OXY Liệu pháp (NỘI KHOA SLIDE)

Estimation of FiO2 provided by nasal cannula Patient of normal ventilatory pattern - each litre/min of nasal O2 increases the FiO2 approximately 4%... Estimation of Fio2 from a low-flow

OXY Liệu pháp

Vận chuyển O2

Thác Oxy

Khí trời (khô) (159 mm Hg)

↓ humidification

Đường hô hấp dưới (ẩm) (150 mm Hg)

↓ O2 consumption and alveolar ventilation

Oxygen Content (Co2)

Lượng O2 chứa trong 100 ml máu

Co2 = O2 hòa tan + O2 chuyên chở bởi Hb Co2 = Po2 × 0.0031 + So2 × Hb × 1.34

(Normal Cao2 = 20 ml/100ml blood

Normal Cvo2 = 15 ml/100ml blood)

C(a-v)o2 = 5 ml/100ml blood

Co2 = arterial oxygen content (vol%)

Hb = hemoglobin (g%)

1.34 = oxygen-carrying capacity of hemoglobin

Po2 = arterial partial pressure of oxygen (mmHg)

0.0031 = solubility coefficient of oxygen in plasma

O2Hb dissociation curve

0 20

Chỉ định O2 liệu pháp

Mục tiêu lâm sàng

1 Sữa chữa giảm oxy máu

2 Giảm triệu chứng do giảm oxy máu

3 Giảm hoạt động hệ tim phổi do giảm oxy máu

Chỉ định

 Giảm oxy

 PaO2 < 60 mmHg hoặc SaO2 < 90% khi thở khí trời

 PaO2 / SaO2 thấp trong một số trường hợp đặc biệt

 Nghi giảm oxy máu: hen, XHTH, sau gây mê, chấn thương…

 Nhồi máu cơ tim

Respir Care 2002;47:707-720

Đánh giá

 1 Khí máu động mạch

 2 SpO2

 3 Khám lâm sàng

PaO2 as an indicator for Oxygen therapy

 PaO2 : 80 – 100 mm Hg : Normal

60 – 80 mm Hg : cold, clammy extremities < 60 mm Hg : cyanosis < 40 mm Hg : mental deficiency memory loss

< 30 mm Hg : bradycardia cardiac arrest

PaO2 < 60 mm Hg is a strong indicator for oxygen therapy

Clinical assessment of hypoxia

mild to moderate severe

CNS : restlessness somnolence, confusion disorientation impaired judgement lassitude loss of coordination

headache obtunded mental status Cardiac : tachycardia bradycardia, arrhythmia mild hypertension hypotension

peripheral vasoconst.

Respiratory: dyspnea increasing dyspnoea, tachypnea tachypnoea, possible shallow & bradypnoea

laboured breathing

Skin : paleness, cold, clammy cyanosis

Theo dõi

 Dấu hiệu thiếu oxy máu cơ năng/thực thể

 Pulse oximetry

Bình oxy khí nén

Máy lọc/cô đặc Oxy

Oxy lỏng

Hệ thống tạo O2

Hệ thống giao O2

Low-Flow Devices

Nasal Cannula

 Easy to fix

 Keeps hands free

 Not much interference with further airway care

Estimation of FiO2 provided by nasal cannula

Patient of normal ventilatory pattern - each litre/min of nasal O2

increases the FiO2 approximately 4%.

E.g A patient using nasal cannula at 4 L/min, has an estimated FiO2 of 37% (21

+ 16)

Nasal catheter

 Good stability

 Disposable

 Low cost

 Difficult to insert

 High flow increases back pressure

 Needs regular changing

 May provoke gagging, air swallowing, aspiration

 Nasal polyps, deviated septum may block insertion

Transtracheal catheter

 A thin polytetrafluoroethylene (Teflon) catheter

 Inserted surgically with a guidewire between 2nd and 3rd tracheal rings

 FiO2 – 22-35%

 Flow – ¼ - 4L/min

 Increased anatomic reservoir

Transtracheal catheter

 Lower O2 use and cost

 Eliminates nasal and skin irritation

Estimation of Fio2 from a low-flow system for patient with normal ventilatory

pattern

Mechanical reservoir None Rate, 20 breaths per min

Anatomic reservoir 50 mL I/E ratio, 1:2

100% O2 provided/sec 100 mL Inspiratory time, 1 sec

Volume inspired O2    expiratory time, 2 sec

Estimation of Fio2 from a low-flow system

↑minute ventilation → ↓ Fio2

↓minute ventilation → ↑Fio2

Reservoir systems

Reservoir cannula

 Must be regularly replaced (3 weekly)

 Breathing pattern affects performance (must exhale through nose to reopen reservoir membrane)

RESERVOIR MASKS

 Commonly used reservoir system

 Three types

1 Simple face mask

2 Partial rebreathing masks

3 Non rebreathing masks

Simple face mask

 Reservoir - 100-200 ml

 Variable performance device

 FiO2 varies with

 O2 input flow,

 mask volume,

 extent of air leakage

 patient’s breathing pattern

 FiO2: 40 – 60%

 Input flow range is 5-8 L/min

 Minimum flow – 5L/min to prevent CO2 rebreathing

Face mask

Merits

 Moderate but variable FiO2.

