Pulse oximetry in general Pulse oximetry in general practicepractice

By Søren Brorson, MD, GPBy Søren Brorson, MD, GP

Introduction to pulse Introduction to pulse oximetryoximetry

Introduced in the early 1980sIntroduced in the early 1980s Measures the percentage of haemoglobin which is saturated with Measures the percentage of haemoglobin which is saturated with

oxygen (SaO2)oxygen (SaO2) Non-invasive, simple, valid, low-cost method of monitoring the Non-invasive, simple, valid, low-cost method of monitoring the

oxygen saturation of patients bloodoxygen saturation of patients blood Detect hypoxia before the patient becomes clinically cyanosed Detect hypoxia before the patient becomes clinically cyanosed

(SaO2<80%)(SaO2<80%) The pulse oximeter is a vital tool in secondary care The pulse oximeter is a vital tool in secondary care

A routine vital sign in the emergency medicineA routine vital sign in the emergency medicine Provides continuous monitoring of oxygenation in anaesthesiology, Provides continuous monitoring of oxygenation in anaesthesiology,

critical care and transportcritical care and transport Viability of limbs after surgery e.g. vascular graftingViability of limbs after surgery e.g. vascular grafting Overnight sleep studies e.g. obstructive sleep apnoeaOvernight sleep studies e.g. obstructive sleep apnoea Exercise testing e.g. shuttle walk testExercise testing e.g. shuttle walk test

How does an oximeter workHow does an oximeter work

Consist of a probe which is attached to the patient’s finger and a Consist of a probe which is attached to the patient’s finger and a computerized unit with a display showing SaO2 and pulse rate computerized unit with a display showing SaO2 and pulse rate

Possesses two light-emitting diodes Possesses two light-emitting diodes (LEDs), one red and one infrared, (LEDs), one red and one infrared, and a detector, which derives the and a detector, which derives the oxygen saturation from the intensity oxygen saturation from the intensity of transmitted light during a pulse beat of transmitted light during a pulse beat

Plethysmographic waveform display Plethysmographic waveform display which are useful in assessing the which are useful in assessing the quality of the signal and the effects of quality of the signal and the effects of artefact artefact

Calibrated during manufacture and automatically check their Calibrated during manufacture and automatically check their internal circuits when switched oninternal circuits when switched on

Pulse oximeter calibratorPulse oximeter calibrator

Limitations of pulse Limitations of pulse oximetryoximetry

The full picture is not provided, only SaO2The full picture is not provided, only SaO2 Arterial CO2 can rise to dangerous levels Arterial CO2 can rise to dangerous levels

with still acceptable oxygen saturations with still acceptable oxygen saturations It does not replace clinical judgementIt does not replace clinical judgement The gold standard for SaO2 is arterial The gold standard for SaO2 is arterial

blood gas analysis (PaO2, PaCO2, acid-blood gas analysis (PaO2, PaCO2, acid-base balance), but is invasive, painful, base balance), but is invasive, painful, time consuming and costlytime consuming and costly

Pulse oximeters are most accurate at Pulse oximeters are most accurate at saturations of 70-99% (+/- 2%)saturations of 70-99% (+/- 2%)

CASE 1CASE 1

45 year-old man brought in to 45 year-old man brought in to emergency departmentemergency department

Unconscious for 10 min. during BBQ in Unconscious for 10 min. during BBQ in the patio where he had set up the grillthe patio where he had set up the grill

Physician finds normal cognitiv Physician finds normal cognitiv function, normal neurology, BT 130/80, function, normal neurology, BT 130/80, normal EKG, SAT 97%normal EKG, SAT 97%

Diagnose? Diagnose?

Limitations of pulse Limitations of pulse oximetryoximetry

Pulse oximetry cannot distinguish between Pulse oximetry cannot distinguish between different forms of haemoglobins e.g. different forms of haemoglobins e.g. methaemoglobin and carboxyhaemoglobin absorb methaemoglobin and carboxyhaemoglobin absorb light at similar wavelengthlight at similar wavelength

Other sources of error lead to signal losses og Other sources of error lead to signal losses og under-/overestimations of oxygen saturationunder-/overestimations of oxygen saturation Reduced perfusion e.g. cold, cardiac failureReduced perfusion e.g. cold, cardiac failure Nail vanish and paintNail vanish and paint Ambient light e.g. bright overhead lightsAmbient light e.g. bright overhead lights

Not SKUB-testedNot SKUB-tested

Does pulse oximetry influence Does pulse oximetry influence the patient managment ?the patient managment ?

