Airway & Respiratory Anatomy

Also known as Airway anatomy · Respiratory anatomy · Larynx · Laryngeal cartilages · Thyroid cartilage · Cricoid cartilage · Arytenoid cartilage · Epiglottis · Vocal cords · Recurrent laryngeal nerve · Superior laryngeal nerve · Cricothyroid membrane · Trachea · Carina · Right main bronchus · Bronchopulmonary segments · Lung lobes · Pleura · Diaphragm · Phrenic nerve · Alveolus · Alveolar-capillary membrane · Surfactant · Type II pneumocyte · Pulmonary vascular tree · Diaphragm innervation

Airway and respiratory anatomy for the ICU First Part: the upper airway (nose, naso-/oro-/laryngopharynx, larynx and its cartilages — thyroid, cricoid as the only complete ring, arytenoid, epiglottis — vocal cords, and the superior and recurrent laryngeal nerves), the lower airway (the trachea 10-12 cm with C-shaped rings, the carina at T4/T5, the right main bronchus wider/shorter/more vertical as the aspiration path), the bronchopulmonary segments (ten right, eight to ten left), lung lobes and hilum, the pleura (visceral and parietal, the pleural space and fluid), the conducting vs respiratory zones (generations 0-23), the alveolar-capillary membrane, the pulmonary vascular tree, and the muscles of breathing (the diaphragm via the phrenic nerv

high18 referencesUpdated 26 July 202628 min readVerification in progress

Practise this topic

8 MCQs

The one-line answer

The airway is one tube from nose to alveolus, and three facts earn most of the marks: the cricoid is the only complete ring, the right main bronchus is wider-shorter-more vertical (the aspiration path), and "C3, 4, 5 keeps the diaphragm alive". The superior laryngeal nerve gives sensation above the cords and motor to the cricothyroid (the tensor); the recurrent laryngeal nerve gives everything else — and the left RLN loops under the aortic arch, so a left cord palsy with no neck surgery demands a chest CT. The trachea bifurcates at the carina (T4/T5); the conducting zone (generations 0 to 16) is dead space, the respiratory zone (17 to 23) exchanges gas. Type I pneumocytes form the blood-gas barrier and cannot divide; type II pneumocytes make surfactant and are the stem cell.^[1]

Meet the patient

A 58-year-old obese man (BMI 42) with severe pneumonia is increasingly hypoxic (SpO2 88 per cent on 15 L), RR 32 with accessory-muscle use and stertorous breathing. Thick neck, full beard, receded mandible, inter-incisor distance 2.5 cm, Mallampati III, known hiatus hernia with reflux. You are called to intubate.^[1]

The question this patient plants is the question every airway decision turns on: what is the narrowest part of the airway, what lies behind it, and where does a too-deep tube or an aspirated tooth go? The answers — the glottis in the adult (the subglottic cricoid in a child), the recurrent laryngeal nerve in the tracheo-oesophageal groove, and the right main bronchus — are the load-bearing facts of airway anatomy. Hold them and the cricoid, the bronchial tree, the alveolus, and the diaphragm fall into place around them.^[1]

References18Show

[1]Weibel ER Lung morphometry: the link between structure and function Cell Tissue Res, 2017.PMID 27981379
[2]Bhatia N, Bhagat H Cricoid pressure: Where do we stand? J Anaesthesiol Clin Pharmacol, 2014.PMID 24574584
[3]Tessarolo E, Alkhouri H, Lelos N, et al. Review article: Effectiveness and risks of cricoid pressure during rapid sequence induction for endotracheal intubation in the emergency department: A systematic review Emerg Med Australas, 2022.PMID 35577760
[4]Dunn D Cricoid Pressure: Contradictory Evidence Regarding a Standard Practice AORN J, 2022.PMID 35476194
[5]Mahfood S, Hix WR, Aaron BL, et al. Reexpansion pulmonary edema Ann Thorac Surg, 1988.PMID 3279931
[6]Nazer RI Topical Ice Slush Adversely Affects Sniff Nasal Inspiratory Force After Coronary Bypass Surgery Heart Lung Circ, 2018.PMID 28473213
[7]Menon R, Vasani SS, Widdicombe NJ, et al. Laryngeal injury following endotracheal intubation: Have you considered reflux? Anaesth Intensive Care, 2023.PMID 36168788
[8]Whitsett JA Review: The intersection of surfactant homeostasis and innate host defense of the lung: lessons from newborn infants Innate Immun, 2010.PMID 20351134
[9]Hüttl TP, Wichmann MW, Reichart B, et al. Laparoscopic diaphragmatic plication: long-term results of a novel surgical technique for postoperative phrenic nerve palsy Surg Endosc, 2004.PMID 15108692
[10]Miserocchi G Physiology and pathophysiology of pleural fluid turnover Eur Respir J, 1997.PMID 9032518
[11]Haefeli-Bleuer B, Weibel ER Morphometry of the human pulmonary acinus Anat Rec, 1988.PMID 3382030
[12]Reed MJ, Dunn MJ, McKeown DW Can an airway assessment score predict difficulty at intubation in the emergency department? Emerg Med J, 2005.PMID 15662057
[13]Tran DT, Newton EK, Mount VA, et al. Rocuronium versus succinylcholine for rapid sequence induction intubation Cochrane Database Syst Rev, 2015.PMID 26512948
[14]Sluga M, Ummenhofer W, Studer W, et al. Rocuronium versus succinylcholine for rapid sequence induction of anesthesia and endotracheal intubation: a prospective, randomized trial in emergent cases Anesth Analg, 2005.PMID 16243994
[15]Frerk C, Mitchell VS, McNarry AF, et al. Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults Br J Anaesth, 2015.PMID 26556848
[16]Brower RG, Matthay MA, Morris A, et al. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome N Engl J Med, 2000.PMID 10793162
[17]Amato MB, Meade MO, Slutsky AS, et al. Driving pressure and survival in the acute respiratory distress syndrome N Engl J Med, 2015.PMID 25693014
[18]Guérin C, Reignier J, Richard JC, et al. Prone positioning in severe acute respiratory distress syndrome N Engl J Med, 2013.PMID 23688302

