Airway Anatomy, Physiology, And Management

1. Which of the following lung volumes cannot be measured with a spirometer?

Tidal Volume

Inspiratory Reserve Volume

Expiratory Reserve Volume

Vital Capacity

Functional Residual Capacity

A spirometer measures the volume of air that a patient moves both during inspiration as well as during expiration, but it has no direct way of quantifying air that is not moving. The volume of air that stays within the lung throughout the breathing cycle is called Residual Volume, and since the Functional Residual Capacity (FRC) is the sum of this Residual Volume and Expiratory Reserve Volume, it also cannot be measured with a spirometer.

Image available at:

http://upload.wikimedia.org/wikipedia/commons/3/3b/Lungvolumes.svg

Explanation

A spirometer measures the volume of air that a patient moves both during inspiration as well as during expiration, but it has no direct way of quantifying air that is not moving. The volume of air that stays within the lung throughout the breathing cycle is called Residual Volume, and since the Functional Residual Capacity (FRC) is the sum of this Residual Volume and Expiratory Reserve Volume, it also cannot be measured with a spirometer.

Image available at:

http://upload.wikimedia.org/wikipedia/commons/3/3b/Lungvolumes.svg

2. A 54 yo F has a total thyroidectomy for medullary carcinoma. During the procedure, the surgeon cuts the recurrent laryngeal nerve on the right side by mistake. Which of the following muscles will the patient still be able to move on the affected side?

Cricothyroid

Thyroarytenoid

Lateral cricoarytenoid

Arytenoid

Posterior cricoarytenoid

The only muscle in the larynx that is not innervated by the recurrent laryngeal nerve is the cricothyroid.

Miller RD and Pardo MC, Basics of Anesthesia 6th Edition, Ch:16 Airway Management, pg 222-3, Elsevier Publishing, 2011.

Explanation

The only muscle in the larynx that is not innervated by the recurrent laryngeal nerve is the cricothyroid.

Miller RD and Pardo MC, Basics of Anesthesia 6th Edition, Ch:16 Airway Management, pg 222-3, Elsevier Publishing, 2011.

3. A 63 yo m with a PMHx of HTN, type II Diabetes, and prostate cancer presents for a prostatectomy. After induction with midazolam, lidocaine, fentanyl, and propofol, mask ventilation produces minimal tidal volumes even after insertion of an oral airway. Intubation is difficult as well with 2 failed attempts and a grade III view with some bleeding from the second attempt. After calling for help, what is the best next step in this situation?

Wake the patient up

Attempt to intubate the patient again

Insert an LMA

Cricothyrotomy

Percutaneous tracheostomy

Suction the airway

The Difficult Airway Algorithm (DAA) details the steps that should be taken when an airway is not secured. In this case, the difficult airway was a surprise, and it is obviously too late to plan an awake intubation. This is perhaps a failure of the airway exam or the history and physical prior to the case. Regardless, this patient has had two unsuccessful intubation attempts and has inadequate mask ventilation, so the next step in the algorithm is to insert an LMA. If the LMA does not improve the patient's oxygen saturation, then it is time to create a surgical airway either with a cricothyrotomy or a tracheostomy.

image available at: http://airwayeducation.homestead.com/ASA-DiffAirwayAlgorithm.gif

Explanation

The Difficult Airway Algorithm (DAA) details the steps that should be taken when an airway is not secured. In this case, the difficult airway was a surprise, and it is obviously too late to plan an awake intubation. This is perhaps a failure of the airway exam or the history and physical prior to the case. Regardless, this patient has had two unsuccessful intubation attempts and has inadequate mask ventilation, so the next step in the algorithm is to insert an LMA. If the LMA does not improve the patient's oxygen saturation, then it is time to create a surgical airway either with a cricothyrotomy or a tracheostomy.

image available at: http://airwayeducation.homestead.com/ASA-DiffAirwayAlgorithm.gif

4. Rank the following from greatest to least volume in a patient with no PMHx on a ventilator during an elective inguinal hernia repair: 1. Alveolar dead space 2. Ventilator dead space 3. Anatomical dead space

1, 2, 3

2, 3, 1

3, 2, 1

1, 3, 2

Anatomical dead space refers to the volume of air that remains in the conducting airways and does not participate in gas exchange. Ventilator dead space refers to the volume of air that remains in the ventilator tubing and equipment and does not reach the patient's lungs. Alveolar dead space refers to the volume of air that reaches the alveoli but does not participate in gas exchange due to factors such as pulmonary embolism or lung disease. Therefore, the correct ranking from greatest to least volume is 3 (Anatomical dead space), 2 (Ventilator dead space), 1 (Alveolar dead space).

