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