Technical aspects of suction

Vacuum passes through wall outlets in most hospitals. This vacuum is usually produced by a pump in the basement of a hospital and is piped up to the outlets. Some hospitals depend entirely on portable units for their vacuum source, while others use a combination of piped suctioning and portable units.

Most piping systems function in a way that a receiver or reservoir tank located near the pump must be empty so that vacuum is always at the wall outlet. The pump automatically holds the desired vacuum in the receiver. A vacuum switch starts the pump when vacuum drops to a predetermined level and shuts it off again when the vacuum builds back up.

Virtually all new hospitals and many older ones have piped vacuum systems throughout the hospital to such areas as emergency room, operating room, recovery room, critical care unit, patient rooms and other areas. Suctioning available at each vacuum outlet can be used to perform most patient drainage procedures including pharyngeal aspiration, tracheal and surgical suctioning, gastrointestinal and wound drainage and pleural suctioning.

Basic Vacuum

The term "vacuum" means a space devoid of all gases, including air. This term is not usually adhered to, but is used to describe any degree of pressure less than standard atmospheric pressure of 14.7 phi or 760 mm Hg at sea level.

If a vacuum pump is attached to a closed tank and one-half of its contents are removed, the pressure within the tank will be reduced to half of the original pressure. The remaining air will expand to full occupancy of the tank volume. A subatmospheric pressure or vacuum will have been produced within the tank. If a small opening is made in the tank, so that it is open to the atmosphere, the air outside the tank at atmospheric (higher) pressure will flow into the tank which has a subatmospheric (lower) pressure. This movement of air causes "suction" at the tank opening and will continue until the air pressure in the tank is equalized with the one outside the tank.

The amount of suction exerted at any particular time is partly determined by the degree of negative pressure being applied. Pressures are measured in terms of gauge pressure. Gauge pressure is the pressure above or below ambient atmospheric pressure, indicated as zero on ordinary pressure gauges. The usual atmospheric pressure used as "zero" for calibration is 760 mm Hg (14.7 psi), the standard at sea level. Negative pressure is any amount of pressure less than atmospheric or zero on the pressure gauge. Vacuum can be more simply defined, then, as negative pressure, whereas suction is the application of negative pressure and relates to the movement of air, liquids or solids caused by negative pressure.

Measuring Vacuum Pressure

Negative pressure is measured in terms of the amount of vacuum force acting on a given area to lift liquid up a column to a certain height. It is generally indicated by the height of either mercury or water in inches, centimeters or millimeters. Both water and mercury columns are used to measure negative pressures and thus to standardize and calibrate mechanical vacuum gauges. Gauge pressure may, therefore, be expressed in both mercury and water units. A table of conversion factors is included as an aid to understand the differences between the terms used to measure the pressure.

The Rate of Flow

A major consideration in mechanical suctioning is a flow or rate at which air or liquid is removed from a patient. The rate of flow is determined by the amount of negative pressure produced by vacuum source together with resistance of suction apparatus, tubing and catheter, and viscosity of the matter being suctioned or aspirated.

If a collection bottle, suction tubing and catheter are connected to a suction regulator attached to a vacuum source, the vacuum, as the regulator is opened, is transmitted through the apparatus from the source to the end of the suction catheter. Thus, before there can be suction at the tip of the catheter, there must be a degree of vacuum in the collection bottle.

If the negative pressure in the collection bottle is increased, the flow through the tube will also increase. However, as flow increases there is a gradual change from laminar (streamlined) to turbulent flow. In most circumstances when turbulence occurs, the negative pressure in the collection bottle must be increased nearly four times in order to double the flow through the equipment.

Caution must be used in determining the amount of negative pressure applied to the patient. Only the minimum amount of negative pressure necessary to accomplish the suctioning procedure should be used. Where additional flow is necessary, changes in other suction variables may be applicable.

Besides the negative pressure, the resistance of the suction apparatus and the physical characteristics of the matter to be aspirated also affect the flow or rate of removal of fluids from the patient.

All vacuum adaptors, suction regulators and collection systems, because of their mechanical configuration, have a built in resistance to flow. Generally, this resistance to air flow is minimized by the manufacturer through the elimination of small holes and restrictive orifices. Some resistance is unavoidable; however, resulting in a decrease in flow as air passes through the apparatus.

When a length of tubing is added to a suction apparatus, resistance will increase and will result in a decrease in flow. The single most important factor affecting the resistance of the suction apparatus is the inner diameter of tubing, catheter, and catheter connectors. A large increase in flow can be accomplished more easily by increasing the amount of negative pressure. The diameter of tubing connectors must also be taken into consideration as a connector with a small orifice which can cause restriction to the flow. The tubing from the collection unit to the catheter should be as large in diameter and as short as possible. The increase in flow resulting from using a larger tube is far greater than the one resulting from using a shorter length of tubing.

