Respiratory Pathophysiology and airway management Flashcards
What does the diffusing capacity for carbon monoxide tell us?
The diffusing capacity of CO (DLCO) is used to assess how well the lung can exchange gas: normal = 17-25 mL/CO/min/mmHg
using Fick’s law of diffusion, the DLCO tells us 2 key characteristics about the alveolar-capillary interface:
* surface area (decreased by emphysema)
* Thickness (increase by pulmonary fibrosis and pulmonary edema)
Therefore, anything that reduces alveolar surface area and/or increases the thickness of the alveolar-capillary interface reduces DLCO
How is tobacco smoke harmful?
Smoking increases SNS tone, sputum production, carboxyhemoglobin concentration, and the risk of infection
Describe the short and intermediate term benefits of smoking cessation
Short-term effects:
Short term cessation does NOT reduce the risk of postoperative pulmonary complications, but short term benefits include:
* SNS stimulating effects of nicotine dissipate after 20-30 minutes
* P50 returns to near normal in 12 hours (CaO2 improves)
Intermediate-term effects:
The return of normal pulmonary function requires at least 6 weeks and includes:
* airway function
* mucociliary clearance
* sputum production
Compare and contrast pulmonary function tests in obstructive vs restrictive lung disease
Obstructive / Restrictive
FEV1:
little to large decrease/ little to mod decrease
FVC :
normal to big decrease/ lit-mod decrease
FEV1:FVC :
big decrease/ normal
FEF 25-75% :
big decrease/ normal
RV :
normal to increase (gas trap)/ big decrease
FRC:
normal to increase (gas trap)/ big decrease
TLC :
normal to increase (gas trap)/big decrease
give an example of a disease that produces the following pulmonary flow-volume loops: obstructive, Restrictive, and fixed obstruction
Obstructive: COPD
Restrictive: pulmonary fibrosis
Fixed obstruction: tracheal stenosis
What is the treatment for acute bronchospasm
100% FiO2
Deepen anesthetic (volatile agent, propofol, lidocaine, ketamine)
Inhaled beta-2 agonists (albuterol)
Inhaled anticholinergic (ipratropium)
Epinephrine 1mcg/kg IV
Hydrocortisone 2-4 mg/kg IV (takes several hours to take effect)
Aminophylline (bronchodilator)
Helium-oxygen (heliox) reduces airway resistance (Decreases Reynold’s number)
*montelukast is not used in the treatment of acute bronchospasm
What is alpha-1 antitrypsin deficiency
*Alveolar elastase is a naturally occurring enzyme that breaks down pulmonary connective tissue. This enzyme is kept in check by alpha-1 antitrypsin (produced in the liver)
* when there’s a deficiency of alpha-1 antitrypsin, alveolar elastase can wreak havoc on pulmonary connective tissue. This ultimately leads to panlobular emphysema.
* Liver transplant is the definitive treatment for alpha-1 deficiency
Describe the goals and strategies for mechanical ventilation in the patient with COPD
Low Tidal volume (6-8mL/kg IBW)
increased expiratory time to minimize air trapping
Slow inspiratory flow rate optimizes V/Q matching
Low levels of PEEP are ok, so long as air trapping does not occur
Define restrictive lung disease
Decreased lung volumes and capacities
decreased compliance
intact pulmonary flow rates
give examples of intrinsic lung diseases (acute and chronic)
Acute: aspiration, negative pressure pulmonary edema
Chronic: pulmonary fibrosis, sarcoidosis
give examples of extrinsic lung disease (acute and chronic)
affects areas around the lungs:
*Chest wall/mediastinum: kyphoscoliosis, flail chest, neuromuscular disorders, mediastinal mass
* Increased intraabdominal pressure: pregnancy, obesity, ascitis
list the risk factors for aspiration pneumonitis
Risk factors: trauma, emergency surgery, pregnancy, gi obstruction, GERD, peptic ulcer disease, hiatal hernia, ascites, difficult airway management, cricoid pressure, impaired airway reflexes, head injury, seizures, residual neuromuscular blockade
Prophylaxis:
Antacids: sodium citrate, sodium bicarbinate, mag trisilicate
H2 antagonists: ranitidine, cimetidine, famotidine
GI stimulants: metoclopramide
Proton pump inhibitors: omeprazole, lansoprazole, pantoprazole
Antiemetics: droperidol, ondansetron
- routine use of these agents as prophylaxis for patients NOT at risk for aspiration is NOT recommended
***Anticholinergics to reduce the risk of aspiration is NOT recommended
what is mendelson’s syndrome
Mendelson’s syndrome is a chemical aspiration pneumonitis that was first described in OB patients receiving inhalation anesthesia. RIsk factors included:
Gastric pH <2.5
Gastric volume >25mL (0.4mL/kg)
Describe the treatment of aspiration
- tilt the head downward to the side (first action)
- Suction upper airway to remove particulate matter
