Endotracheal suction in intubated critically ill adult patients undergoing mechanical ventilation : a systematic review

Oliveira Favretto, Débora; de Campos Pereira Silveira, Renata Cristina; Marin da Silva Canini, Silvia Rita; Garbin, Livia Maria; Titareli Merízio Martins, Fernanda; Barcellos Dalri, Maria Célia Aspiração endotraqueal em pacientes adultos com via aérea artificial: revisão sistemática Revista Latino-Americana de Enfermagem, vol. 20, núm. 5, septiembre-octubre, 2012, pp. Tela 1-Tela 11 Universidade de São Paulo São Paulo, Brasil


Introduction
Endotracheal suction is a procedure which aims to keep airways patent by mechanically removing accumulated pulmonary secretions, above all in patients with artificial airways (1) .
Despite being a necessary procedure, it can lead to complications, such as lesions in the tracheal mucosa, pain, discomfort, infection, alterations of the hemodynamic parameters and of the arterial gases, bronchoconstriction, atelectasis, increase in intra-cranial pressure, and alterations in cerebral blood flow, among others (1)(2) .
Considering this procedure's complexity, a prior evaluation of the need for suction is indispensable, as this is an invasive, complex procedure that must be undertaken by judicious indication, as it can cause harm to the patient (1,3) .For this procedure, it is important that the nurse has knowledge based on valid scientific evidence concerning the different methods of endotracheal suction and aspects related to it.
Despite there being scientific evidence for the safe and efficient accomplishment of endotracheal suction, many of these recommendations have not been

CINAHL
observed in nurses' clinical practice, due above all to poor knowledge about this procedure (4)

Methods
This is a systematic review of the literature, guided by the recommendations of the Cochrane Collaboration (5) .
The review question, devised based in the PICO strategy (6) , was: considering the different methods and steps of endotracheal suction, what is the most effective and safest way of accomplishing it in criticallyill, intubated adult patients, undergoing mechanical ventilation, so as to keep the airways unobstructed, while avoiding or minimizing its complications?
The inclusion criteria were studies of randomized controlled trials (RCT), published in full, in English, Portuguese or Spanish, undertaken with adult patients (≥ 18 years old), who were critically ill, intubated and undergoing mechanical ventilation, and which addressed the effectiveness and safety of endotracheal suction.
The search was carried out in the databases PubMed, EMBASE, CENTRAL, CINAHL and LILACS.The search strategy considered sets of terms related to the study population (P); to the intervention evaluated (I); to the type of study to be included (type of study) and to the exclusion of pediatric and neonatal studies (limits).Descriptors were selected from each database's controlled vocabulary, as well as non-controlled descriptors, which were combined within each set of terms using the Boolean connector OR.The search strategy proposed by the Cochrane Collaboration (5) was adapted for finding the ECCRs (Figure 1).
(The Figure 1      A data collection form devised for the present study was used for the extraction of the data.It took into consideration the instructions on content and appearance presented by the Cochrane Collaboration (5) .
The extraction of the data from each study was undertaken by two reviewers.Initially, the principal reviewer extracted the data from all of the studies selected.Next, the studies were distributed among three reviewers, who acted as independent validators.
The studies were also evaluated for risk of bias, taking into account the sequence generation, allocation concealment, blinding of participants, care providers and the evaluators of the outcomes, incomplete data on outcomes, selective reporting and other sources of bias (5,7) .It is considered that studies with a low risk of bias are unlikely to have serious alterations in their Favretto DO, Silveira RCCP, Canini SRMS, Garbin LM, Martins FTM, Dalri MCB.
results.An uncertain level of risk, on the other hand, raises doubts about the reliability of the studies' results, and a high risk of bias seriously weakens the results' reliability (7) .
Finally, the data extracted from the studies included in this systematic review was analyzed and presented in a descriptive form.

Results
The The results of the studies allowed the grouping of evidence into six categories of intervention related to endotracheal suction: research-based endotracheal suction compared to normal endotracheal suction, in one study (8) ; routine endotracheal suction compared to minimally-invasive endotracheal suction, in two studies (9)(10) ; open system endotracheal suctioning compared to closed system endotracheal suctioning, in eight studies (11)(12)(13)(14)(15)(16)(17)(18) ; change of closed system at 24 compared to 48 hours, in two studies (19)(20) ; daily change of the closed system compared to non-routine change, in one study (21) ; and saline instillation compared to nonsaline instillation, in three studies (22)(23)(24) .
The interventions were undertaken analyzing outcomes referent to hemodynamic alterations, alterations in blood gases, microbial colonization and nosocomial infection, quantity of secretion suctioned, pulmonary alterations, memory of the experience of endotracheal suction on the part of the patient, and discomfort related to the suction.
The results of the outcomes analyzed for the intervention categories in the studies selected are presented in Figure 3.
Authors: Celik, Elbas (8) Groups studied Group 1 (n=38): Research-based endotracheal suction Group 2 (n=42): Normal endotracheal suction Outcome Result CF Group 1: 1 min before the procedure, 20 patients had normal values and 18 had abnormal values; 15 min after the procedure, 36 had normal values and 2 had abnormal values (p<0.05).Group 2: no statistical difference between the points in which the outcome was measured (p>0.05).There was a statistically-significant difference between the groups only in the 15 min after the procedure (p<0.05).

