Oxygen therapy in acutely ill patients

OXYGEN THERAPY IN ACUTE ILL PATIENTS

Dr. Adel HamadaMD, Pulmonary medicine

EDIC

By

By the end of this lecture we will be able to

Understand the principle of oxygen delivery.

Know the differences between hypoxia and hypoxemia

Prescribe oxygen therapy.

Understand the different devices used to deliver oxygen.

Know limitations of pulse oximetry.

Apply this to your clinical practice.

Aim of resuscitation in acutly ill patient

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Assure patient safety and optimize Oxygen Delivery

to Tissues

Assure patient safety and optimize oxygen delivery

Oxygen Cascade

resp

CO

BLOODAneorobi

c threshold

Oxygen Delivery

HRSVHbSpO2

90%

Hypoxaemia and hypoxia

Hypoxia: is the reduction below normal levels of oxygen in the tissues and leads to organ damage.

Hypoxaemia: is defined as the reduction below normal levels of oxygen in arterial blood.

Causes of Tissue Hypoxia

Arterial hypoxemi

a

Impaired delivery

misuse

Circulatory hypoxia

Abnormal blood oxygen transport

Maldistribution

Impaired delivery

Causes of Tissue Hypoxia

Low cardiac output states, systemic hypovolemia,and arterial insufficiency of peripheral tissues.

Hb

SIRS , and Septic shock

misuseCauses of Tissue Hypoxia

Cyanide poisoning

Demand hypoxia

Oxygen therapy

It is the supplementation of oxygen concentration greater than 21%

Indications of oxygen therapy

A Survey was done in UK about oxygen therapy in which 50

qualified medical and nursing staff working in acute areas

were asked about oxygen masks and the concentration of

oxygen delivered by each and also asked which mask was most

appropriate for a range of clinical situations. (Cooper, 2002).

Misunderstanding of oxygen therapy

The results were:1-Many staff could not name the different types of oxygen mask, and the difference between oxygen flow and concentration was poorly understood.

2-One third chose a 28% Venturi mask for an unwell asthmatic.

Misunderstanding of oxygen therapy is widespread and the result is that many patients are treated suboptimally.

Oxygen is a drug with a correct concentration and side effects.

So

Oxygen masks

Low flow masks

High flow masks

deliver a proportion of or the entire ventilatory

requirement

deliver the entire

ventilatory requirement

Nasal cannulae

Hudson (or MC) masks

reservoir bag masks

Venturi masks

Nasal cannulae

Nasal cannulae are commonly used because they are convenient and comfortable.

Theoretical oxygen concentrations for nasal cannulae.

SO LOW FLOW DEVICES GIVE VARIABLE FIO2

Because nasal cannulae in fact deliver a

variable concentration of oxygen, there are several case

reports on the ‘dangers of low flow oxygen’ during exacerbations of chronic obstructive

pulmonary disease (COPD) where low inspiratory flow

rates can occur (and therefore higher oxygen

concentrations).

SO

Oxygen masks

Low flow masks

High flow masks

deliver a proportion of or the entire ventilatory

requirement

deliver the entire

ventilatory requirement

Nasal cannulae

Hudson (or MC) masks

Hudson or MC masks

•Hudson or MC (named after Mary Catterall but also referred to as ‘medium concentration’) masks are also sometimes called ‘simple face masks’.

•They are said to deliver around 50% oxygen when set to 10–15 l/min. The mask provides an additional 100–200 ml oxygen reservoir and that is why a higher concentration of oxygen is delivered compared with nasal cannulae

•Importantly significant rebreathing of CO2 can occur if the oxygen flow rate is set to less than 5 l/min because exhaled air may not be adequately flushed from the mask. Nasal cannulae should be used if less than 5 l/min of low flow oxygen is required.

Reservoir bag masks

•Partial rebreathe masks. •non-rebreathe masks.

•the reservoir should be filled with oxygen before the mask is placed on the patient and the bag should not deflate by more than two-thirds with each breath in order to be effective.

