temperature, an oxygen fraction, a carbon dioxide fraction, a chemical composition, an anesthetic concentration, an anesthetic partial pressure, or a combination comprising at least one of the foregoing from the fluid source; an oxygenator fluidly connected to the fluid source, wherein the oxygenator is configured to have a subatmospheric pressure, and wherein the oxygenator is configured to oxygenate blood and/or other fluids from a separate fluid source; an optional sweep gas reservoir fluidly connected to the fluid source and the oxygenator; an oxygenator inflow sensor fluidly connected to the oxygenator, the oxygenator inflow sensor configured to measure one or more of a flow rate, a fluid composition, a pressure, a temperature, an oxygen fraction, a carbon dioxide fraction, a chemical composition, an anesthetic concentration, an anesthetic partial pressure, or a combination comprising at least one of the foregoing from the sweep gas reservoir when present or from an anesthetic vaporizer or from the fluid source; an oxygenator inflow flow controller fluidly connected to the sweep gas reservoir when present or to the anesthetic vaporizer or to the fluid source, wherein the oxygenator inflow flow controller 9 is configured to control the flow rate of fluid from the sweep gas reservoir when present or the anesthetic vaporizer or the fluid source, wherein the oxygenator inflow sensor is between the oxygenator and the oxygenator inflow flow controller; an optional outflow sensor fluidly connected to the oxygenator, the outflow sensor configured to measure a flow rate, a fluid composition, a pressure, a temperature, an oxygen fraction, a carbon dioxide fraction, a chemical composition, an anesthetic concentration, an anesthetic partial pressure, or a combination comprising at least one of the foregoing from the oxygenated fluid; an outflow flow controller fluidly connected to the oxygenator, wherein the outflow flow controller is configured to control the flow rate of fluid from the oxygenator; a controller configured to control the inflow flow controller (2,) the oxygenator inflow flow controller, or the outflow flow controller, or a combination comprising at least one of the foregoing, in response to a measurement from the inflow sensor, the oxygenator inflow sensor, the outflow sensor when present, or a combination comprising at least one of the foregoing; and a vacuum source downstream of the oxygenator.