Explanation

Anatomical dead space refers to the volume of air that remains in the conducting airways and does not participate in gas exchange. Ventilator dead space refers to the volume of air that remains in the ventilator tubing and equipment and does not reach the patient's lungs. Alveolar dead space refers to the volume of air that reaches the alveoli but does not participate in gas exchange due to factors such as pulmonary embolism or lung disease. Therefore, the correct ranking from greatest to least volume is 3 (Anatomical dead space), 2 (Ventilator dead space), 1 (Alveolar dead space).

5. Which size in cuffed ET tube would most likely be appropriate for an 8 yo girl in the 50th percentile for weight and height?

3 mm

4 mm

5 mm

6 mm

7 mm

While there is of course variation between individuals, a typical 8 yo child requires a 6 mm uncuffed ET tube. A helpful formula is: (patient age +16) / 4. The measurement is the internal diameter of the tube.

Miller RD and Pardo MC, Basics of Anesthesia 6th Edition, Ch:16 Airway Management, pg 230-1, Elsevier Publishing, 2011.

Explanation

While there is of course variation between individuals, a typical 8 yo child requires a 6 mm uncuffed ET tube. A helpful formula is: (patient age +16) / 4. The measurement is the internal diameter of the tube.

Miller RD and Pardo MC, Basics of Anesthesia 6th Edition, Ch:16 Airway Management, pg 230-1, Elsevier Publishing, 2011.

6. Cricoid pressure during a rapid sequence intubation (RSI) not contraindicated in which of the following patients?

A 44 yo m with a history of GERD, last meal two hours ago presenting for an emergency exploratory laparotomy

A 16 yo F in a miami j collar after a fall

A 25 yo m presenting 30 minutes after a bar fight where he sustained a punch to the neck

Cricoid pressure was once the standard of care for any RSI because the thinking was that closing the airway must reduce the risk of aspiration. But more recent evidence shows that this might not be the case because in approximately 50% of patients, the esophagus is lateral and not posterior to the airway. This means that cricoid pressure can only move the esophagus further laterally in half of cases and does nothing to decrease aspiration risk.

In addition, cricoid pressure has been associated with poor outcomes in patients who are actively vomiting and patients with a suspected fracture in the cervical spine or the larynx. For a vomiting patient, the gastric pressure rises to 40-45 mmHg from the stomach muscle contractions, and if this pressure meets with an obstructed esophagus, the risk of rupture is increased significantly.

Barash, Clinical Anesthesiology, 6th Edition, Chapter 29: Airway Management, pg 767, 2009.

Explanation

Cricoid pressure was once the standard of care for any RSI because the thinking was that closing the airway must reduce the risk of aspiration. But more recent evidence shows that this might not be the case because in approximately 50% of patients, the esophagus is lateral and not posterior to the airway. This means that cricoid pressure can only move the esophagus further laterally in half of cases and does nothing to decrease aspiration risk.

In addition, cricoid pressure has been associated with poor outcomes in patients who are actively vomiting and patients with a suspected fracture in the cervical spine or the larynx. For a vomiting patient, the gastric pressure rises to 40-45 mmHg from the stomach muscle contractions, and if this pressure meets with an obstructed esophagus, the risk of rupture is increased significantly.

Barash, Clinical Anesthesiology, 6th Edition, Chapter 29: Airway Management, pg 767, 2009.

7. Which of the following is proportionally smaller in children than in adults?

Airway compliance

Epiglottis

Oxygen consumption

FRC

Tongue

The FRC is relatively smaller in kids because of their proportionally smaller chest wall, increased airway compliance, and relatively greater abdominal content, which causes the diaphram to press more significantly on the lower lung especially when the patient is supine. This is clinically significant as it is a large part of why children desaturate more quickly.

