Introduction

Suctioning respiratory secretions is a necessary procedure in patients with artificial airway in order to remove respiratory secretions and to maintain the airway permeable, but this method may cause various complications [1, 2, 3, 4, 5, 6, 7, 8] such as bronchial traumatism, bronchospasm, haemodynamic impairment, hypoxaemia and cross transmission of respiratory infections.

There are two types of tracheal suction systems: (a) open tracheal suction systems (OTSS), which need to be disconnected from the respiratory circuit and employ single-use suctioning catheters; and (b) closed tracheal suction systems (CTSS), which do not need to be disconnected from the respiratory circuit and employ multi-use suctioning catheters.

The CTSS have several potential advantages with respect to OTSS:

  1. 1.

    Lower gasometrical and haemodynamic impairment during suction of respiratory secretions [9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19], since they decrease fraction inspired oxygen and positive end-expiratory pressure loss, so the hypoxaemia associated with aspiration is decreased

  2. 2.

    Possibility of a protective effect against nosocomial pneumonia, since the suctioning catheter is not touched directly (it is protected by a plastic envelope), an effect that has been proved in one study [20] but not in others [21, 22, 23, 24, 25, 26]

  3. 3.

    Less time required to perform an aspiration [16, 21, 27, 28], because it is not necessary to wear facial masks, wash hands, wear gloves, open the suctioning catheter sterile envelope or disconnect it from the artificial airway respiratory circuit, causing a decrease in patient anxiety and in the daily work of the nursing staff

  4. 4.

    Decrease of environmental contamination from respiratory microorganisms [29].

The CTSS have several disadvantages with respect to OTSS: (a) higher cost [9, 16, 22, 23, 26, 28] due to the need for a complete daily change as recommended by the manufacturer; however, the necessity of such a complete daily change has not been demonstrated; (b) less effective to remove secretions because part of the gas flow through the suction catheter comes directly from the ventilator [30]; and (c) may cause unpredictable and high levels of intrinsic positive end-expiratory pressure during insertion of the catheter and CTSS may interfere with the regulation of the ventilator during pressure-regulated volume-guaranteed ventilation [31]. The guidelines for the prevention of ventilator-associated pneumonia (VAP) of the Centers for Diseases Control and Prevention 2004 [32] do not establish a recommendation about the frequency of routinely changing the closed-suction system, applying the category “unresolved issue” for this practice. They only mention one study which found no difference in VAP incidence between CTSS with or without routine change every 24 h [33].

In a previous study comparing CTSS with routine change every 24 h vs OTSS, we found no difference in the incidence of VAP, but the economic cost was higher with CTSS [26]; therefore, we designed this study in order to determine the incidence of VAP and the suctioning cost comparing OTSS and CTSS without daily change.

Patients and methods

The study design was approved by our hospital Ethics Committee and informed written consent for inclusion in this study was obtained from all participants or their legal guardians. The study was conducted at the 24-bed medical-surgical Intensive Care Unit of the Canary Islands University Hospital (Tenerife, Spain), a 650-bed hospital. We performed a prospective, randomised study of 9-month duration from 1 January to 30 September 2004. All patients requiring mechanical ventilation were included in the study. Patients were randomly assigned to one of two groups at the time of intubation: in one group of patients the suction of secretions was carried out using CTSS without complete daily change, and in the other group OTSS was used.

Description of the CTSS

The CTSS used was Hi-Care (Mallinckrodt, Mirandola, Italy). This device has two parts: a suction catheter (enveloped in a protective plastic) with suction valve, detachable from the elbow, which is equipped with rotating patient access valve (bronchoscope valve). This division in two parts means that the suctioning catheter and its protective plastic envelope can be disconnected and changed without changing the whole system (partial change).

To perform tracheo-bronchial suction the system Hi-Care must be connected to the respiratory circuit by placing it directly between the Y piece of the respiratory circuit and the endotracheal tube, and attached to it by means of the catheter mount connections. The proximal end of the vacuum valve is connected to the vacuum suction source, after removing the protection cap. The suction catheter is inserted inside the endotracheal tube, then must press the vacuum valve to apply vacuum and proceed to aspirate the secretions.

To perform instillation into the respiratory airway it must be ensured that the mount valve is in open position, connect a syringe with saline solution to the flushing line and finally proceeding with suctioning.

After suctioning, the residual secretions of the suction catheter must be removed, turning the mount valve until closed position, connecting a syringe with saline solution to the flushing line and activating suction valve to set vacuum and simultaneously injecting washing solution.

