Anesthesia for Thoracic Surgery
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Why are smokers and pts with COPD more prone to hypoxia and atelectesis post-op?
- CC > FRC (alveoli close at a higher lung volume)
- Low expiratory flow
How is severe exertional dyspnea defined?
- Inability to walk on flat ground without DOE
- FEV1 < 1500 ml
What is FEV1?
- Forced expiratory volume in 1 second
- Normal volume = 80% of TLC (5L)= 4L
Besides FEV1, what other PFT is indicative of increased risk for post-op complications and mortality?
Vital capacity < 50% or < 2L
What PFT is used to assess a pts ability to tolerate a lung resection?
Is this a single or whole lung test?
- FEV1< 800 ml
- Single lung test
What does the RV/ TLC ratio tell us? What is the normal value?
- Amount of gas trapping that's occurring.
- Normal RV= 1L, TLC = 6L
- High risk for gas trapping = ratio >50%
Which subtype of COPD pts are prone to hypoxia and are CO2 insensitive?
What are anesthesia considerations?
- Blue bloaters, aka chronic bronchitis
- CO2 ventilatory drive is lost, rely on hypoxic drive
- Avoid high FiO2 with this pts, GA further decreases sensitivity to CO2
Common first symptoms of lung cancer
cough and hemoptysis
Expected ABG values from a chronic bronchitis pt (blue bloater)
Expected ABG values from an emphysema pt (pink puffer)?
- Relatively normal
- Pts increase their MV to normalize their CO2, hence they have an increased WOB and dyspnea
PFTs associated with increased operative risk
- RV/ TLC > 50%
- MBC < 50% of predicted
- FEV1 < 2L or < 50% of FVC
What does a mean PA pressure of > 40 mmHg mean (occlude PA on side where lung is to be removed)?
High operative risk
Major characteristic of the flow volume loop of a pt with obstructive lung disease
- High lung volumes
- Scooped out pattern (due to slow exhalation)
How are the inspiratory and expiratory lung volumes altered with a fixed obstruction?
- Insp and exp are both obstructed
- Ex: tracheal stenosis
What is variable intrathoracic obstruction? Give an example.
- Normal inh, abn exh; issue with lung itself
What is variable extrathoracic obstruction? Give an example.
- Inhalation is compromised
- Mediastinal mass
How does mean PA pressure change as CO increases in a normal pulmonary vascular bed? What about in a pt with a rx pulmonary vascular bed?
In what situation would this apply to? And what is the end result
- Normally PA pressures won't increase until CO increases by 2.5
- In a pt with a rx pulm vascular bed any increase in CO increases PA pressure
- This applies in a pt with a pneumonectomy (half of the pulmonary circulation is now gone).
- Pulmonary HTN results
Risks associated with 1 lung ventilation
- Increased shunt
- Trauma and edema to the operative lung
- Edema to the dependent lung (due to increased perfusion to this lung and increased pulmonary capillary pressure)
Why is an arterial line helpful with 1 lung ventilation?
- Due to V/Q mismatch and high degree of shunt
- O2 sat correlates poorly with PaO2
- ETCO2 inaccurate when there's dead space (possible high A-a CO2 gradient)
Tell me about the accuracy of a PA line in the right PA when right lung is down (deflated)?
Inaccurate because of HPV there is decreased flow to the operative (right) lung
Tell me about the accuracy of a PA line in the right PA when there is CPAP applied to the operative, right lung.
Inaccurate, CPAP will squish the pulmonary vessels
Tell me about the accuracy of a PA line the left PA, when the right lung is the operative lung.
Explain why allowing a pt to breath spontaneously intraop with an open chest is a bad idea
Risk of paradoxical breathing and mediastinal shift
What is paradoxical breathing?
Due to the negative pressure of the intact hemithorax (dependent lung), compared to the positive (atm P) in the operative (non dependent) lung, air moves from the non-dependent to the dependent lung during inspiration. Air moves the opposite way with expiration.
Explain why a mediastinal shift could occur in a pt breathing spontaneously during thoracotomy?
