Anesthesia for Thoracic Surgery Flashcards
What are major challenges in thoracic surgery?
Physiologic derangements caused by lateral position
Open pneumothorax
Surgical manipulation, interfering with heart/lung function
Risk of rapid, massive blood loss
Necessity for one lung ventilation
How does the lateral position alter normal lung physiology?
Disrupts ventilation/perfusion relationships
In addition to the lateral position, what other factors affect Q/V in thoracic surgery?
Anesthesia, NMBA, opening the chest and surgical retraction
What causes HoTN in the lateral position?
Blood pooling in dependent portions
What nerve injuries can occur in the lateral position?
Brachial plexus and peroneal nerve injuries
What injuries to the body can be caused by the lateral position?
Outer ear ischemia
Axillary artery compression
Monocular blindness
In an upright patient spontaneously breathing with a closed chest, where does maximal ventilation occur?
At the base of the lungs
Where does the most perfusion occur in an upright, spontaneously breathing closed chest patient?
Also favors the bases of the lungs, V/Q matching is preserved
What alveoli of the lungs are the most compliant?
Base alveoli more compliant, they can expand for a greater volume for a given pressure change
How is V/Q matching preserved in a spontaneously breathing patient with a closed chest in the lateral position?
Dependent lung receives more ventilation and perfusion than the upper lung (non dependent)
Gravity provides more perfusion and lower diaphragm on the dependent lung able to contract more efficiently during spontaneous respirations, more TV
What factors further press the diaphragm cephalad?
Supine position
Induction of anesthesia
Paralysis
Surgical position and displacement
What V/Q mis-match occurs in the anesthetized and paralyzed patient in the lateral position with a closed chest?
The dependent lung receives more perfusion while the non dependent lung receives more ventilation
What intervention can help restore V/Q in the paralyzed and anesthetized patient in the lateral position with a closed chest?
PEEP, restores ventilation to the dependent lung to a steeper more favorable portion of the pressure volume curve
Why does V/Q mismatch occur when the anesthetized patient is in the lateral position with an open chest?
Perfusion remains greater in the dependent lung but the upper lung collapse leads to progressive hypoxemia
What can be seen in the anesthetized patient in the lateral position with an OPEN chest without paralysis?
Mediastinal shift and Paradoxical respirations
What causes paradoxical breathing in the anesthetized patient in the lateral position with an OPEN chest without paralysis?
To and Fro gas exchange between the non-dependent lung and the dependent lung
Why does positive pressure ventilation make V/Q worse in the anesthetized and paralyzed patient in the lateral position with an OPEN chest?
Controlled PPV favors the upper lung, more compliant, paralytic further enhances this by allowing the abdominal contents to rise further up on the dependent diaphragm and impede ventilation
What is hypoxic pulmonary vasoconstriction?
Diverts blood away from the hypoxic regions of the lung, helps improve arterial oxygen content, improving hypoxia
What is the blood flow distribution in two lung ventilation when the left lung is non dependent?
Non dependent 35%
Dependent 65%
What is the blood flow distribution in two lung ventilation when the right lung is non dependent?
Non dependent 45%
Dependent 55%
What is the average of both lungs being nondependent?
Non dependent 40%
Dependent 60%
How does HPV affect average of blood flow to the non dependent and dependent lungs during one lung ventilation?
Non dependent 40% –> 20%
Dependent 60% –> 80%
How much shunt is normally present during two lung ventilation in the lateral position?
10% –> assumed to be distributed equally 5% each lung
What factors inhibit HPV?
High pulmonary vascular resistance Hypocapnia High or very low mixed venous PO2 Vasodilators Pulmonary infection Inhaled anesthetics
How much does 1 MAC increase pulmonary shunt?
1 MAC = 4% increase in shunt
What factors send blood to the dependent lung?
Gravity
Surgical interference
HPV
What five factors cause interference in ventilating the dependent lung?
GA Paralysis Circumferential compression 100% O2 (absorption atelectasis) Difficulty removing secretions
What are the benefits of one lung ventilation?
Surgical exposure, access to aorta and esophagus, prevents cross contamination and prevents loss of anesthetic gases with bronchopleural fistula
What are relative contraindications for one lung ventilation?