MAP
Group 1: 1 min before the procedure, 20 patients had normal values and 18 had abnormal values; 15 min after the procedure, 34 had normal values and 4 had abnormal values (p<0.05).Group 2: no statistical difference between the points in which the outcome was measured (p>0.05).There was a statistically-significant difference between the groups only in the 15 min after the procedure (p<0.05).

SatO 2
No statistical difference between the points in which the outcome was measured for both groups (p>0.05).
PaO 2 Group 1: 1 min before the procedure, 5 patients had normal values and 33 had abnormal values; 15 min after the procedure, 16 had normal values and 22 had abnormal values (p<0.05).Group 2: no statistical difference between the points in which the outcome was measured (p>0.05).There was a statistically-significant difference between the groups only in the 15 min after the procedure (p<0.05).
PaCO 2 Group 1: 1 min before the procedure, 12 patients had normal values and 26 had abnormal values; 15 min after the procedure, 33 had normal values and 5 had abnormal values (p<0.05).Group 2: there was no statistical difference between the moments in which the outcome was measured (p>0.05).There was a statistically-significant difference between the groups only in the 15 min after the procedure (p<0.05).
According to the Cox model the relative risk indicated a risk 3.4 times greater of VAP occurring in Group 1 (p=0,05) Authors: Johnson et al. (13) Groups studied: Group 1 (n=19): Open system; Group 2 (n=16): Closed system Outcome Result CF After aspiration, both groups presented higher values compared to the baseline (before aspiration).Only 30 min after aspiration was there a significant difference between the groups (p=0.02).

AP
After aspiration, both the groups presented high values compared to the baseline.There was a significant difference between the groups at all points observed (p<0.05).

SatO 2
There was a significant difference between the groups at all points observed (p<0.05).The open system presented a fall in values and the closed system presented an increase, relative to the baseline.

Microbial colonization
In the ventilator tubing.Group 1: 13 (59.1%).Group 2: 16 (80%).p=0.14 Authors: Zeitoun et al. (18) Groups studied: Group 1 (n=24): Open system; Group 2 (n=23): Closed system  The study selected which covered this category of intervention (8) shows various methodological limitations, as shown in the analysis of risk of bias.A low risk of bias was observed in only one of the areas analyzed.Due to this, the study results may be questioned.