- Lower airway suction is only useful for removing particulate matter. It doesn’t help the chemical burn from gastric acid
- secure the airway to support oxygenation
- apply PEEP to reduce shunt
- Administer bronchodilators to reduce wheezing
- administer lidocaine to reduce neutrophil response
- Steroids probably won’t help
- Antibiotics are only indicated if the patient develops a fever or an increased WBC >48 hours
Discuss the pathophysiology and treatment of a flail chest
Flail chest is a consequence of blunt chest trauma with multiple rib fractures. The key characteristic is the paradoxical movement of the chest wall at the site of the fractures,
Inspiration (negative intrathoracic pressure)
* normal: the chest wall moves out and the lungs expand
flail chest: the injured ribs move inward and collapse the affected region
Expiration (positive intrathoracic pressure)
normal: the chest wall moves inward and the lungs empty
flail chest: the injured ribs move outward and the affected region doesn’t empty
Treatment : epidural catheter or intercostal nerve blocks (higher risk of LA toxicity)
Define pulmonary HTN, and discuss the goals of anesthetic management
Pulmonary HTN is defined as a PAP>25mmHg
Causes: COPD, left sided heart disease, connective tissue disorder
Goals: optimize PVR
Increases PVR: Hypoxemia, hypercarbia, acidosis, SNS stimulation, Pain, hypothermia, increased intrathoracic pressure, PEEP, Mechanical ventilation, Drugs: nitrous oxide (by reducing pulmonary blood flow), ketamine, desflurane
Decreases: Increased PaO2, Hypocarbia, alkalosis, decreased intrathoracic pressure, preventing coughing/straining, spontaneous ventilation, Drugs: Inhaled nitric oxide, Nitroglycerin, phosphodiesterase inhibitors (sildenafil), prostaglandins PGE1 and PGI2,
Calcium channel blockers, ACE inhibitors
Discuss the pathophysiology of carbon monoxide poisoning
Carbon monoxide reduces the oxygen carrying capacity of blood (left shift). It latches to the oxygen binding site on hemoglobin with an affinity 200x that of oxygen. oxidative phosphorylation is impaired, and metabolic acidosis results.
* A co-oximeter (not pulse oximeter) measures CO
* patients take on a cherry red appearance (not cyanosis)
* SNS stimulation may be confused with light anesthesia or pain
* if soda lime is desiccated, the volatile anesthetics can produce CO (Des>Iso»> Sevo)
Discuss the treatment of carbon monoxide poisoning
100% FiO2 until CoHgb is less than 5% or for 6 hours
Hyperbaric oxygen if CoHgb is >25% or the patient is symptomatic
list the absolute and relative indication to one-lung ventilation
Absolute:
Avoid contamination: infection, massive hemorrhage
Control distribution of ventilation: Bronchopleural fistula, surgical opening of major airway, large unilateral lung cyst or bulla, life threatening hypoxemia due to lung disease
Unilateral bronchopulmonary lavage: Pulmonary alveolar proteinosis
Relative:
Surgical Exposure (high priority): thoracic aortic aneurysm, pneumonectomy, thoracoscopy, upper lobectomy, mediastinal exposure
Surgical exposure (low priority): Middle and lower lobectomy, esophageal resection, thoracic spinal surgery
Pulmonary edema s/p CABG or robotic mitral valve surgery
Severe hypoxemia due to lung disease
Discuss how anesthesia in the lateral decubitus position affects the V/Q relationship
Nondependent lung:
* moves from a flatter region (less compliant) to an area of better compliance (slope)
* ventilation is optimal in this lung
Dependent lung:
* moves from the slope to the lower, flatter area of the curve (less compliant)
* perfusion is best in the lung (effect of gravity)
A reduction of alveolar volume contributes to atelectasis
the net effect is that ventilation is better in the nondependent lung, and perfusion is better in the dependent lung. This creates a V/Q mismatch and increases the risk of hypoxemia during OLV
Discuss the management of hypoxemia during one-lung ventilation
100% FiO2
Confirm DLT position with bronchoscope (poor position is the most common DLT complication)
CPAP 2-10 cm H2O to non-dependent lung
PEEP 5-10 cm H2O to dependent lung
Alveolar recruitment maneuver
clamp pulmonary artery to the non-dependent lung
Resume two-lung ventilation
** if hypoxemia is severe, then it’s prudent to resume two lung ventilation promptly
list 5 indications for the use of a bronchial blocker
Bronchial blockers are indicated for patients requiring lung separation who:
* are children <8 years of age (smallest DLT+ 26F for 8-10 year olds)
* require nasotracheal intubation
* have a tracheostomy
* have a single lumen ETT in place
* Require intubation after surgery, and you want to avoid changing the DLT to a single-lumen ETT at the end of the case
How can the lumen of the bronchial blocker be used during OLV?