When the mount valve is in closed position, it is possible to remove the suction catheter. Once the suction catheter has been removed, the cap must be placed in the distal end of the suction catheter. Once these manoeuvres are done, it is possible to perform bronchoscopic or pulmonary sampling, turning the mount valve to open position, inserting device and performing procedure.

Study protocol

In the OTSS group a suctioning catheter for each aspiration was used. Each suction was performed with aseptic techniques (facial masks, hand washing before and after suctioning and sterile gloves).

In CTSS group the tracheal suctioning procedure was performed by universal precautions, such as hand washing and non-sterile gloves. This division in two parts means that the suctioning catheter and its protective envelope can be disconnected and changed without changing the whole system (partial change). The closed system that we used was not routinely changed but only when it presented mechanical failure (e.g. valve dysfunction with air entering the protective catheter envelope or protective envelope breakage) or soiling (with blood or vomit), or when the patient needed re-intubation. On re-intubation or valve dysfunction, a total change of the system was performed. When the protective envelope became torn or soiled, a partial change of the system was performed (only the suctioning catheter and the protective envelope). When patients needed to be moved for a surgical or radiological procedure, they continued using the same system.

Identical measures were used for the prevention of nosocomial pneumonia in both groups: gas humidification with a heat and moisture exchanger (changed every 48 h); not periodically changing ventilator circuits; endotracheal tube without sub-glottic aspiration; semi-erect posture at 40°; continuous enteric nutrition; periodic verification of residual gastric volume; ranitidine for prophylaxis of stress ulcers; and and oral washing with chlorhexidine.

Tracheal aspirate was taken during orotracheal intubation, then twice weekly, and lastly at the moment of the orotracheal extubation, in order to diagnose respiratory infection. Throat swabs were taken on admission to the Intensive Care Unit, then twice a week and at the moment of discharge from the unit in order to classify nosocomial pneumonia as either exogenous or endogenous.

The adherence to study protocol was controlled by the nurse responsible for each shift of work. The following variables were recorded for each patient: gender; age; Acute Physiology and Health Evaluation II score (APACHE II), days of mechanical ventilation, number of endotracheal aspirations per day, mortality and diagnostic group. Each type of diagnosis group included the following diagnosis:

  1. 1.

    Cardiac surgery group included coronary artery bypass grafting or valvular or aortic dissection.

  2. 2.

    Cardiology group included cardiac arrest or cardiac failure.

  3. 3.

    Respiratory group included exacerbation of chronic pulmonary disease, asthma attack or community-acquired pneumonia.

  4. 4.

    Digestive group included pancreatitis or gastrointestinal haemorrhage or abdominal sepsis.

  5. 5.

    Neurological group included cerebrovascular accident, myasthenia gravis, polyradiculoneurits or central nervous system infection.

  6. 6.

    Traumatology group included brain trauma, thoracic trauma, abdominal trauma, polytrauma or burns.

  7. 7.

    Intoxication group included central nervous system drugs or drugs of abuse or analgesics or pesticides.

The diagnosis of pneumonia was established when all the following criteria were fulfilled: new onset of bronchial purulent sputum; body temperature > 38°C or < 35.5°C; white blood cell count > 10,000/mm 3 or < 4.000/mm 3; chest X-ray showing new or progressive infiltrates; and culture of significant respiratory secretions (tracheal aspirate of > 10 6 cfu/ml, bronchoalveolar lavage of > 10 4 cfu/ml or protected brush catheter of > 10 3 cfu/ml), or blood culture coinciding with the culture of respiratory secretions.

Pneumonia was considered associated with mechanical ventilation when it was diagnosed during the mechanical ventilation and it was not present at the time of establishing the mechanical ventilation.

Pneumonias were classified by the throat flora [34] as endogenous (those produced by microorganisms colonizing the throat at the moment of the diagnosis) and exogenous (those caused by microorganisms not present at the moment of diagnosis).

We compared the cost per patient per day for each method of respiratory secretion suctioning. The cost of each tracheal suctioning procedure with OTSS was 0.30 Euros (which includes the disposable suctioning catheter, facial mask and sterile gloves). The cost of the complete closed system was 10 Euros and that of the partial system (which includes only the suctioning catheter and the protective envelope) was 5 Euros.

The percentage of patients who developed ventilator-associated pneumonia (VAP), the number of VAP per 1000 days of mechanical ventilation and suctioning costs were analysed globally and by different periods of mechanical ventilation duration: < 1 day; 1–2 days; 3–4 days; 5–14 days; 15–24 days; and 25 or more days.