Other key differences in the pediatric vs. adult airway include:

1. Proportionally larger head and tongue

2. Proportionally larger, floppy epiglottis

3. Larynx is higher in the neck

4. Smaller, shorter trachea

5. Increased oxygen consumption 7-9mg/kg vs. 3-4mg/kg for adults

http://peds.stanford.edu/Rotations/picu/pdfs/10_Peds_Airway.pdf

Explanation

The FRC is relatively smaller in kids because of their proportionally smaller chest wall, increased airway compliance, and relatively greater abdominal content, which causes the diaphram to press more significantly on the lower lung especially when the patient is supine. This is clinically significant as it is a large part of why children desaturate more quickly.

Other key differences in the pediatric vs. adult airway include:

1. Proportionally larger head and tongue

2. Proportionally larger, floppy epiglottis

3. Larynx is higher in the neck

4. Smaller, shorter trachea

5. Increased oxygen consumption 7-9mg/kg vs. 3-4mg/kg for adults

http://peds.stanford.edu/Rotations/picu/pdfs/10_Peds_Airway.pdf

8. How many risk factors for a difficult mask ventilation are listed here? 1. Presence of a beard 2. BMI > 26kg / m2 3. Upper and lower dentures 4. Age > 55 5. History of snoring 6. Neck circumference > 20 cm 7. Male sex 8. Age < 6 months 9. History of smoking 10. History of GERD

5

6

7

8

9

10

Criteria for a difficult mask ventilation include: inability for an experienced anesthesiologist to maintain SpO2 > 92%, significant leak around the mask, no chest movement, need for > 4 Liters per minute of gas flow, or requiring two handed ventilation and assistance.

Of the qualities listed, only the first give are independent risk factors for difficulty with mask ventilation.

Patient characteristic (odds ratio)

Presence of a beard (3.18)

Body mass index > 26 kg/m2 (2.75)

Lack of teeth (2.28)

Age > 55 years (2.26)

History of snoring (1.84)

Barash PG and Cullen BF, Clinical Anesthesia 6th edition, chapter 29, table 29-6.

Explanation

Criteria for a difficult mask ventilation include: inability for an experienced anesthesiologist to maintain SpO2 > 92%, significant leak around the mask, no chest movement, need for > 4 Liters per minute of gas flow, or requiring two handed ventilation and assistance.

Of the qualities listed, only the first give are independent risk factors for difficulty with mask ventilation.

Patient characteristic (odds ratio)

Presence of a beard (3.18)

Body mass index > 26 kg/m2 (2.75)

Lack of teeth (2.28)

Age > 55 years (2.26)

History of snoring (1.84)

Barash PG and Cullen BF, Clinical Anesthesia 6th edition, chapter 29, table 29-6.

9. Which of the following is adequate but not more than adequate for denitrogenation in a healthy patient prior to induction for elective surgery?

4 deep breaths at FRC of 100% O2

6 deep breaths at FRC of 100% O2

10 deep breaths at FRC of 100% O2

Breathing 100% O2 at TV for 3 minutes

Breathing 100% O2 at TV for 5 minutes

Breathing 100% O2 at TV for 7 minutes

Studies show breathing 100% O2 at TV for 3 minutes or 8 breaths of 100% O2 at FRC are optimal for preoxygenation.

For further discussion click link: http://www.anesthesiologyrounds.ca/crus/anestheng_1106.pdf

Explanation

Studies show breathing 100% O2 at TV for 3 minutes or 8 breaths of 100% O2 at FRC are optimal for preoxygenation.

For further discussion click link: http://www.anesthesiologyrounds.ca/crus/anestheng_1106.pdf

10. Which of the following has not been shown to increase a patient's risk of aspiration?

BMI > 30

Pregnancy

History of smoking

History of GERD

Emergency procedures

Procedures between midnight at 6 AM

The overal incidence of aspiration is approximately 1 per 2000-3000 adults given anesthesia and 1 per 2600 pediatric cases. Risk factors such as obesity, pregnancy, abdominal disease, overnight procedures, history of GERD, and emergencies increase this risk significantly.

Kalinowski and Kirsch, Strategies for prophylaxis and treatment of aspiration, Best Practice and Research Clinical Anesthesia, Vol. 18, No. 4, pp 718-737.

available at: http://www.sassit.co.za/Journals/Peri-operative%20care/respiratory/prophylaxis%20and%20treatment%20for%20aspiration.pdf

Explanation

The overal incidence of aspiration is approximately 1 per 2000-3000 adults given anesthesia and 1 per 2600 pediatric cases. Risk factors such as obesity, pregnancy, abdominal disease, overnight procedures, history of GERD, and emergencies increase this risk significantly.

