Issue 24, June 2008 Airway Suction and Lung Spirometry

Endotracheal suction - do it right or close the lung

Birgitta Almgren, PhD, RN

Birgitta Almgren, PhD, RN Danderyd University Hospital Karolinska Institutet Department of Clinical Sciences Division of Anaesthesia and Intensive Care Stockholm, Sweden

Correspondence: Birgitta Almgren, Danderyn University Hospital, Karolinska Institutet, Stockholm, Sweden. (E-mail and other contact info can be obtained from CWWJ’s Editor-in-Chief).

Key Words: Lung function, mechanical ventilation, airway suction
Running title: Endotracheal suction

Clinical Window Web Journal #24: Endotracheal suction - do it right or close the lung (June 2008). ISSN 1795-6269.

Danderyd University Hospital (Photo by Rolf Andersson)

Introduction

Patients being mechanically ventilated are often connected to the ventilator by an endotracheal (ET) tube. The ET tube and the airways occasionally need to be cleared of mucus by suction. Because the normal coughing mechanism is disrupted, mucus production is increased and mucus clearance depressed, leading to mucus accumulation. Repeated endotracheal suction is often needed to avoid tube occlusion. If the patient is disconnected from the ventilator during ET suction, there is a risk of lung volume loss. Moreover, suction can negatively affect the patient by causing additional lung volume loss, hypoxemia and arrhythmias (1-3). The number and severity of negative effects resulting from ET suction is related to the patient’s conditions and the suction method. Therefore, various methods have been proposed to limit the risks, e.g. closed suction systems, preoxygenation and lung recruitment.

Ventilator induced lung injury

Acute lung injury and acute respiratory distress syndrome is caused by different conditions, i.e. trauma, sepsis and airway infections. Furthermore, mechanical ventilation can cause lung injury (4). Responsible for ventilator-induced lung injury are alveolar over distention and repetitive derecruitment and reopening of unstable alveolar units (5). Repeated derecruitments might accentuate lung injury, expressed in histopathology of the bronchiolar epithelium (6). Therefore, repeated suctioning might accentuate lung injury (7).

Lung protective ventilation
lung protective ventilation includes a PEEP high enough to avoid derecruitment, and a tidal volume small enough to avoid high airway pressures. This strategy has been shown to improve PaO2 and to decrease length of stay in the ICU and mortality rate (8). To regain lung volume and stabilize collapsed alveoli, recruitment maneuvers are used in combination with lung protective ventilation. Non-aerated lungs can be recruited in patients with acute respiratory distress syndrome, without impairment of chest wall mechanics, by treating with a protective ventilatory strategy for 1-2 days (9). Lung collapse and recruitment are rapid processes that occur within seconds of breath-holding procedures (10). By using the open lung approach, improvements in gas exchange can be provided (11).


Suction methods

Open and closed suction system
Different ET suction systems are used, i.e., open, quasi-closed and closed systems (Figure 1). When an open suction system is used, the ET tube is disconnected at the Y-piece and the suction catheter is inserted into the ET tube before suction. The disconnection allows airway pressure to fall to atmospheric pressure before the suction starts. In a lung injury model, derecruitment was induced by disconnection of the ET tube from the ventilator for 1 min at 0-, 10-, 20-, 30-, and 40-min points during each hour over three hours. A progressive decline in PaO2 was found and this was avoided when a recruitment maneuver was included (12). Hourly open suction, without a recruitment maneuver, resulted in a decrease in VT, Crs and ETCO2 (13).

Figure 1. Suction systems. Left: Open system, disconnection from ventilator. Right: Closed system, no disconnection from the ventilator.

Since the disconnection itself results in a pressure drop, a quasi-closed system consisting of a suction adaptor can be used. By the use of this adaptor, the suction catheter can be passed through a side hole, and disconnection of the patient from the ventilator is avoided. By the usage of a quasi-closed system, lung volume loss due to ET suction can be reduced. The closed suction system has a catheter continuously placed between the ET tube and the Y-piece of the ventilator. The suction catheter is introduced into the trachea without the ET tube being disconnected. Different studies have described both advantages and disadvantages to the use of closed system, although, based on the results of a meta-analysis, there is no evidence to prefer the closed system over the open system (14).

