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RESPIRATORY

RESPIRATORY SYSTEM

“Sistem pernafasan iaitu kombinasi organ dan tisu berhubungan dengan pernafsan. Ia termasuklah kaviti nasal, farinks, larinks, trakea, bronki dan paru-paru.”

  • Acute Respiratory Failure

PaO2 < 60 mmHg or PaCO2 > 50 mmHg or both at rest, breathing air (FiO2 0.21) at sea level (PBeta 760 mmHg).

Causes Of Respiratory Failure
  1. Ventilatory Pump Failure
  2. Gas Exchange Failure

Ventilatory Pump Failure
  1. Brain
  2. Spinal Cord
  3. Anterior Horn Cell
  4. Peripheral Nerve
  5. Neuromuscular Junction
  6. Respiratory Muscle
  7. Pleura
  8. Chest Wall
  9. Airway

Gas Exchange Failure
Lung – ARDS, pneumonia, lung contusion, haemorrhage.

Clinical Features of Respiratory Failure
  1. Non-specific signs
  2. Dypsnoea , tachypnoea
  3. Sign of underlying disease
  4. Fever, purulent sputum, fractured ribs
  5. ABG abnormalities

Hypoxia
  • Mental changes – drowsiness, restlessness, confusion
  • Tachycardia, then bradycardia, myocardial ischaemia and ventricular arrythmias
  • Cyanosis

Hypercarbia
  • Peripheral vasodilatation
  • Cerebral vasodilatation
  • Rise in BP and pulse pressure
  • Asterixis
  • Carbon dioxide narcosis
Treatment of Respiratory Failure
  1. Specific measures for underlying etiology
  2. patent airway
  3. Oxygen therapy
  4. mechanical ventilation
  5. clearance of secretions




OXYGEN THERAPY

O2 delivery to tissues = O2 in blood x blood flow ( O2 attached to Hb + plasma O2 content).

Oxygen Delivery Devices
The O2 concentration we are able deliver depends on
  1. Delivery device
  2. O2 flow rate
  3. Patient’s breathing pattern, rate and volume.

Classification Of  Devices

  1. Fixed Performance Systems
(FiO2 is independent of patient factors)

High flow Venturi mask
These masks give an accurate FiO2 which depends on their construction and the O2 flow rate (which is written on the mask with the O2 percentage). They are color – coded.

  1. Variable Performance Systems
(FiO2 depends on O2 flow , device factor and patient factors)

  1. Nasal Cannula
(FiO2 varies with O2 flow rate and patient’s ventilation.)

Advantage
  • cheap
  • patient is able to eat and drink
  • less claustrophobic compared to masks
  • CO2 rebreathing does not occur

Disadvantage
  • Mouth breathing reduces their performance
  • High flow rates cause drying of nasal mucosa and discomfort

  1. Simple Face Masks (e.g. Hudson , CIG)
This is a simple semi-rigid plastic mask which is the commonest one available in most hospitals. The O2 flow rate should be at least 4L/ min to prevent CO2 rebreathing.

APPROXIMATE O2 CONCENTRATIONS RELATED TO FLOW RATES OF SEMI-RIGID MASKS

            O2 Flow Rate (l/min)       =     Approximate FiO2
                        4                           =                 0.35
                        6                           =                 0.50
                        8                           =                 0.55
                        10                         =                 0.60
                        12                         =                 0.65
                        15                         =                 0.70

Tracheostomy masks
These are small plastic masks placed over the tracheostomy tube or stoma. They perform similarly to simple face masks.

A T-piece is a simple, large-bore, non-rebreathing circuit attached directly to an endotracheal or tracheostomy tube. Humidified oxygen is delivered through one limb of the “T” and expired gas leaves via the other limb.

Face tent
This is a large, semi-rigid plastic half-mask which wraps around the chin and cheeks. The oxygen mixture is delivered from the bottom of the and the gases are exhaled through the open upper part.

High-flow mask
These masks have an added reservoir bag and thus a large effective dead space. FiO2 greater than semi-rigid masks are possible, but considerable CO2 rebreathing occurs if the oxygen supply fails or is reduced. They are potentially dangerous and should be used with high oxygen flow rates. Rebreathing can be eliminated if unidirectional valves are added.

Oxygen headbox
Oxygen is delivered into a box encasing the child’s head and neck. The FiO2 depends on the fresh gas flow, size of box, leak around the neck, head position and how often the box is removed. It is a useful method in infants and small children, but high flow rates should be supplied and monitoring of oxygen concentration near the face is essential.

Incubator
Incubators provide oxygen as well as a thermoneutral environment. Patient access and recovery of oxygen concentration after opening the incubator are problems.
DEVICES FOR OXYGEN THERAPY

Nasal cannulae ( 2-6 l/min) = 25 – 40 FiO2
Simple face mask (4 – 15 l/min) = 35- 70 Fio2
Venturi mask ( 6 – 12 l/min ) = 24,28,35,40,50,60 FiO2
High-flow mask (10 – 15 l/ min) = 60-80 FiO2

HAZARDS OF OXYGEN THERAPY

1. Oxygen toxicity
Lung toxicity
Concentrations greater than 50% can cause lung damage if given for long periods of time.

Retinopathy of Prematurity
This occurs in premature babies exposed to high concentrations of oxygen. PaO2 should be kept between 50-80 mmHg.

Bronchopulmonary dysplasia
This is chronic paediatric lung disease. It is seen when immature lungs are ventilated with high FiO2.

Neurological effects
Hyperbaric (3 atm) oxygen can precipitate convulsions.

2. Carbon dioxide narcosis
When high oxygen concentrations are administered to patients with ventilatory failure who are dependent on hypoxic drive, serve respiratory depression may occur, with loss of consciousness (narcosis). This is seen particularly in patients with acute exacerbation of chronic bronchitis. Controlled oxygen therapy is needed in such cases. Nevertheless, it is important to remember that a hypoxic patient will die quickly compared to one who is not hypoxic despite being hypercarbic.

3. Fire hazard


HUMIDIFICATION

  • All intubated patients must have adequate humidification of inspired gases for optimal mucocillary function and conservation of heat.
  • Requirements for optimal humidification :

a)      Delivery of gas to trachea at a constant temperature (32 – 36 ◦C)
b)      Relative humidity 75 – 100% saturation
c)      No increase in circuit resistance
d)      No increase in circuit dead space
e)      Applicable to both spontaneous and controlled ventilation
f)        Sterile inspired gases

  • Types of humidifiers
1)      Heat / moisture exchangers (HME)
·        Effective for most patients
·        Minute volume must >10L/min
·        Has bacterial filter
·        Change daily or when necessary especially in bronchorrhoea or mucous inspissation
2)      Fisher- Paykel evaporative humidifier
·        In patients with bronchorrhoea or mucous inspissation
·        Hypothermia or heat loss in susceptible patients (e.g.burns)


Complications of Humidification
  1. Overhydration
  2. Overheating
  3. Disconnection
  4. Electrical hazards



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