Flow is greatly affected by the physical characteristics of the fluids being aspirated, i.e. viscosity and cohesion. When aspirated material enters the collection bottle, it no longer forms part of the resistance to flow. Using a short length of large I.D. tubing will cut out resistance from both the tube and the fluid. Fluids that are highly viscous are commonly encountered during tracheal suction. They are drawn into the suction catheter only by using an increased level of vacuum, and even then they resist flow by sticking to the tissue and the wall of the catheter and suction tube.

Suction Tubing

Clear tubing is recommended as it allows observing the materials passing through during suctioning. Disposable tubing avoids the possibility of cross-contamination from reuse. Because it is disposable, the need for cleaning and sterilizing is eliminated. Wall thickness of tubing should be adequate in order to avoid collapse when the tube is exposed to high negative pressures.

Abbott markets a clear disposable suction tubing. It can be ordered in either 24 in. length PVC suction tubing 0.3 in. (0.8cm) I.D. or 100 ft. roll PVC suction tubing 9.3 in (0.8 cm) I.D. List # for the 100 ft. roll of PVC tubing is 43455-0 (domestic) or E122 (international).

 

Clinical aspects of suction

Pharyngeal Aspiration

Suction is frequently used to remove excessive secretions from pharyngeal cavities. It is generally used to aid an unconscious patient, a patient recovering from anesthesia, or a critically ill patient. Pharyngeal suctioning is commonly needed in operating room, intensive care area, delivery room, recovery room, emergency room, nurseries and neurological nursing care unit.

Use of the following equipment is ordinarily indicated in pharyngeal suctioning: vacuum source, suction regulator, collection unit with shut-off valve, connecting tubing, "Y", "T" or fingertip flow control and catheter or tonsil tip suction unit.

A wide bore catheter is generally used to avoid causing excess restrictions to flow. Increased flow will result in quicker aspiration and less change of occlusion of the tubing. Catheters should be of the whistle tip type. It is suggested that a sterile catheter be used to avoid the possibility of cross-contamination. The degree of negative pressure used for pharyngeal suctioning is generally quite high in order to aid in quicker aspiration of secretions.

Although aspiration of the pharyngeal area should be performed as often as necessary, indiscriminate aspiration should be avoided as it may cause trauma of mucous membranes, or edema of soft tissues.

Tracheal Suctioning

Tracheal suctioning is used to clear the trachea or tracheobronchial tree of excess secretions and thus to maintain a patent airway in those patients who need assistance. Tracheal suctioning is deeper suctioning than pharyngeal, and is done either directly or through an endotracheal tube or tracheostomy cannula. As a specific example, tracheal suctioning may be used for post-operative care of thoracic surgical patients. It is also useful for post-anesthesia patients and for those in the intensive care unit who need artificial ventilation via endotracheal tube or tracheostomy cannula, and who cannot cough effectively. Tracheal suctioning is commonly used in operating room, recovery room, post-operative room, patient room and intensive care unit.

The procedures and precautions for tracheal suctioning are more stringent than those for pharyngeal aspiration. The following equipment is generally indicated for use: vacuum source, suction regulator, collection unit with overflow shutoff valve, connecting tubing, "Y", "T" or finger-tip flow control, and sterile catheter. Using the sterile catheter helps to minimize contamination and prevent systemic infection.

Never attach a suction system directly to an endotracheal or tracheostomy tube. When suction is applied in this way, the pressure in the lungs will fall until it reaches the maximum negative pressure of the suction system, resulting in severe, acute pulmonary distress and failure.

Negative pressure in the tracheobronchial tree can have several effects on the lungs. Lung volume can be reduced causing atelectasis. If trachea or endotracheal tube is completely occluded by the catheter, massive atelectasis can occur resulting in hypoxia and death. This danger can be minimized by utilizing large endotracheal or tracheostomy tubes, or the smallest suction catheter that will effectively suction the secretions, or by limiting the duration of suction to the actually required time. The use of "T" or finger-tip flow control allows for more complete control of the suctioning.

Even when a catheter is employed and the respiratory system is open to atmosphere, there is some fall in pressure in the lungs during tracheal suctioning. The total drop in pressure which develops in the lungs is dependant on how closely the catheter fits the endotracheal (or tracheostomy) tube. An exact fit will have the same effect as applying suction directly to an endotracheal tube; communication with the atmosphere will be shut off. Suction can be effective and safe only when air can flow down outside walls of a catheter in a volume sufficient enough to prevent too great a negative intrapulmonary pressure.

Thus the size of the catheter used for tracheal suctioning is very important. As the size of the suction catheter is increased, the negative pressure in the lungs may increase. The diameter of the catheter should not be so small as to severely restrict flow; yet it must be small enough to fit into endotracheal tube while leaving an airway. A rule of thumb means that the outside diameter of the catheter should be no greater than ½ of the inside diameter of the endotracheal or tracheostomy tube.

