i, AUSTRALIAN NURSING JOURNAL 27

by Glenn Eastwood,

Professor Anne Gardner and

Professor Bev O'Connell

low-now oxygen therapydevicesExcluding anaesthetic circuits andhyperbaric oxygen chambers,

oxygen therapy devices areclassified as high-flow or low-flowsystems (O'Connor and Vender

1995, Oh and Duncan 1988). High­flow systems deliver a consistent

fraction of inspired oxygenconcentrations (Fi02) as theoxygen flow rate is sufficient to

meet or exceed the patient'sinspiratory volume and peakinspiratory flow rate (PI FR).

II pulmonary function (breath

sounds and chest wallsymmetry),

II adequacy of respiration and

normal parameters ofrespiration (Sp02/Sa02),

II ventilation (respiratory rate and

depth, PaC02),

II signs and symptoms of therapy­

related complications (iepressure sores on the nares

or around the base of nose,excessive drying of mucous

membranes of the upperairway),

II cardiac function (heart rate and

blood pressure),

II co-morbidities or medications

that may effect respiratory

function, eg chronic obstructiveairways disease, narcoticanalgesics or anaesthetic agents.

II conscious state,

oxygen from being given to a

hypoxaerriic patient.

When caring for a patient receiving

oxygen it is important to assess

their:

II shortness of breath (dyspnoea),

II alteration in respiratory rate

(bradypnoea or tachypnoea),

II anxiety and agitation.

Indications for initiating oxygen

therapy (Kallstrom 2002) include:

o hypoxaemia (Sa02 < 90),

o respiratory distress,

II post anaesthesia recovery,

II cardiac and respiratory arrest,

II systemic hypotension (systolic

BP < 100mmHg),

II low cardiac output statesand metabolic acidosis

(HC03- < 18mmol/l).

Administering oxygen does havesome risks (O'Connor and Vender

1995). These comprise, but are not

limited to:

II pulmonary - oxygen toxicity,

absorption atelectasis, C02

retention,

II equipment - device malfunction

or oxygen supply failure,

II occupational- increased fire

hazard.

The incidence and extent of theserisks is not clearly reported in the

literature. In all cases however,risks associated with oxygentherapy should never prevent

result in the progressivedeterioration of the patient,beginning with cell death, and if

prolonged, organ failure andultimately body system failure anddeath (Considine 2oo5a).

Early clinical signs and symptoms

of hypoxaemia (Considine 2005a)

are:

Principles of low-Howoxygen therapyOxygen (02) is a physiologic

requirement for normal cellularfunction (energy productionthrough aerobic metabolism), and

is vital to sustaining human life

(Treacher and Leach 1993). Thenormal partial pressure of arterialoxygen (Pa02) at atmospheric

pressure (760 mmHg) is 80 to 100mmHg. This equates with a normal

oxygen saturation of ~ 95% whenmeasured by arterial blood

sampling (Sa02) or by pulseoximetry (Sp02) (Considine

2005a).

Oxygen therapy is the therapeutic

administration of oxygen topatients for the treatment orprevention of hypoxaemia (low­blood oxygen levels) or hypoxia(inadequate oxygen at the cellularlevel). A failure to maintainadequate blood oxygen levels can

lntroducticmLow-flow oxygen therapy devicesare often the first choice for the

treatment of mild to moderate

hypoxaemia (Sp02 90-95%)(Pierce 1995). Ensuring thatoxygen is administered in a timely

and appropriate way using theright device is an important aspectof patient care. Selecting the right

device can be difficult as there area variety to choose from and a lack

of practical information onselection (Eastwood et al 2004).This paper provides an overview of

oxygen therapy principles,describing the indications and care

requirements of three low-flowoxygen therapy devices and

providing an algorithm formanaging refractory hypoxaemia.

visible just below the soft palate.The catheter is secured in positionby an adhesive dressing or tapeplaced on the patient's cheek.Oxygen tubing is then connected

to the distal end of the catheter.Oxygen flow rates are adjustedto meet target blood oxygenconcentrations (Sp02/Sa02)(Eastwood and Dennis 2006).

Care requirements for NPOtherapy:

~ ensure catheter is placed correctly(tip just visible below the softpalate when mouth open),

e removal of catheter for cleaning

with sterile water 12-24 hourly(to reduced the risk ofobstruction),

e use oxygen flow rates::;; 6 Llmin,

e observe for catheter relatedpressure on the nares, drying of

the back of the throat, andbleeding from the nose(Eastwood and Dennis 2006).

Nasal prongsNasal prongs (also known as nasal

cannula or nasal spectacles)consist of two short taperedprongs (about 1 cm in length).