 Good for patients with blocked nasal passages

and mouth breathers

 Easy to apply

Demerits

 Uncomfortable

 Interfere with further airway care

 Proper fitting is required

 Risk of aspiration in unconscious pt

 Rebreathing (if input flow is less than 5 L/min)

O2 Flowrate (L/min)

Fi O2

Reservoir masks

Partial rebreathing mask Nonrebreathing mask

Partial rebreathing mask

 No valves

 Mechanics – Exp: O2 + first 1/3 of exhaled gas (anatomic dead space) enters the bag and last 2/3 of exhalation escapes out through ports

Insp: the first exhaled gas and O2 are inhaled

 FiO2 - 60-80%

 FGF > 8L/min

 The bag should remain inflated to ensure the highest FiO2 and to prevent CO2 rebreathing

Non-rebreathing mask

 Has 3 unidirectional valves

 Expiratory valves prevents air entrainment

 Inspiratory valve prevents exhaled gas flow into reservoir bag

 FiO2 - 0.80 – 0.90

 FGF – 10 – 15L/min

 To deliver ~100% O2, bag should remain inflated

 Factors affecting FiO2

 air leakage and

 pt’s breathing patternO2

Reservoir One-way valves

Tracheostomy Mask

 Used primarily to deliver humidity to patients with artificial airways.

 Variable performance device

Air entrainment devices

Blending systems

High-Flow systems

Air entrainment devices

Based on Bernoulli principle –

A rapid velocity of gas exiting from a restricted orifice will create subatmospheric

mainstream.

Principle of Air entrainment devices

Principle of constant-pressure jet mixing – a rapid velocity of gas through

a restricted orifice creates “ viscous shearing forces ” that entrain air into the

mainstream.

( Egan’s fundamentals of respiratory care;

Shapiro’s Clinical application of blood gases)

Mechanism of Air entrainment devices

oxygen

room air

exhaled gas

Characteristics of Air entrainment devices

 Amount of air entrained varies directly with

 size of the port and the velocity of O2 at jet

 They dilute O2 source with air - FiO2 < 100%

 The more air they entrain, the higher is the total output flow but the lower is the delivered FiO2

Principles of gas mixing

 All High flow systems mix air and O2 to achieve a given FiO2

 An air entrainment device or blending system is used

VFCF = V1C1 + V2C2

V1 and V2- volumes of 2 gases mixed

C1 and C2- oxygen conc in these 2 volumes

VF - the final volume

CF - conc of resulting mixture

% O2 = ( air flow x 21) + (O2 flow x 100)

total flow

Air = 100 - %O2 O2 % O2 - 21

Calculation of Air to O2 Entrainment Ratio using a magic box

Approximate Air Entrainment Ratio and Gas Flows for different Fio2

2 most common air-entrainment systems are

1 Air-Entrainment mask (venti-mask)

2 Air-Entrainment nebulizer

Venturi / Venti / HAFOE Mask

 Mask consists of a jet orifice around which is an air entrainment port.

 FiO2 regulated by size of jet orifice and air entrainment port

 FiO2 – Low to moderate (0.24 – 0.60)

 HIGH FLOW FIXED PERFORMANCE DEVICE

Varieties of Venti Masks

Air entrainment nebulizer

 Have a fixed orifice, thus, air-to-O2 ratio can be altered by varying entrainment port size

 Fixed performance device

 Deliver FiO2 from 28-100%

 Max gas flows – 14-16L/min

 Device of choice for delivering O2 to patients with artificial tracheal airways

 Provides humidity and temperature control

Air entrainment nebulizer

collar

T tube

How to increase the FiO2 capabilities of air-entrainment nebulizers?

1 Adding open reservoir (50-150ml aerosol tube)

2 Provide inspiratory reservoir (a 3-5 L anaesthesia bag) with a one

way expiratory valve

3 Connect two or more nebulizers in parallel

4 Set nebulizer to low conc (to generate high flow) and providing

supplemental O2 into delivery tube

Blending systems

 With a blending system, separate pressurized air and oxygen sources are input

 The gases are mixed either manually

or with a blender

 FiO2 – 24 – 100%

 Provide flow > 60L/min

 Allows precise control over both FiO2

and total flow output - True fixed

performance devices

OXYGEN BLENDER

 Oxygen tent

 Hood

 Incubator

ENCLOSURES

OXYGEN TENT

head and shoulders or over the entire body of a patient 

 FiO2 – 40-50% @12-15L/minO2

 Variable performance device

 Provides concurrent aerosol therapy

OXYGEN HOOD

 An oxygen hood covers only the head of the infant

 O2 is delivered to hood through either a heated entrainment nebulizer or a blending system