•Set flow 10 to 15 L per min

Partial rebreathe masks.(70-80%Fio2)

Partial rebreathe masks conserve oxygen supplies ( useful if traveling with a cylinder). The first one-third of the patient’s exhaled gas fills the reservoir bag, but as this is primarily from the anatomical dead space, it contains little CO2. The patient then inspires a mixture of exhaled gas and fresh gas (mainly oxygen)

Non-rebreathe masks. (85-95%Fio2)If the oxygen flow rate and oxygen reservoir are insufficient to meet the inspiratory demands of a patient with a particularly high inspiratory flow rate, the bag may collapse and the patient’s oxygenation could be compromised.

o prevent this, reservoir bag masks must be used with a minimum of 10 l/min of oxygen and one of the exhalation valves is removed.

Venturi masks1-high flow masks. 2-The Venturi valve utilizes the Bernoulli principle and has the effect of increasing the gas flow to above the patient’s peak inspiratory flow rate (which is why these masks make more noise)and changing inspiratory pattern does not affect the delivered oxygen concentration.(controlled oxygen therapy)

There are two types of Venturi systems: colour-coded valve masks and a variable model. With colour-coded valve masks (labeled 24%, 28%, 35%, 40% and 60%), each is designed to deliver a fixed percentage of oxygen when set to the appropriate flow rate

Flow to venturi

Flow to patient

Change in flow=change in flow to patient

Change in oxygen hole and side holes =change in oxygen concentration

variable model

Venturi mask flow rates

Humidified oxygendry oxygen may lead to the following:

1. ciliary dysfunction.2. impaired mucous transport.3. retention of secretions.4. Atelectasis.5. and even bacterial infiltration of

the pulmonary mucosa and pneumonia.**Specially if an artificial airway bypasses the nasopharynx.

SOHumidified oxygen is given to avoid this, and is particularly important when prolonged high-concentration oxygen is administered and in pneumonia or post-operative respiratory failure where the expectoration of secretions is important.

In summaryflow is not the same as concentration! Low flow masks can deliver high concentrations of oxygen and high flow masks can deliver low concentrations of oxygen.

When giving instructions or prescribing oxygen therapy, two parts are required: the type of mask and the flow rate.

Cardio-respiratory arrest or peri-arrest situation – 15 l/min reservoir bag mask

Other situations*Does the patient have COPD or other cause of chronic respiratory failure?

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s no• Use Venturi masks only• Start at 28% and do arterial blood gases• Aim for PaO2 around 8 kPa and normal pH• NIV is indicated in acute respiratory acidosis after full medicaltherapy

• Use MC or RB mask to get saturations 93%

Simple guide to oxygen therapy

Can oxygen therapy be harmful?*Hyperoxaemia can sometimes have adverse effects. Prolonged exposure to high concentrations of oxygen (above 50%) can lead to atelectasis and acute lung injury, usually in an ICU setting.*There is also a group of patients with chronic respiratory failure who may develop hypercapnia when given high concentrations of oxygen. But!!! Hypoxaemia

killsThere have been cases of negligence in which doctors have withheld oxygen therapy from acutely ill patients due to an unfounded fear of exacerbating hypercapnia.

Measure haemoglobin oxygen saturation using oximetry

By

orco-oximeter

(So2)component of

most blood gas machines

pulse oximeter(Spo2)

peripheral probe and a central processing and

display unit

Pulse oximetryIt measures SpO2.

They are only accurate between 80% and 100% saturation.

Enabling the concentration of HbO2 and Hb, and therefore haemoglobin saturation to be calculated.

The technical limitations of pulse oximetry1-Motion artifact – excessive movement (e.g. in the back of an ambulance) interferes with the signal.

2-Injectable dyes such as methylene blue can interfere with SpO2 readings for several hours.

3-Dark nail polish may interfere with the signal

4-Abnormal haemoglobins – methaemoglobin reduces SpO2 despite a normal PaO2, and carboxyhaemoglobin is not detected by pulse oximetry despite a low PaO2.

NBDark skin has been studied and does not affect the accuracy of pulse oximetry.

THANK YOU