The amount of negative pressure needed during tracheal suctioning is dependent on a number of factors, including diameter of the catheter and physical properties of the secretions to be removed. The minimum amount of vacuum necessary to draw secretions into the collection bottle should be used. Various references suggest a range of 80 to 175 mm Hg. In case of exceptionally thick secretions, higher pressures may be needed.

 

Types of suction procedures

Gastrointestinal suction

There are several situations in medicine which call for use of gastrointestinal suction; the primary purpose of which is the evacuation of semi-solids, liquids and gases from the stomach and intestinal tract.

Main reasons for gastric or intestinal suction are to remove accumulated gastric contents (air or liquids), to prevent build up of gastric contents, and to prevent the accumulation of swallowed air. Gastrointestinal suction is commonly used in both medical and surgical wards as well as in the intensive care unit and emergency room. If applied haphazardly and without proper precautions, gastrointestinal suction can have detrimental effects. Mucous from specialized mucosal cells lining the gastrointestinal tract protects the underlying tissue from the otherwise erosive effects of acidic secretions and enzymes secreted in the normal digestive process. As suction is applied to the stomach and the contents are removed, the stomach tends to collapse around the suction tube. The entry hole in the suction tube may draw itself toward the tissue surface as the stomach collapses, resulting in steady suction on one spot of the stomach lining. Not only does this block the drainage tube allowing secreted fluids to accumulate in other areas of the gastrointestinal tract, but also excessive suction on one spot of the stomach wall may wear away the mucosal lining and cause ulcerations, hemorrhage, or perforation at the spot.

Intermittent suction can minimize damage to the gastrointestinal mucosal lining, and blockage of the catheter tip, should it become drawn against the intestinal wall. During one full cycle of intermittent suction, the catheter tip will drop away from the wall as the suction is reduced to atmospheric pressure for a predetermined and, in some cases, adjustable interval. In addition, intermittent suction can provide a measurably more efficient means for draining the cavity of non-homogenous matter than does the continuous drainage method. Gastrointestinal suction apparatus should therefore provide moderate intermittent vacuum wit low flow rates.

The prominent American surgeon, Wangensteen, developed a three bottle, water displacement suction apparatus. The force of the water flowing from the top bottle into the bottom bottle (due to the pull of gravity) produces mild suction. The amount of negative pressure can be adjusted by increasing or decreasing the distance between the two bottles.

Another type of gastrointestinal suction device is a portable thermotic pump. It is a non-mechanical, electrically powered unit which operates on the principle that air expands and contracts when subjected to variations in heat. A volume of air in the enclosed space is heated, the air expands and some of it escapes through one-way valve. The heating cycle stops, allowing the air in the closed space to cool and thus contract creating a subatmospheric pressure. The thermotic pump provides interrupted suction (due to the "on" and "off" of the heating cycle), however, the pressure in the apparatus does not return to atmosphere during the "off" cycle. This type of unit cannot be adjusted for various negative pressures, but is limited to a low of approximately 90 mm Hg, and a high of approximately 120 mm Hg.

A specialized gastrointestinal vacuum regulator used with a central pipeline vacuum system provides a relatively simple, compact apparatus for gastric suction. This type of setup generally has few connections, while offering sometimes desirable feature of intermittent (or at least interrupted) suction.

In order to take advantage of hydraulic push action, available with intermittent suctioning, the collection receptacle must be located above the level of the patient. If fluids are pulled up the tube by suction, gravity will tend to pull them back toward the patient when suction is released. If the collection bottle is placed at a level below the patient, a siphon action will develop resulting in continuous rather than intermittent suction.

When the collection receptacle is located above the patient, a greater amount of vacuum is required to lift the liquid up the tube than would be required of a continuous suction system where the collection bottle is on the floor. The chart in Appendix X indicates approximate increases in gauge pressure corresponding to the height of the collection bottle above the patient. Generally, some medium (80 to 120 mm Hg) negative pressure vacuum setting plus approximately 20 mm Hg negative pressure is adequate. Hospital personnel would use only as much vacuum as is required to bring fluids up the tubing and into the collection bottle.

If the collection bottle is located 18 inches above the patient, it will require 34 mm Hg negative pressure to lift water up the suction tube and into the collection bottle. If 90 mm Hg vacuum is prescribed for use, 3 mm Hg should be added to the negative pressure setting so that it reads approximately 124 mm Hg negative pressure. As long as liquid completely fills the tubing, the patient will not receive more than 90 mm Hg vacuum. Since ISU (intermittent suction unit) is adjustable on either the constant or intermittent mode throughout the range of 0 to 200 mm Hg, there should be no problem in achieving the desired level of negative pressure.

