FEATURE CRITICAL CARE 051
Table 1: Proposed guidelines for suction catheter selection based on in vitro investigations Age
Weight (Kg)
Newborn Newborn Newborn Newborn 3 Months 1 Year 2 Years 3 Years 4 Years 6 Years 8 Years
10 Years 12 Years
<1 1 2
3.5 6
10 12 14 16 20 24 30
>30 ETT size
2.0 2.5 3.0 3.5 3.5 4.0 4.5 4.5 5.0 5.5 6.0 6.5 7.0
ventilator gases, as seen in closed suction, pushes secretions away from catheter tip making it more difficult to recover them. Remembering our goal of reducing the number of suction passes
that our patients have to endure to the minimum required to maintain effective ventilation and oxygenation, the above studies are very important. It means that the bedside practitioner should make a decision as to whether closed or open suction is more appropriate based on the pressure-dependence of the patient and on the requirement to clear the chest of heavy secretions. This should not be a matter of ‘tradition’ or slavish adherence to protocols, but be based on a critical analysis of the individual patient.
CONTROVERSY #3: SUCTION CATHETER SIZE AND SUCTION LEVEL? As noted above overlarge suction catheters can cause greater lung volume loss even if closed suction systems are used. If a catheter largely or completely occludes a bronchus, the full suction pressure may be transmitted to one por tion of the airway leading to massive atelectasis. Simple guidance can be obtained from ready-reckoners such as the Broselow char t but Morrow, Futter & Argent (2004), through laboratory studies, designed a more detailed char t for practitioners which also gives indications for the types of secretions being encountered (see table 1). This more detailed approach allows the practitioner to use the minimum appropriate size of catheter that will allow for effective secretion recovery. A balance between reducing the number of passes made and the risk of causing atelectasis can therefore be made. As regards suction level many authors recommend between
70 to 150 mm Hg but it is wor th noting a neonatal study by Kohlhauser et Al (2000) in which suction pressures between 200 and 300 mm Hg were used with no notable deleterious physiological parameter changes. Again the bedside practitioner needs to use critical judgment and the evidence provided by studies such as this to decide on the likely benefit or detriment of using a higher suction pressure with its potential for lung volume loss versus a lower level that may lead to a requirement for repeated suction passes and the increased risk of mucosal damage that this implies.
CONTROVERSY #3: HOW FAR DOWN AND HOW LONG FOR? There is currently no strong evidence suppor ting an appropriate duration of suctioning. Most authors recommend between 10 and 15 seconds with the actual time of negative pressure application during suctioning of children limited to five seconds.
Mucous consistency and suggested catheter size [French Gauge] Liquid 5 5 5 5 5 6 6 6 7 7 8 8 8
Medium 5 5 6 6 6 7 7 7 8 8
10 10 10
Thick 5 6 6 7 7 7 8 8 8 8
10 12 12
What is more impor tant is to clearly differentiate between deep
suctioning (DS) and shallow suctioning (SS). In SS the catheter passes only to the tip of the endotracheal tube but in DS the catheter passes into the trachea or bronchi. Whilst there appears to be little difference in SpO2
or hear t rate responses between SS
and DS even in high-risk patients, the evidence for considerable numbers of fresh clustered columnar cells being detached from the respiratory epithelium during DS is significant. We need to consider that during any ICU stay a patient will be suctioned at a minimum four hourly and this is likely to increase in patients with heavy secretions. The damage that DS can cause, if we pass the catheter ‘until resistance is felt’, can potentially be enormous. Passing the catheter no fur ther than one centimeter beyond the endotracheal tube is cer tainly to be recommended.
THE LAST CONTROVERSY: HOW OFTEN? Suction should ‘not be performed as a routine intervention, but as indicated after a thorough clinical assessment’ and the decision on whether to suction should be based on changes in clinical signs and patient behavior. A review of the criteria used by exper t paediatric nurses was given by Thomas and Fothergill-Bourbonnais (2005) and is useful for those creating Practice Guidelines for Paediatric ICUs. The criteria were: Audible or visible secretions in the ETT Coarse breath sounds on auscultation Coughing Increased work of breathing Ar terial desaturation Bradycardia as a result of secretions Decreased tidal volume during pressure-controlled ventilation After chest physiotherapy to clear mobilized secretions Rising PaCO2
level.
CONCLUDING THOUGHTS As bedside practitioners we must not think of suction as a routine and mundane task but rather one that requires critical analysis of the patient. We have an oppor tunity to make an enormous difference to the physical and psychological status of these highly vulnerable patients by taking a critical approach to this basic element of critical care.
REFERENCES References available on request (
magazine@informa.com)
www.lifesciencesmagazines.com
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