Regarding minimally-invasive endotracheal
suctioning (9)(10) , the results obtained evidence that this intervention is responsible for the lowest occurrence of adverse effects (hemodynamic alterations, O 2 saturation, and presence of blood in the mucous), compared to normal endotracheal suctioning.This also applied to the memory of undergoing suctioning, which contributes to reducing the number of people who experience discomfort with the intervention.Despite the minimally-invasive suction producing the best results, a high number of protocol deviations were observed, in which patients allocated to the minimally-invasive suctioning group were, at some point, aspirated in the usual way (9) .This led to a high risk of bias in the area "other sources of bias" and suggests that, depending on the patient's condition, this form of aspiration may not be the most appropriate.The study in question (9) reports that, probably, such an intervention would not be able to aspirate all the secretions present in the airways, causing its accumulation.
Regarding the studies which compared the open system of endotracheal suction with the closed system (11)(12)(13)(14)(15)(16)(17)(18) , it was observed that few presented a low risk of bias in relation to the allocation of subjects, allocation concealment and blinding.Prominent among the outcomes analyzed is the occurrence of ventilationassociated pneumonia (VAP).The criteria used for its diagnosis varied between the studies, however, there was no difference in the occurrence of VAP when the two systems of aspiration were compared.
In relation to cardiac frequency, arterial pressure and O 2 saturation, the results found are in line with another review (25) , which included crossover studies, in addition to randomized controlled trials, with the best results occurring with the use of the closed system when compared to the open.
On analyzing the time interval for changing the closed suction system, the selected studies (19)(20)(21) presented a low risk of bias for the majority of their areas.Differences were not identified between the Groups where the systems were changed every 24 hours compared to every 48 hours, or with daily changing compared to non-routine changing, for any of the outcomes analyzed.
Regarding the instillation of normal saline before the endotracheal suction, compared to non-instillation, the selected studies (22)(23)(24) present differences concerning how the suction was accomplished.Thus, different outcomes were observed, which made it impossible to undertake comparison between the studies.In relation to the results obtained for the outcomes analyzed, only oxygen saturation levels presented a result which was Favretto DO, Silveira RCCP, Canini SRMS, Garbin LM, Martins FTM, Dalri MCB.
unfavorable to the saline instillation.Differences were not found between the Groups studied for cardiac frequency, arterial pressure, partial pressure of oxygen and atelectasis.The Group with saline instillation presented the best results regarding quantity of secretion aspirated.These results are questionable, however, as the quantity of normal saline instilled was not discounted from the measurement of the quantity of secretion collected.Further, in the case of this intervention, the study with the lowest risk of bias and the largest sample (24) reported results favorable to saline instillation in the prevention of VAP.
Results of the analysis of these outcomes for the same intervention were found in other literature reviews (26)(27) .One narrative review on the issue (26) showed that despite including predominantly nonrandomized studies, and not evaluating the quality and risk of bias in said studies, the results obtained are similar to those found in the present review, in relation to cardiac frequency, arterial pressure and O 2 saturation levels.Regarding the partial pressure of oxygen, results were found which contra-indicated the instillation of normal saline; differences were not found in relation to the quantity of secretion aspirated among the Groups studied.Further, evidence was found that the saline instillation increases the displacement of microorganisms from the endotracheal cannula to the lower airways, which would increase the risk of nosocomial pneumonia.
Another systematic review (27) on instillation of normal saline, which included other methodological designs and studies with pediatric and neonatal patients, found results similar to those of the present review for cardiac frequency, arterial pressure and partial pressure of oxygen, O 2 saturation, and quantity of secretion aspirated.In relation to the occurrence of VAP, this review identified one study which did not find differences between the Groups analyzed.
It may be observed, therefore, that the evidence on instillation of normal saline remains contradictory.
However, other studies (1)(2)4) , which reviewed the practices of endotracheal suction, including studies with diverse methodological designs and populations (adult, pediatric, neonatal), submit recommendations which contra-indicate the instillation of normal saline.
From this review's findings, one may observe the lack of randomized controlled trials which cover the diverse aspects of endotracheal suction and outcomes.
Due to this, guidelines put forward recommendations based in studies with lower levels of evidence, such as non-randomized, observational, quasi-experimental studies (1) .
An ongoing controversy was also observed in the studies selected concerning the results of the outcomes analyzed for the interventions studied, due to there being few studies on specific interventions or outcomes, or due to differing results being found among the studies.
Another aspect observed was the lack of methodological information in the studies selected, compromising the analysis of risk of bias and, consequently, the evaluation of the results' reliability and validity.The importance can be seen, therefore, of publishing the RCT in line with the CONSORT recommendations (Consolidated Standards of Reporting Trials) (28) , describing the methodological steps with enough detail for the studies' reliable comprehension, as well as making it possible to identify possible limitations.
Endotracheal suction is an intervention which requires specific knowledge about the patient's clinical condition, physio-pathological aspects, mechanical ventilation and respiratory therapy; therefore, studies for obtaining evidence upon which the practice is based are crucial.Based on the results obtained and the considerations made, it may be noted that although important evidence on endotracheal aspiration exists, this intervention still needs extensive investigation, principally through RCT.

Conclusion
Based on the results obtained from this systematic review, the following evidence on endotracheal suction was found: - -The changing of the closed suction system every 48 hours or non-routinely, and its changing every 24 hours do not differ in terms of the occurrence of VAP.Neither was there any difference in microbial colonization of the endotracheal secretions and suction catheter, when the system was changed every 24 or 48 hours.
-Saline instillation and non-saline instillation do not differ in terms of cardiac frequency, arterial pressure, partial pressure of oxygen and the occurrence of atelectasis.
Regarding the quantity of secretion aspirated, although results were identified which were favorable to the instillation of 05mL of normal saline (compared to the instillation of 10mL and non-saline instillation), conclusive evidence was not found about this outcome, due to the study's methodological limitations.In addition, the saline instillation was associated with lower occurrence of VAP, compared to non-saline instillation.
The methodological limitations and risks of bias found in the studies selected reduce the reliability of the evidence found, demonstrating the need for further studies.

P
= Patient; I = intervention; MESH = Controlled vocabulary in PUBMED database; NCD = Non-controlled descriptors; EMTREE = Controlled vocabulary from the EMBASE database; Titles = Controlled vocabulary from the CINAHL database; DECS = Controlled vocabulary from the LILACS database.

Figure 1 -
Figure 1 -Controlled and non-controlled descriptors used in the search strategy for population, intervention, study design and limits, according to database.Ribeirão Preto, São Paulo, Brazil, 2012

Figure 4 -
Figure 4 -Summary of the risk of bias according to study selected.Ribeirão Preto, São Paulo, Brazil, 2011 Research-based endotracheal suction produced the best results for mean arterial pressure, cardiac frequency, partial pressure of oxygen and partial pressure of carbon dioxide, when compared to usual aspiration; -Minimally-invasive endotracheal suction, compared to routine endotracheal aspiration, results in fewer side effects (increase in systolic arterial pressure, increase in pulse pressure and drop in oxygen saturation levels) and less memories, in the patient, of having been suctioned; -The closed system of endotracheal suction had better results related to cardiac frequency, arterial pressure, cardiac rhythm, oxygen saturation levels and crosscontamination between the bronchial system and gastric juice, when compared to the open system.However, there was no difference between the two suction systems concerning the occurrence of VAP and microbial colonization of the endotracheal secretions and tubing of the ventilator; Rev. Latino-Am.Enfermagem 2012 Sept.-Oct.;20(5):997-1007.