Oxygen Therapy & respiration

Question 1

Hypoxia

Answer 1

Lack of O2 in the tissues - leads to ischaemia and necrosis
Can be caused by Hypoxyaemia, poor blood flow, low Hb, haemoglobinopathies, impaired cellular useage (sepsis, cyanide poisoning)

Question 2

Hypoxaemia

Answer 2

Low arterial Pa02
Can be due to: decreased inspired O2 (altitude), hypoventilation or type II resp failure, Shunts (ARDs), VQ mismatching (bronchospasm or PE) or diffusion defects (pulmonary fibrosis)

Question 3

PaO2

Answer 3

The amount of O2 dissolved in the plasma - generally a small fraction of the total oxygen carried by the blood
Oxygen therapy is usually required when it falls to 60mmHg/8kPa (SaO2 around 90%)

Question 4

SaO2

Answer 4

The Hb saturation with oxygen - produces a curve which moves depending on the physical and chemical states
Problematic below 90%

Question 5

Oxygen dissociation curve

Answer 5

The curve of Hb oxygen saturation by amount of oxygen in the blood –> Moving it to the left increases oxygen binding while moving it to the right decreases oxygen binding

Question 6

Factors which increase Hbs affinity for O2 (left shift) (5)

Answer 6

Hypothermia Alkalosis
Decreased PCO2 Decreased 2-3 DPG
Different forms of Hb (carboxy-, met-, foetal)

Question 7

Factors which decrease Hbs affinity for O2 (right shift) (4)

Answer 7

Hyperthermia                                   Acidosis
Increased PCO2 (Bohr)                   Increased 2-3 DPG

Question 8

Clinical assessment of oxygen transport (3)

Answer 8

Central or peripheral cyanosis (difficult if dark skin)
Increasing Resp Rate
Increased HR

Question 9

Pulse oximetry

Answer 9

Measure SaO2 by the absorption spectra of the blood
Will be confused if they have nail polish on or if there is CO poisoning –> would need to send to a hyperbaric oxygen chamber

Question 10

Arterial blood gases

Answer 10

This tells you the arterial PO2 and PCO2 and give a good picture –> make sure to correct for any oxygen therapy the patient is already on

Question 11

Oxygen uptake

Answer 11

VO2

about 200-250mls/min

Question 12

Oxygen delivery

Answer 12

DO2=(1.39xHb(g/dL)xSaO2/100) x cardiac output (ml/min)

Usually 1000mls/min

Question 13

Indications for oxygen therapy (7)

Answer 13

Cardiorespiratory arrest or resp failure (PaO2<8) type I/II
MI or heart failure, shock, Post-operative, CO poisoning
Increased metabolic demand

Question 14

Variable performance systems of oxygen therapy

Answer 14

No capacity systems –> nasal cannulae semi-rigid masks (MC, Hudson) - flow should be at least 4L/min to prevent rebreathing
Large capacity –> soft bag masks (pneumask, oxyaire)

Question 15

Fixed performance systems of oxygen therapy

Answer 15

In these case the FiO2 is fixed - venture masks where % is controlled by the entrainment disc size (24,28,35,40%)
Low-flow breathing circuits with a reservoir to deliver a fixed FiO2

Question 16

Hazards of Oxygen therapy

Answer 16

CO2 narcosis (COPD)--> loss of hypoxic drive, V/Q inequalities, Haldane effect
Pulmonary and neurological Oxygen toxicity ICU (FiO2 >0.6). Retrolental fibroplasias in neonates

Question 17

Indications for Mechanical ventilation (6)

Answer 17

To ensure high FiO2 and CO2 removal
To protect the airway of unconscious patients
Resp failure (type I or II), head injuries effecting CO2 elimination centres, heart failure causing a drop in CO,
Prophylactically in severe sepsis

Question 18

CPAP

Answer 18

Continuous positive airway pressure
+5-12cmH20 pressure continuously
Reduce work of breathing and can open up atelectatic areas

Question 19

PEEP

Answer 19

Positive end-expiratory pressure

+5-12cmH20 pressure at points during breathing Reduce work of breathing and can open up atelectatic areas

Question 20

Oxygenation while under mechanical ventilation depends on four things

Answer 20

The FiP2 (fractional inspired oxygen)
Patent airways (mean airway pressure)
Blood suppy to the ventilated alveoli
Diffusion from the blood

Question 21

Contraindications for non-invasive mechanical ventilation (5)

Answer 21

Severe hypoxia
Low consciousness level
Facial injuries or surgery
Excessive secretions 
GI obstruction

Question 22

Modes of mechanical ventilation

Answer 22

Spontaneous –> NIV,BiPAP, patient must be able to initiate breaths themselves
Controlled –> ventilator initiates breaths but can usually allow a degree of spontaneous breathing by the patient

Question 23

FiO2

Answer 23

Fraction of inspired oxygen –> eg 28%

Depends on oxygen flow, device and patient factors (breathing rate and vital capacity)

Question 24

CPAP

Answer 24

Continuous positive airway pressure - used for patients with sleep apnea, COPD/Type II respiratory failure or HF. Used in a spontaneously breathing patient. Can be used nasally or orally in infants. Can also be used where the patient is tiring to delay needing invasive ventilation.

Question 25

Non-invasive ventilation

Answer 25

Mainly used for COPD in respiratory acidosis or any form of type II respiratory failure.
It can be used in Cardiogenic pulmonary oedema unresponsive to CPAP or to wean off tracheal intubation.

Question 26

BPAP

Answer 26

A form of CPAP with changes in the applied pressure level depending on the stage in the breathing cycle.

Question 27

PEEP

Answer 27

Positive end-expiratory pressure. Just used to apply pressure at the end of the breathing cycle.