Week 8 - Anesthesia for Thoracic Surgery Flashcards
Define Total Lung Capacity (TLC). What is the typical volume?
The gas volume in the lung after a MAXIMUM inspiration
-typical volume = 6-8L
What increases and decreases total lung capacity?
- Can be increased in pts with COPD due to hyperinflation or destruction of alveolar wall and resultant loss of elastic tissue
- Can be decreased in restrictive disorders such as pulmonary fibrosis – decrease is in proportion to the severity of the fibrotic process
Define Residual Volume (RV) of the lungs
The volume of gas remaining in the lung after a MAXIMUM expiratory effort
-typical volume is 2 - 2.5 L
Define Vital Capacity (VC) of the lung
The maximum volume that can be inspired and expired
- difference between TLC and RV
- typical volume is 4-6 L
Define Expiratory Reserve Volume (ERV) of the lungs
Volume of gas that can be expelled beyond the tidal exhalation with a forced exhalation maneuver
Define Functional Residual Capacity (FRC) of the lungs
Volume of gas remaining in the lung after an ordinary expiration
- typical FRC is 3-4 L
- most important for anesthesia
Why do we care so much about FRC in anesthesia?
Preoxygenation
-the higher the concentration of O2 in the FRC the greater amount of apnea time we have before desaturation occurs
What 4 factors is FRC dependent on?
- Age
- Height
- Sex
- Weight
- FRC goes UP with age (loss of elastic lung recoil) and height (more space and volume is greater)
- FRC goes DOWN with Female sex (smaller volumes) and Weight (external pressures on thoracic cavity)
How does the FRC change in pts with COPD or restrictive lung disease?
COPD: FRC is increased – increase in FRC is accelerated in pts with COPD over the normal aging increase due to chronic air trapping and more severe loss of elastic tissue
Restrictive Lung Disease: FRC is decreased – i.e. pulmonary fibrosis
What does Bordy’s equation measure? How do you calculate it?
Oxygen consumption
weight (kg)^3/4 x 10
*for the average 70kg adult, this results in an oxygen consumption of approx 240 mL/min
How can you calculate CO2 production?
CO2 production per min can be calculated as:
oxygen consumption x 0.8
During periods of apnea, PaCO2 will rise _____ mmHg during the 1st min and _______ mmHg each subsequent minute.
During periods of apnea, PaCO2 will rise 6 mmHg during the 1st min and 3 mmHg each subsequent minute.
What is pulmonary perfusion largely dependent on?
Gravity
-West’s 4 lung zones
What are the four main causes of Hypoxemia?
- Hypoventilation
- V/Q Mismatch
- Impaired Diffusion
- Right-to-Left Shunt
What is Hypoxic Pulmonary Vasoconstriction?
A compensatory mechanism which reduces blood flow in hypoxic lung regions
- major stimulus for this is low alveolar oxygen tension (can be caused by hypoventilation or delivery of gas with a low PO2)
- has a rapid onset over the first 30 min and then a slower increase to a maximal response at approx 2 hrs
What is the benefit of hypoxic pulmonary vasoconstriction?
Decrease in blood flow to hypoxic areas functions to correct right-left shunt (redirects flow)
Decrease in shunt will maximize oxygenation of pulmonary circulation
What can Hypoxic Pulmonary Vasoconstriction be inhibited by?
- Inhaled anesthetics greater than 1 MAC (Iso shows the least effect, Des shows greatest effect) – relatively weak inhibitors
- Nitro vasodilators
- Extremes of acidosis/alkalosis
- Hypothermia
- Calcium Channel Blockers
*we do NOT want to inhibit
What effects does anesthesia have on respiratory function?
- FRC is decreased by 0.8-1L from supine positioning and 0.4-0.5L from induction of general anesthesia
- Compliance is decreased
- Overall resistance is increased
What are indications for thoracic surgery?
- Thoracic malignancies
- Chest trauma
- Mediastinal tumors
- Esophageal disease
- Tracheal resections
- Lung transplantation
What is the role of the anesthetist in the preop process for thoracic surgery?
- Interpret given info
- Assess risk
- Develop a plan to minimize the risk of periop complications
*preop testing to be evaluated includes Pulmonary Function Tests, Lung parenchymal function, and cardiopulmonary interactions
What portion of Pulmonary Function Tests should you focus on? What are normal values?
Focus on FEV1, FVC, and FEV1/FVC ratio
FEV1 = 4L
FVC = 5L
FEV1/FVC ratio = 0.8
*should be remembered the “normal” values will decrease with age, so analysis of how the pt performed in their PFT compared to their predicted values given their demographics must be considered
What does the FEV1/FVC ratio help determine?
Helps determine whether we have a normal, obstructive, or restrictive respiratory pattern
What FEV1/FVC ratio represents an obstructive defect and a restrictive defect?
Obstructive: ratio is LESS than the lower limit of normal
Restrictive: ratio is GREATER than the lower limit of normal and the FVC is decreased
What lung parenchymal testing values are used as cut-offs for candidacy for pulmonary resection?
PaO2 of <60 mmHg or PaCO2 of >45 mmHg
What is the Diffusing Capacity for Carbon Monoxide (DLCO) used to determine?
the ability of the lung to exchange oxygen and carbon dioxide between the pulmonary vascular bed and the alveoli
-a post-operative DLCO of <40% indicates increased post-op risk of respiratory compromise and <20% represents an unacceptably high risk for resection
What do cardiopulmonary interactions test?
The maximal oxygen consumption (VO2 Max)
-normal levels of VO2 Max range from 26 mL/kg/min (female) to 34 mL/kg/min (male)
- Pts with VO2 <15 mL/kg/min preop have an unacceptably high risk for lung resection
- > 20 mL/kg/min rarely have respiratory complications
What pulmonary function testing values for the following place a patient at HIGH RISK?