In the open lung concept, prevention of lung derecruitment during endotracheal suctioning is important. The closed suction system maintains connection with the mechanical ventilator during tracheal suctioning. When a closed suction system was introduced, significantly lower levels of environmental contamination were observed (15). Furthermore, suction-related lung volume loss was avoided when a closed system was used during volume control ventilation (16).

However, the goal of suctioning is to remove secretions, and different studies have shown less efficacy when closed systems are used. Irrespective of catheter size, open and closed suction were markedly more effective during CPAP 0 cmH2O than was closed suction during pressure controlled ventilation and CPAP 10 cmH2O (17-18).

Vacuum pressure
In clinical practice, it is recommended to set the vacuum pressure between –100 to –125 mmHg. However, in studies of ET suction, different vacuum pressures have been used. Negative pressure during suctioning might cause tracheobronchial trauma (12).

Catheter sizes
The recommendation is to use a suction catheter with an outer diameter not exceeding half the ET tube inner diameter. As an example, an ET tube 8 mm inner diameter requires a 12 French (Fr) suction catheter. Suction catheters with larger outer diameters create more negative pressure (19). If the recommendation is followed, tracheal pressures will be not more than 2 mmHg sub atmospheric (20). Furthermore, tracheal pressure during suctioning with OSS produces more negative pressure compared to CSS (13).
One risk of the use of closed suction system is the production of extreme negative pressures. Large suction catheters generate potentially dangerous levels of sub atmospheric pressure. If a large suction catheter is combined with insufficient triggering of the ventilator, pressures of – 500 cm H2O can be created (21). However, if larger suction catheters are used, the risk of very negative tracheal pressure is the same for an open and closed system (13). However, negative pressure applied during suction is desirable to clear away mucus.

There is a risk of intrinsic positive end-expiratory pressure caused by insertion of the closed suction catheter in volume-controlled ventilation (13, 21). By limiting the catheter sizes and avoiding closed suction systems during volume control ventilation, the risk can be limited (13). In well-sedated patients, endotracheal suctioning caused an increase in intracranial pressure. In patients who coughed or moved in response to suctioning, there was a slight and significant decrease in cerebral perfusion pressure and SpO2. In patients with head injuries, who cough or move during endotracheal suctioning, it is recommended deepening the level of sedation before completing the procedure, to reduce the risk of adverse effects (22).

Through the use of closed suction system, desaturation can be minimized in patients with positive PEEP settings exceeding 8 cmH2O. In contrast, suction with a closed system without any breaths delivered during suction and with a PEEP of 10 cmH2O can influence the cardiovascular system more than suction with an open system. The use of a closed system has also been shown to prevent arterial and systemic venous oxygen desaturation, as well as lung collapse, during volume control ventilation (23-25). When closed, quasi-closed (suction adaptor) and open suction were compared in patients without severe lung disease, lung volume loss was rapidly reversed (i.e. within 10 minutes) in every patient (26).

Preoxygenation
One method to prevent desaturation is to increase inspired oxygen (preoxygenate) before ET suction (27). However, 100% oxygen can contribute to absorption atelectasis (28). Preoxygenation before suction, combined with a post suction recruitment maneuver by 20 VT breaths each of 20 ml kg–1 volume immediately after suction, reverses side-effects (29). On the other hand, results from studies suggest that hyper-oxygenation with 100% oxygen for a minimum of 1 min (or 20 breaths), should be the method of choice for all hyper-oxygenation procedures, to avoid a decrease in PaO2 following suctioning (30).

Ventilator associated pneumonia
The closed suction system limits the incidence of nosocomial infection and exposure of personnel in the surrounding area (31-32). However, after only 24 hours use, the ET tube narrows because of mucus buildup and the intraluminal diameter is reduced (33). Closed suction results in increased in colonization rates of ventilator tubing, but no increase of ventilator associated pneumonia (VAP) compared with open endotracheal suction (34). In a comparison of open and closed suction systems, no significant differences were found in either the percentage of patients who developed VAP or in the number of VAP cases per 1000 mechanical ventilation-days (35).

