Normal Saline Instillation during Endotracheal Suctioning “Helpful or Harmful?”
A national survey of pediatric intensive care unit nurses indicated that virtually every nurse used a saline irrigant when suctioning (Swartz, 1996) while a recently published survey of ET tube suctioning routines in adult critical care units found that 74% of suctioning policies used normal saline for thick secretions (Sole ML et al, 2003). Likewise, a survey of practices in a large university hospital found that most respiratory therapists of 71% frequently instilled saline before suctioning, but a majority of nurses 64% rarely used it (Schwenker et al, 2004). These indicate that there is no standardized practice for saline installation but wide institutional and practitioner-dependent variations.
Since interventions are used to improve the patient’s condition, one would expect a pulmonary function to improve after suctioning with saline instillation, but studies suggest that pulmonary function after suctioning with saline instillation found no improvement (Reynolds et al, 1990). In addition, many studies in the adult and the pediatric intensive care population indicated that saline instillation has an adverse effect on oxygenation (O’Neal et al, 2001).
Another consideration is the potential to contribute to ventilator-associated pneumonia by instilling saline before the insertion of a suction catheter. Saline instillation may dislodge bacteria from a colonized ET tube, sending it down into the lower airway. Hagler (1994)suggested that 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.
It is a common rationale or indication for saline instillation before suctioning to thin or liquify thick/tenacious secretions but mucus cannot be mixed with saline even with vigorous shaking. The intention of thinning mucus to ease removal lacks supporting evidence, according to Ackerman (1996). One study found only 20% of the saline instilled is retrieved by suction (Hanley, 1978). Other research in neonates by Darlow et al (1997) and adults by Lerga et al (1997) found no difference in the amount of mucus retrieved through suctioning with and without saline lavage.
The mentioned studies point to an absence of positive effect from saline installation as it neither improves pulmonary function nor thin secretions or promote their removal. However, the practice persists despite a high risk for negative sequelae related to it, as well as lower oxygen saturation and increased potential for lower airway bacterial colonization.
Blackwood (1999) strongly suggest that a procedure that lacks research-based evidence to support it, has no proven benefit, and has a potential for harm should be abandoned.
Mucus is 95% water and becomes a semisolid similar to gelatin when formed and incorporates further liquid poorly (Connoly, 1995). There was no evidence found to support that NSI acts as a lubricant to facilitate secretion removal and researchers also found that: 1) no significant differences (Bostick, 1987); 2) statistically significant increases with NSI, but the differences were clinically insignificant and the studies failed to account for the weight of the saline(Gray et al, 1990); and 3) significant increases with an initial NSI in a small study (n=12) that did not demonstrate significant differences with a second suction episode (Reynolds et al, 1990).
A few evidence supports the fact that coughing loosens and dislodges thick, dried secretions and may increase the amount of secretions obtained with suctioning (Gray et al, 1990). Ackerman et al (1996) suggested that while coughing help propel secretions out of the airway, forceful bagging or inspiration by the patient combined with the potential shearing force of the saline, may move secretions lower in the airway. However, Hagler and Traver (1994) showed in a small study the in vitro ability of a 5 ml saline instillation to dislodge five times the number of bacteria from the inner lumen of endotracheal tubes during simulated suctioning than with a suction catheter alone (n=10).
References
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