103. Lungs

Question 1

lung lobes

Answer 1

6left: cranial (cranial and caudal parts) and caudal loberight: cranial, middle, caudal, accessory

Question 2

why is normal alveolar surface tension low

Answer 2

low because of surfactant produced by alveolar type II cellsindirectly increases lung compliance by decreasing the amount of work needed to inflate the lungalso prevent collapse of alveoli

Question 3

pulmonary compliance based on a pressure volume curve

Answer 3

increased compliance = steep slopecompliance can be modified by fibrosis or edema

Question 4

contributors to normal inspiratory airway resistance

Answer 4

nares 75%larynx 5%lower airways 20%

Question 5

chemoreceptors modulate ventilation based on what parameters

Answer 5

–PaO2–PaCO2 (biggest driving force)–pHcentral (ventral medulla) and peripheral chemoreceptors

Question 6

oxygen–HB dissociation curve

Answer 6

incr temp, incr PaCO2, decr pH and incr 2.3 DPG shift Hb dissociation curve to the RIGHT (decreased affinity)decr temp, decr PaCO2, incr pH and decr 2,3 DPG shift Hb dissociation curve to the LEFT (increased affinity)plateau–decr in partial pressure of alveolar gas will have little effect on oxygen saturation if pressures are >80 mm Hgslope–peripheral tissues can withdraw a large amount of oxygen for only a small decrease in capillary oxygen partial pressure

Question 7

T/Fthe diffusion coefficient of PaCO2 is 20x greater than oxygen

Answer 7

TRUE

Question 8

oxygen saturation for arterial vs venous samples

Answer 8

97.5% saturated PaO2 100 mm Hg (arterial)75% saturated PvO2 40 mm Hg (venous)

Question 9

arterial oxygen content in blood equation

Answer 9

CaO2 = (1.36 x Hb x SPO2) + (0.003 x PaO2)Hb and blood transfusions improve oxygen carrying capacity to a greater extent than just oxygen supplementation alone

Question 10

how are oxygen and CO2 carried in blood (mostly)

Answer 10

oxygen—hemoglobin A (ferrous form)ferric form of hemoglobin A transport methemoglobin (unable to carry oxygen)CO2—bicarbonatein RBC, combine with water–>carbonic acid via carbonic anhydrase–>then dissociates to H+ and Hco3 (bicarb–which diffuses out)

Question 11

3 mechanisms of impaired gas exchange

Answer 11

1. Ventilation perfusion mismatch (incr V/Q with PTE, decr V/Q with pneumonia, alveolar collapse)2. Diffusion impairment (incr thickness–fibrosis/edema)3. shunting (right to left PDA–do not respond to O2 therapy)

Question 12

equation to calculate or quantify the severity of gas exchange impairment

Answer 12

alveolar-arterial oxygen gradient/differencePAO2-PaO2 =[FI02 x (Pbaro - 47)-1.2 x PaCO2] - Pa02if breathing room air PAo2-PaO2 should be less than 10 mmHgif the gradient is >30 mm Hg there is severe gas exchange impairment

Question 13

consequences of thoracotomy on pulmonary physiology

Answer 13

—hypoxemia (decreased FIO2, hypo ventilating, diffusion impairment, shunting, VQ mismatch from atelectasis)–residual pneumothorax/pleural effusion (impairs lung ability to reexpand)–pain (prevents full thoracic wall excursion)

Question 14

surgical approaches to the chest

Answer 14

1. lateral thoracotomy2. median sternotomy3. thoracoscopy (transdiaphragmatic or intercostal approach)4. keyhole technique (if diffuse disease)

Question 15

layers to enter upon a lateral thoracotomy

Answer 15

skin, SQ, CTMlatissimusserratus ventralisscalenus (cranial to fifth rib); rectus abdominus (cd to 5th rib)external and internal intercostal musclespleuracaution: ventrally internal thoracic artery

Question 16

pulmonary cysts, bullae, blebs

Answer 16

cysts: epith lined, fill with air or fluid, mostly from pulmonary contusionbullae and blebs are pseudocysts (not epith lined)bullae: large and within the parenchymablebs: small accumulations of air within parenchymal and visceral pleuramay lead to abscess if infected OR SPONTANEOUS pneumothorax (CT_lung lobectomy)

Question 17

spontaneous pneumothorax

Answer 17

none responded to thoracocentesis/thoracostomy tube drainageCT and lung lobectomy with median sternotomy (for complete exploration) recommended +/- mechanical pleurodesismany lesions may be bilateralmost dogs have lesions in the cranial lung lobes

Question 18

broncho or tracheoesophageal fistula

Answer 18

congenital is rareusually acquired secondarily from esophageal FBdiagnosis based on thoracic contrast radiography with nonionic, water soluble, iodinated contrast (iohexol but can also use barium); endoscopy, tracheobronchoscopytx: lung lobectomy and fistula removal via lateral thoracotomy

Question 19

what is decortication

Answer 19

removal of sheets of fibrin covering the lung surfaces (in order to prevent chronic restrictive changes and allow for lung expansion)may lead to lesions in lung parenchyma and induction of air leakage therefore lung lobectomy may be preferred

Question 20

closure of lung lobe laceration

Answer 20

1. superficial: interrupted lembert mattress suture2. deep: hemostatic mattress interrupted sutures followed by apposition with simple continuous layeralternatively: partial lung lobectomy

Question 21

lung lobe torsion

Answer 21

–large dogs with deep narrow chests–right middle or left cranial lung lobe–male pugs left cranial lobe; Afghan hounds 133x more likely to have lung lobe torsion–acute or chronic presentation–dyspnea, cough (hemoptysis), lethargy, wt loss, tachypneic

Question 22

radiographic findings of lung lobe torsion

Answer 22

–displaced bronchi, abrupt termination–air bronchogram (early bc later it is filled with fluid)–mediastinal shift–dorsal tracheal displacement–increased soft tissue opacity/lung consolidation–pleural effusion

Question 23

diagnostics for lung lobe torsion

Answer 23

–radiographs–positive contrast bronchography–CT (abrupt/narrow bronchi, no contrast enhancement)–bronchoscopy (wrinkled mucosa)

Question 24

outcome/prognosis with surgery and lung lobe prognosis

Answer 24

guarded 50-60% survival(potentially more favorable in pugs 11/12 survived)

Question 25

pulmonary neoplasia

Answer 25

most malignantprimary tumors are likely carcinomas of bronchial or alveolar origincaudal lung fieldspx is best if well differentiated, smaller than 5 cm, no regional mets, no malignant pleural effusion 50% survive up to a year or even 500-600 dayscat outcome depends on degree of differentiation 700 days vs poor differentiation 75 days

Question 26

tolerance of pneumonectomy

Answer 26

left lung 42% lung volumeright lung 58% lung volumedogs tolerate 50% removed but NOT 75% (die)acute removal of right side can be fatal, however, if the disease process was chronic and slowly reduced lung function, right sided pneumonectomy is possiblelungs can regenerate; can survive with 1.5 caudal lung lobes