Nasopharyngealoxygen cathetersNasopharyngeal oxygen therapy

(NPO) is the delivery ofsupplemental oxygen directly into

the nasopharynx via an oxygencatheter (size 10 FG for adults)

(Eastwood et al 2004, Frey andShann 2003). When positionedcorrectly the tip of the catheter is

alternative to these two devicesis the use of oxygen catheters toachieve nasopharyngeal oxygentherapy (N PO) in adult patients(Eastwood and Dennis 2006,

Eastwood et aI2004). Adescription and list of carerequirements for NPO therapy:

NP, and FM is provided below.A comparison of these devices isshown in table 1 below.

Other low-flow oxygen devicessuch as partial rebreather masksand non-rebreather masks have

been excluded from this paper asthey are typically used to treatmore severe forms of hypoxaemiaand often require specialisednursing knowledge and care

during their use. Each device willnow be described in detail with itsaccompanying nursing care.

Low-flow systems also deliver avariable Fi02 because of changesin ventilatory pattern (tidal volume,respiratory rate, and PI FR); theentrainment of room air in orderto meet inspiratory volume and;

device-related characteristicssuch as shape and oxygen flowcapabilities (Barnes 2000,

O'Connor and Vender 1995,

Calianno et aI1995).

Low-flow oxygen therapy devices

are generally used in patients withminimal respiratory distress,adequate ventilatory patterns butstill require supplemental oxygenfor therapeutic reasons (Calianno

et a11995, Oh and Duncan 1988).low-flow oxygen therapy devicesare generally easily accessible and

often the first choice for thetreatment of mild to moderate

hypoxaemia (Sp02 90-95%).Low-flow oxygen devices are stillcapable of providing high Fi02

if a patient was to have a slow,shallow ventilatory pattern

(O'Connor and Vender 1995).

Two of the most commonly usedlow-flow oxygen therapy devices

are nasal prongs (NP) and simpleface masks (FM). An emerging

28 AUSTRALIAN NURSING JOURNAL

Each prong lies approximately 1 cmwithin each nostril. Tubing of thenasal prongs is looped over theears and secured under the chin.

Oxygen tubing of the nasal prongsis then connected to an oxygenoutlet (McConnell 1996). Oxygenflows are adjusted to meet targetblood oxygen concentrations(Sp02/Sa02). They are relatively

cheap, easy to apply, and generallytolerated well by patients. Theyrarely interfere with a patient's

ability to eat, talk, sleep and cough

(Costello et a1199S, Fairfield et al1991, Stewart and Howard 1990).However they can be easily

dislodged, which may result in anunacceptable drop in blood oxygen

levels (Hess et aI1984).

Care requirements for nasal

prongs:

• ensure nasal prongs arecorrectly placed (prong in eachnostril) and secured,

III be vigilant for prongdislodgement or displacement,

• observe for catheter relatedpressure on the nares, drying ofthe back of the throat, and

bleeding from the nose

(McConnell 1996).

Simple face masksSimple face masks are half-pearshaped, made of plastic, and worn

over the nose and mouth (Barnes2000). Mask strapping is tightened

around the patient's head toensure a secure fit. Oxygen tubingis then connected from the maskto the oxygen outlet. Administered

oxygen flow rates are faster thanthat of NPO or NP therapy. Facemask oxygen therapy however can

induce claustrophobic sensationsin some patients; cause drying of

the mouth and nose; hinder thepassage of vomitus and; requireremoval for eating and drinking

(Eastwood and Dennis 2006).

Care requirements for FM:

• ensure mask is fitted correctly(covering nose and mouth),

e maintain oxygen flow rates> 6

L/min (to limit carbon dioxide

re-breathing),

• be watchful for the frequentremoval of the mask by the

patient,

e observe for device-related

complications such as thedevelopment of pressure areason the bridge of the nose or skin

irritation around the ears

(Nerlich 1997, McConnell 1997).

Selecting the right deviceSelecting the right device can leadto more efficient use of resources(ie oxygen, oxygen therapyequipment and nursing time),treatment tailored to better meet

patient needs, health care costsavings, and increased patientsatisfaction and compliance withlow-flow oxygen therapy. Foreffective oxygen administration

nurses need to select theappropriate device and oxygenflow rates.

Several questions can assist in theprocess of device selection.

• What low-flow oxygen therapydevices are available?

• Do I have the knowledge andskill to effectively use these

devices?

III Will the device selected be able

to meet the patient's oxygenrequirements?

• Are there any patient-relatedfactors that would prevent a

particular device being used?

e Are there any device-related

factors that would prevent its

use?