The collection receptacle may be used at a level lower than the patient. The ISU will cycle "on" and "off", but because of the siphon effect that develops, the flow into the bottle will be continuous rather than intermittent.

A wide variety of gastrointestinal tubes of special design and purpose are available. These range in size from 12 to 18 French. Size 14 French is most frequently used for the adult patient. (See Appendix X)

When setting up the gastrointestinal suction apparatus, be sure there is no draping of the connection tubing between the collection receptacle and the patient. The length of tubing should be as short as possible, since longer tubing will cause greater restrictions to flow.

Occasionally during intermittent suction, liquid will travel only part way up the tubing during each "on" cycle. Reasons for this include:

  • The negative pressure may not be high enough to lift the liquid all the way up the tube and into the bottle.
  • The stomach may be completely drained of liquid, in which case the system should be irrigated in order to determine if the stomach is in fact empty.
  • There may be more solid than liquid in the stomach causing some blockage of the tubing. In this situation, it is commonly observed that the material rises a little closer to the bottle with each "on" cycle.

Pleural suctioning

The main objectives of thoracic drainage are reduction of pneumothorax and the removal of blood and exudate, both resulting in expansion of the lung. Air may enter the thoracic or pleural cavity through the chest due to a surgical opening of the thorax, or an accidental chest wound. A pneumothorax (presence of air or gas in the pleural cavity) can also be the result of leakage of air through the lung caused by a ruptured bleb or by a puncture of the lung due to some type of wound, such as a fractured rib or a surgical opening. Fluid within the pleural cavity may also be caused by a variety of diseases or thoracic injury.

If air, blood, or other fluids get into the intrapleural area, they cause the lung to collapse. A slight negative pressure must be maintained in the pleural cavity as negative intrapleural pressure is essential for normal respiratory function. The purpose of thoracic drainage is to remove both fluids and air from the chest, allowing the lung to re-expand while maintaining negative pressure in the pleural space. It is commonly used in critical care areas, recovery room and patient room.

Sometimes ordinary water seal drainage will suffice in bringing about proper re-expansion of the lung since air and fluid will leave the pleural cavity during the exhalation phase of respiration, but the re-entry of air during inspiration is prevented by the water seal. In cases where significant air leaks are present, it may be necessary to assist the water seal drainage with mechanical suction. This is guaranteed when there is a continuous movement of air into the chest as it is possible from a spontaneous pneumothorax, puncture wound of the chest, or an open surface following partial transaction of the lung. Excessive fluid production within the pleural cavity may also necessitate mechanically assisted pleural drainage. If suction is applied when there is no leakage of air into the chest, the drainage tube may adhere to the lung, thus occluding the tube opening and preventing drainage. This danger is minimized by the use of multiple hole catheters.

Excessive negative pressure in the pleural cavity may prevent normal sealing of ruptured or torn alveoli. An accurate pressure limiting device is necessary for thoracic suctioning. The normal range of negative pressure in the intrapleural area is 5 to 20 cm H2O. This range in pressures is generally used as a guide in determining the amount of pressure applied to the patient.

The apparatus for thoracic drainage may employ as many as three receptacles; underwater seal receptacle, collection receptacle and vacuum regulation receptacle. The underwater seal receptacle and the collection receptacle are used with or without suction; the vacuum regulation receptacle is needed when suction is applied to the system.

The underwater seal receptacle can be used alone. It then serves both as an underwater seal and a collection receptacle. It has a tight fitting cap containing two hollow tubes; a short one, which extends about one inch into the receptacle, and a long one, which extends almost to the bottom of the receptacle.

The receptacle is partially filled with water to a level of 2 cm above the bottom of the long tube. The tubing running from the patient's chest is connected to the long tube in the underwater seal receptacle. This set-up works as follows: as the chest is contracted due to expiration or coughing, air and fluids are forced through the drainage tube which extends beneath the water in the bottle. During inspiration the negative intrapleural pressure increases and water is sucked partially up the drainage tube. The water will only be drawn up the tube to a height equal to that of the negative pressure in the chest. The receptacle should be placed at a level somewhat below the level of the patient's chest so that there is no possibility of water in the tube being risen high enough to be drawn into the chest cavity. The water will provide a seal to prevent air from re-entering the intrapleural area. The depth of the water in the bottle must be adequate for the fluctuation of water in the tube. When, during inspiration, the water in the tube rises, the bottom of the tube must remain immersed in the water to maintain the seal.

As fluids drain from the chest, the level of the fluid in the underwater seal receptacle will rise. As the height of the fluid in the receptacle increases, the amount of pressure required in the pleural cavity to force down the level of fluid in the underwater drainage tube will also increase. For this reason, a collection receptacle is usually placed between the patient and the underwater seal receptacle. The collection receptacle has a tight fitting cap containing two short tubes. One tube is connected to the patient tubing and the other to the long tube in the underwater seal receptacle. Fluid flows out of the tubing and drops off into the collection receptacle. The air continues into the underwater seal receptacle which, due to the fact that the system is closed, functions in the same manner as it did when used alone. Use of the collection receptacle allows an accurate measurement of the fluid drainage. Also, the characteristics of the aspirated fluid become visible.