Ventilator settings
The ventilator can be set in different ventilation modes, e.g. volume-controlled mode or pressure-controlled mode. Open and closed ET suction causes lung collapse leading to impaired gas exchange, which is more severe and persistent in pressure controlled mode than in volume controlled mode (36). However, PaO2/FIO2 was better maintained during closed suction with both volume and pressure controlled modes during lung-protective ventilation for acute respiratory distress syndrome, as compared with open suction, and shunt fraction post suctioning changed least with pressure controlled mode in a lung lavage animal model (7).

Different settings of the ventilator have been suggested during ET suction, to limit the side effects due to the negative pressure in trachea. A constant flow of air delivered by the ventilator during ET suction has been shown to prevent desaturation (37). The ventilator can be set so that high-pressure supported breaths can be triggered during closed suctioning, and loss of lung volume can be avoided (38).
When a closed suction system is used, trigger sensitivity is important, and the sensitivity can be set so that breaths can be triggered due to suction (16).

Danderyd in spring (Photo by Rolf Andersson)

Post suction lung recruitment

Lung volume loss after endotracheal suction is greater in patients with lung damage compared to patients with normal lungs (39). Moreover, lung volume loss is greater when an open suction system is used compared to close suction system. The two dorsal regions are most affected by disconnection and suctioning with marked decreases in compliance (40).

During lung protective ventilation, small VT is used, and therefore there is a risk of derecruitment. The lung is kept open with PEEP, and recruitment maneuvers are used to regain lung volume. However, the increase in airway pressure by recruitment maneuvers might affect hemodynamics. High-pressure recruitments by vital capacity maneuvers involving lung inflation at pressures of 40 cmH2O during one minute are associated with more hemodynamic depression compared to recruitment during ongoing ventilation in pressure controlled ventilation with 40/20 cm H2O in endotoxinemic animals (41).

One method to restore lung volume after suction is to include a recruitment maneuver after suction, i.e. a post-suction recruitment maneuver (42). After ET suction with an open system, a lung recruitment maneuver by repetitive airway pressure peaks of 45 cmH2O for 20 seconds has been shown to restore lung volume and oxygenation (43). Another way is to use volume-controlled ventilation to rapidly restore lung aeration and oxygenation after lung collapse induced by open suctioning. Closed suction followed by a recruitment maneuver prevents hypoxemia, but decreases secretion removal (44). In a lavage model of acute lung injury, alveolar recruitment could be achieved with a slow lower pressure recruitment maneuver with less circulatory depression and negative lung mechanic side effects than with higher pressure recruitment maneuvers (45). The post suction recruitment needs to be performed as soon as possible after endotracheal suction. If the recruitment is delayed, higher pressure levels might be needed to restore the lung (13).

Conclusion

Strategies for mechanical ventilation have changed, but the endotracheal procedures are not yet harmonized to these new strategies. Moreover, not only ventilator settings, but also suction methods, suction systems, catheter sizes, and vacuum levels have large impact, and sometimes negative effects.

• Suctioning should be performed effectively when absolutely indicated.
  
• Side-effects should be observed and handled adequately.
  
• Open suction systems are more effective for mucus removal compared to closed suction systems.
  
• Larger suction catheters are more effective for mucus removal.
  
• Open endotracheal suction causes more severe gas exchange changes in pressure-controlled mode than in volume-controlled mode.
  
• Negative side-effects after suction can be avoided by a post-suction recruitment maneuver in both pressure-controlled and volume-controlled mode.
  
• The post-suction recruitment maneuver should be applied directly after suction.
  
• There is no difference in VAP incidence between open and closed suction systems.

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Clinical Window Web Journal #24: Endotracheal suction - do it right or close the lung (June 2008). ISSN 1795-6269.

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