Kalinowski and Kirsch, Strategies for prophylaxis and treatment of aspiration, Best Practice and Research Clinical Anesthesia, Vol. 18, No. 4, pp 718-737.

available at: http://www.sassit.co.za/Journals/Peri-operative%20care/respiratory/prophylaxis%20and%20treatment%20for%20aspiration.pdf

11. A 17 yo M with unknown PMHx is rushed to the OR for an exploratory laparotomy after a gunshot wound to the abdomen. He vomits during induction. Which of the following is not part of the management of this situation?

Empirical administration of antibiotics

Rapid sequence intubation

Bronchoscopy

Shifting the patient to the trendelenburg position

Clearing the airway with suction and forceps

When a patient aspirates, goals are to maintain oxygenation, secure the airway, and decrease the chance of aspiration pneumonia or pneumonitis by clearing as much of the airway as possible. This patient should have a rapid sequence intubation with head down to minimize lung contamination followed by aggressive suctioning and possible bronchoscopy.

Current evidence is that patients who aspirate should only receive antibiotics when there is evidence of pneumonia, which occurs in 20-30% of cases.

King, Wendy, Pulmonary Aspirate of Gastric Contents, Update in Anesthesia, available at: http://update.anaesthesiologists.org/wp-content/uploads/2011/03/Pulmonary-aspiration-of-gastric-contents.pdf

Kalinowski CP and Kirsch JP, Strategies for prophylaxis and treatment of aspiration, Clinical Anesthesiology, Vol 18, No 4, pp 719-737, 2004 available at: http://www.sassit.co.za/Journals/Peri-operative%20care/respiratory/prophylaxis%20and%20treatment%20for%20aspiration.pdf

Explanation

When a patient aspirates, goals are to maintain oxygenation, secure the airway, and decrease the chance of aspiration pneumonia or pneumonitis by clearing as much of the airway as possible. This patient should have a rapid sequence intubation with head down to minimize lung contamination followed by aggressive suctioning and possible bronchoscopy.

Current evidence is that patients who aspirate should only receive antibiotics when there is evidence of pneumonia, which occurs in 20-30% of cases.

King, Wendy, Pulmonary Aspirate of Gastric Contents, Update in Anesthesia, available at: http://update.anaesthesiologists.org/wp-content/uploads/2011/03/Pulmonary-aspiration-of-gastric-contents.pdf

Kalinowski CP and Kirsch JP, Strategies for prophylaxis and treatment of aspiration, Clinical Anesthesiology, Vol 18, No 4, pp 719-737, 2004 available at: http://www.sassit.co.za/Journals/Peri-operative%20care/respiratory/prophylaxis%20and%20treatment%20for%20aspiration.pdf

12. All of the following are true statements with respect to lung perfusion EXCEPT:

Zone I receives ventilation with minimal perfusion

In zone I, PA > Pa > Pv

In zone II, Pa > PA > Pv

In zone III, Pa > PA > Pv

In zone III, perfusion is in excess of ventilation

Question from CLazar, MD

Explanation

Question from CLazar, MD

13. Which of the following physical exam findings is a reliable predictor of a difficult intubation?

Mallampati classification

Thyromental distance

Sternomental distance

Mouth opening > 6 cm

None of the above

Physical exam findings have low sensitivity in detecting a difficult intubation. The most sensitive test is sternomental distance (62%), and the much emphasized Mallampati is only 49% sensitive. Studies show that it is better to use physical findings as a group, but even a composite physical exam is far from an exact science (90% sensitive from one study).

Barash, Clinical Anesthesia, 6th edition, Chapter 29: Airway Management, 2009.

Explanation

Physical exam findings have low sensitivity in detecting a difficult intubation. The most sensitive test is sternomental distance (62%), and the much emphasized Mallampati is only 49% sensitive. Studies show that it is better to use physical findings as a group, but even a composite physical exam is far from an exact science (90% sensitive from one study).

Barash, Clinical Anesthesia, 6th edition, Chapter 29: Airway Management, 2009.

14. Approximately how much positive pressure is required to ventilate an adult with average lung compliance?

15-20 cm H2O

20-25cm H2O

25-30 cm H2O

30-35 cm H2O

No more than 20-25cm H2O should be needed to inflate the lungs of an adult with normal chest compliance. If more pressure is required, it is prudent to check the mask fit, insert an oral and/or nasal airway, or ask for help and try a two-handed mask hold.