Airway & Respiratory Anatomy

high18 referencesUpdated 26 July 202628 min readVerification in progress

Practise this topic

8 MCQs

Meet the patient

References18Show

[1]Weibel ER Lung morphometry: the link between structure and function Cell Tissue Res, 2017.PMID 27981379
[2]Bhatia N, Bhagat H Cricoid pressure: Where do we stand? J Anaesthesiol Clin Pharmacol, 2014.PMID 24574584
[3]Tessarolo E, Alkhouri H, Lelos N, et al. Review article: Effectiveness and risks of cricoid pressure during rapid sequence induction for endotracheal intubation in the emergency department: A systematic review Emerg Med Australas, 2022.PMID 35577760
[4]Dunn D Cricoid Pressure: Contradictory Evidence Regarding a Standard Practice AORN J, 2022.PMID 35476194
[5]Mahfood S, Hix WR, Aaron BL, et al. Reexpansion pulmonary edema Ann Thorac Surg, 1988.PMID 3279931
[6]Nazer RI Topical Ice Slush Adversely Affects Sniff Nasal Inspiratory Force After Coronary Bypass Surgery Heart Lung Circ, 2018.PMID 28473213
[7]Menon R, Vasani SS, Widdicombe NJ, et al. Laryngeal injury following endotracheal intubation: Have you considered reflux? Anaesth Intensive Care, 2023.PMID 36168788
[8]Whitsett JA Review: The intersection of surfactant homeostasis and innate host defense of the lung: lessons from newborn infants Innate Immun, 2010.PMID 20351134
[9]Hüttl TP, Wichmann MW, Reichart B, et al. Laparoscopic diaphragmatic plication: long-term results of a novel surgical technique for postoperative phrenic nerve palsy Surg Endosc, 2004.PMID 15108692
[10]Miserocchi G Physiology and pathophysiology of pleural fluid turnover Eur Respir J, 1997.PMID 9032518
[11]Haefeli-Bleuer B, Weibel ER Morphometry of the human pulmonary acinus Anat Rec, 1988.PMID 3382030
[12]Reed MJ, Dunn MJ, McKeown DW Can an airway assessment score predict difficulty at intubation in the emergency department? Emerg Med J, 2005.PMID 15662057
[13]Tran DT, Newton EK, Mount VA, et al. Rocuronium versus succinylcholine for rapid sequence induction intubation Cochrane Database Syst Rev, 2015.PMID 26512948
[14]Sluga M, Ummenhofer W, Studer W, et al. Rocuronium versus succinylcholine for rapid sequence induction of anesthesia and endotracheal intubation: a prospective, randomized trial in emergent cases Anesth Analg, 2005.PMID 16243994
[15]Frerk C, Mitchell VS, McNarry AF, et al. Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults Br J Anaesth, 2015.PMID 26556848
[16]Brower RG, Matthay MA, Morris A, et al. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome N Engl J Med, 2000.PMID 10793162
[17]Amato MB, Meade MO, Slutsky AS, et al. Driving pressure and survival in the acute respiratory distress syndrome N Engl J Med, 2015.PMID 25693014
[18]Guérin C, Reignier J, Richard JC, et al. Prone positioning in severe acute respiratory distress syndrome N Engl J Med, 2013.PMID 23688302