Mower ét al. Chest 1995Mower ét al. Chest 1995 Physicians were significantly more likely to change the medical Physicians were significantly more likely to change the medical

treatment of patients with SaO2<95% compared with patients treatment of patients with SaO2<95% compared with patients with SaO2with SaO2>>95%95%

The oximetry results altered management because the The oximetry results altered management because the physicians failed to recognize underlying cardiopulmonary physicians failed to recognize underlying cardiopulmonary difficulties or because they did not realize the severity of the difficulties or because they did not realize the severity of the illnessillness

Anderson ét al. Ped Emerg Care 1991Anderson ét al. Ped Emerg Care 1991 SaO2 measurements changed the previously assessed degree SaO2 measurements changed the previously assessed degree

of illness in 53% of the patients of illness in 53% of the patients 13% were deemed more ill and 37% less ill than at the initial 13% were deemed more ill and 37% less ill than at the initial

assessmentassessment 17% had their management plan changed, 8% were treated 17% had their management plan changed, 8% were treated

more aggressively and 11% less aggressivelymore aggressively and 11% less aggressively

CASE 2CASE 2

5 year-old boy, no history of astma or 5 year-old boy, no history of astma or atopiatopi

2 days with coughing and difficulty in 2 days with coughing and difficulty in breathing, no feverbreathing, no fever

A little pale, quiet, tachypnoea, use of A little pale, quiet, tachypnoea, use of accessoric muscles, CRP<10, puls 90, accessoric muscles, CRP<10, puls 90, St.p.: rhonchi bilat. SaO2 86% St.p.: rhonchi bilat. SaO2 86%

O2 10 L/min, Ventoline inhalations. O2 10 L/min, Ventoline inhalations. SaO2 rises to 96%. Admited to hospital.SaO2 rises to 96%. Admited to hospital.

CXR: Pneumonia dxt. CXR: Pneumonia dxt.

Recognition of hypoxia Recognition of hypoxia

Respiratory rate is not a reliable screen for hypoxia and is Respiratory rate is not a reliable screen for hypoxia and is not closely correlated with pulse oximetry measurements not closely correlated with pulse oximetry measurements

Studies shows that observers have difficulty detecting Studies shows that observers have difficulty detecting hypoxaemia undtil SaO2<80%hypoxaemia undtil SaO2<80%

In one study the pulse oximeter measured SaO2 in 50 pt.’s In one study the pulse oximeter measured SaO2 in 50 pt.’s in A&E. The oximeter identified 21 pt.’s (42%) with clinically in A&E. The oximeter identified 21 pt.’s (42%) with clinically unsuspected hypoxia unsuspected hypoxia

Pulse oximeters in GP may have a role in recognizing Pulse oximeters in GP may have a role in recognizing hypoxia which otherwise may go undetected hypoxia which otherwise may go undetected

- leading to a difference in managment- leading to a difference in managment

Recognition of COPDRecognition of COPD

Garcia-Pachon, Prim Care Respir J 2004Garcia-Pachon, Prim Care Respir J 2004 Early identification of COPD: Although SaO2 Early identification of COPD: Although SaO2

levels correlated with FEV1 pulse oximetry is levels correlated with FEV1 pulse oximetry is not a useful test for the selection of patients not a useful test for the selection of patients for screening spirometryfor screening spirometry

With a cut-off value (SaO2<98%) they could With a cut-off value (SaO2<98%) they could detect 79% of COPD patients, with a specificity detect 79% of COPD patients, with a specificity of 37%of 37%

23% with significant COPD (FEV1<50%) had 23% with significant COPD (FEV1<50%) had normal SaO2 (SaO2normal SaO2 (SaO2>>95%)95%)

Screening patients with COPD Screening patients with COPD for LTOT using pulse oximetryfor LTOT using pulse oximetry

LTOT for > 15 hours a day increase life expectancy and quality of LTOT for > 15 hours a day increase life expectancy and quality of life in COPD patients with servere hypoxia life in COPD patients with servere hypoxia

Over a 12-month period 114 patients with COPD were screened Over a 12-month period 114 patients with COPD were screened with pulse oximetry in two practices with a combined list size of with pulse oximetry in two practices with a combined list size of 1574215742 13 had SaO213 had SaO2<<92% and went to hospital for arterial blood gas 92% and went to hospital for arterial blood gas

analysisanalysis 3 had PaO2<7,3 kPa and received LTOT 3 had PaO2<7,3 kPa and received LTOT

SaO2SaO2<<92% is the cutt off point for92% is the cutt off point for selecting selecting patients who require arterial blood gas patients who require arterial blood gas analysis. Sensitivity 100% an specificity analysis. Sensitivity 100% an specificity 69% in detection of PaO2<7,3 kPa. 69% in detection of PaO2<7,3 kPa.

