Lecture 9: One Lung Ventilation/Malignant Hyperthermia Flashcards
What is most often the position for thoracic surgery?
Lateral decubitus position
Dependent lung =
Lower lung
Nondependent lung =
Upper lung
___ of the upper lung provides access to the surgical field
Iatrogenic pneumothorax
Where is the axillary roll placed during thoracic surgery?
Placed on upper chest wall, NOT in the axilla
Why do you restrict IVFs to basic maintenance during thoracic surgery?
D/t risk of gravity dependent transudation of fluid to lower lung and edema of the collapsed lung
In the awake and lateral position, the ___ lung is better perfused (gravity) and ventilated
Dependent
With induction of anesthesia, there is a ___ in FRC, the upper lung ventilates ___, and there is a ___
Decrease in FRC, the upper lung ventilates more, V/Q mismatch
Positive pressure ventilation favors the ___ because it is more compliant
Upper lung
Muscle paralysis favors ventilation of the ___ due to abdominal contents pushing up more on the dependent hemidiaphragm
Upper lung
Open PTX of the upper lung ___ compliance, favoring ventilation of ___
Increases compliance, favoring ventilation of upper lung
The effect of anesthesia on lung compliance in the lateral decubitus position—the ___ lung assumes a more favorable position, while the ___ becomes less compliant
Upper lung, lower lung
Open pneumothorax—normal negative pleural pressure is ___, causing the lung to ___
Lost, causing the lung to recoil and collapse
Open pneumo is overcome by the use of ___ ventilation
Positive pressure
Intentional collapse of the ___ lung facilitates the thoracic procedure
Nondependent lunges
Upper lung during thoracic surgery is not ___ but is still ___ (although less than dependent lung); this causes a large ___ intrapulmonary shunt (20-30%)
Ventilated, but is still perfused; this causes a large right to left intrapulmonary shunt (20-30%)
Increased PA-a (alveolar to arterial) O2 gradient can lead to ___
Hypoxemia
Blood flow to the nonventilated/nondependent upper lung is ___ by HPV
Decreased by HPV—this improves the right to left shunt
What can also decrease blood flow to the upper lung?
Surgical compression, which improves the shunt
Factors that inhibit hypoxic pulmonary vasoconstriction (6):
- Very high or very low pulmonary artery pressures
- Hypocapnia***
- High or very low mixed venous PO2
- Vasodilators***
- Pulmonary infections
- Inhalation agents***
What vasodilators (4) inhibit hypoxic pulmonary vasoconstriction?
- NTG
- Nitroprusside (SNP)
- B-adrenergic agonists (dobutamine)
- Calcium channel blockers
What factors (5) decrease blood flow to dependent lung?
- Worsens R to L shunt by sending more blood to the nondependent or collapsed lung
- High mean airway pressures in ventilated lung from PEEP, hyperventilation, or increased PIP
- Low FiO2 causes HPV in ventilated lung
- Vasoconstrictors which may have a greater effect on norms ic vessels compared to hypoxic ones
- Intrinsic PEEP which develops from inadequate expiratory times
CO2 elimination is usually ___ by one lung ventilation
NOT affected
CO2 elimination is not affected by one lung ventilation, provided what two things?
1) minute ventilation is unchanged
2) pre-existing CO2 retention was NOT present pre-op (COPD)
During one lung ventilation, tidal volumes are kept ___ as two lung ventilation
Roughly the same—around 10 cc/kg; may adjust d/t changes in PIP, RR altered to maintain normocapnia
FiO2 during one lung ventilation is usually kept ___
HIGH as a safety margin against hypoxia
What is apneic oxygenation?
Ventilation can be stopped for short periods, as long as O2 is supplied more than consumption (250-300 cc/min)
During apnea, PCO2 increases ___ for the first minute, and then ___ for each additional minute of apnea
5 mm Hg, then 3 mm Hg
Example: If PCO2 was 40, then after 10 minutes of apnea, the PCO2 will be 72
Progressive respiratory acidosis that occurs with apneic oxygenation limits the technique to ___ minutes
10-20 minutes
FiO2 of ___ to ___ during one lung ventilation
0.8 to 1.0
Tidal volumes during one lung ventilation
10 cc/kg
What is used to ensure proper ETT placement during one lung ventilation?
Fiber optic scope
One lung ventilation—adjust RR to keep PaCO2 at ___
40 mm Hg
Add ___ to nondependent lung—warn surgeon
5 cm H2O CPAP
Add ___ to dependent lung—treats __ but may increase ___
5 cm H2O PEEP, treats atelectasis but may increase vascular resistance
Increase both CPAP and PEEP ___
Slowly
Operability for pneumonectomy—clinical decision if patient can survive ___
Resection of one lung
What is used to make the decision of operability for pneumonectomy?
