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Preoxygenation and Prevention of Desaturation During Emergency Airway Management
• Based on the article by Scott Weingart and Richard Levitan , Ann. Emerg. Med. 2012:59:165-175
• Patients requiring emergency airway management are at great risk of hypoxemia.. You can minimize the risk of critical hypoxia while securing a tracheal tube rapidly.
Safe Apnea
Duration of Apnea until O2 sat 88-90 %Obese patients desaturate fasterCritically ill patients desaturate fasterA. Increased metabolic demandsB. Volume depletionC. ShuntingD. AnemiaRemember that Pulse Oximetry lags by 30-60 seconds.
Oxyhemoglobin Dissociation Curve
Hypoxic below 60% High Risk Below 89%• Weingart SD. AnnEmergMed 2013.
Safe Apnea Cont’d
• In a patient breathing room air before intubation, desaturation will occur in 45-60 seconds. If , prior to administering the paralytic, the patient’s lungs are filled with O2, the time to desaturate will be a lot longer…
• There are 3 goals: bring the O2 sat as close to 100% as possible, get rid of all the nitrogen and fill those spaces with oxygen [78 % vs 21, normally], maximize the O2 in the bloodstream .
How to give the O2
• A nonrebreather face mask will deliver only 60-70 % O2 when it is set at 15 LPM. If you turn the flow rate up to 30-60 LPM you can deliver 90 % FIO2. A tight seal must be achieved to deliver more than ambient O2, [21 % ] .
• A standard reservoir facemask with theflow rate set as high as possible is the best source of O2.
Concepts
• Risk stratification by O2 saturation• Apneic Oxygenation [when the patient is not
breathing you are still oxygenating them]• Preintubation CPAP in patients who remain
hypoxic, in spite of your efforts
Risk categorization, during preoxygenation
• The Risk categories are based on a patient’s response to high flow O2 with a nonrebreather mask. Patients with an O2 sat of 96 % or greater are at low risk of desaturation during intubation.
• Low Risk, SPO2 of 96-100 %, preoxygenate for 3 minutes with a nonrebreather mask with maximal oxygen flow rate. One minute prior to intubation use the non rebreather mask AND a NASAL CANNULA at 15 LPM. During intubation leave the nasal cannula in place
Risk Categorization Cont’d
• Moderate Risk , SPO2 of 91-95 %. High Risk, hypoxic with an SPO2 of 90% or less while receiving high flow O2
• For 3 minutes preoxygenation using CPAP or a BVM with PEEP.
• One minute before intubating add a NASAL CANNULA at 15 LPM, in addition to the CPAP or BVM with PEEP
• During intubation continue the Nasal Cannula at 15 LPM
Improving Your Chances
• Positioning• Preoxygenation and Denitrogenation• Positive pressure Devices• Passive Apneic Oxygenation
Positioning• Put the head of the bed UP 20 degrees• Why? When we are flat it is harder to take a
full breath and more of the posterior lung becomes atelectatic. The diaphragms are higher and the total lung volume is less. This will increase the safe apnea time.
• THIS WILL ADD 90 SECONDS
Preoxygenation and Denitrogenation
When breathing room air 450 mls of O2 is present in the lungs. When you replace the nitrogen with O2 there is 3000 ml of O2 present in the lungs! Oxygen consumption during apnea is 250ml/min. In healthy patients the safe apnea time is 1 minute with room air. You can prolong the safe apnea period to 8 minutes! THIS IS THE KEY
Positive Pressure Devices
• If unable to achieve O2 sat > 93% - 95% with high FiO2
• CPAP / BiPAP • BVM with a PEEP valve • If patients are unable to achieve an O2 sat >
95 % then they are likely to desaturate during your intubation attempt. You must get the alveoli open with positive pressure to increase the O2 sat still higher.
Apneic Oxygenation
Why the nasal cannula? The O2 is under pressure and is being forced into the lungs and across the alveoli during your intubation. This will prolong the time it takes to desaturate . You are keeping the patient alive longer. They will become hypoxic more slowly. The times to desaturation are 8 minutes in healthy adults 5 minutes in moderately ill adults and 2.7 minutes in obese adults.. APNEIC OXYGENATION.
SUMMARY
• Position the patient at 20 Degrees• Tight seal with Non rebreather• Turn Flow rate to maximal• Try to get O2 Sat to 100%• Keep the O2 sat at 100% for 3 Minutes• If Unable to get sat to 100%, Use CPAP• Prior to Intubating, Use a NC at MAX FLOW