Barash, Clinical Anesthesiology, 6th edition, Chapter 29, Airway Management, 2009.

Explanation

No more than 20-25cm H2O should be needed to inflate the lungs of an adult with normal chest compliance. If more pressure is required, it is prudent to check the mask fit, insert an oral and/or nasal airway, or ask for help and try a two-handed mask hold.

Barash, Clinical Anesthesiology, 6th edition, Chapter 29, Airway Management, 2009.

15. Which of the following is false concerning the pediatric airway when compared to adults?

Larger tongue

Angled vocal cords

Proportionally smaller epiglottis

Narrowest at the cricoid ring instead of the vocal cords

More superior larynx

All of the above are true

Compred with an adult, a pediatric patient will have a proportionally larger head and tongue and a relatively larger epiglottis that is less firm than in an adult. The vocal cords are also angled posteriorly in kids while they are straight up and down in an adult. Other important differences include:

1. Pediatric airway is narrowest at the cricoid ring instead of the vocal cords as in an adult

2. The larynx is located higher in the neck in kids with the hyoid bone at C2-C3 and descending to C6 at maturity.

3. Obligate nasal breathing in newborns until 6 months

4. A smaller and relatively shorter trachea

Picture located at: http://www.ceu-emt.com/images/childadultupperair.gif

For further discussion: http://peds.stanford.edu/Rotations/picu/pdfs/10_Peds_Airway.pdf

Explanation

Compred with an adult, a pediatric patient will have a proportionally larger head and tongue and a relatively larger epiglottis that is less firm than in an adult. The vocal cords are also angled posteriorly in kids while they are straight up and down in an adult. Other important differences include:

1. Pediatric airway is narrowest at the cricoid ring instead of the vocal cords as in an adult

2. The larynx is located higher in the neck in kids with the hyoid bone at C2-C3 and descending to C6 at maturity.

3. Obligate nasal breathing in newborns until 6 months

4. A smaller and relatively shorter trachea

Picture located at: http://www.ceu-emt.com/images/childadultupperair.gif

For further discussion: http://peds.stanford.edu/Rotations/picu/pdfs/10_Peds_Airway.pdf

16. Coughing that occurs during awake intubation is prevented by a local anesthetic block of which of the following nerves?

Glossopharyngeal

Hypoglossal

Recurrent laryngeal and glossopharyngeal

Recurrent laryngeal and superior laryngeal

Superior laryngeal and glossopharyngeal

The recurrent laryngeal nerve innervates all of the muscles of the larynx except the cricothyroid, and the superior laryngeal nerve provides sensation to this area. The hypoglossal provides motor innvervation to the tongue, and the glossopharyngeal provides sensation superiorly to where the coughing takes place.

Question from 1996 ITE, explanation by MJensen, MD

Picture available at:

http://polanest.webd.pl/pliki/varia/books/AtRegAn/micro189.lib3.hawaii.edu_3a2127/das/book/body/0/1353/f4-u1.0-b1-4160-2239-2..50031-x..f027002.jpg

Explanation

The recurrent laryngeal nerve innervates all of the muscles of the larynx except the cricothyroid, and the superior laryngeal nerve provides sensation to this area. The hypoglossal provides motor innvervation to the tongue, and the glossopharyngeal provides sensation superiorly to where the coughing takes place.

Question from 1996 ITE, explanation by MJensen, MD

Picture available at:

http://polanest.webd.pl/pliki/varia/books/AtRegAn/micro189.lib3.hawaii.edu_3a2127/das/book/body/0/1353/f4-u1.0-b1-4160-2239-2..50031-x..f027002.jpg

17. A 2 to boy with PMHx of obstructive sleep apnea presents for tonsillectomy and adenoidectomy. After induction with propofol, lidocaine, and midazolam, he is impossible to ventilate and intubate. An LMA is placed, but the tidal volume is minimal. With the patient desaturating below 70%, which of the following is the next best step?

Tracheostomy

Cricothyrotomy

Needle cricothyrotomy

Fiberoptic intubation

Retrograde intubation

This patient does not have time for a fiberoptic or retrograde intubation; he needs an immediate surgical airway. While cricothyrotomy would be the procedure of choice in adults, it is contraindicated in kids because the cricothyroid ring is smaller and the airway is narrowest at that point. Instead, a 12 or 14 gauge needle should be inserted into the cricothyroid membrane and attached to the bag mask to reoxygenate the patient.