PFTs
Most common criterion for operability for pneumonectomy is a predicted post-op FEV1 of > ___
800 ccs
Pre-op FEV1 for pneumonectomy should be > ___
2L
High-risk patients for pneumonectomy—PaCO2 ___
> 45 mm Hg (on room air)
High-risk patients for pneumonectomy—FEV1 ___
< 2 L
High-risk patients for pneumonectomy—FEV1/FVC ___
< 50% of predicted
High-risk patients for pneumonectomy—Maximum breathing capacity ___
< 50% of predicted
Double lumen tubes come in ___ and ___ types
Left and right
___ for most women
39 Fr
___ for most men
41 Fr
Double lumen ETT sizes
35, 37, 39, 41
Bronchial lumen on double lumen ETT
Longer bronchial lumen with a blue cuff
Tracheal lumen on double lumen ETT
Shorter tracheal lumen with a larger clear cuff
Curve double lumen ETT at ___ to allow endobronchial placement
Tip
Double lumen ETT allow for ___ and __ of each lung indepdently
Ventilating and suctioning
Complications of double lumen ETT (4):
- Traumatic laryngitis
- Hypoxemia due to malpositioned tube
- Bronchial trauma from over inflation of cuff
- Inadvertent suturing of tube
What is the most commonly used double lumen ETT?
Left double lumen tube—easier to place due to anatomic differences in the bronchi
Bronchial lumen of left double lumen ETT is placed ___
Down left mainstem bronchus
Symmetric cuff on left double lumen tube is inflated with ___ of air
1-2 ccs
Tracheal lumen of left double lumen tube is located ___ and ventilates ___
Above the carina (with cuff up), ventilates the right lung
More room to place left double lumen tube due to ___
Length of left mainstem
Left double lumen ETT can be used for all thoracic cases except for ___
Surgery on left mainstem bronchus
Right double lumen ETT is rarely used due to ___
Difficult placement
Right double lumen ETT is indicated for ___
Left mainstem bronchus surgery
Bronchial lumen of right double lumen tube is placed ___ and must align up with opening to the ___
To the right, must align up with the opening to the right upper lobe bronchus
What kind of cuff is inflated on the right double lumen ETT?
An asymmetrical cuff with a slotted opening
What blade gives better visualization for placement of double lumen ETT?
Mac blade
Once you are past the cords, rotate tube ___ as you slowly advance, never forcing, until resistance is felt
90 degrees counter clockwise
Average depth of double lumen tube is ___
29 cm at the teeth
Inflate ___ cuff first
Tracheal; look for ETCO2, then inflate bronchial cuff gently, listen for breath sounds as each side is occluded
Reconfirm position of double lumen tube with ___
Fiber optic scope
MH triggers (top 2):
- Depolarizing agent—succinylcholine
- Inhalational agents—halothane, isoflurane, sevoflurane, desflurane, enflurane
First sign of MH/most sensitive =
Unexplained tachycardia
Most specific sign of MH =
Increasing ETCO2
ABG in MH—initial and then
Initially metabolic acidosis, then a combined metabolic and respiratory acidosis
Treatment of MH
Dantrolene 2.5 mg/kg IV ASAP
Max dose of dantrolene
10 mg/kg total
In order to prevent recurrence of MH, continue dantrolene ___
1 mg/kg IV q6 hours for 72 hours
What drug should not be given while on dantrolene and why?
Calcium channel blockers—d/t life-threatening hyperkalemia and myocardial depression that may occur
How does dantrolene work?
It is a muscle relaxant that works directly on the ryanodine receptor to prevent the release of calcium
Dantrolene directly interferes with muscle contraction by inhibiting ___
Ca release from the sarcoplasmic reticulum—intracellular dissociation of excitation-contraction coupling
Side effects of dantrolene
Safe, may cause generalized muscle weakness which may lead to respiratory insufficiency or aspiration pneumonia; GI upset; thrombophlebitis
Use dantrolene with extreme caution in what patient population?
Patients with pre-existing muscle disease—may cause significant muscle weakness
Gold standard pre-op test for MH =
Muscle biopsy with halothane-caffeine contracture test—78% specific, 97% sensitive
Halothane-caffeine contracture test—caffeine causes muscle to ___; halothane in the MH pt causes ___
Contract; more forceful contraction
Prior uneventful general anesthetic does not rule out ___
The possibility of MH
MH is more common in __
Children than adults
Symptoms of MH usually develop within ___ after exposure to trigger substances
One hour; may even occur several hours later in rare instances
MH does not occur with every exposure to ___
Triggering agents; susceptible patients may undergo multiple uneventful episodes of anesthesia before developing an episode of MH
The only sure way to prevent MH is ___
Avoid the use of triggering agents in patients known or suspected of being susceptible to MH
