Hamilton G5 - Gas Monitoring with the Flow Sensor

1-12 624074/07
1 General information
Gas exhaled by the patient passes through the expiratory limb
breathing circuit parts, including flex tubes, the flow sensor,
the Y-piece, a humidifier or HME, and an expiratory valve cover
and membrane. Gas is vented through the expiratory valve
cover such that no exhaled gas comes into contact with any
internal components of the device. Measurements taken at the
flow sensor are used in the pressure, flow, and volume mea-
surements.
An oxygen cell (sensor) monitors the oxygen concentration of
the gas to be delivered to the patient, which is the same as the
reservoir concentration. This galvanic cell generates a voltage
proportional to the partial pressure of oxygen in the delivered
gas. Neither the pressure nor the humidity of the inspired gas
affects the oxygen measurement. The ventilator alarms if the
monitored oxygen concentration is more than 5% above or
below the oxygen setting, less than 18%, or more than 105%.
The mainstream/ sidestream CO
2
sensor continuously monitors
carbon dioxide and reports EtCO
2
and inhaled/exhaled CO
2
.
The SpO
2
sensor attached to the patient continuously monitors
the saturation of hemoglobin with oxygen in the blood and a
plethysmographic curve which is used to assess heart-lung
interaction. A second sensor may be used to secure the SpO
2
information.
The operations of the inspiratory and expiratory valves are
coordinated to maintain system pressure levels.
1.2.3 Gas monitoring with the flow sensor
The device accurately measures flow, volume, and pressure in
the patient’s airway with the HAMILTON MEDICAL flow sensor.
This proximal flow sensor lets the device sense even weak
patient breathing efforts. Between its highly sensitive flow trig-
ger and fast response time, the device helps minimize the
patient’s work of breathing.
The flow sensor contains a thin, diamond-shaped membrane
within the outer housing and has a pressure port on either
side. The membrane allows bidirectional flow through its vari-
able orifice (Figure 1-5).