Barash, Clinical Anesthesia, 6th Edition, Chapter 29: Airway Management, pg. 788-9, 2009.

Explanation

This patient does not have time for a fiberoptic or retrograde intubation; he needs an immediate surgical airway. While cricothyrotomy would be the procedure of choice in adults, it is contraindicated in kids because the cricothyroid ring is smaller and the airway is narrowest at that point. Instead, a 12 or 14 gauge needle should be inserted into the cricothyroid membrane and attached to the bag mask to reoxygenate the patient.

Barash, Clinical Anesthesia, 6th Edition, Chapter 29: Airway Management, pg. 788-9, 2009.

18. A 72 yo F with a PMHx of HTN, DM2, asthma, and 40 pack years cigarette smoking presents for a left nephrectomy after being diagnosed with renal cell carcinoma. She lost 1.5L of blood during the procedure, and received 6mg morphine prior to extubation. Two hours later she develops respiratory distress in the PACU. Her blood gases on room air were: PaO2 = 60 pH = 7.43 PaCO2 = 37 HCO3 = 22 Vitals: 88, 126/65, 37.2, 15, 89% on RA What is the cause of her respiratory distress?

Hypoventilation

Atelectasis

Anemia

Aspiration pneumonia

Low FiO2

The most common cause of postoperative respiratory distress is atelectasis. This comes from a combination of postoperative pain and sedation that results in poor inspiratory effort. A more scientific way to the answer is to calculate the alveolar-arterial (A-a) gradient. The formula for this is PAO2 - PaO2 with PAO2 = 150 x 1.25(PCO2). PAO2 = 103.75, which is far above normal. This means that the source of the patient's respiratory distress must be a mismatch of ventilation and perfusion within the lung. Hypoventilation and anemia would not produce an elevated A-a gradient. Of the choices remaining, aspiration is unlikely without a fever or any signs on physical exam, and as the patient is breathing room air, low FiO2 is also unlikely. As mentioned, atelectasis is very common postoperatively and can be treated with an incentive spirometer, better pain control, and sitting the patient up in bed.

Explanation

The most common cause of postoperative respiratory distress is atelectasis. This comes from a combination of postoperative pain and sedation that results in poor inspiratory effort. A more scientific way to the answer is to calculate the alveolar-arterial (A-a) gradient. The formula for this is PAO2 - PaO2 with PAO2 = 150 x 1.25(PCO2). PAO2 = 103.75, which is far above normal. This means that the source of the patient's respiratory distress must be a mismatch of ventilation and perfusion within the lung. Hypoventilation and anemia would not produce an elevated A-a gradient. Of the choices remaining, aspiration is unlikely without a fever or any signs on physical exam, and as the patient is breathing room air, low FiO2 is also unlikely. As mentioned, atelectasis is very common postoperatively and can be treated with an incentive spirometer, better pain control, and sitting the patient up in bed.

19. Which of the following could occur before placement of an endotrachial tube in a true rapid sequence intubation? 1. Propofol 150mg IVP 2. Gentle mask ventilation 3. Succinylcholine 50mg IVP 4. Rocuronium 50mg IVP 5. Midazolam 2mg IVP 6. Fentanyl 150mcg IVP 7. Preoxygenation 8. Sellick's Maneuver

1, 2, 3, 7, 8

1, 3, 4, 7, 8

1, 3, 4, 5, 7

1, 3, 6, 7, 8

2, 3, 4, 7, 8

The purpose of a rapid sequence intubation (RSI) is to decrease the risk of aspiration by reducing the time between unconsciousness and placement of the endotrachial tube. The sequence of events in a true RSI is:

1. Preoxygenation with the patient awake for 3-5 minutes breathing at tidal volume

2. Unconsciousness with propofol / ketamine / etomidate

3. Paralysis with succinylcholine or a nondepolarizing agent

4. Application of cricoid pressure (Sellick's maneuver -- although it is controversial)

5. Placement of ET tube

Pretreating with midazolam or fentanyl only makes the patient sedated, which increases aspiration risk. Also, mask ventilation-- even at low pressures -- is thought to contribute to insufflation of the stomach and increase the risk of aspiration. Including mask ventilation or some sedation prior to induction is called a modified rapid sequence.

