Page 44 - TNFlipTest

A10
Anesthesia
pH
 2,3-BPG Temp
Airway Management Toronto Notes 2019 Oxygen Therapy
• ingeneral,thegoalofoxygentherapyistomaintainarterialoxygensaturation(SaO2)ataminimum,> 90%
• small decrease in saturation below SaO2 of 90% corresponds to a large drop in PaO2
• in intubated patients, oxygen is delivered via the ETT
• in patients not intubated, there are many oxygen delivery systems available; the choice depends on
oxygen requirements (FiO2) and the degree to which precise control of delivery is needed • cyanosis can be detected at SaO2 <85%, frank cyanosis at SaO2 = 67%
Low Flow Systems
• provideO2atflowsbetween0-10L/min
• acceptableiftidalvolume300-700mL,respiratoryrate(RR)<25,consistentventilationpattern • dilutionofoxygenwithroomairresultsinadecreaseinFiO2
• anincreaseinminuteventilation(tidalvolumexRR)resultsinadecreaseinFiO2
• e.g.nasalcannula(prongs)
■ well tolerated if flow rates <5-6 L/min; drying of nasal mucosa at higher flows
■ nasopharynx acts as an anatomic reservoir that collects O2
■ delivered oxygen concentration (FiO2) can be estimated by adding 4% for every additional litre of
O2 delivered
■ provides FiO2 of 24-44% at O2 flow rates of 1-6 L/min
Reservoir Systems
• useavolumereservoirtoaccumulateoxygenduringexhalationthusincreasingtheamountofoxygen available for the next breath
• simplefacemask
■ covers patient’s nose and mouth and provides an additional reservoir beyond nasopharynx ■ fed by small bore O2 tubing at a rate of at least 6 L/min to ensure that exhaled CO2 is flushed
through the exhalation ports and not rebreathed ■ provides FiO2 of 55% at O2 flow rates of 10 L/min
• non-rebreathermask
■ a reservoir bag and a series of one-way valves prevent expired gases from re-entering the bag ■ during the exhalation phase, the bag accumulates with oxygen
■ provides FiO2 of 80% at O2 flow rates of 10-15 L/min
High Flow Systems
• generateflowsofupto50-60L/min
• meet/exceedpatient’sinspiratoryflowrequirement
• deliverconsistentandpredictableconcentrationofO2 • Venturimask
■ delivers specific FiO2 by varying the size of air entrapment
■ oxygen concentration determined by mask’s port and NOT the wall flow rate ■ enables control of gas humidity
■ FiO2 ranges from 24-50%
Ventilation
• ventilationismaintainedwithPPVinpatientsgivenmusclerelaxants
• assistedorcontrolledventilationcanalsobeusedtoassistspontaneousrespirationsinpatientsnot
given muscle relaxants as an artificial means of supporting ventilation and oxygenation
Mechanical Ventilation
• indicationsformechanicalventilation ■ apnea
■ hypoventilation/acute respiratory acidosis
■ intraoperative positioning limiting respiratory excursion (e.g. prone, Trendelenburg) ■ required hyperventilation (to lower ICP)
■ deliver positive end expiratory pressure (PEEP)
■ increased intrathoracic pressure (e.g. laparoscopic procedure)
• complicationsofmechanicalventilation ■ airway complications
◆ tracheal stenosis, laryngeal edema
◆ alveolar complications
◆ ventilator-induced lung injury (barotrauma, volutrauma, atelectatrauma), ventilator-associated
pneumonia (nosocomial pneumonia), inflammation, auto-PEEP, patient-ventilator asynchrony ◆ cardiovascular complications
◆ reduced venous return (secondary to increased intrathoracic pressure), reduced cardiac output,
hypotension
100 90 80 70 60 50 40 30 20 10 0
pH
 2,3-BPG Temp
0 10 2030 40 5060 7080 90100
PaO2 Figure 8. HbO2 saturation curve
Composition of Air
78.1% nitrogen 20.9% oxygen 0.9% argon
0.04% carbon dioxide
Changes in peak pressures in ACV and tidal volumes in PCV may reflect changes in lung compliance and/or airway resistance – patient may be getting better or worse
Positive End Expiratory Pressure (PEEP)
• Positive pressure applied at the end of ventilation that helps to keep alveoli open, decreasing V/Q mismatch
• Used with all invasive modes of ventilation
Tracheostomy
• Tracheostomy should be considered in patients who require ventilator support for extended periods of time
• Shown to improve patient comfort and give patients a better ability to participate in rehabilitation activities
© Joshua Lai 2014
SaO2