Statistical analysis

Quantitative variables were reported as mean ± standard deviation and were compared using Student's t-test. Qualitative variables were reported as percentages and were compared with chi-squared test, or with Fisher's exact test, in the case of small samples. An analysis of variance was carried out for comparing mean costs per patient/day per length of mechanical ventilation between both suction systems. Later, a post-hoc analysis with Scheffé test was carried out. Statistical significance was defined as p < 0.05. For statistical analyses we used the SPSS v. 11.0 (SPSS, Chicago, Ill.) and Statistica v. 7.1 (StatSoft, Tulsa, Okla.).

Calculation of the exact sample size per arm of equivalence test for two binomial populations was made using StatXact v. 5.0 (Cytel Soft, Cambridge, Mass.). Calculation of the exact sample size per arm of equivalence test for two binomial populations resulted in 213 subjects per arm of treatment with a power of 80%, a type-I error of 5%, an equivalence margin (δ0) of 10% (percentage of VAP accepted as equivalent) and an hypothesized difference within equivalence margin (δ1) of 0% (Π2 = 0,14 and Π1 = 0,14), where Π2 is the probability of developing VAP in the population treated with CTSS, and Π1 is the probability of developing VAP in the population treated with OTSS.

Results

A total of 457 patients (236 receiving CTSS and 221 receiving OTSS) were included. We found no significant differences between the two groups with respect to demographic and clinical variables (gender, age, APACHE II, diagnostic groups, mechanical ventilation duration, number of endotracheal aspirations per patient/day and mortality; Table 1).

Table 1 Characteristics of the two groups of patients. CTSS closed tracheal suction system, OTSS open tracheal suction system, APACHE Acute Physiology and Chronic Health Evaluation

As shown in Table 2, there were no significant differences in percentages of patients receiving CTSS and OTSS who developed VAP, both in the total amount of patients (13.9 vs 14.1%) and by periods of mechanical ventilation.

Table 2 Percentage of patients with ventilator-associated pneumonia per period of mechanical ventilation

Neither did we find significant differences in incidence density of VAP between CTSS and OTSS, both in the total amount of patients (14.1 vs 14.6 per 1000 days of mechanical ventilation) and by periods of mechanical ventilation (Table 3).

Table 3 Number of ventilator-associated pneumonia per 1000 days of mechanical ventilation (MV) per period of MV

Table 4 shows the microorganisms responsible for VAP. There were no significant differences in the percentage of patients who developed VAP due to any particular microorganism group (Table 5). Microorganisms were divided into five groups for statistical analysis: (a) Staphylococcus aureus; (b) Streptococcus pneumoniae; (c) nonfermentative gram-negative bacteria (Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Acinetobacter spp); (d) other gram-negative bacteria (Escherichia coli, Klebsiella spp, Enterobacter spp, Serratia marescens, Haemophilus influenzae); and (e) fungi (Candida albicans).

Table 4 Microorganisms isolated in ventilator-associated pneumonia. GPC Gram-positive cocci, GNB Gram-negative bacteria
Table 5 Number of patients who developed ventilator-associated pneumonia by a determined microorganism. GPC Gram-positive cocci, NFGNB non-fermentative Gram-negative bacteria, GNB Gram-negative bacteria

Only one case of exogenous VAP developed in each group of patients. We found no significant differences between the groups with respect to the percentage of patients who developed exogenous VAP [1 of 236 (0.4%) vs 1 of 221 (0.5%); p = 0.99], the number of exogenous VAP per 1000 days of mechanical ventilation [1 of 2336 (0.4) vs 1 of 2113 (0.5), p = 0.99], or in the percentage of exogenous VAP with respect to the total number of VAPs [1 of 33 (3.1%) vs 1 of 31 (3.2%); p = 0.99].

The suctioning cost of the 236 patients with CTSS during 2336 days of mechanical ventilation was 5345 Euros, needing 286 complete CTSS (236 in the first intubation and later 50 complete changes, 37 due to reintubation and 13 due to valve dysfunction) and 497 partial CTSS (424 due to protective envelope breakage and 73 due to protective envelope soiling). The suctioning cost of the 221 patients with OTSS during 2113 days of mechanical ventilation was 5049 Euros, needing 16833 suctioning.