Difficult airway with poor visualization of the larynx
Lesion in bronchial airway precluding bronchial intubation
What techniques can be used to achieve one lung ventilation?
Double lumen ETT Bronchial blocker (used with single lumen ETT)
Where does the trachea begin in the adult?
C6 (11-12cm long)
What are important characteristics of the right bronchus?
Wider
Diverges away from the trachea at a 20-25 degree angle
Orifice of the RUL sits only 1-2cm to carina
What are important characteristics of the left bronchus?
Narrower than right
Diverges away from trachea at 40-45 degree angle
Orifice of LUL sits about 5cm distal to carina
When using a fiberoptic scope, how can the provider tell the right from the left bronchus?
The provider can see three lumens inside right bronchus
Anterior bronchus
Posterior bronchus
Apical bronchus
Why is it common practice to place a left sided double lumen tube?
When placing a right sided DLT often occludes RUL and can cause atelectasis
What is the most common DLT used in practice?
Robert Shaw
What is the difference between the Robert Shaw DLT and the Carlens and White?
Robert Shaw does not have a carinal hook and is D-shaped
What is the purpose of the carina hook on White and Carlens DLT?
Should hook onto the carina, if inserting tube blindly it can confirm placement
What is the optimal size of DLT for patients?
The largest size that fits in the bronchus with a small air leak detectable when the bronchial cuff is deflated
Why is it necessary for the provider to place the largest DLT possible?
These tubes have small internal diameters which interfere with expiration and cause air trapping and auto peep
What factors determine the size of DLT for a patient?
Height and gender
What size DLT should be used for a female less than 5’3?
35 F (ID 5.0)
What size DLT should be used for a female greater than 5’3?
37 F (ID 5.5)
What size DLT should be used for a male less than 5’7?
39 F (ID 6.0)
What size DLT should be used for a male greater than 5’7?
41 F (ID 6.5)
What is the average depth of insertion for a DLT?
28-29cm
What formula can be used to determine depth of a DLT?
depth = 12.5 + (0.1 x height in cm)
What type of blade is best to use when placing a DLT?
Curved blade provides optimal space to place DLT
How should a DLT be placed?
Passed with distal curvature concave anteriorly, then rotate 90 degrees towards the side that is to be intubates after the tip enters the larynx
What are ways to confirm the DLT is in the correct place?
Pediatric bronchoscope or Clamping and listening to each side
What should occur to the side of the lung that is clamped when ventilating the other lung?
No change in moisture
Ipsilateral hemithorax des not move
Ipsilateral breath sounds disappear
How much air should be added to the tracheal cuff?
5-10mL
How much air should be added to the bronchia cuff?
1-2mL
On a left DLT what breath sounds should be heard when the tracheal lumen is clamped?
Breath sounds on the left side
What is the problem when bilateral breath sounds are heard when the trachea lumen is clamped in a left sided DLT?
Indicates bronchial opening still in trachea and the tube should be advanced
What is the problem when right sided breath sounds are heard when the trachea lumen is clamped in a left sided DLT?
Indicates incorrect entry of the tube into the right bronchus
On a left DLT what breath sounds should be heard when the bronchial lumen is clamped?
Unilateral right sided breath sounds
What is the desired view down the bronchial lumen with a FOI scope?
Bronchial carina and Very slight luminal narrowing
Why might the provider adjust the DLT after visualization of the bronchial lumen?
If excessive luminal narrowing is visualized
What is the desired view down the tracheal lumen with a FOI scope?
Tracheal carina
Left lumen going off to the left side and the upper left surface of left bronchial cuff
Why might the provider adjust the DLT after visualization of the tracheal lumen?
Rightward tracheal carinal deviation
Herniation of bronchial cuff
What is the most common problem encountered when positioning a left endobronchial tube?
Inserting too deeply and excluding the right lung from ventilation
What is the most common problem encountered when positioning a right endobronchial tube?
Excluding the right upper lobe from ventilation
What are the three types of malposition in DLT?
In too far on the left side
Out too far in the trachea
In too far on the right side