Should Normal Saline be Used When Suctioning the Endotracheal Tube of the Neonate?

Mary L. Puchalski, MS, RNC, APN/CNS

Disclosures

March 14, 2007

Question

I have heard that it is not a good idea to use normal saline when suctioning endotracheal tubes in neonates, yet this is still widely practiced by both nurses and respiratory therapists. What is the latest evidence on this practice?

Response from Mary L. Puchalski, MS, RNC, APN/CNS

Historically, suctioning an endotracheal (ET) tube has been used routinely to remove pulmonary secretions that can block an endotracheal tube and impair air exchange in intubated patients of all ages. Patients who have experienced endotracheal suctioning describe it as profoundly unpleasant and even painful. One adult reported the experience as the "worst possible" -- a 10 of 10 -- on a pain rating scale. She described the experience of saline instillation as feeling "like she was drowning." Then the suction catheter would be "shoved" in until it made her cough against the ET tube, which she reported as "excruciating." Finally, "every bit of breath [she] had would be sucked out" (patient, personal communication, 2007).

Such a distressing and painful intervention should be performed with thought and discretion. What are the indications for suctioning? What is the expected outcome of the intervention? What might the possible negative effects and/or risks of the intervention be?

Before insertion of the suction catheter, some practitioners routinely instill a small amount of sterile normal saline (0.2 to 5 mL). The purpose of the saline is to "thin out" thick or tenacious secretions or to moisturize and loosen dried secretions within the ET tube to mobilize them and assist in their removal. The question is, does evidence exist to support the efficacy of using saline instillation, and should it be used when suctioning the endotracheal tube of the neonate?

A 1996 national survey of pediatric intensive care unit nurses found virtually every nurse used a saline irrigant when suctioning.[1] A recently published survey of ET tube suctioning routines in adult critical care units found that 74% of suctioning policies included the use of normal saline for thick secretions.[2] Another survey of practices in a large university hospital revealed that most respiratory therapists (71%) frequently instilled saline before suctioning, but conversely, a majority of nurses (64%) rarely used it.[3] It appears that there is no standardized practice for saline instillation -- just wide institutional- and practitioner- dependent variations.

There is a paucity of published research about saline instillation in neonates. In 1991 researchers found no difference in heart rate and blood pressure values when a small volume of saline was instilled.[4] A 1992 study with a very small sample size performed at a single institution found no deleterious effects of saline instillation in neonates with respiratory distress syndrome and meconium aspiration syndrome.[5] Nor did either of these studies identify any potential benefit of saline instillation.

Recently, researchers demonstrated markedly increased lung opening pressures in an infant animal model after saline instillation and suctioning, and identified a need to increase positive end-expiratory pressure to compensate for these changes.[6] A similar study found a greater decline in heart rate and greater alterations in arterial blood gas parameters in the normal saline instillation group.[7]

Since interventions are used to improve the patient’s condition, one would expect pulmonary function to improve subsequent to suctioning with saline instillation. Studies that examined pulmonary function following suctioning with saline instillation found no improvement.[8] Furthermore, multiple studies in the adult and the pediatric intensive care population demonstrate that saline instillation has an adverse effect on oxygenation.[9,10,11,12,13,14,15,16]

There also exists the potential to contribute to ventilator-associated pneumonia by instilling saline before insertion of a suction catheter. Saline instillation may dislodge bacteria from a colonized ET tube, sending it down into the lower airway.[17,18] The researchers found suctioning alone has the potential to dislodge up to 60,000 viable bacterial colonies and when 5 mL normal saline was instilled, up to 310,000 viable bacterial colonies were dislodged -- a 5-fold increased risk.

The common rationale or indication for saline instillation before suctioning is to thin or liquify thick/tenacious secretions. Unfortunately, mucus is not miscible with saline -- even with vigorous shaking, so the intention of thinning mucus to ease removal completely lacks supporting evidence.[19,20] In addition, one study found only 20% of the saline instilled is retrieved by suction.[21] Other research in neonates[22] and adults[23] found no difference in the amount of mucus retrieved through suctioning with and without saline lavage.

All of the scientific evidence suggests an absence of positive effect from saline instillation -- it does not improve pulmonary function, and it does not thin secretions or promote their removal. Yet the practice persists despite a high risk for negative sequelae related to it, including lower oxygen saturation and increased potential for lower airway bacterial colonization.

In answer to the question "should saline be instilled when suctioning the neonate?" there should be a resounding "No." A procedure that lacks research-based evidence to support it, has no proven benefit, and has a potential for harm should be abandoned.[24]

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