Oxygen Therapy and Respiratory Monitoring Marianna Balázs University of Szeged, Department of Anaesthesiology and Intensive Therapy

Reason to give O 2 supplementation  to increase tissue oxygenation  circulatory failure (shock) = tissue hypoxia

DO 2 /VO 2 DO 2 = CO x CaO 2 DO 2 =(HR x SV) x (1.39 x Hb x SaO 2 + (PaO 2 x 0.003)) VO 2 = CO x (CaO 2 - CvO 2 )

O 2 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  …

O 2 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 O 2 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 O 2 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 vapour  pin-index system  colour-coded  Should 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

O 2 cylinders on room temperature:  Gas state  kPa of pressure in a full cylinder

Maths face mask, O 2 flow 10 l/min CT transport 20 ~min. 5 l O 2 cylinder Pressure of 60 bar Enough O 2 for the transport? 5x60=300 liter O /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

Problems in practice and safety features : static electricity (inaccuracies of about 35%) to be read in a vertical position dirt

Basics of O 2 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  FiO 2 (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.  FiO 2 = 0.28 – 0.36

Face mask  Incresing dead space  5-10 l/min gas flow  FiO 2 ~ 0.5

Non-rebreathing face mask  5-15 l/min gas flow  reservoir bag  FiO 2 ~ 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  FiO 2 : 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= x V A  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 % -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 regardingCO 2 elimination

Pulse oximetry - sources of error MetHbfalse low reading CoHbfalse high reading bilirubinnot a problem dark skin not a problem methylane blue false low reading indocyanine greenfalse low reading nail vanish false low reading

O 2 – 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 CO 2 from anatomical dead space B: elimination of mixed dead space/alveolar CO 2 C: alveolar CO 2 plateau D: end-tidal carbon dioxide/EtCO 2

Capnograms Some typical and abnormal waveforms:

Capnographs in breathing systems side-stream sensormain-stream sensor

Goals of securing airway patency gas 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 obstruction  easier bag and mask ventilation  unconsciousness  different sizes  to 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.