The main effect for suction system was not significant in cost per patient/day. No difference was found between the group of patients with CTSS and the group with OTSS (2.3 ± 3.7 vs 2.4 ± 0.5 Euros; p = 0.96). An interaction effect was found between suction system and length of mechanical ventilation. When length of mechanical ventilation is lower than 4 days, the cost in CTSS group (7.2 ± 4.7 Euros) is higher than in OTSS group (1.9 ± 0.6 Euros; p< 0.001); however, when length of mechanical ventilation is > 4 days, the cost is lower in CTSS group (1.6 ± 2.8 Euros) than in OTSS group (2.5 ± 0.5 Euros; p< 0.001; see Fig. 1).

Fig. 1
figure 1

Comparison of cost per patient/day (Euros) between closed tracheal suction system (CTSS; black colour) and open tracheal suction system (OTSS; grey colour) according to the length of mechanical ventilation. Results are expressed with mean (dots) and 95% confidence interval (whiskers). F5, 23701=448.4; ** p \lt; 0.001, * p = 0.001

Discussion

In the present study we did not find differences between the two groups of patients (CTSS without complete daily change vs OTSS) in the incidence of VAP; and the suctioning cost per patient/day was lower with OTSS when length of mechanical ventilation was < 4 days, and was lower with CTSS when length of mechanical ventilation was > 4 days.

With respect to the VAP incidence, the CTSS decreased it in one study [20] but not in others [21, 22, 23, 24, 25, 26]. In our study, we did not find significant differences between the two groups of patients (CTSS without complete routine daily change vs OTSS) in the percentage of patients who developed VAP and in the number of VAP for 1000 days of mechanical ventilation, neither in global nor in each period of mechanical ventilation. We also did not find significant differences in the microorganism responsible of VAP. Neither did we find significant differences in the incidence of exogenous VAP.

An objection to CTSS without complete routine daily change is the possibility of auto-contamination and the risk of VAP. The suctioning system is maintained until change is required, and the suctioning catheter may become contaminated upon insertion into the endotracheal tube. Repetitive manipulation increases the risk of re-entrance of contaminated secretions in the following aspirations [24]. To minimize this problem of auto-contamination, it is necessary to maintain the suctioning catheter as clean as possible, and thus the CTSS used in our study had a lumen to introduce saline solution throughout, to remove residual secretions from the catheter after aspiration. As mentioned previously, there were no significant differences in the incidence of VAP between the two groups.

With respect to the suctioning cost, several studies have evaluated CTSS costs compared with open systems [9, 16, 22, 23, 26, 28]. In these studies, including ours [26], routine CTSS change was performed every 24 h following the manufacturer's recommendations but without scientific evidence demonstrating the necessity of this daily change. A somewhat similar situation occurred with the periodic change of ventilator circuits. The Centers for Diseases Control and Prevention Guidelines in 1983 [35] recommended changing ventilator circuits every 24 h, but in 1994 [36] and 1997 [37], they recommended not changing them before 48 h, and in 2004 [32] they recommended not changing them routinely. There is one previous study where the use of CTSS was prolonged [33]: Kollef et al. [33] analysed 521 patients and found no significant differences in VAP incidence between patients with and without routine 24-hourly change of CTSS [14.7% (38 of 258) vs 14.8% (39 of 263); RR = 0.99; IC 95% = 0.66–1.50].

As the results of the present study indicate, CTSS is the optimal option for patients needing suction longer than 4 days. Whilst the frequency of suctioning and length of mechanical ventilation increase, suctioning lost by CTSS becomes lower. In addition to not routinely changing CTSS, the type of CTSS used provides the possibility of a partial change of the system (only the suctioning catheter and the protective envelope). With other types of CTSS it is not possible to make the partial change, and perhaps would not result in a decrease in the cost of each aspiration.

Our study had some limitations: Firstly, the airway colonization can precede the development of pneumonia, but we did not report data on tracheal colonization. On the other hand, an objection to CTSS without daily change may be the possibility of auto-contamination of the CTSS, but we did not take samples from the suctioning system; thus, it is not possible to determine the degree and time course of bacterial contamination of the suctioning line. Another limitation is that we do not have direct or indirect data about the efficacy of suctioning (e.g. incidence of atelectasis). Another point is that in our medical-surgical Intensive Care Unit approximately half of patients are postoperative cardiac surgery patients, and a large portion of the patients underwent mechanical ventilation for less than 48 h. Compared with another population of Intensive Care Unit patients, the incidence of VAP may be different, but in our study the incidence of VAP was not different in the two groups of patients (CTSS and OTSS).

Conclusion

Due to no demonstrable difference in VAP incidence between patients receiving CTSS without daily change and those receiving OTSS, CTSS is the optimal option for patients needing suction longer than 4 days. Whilst the frequency of suctioning and length of mechanical ventilation increase, suctioning lost by CTSS becomes lower.