Page 367 - ACCCN's Critical Care Nursing

344 P R I N C I P L E S A N D P R A C T I C E O F C R I T I C A L C A R E

PAO 2 and PaO 2 , the larger the degree of intrapulmonary administration of nebulised saline (isotonic or hyper-
58
shunting. 54 tonic) can assist in producing a sample. There is no
evidence to support this for mechanically ventilated
The PaO 2 /FiO 2 ratio was introduced as a simpler way of
estimating pulmonary shunting, even though it does not patients, but anecdotally nebulised normal saline may
formally measure alveolar partial pressure. It remains assist in moistening the airways and thinning secretions
widely used to define ALI or ARDS. A PaO 2 /FiO 2 ratio of to facilitate sputum production. Physiotherapy is often
59,60
<300 indicates ALI and a ratio of <200 indicates ARDS. useful in producing a sputum sample, as manual
For example, for a patient receiving an FiO 2 of 0.65 with hyperinflation and head downtilt during the physiother-
61,62
a PaO 2 of 90 mmHg (12 kPa), their PaO 2 /FiO 2 ratio is apy session has increased sputum production.
138.5, indicating an ARDS state. 55 Instilling normal saline in an endotracheal tube (ETT) to
facilitate clearance of tenacious sputum and obtain a tra-
BLOOD TESTS cheal aspirate remains a controversial issue. There is no
Investigation of haematology and biochemistry values for evidence that instillation facilitates secretion clearance,
a patient with respiratory dysfunction can aid their overall while there is some evidence that it is more uncomfort-
treatment. Full blood count (FBC), including a leukocyte able for a patient and increases the risk of contamination
differential count, can track a patient’s white cell count of the lower airway with bacteria. The practice is therefore
63
(WCC) if they have a confirmed or suspected infective not recommended.
process. When infections are severe, the FBC will show a Nasopharyngeal aspirates (NPA) or nasopharyngeal
dramatic rise in the number of immature neutrophils. swabs (NPS) may be necessary to diagnose viral respira-
Blood cultures can also be drawn to assist in diagnosis tory infections. The NPA is collected by inserting a fine
of bacterial or yeast infections and isolation of the caus- sterile suction catheter (8 or 10 F), attached to a sputum
ative organism. Viral studies may be conducted to aid trap and suction, through the nare and back to the naso-
diagnosis for respiratory infections of unknown origin. pharynx. Suction is applied while withdrawing the cath-
If the patient is suspected of having a pulmonary embo- eter slowly using a rotating motion. Flush the catheter
lism, a D-dimer test can determine the presence of a through to the sputum trap with sterile normal saline or
thrombus. Urea and electrolytes will also be routinely transport medium if available. A NPS is collected by
measured to monitor a patient’s renal function and acid– inserting a specially designed swab to the back of the
base status. 56 nasopharynx and rotating for 5–10 seconds, withdrawing
slowly then placing the swab into the plastic vial contain-
ing transport medium. 64
Practice tip
DIAGNOSTIC PROCEDURES
Monitoring lactate levels is important as this reflects the effec- Assessment and monitoring of the respiratory status of a
tiveness and efficiency of resuscitative therapies. A persistently critically ill patient commonly relies on diagnostic tests,
elevated lactate level is associated with higher morbidity and including various medical imaging tests and bronchos-
poorer patient outcomes.
copy. Data generated through diagnostic procedures are
used to determine the cause of illness, the severity of the
illness episode, relevant comorbidities and the patient’s
SPUTUM, TRACHEAL ASPIRATES AND response to treatment.
NASOPHARYNGEAL ASPIRATES
Colour, consistency and volume of sputum provides MEDICAL IMAGING
useful information in determining changes in a patient’s A range of imaging techniques may be available for sup-
respiratory status and progress. Regular cultures of tracheal porting care of a critically ill patient with a respiratory
sputum facilitates tracking of colonisation by opportunis- dysfunction, depending on the level of broader health
tic organisms, or the identification of the cause of an acute service resources available. This sub-section describes
chest infection or sepsis. Many ICUs have routine surveil- X-ray, ultrasound, computerised tomography, magnetic
lance monitoring (weekly or twice-weekly) of tracheal resonance imaging and ventilation/perfusion scan
aspirates in long-term mechanically-ventilated patients. techniques.
In spontaneously breathing patients, sputum specimens
can be provided into a sterile specimen receptacle. These Chest X-ray
specimens are best collected early in the morning and
assisting the patient to clean their teeth prior to sample Chest X-ray (CXR) is a common diagnostic tool used for
collection prevents secondary contamination. In an intu- respiratory examination of critically ill patients. Chest
bated patient, a sputum sample is collected by suctioning radiography allows basic information regarding abnor-
the artificial airway using a sputum trap between the malities in the chest to be obtained relatively quickly. The
suction catheter and suction tubing. Maintain a sterile image provides information about lung fields and other
technique so that the specimen is not contaminated. 57 thoracic structures as well as the placement of various
invasive lines and tubes. 65,66 In the critically ill ventilated
If obtaining an adequate sputum specimen in non- patient, serial chest X-rays also enable sequential assess-
intubated patients is difficult, there is evidence that ment of lung status in relation to therapy. 66