Outcome 2.2 – Oxygen Delivery Systems – Flashcards
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High flow system vs low flow system
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high:device that meets al of the patient's inspiratory flow demands low: does not meet patient's insp. demands. NOTE: nothing to do with how much FiO2 delivered by device
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FiO2 depends on:
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reservoir size patient's ventilator system oxygen flow
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Low flow system: pros and cons
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pro: convenient, easy to set up. can deliver high and low FiO2. cons: FiO2 variable.
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Low flow system is suitable when
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Vt (tidal volume) is 300-700mL RR < 25 Ventilatory patter regular and consistent consistent and predictable FiO2 not required
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To determine patient's high flow requirements you need to know some of these:
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Minute Volume: (Vt)(RR) Cycle time: start of inspiration to end of expiration Inspiratory time Expiratory time Inspiratory flow
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Pros and Cons of high flow systems
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Pros: high and low FiO2, constant and predictable FiO2, depending on system can control temperature, humidity Cons: set up time consuming, requires regular monitoring, usually more expensive. Suitable anytime consistent and predictable FiO2
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Low Flow systems: Nasal Cannula
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FiO2's: 0.24-0.44 Flow: up to 6 Lpm Application: cannula sits inside nares, while tubing rests over top of ears Pros: uses upper airway as gas reservoir, commonly used Cons: uncomfortable at higher flows, due to dryness
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Low Flow systems: Nasal Catheter
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FiO2: 0.24-0.44 Flow: 1-6Lpm application: inserted through nasal passage until the tip sits behind uvula. pros: none cons: uncomfortable, need to be changed regularly
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Low Flow systems: High flow nasal cannula
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like regular NC, but tubing is a wider bore so flows can be higher and FiO2 delivery is higher. flows up to 15 Lpm replaces partial rebreather mask for FiO2 delivery
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Low Flow systems: simple mask
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FiO2's: 0.4-0.6 flow: 6-10 Lpm application: mask covers mouth and nose, adjustable metal tab covering bridge of nose, flexible straps behind bask
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Simple Mask, pros and cons
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pros:higher FiO2's possible because mask acts as additional oxygen reservoir, can attach to a nebulizer to deliver medications, humidity cons: patient unable to eat, speech may be muffled, flow must be >5Lpm to avoid dangerous CO2 buildup
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Low Flow systems: partial rebreathing mask
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FiO2's: 0.6-0.8+ Flow: is set so bag does not collapse during inspiration. in practice this is 6-15Lpm, at minimum of 6Lpm application: same as simple mask
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Low Flow systems: non rebreathing mask
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FiO2's: 0.8+ flow: as with partial rebreather, flow is set to keep bag inflated application: comes with 3 valves, be sure to remove one for safety. exhaled air does not go into bag. valves on mask to minimize entrainment of room air on inspiration
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Low Flow systems: Trans Tracheal Catheter
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used rarely, almost always in emergency situation placed either through cricoid cartilage or between the second and third tracheal ring uses upper and lower airway as reservoir.
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High Flow systems: air entrainment mask
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•A source gas (in this case oxygen) is diluted by air via jet to produce the desired FiO2 •If we think back to Bernouilli's principle we know that as gas velocity increases, lateral pressure decreases and this allows atmospheric gas to rush in. •An air entrainment mask uses this principle, by altering jet size, and the size of the entrainment port we can control FiO2 and total flow to the patient
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High Flow systems: optiflow; description
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heated, humidified high flow oxygen therapy. wide bore nasal prongs to deliver flow to patient. capable of 0-60 Lpm as either high or low system. theoretically provides PEEP to patient. Two *separate* components: blender to select FiO2; flowmeter to select flow delivery to patient.
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High Flow systems: optiflow; initiation
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start at 35-40 Lpm, based on patient RR. flow can be titrated up or down based on the work of breathing. more flow may help alleviate some work of breathing. start FiO2 at 1.0 then quickly wean until you reach your target saturation. set humidifier to invasive mode (37C)
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High Flow systems: optiflow; weaning
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start by weaning FiO2 as long as you are maintaining your target O2 saturation. once FiO2 below .4, start weaning the flow as long as work of breathing doesn't deteriorate. general rule: consider an FiO2 of .35 and a flow of 20Lpm to be roughly equivalent to 6Lpm via traditional nasal cannula
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High Flow systems: T piece for tracheotomy patients
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similar to optiflow, humidified high flow system. T attaches directly to tracheostomy tube. ensure you have pressure release valve somewhere in system.