Oximetry has a valuable role in the selection of patients who Oximetry has a valuable role in the selection of patients who need definitive arterial blood gas analysis need definitive arterial blood gas analysis

Acute exacerbations of Acute exacerbations of COPDCOPD

Oxygen saturation measured by pulse Oxygen saturation measured by pulse oximetry can not replace analysis of an oximetry can not replace analysis of an arterial blood gas samplearterial blood gas sample

But pulse oximetry can be an effective But pulse oximetry can be an effective screening test for systemic hypoxia screening test for systemic hypoxia (PaO2<8 kPa)(PaO2<8 kPa)

Patients with SaO2<92% should have Patients with SaO2<92% should have arterial blood gases preformedarterial blood gases preformed

DSAM clinical recommendation on COPD DSAM clinical recommendation on COPD SaO2 <90% => consider hospitalizingSaO2 <90% => consider hospitalizing

Patients with acute respiratory Patients with acute respiratory problems or dyspnoea of unknown problems or dyspnoea of unknown

causecause

A supporting tool alongside history and examination when A supporting tool alongside history and examination when

managing patients with acute dyspnoea or dyspnoea of managing patients with acute dyspnoea or dyspnoea of unknown cause in general practice – unknown cause in general practice – can be used as a can be used as a red flagred flag

Routine use of pulse oximetry in patients suspected for Routine use of pulse oximetry in patients suspected for pneumonia can detect clinically unrecognized hypoxaemia pneumonia can detect clinically unrecognized hypoxaemia A study found that 10% of the patients with a pneumonia A study found that 10% of the patients with a pneumonia

where hypoxicwhere hypoxic

A study concluded that pulse oximetry was not a useful A study concluded that pulse oximetry was not a useful method of excluding pneumonia in infants and should not method of excluding pneumonia in infants and should not influence the decision to obtain a CXRinfluence the decision to obtain a CXR

Case 3Case 3

60 year-old woman, history of astma, visit 60 year-old woman, history of astma, visit her GPher GP

2 days with coughing, dyspnoea, pain in 2 days with coughing, dyspnoea, pain in the left side of the thorax when coughingthe left side of the thorax when coughing

Afebril, normal skin colour, normal heart Afebril, normal skin colour, normal heart & lung stethoscopy, puls 76, CRP<10, & lung stethoscopy, puls 76, CRP<10, normal EKGnormal EKG

Diagnose?Diagnose?

Future uses of pulse oximetry Future uses of pulse oximetry in primary carein primary care

In patients with DM lower-extremity arterial In patients with DM lower-extremity arterial disease is common and under diagnoseddisease is common and under diagnosed

Pulse oximetry of the toes was found to be as Pulse oximetry of the toes was found to be as accurate as the ankel-brachial index to screen accurate as the ankel-brachial index to screen for LEAD in pt.’s with DMfor LEAD in pt.’s with DM Pulse oximetry of the toes was considered Pulse oximetry of the toes was considered

abnormal if the SaO2 was more than 2% lower abnormal if the SaO2 was more than 2% lower from the fingerfrom the finger

A combination of the two test was found to A combination of the two test was found to increase sensitivity from PO 77% (ABI 63%) to increase sensitivity from PO 77% (ABI 63%) to 86%86%

ConclusionConclusion Non-invasive, simple, valide, low-costed method of Non-invasive, simple, valide, low-costed method of

monitoring SaO2 monitoring SaO2 Oxymetry in primary care help in the assessment of Oxymetry in primary care help in the assessment of

hypoxia and in identifying unsuspected hypoxiahypoxia and in identifying unsuspected hypoxia It does have numerous indicationsIt does have numerous indications

Assessment for LTOT in patients with COPD (SaO2Assessment for LTOT in patients with COPD (SaO2<<92%)92%) Exacerbations of COPD (obs SaO2<92%)Exacerbations of COPD (obs SaO2<92%) Acute severe asthma in children and adultsAcute severe asthma in children and adults Other acute respiratory problems e.g. pneumoniaOther acute respiratory problems e.g. pneumonia Dyspnoea of unknown causeDyspnoea of unknown cause

Pulse oximetry has some limitsPulse oximetry has some limits Cannot distinguish between different forms of haemoglobins Cannot distinguish between different forms of haemoglobins

e.g. carboxyhaemoglobine.g. carboxyhaemoglobin Reduced perfusion e.g. cold, cardiac failureReduced perfusion e.g. cold, cardiac failure Nail vanish and paintNail vanish and paint