• What alternative devices can Iaccess should the initial device

fail to achieve adequate bloodoxygen levels?

As a guide, NPO therapy should beconsidered in patients who requiremodest increases in Fi02 but are

unable to wear a FM or toovercome some of thedisadvantages associated with NP

oxygen therapy (ie that the prongscan easily dislodge or cause skin

irritation around the ears andnares). Nasal prongs are forpatients who require small tomodest increases in Fi02, are still

able to eat and talk unhindered, orfind the wearing of a FMuncomfortable or distressing. Face

masks can be reserved for patientswith greater Fi02 requirements ortemporary abnormal lung

ventilation patterns (ie theimmediate post-operative period).

If a patient finds the experience ofoxygen therapy uncomfortable or

distressing, informing them of thereason for therapy may providereassurance and alleviate concern.

Additionally, it maybe beneficial totrial a different device and discussits comfort, as this may improve

compliance with treatment whilestill maintaining satisfactory blood

oxygen levels.

Treatment of refractoryhypoxaemiaRefractory or unresolvedhypoxaemia is potentially life­threatening. Nurses playa pivotalrole in the management ofhypoxaemic states (Considine

200Sb). Current publishedprotocols and reviews for oxygenadministration however often failto provide practical information toassist with the selection and use ofoxygen devices (Kallstrom 2002,

Cunningham 1997, Treacher andLeach 1998, O'Connor and Vender

1995). In response, a five steppractical approach to themanagement of refractoryhypoxaemia will now be described

and a treatment plan shown intable 2 (next page). As well as itstherapeutic benefit managing

refractory hypoxaemia in asystematic way minimizes theharmful effects of low-bloodoxygen levels.

Step one: identify and treatunderlying cause of hypoxaemia if

possible.

The major causes of hypoxaemia

are hypoventilation, ventilation­perfusion inequalities, lungdisease, or low Pa02 (as

experienced at high altitude).

Step two: establish a target

Sp02/Sa02.

Because different patients havedifferent oxygen therapyrequirements it is important to

establish a target Sp02/Sa02 inconsultation with the patient'streating physician.

It is important to note that within

the group of patients with ChronicObstructive Airways Disease(COAD) who rely on their hypoxic

drive to stimulate breathing;incorrect administration of

supplemental oxygen can causerespiratory depression. Thesepatients require carefully

controlled oxygen therapy withclose monitoring of Sp02 or Pa02

concentrations (Nerlich 1997,Doyle 1992). Additionally, toprevent tissue hypoxia there areclinical conditions where oxygen is

administered in the presence ofnormal Pa02/Sa02. Theseconditions include myocardial

infarction and carbon monoxidepoisoning (Considine 200S).

Step three: select an appropriatelow-flow oxygen therapy device.

Consider patient-related, nurse­related, and context specific

1+ AUSTRALIAN NURSING JOURNAL 29

Abbreviations.Air entrainment mask (AEM); cardiacoutput (CO); haemoglobin (Hb); nasalprong (NP); nasopharyngeal oxygen(NPO); oxygen (Oz); face mask (FM);Saturation of arterial oxygen (SaOz);ventilation/perfusion match (V/Qmatch). Adapted from Oxygen Therapy,Lecture by Dennis M, Z003, School ofNursing, Deakin University, Victoria.

Oh~ T.~JV" /i./iedfcal journof of Austrol/o;i/t 9\ 3) :'.141.-1116.

practice. Until appropriateguidelines are developed, when

supplemental oxygen is needed,the simplest, most effective form

of therapy should be given.

References

Achieving the target Sp02/Sa02concentration is the fundamentaldeterminant of therapy

effectiveness. Effectiveness mayalso be measured for the patient interms of comfort and compliance

with therapy; the nurse in terms oftime and user-friendliness; and for

the hospital in terms of cost and

use.

Nurses make decisions every dayregarding the selection andmanagement of low-flow oxygen

therapy devices. Improvements inthe selection process however are

warranted. The development andimplementation of clinical practiceguidelines supported by bestavailable evidence has the

potential to improve this aspect of

factors that may impact on theadministration of oxygen.

Step four: fit device and adjustoxygen flow rates to achieve target

Sp02/Sa02.

Correct fit and patient education

for the reasons of oxygen therapyis essential to optimising effective

oxygen therapy. Adjuncts tooxygen therapy include:

• optimum patient positioning,

• analgesia,

• patient education, and

41 chest physiotherapy.

Step five: evaluate oxygen therapy

effectiveness.

TABLE 2: TREATMENT PLAN FOR REFRACTORY HYPOXAEMIA

30 AUSTRALIAN NURSING JOURNAL

30

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