Oxygen Therapy and Respiratory Monitoring

Marianna Balázs

University of Szeged, Department of Anaesthesiology and Intensive Therapy

24.09.2015.

Reason to give O2 supplementation

to increase tissue oxygenation circulatory failure (shock) = tissue hypoxia

DO2/VO2

DO2= CO x CaO2

DO2=(HR x SV) x (1.39 x Hb x SaO2 + (PaO2 x 0.003))

VO2= CO x (CaO2 - CvO2)

O2 therapy

indications = suspected and/or confirmed tissue hypoxia

sepsis critically ill patient metabolic acidosis sever trauma, high volume of blood loss deranged mental state poisoning respiratory distress perioperatively acute coronary syndrome …

O2 supply in Medicine

cylinders

PMGV (piped medical gas and vacuum)

PMGV (piped medical gas and vacuum)

components:

1. central supply points (cylinder banks or liquid O2 storage tank)

PMGV (piped medical gas abd vacuum)2. pipework (high quality copper alloy - bacteriostatic)

3. outlets (colour-coded, named, different shapes)

4. hoses (connecting the outlets to the respirator) (colour-coded, non-interchangeable)

Central supply points – cylinder banks

Central supply points – liquid O2 storage tank

Problems in practice and safety features:

Reserve banks of cylinders need to be kept in case of supply failure.Should be housed away from tha main buildings.cold burns, frostbite, hypothermia

Cylinders

Problems in practice and safety features:free of water vapourpin-index systemcolour-codedShould be checked regularly (sufficient content, leaks)!Kept in dry, well-ventilated, fireproof rooms.Full and empty cylinders should be stored separately.overpressurized cylinders – out of use

O2 cylinders

on room temperature:

Gas state

13 700 kPa of pressure in a full cylinder

Maths

face mask, O2 flow 10 l/min

CT transport 20 ~min.5 l O2 cylinder

Pressure of 60 barEnough O2 for the transport?

5x60=300 liter O2.

300/10=30 min.

Measures pressure in cylinder or pipeline. Pressure acts to straighten a coiled tube. Coloure-coded, calibrated for a particular

gas or vapour .

Pressure gauge

Pressure regulator (reducing valve)

A regulator reduces the variable cylinder pressure to a constant safer operating pressure of about 400 kPa. Allows fine control of gas flow.Protects the respirator and anaesthetic machine from high pressure.

Flowmeters

Measures the flow rate of a gas passing through them.Individually calibrated for each gas.Calibrated on room temperature and 1atm (=100kPa=1bar) of pressure.Accuracy of about +/- 2,5% components: 1. flow control valve 2. tapered, transparent plastic or glass tube 3. light weight rotating bobbin or ball

Flowmeters

When the flow control valve is open, gas flows through the tapered tube. Greater the flow, higher the bobbin or ball elevates. Gravity acts against the flow. The bobbin could be marked to visualise whether it rotates or got sticked to the tube wall. Different reading points for bobbins and balls.

Flowmeters

Flowmeters

Problems in practice and safety features:

static electricity (inaccuracies of about 35%)to be read in a vertical positiondirt

Basics of O2 therapy

phases of respiration (3)

peak inspiratory flow (PIF): at rest: 30 l/min doubled in case of distress

work of breathing

Variable performance devices

FiO2 (fraction of inspired oxygen) depends on PIF

FGF (fresh gas flow) < PIF

Respiratory pattern influences performance of the equipment.

devices: nasal cannula face mask non-rebreathing face mask

Nasal cannula

2-4 l/min gas flow Drying the nasal mucuos membrane. FiO2 = 0.28 – 0.36

Face mask

Incresing dead space 5-10 l/min gas flow FiO2 ~ 0.5

Non-rebreathing face mask

5-15 l/min gas flow reservoir bag FiO2 ~ 0.8

Fixed performance devices

FGF>PIF Their performance do not depend on the

patient’s respiratory pattern.

devices:

Venturi masks Mapleson systems respirators

Bernoulli principle (1778.)

As the flow of O2 passes through the constriction, a negative pressure created.

Venturi masks

coloure-coded FiO2: 0.24, 0.28, 0.31, 0.35, 0.4 or 0.6

Mapleson C

Not economical due to high need of fresh gas flow.

FGF= 1.5-3 x VA

advantage: portable, PEEP

Ideal device for resuscitation.

Respiratory Monitoring

Sensory organs

FEEL

- airflow through the nostrils

LOOK

- skin colour- moving chest- use of

accessory muscles

- respiratory rate

LISTEN

- stridor- bronchospasm- pulmonary

oedema

Cannot be used continuously. Subjective, not reliable. Alarm limits

cannot be set .

Optimal respiratory monitor

- non-invasive

- operating continuous

- accurate, reliable

- easy to use

- operator friendly

- cheap

Pulse oximetry

Revolutionised patient monitoring, significantly improved patient safety.

Pulse oximetry - sensor

- LED: emission of light on 660 and 940 nm wavelength- photodetector opposite to the LED- 30 impulses/sec- oxygenated/deoxygenated hemoglobin

Pulse oximetry – display

- displaying and analysing signs- setting of alarm limits

plethysmographic waveform of the pulse

oxygen saturation

pulse

Problems and practice in safety

- It is accurate (+/-2%) in range of 70-100%- Readings are extrapolated below saturation of 70%.- Hypoperfusion, vasoconstriction affect its performance.- Does not give information regarding oxygen delivery.- Variable response time.- Patient movement, sensor malposition affect its performance.- Can cause pressure sore.- Does not give information regardingCO2 elimination

Pulse oximetry - sources of error

MetHb false low readingCoHb false high readingbilirubin not a problemdark skin not a problemmethylane blue false low readingindocyanine green false low readingnail vanish false low reading

O2 – Hb dissociation curve

Capnography

Gases with molecules that contain at least two dissimilar atoms absorb

radiation in the infrared region of the spectrum.

Capnography

Analysis of the capnograph wave

A: elimination of CO2 from anatomical

dead space

B: elimination of mixed dead

space/alveolar CO2

C: alveolar CO2 plateau

D: end-tidal carbon dioxide/EtCO2

Capnograms

Some typical and abnormal waveforms:

Capnographs in breathing systems

side-stream sensor main-stream sensor

Goals of securing airway

patencygas exchange

Securing airway - equipments

Simple maneuver I.

Securing airway - equipments

Simple maneuver II.

Securing airway - equipments

suction

Securing airway - equipments

oropharyngeal tube/Guedel

Securing airway - equipments

oropharyngeal tube:

upper airway obstructioneasier bag and mask ventilationunconsciousnessdifferent sizesto suction upper airway demage

Securing airway - equipments

nasopharyngeal tube:

Securing airway - equipments

nasopharyngeal tube:

upper airway obstruction awake patient diffenent sizes upper airway suction bleeding head trauma - avoid safety pin

Securing airway - equipments

laryngeal mask airway (LMA)

Securing airway - equipments

laryngeal mask:

difficult airway scenario not an option for glottic/subglottic obstruction aspiration - possible laryngospasm unconsciousness/anaesthesia CPR ProSeal, I-Gel, ILMA...

Securing airway - equipments

endotracheal tube (ETT)

Securing airway - equipments

endotracheal tube:

needs special skill laryngoscopy protects against aspiratin unconsciousness/anaesthesia

Securing airway - equipments

Surgical airway I. - Cricothyreoidotomy

Securing airway - equipments

Surgical airway II. - Tracheostomy

Thanks for attention.