oxygen therapy

Oxygen Therapysurgical department

Aishamudin bin Abdul RahmanNorsafina binti Zainun

Supervisor : Dr. Muhaimin

Outline

1. Introduction2. Indication3. Principles of Oxygen Therapy4. Oxygen Supplementation Devices5. Hazards of Oxygen Therapy6. Take Home Messages

Introduction

Oxygen is a colorless, odorless, tasteless gas that is essential for the body to function properly and to survive.

The air that we breathe in contains approximately 21% oxygen Oxygen therapy is administration of O2 at concentrations greater than that in

room air to treat or prevent hypoxemia.

• Hypoxemia : • reduction of oxygen levels in arterial blood• a PaO2 of less than 8.0 kPa (60 mmHg) or• oxygen saturations less than 93%.

• Hypoxia : • insufficient oxygen supply in the tissues • leads to organ damage

Recognition of Hypoxia

Clinical signs and symptoms include:• Altered mental status (agitation, confusion, drowsiness, coma)• Cyanosis• Dyspnoea, tachypnea• Restlessness• Hypoventilation

• It is defined as a PaO2 < 8 kPa (60 mmHg) and subdivided into 2 types according to PaCO2 level.

Type 1 Type 2

PaO2 < 60mmHg with a normal or low

PaCO2

PaO2 < 60mmHg with hypercapnia

(PaCO2 > 50mmHg)

Caused primarily by ventilation/perfusion (V/Q) mismatch

Caused by alveolar hypoventilation with or without V/Q mismatch

e.g.:•Pneumonia•Asthma•Pulmonary embolism•ARDS

e.g.: •Pulmonary diseases: COPD•Reduced respiratory drive: sedation, CNS tumour, trauma•Neuromuscular ds: cervical cord lesion, diaphragmatic paralysis, myasthenia gravis•Thoracic wall disease: flail chest, kyphoscoliosis

RESPIRATORY FAILURE

Indication of oxygen therapy

• Documented hypoxemia as evidenced by • PaO2 or SaO2 below desirable range for a specific clinical situation

• Respiratory distress (RR > 24/min)• Acute care situations in which hypoxemia is suspected• Increased metabolic demands (Burns, multiple injuries, severe sepsis)• Cardiac failure or myocardial infarction• Short term therapy (Post anaesthesia recovery)

Goals of oxygen therapy

1. Correcting Hypoxemia• By raising Alveolar & blood level of oxygen

2 Decreasing symptoms of Hypoxemia• Supplemental O2 can relieve symptoms

• Lessen dyspnea/ work of breathing• Improve mental function

3 Minimizing Cardiopulmonary workload• Cardiopulmonary system will compensate for hypoxemia by:

• Increase ventilation to get more O2• Increasing cardiac output to get oxygenated blood to tissues

• Starting patient on oxygen therapy• Critically ill patient:

• Give high dose oxygen first (HFM or manual bagging)• Manual bagging if during resuscitation. Consider invasive ventilation

• Serous illness requiring moderate level of supplemental oxygen:• NPO2 2-6L/min or simple face mask 5-10L/min• HFM if SPO2 <85%

• Monitoring patient on oxygen therapy• Clinically: patient less breathlessness, less tachypneic, pink• SpO2 using pulse oximetry. Aim SPO2 94-98%• ABG STAT

• pO2• pCO2

Principle of Oxygen Therapy

• Monitoring first hour of oxygen therapy• Observe SPO2 at least 5 mins after starting oxygen.• If SPO2 94-98%:

• treat appropriately.• ABG after 1 hour.

• If SPO2 <94%: Change to HFM assessment by senior medical staff Consider invasive ventilation if respiratory deterioration

• Titrate the oxygen up or down• To maintain the target oxygen saturation• choose the most suitable delivery system and flow rate

• Discontinue oxygen therapy in stable patient: Step down to next lower oxygen therapy dose Stop if patient clinically stable on low dose oxygen SpO2 should be monitored for 5 mins after stopping oxygen

therapy

Oxygen device

Oxygen supplementation devices

The oxygen concentration that can be deliver to patients depends on the;

• Delivery device• Oxygen flow rate • Patient’s breathing pattern, rate and volume.

Oxygen delivery devicesFixed performance system Variable performance system

FiO2 is independent of patient factor. FiO2 depends on O2 flow, device factors and patients factor.

Provide relatively constant o2 concentration to the lungs.

Provide variable o2 concentrations depending the patient’s ventilation pattern.

Air entrapment mask (venturi mask) Nasal canulaSimple face maskTracheostomy masksHigh flow maskOxygen headboxIncubator

Fraction of inspired oxygen (FiO2) is the fraction or percentage of oxygen in the space being measured

Fixed performance FiO2

Venturi mask • Goal- to create an open system with high flow about the nose and

mouth, with a fixed FiO2.• Operate the Bernoulli principle.

•

• As gas flows through a tube at high linear velocity -> lateral wall pressure of the tube can become subatmospheric ->causing the entrainment of room air through the ports located along the side of tube.

• The smaller the orifice of the adapter ->the lesser air being entrained -> the higher the 02 concentration delivered to patient.