When air is continually leaking from the lung, suction may be added to the drainage apparatus. Suction keeps the negative pressure in the pleural cavity and removes fluid and air more rapidly. A vacuum regulation receptacle is added to the two bottle system when suction is used. It is connected to the vacuum source and is used to maintain very low negative pressure (-5 to -30cm H2O). The cap of the third receptacle has three tubes running through it; two short ones and a long one which extends down the middle of the receptacle. One short tube is connected to the short tube in the underwater seal receptacle, and the other is connected to the suction source. The long tube is open to atmosphere and extends into the water in the receptacle. If the long tube is inserted 10 cm into the water, the suction regulation bottle will allow only 10 cm H2O negative pressure to pass through the system. As suction causes the negative pressure inside the receptacle to increase, the fluid in the long tube descends. This happens because the air above the water in the tube at atmospheric pressure is pushing the fluid into the receptacle which has a sub-atmospheric pressure. When the negative pressure becomes equal to 10 cm of water, the water level in the long tube has descended and reached the bottom of the tube. When the negative pressure exceeds 10 cm of water, air is sucked trough this tube into the system, bubbling up through the water. The negative pressure within the regulation receptacle, and therefore throughout the entire system, cannot exceed 10 cm of water. There should be relatively slow constant bubbling in this receptacle as an indication that the negative pressure is being maintained at 10 cm H2O.

The third receptacle will control negative pressure at any preset level. For instance, if the long tube is extended 20 cm in to the water in the receptacle, the negative pressure within the receptacle will not exceed 20 cm H2O.

Except where the long pressure regulation tube is open to the atmosphere, the entire three bottle system must be air tight in order to function properly. See the RECEPTASEAL® manual for more information on pleural suctioning.

Surgical suction

Suction is essential in operating room and delivery room. It is used to keep the operating field clear of blood, secretions and other materials. At the same time pharyngeal and tracheal suctioning may be performed by an anesthesiologist in order to maintain a patent airway. At the completion of surgery, tubes (gastrointestinal, pleural) may be inserted for postoperative drainage. These are frequently tested before the patient is sent to the recovery room.

All areas of a hospital, especially the operating room, should utilize large bore tubings and suction system fittings to avoid compromising flow rate. Since some operative procedures yield large liquid volume production in short periods of time, the suction system must be able to remove accumulated fluid quickly. Small bore catheters are incapable of performing this task.

Sump tubes are used to keep the surgical site free of accumulatory fluids when production is continuous and very slow. Yankauer-type suction tips are used to clear surgical sites of acute fluid production. Pressure regulated suction flow can be diverted through a catheter or suction tip by using a fingertip flow control. Once the regulator is set at a predetermined suction level, the person using the system can have suction supplied to the catheter tip by placing his/her thumb over the flow control opening. When used with a catheter, one hand holds the flow control valve, while the other controls placement of the catheter. When the control valve is used with a Yankauer-type suction tip, the flow control is built into the handle of the tip, allowing one hand operation.

The collection receptacle for surgical wound drainage should be placed on the floor as close to the patient as possible, instead of placing it on the wall above the patient level. This eliminates the need for additional negative pressure that would be required to lift materials up into the receptacle. Also, placement of the collection receptacle on the floor reduces the possibility of occlusion of the tubing. It is recommended that a shutoff valve be used with the collection receptacle as protection against seepage of fluids into the system.

Maintenance of suction equipment

Routine maintenance and inspection are important to the performance of suction apparatus. Good suction is dependent upon clean equipment. Even the best vacuum pump will be made useless with clogged vacuum accessories.

Every hospital should have a preventive maintenance program for their suction systems to preclude costly breakdowns and keep their equipment at peak efficiency. Inefficient operation of a suction system usually develops as a result of aspirated fluids getting into the system which is often caused by:

  • Failure of protective valve, or trap bottle, that prevent fluid from entering the system. Over a period of time, even though the valve or trap bottle may not fail, airborne vapor which condenses in the vacuum line can result in an occlusive buildup.
  • In case glass bottles are being used, inadequate washing plus inadequate cleaning of tubing, metal connectors, etc., because it does not result in removal of all organic material, can contribute to the buildup.

Often connection adaptors, line valves, etc., become partially occluded with lint or other debris which, over a period of time, can contribute to ineffective suctioning. We have found that placing an air filter in the vacuum line at problem locations can usually prevent, or at least slow down, the accumulation of such debris.

All sales districts have been furnished with vacuum flow detector equipment which our representatives use in assisting hospital staff to detect areas of restriction in vacuum lines. The American Compressed Gas Association has published acceptable flow rates for vacuum outlets. This is included in the maintenance section of the manual.

