Medical suction is an essential part of clinical practice. Since the 1920s, it has been used to empty the stomach, and in the 1950s, airway suction levels were first regulated for safety. Today, medical suction is used for neonates and seniors—and for patients weighing between 500 grams and 500 pounds. Medical suction clears the airway, empties the stomach, decompresses the chest, and keeps the operative field clear. It is essential that clinicians have reliable equipment that is accurate and easy to use.

Why a Safety Mindset Is Important

The current focus on patient safety extends to suction procedures and routines. When suction pressures are too high, mucosal damage occurs, both in the airway1 and in the stomach. If too much negative pressure is applied through a chest tube, lung tissue can be drawn into the eyelets of the thoracic catheter.2 Researchers are examining the connection between airway mucosal damage and ventilator-associated pneumonia. In pediatrics, airway suction catheters are inserted to a premeasured length that avoids letting the suction catheter come in contact with the tracheal mucosa distal to the endotracheal tube.3 Mucosal damage can also be mitigated with appropriate suction techniques, and every effort should be made to reduce this insult to the immune system of patients who are already compromised. Damaged airway mucosa releases nutrients that support bacterial growth,4 and Pseudomonas aeruginosa and other organisms are drawn to damaged epithelium.5,6 Mucosal damage in the stomach can result in bleeding and anemia as well as formation of scar tissue.

Physics of Suction

Flow rate is the term used to describe how fast air, fluid, or secretions are removed from the patient. Ideally, clinicians need the best flow rate out of a vacuum system at the lowest negative pressure. Three main factors affect the flow rate of a suction system:

  • The amount of negative pressure (vacuum)
  • The resistance of the suction system
  • The viscosity of the matter being removed

The negative pressure used establishes the pressure gradient that will move air, fluid, or secretions. Material will move from an area of higher pressure in the patient to an area of lower pressure in the suction apparatus. The resistance of the system is determined primarily by the most narrow part of the system—typically, a tubing connector—but the length of tubing in the system can increase resistance as well. Watery fluids such as blood will move through the suction system much more quickly than will thick substances such as sputum. At one time, it was thought that instilling normal saline into an artificial airway would thin secretions, enhancing the flow of secretions out of the airway, but research shows that no thinning occurs and that patients’ oxygenation drops with saline installation. Thus, the practice should be abandoned.7,8

Set a Safe Level

A nurse passing the bedside of an infant in the ICU saw blood inside the tube used for airway suction. After checking the child’s condition, it was evident that bleeding was not expected.

Further investigation determined the maximum level of negative pressure set on the wall regulator was -200 mm Hg, far more than recommended suction levels for infants. The nurse performing the suctioning did not occlude the tubing to set a safe maximum level of negative pressure (personal communication to Ohio Medical Corporation).

Increasing the internal diameter of suction tubing or catheters will increase flow better than will increasing the negative pressure or shortening the length of the tube. In most clinical applications, however, the size of the patient will be the key factor determining what size catheter can be safely used. Researchers at the Madigan Army Medical Center explored factors affecting evacuation of the oropharynx for emergency airway management. They tested three substances—90 mL of water, activated charcoal, and vegetable soup—with three different suction systems, progressing from a standard 0.25-inch internal diameter to a 0.625-inch internal diameter at its most restrictive point. All systems evacuated water in 3 seconds. The larger diameter tubing removed the soup 10 seconds faster and the charcoal mixture 40 seconds faster than the traditional systems. The researchers note that this advantage in removing particulate material can speed airway management and reduce the risk or minimize the complications from aspiration.9-11

Occlude to Set for Safety

Vacuum regulators are ever-present in the hospital setting. Clinicians use them daily and may not be as attentive to this equipment, what with the demands of monitors and devices alarming and competing for the clinician’s attention and time. Few clinicians learn the finer points of setting up suction systems. A nursing fundamentals text published in 200712 does not specify critical elements except to tell the nurse to follow manufacturers’ instructions. The text leaves out the critical, universal “occlude to set” step recommended by all North American manufacturers of vacuum regulators.

While a number of organizations have published guidelines, ultimately the clinician must determine the maximum allowable level of negative pressure that can be applied to the patient. This is determined by a number of factors: where the suction pressure is applied (airway, stomach, oropharynx, pleural space, operative field), the age and size of the patient, the susceptibility for mucosal or other tissue damage, and the risks associated with removing air during the suction procedure.

Once the maximum level has been determined, the vacuum regulator must be adjusted so that the maximum pressure is locked in; that is, the regulator must be set correctly so it will not permit a higher pressure to be transmitted to the patient. With traditional technology, the clinician must actively occlude the system by either pinching the suction tubing closed, or occluding the nipple adaptor (where the tubing is attached) with a finger. Once the system is occluded, the regulator is set to the maximum desired pressure; then the occlusion is released. If the system is not occluded during setup, the maximum pressure is then unregulated and can spike to harmful levels (see Figures 1,2).

Figure 1

Suctioning is a dynamic process. As catheters are used to remove substances from the body, the degree of open flow continually changes based on the fill of the catheter and the viscosity of the substance being removed. Under these dynamic conditions, the regulator continually compensates by adjusting flow rate within the device and the tubing to maintain the desired negative pressure. Periodically, mucus plugs or particulate matter will occlude the patient tube. If the system was not occluded to establish the maximum safe pressure at setup, pressure will spike to clear the occlusion, and once the occlusion passes, the patient will be subjected to potentially dangerous, unregulated vacuum pressures (see Figure 1).