 Fixed performance device

 Fio2 – 21-100%

 Minimum Flow > 7/min to prevent CO2 accumulation

 Incubators are polymethyl methacrylate enclosures that combine servo-controlled convection heating with supplemental O2

 Provides temperature control

 FiO2 – 40-50% @ flow of 8-15 L/min

 Variable performance device

Hyperbaric O2 Therapy (HBOT)

the patient breathes 100% oxygen at a pressure greater than one Atmosphere Absolute (1 ATA)

Basis of Hyperbaric O2 Therapy

Dissolved O2 in plasma :

0.003ml / 100ml of blood / mm PO2

(Henry’s Law -The concentration of any gas in solution is

proportional to its partial pressure.)

Breathing Air (PaO2 100mm Hg)

Physiological effects of HBO

 Bubble reduction ( boyle’s law)

 Hyperoxia of blood

 Enhanced host immune function

 Neovascularization

 Vasoconstriction

INDICATIONS OF HBOT

 Decompression sickness

 Air embolism

 Carbon monoxide poisoning

 Severe crush injuries

 Thermal burns

 Acute arterial insufficiency

 Clostridial gangrene

 Necrotizing soft-tissue infection

 Ischemic skin graft or flap

 Radiation necrosis

 Diabetic wounds of lower limbs

 Refratory osteomyelitis

 Actinomycosis (chronic systemic abscesses)

METHODS OF ADMINISTRATION of HBOT

Problems with HBOT

 Barotrauma

 Ear/ sinus trauma

Complications of Oxygen therapy

Complications of Oxygen therapy

1 O2 Toxicity

 Primarily affects lung and CNS

 2 factors: PaO2 & exposure time

 CNS O2 toxicity (Paul Bert effect)

 occurs on breathing O2 at pressure > 1 atm

 tremors, twitching, convulsions

Pulmonary Oxygen toxicity

C/F

 acute tracheobronchitis

 Cough and substernal pain

 ARDS like state

Pulmonary O2 Toxicity (Lorrain-Smith effect)

Mechanism: High pO2 for a prolonged period of time

Interstitial edema Thickened alveolar capillary membrane ↓

Pulmonary fibrosis and hypertension

A Vicious Cycle

How much O2 is safe?

100% - not more than 12hrs

80% - not more than 24hrs

60% - not more than 36hrs

Goal should be to use lowest possible FiO2 compatible with adequate tissue oxygenation

Indications for 70% - 100% oxygen therapy

1 Resuscitation

2 Periods of acute cardiopulmonary instability

3 Patient transport

3 Retinopathy of prematurity (ROP)

↑PaO2 ↓ retinal vasoconstriction

↓ necrosis of blood vessels

↓ new vessels formation

↓ Hemorrhage → retinal detachment and blindness

To minimize the risk of ROP - PaO2 below 80 mmHg

Denitrogenation Absorption atelectasis

The “denitrogenation” absorption atelectasis is because of collapse of

underventilated alveoli (which depends on nitrogen volume to remain above

critical volume )

↓

Increased physiological shunt

5 Fire hazard

 High FiO2 increases the risk of fire

 Preventive measures

 Lowest effective FiO2 should be used

 Use of scavenging systems

 Avoid use of outdated equipment such as aluminium gas regulators

 Fire prevention protocols should be followed for hyperbaric O2 therapy

Oxygen challenge concept

↑ FiO2 by 0.2

↑ PaO2 > 10 mmHg ↑ PaO2 < 10 mmHg

( true shunt – 15 %) ( true shunt – 30 %)

↑ PaO2 < 10 mmHg in response to an oxygen challenge of 0.2 – refractory hypoxemia

Implications of Oxygen challenge concept

 To identify refractory hpoxemia (as it does not respond to increased FiO2)

 Refractory hpoxemia depends on increased cardiac output to maintain acceptable FiO2

 Potentially deleterious effect of increased FiO2 can be avoided

 Therapeutic effectiveness of oxygen therapy is limited to 25% - 50%

• Low V/Q hypoxemia is reversed with less than 50%

• DAA occurs with FiO2 more than 50%

• Pulmonary oxygen toxicity is a potential risk factor with FiO2 more than 50%

 Bronchodilators, bronchial hygiene therapy and diuretic therapy decreases the need for high FiO2

Oxygen is a drug

When appropriately used, it is extremely beneficial When misused or abused, it is potentially harmful

References

 Medical gas therapy Egan’s Fundamentals of respiratory care 9th ed

 Oxygen delivery systems, inhalation therapy and respiratory therapy Benumof’s Airway management 2nd ed

 Shapiro BA Hypoxemia and oxygen therapy Clinical application of blood gases 5TH ed

 Oxygen and associated gases Wiley 5th ed

 Miller’s Anaesthesia 7th ed

 Paul L Marino The ICU Book 3rd ed

Thank you….