Negative pressure of the intact (dependent) hemithorax, compared to the higher pressures of the non dependent (operative) lung cause the mediastinum to shift downward during inspiration.
In an awake pt in the lateral position, which lung receives more ventilation? How does this affect V/Q matching?
Dependent lung, this lung also receives more perfusion, so V/Q is matched.
In an anesthetized pt in the lateral position, which lung receives more ventilation? How does this affect V/Q matching?
- Non dependent lung receives more ventilation. Dependent lung receives more perfusion.
- V/Q mismatch occurs.
How does GA affect FRC and overall lung volumes
both are decreased
What effect does going from 2 lung ventilation to 1 lung ventilation under GA have on Qs/Qt? Why?
- Shunt is increased
- The non dependent (and non ventilated lung) still receives a degree of blood flow (despite HPV), this results in shunt
What is the expected PaO2 of a pt receiving single lung ventilation on 100% FiO2?
Blood flow to areas with no ventilation
Ventilation with no blood flow
V/Q of dead space
One lung ventilation exemplifies ____.
Normal amount of shunt?
Normal amount of shunt under GA?
Absolute indications for 1 lung anesthesia
- Lung infection to isolate 1 lung
- Bronchopleural fistula
- Unilateral lavage (ex: CF pt)
Relative indications for 1 lung anesthesia
How many cc of air does the bronchial cuff of a DLT require?
3 ml max!!
Which is used more commonly L or R sided DLT? Why?
- L sided, 4-5 cm of space between carina and LUL bronchus
- If a right sided tube were used it's possible that the RUL wouldn't be ventilated as there's only 2.5 cm between the carina and the RUL bronchus
Usual DLT size for a F? M?
How is placement of a DLT performed?
- Fiberoptic scope visualization
Should with performed with pt in the lateral position.
Can a DLT be used post-op?
No, must be exchanged to a single lumen as each lumen is very small and provides too much rx to breathing.
- An alternative to the DLT
- Use a FO scope to direct balloon to area you want blocked
Benefits of a bronchial blocker
- Beneficial for s/o who's a difficult intubation
- Tube does not need to be replaced pre-op
Risks of a bronchial blocker
- Slips out of place easily
- Harder to place
- Can't sx one lung
TV for 1 lung ventilation
5-8 ml / kg
Risks associated with using high TV with 1 lung ventilation
Inhibits HPV due to increased PVR
1 lung ventilation- risk of using PEEP on the dependent lung
Inhibit HPV and direct blood to the non ventilated lung
1 lung ventilation- risk of using CPAP on the operative lung
- Beneficial as it directs flow away from the non ventilated lung
- May obscure the surgeon's view
Anesthestic agents and 1 lung anesthesia
- Avoid inhibiting HPV!
- Avoid large doses of volatiles (VD and thus may inhibit HPV), but they also bronchodilate, avoid > 1 MAC
- Propofol beneficial as it does not VD and thus not inhibit HPV
- Avoid histamine releasing drugs (pts prone to bronchospasm due to underlying lung disease and surgical manipulation)
Considerations regarding airway management with thoracic anesthesia
- Deep intubation (use lido and fentanyl)
- Use lido on extubation
- Careful IVF replacement (maintenance requirements only) to avoid dependent edema
Strategies if hypoxia occurs with 1 lung ventilation
- Check position of DLT
- Check HD
- CPAP to non dependent lung
- PEEP to dependent lung
- Intermittent 2 lung ventilation
1 MAC of volatile agent increases ____ by ___%.
Risks associated with flexible bronchoscopy
Worsened obstruction and pulmonary swelling up to 24 hours post-op
Considerations for rigid bronchoscopy
- Damage to mouth or teeth
- Pt must be paralyzed throughout
- Very stimulating
Right innominate artery
- Risk of compression with mediastinoscopy
- Place pulse ox on right side
Pain management for a pt with an incision close to the diaphragm
- Pain score = 10/10
- Epidural is the only way to interrupt the diaphragm inhibition reflex
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