Suction System Setup

  • Vacuum regulator
  • 12-inch connecting tube
  • 1500 cc (empty) collection bottle
  • 6-foot standard connecting tubing 14 Fr. Suction catheter

Figure 2.

Figure 1 illustrates results of a bench test of two suction systems. The systems were set up identically as noted in Figure 2. The desired maximum level of suction is 100 mm Hg (A). One system was set at 100 mm Hg with the system open to flow (red line); the other was set by occluding the system to set 100 mm Hg (green line). During open flow, the “occlude to set” system will have a lower pressure than the desired maximum pressure because there are no occlusions in the system (B). Once suctioning begins, a dynamic flow condition occurs with varying levels of obstruction, and pressure rises in both systems. The point of maximum suction is key. In the “occlude to set” system, the pressure never rises above the desired maximum pressure of 100 mm Hg. In the other system, pressure in this bench test spiked to 125 mm Hg of unregulated suction. Without “occlude to set,” the pressure can rise to 25% higher than the desired maximum level or more, exposing the patient to a safety hazard when regulated suction is needed.

Higher negative pressure is a particular hazard for patients with friable mucosa in the airway or stomach, making it more susceptible to traumatic tears. It is also a hazard for infants who have small lung volumes. When all other variables are stable, a 25% increase in negative pressure will increase the amount of air pulled through the system by 25%. That increase could result in a significant loss of lung volume in intubated neonates and infants.13

New Technologies Enhance Safety

An ideal patient safety device removes clinician variables as much as possible by providing the added safety passively while the clinician carries out the procedure. Traditionally, the optimal safety of regulated vacuum pressure has depended on the clinician’s action to occlude the system to set maximum pressure. New technology, an intermittent suction unit (ISU), occludes the system automatically when the clinician adjusts the pressure level. This creates an effective, passive safety system that removes the clinician variable and protects the patient from unintended, unregulated pressure spikes during suction procedures. The “push to set” option assures the clinician that the patient will not be subjected to pressure higher than that set on the regulator. Another key safety aspect of any vacuum regulator is the ability to quickly adjust to full vacuum mode when emergency strikes and rapid evacuation is essential. A dual-spring design of the regulating module contained within the vacuum regulator provides the clinician with the ability to control vacuum levels more precisely in the clinical range of 0-200 mm Hg as well as the ability to achieve full vacuum when needed with only two turns of the knob on the regulator. In other regulators, six or more knob turns are needed to achieve “full vacuum,” and “full vacuum” capability may be limited to the clinical range. Since full vacuum is needed in emergency conditions, this enhanced responsiveness saves time when seconds are critical. While vacuum regulators are often considered basic equipment in the hospital, research and innovation has shown vacuum regulators do have a role in enhancing patient safety in clinical settings. Clinicians should advocate for technology that provides passive safety protection, enhanced control of vacuum pressures, rapid response, and ease of use—all of which contribute to a culture of safety around the patient.

Patricia Carroll, RN, BC, CEN, RRT, MS, is the quality management coordinator at Franciscan Home Care and Hospice Care in Meriden, Conn. For further information, contact [email protected].


  1. Czarnik RE, Stone KS, Everhart CC, Preusser BA. Differential effects of continuous versus intermittent suction on tracheal tissue. Heart Lung. 1991;20:144-51.
  2. Duncan C, Erickson R. Pressures associated with chest tube stripping. Heart Lung. 1992;11(2):166-171.
  3. Altimier L. Editorial [Evidence-based neonatal respiratory management policy]. Newborn and Infant Nursing Reviews. 2006;6:43-51.
  4. Wilson R. Bacteria and airway inflammation in chronic obstructive pulmonary disease: more evidence. Am J Respir Crit Care Med. 2005;172:147-8.
  5. Dowling RB, Johnson M, Cole PJ, Wilson R. Effect of fluticasone propionate and salmeterol on Pseudomonas aeruginosa infection of the respiratory mucosa in vitro. Eur Respir J. 1999;14:363-9.
  6. Rutman A, Dowling R, Wills P, Feldman C, Cole PJ, Wilson R. Effect of dirithromycin on Haemophilus influenzae infection on the respiratory mucosa. Antimicrob Agents Chemother. 1998;42:772-8.
  7. Ackerman MH, Ecklund MM, Abu-Jumah. A review of normal saline installation: implications for practice. Dimens Crit Care Nurs. 1996;15:1531-8.
  8. Raymond SJ. Normal saline instillation before suctioning: helpful or harmful? A review of the literature. Am J Crit Care. 1995;4:267-71.
  9. Vandenberg JT, Rudman NT, Burke TF, Ramos DE. Large-diameter suction tubing significantly improves evacuation time of simulated vomitus. Am J Emerg Med. 1998;16:242-4.
  10. Vandenberg JT, Lutz RH, Vinson DR. Large-diameter suction system reduces oropharyngeal evacuation time. J Emerg Med. 1999;17:941-4.
  11. Vandenberg JT, Vinson DR. The inadequacies of contemporary oropharyngeal suction. Am J Emerg Med. 1999;17:611-3.
  12. Wilkinson JM, VanLeuven K. Fundamentals of Nursing: Thinking and Doing. Vol 2. Philadelphia: FA Davis Company; 2007.
  13. Morrow BR, Futter MJ, Argent AC. Endotracheal suctioning: from principles to practice. Neonatal and Pediatric Intensive Care. 2004;30:1167-74.