A patient support system comprises an inflatable mattress supported on a platform of articulable links by a support system mounted on a weigh frame. The weigh frame is supported on a base frame supported relative to a floor. A pneumatic system includes a platform-mounted blower directing air through passageways in the articulable links. An exhaust passageway parallels the pressure passageway for exhausting opposite the blower. Air flow into and out of air cells in the mattress are controlled by valves coupling the pressurized air chamber and exhaust chamber to cell ports. A connector assembly is used to couple the cells to the platform, to adjacent cells, and to tubes connected to other cells. A footboard assembly is formed as two gates that swing out from the foot of the bed. Each gate has a storable tray that is positionable on either side of the gate. A headboard has a removable central panel for providing emergency patient access. Additionally, each corner of the headboard has a telescoping equipment support post positionable at a variety of heights and having equipment supports that automatically drop into place upon removal from storage in the headboard. A three-point weight sensing system tracks patient weight and generates pre-exit and exit alarms based on sensed movement of the patient on the mattress. A portable control unit wraps around a guard rail to provide both patient and nurse controls, and uses a unitary membrane to cover exposed faces of the controls and resiliently wrap around the guard rail. Selectively engagable guide or fifth wheels are mounted to the base frame to provide direction stability during bed movement. The platform is articulable to allow a patient to enter or exit the bed in a standing position. An adjustable stand up board is selectively positionable at the foot of the bed to take the patient's weight during this process. A vertically telescoping guard rail elevation system provides energy storage to resist lowering and assist raising the guard rail. A brace is provided for seating the platform on the weigh frame when the bed is in a low position and to assist in movement of the bed longitudinally when in the low position.