SEM2WEEK4 DFI Flashcards
point of cricoid pressure? evidence for or against?
it is used to compress the oesophagus and prevent regurgitation of gastric contents until the tube is placed. Evidence suggests that this procedure actually does not reduce the incidence of aspiration. Should be released if obstructing view for laryngoscopy.
3 goals of pre oxygenation
bring the patients saturations as close to 100% as possible. To denitrogenate the residual capacity of the lungs (maximising oxygen storage in the lungs) and to denitrogenate and maximally oxygenate the blood stream.
* the first two goals are imperative, denitrogenating and oxygenating the blood adds little to the duration of safe apnoea because oxygen is poorly soluble in the blood and the bloodstream is a comparatively small oxygen reservoir compared with the lungs (5 vs 95%)
what is the best source of high FiO2 for preoxygenation
- Bag valve mask ventilations- BVM’s lacking 1 way inhalation and exhalation ports will deliver only close to room air FiO2 when not actively assisting ventilations. Even with 1 way valves the bags will only deliver oxygen in two circumstances: the patient generates enough inspiratory force to open the valve OR the practitioner squeezes the bag. In both circumstances, to obtain any FiO2 above that of room air a tight seal must be achieved usually with 2 handed technique. A BVM device hovering above the patients face only provides ambient FiO2
For what period of time should the patient receive pre oxygenation?
- 3/60 worth of tidal volume breathing (the patient’s normal respiratory pattern) with a high FiO2 source is an acceptable duration for most patients.
- The above times are predicted on a source of FiO2 greater than or equal to 90% and a tightly fitting mask that prevents entrainment of room air.
How long will it take for patients to desaturate after preoxygenation?
- When a patient is breathing room air, 450ml of oxygen is present in the lungs. This increases to 3,000ml when a patient breathes 100% oxygen for a sufficient time to replace alveolar nitrogen.
- Oxygen consumption during apnoea is approx. 250ml/min in healthy patients, the duration of safe apnoea on room air is approx. 1 minute compared with approx. 8 minutes when breathing at a high FiO2 level
Can apnoeic oxygenation extend the duration of safe apnoea?
- Alveoli will continue to take up oxygen even without diaphragmatic movements or lung expansion.
- In the apnoeic patient, approx. 250ml/minute oxygen will move from the alveoli into the blood stream. Conversely only 8-20ml/minute of CO2 moves into the alveoli during apnoea, with the remainder being buffered in the blood stream.
- Nasal cannulas provide limited FiO2 to a spontaneously breathing patient, but the decreased oxygen demands of the apnoeic state will allow the device to fill the pharynx with a high level of FiO2 gas. By increasing the flow rate to 15Lmin, near 100% FiO2 can be achieved.
why do critical illnesses short the safe apnoea time?
increased metabolic demand, low functional reserve, airway obstruction and shunt physiology
define apnoeic oxygenation and how does it work
- Oxygenation in the absence of spontaneous or mechanical ventilation
- Passive oxygenation via nasal cannula to continue diffusion of oxygen and prolong our period of safe saturation levels
- In the apnoeic patient, extraction of oxygen from the alveolus into the blood causes alveolar pressure to become sub atmospheric
- Generating a pressure gradient which enables the movement of additional administered oxygen into the alveoli
aims of anaethesia
unconsciousness
amnesia
analgesia
hierarchy of need
top to bottow
no awareness
no memory
no pain
no physiological compromise
alive
HOPS KILLERS
3 physiological parameters that increase risk of compromise, morbidity or mortality
Hypotension
oxygenation
pH
