Assembly for measuring the flow rate of patient during mechanical ventilation, having: - a Y-shaped piece for connecting an inspiration branch from a ventilation machine and an expiration branch to a tube connector; - a first pneumatic resistance element in the inspiration branch and a second pneumatic resistance element in the expiration branch, and - a differential pressure sensor, characterised in that - the first pneumatic resistance element and the second pneumatic resistance element are monolithically integrated into the Y-shaped piece; - the Y-shaped piece contains, for each of its monolithically integrated pneumatic resistance elements, a fluid measurement outlet near the patient and a fluid measurement outlet remote from the patient, which are in fluidic connection with said Y-shaped piece, and additionally a centrally arranged fifth fluid measurement outlet, which each have a germ barrier device; - the Y-shaped piece is designed as a disposable unit; - the assembly has a separate electronics module which comprises the differential pressure sensor, a second differential pressure sensor, a pressure sensor, an evaluation unit connected to the pressure sensor and the differential pressure sensors, and pneumatic connecting lines, wherein the pneumatic connecting lines connect the pressure sensor and the differential pressure sensors in each case to fluid measurement inlets incorporated in a housing of the electronics module; - the electronics module is detachably connectable to the Y-shaped piece, wherein in the connected state a gas-tight connection is formed between the fluid measurement inlets of the electronics module and the fluid measurement outlets (3, 4, 5) of the Y-shaped piece; and - the electronics module is designed as a reusable unit. - a Y-shaped piece for connecting an inspiration branch from a ventilation machine and an expiration branch to a tube connector; - a first pneumatic resistance element in the inspiration branch and a second pneumatic resistance element in the expiration branch, and - a differential pressure sensor, characterised in that - the first pneumatic resistance element and the second pneumatic resistance element are monolithically integrated into the Y-shaped piece; - the Y-shaped piece contains, for each of its monolithically integrated pneumatic resistance elements, a fluid measurement outlet near the patient and a fluid measurement outlet remote from the patient, which are in fluidic connection with said Y-shaped piece, and additionally a centrally arranged fifth fluid measurement outlet, which each have a germ barrier device; - the Y-shaped piece is designed as a disposable unit; - the assembly has a separate electronics module which comprises the differential pressure sensor, a second differential pressure sensor, a pressure sensor, an evaluation unit connected to the pressure sensor and the differential pressure sensors, and pneumatic connecting lines, wherein the pneumatic connecting lines connect the pressure sensor and the differential pressure sensors in each case to fluid measurement inlets incorporated in a housing of the electronics module; - the electronics module is detachably connectable to the Y-shaped piece, wherein in the connected state a gas-tight connection is formed between the fluid measurement inlets of the electronics module and the fluid measurement outlets (3, 4, 5) of the Y-shaped piece; and - the electronics module is designed as a reusable unit.