For further information please refer to the section of Maintenance of Suction Equipment.

Vacuum

Vacuum is defined as the difference between atmospheric pressure and subatmospheric pressure, created by a vacuum-producing device such as a vacuum pump.

By convention, pressures lower than atmospheric pressure are called negative.

Strictly speaking, the term vacuum means that a chamber is devoid of all gases, including air. Hence, the traditional vacuum bottle is one that has all of its gases pumped out of it, even molecules of air.

The maximum amount of negative pressure a vacuum pump can produce is -1.0 atmosphere, or 760 mm Hg (29.2 in Hg) when measured by a vacuum gauge. Once molecules are removed totally from space, it is not possible to remove anything else. Hence, it is impossible to remove more than one atmosphere when creating negative vacuum pressures.

Negative vacuum pressures are generally expressed as millimeters of mercury (mm Hg) or inches of mercury (in Hg). Thoracic gauges, used for low suction procedures, are frequently scaled in cm H2O.

Suction

Suction is defined as the flow of air or fluid, and in some cases solids such as clots and tissue, through suction tubing. Flow has been created by lowering the pressure at one end of the tube. Hence, the drawing below illustrates how room air flows into the end of patient tubing when vacuum is applied.

Suction is the clinical use of flow rates generated by vacuum systems.

Flow rate

Flow rate refers to how fast vacuum pressures draw fluids and air into collection vessel systems during suctioning procedures. Air flow rates are generally expressed in standard cubic feet per minute (SCFM) or in liters per minute (L/min). Fluid flow rates (e.g. blood or normal saline) are generally expressed in milliliters per second (ml/sec).

Free air flow is the maximum flow of air into a vacuum producing device. For all practical purposes, free air flow can be measured at the wall or column outlet to determine the maximum flow rate potential of the vacuum system at a particular location in a hospital. This should be done prior to adding restrictive elements such as regulators, canisters, connectors, adaptors, tubing, wands, etc. The restrictive effect of these elements can be measured individually as they are added to the collection vessel system, and then, if necessary, modified in order to improve flow rates.

If a regulator is necessary to access the central vacuum system, and it appears that the regulator itself may be restricting the flow rate, replace the regulator with one from another outlet and determine if the flow rate increases. If it does, the original regulator may need to be cleaned or serviced. Other regulators may need to be checked to confirm your findings.

Resistance

Resistance causes reduction in flow rates and prevents maximum flow potential from being achieved. Simply speaking, too much resistance may compromise the functional efficacy of a suction collection system to the point where potentially life-threatening situations in clinical setting could occur.

Four basic factors contribute to resistance:

  • inside diameter
  • friction
  • tubing length
  • fluid density

Practically speaking, resistance is caused by clogged tubing adaptors and/or regulators and outlets; collapsed or pinched tubing; small bore tubing; small bore connectors and adaptors; and tubing that is too long. A tortuous flow path through the complete suction system may also restrict flow rates.

By far the most influential factor affecting the resistance of a suction system is the inner diameter of its individual components. An increase in flow rate can be accomplished easily by increasing the inner diameter of various parts of the system. In effect, clogged tubing results in a reduced diameter, which in turn reduces flow rate. Therefore, it is critical that connectors, adaptors, tubing and regulators be kept clean and free of restricting debris.

The type of flow commonly occurring in suction collection systems is turbulent as opposed to laminar. Turbulence results primarily from mixing the air and aspirate during the suctioning procedure.

In general, when tubing length is halved, flow rate increases almost one and one-half times (1.41X). From the data in Table 5. users could increase suction flow rates by as much as 12%, if 16' lengths of tubing were used instead of 20'. If 12' lengths could be used, a 29% increase in flow rate would be realized, so long as all other factors were held constant.

By increasing the diameter of tubing and connectors, as well as shortening the length of tubing used, one can begin to optimize the flow rate potential of a suction collection system.

The density of fluid being aspirated also affects flow rate. The more dense and viscous the fluid, the slower the flow rate will be. Since practitioners rarely have control over the type of fluids being aspirated, this factor of resistance is less manageable.

Clinical considerations

High Negative Pressure/High SCFM

This condition represents optimum condition in clinical setting. A high negative pressure reading (over 300 mm Hg) indicates a properly functioning vacuum system, capable of providing high levels of negative pressures and flow rates when needed. It also demonstrates a distinct absence of significant air leaks in the vacuum system. Vacuum leaks reduce the maximum vacuum potential of a suction system.

High SCFM, or free air flow, indicates that suction system's components (connectors, adaptors, tubing, regulator, suction container itself) are not restricting free flow of air or, in clinical setting, of fluid.