- FEV1
- Predicted Post-op FEV1
- Max VO2
- FEV1/FVC
- FEV1 of < 2L
- Predicted Post-op FEV1 of < 0.8 or <40% of predicted
- Max VO2 of <10 mL/kg/min
- FEV1/FVC < 50% of predicted
What pain management techniques are used in thoracic surgery?
Neuraxial: thoracic epidural (T5-T8) – doesn’t cover chest tube discomfort
IV: opioids (like to avoid due to resp depression), ketamine 1mg/kg IM, Precedex, NSAIDs, IV Tylenol
Regional: paravertebral block, intercostal nerve blocks
What are the indications for lung isolation in thoracic surgery?
- Surgery in the chest cavity
- Protection of contralateral lung from soiling in cases like bronchopleural fistula
- Pulmonary hemorrhage
- Whole lung lavage
What three methods may be employed to isolate a lung in thoracic surgery?
- Double Lumen Tube
- Bronchial Blockers (main-stem bronchus is occluded to allow for distal collapse of the lung)
- Single Lumen Endotracheal Tubes
What is the sizing of double lumen tubes for males and females?
Female <160cm = 35 Fr
Female >160cm = 37 Fr
Male <170cm = 39 Fr
Male >170cm = 41 Fr
What are anesthetic considerations for one lung ventilation?
- Modern inhaled anesthetics inhibit Hypoxic Pulmonary Vasoconstriction equally at 1 MAC
- The increase in shunt caused by inhaled anesthetics at 1 MAC is not clinically significant
- No benefit of TIVA over inhaled anesthetics with regards to oxygenation
- Pain control with epidural and IV narcotics
- Paralysis is very important
What are fluid management considerations with one lung ventilation?
“Don’t Drown the Down Lung”
- due to hydrostatic effects, dependent lung is very susceptible to pulmonary edema
- very bad as this is the only lung participating in gas exchange
What are the fluid management recommendations for one lung ventilation?
- Total positive fluid balance in the first 24 hr periop period should not exceed 20 mL/kg
- Crystalloid admin should be limited to <3L in first 24 hrs (for average adult pt)
- No fluid admin for third space fluid losses
- Urine output >0.5 mL/kg/hr is unnecessary
- If increased tissue perfusion is needed postop, it is preferable to use invasive monitoring and inotropes rather than to cause fluid overload
What are positioning considerations for one lung ventilation?
Lateral – careful positioning takes time and must be done well, small movements with double lumen tube is positioned can move tube out of place
-many pressure points to consider
Dependent arm – compression injuries
Nondependent arm – stretch injuries
What are the ventilation guidelines for the following for one lung ventilation?
- Tidal volume
- PEEP
- Respiratory Rate
- Mode
Tidal Volume: 5-6 mL/kg – maintain peak airway pressure <35 and plateau airway pressure <25
PEEP: 5 cmH2O – pt with COPD no PEEP
Respiratory Rate: 12 breaths per min – maintain normal PaCO2, ETCO2 will usually increased 1-2 mmHg during OLV
Mode: volume or pressure controlled – pressure control for pts at risk of lung injury
What are possible complications of one lung ventilation?
Hypoxemia
Tube displacement
Positioning difficulties
Barotrauma
What should you do if the pt develops severe or precipitous desaturation during one lung ventilation?
Resume two-lung ventilation (if possible)
What should you do if the pt develops gradual desaturation during one lung ventilation?
- Ensure that delivered FiO2 is 100%
- Check position of double-lumen tube or blocker w/ fiberoptic bronchoscopy
- Ensure CO is optimal, decrease volatile anesthetics to <1 MAC
- Apply a recruitment maneuver to the ventilated lung (will transiently make hypoxemia worse)
- Apply PEEP 5 cmH2O to the ventilated lung (except in pts with emphysema)
- Apply CPAP 1-2 cmH2O to the nonventilated lung
- Intermittent reinflation of the nonventilated lung
- Partial ventilation techniques to nonventilated lung (oxygen insufflation, high frequency ventilation, lobar collapse using a bronchial blocker)
- Mechanical restriction of the blood flow to the nonventilated lung
What is a mediastinoscopy?
Standard method for the evaluation of mediastinal lymph nodes in the staging of NSCLC
Used to aid in the diagnosis of anterior/superior mediastinal masses
What are complications of a mediastinoscopy?
- Massive Hemorrhage is MOST SEVERE
- Compression of the innominate artery
- Pneumothorax
- Paresis of the recurrent laryngeal nerve
- Phrenic nerve injury
- Esophageal injury
- Chylothorax
- Air embolism
What is the anesthetic management for a mediastinoscopy?
- Single lumen tube
- Art Line
- 2 large bore IVs
- Must monitor pulse in right either by art line or pulse ox
- Deep anesthesia necessary (bucking is BAD) – short acting agents (Des/Remi)
- Type and cross match with blood in room
What is an esophagectomy?
Indicated for esophageal cancer
- Transthoracic approach
- Transhiatal approach
- Minimally invasive approach (Laparoscopic)
What is the most common anesthetic complication with mediastinal masses?
Airway obstruction during induction of general anesthesia in pts with an anterior or superior mediastinal mass
What type of mediastinal mass does the following flow volume loop represent?
Variable extrathoracic defect with inspiratory flattening
What type of mediastinal mass does the following flow volume loop represent?
Variable intrathoracic defect with expiratory flattening
What type of mediastinal mass does the following flow volume loop represent?
Fixed defect with inspiratory and expiratory flattening
