Transcript Dias nummer 1 - Nordic Congress > Welcome

Pulse oximetry in general
practice
By Søren Brorson, MD, GP
Introduction to pulse oximetry
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Introduced in the early 1980s
Measures the percentage of haemoglobin which is saturated with oxygen
(SaO2)
Non-invasive, simple, valid, low-cost method of monitoring the oxygen
saturation of patients blood
Detect hypoxia before the patient becomes clinically cyanosed (SaO2<80%)
The pulse oximeter is a vital tool in secondary care
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A routine vital sign in the emergency medicine
Provides continuous monitoring of oxygenation in anaesthesiology, critical care
and transport
Viability of limbs after surgery e.g. vascular grafting
Overnight sleep studies e.g. obstructive sleep apnoea
Exercise testing e.g. shuttle walk test
How does an oximeter work
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Consist of a probe which is attached to the patient’s finger and a
computerized unit with a display showing SaO2 and pulse rate
Possesses two light-emitting diodes
(LEDs), one red and one infrared,
a detector, which derives the
saturation from the intensity
transmitted light during a pulse beat
Plethysmographic waveform display
which are useful in assessing the
of the signal and the effects of
oxygen
of
and
quality
artefact
Calibrated during manufacture and automatically check their internal circuits
when switched on
Pulse oximeter calibrator
Limitations of pulse oximetry
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The full picture is not provided, only SaO2
Arterial CO2 can rise to dangerous levels with
still acceptable oxygen saturations
It does not replace clinical judgement
The gold standard for SaO2 is arterial blood gas
analysis (PaO2, PaCO2, acid-base balance), but
is invasive, painful, time consuming and costly
Pulse oximeters are most accurate at saturations
of 70-99% (+/- 2%)
CASE 1
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45 year-old man brought in to emergency
department
Unconscious for 10 min. during BBQ in
the patio where he had set up the grill
Physician finds normal cognitiv function,
normal neurology, BT 130/80, normal
EKG, SAT 97%
Diagnose?
Limitations of pulse oximetry
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Pulse oximetry cannot distinguish between different
forms of haemoglobins e.g. methaemoglobin and
carboxyhaemoglobin absorb light at similar wavelength
Other sources of error lead to signal losses og under/overestimations of oxygen saturation
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Reduced perfusion e.g. cold, cardiac failure
Nail vanish and paint
Ambient light e.g. bright overhead lights
Not SKUB-tested
Does pulse oximetry influence the
patient managment ?
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Mower ét al. Chest 1995
 Physicians were significantly more likely to change the medical
treatment of patients with SaO2<95% compared with patients with
SaO2>95%
 The oximetry results altered management because the physicians failed
to recognize underlying cardiopulmonary difficulties or because they did
not realize the severity of the illness
Anderson ét al. Ped Emerg Care 1991
 SaO2 measurements changed the previously assessed degree of illness
in 53% of the patients
 13% were deemed more ill and 37% less ill than at the initial
assessment
 17% had their management plan changed, 8% were treated more
aggressively and 11% less aggressively
CASE 2
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5 year-old boy, no history of astma or atopi
2 days with coughing and difficulty in breathing,
no fever
A little pale, quiet, tachypnoea, use of accessoric
muscles, CRP<10, puls 90, St.p.: rhonchi bilat.
SaO2 86%
O2 10 L/min, Ventoline inhalations.
SaO2 rises to 96%. Admited to hospital.
CXR: Pneumonia dxt.
Recognition of hypoxia
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Respiratory rate is not a reliable screen for hypoxia and is not
closely correlated with pulse oximetry measurements
Studies shows that observers have difficulty detecting hypoxaemia
undtil SaO2<80%
In one study the pulse oximeter measured SaO2 in 50 pt.’s in A&E.
The oximeter identified 21 pt.’s (42%) with clinically unsuspected
hypoxia
Pulse oximeters in GP may have a role in recognizing hypoxia
which otherwise may go undetected
- leading to a difference in managment
Recognition of COPD
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Garcia-Pachon, Prim Care Respir J 2004
 Early identification of COPD: Although SaO2 levels
correlated with FEV1 pulse oximetry is not a useful
test for the selection of patients for screening
spirometry
 With a cut-off value (SaO2<98%) they could detect
79% of COPD patients, with a specificity of 37%
 23% with significant COPD (FEV1<50%) had normal
SaO2 (SaO2>95%)
Screening patients with COPD for
LTOT using pulse oximetry
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LTOT for > 15 hours a day increase life expectancy and quality of
life in COPD patients with servere hypoxia
Over a 12-month period 114 patients with COPD were screened with
pulse oximetry in two practices with a combined list size of 15742
 13 had SaO2<92% and went to hospital for arterial blood gas
analysis
 3 had PaO2<7,3 kPa and received LTOT
SaO2<92% is the cutt off point for
selecting patients who require arterial
blood gas analysis. Sensitivity 100%
an specificity 69% in detection of
PaO2<7,3 kPa.
Oximetry has a valuable role in the selection of patients who
need definitive arterial blood gas analysis
Acute exacerbations of COPD
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Oxygen saturation measured by pulse oximetry
can not replace analysis of an arterial blood gas
sample
But pulse oximetry can be an effective screening
test for systemic hypoxia (PaO2<8 kPa)
Patients with SaO2<92% should have arterial
blood gases preformed
DSAM clinical recommendation on COPD SaO2
<90% => consider hospitalizing
Patients with acute respiratory problems or
dyspnoea of unknown cause
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A supporting tool alongside history and examination when managing
patients with acute dyspnoea or dyspnoea of unknown cause in
general practice – can be used as a red flag
Routine use of pulse oximetry in patients suspected
for
pneumonia can detect clinically unrecognized hypoxaemia
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A study found that 10% of the patients with a pneumonia where
hypoxic
A study concluded that pulse oximetry was not a useful method of
excluding pneumonia in infants and should not influence the
decision to obtain a CXR
Case 3
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60 year-old woman, history of astma, visit
her GP
2 days with coughing, dyspnoea, pain in
the left side of the thorax when coughing
Afebril, normal skin colour, normal heart &
lung stethoscopy, puls 76, CRP<10,
normal EKG
Diagnose?
Future uses of pulse oximetry in
primary care
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In patients with DM lower-extremity arterial
disease is common and under diagnosed
Pulse oximetry of the toes was found to be as
accurate as the ankel-brachial index to screen
for LEAD in pt.’s with DM
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Pulse oximetry of the toes was considered abnormal if
the SaO2 was more than 2% lower from the finger
A combination of the two test was found to
increase sensitivity from PO 77% (ABI 63%) to
86%
Conclusion
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Non-invasive, simple, valide, low-costed method of monitoring SaO2
Oxymetry in primary care help in the assessment of hypoxia and in
identifying unsuspected hypoxia
It does have numerous indications
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Assessment for LTOT in patients with COPD (SaO2<92%)
Exacerbations of COPD (obs SaO2<92%)
Acute severe asthma in children and adults
Other acute respiratory problems e.g. pneumonia
Dyspnoea of unknown cause
Pulse oximetry has some limits
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Cannot distinguish between different forms of haemoglobins e.g.
carboxyhaemoglobin
Reduced perfusion e.g. cold, cardiac failure
Nail vanish and paint