• These mask are used when it is necessary to control the FiO2 or to know the FiO2.

•These masks give an accurate FiO2 which depends on their construction and the O2 flow rate administered.•Colour coded.

24% 2L

28% 4L

31% 6L

35% 8L

40% 10L

60% 15L

24% 28% 31%

35% 40% 50%

60%

Variable performance FiO2

Nasal cannula• FiO2 varies with O2 flow rate and patient’s ventilation.

• changes in minute ventilation and inspiratory flow affect air entrainment-> fluctuation in FiO2.

• normal flow rate administer is 2-3 L/min• > 3 L/min may cause discomfort to patient, may get dislodged and cause

nasal trauma.

• For each 1 L/min increase in flow, the FiO2 is assumed to increase 4%.

• FiO2 = 20% + (4 × oxygen litre flow)

Flow rate ( L/min) Approximate FiO2

1 0.24

2 0.28

3 0.32

4 0.36

5 0.40

6 0.44

Advantages Disadvantages

• Easy and comfortable• Cheap• Less claustrophobic compared to mask• CO2 re-breathing does not occur.

• Provides unreliable FiO2• May cause dryness of nasal mucosa• Mucosa edema• Deviated septum

Simple face masks• Simple semi-rigid plastic mask• The 02 flow rate should be at least 5L/min

• to prevent re-breathing CO2.

• Usual flow rate 5-6 L/min.• Patients may feel claustrophobic and its usage

interferes with feeding.

Tracheostomy mask• These are small plastic masks placed over the

tracheostomy tube or stoma.• Perform similarly to simple face masks• The usual flow rate is 5-6 L/min.

High flow mask• FiO2 greater than simple face masks• Reservoir bag

• provide a large effective dead space.• should be at least 1/3 full at all time.• Minimum flow rate 10- 15 L/min must be applied to prevent

collapse bag.• CO2 rebreathing occurs if the oxygen supply fails or is reduced.

One way valve

Symptoms of CO2 rebreathing:• Discomfort• Fatigue• Dizziness• headache• muscular weakness.

Rebreathing can be eliminated if unidirectional valves are added.

1. Between mask and reservoir bag• to prevent exhaled air from returning to bag

2. At the exhalation ports• to prevent dilution of 02 with air entrainment.

Positive pressure ventilation

Positive Pressure Ventilation

Forces air into the lungsPrevent alveoli collapse at the end of respirationless work required from respiratory muscle

creates greater functional residual capacityUsing a bag valve mask or mechanical ventilation

Continuous Positive Airway Pressure (CPAP) • Delivers a set positive airway

pressure throughout each cycle of inhalation and exhalation.

• Effect is to open collapsed alveoli.

• Patients who may benefit include those with:

• atelectasis after surgery or • cardiac-induced pulmonary edema• sleep apnea.

Bilavel positive airway Pressure (BiPAP)

• Delivers a set inspiratory positive airway pressure each time the patient begins to inspire.

• At exhalation, it delivers a lower set end-expiratory pressure.

• Together the two pressures improve tidal volume.

• positive pressure keep the alveoli open and improve gas exchange

Hazards of Oxygen therapy

Oxygen toxicity

• Only a problem when high concentration which is >50% are given for long periods of time

Neurological effects

• Hyperbaric oxygen can precipitate convulsion.

Carbon dioxide narcosis

• Severe respiratory depression with LOC can occur when high oxygen concentrations are administered to patients with ventilator y failure who are dependent on hypoxic drive.

Bronchopulmonary dysplasia

• Seen when immature lungs are ventilated with high FiO2.

Retinopathy of prematurity

• Occurs in premature babies who exposed to Pa02 more than 80mm Hg.

Take home messages

• Primary goal of oxygen therapy is to correct alveolar and tissue hypoxia, aim for PaO2 > 60mmHg or oxygen saturation more than 93%.

• 02 dissociation curves shift to the right or reducd affinity when increase in body temperature, acidosis and increase in 2,3-DPG.

• At tissue level, mitochodrial activity requires oxygen for aerobic ATP syntesis for cellular activity.• Observe spO2 for 5 minutes after changing of oxygen therapy and repeat ABG after 1 hour after the

oxygen therapy.• Consider invasive ventilation if respiratory failure or deterioration on HFM/ manual bagging• Nasal mucosa dryness, mucosa edema or a deviated septum can be caused by O2 rate > 3L/ min

delivered through the nasal cannula.• In simple face masks, the O2 flow rate should more than 5L/min to prevent CO2 re-breathing.• Minimum flow rate 10-15 L/min should be used in high flow mask to prevent collapse of reservoir

bag.• Oxygen toxicity is only a problem when administered over prolonged period of time.

Refferences

• Kumar and Clark 8th edition. • The Principles of Oxygen Therapy

• American Thoracic Society.• Oxygen Therapy 2013. www.thoracic.org/statement

• British Thoracic Society • https://www.brit-thoracic.org.uk/guidelines-and-quality-standards/emergency-oxygen-use-

in-adult-patients-guideline/

• Anesthesiology for Medical Field• International Islamic University Malaysia, 2011