Airway anatomy Flashcards
Function and innervation:
Crycothyroid
Thyroarytenoid
Lateral Cricoarytenoid
Posterior Cricoarytenoid
C- Elongates (tenses) Vocal Cords “Come Together” - SLN external
T- Shortens (relaxes) vocal cords, adducts vocal folds (closes glottis) “They Relax” RLN
L- Adducts vocal folds (closes glottis) “Lets Close Airway”- RLN
P- Abducts vocal folds (opens glottis) “Please come apart” RLN
Cranial nerves that innervate the upper airway
Trigeminal CN 5- primary nerve that provides sensory innervation to the face and head. Divides into V1 : opthalmic (anterior ethmoidal)- nares and anterior 1/3 of nasal septum. V2: maxillary (sphenopalatine) Turbinates and septum. V3 Mandibular (lingual) Anterior 2/3 of tongue
Glossopharyngeal CN 9- Soft palate, oropharynx, Tonsils, Posterior 1/3 of tongue, Vallecula, anterior side of epiglottis (afferent limb of gag reflex)
The Vagus Nerve CN 10- Innervate the larynx and divides into the SLN (internal and external branches) and the RLN. SLN external -Motor, Internal-sensory. RLN- Motor- all intrinsic laryngeal muscles except cricothyroids, Sensory: Below level of vocal cords to trachea
What can cause Right and Left RLN Injury
Either Side: External pressure from ETT/LMA
Surgery: thyroid/parathyroid, Neck Stretching, Neck Tumor
Left side: PDA ligation, Left atrial enlargement (mitral Stenosis), Aortic arch aneurysm, Thoracic Tumor
SLN Injury
Injury to the trunk of the superior laryngeal nerve or the external branch causes hoarseness because the vocal cords cant be tensed. The cord on the affected side may appear “wavy”. Serves as the tuning fork, no respiratory distress.
RLN injury (Unilateral)
Causes paralysis of the ipsilateral vocal cord Abductors (drawn to midline). Causes hoarseness, but no respiratory distress. Common after subtotal thyroidectomy.
RLN Injury (bilateral)
Acute injury- Tensing action of the cricothyroid muscles acts unopposed: stridor and respiratory distress (emergency). Treatment includes emergent intubation or surgical airway.
Chronic- typically well tolerated
5 types of topical techniques to anesthetize the upper airway.
- Cotton soaked pledgets in the nares. 4% lidocaine and vasoconstrictor. Cocaine (caution PChE deficiency, increased SNS tone, MAOI drugs)
- Instill topical local anesthetic into each nare.
- Swish and Swallow- 4% viscous lidocaine (risk of N/V)
- Local anesthetic spray- 20% benzocaine (methemoglobinemia). treatment is methylene blue.
- Nebulization.
- Atomization- typically works better than nebulization
3 topical techniques to anesthetize vocal cords
- Inject local anesthetic through a nasal airway or ETT positioned just above the vocal cords
- Spray as you go with flexible fiberoptic scope
- inject local anesthetic through a multi-orifice epidural catheter that’s inserted into the suction port of a flexible fiberoptic catheter
Airway blocks: Glossopharyngeal
Insert need at the base of the palatoglossal arch to the depth of 0.25- 0.5 cm. Aspiration of air= too deep. Blood aspiration= could be carotid, withdraw and redirect
Once correct position 1-2 mL and then repeat on contralateral side
if injected into carotid leads to seizure risk
SLN block
Anesthetic is inject at the inferior boarder of the greater cornu of the hyoid bone
One mL is injected outside the thyrohyoid membrane, then 2mL is injected 2-3 mm deep to the thyrohyoid membrane, Repeat opposite side. Aspiration of air=too deep
RLN block
transtracheal approach- puncture the cricothyroid membrane, and advance the needle in a caudal direction (reduces risk of vocal cord injury)
after aspiration, but before injection, tell pt to take deep breath.
during inspiration, inject 3-5mL of LA into the tracheal lumen
the patient will cough, spraying the local anesthetic toward through the cords.
Laryngeal Anatomy
Adults sits at C3-C6 and has three functions: airway protection, respiration, and phonation
Consists of the hyoid bone (main support), Thyrohyoid ligament (membrane), Cricothyroid ligament (membrane)-used in cricothyroidotomy and performing transtracheal block, (3 paired and unpaired cartilages)
3 unpaired: Epiglottis, thyroid, cricoid
3 paired: corniculate, arytenoid, cuneiform
Narrowest region of the airway
determines the maximum ETT diameter.
