What Is Medical Suction Measured In: Vacuum, Flow and Typical Settings

Vacuum: suction pressure in kPa, mmHg and mbar

Suction pressure is a negative pressure measured relative to the atmosphere. It appears in several units depending on country and manufacturer: kilopascals (kPa), millimetres of mercury (mmHg), millibar (mbar) and bar. The useful conversions are 1 kPa = 10 mbar = 7.5 mmHg, and 100 kPa = 1 bar = about 750 mmHg.

A reading is usually printed with a minus sign, such as −98 kPa. For example, the ATMOS Record 55 lists a maximum vacuum of −98 kPa (−980 mbar), and the ATMOS C 451 lists −91 kPa (−910 mbar). When a supplier quotes a suction pressure kPa figure and another quotes suction pressure mmHg, convert them before comparing.

• 1 kPa = 10 mbar = 7.5 mmHg
• 100 kPa = 1 bar = approximately 750 mmHg
• −90 kPa corresponds to about −675 mmHg

Flow: suction flow rate in l/min

Flow tells you how much air the pump can move, usually quoted as free air at the pump inlet. It determines how fast the unit clears fluid and how quickly vacuum recovers when the tubing opens. The ATMOS Record 55 is rated at 55 l/min and the ATMOS C 451 at 45 l/min.

A unit with high maximum vacuum but low flow will reach a high gauge reading when the tubing is clamped, yet clear a bleeding wound slowly. That is why a high vacuum high flow suction specification is the typical requirement for operating rooms, while drainage applications require the opposite.

Typical settings by application

Required vacuum depends on the application and is set by clinical protocol. In general, airway suction and OR suction use moderate to high vacuum with high flow; gastric suction often uses low, sometimes intermittent vacuum; chest drainage uses very low vacuum, measured in millibar; and neonatal suction uses reduced vacuum. See our guide on neonatal suction for the special case of newborns.

The maximum a unit can produce is not the setting you use. A good unit lets you set the working vacuum accurately and limits what can reach the patient, often through a regulator; see medical suction regulators. For the broader context of device types, read types of medical suction.

How standards classify suction equipment

ISO 10079 is the family of standards for medical suction equipment, and it classifies equipment by vacuum and flow as well as by power source. Equipment is typically described as high vacuum/high flow, high vacuum/low flow or low vacuum/low flow, with overflow protection and a bacterial filter among the safety requirements. Check the current edition of the standard and ask the supplier for the declaration of conformity; our article on ISO 10079 explains the points.

Neither figure alone describes performance. Ask the supplier for a curve or table showing flow at several vacuum levels, and for the test conditions, including tubing length and canister size.

How to specify suction when buying

Write the specification as a pair of numbers for each use: for example, minimum vacuum at the gauge, minimum flow at the working vacuum, noise limit and canister volume. Include the operating mode (continuous or intermittent), the mains frequency, and whether battery operation is required.

Compare real devices on the same basis, for instance the ATMOS Record 55 against the ATMOS C 451, and test with your own tubing. Confirm UAE registration and contact Beckfinity for a quote or consultation on specifying your suction units.