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Pulse Oximetry. tool used to assess:
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the need for oxygen therapy effectiveness of our current oxygen therapy
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Pulse Oximetry, method of operation
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oxygenated hemoglobin absorbs different wavelengths of light than non oxygenated. calculate relative concentrations of oxy and de-oxy hemoglobin based on their different reactions of light
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Pulse Oximetry; features
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non invasive measures oxygen saturation of hemoglobin can also measure heart rate functions by measures of photospectrometry principle of light absorption
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Spectrophotometry in pulse oximetry
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used to determine oxy and deoxy hemoglobin only shines diff wavelengths of light through blood red (660nm) deoxygenated HgB infrared (940nm) oxygenated HgB also relies on pulsatile arterial flow; during systole the increased volume of blood increases the light absorbed during diastole the lower volume of blood decreases absorption
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Pulse oximetry; principle of operation
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2 LED's transmit the red, infrared light through the vascular bed a photodiode measures light which passes through the vascular bed. (finger, toe, hand/foot, earlobe, forehead) Ratios between the amplitude of the two plethysmographic waveforms are converted into an arterial oxygen saturation
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Accuracy of pulse oximeter
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check pulse index (around 1.0) check actual pulse, for correlation to sensor check waveform on monitor
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oxyhemoglobin dissociation curve
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left shift - hemoglobin have high affinity for oxygen higher pH, Lower DPG, lower temp right shift - hemoglobin have low affinity for oxygen. lower pH, higher DPG, higher temp
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pulse oximeter device limitations
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if dyshemoglobins are present in patients, may lead to inaccuracies: carboxyhemoglobin -ex smoke inhalation. binds strongly to hemoglobin. creates bright cherry red color to arterial blood methemoglobin -iron molecule in hemoglobin oxidizes. turns blood muddy brown. dyes and pigments: intravascular, nail polish, deeply pigmented skin
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pulse oximeter device limitations con't
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perfusion: ex cold room motion artifact high intensity light cannot read hyperoxemia diminished accuracy of <80%
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Lambert-Beers Law
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•Used when converting light absorbance into concentrations •Measured absorbance for a single substance is directly proportional to its concentration and the length of the light path through the sample
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Lambert-Beers Law Formula and coefficients
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A = e × c × l A = absorbance e = extinction coefficient (how light fades through a substance) c = concentration l = length of light path
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Different Hemoglobins (6)
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HHb O2Hb COHb MetHb SHb Bilirubin
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Dyshemoglobins: Carboxyhemoglobin COHb
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In COHb the binding sites are occupied by carbon-monoxide. • Cherry red discoloration of blood • Caused by inhalation from: Tobacco fumes, Exhaust gases, Fires • Therapy: Maintenance of adequate ventilation, high FIO2, hyperbaric oxygen therapy • The Oxygen Dissociation Curve is shifted to the left
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Dyshemoglobins: Methemoglobin - MetHb
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In MetHb the iron atom in one to four hemes of the hemoglobin tetramer is in ferri state. The hemes in this iron-state do not bind O2 but bind water. • Brownish discoloration of blood caused by oxidizing chemicals or drugs • Caused by chemicals: Aniline dyes - Nitrobenzene - Nitrotoluene -Naphthalene - Phenylhydrazine and medicine: Nitrites - Para-aminosalicylic acid - Prilocaine - Benzocaine - Lidocaine - Nitric Oxide • Therapy: Methylene blue, Ascorbic Acid • The Oxygen Dissociation Curve is shifted to the left
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Dyshemoglobins: Sulfhemoglobin - SulfHb
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one or two hemes of the hemoglobin tetramer are sulfated. The compound is very stable and has reduced affinity for oxygen. • Greenish discoloration of blood • Caused by medicine containing sulphur • Therapy: No therapy available, once formed sulfhemoglobinemia will persist for the life of the red cell (~ 120 days) and cause cyanosis for several months after toxic exposure • The Oxygen Dissociation Curve is shifted to the right