Use to : Insufflate oxygen into the non-ventilated lung, Suction air from the non-ventilated lung (improves surgical exposure)
Do not use to: Ventilate, suction blood, pus, or secretions from the non-ventilated lung
What is mediastinoscopy, and why is it performed?
Mediastinoscopy is performed to obtain biopsy of the paratracheal lymph nodes at the level of the carina. This helps the surgeon stage the tumor before lung resection.
what are the potential complications of mediastinoscopy? what is the most common?
- Hemorrhage (#1 most common serious complication - look at the major vessels near the scope)
- pneumothorax (#2 most common serious complication - usually on the right side)
- thoracic aorta (hemorrhage and reflex bradycardia)
- Innominate artery (decreased carotid blood flow and cerebral blood flow)
- Vena Cava (hemorrhage)
- Trachea (airway obstruction)
- Thoracic duct ( chylothorax)
- Phrenic and recurrent laryngeal nerve
Where should you place the pulse oximeter and NIBP for mediastinoscopy?
Place the pulse ox or art line on the right upper extremity
* if the scope compresses the innominate artery the SpO2 or A line waveform will dampen or disappear. If this happens the scope must be repositioned (the pt is at risk for cerebral hypoxia)
Place the NIBP cuff on the left upper extremity,
* if the scope compresses the innominate artery the blood pressure reading on the left arm won’t be affected. This allows you to measure the patient’s BP even if the innominate artery is compressed
Describe mallampati score
Assess oropharyngeal space
mnemonic PUSH
class 1 = posterior pillars, uvula, soft palate, hard palate
class 2= uvula, soft palate, hard palate
Class 3= soft palate, hard palate
Class 4= Hard palate
Describe the inter-incisor gap, what is normal?
the pt’s ability to open the mouth directly affects your ability to align the oral, pharyngeal, and laryngeal axes. A small inter-incisor gap creates a more acute angle between the oral and glottic openings, increasing the difficulty of intubation
* normal = 2 -3 finger breadths or 4cm
What is they thyromental distance, and what values suggest and increased risk of difficult intubation?
The thyromental distance helps us estimate the size of the submandibular space
with the neck extended and mouth closed, you can measure the distance from the tip of the thyroid cartilage to the tip of the mentum. Laryngoscopy may be more difficult if the TMD is less than 6cm (3 fingerbreadths) or greater than 9cm
What is the mandibular protrusion test, and what values suggest an increased risk of difficult intubation
The MPT assesses the function of the temporomandibular joint. the patient is asked to sublux the jaw, and the position of the lower incisors it compared the position of the upper incisors.
Class 1= patient can move L1 past UI and bite the vermilion of the lip ( where the lip meets the facial skin)
Class 2= patient can move L1 in line with UI
Class 3= patient cannot move L1 past UI (increased risk of difficult intubation)
What conditions impair antlanto-occipital joint mobility?
Degenerative joint disease
RA
Ankylosis spondylitis (inflammatory arthritis affecting the spine and large joints)
Trauma
Surgical fixation
Klippel-Feil
Down syndrome
List 5 risk factors for difficult mask ventilation
Mnemonic BONES
Beard
Obese/Obstruction (BMI>26 kg/m2)
No teeth
Elderly (age>55)
Snoring
List 10 risk factors for difficult tracheal intubation
small mouth opening
palate is narrow with a high arch
long upper incisors
interincisor distance <3cm
Mallampati class 3 or 4
Mandibular protrusion test class 3
Poor compliance of submandibular space
Thyromental distance <6cm (<3 fingerbreadths) or >9cm
Neck is thick and short
Limited AO joint mobility (can’t touch chin to chest and/or can’t extend the neck)
List 6 risk factors for difficult supraglottic device placement
*limited mouth opening
*upper airway obstruction (prevents the passage of the device into pharynx)
*Altered pharyngeal anatomy (prevents seal)
* Poor airway compliance (requires excessive PIP)
*Increased airway resistance (requires excessive PIP)
* lower airway obstruction
List 5 risk factors for difficult invasive airway placement
Abnormal neck anatomy (tumor, hematoma, abscess, hx of radiation)
Obesity (Can’t ID cricothyroid membrane)
Short neck (can’t ID cricothyroid membrane)
Limited access to the cricothyroid membrane (halo, neck flexion deformity)
Laryngeal trauma
Describe the practice guidelines for preoperative fasting and use of pharmacologic agents to reduce the risk of pulmonary aspiration
most current rec’s:
2hrs = clear liquids
4hrs = breast milk
6 hrs= nonhuman milk, infant formula, solid food
8 hrs = fried or fatty foods
ingestion of clear liquids 2 hrs before surgery reduces gastric volume and increases gastric pH
What is angioedema
Angioedema is the result of increased vascular permeability that can lead to swelling of the face, tongue, and airway. Airway obstruction is an extreme concern.