High Negative Pressure/Low SCFM

This condition indicates that while the hospital's vacuum system is functioning properly, the elements or components comprising the suction collection system are restricting free air flow. Areas to examine during servicing would include:

  • pinched or crimped tubing
  • clogged tubing
  • tubing diameter too small
  • collapsed tubing
  • tubing too long
  • adaptors clogged
  • adaptor orifice too small
  • regulator clogged
  • regulator orifice too small
  • outlet clogged
  • outlet orifice too small

Examine each element or component of the complete suction system. Replace pinched or clogged tubing, clean out adaptors, and insure that nothing impedes the free flow of air into the system. If you suspect that the regulator or the outlet are clogged, or that the orifices are too small, contact Maintenance Department personnel and recommend appropriate measures to be taken in order to improve flow rate. Do not clean or otherwise temper with regulators, or wall outlets, without express permission of Maintenance Department personnel.

Low Negative Pressure/Low SCFM

This negative condition is unacceptable for most clinical situations. The primary difficulty may be an improperly functioning central vacuum system, portable pump or defective gauge. Be certain the regulator or gauge is open to FULL vacuum and then determine whether or not the low SCFM condition is being caused by the items in the troubleshooting list shown above. If the suction system is "restriction free", the problem lies with the vacuum source, defective gauge, or regulator, and should be reported to Maintenance Department personnel.

A defective regulator or gauge could be set at FULL vacuum and still leak enough to compromise vacuum potential. To check for defective gauges and regulators, follow the same procedure outlined earlier under the section entitled RESISTANCE. The Compressed Gas Association recommends a minimum vacuum of 15 inches (381 mm Hg).

Recommended Flow Rates by Procedure Area

Table 6 lists the recommended SCFM flow rates by department location within a hospital. "Simultaneous Usage Factor" indicates the level of SCFM recommended when all vacuum outlets in a room or on a "per bed" designation are being used at the same time. For example, if an operating room has four outlets, each outlet should be capable of transporting 100% of the recommended SCFM, even if all are being used at the same time. On the other hand, if two outlets per bed in recovery are used simultaneously, 50% of the recommended SCFM is permissible. This table is prepared and published by the Compressed Gas Association, Inc., Arlington, VA, which provides recommendations for medical surgical vacuum systems in health care facilities throughout the United States.

Using the vacuum gauge / rotometer instrument

The Sorensen vacuum gauge/rotometer instrument is an expensive and delicate piece of equipment. It is designed to measure the amount of flow and vacuum at any given point in a suction system. While the gauge and rotometer are carefully calibrated at the factory and provide accurate readings, the instrument is not designed nor intended to calibrate or certify hospitals' central vacuum systems.

The vacuum gauge/rotometer instrument is useful in diagnosing sources of restriction and broken or leaking connectors and adaptors. It is helpful in identifying the cause of low vacuum and/or low SCFM flow rates. Appropriate repairs or cleaning can then be carried out to bring the vacuum system back to a more favorable operating condition.

Carefully remove the vacuum gauge/rotometer instrument from its foam rubber carrying case. Remove the protective cap from the rotometer tapers and store them in the case until finished using the instrument. Protective caps should always be replaced after use in order to prevent dust, lint and other particles and debris from getting inside the instrument. Build up of foreign debris could eventually compromise the functional efficacy of the instrument.

Using the connective tubing provided in the kit:

  • Connect the universal connector to the top male taper on the rotometer.
  • Place the elbow over the male taper on the bottom of the hospital's regulator or gauge, or on the patient port of the suction canister. If desired, SCFM may be measured at the end of the patient tubing by utilizing List Number 43473-01 (TTP14).
  • Open the hospital's vacuum regulator or gauge to FULL vacuum.
  • Read the SCFM flow rate off the rotometer scale.

The SCFM reading indicates how well air is flowing through the suction device in its present configuration. It also gives an indication of how well the suction apparatus will function in a clinical setting. If the SCFM reading is low, then clinicians could reasonably expect the apparatus to have a lower capability of suctioning aspiration.

Deadhead negative pressure, or a vacuum potential of a hospital central vacuum system, can be determined by hooking up the vacuum gauge/rotometer instrument in the same fashion as if measuring SCFM. With the vacuum gauge or regulator set at a FULL position, occlude airflow by placing your finger over the end of the male taper at the bottom of the rotometer. The ball in the rotometer will drop immediately since air is no longer flowing through the system. The needle on the gauge, however, will start to rise, indicating negative pressure build up. When the needle comes to rest, the reading on the scale will reflect the maximum vacuum potential of the system. If a defective gauge or regulator is suspected, substitute a gauge from another outlet to verify deadhead pressure. If the substitute gauge reads the same, the original gauge is probably not defective. Defective gauges should be reported to Maintenance Department personnel. Several factors affect the vacuum potential of a hospital's central vacuum system. Almost all central vacuum systems have a backup pump which "kicks in" when the vacuum potential of the primary pump drops below the set level of the negative pressure. When the secondary pump "kicks in", an increase in negative pressure occurs and returns the vacuum potential of the system to its desired level. The deadhead negative pressure level should be noted on the Sorensen Suction Service Report Form. Generally speaking, deadhead pressure will be over 300 mm Hg. In instances where it is less than 300 mm Hg, it will be necessary to determine whether or not the gauge is defective, or whether or not hardware and fittings are loose, therefore compromising the vacuum potential of the system. Only under extremely high levels of negative pressure, generally over 500 mm HG, will the needle on the gauge rise above zero in the open position.

