Method for monitoring a measuring system for the artificial ventilation of a patient, wherein the measuring system comprises - a gas sensor arrangement and - a gas sensor fluid-guiding unit, in particular a hose, wherein the method is performed while, with the aid of a patient-side fluid-guiding unit, a fluidic connection between - the patient and - a medical appliance, in particular a ventilator or an anaesthesia appliance or a patient monitor, is established, and wherein the method comprises the automatically performed steps of a gas sample - being suctioned from the patient-side fluid-guiding unit and - being guided through the gas sensor fluid-guiding unit to the gas sensor arrangement, using measured values of the gas sensor arrangement to calculate - a measure of the time curve (CO2sk) of the concentration of carbon dioxide in the suctioned gas sample and - a measure of the time curve (O2sk) of the concentration of a further gas, different from carbon dioxide, which preferably comprises oxygen, in the suctioned gas sample, using the two time-related concentration curves (CO2sk, O2sk) to calculate - a measure (ΔCO2sk) of a time curve of the temporal change of the CO2 concentration and - a measure (ΔO2sk) of a time curve of the temporal change of the concentration of the further gas, searching for each same-sign time period, that is a time period in which the two concentration change curves (ΔCO2sk, ΔO2sk) have the same sign throughout, i.e. both are greater than zero or both are less than zero, and, if at least one such same-sign time period is detected, - checking whether the two concentration change curves (ΔCO2sk, ΔO2sk) meet a predefined first leakage criterion (DiPhaC) in the or at least one, preferably in each, detected same-sign time period, and, - if the first leakage criterion (DiPhaC) is met, concluding that a leakage has occurred between the patient-side fluid-guiding unit and the gas sensor arrangement or that an indication of such a leakage has occurred. wherein the measuring system comprises - a gas sensor arrangement and - a gas sensor fluid-guiding unit, in particular a hose, - a gas sensor arrangement and - a gas sensor fluid-guiding unit, in particular a hose, wherein the method is performed while, with the aid of a patient-side fluid-guiding unit, a fluidic connection between - the patient and - a medical appliance, in particular a ventilator or an anaesthesia appliance or a patient monitor, is established, and - the patient and - a medical appliance, in particular a ventilator or an anaesthesia appliance or a patient monitor, is established, and wherein the method comprises the automatically performed steps of a gas sample - being suctioned from the patient-side fluid-guiding unit and - being guided through the gas sensor fluid-guiding unit to the gas sensor arrangement, - being suctioned from the patient-side fluid-guiding unit and - being guided through the gas sensor fluid-guiding unit to the gas sensor arrangement, using measured values of the gas sensor arrangement to calculate - a measure of the time curve (CO2sk) of the concentration of carbon dioxide in the suctioned gas sample and - a measure of the time curve (O2sk) of the concentration of a further gas, different from carbon dioxide, which preferably comprises oxygen, in the suctioned gas sample, - a measure of the time curve (CO2sk) of the concentration of carbon dioxide in the suctioned gas sample and - a measure of the time curve (O2sk) of the concentration of a further gas, different from carbon dioxide, which preferably comprises oxygen, in the suctioned gas sample, using the two time-related concentration curves (CO2sk, O2sk) to calculate - a measure (ΔCO2sk) of a time curve of the temporal change of the CO2 concentration and - a measure (ΔO2sk) of a time curve of the temporal change of the concentration of the further gas, - a measure (ΔCO2sk) of a time curve of the temporal change of the CO2 concentration and - a measure (ΔO2sk) of a time curve of the temporal change of the concentration of the further gas, searching for each same-sign time period, that is a time period in which the two concentration change curves (ΔCO2sk, ΔO2sk) have the same sign throughout, i.e. both are greater than zero or both are less than zero, and, if at least one such same-sign time period is detected, - checking whether the two concentration change curves (ΔCO2sk, ΔO2sk) meet a predefined first leakage criterion (DiPhaC) in the or at least one, preferably in each, detected same-sign time period, and, - if the first leakage criterion (DiPhaC) is met, concluding that a leakage has occurred between the patient-side fluid-guiding unit and the gas sensor arrangement or that an indication of such a leakage has occurred. - checking whether the two concentration change curves (ΔCO2sk, ΔO2sk) meet a predefined first leakage criterion (DiPhaC) in the or at least one, preferably in each, detected same-sign time period, and, - if the first leakage criterion (DiPhaC) is met, concluding that a leakage has occurred between the patient-side fluid-guiding unit and the gas sensor arrangement or that an indication of such a leakage has occurred.