What are two common causes of angioedema? what is the treatment for each?
Angioedema caused by anaphylaxis is best treated with epi, antihistamines, and steroids.
Angioedema caused by ACE inhibitors or C1 esterase deficiency is best treated with icatibant, ecallantide, FFP, or C1 esterase concentrate.
What is ludwig’s angina
Ludwigs angina is a bacterial infection characterized by a rapidly progressing cellulitis in the floor of the mouth. Inflammation and edema compress the submandibular, submaxillary, and sublingual spaces.
The most significant concern is a posterior displacement of the tongue resulting in complete, supraglottic airway obstruction
What is the best way to secure the airway in the patient with ludwig’s angina?
The best way to secure the airway is with the patient awake
Awake nasal intubation
awake tracheostomy
What are 4 types of oropharyngeal airways. which are best suited for fiberoptic intubation
Guedel
Berman
Williams : specific use: blind orotracheal intubation, fiberoptic intubation
Ovassapian; fiberoptic intubation
When is nasopharyngeal airway contraindicated?
Cribriform plate injure (risk of brain injury):
* lefort 2 or 3 fracture
* basilar skull fracture
* CSF rhinorrhea
* Raccoon eyes
* periorbital edema
* Coagulopathy
* previous transsphenoidal hypophysectomy ( removal of pituitary and other intrasellar tumors)
* Previous caldwell-luc procedure (technique to remove infected mucosa from maxillary sinus)
Nasal fracture
*caution during pregnancy (risk of epistaxis)
Contrast the maximum recommended cuff pressures for an endotracheal tube versus LMA
ETT <25 cmH2O
LMA< 60cm H2O
What is the largest ETT that can be passed through each LMA size
What is the largest ETT that can be passed through each LMA size
What is the maximum recommended peak inspiratory pressures for an LMA-unique vs LMA Proseal vs LMA supreme
LMA Unique <20
LMA-Proseal< 30
LMA Supreme <30 cm H2O
List 6 indications for the bullard laryngoscope.
the bullard laryngoscope is a rigid, fiberoptic device used for indirect laryngoscopy
Indications: small mouth opening (minimum 7 mm), impaired cervical spine mobility, short, thick neck, treacher collins syndrome, pierre-robin sequence
when is the best time to use an Eschmann introducer?
The Eschmann introducer is best used when a grade 3 view is obtained during laryngoscopy (grade 2 is the next best time). During a grade 4 view, the likelihood of successful intubation is unacceptable low
Describe the proper placement of the lighted stylet
When the patient is supine, the trachea is anterior to the esophagus. Therefore, we can look at the quality of the light shining through the neck to determine the tip of the device is located in the trachea or esophagus
* when the lighted stylet is the in the trachea, the light has to travel through less tissue, so you observe a well defined circumscribed glow below the thyroid prominence.
* When the lighted stylet is in the esophagus, the light has to travel through more tissue, so you’ll observe a more diffuse transillumination of the neck without the circumscribed glow
List 2 indications for retrograde intubation
Unstable cervical spine (most common use of RI)
Upper airway bleeding (can’t visualize glottis)
Since RI requires time ( around 5-7 minutes for experienced practitioners), use when intubation has failed, but ventilation is still possible
Per the latest ASA difficult airway with general guidlines, what paralytic and reversal is recommended?
Rocuronium and sugammadex
An awake intubation should be considered if an anticipated difficult intubation is coupled with what 4 risks
- Suspected difficult ventilation with facemask
- suspected difficult ventilation with a supraglottic airway device (SGA)
- Significantly increased risk of aspiration
- increased risk of rapid desaturation (apnea intolerance)
Compare and contrast the benefits of awake vs deep extubation
Awake
Pros: Airway reflexes intact, ability to maintain airway patency, decreased risk of aspiration
Cons: Increase: CV and SNS stimulation, coughing, intracranial pressure, intraocular pressure, intraabdominal pressure
Deep
Pros: Decreased CV and SNS stimulation and coughing
Cons: Airway reflexes are ineffective: increased risk of airway obstruction and risk of aspiration