Barash, Clinical Anesthesiology, 6th Edition, Chapter 29: Airway Management, 2009, pg. 767.

Explanation

The purpose of a rapid sequence intubation (RSI) is to decrease the risk of aspiration by reducing the time between unconsciousness and placement of the endotrachial tube. The sequence of events in a true RSI is:

1. Preoxygenation with the patient awake for 3-5 minutes breathing at tidal volume

2. Unconsciousness with propofol / ketamine / etomidate

3. Paralysis with succinylcholine or a nondepolarizing agent

4. Application of cricoid pressure (Sellick's maneuver -- although it is controversial)

5. Placement of ET tube

Pretreating with midazolam or fentanyl only makes the patient sedated, which increases aspiration risk. Also, mask ventilation-- even at low pressures -- is thought to contribute to insufflation of the stomach and increase the risk of aspiration. Including mask ventilation or some sedation prior to induction is called a modified rapid sequence.

Barash, Clinical Anesthesiology, 6th Edition, Chapter 29: Airway Management, 2009, pg. 767.

20. A 4 yo m presents emergently for appendicitis. After a successful surgery, he desaturates in the PACU. On exam his abdomen and chest are moving paradoxically, and no air is coming out of his mouth and nose. Which of the following is not part of the treatment algorithm for this patient's condition?

Jaw thrust

Positive pressure ventilation

Insertion of an LMA

Succinylcholine

Propofol

Insertion of a nasal airway

This is a classic case of laryngospasm, which is an involuntary closure of the vocal cords causing airway obstruction. Laryngospasm is a reflex to prevent aspiration and occurs most commonly during emergence due to airway irritation from secretions or stimulation. It is especially dangerous in children as they can desaturate rapidly and go into cardiac arrest. The first line treatment for laryngospasm is jaw thrust with positive pressure ventilation, and if this fails, deepening anesthesia with propofol (0.25 - 0.8 mg/kg) or relaxing the larynx with succinylcholine (0.1 - 0.3 mg/kg) is second line. Inserting an LMA is not productive as it sits above the larynx and does not address the obstruction. In fact, LMAs are a well-known cause of laryngospasm as they irritate the throat.

Further discussion available at:

http://www.ntuh.gov.tw/ENT/DocLib7/Laryngospasm%2020081223.pdf

Explanation

This is a classic case of laryngospasm, which is an involuntary closure of the vocal cords causing airway obstruction. Laryngospasm is a reflex to prevent aspiration and occurs most commonly during emergence due to airway irritation from secretions or stimulation. It is especially dangerous in children as they can desaturate rapidly and go into cardiac arrest. The first line treatment for laryngospasm is jaw thrust with positive pressure ventilation, and if this fails, deepening anesthesia with propofol (0.25 - 0.8 mg/kg) or relaxing the larynx with succinylcholine (0.1 - 0.3 mg/kg) is second line. Inserting an LMA is not productive as it sits above the larynx and does not address the obstruction. In fact, LMAs are a well-known cause of laryngospasm as they irritate the throat.

Further discussion available at:

http://www.ntuh.gov.tw/ENT/DocLib7/Laryngospasm%2020081223.pdf

21. Which of the following is not associated with increased airway resistance?

Increased gas flow rate

Decreased tidal volume

Intubation with an 8mm ET tube with the ventilator on spontaneous mode

Positive End Expiratory Pressure

Increasing respiratory rate

All of the above increase airway resistance

Positive End Expiratory Pressure (PEEP) is a technique used in mechanical ventilation to maintain positive pressure in the airways at the end of expiration. It helps to prevent alveolar collapse and improve oxygenation. PEEP does not directly increase airway resistance, but rather helps to keep the airways open and decrease resistance. Increased gas flow rate, decreased tidal volume, intubation with an 8mm ET tube, and increasing respiratory rate can all lead to increased airway resistance by various mechanisms such as narrowing of the airways or increased resistance to airflow.

Explanation

Positive End Expiratory Pressure (PEEP) is a technique used in mechanical ventilation to maintain positive pressure in the airways at the end of expiration. It helps to prevent alveolar collapse and improve oxygenation. PEEP does not directly increase airway resistance, but rather helps to keep the airways open and decrease resistance. Increased gas flow rate, decreased tidal volume, intubation with an 8mm ET tube, and increasing respiratory rate can all lead to increased airway resistance by various mechanisms such as narrowing of the airways or increased resistance to airflow.