Adults: glottic opening
Pediatric (under 5) : cricoid ring (fixed diameter)
vocal cords- narrowest dynamic region
Laryngospasm complications
complications: airway obstruction, negative pressure pulmonary edema, pulmonary aspiration of gastric contents, cardiac dysrhythmias, cardiac arrest, and death.
internal branch of SLN->afferent limb->brain->efferent limb ->External SLN (cricothyroid tenses cord-elongates) and RLN (Lateral cricoarytenoid and thyroarytenoid both close glottis)
Signs of laryngospasm
inspiratory stridor
suprasternal and supraclavicular retraction during inspiration
rocking horse appearance of the chest wall (paradoxical movement)
Increased diaphragmatic excursion
lower rib flailing
absent or altered EtCO2
Risk factors for laryngospasm
Pre anesthetic: Active or recent upper respiratory tract infection (<2 weeks), Exposure to second hand smoke, reactive airway disease, GERD, Age <1 year
In the OR: Light anesthesia, saliva or blood in the airway, hyperventilation/hypocapnia, surgical procedures (tonsillectomy, adenoidectomy, nasal/sinus, laryngoscopy, bronchoscopy, palatal
Interventions that reduce the risk and treatment or laryngospasm
interventions: avoid airway manipulation during light anesthesia, CPAP 5-10 during inhalation induction and right after extubation, remove secretions/blood before extubation, extubation stage 1 or 3 not 2, laryngeal lidocaine, IV lidocaine prior to extubation
tx: FiO2 100%, remove noxious stimuli, deepen anesthesia by increasing gas (can’t if spasming), CPAP 15-20 (head extension, chin lift, larson’s maneuver), Succs: IV: peds- 0.5-3 mg/kg, adult -0.5-2 mg/kg. IM peds 5mg/kg, adult 4mg/kg. given submental for fastest onset, IM roc if succs contraindicated
When administering succs to children <5, administer 0.02mg/kg of atropine to prevent bradycardia
Valsalva Maneuver and Muller’s Maneuver
Valsalva- Exhalation against a closed glottis
Examples-Coughing, bucking, or bearing down
risk- increased pressure in thorax, abdomen, and brain
Muller’s- inhalation against a closed glottis (or obstruction)
Example- patient bites down on ETT and takes a deep breath
Risk- subatmospheric pressure in the thorax-> negative pressure pulmonary edema
Upper airway anatomy
primary functions are warming and humidifying inspired air, filtering particulate matter, and preventing aspiration
Nasal turbinates (3 on each side) project from lateral wall and are highly vascular. To reduce trauma, the nasal device should be directed between the inferior turbinate and the floor of the nasal cavity
Upper airway patency
Pharynx is formed by the borders of the tongue, soft palate, pharyngeal tissue, and cervical spine. During normal inspiration, diaphragmatic contraction and chest wall expansion produce a negative pressure gradient that draws air into the lungs- this can cause airway collapse.
Tensor palatine - opens the nasopharynx, Genioglossus- opens the oropharynx (most common to relax due to anesthesia), hyoid muscles- opens the hypopharynx
Lower Airway
Trachea- begins at C6, Ends at T4-5 at the carina, semi-circular rings open posteriorly, Vagus innervated
Alveoli- 300million by age 9, pores of kohn allow air movement between alveoli
Pneumocytes- Type1: provides surface for gas exchange, Type2- produce surfactant, capable of cell division, can produce type 1 cells, Type 3- are macrophages, fight lung infection, produce inflammatory response. Neutrophils are present in patient that smoke and Acute lung injury
Carina- T4-5, corresponds with angle of louis, ciliated columnar epithelium.
Mainstem bronchi- Right: 2.5cm long, 25 degree take off, Left- 5 cm long, 45 degree take off
Lower airway key points
Incisors to the larynx is approx. 13 cm, larynx to carina is approx 13cm
Neck flexion makes distance shorter, neck extension= longer
Right mainstem intubation great likelihood as well as aspiration of foreign body to go
As airway bifurcates: number of airways increases and total cross sectional area
Decrease as bifurcates: airflow velocity, amount of cartilage, Goblet cells (produce mucus), Ciliated cells (clears mucus)
Variable as bifurcates: muscular layer