Cleaning vacuum equipment and lines

If aspirate is inadvertently drawn beyond a suction collection vessel, then build up of blood, body fluids, and other exudates frequently restrict flow rate by decreasing the diameter of the various connecting lumens within the fittings or within the gauge itself.

The Sorensen Suction Service Kit contains a bottle of Freon – a non-volatile, general purpose cleaner – which is effective in dissolving and removing foreign material generally found in suction apparatus. An equally effective cleaner is hydrogen peroxide which can be purchased at nominal cost from most drugstore pharmacies. Freon is used within the electronics industry to clean tape heads and other electronic equipment. It can be purchased at most electronic supply houses. The cost is considerably higher, however, if purchased through retail outlets such as Radio Shack.

If hydrogen peroxide is chosen as the cleaner, the translucent bottle in the Suction Service Kit should be wrapped carefully with adhesive tape to block out light. When exposed to light, hydrogen peroxide breaks down into oxygen and water. Thus cleaning efficacy of hydrogen peroxide is reduced if exposed to light for any length of time.

Also included in the Sorensen Suction Service Kit is a long, extra large pipe cleaner for use in cleaning debris from fittings and adaptors. Additional pipe cleaners may be purchased through almost any arts and crafts store at nominal cost. The Company will not supply additional pipe cleaners or cleaning solvent.

For effective cleaning:

  • Apply Freon or hydrogen peroxide generously to the pipe cleaner.
  • Push the pipe cleaner back and forth through the various connectors and adaptors, as well as into the orifices found on the gauge or regulator.
  • Do not insert used pipe cleaner back into the cleaning solution since doing so could contaminate the solution and render it less effective as a cleaning agent. The bottle cap is designed to function as an applicator and should be used to saturate the pipe cleaner.

To clean vacuum lines:

If vacuum lines, outlets or regulators and gauges appear to be clogged, contact the Maintenance Department and recommend that the equipment be flushed with cleaning solution. Cleaning solutions for vacuum lines can also include a 50% mixture of vinegar and hot water, as well as the two solutions mentioned above. Follow the steps below for cleaning hospital vacuum lines.

  • Check to see that the central vacuum system has a trap tank or container to prevent fluid from running into the pump. Insure that the trap is empty, or at least low enough, to be capable of holding the volume of fluid to be flushed through the lines.
  • Dilute the hydrogen peroxide or vinegar solution with hot water by filling an EZE-VAC canister half full of water and half full of the cleaning agent. More concentrated mixtures may be used if necessary.
  • After removing the gauge or regulator, run a length of vacuum tubing from the male portion of the quick disconnect outlet device into the cleaning solution. Engage the quick disconnect device into the wall outlet and suction the cleaning solution through the system. While suctioning the fluid, jerk the tubing in and out of the solution to create turbulence. Turbulence helps break dry blood and other body secretions which may be deposited inside the vacuum line.
  • When the entire amount of solution has been flushed through the line, check the flow rate of the vacuum system with the vacuum gauge and rotometer instrument to determine the degree of flow rate improvement. If improvement is negligible, repeat the exercise. The same cleaning solution may be drained from the trap near the central vacuum system pump and reused. Continue flushing the lines until flow rates return to favorable operating conditions.

With respect to regulators and gauges, cleaning solution should not be run through since most of the internal workings are made of brass which corrodes if an acidic cleansing solution is used (such as vinegar, acetic acid), or oxidizes if an alkaline solution, such as hydrogen peroxide, is used.

Cleaning Canister

Canisters can be cleaned with any commercially available cleaner. The canisters are made of lexan (the material used for airplane windows). Betadine or any cleaner with a tint in it could conceivably discolor the canisters over a long period of time. When cleaning canisters, be sure to clean out the inside of the yellow canister tee. If you autoclave the canister with dirt in the tee, it will only bake it on.

Canisters should be checked for cracking around the yellow tee or what is called "starring". If this occurs, vacuum inside the canister will be lost and the liner will not stay inflated.

When cleaning or installing canisters, always check the yellow tee to make sure it is screwed in tightly.

Also always check the top rim of the canister to make sure it is smooth. If it is notched or cracked, the liner lid will not snap in smoothly, and the liner will not stay properly inflated.