Thoracic HPV and OLV

Question 1

What is Hypoxic Pulmonary Vasoconstriction (HPV)?

Answer 1

The constriction that occurs in the lung vasculature with lower oxygen tension.
-Increases PVR
-A normal, protective body response
-Normally, vasculature in the lung matches ventilation. Picks up appropriate amount of O2.
-When O2 tension falls, and no longer ventilating a lung, body wants to increase pulmonary vascular resistance in that area.
-Don’t send blood flow to a non-ventilated area.
-Not always benign: Increasing PVR means higher pressures for the R heart to work against.
-May need PA catheter to monitor PA pressures if concern for Right sided HF.

Nagelhout:
-The lungs have a compensatory mechanism of increasing vascular resistance in hypoxic areas of the lungs, and this diverts some blood flow to areas of better ventilation and oxygenation. This mechanism is termed HPV.
-HPV is a reflex intrapulmonary feedback mechanism in homogeneous lungs that improves gas exchange and arterial oxygenation. Whereas hypoxemia causes vasodilation in the general circulation, alveolar hypoxia has the opposite effect on pulmonary arteries. HPV is a unique compensatory mechanism, suited specifically to matching pulmonary blood flow with well-oxygenated areas of the lung.

Question 2

What is HPV dependent on?

Answer 2

-Alveolar, Venous, and Arterial oxygenation
-PAO2 (Alveolar) is the most important
-HPV functions best when 30-70% of the lung is hypoxic
-Can become sensitized

Question 3

Why does HPV function best when 30-70% of the lung is hypoxic?

Answer 3

Of note, HPV functions best when 30-70% of the lung is hypoxic.
- if < 30% of the lung is hypoxic, and there is not enough hypoxic lung to shunt from
- if more than 70% of the lung is hypoxic, there is no place to shunt the hypoxic blood

Nagelhout:
-When less than 20% of the lung is hypoxic, the total amount of shunt is not significant. -When more than 80% of the lung is hypoxic, HPV increases PVR, but the amount of well-perfused lung is not sufficient to accept enough diverted flow to maintain arterial oxygenation.

Question 4

How can HPV become sensitized?

Answer 4

Repeated incidence of hypoxemia produces more significant response than the first.
- Ex: 1st time, get 50% HPV. 2nd time, get 70%.

Question 5

In what ways does Anesthesia/our actions INHIBIT HPV (bad)?

Answer 5

-Inhaled anesthetics (>1 MAC)
-Vasodilators like nitroglycerin, nipride, some Ca channel blockers (Cardene effect is minimal)
-Factors associated with an increase in pulmonary artery pressure antagonize the effect of HPV to the hypoxic area.
-Examples include volume overload (body dilates to accommodate inc blood flow), hypothermia (HPV is not as effective), infection (vasodilation due to H+ ions), acidosis (inhibits HPV), alkalosis (inhibits HPV), and hypocarbia (inhibits HPV).

Nagelhout:
Factors that reduce effectiveness of HPV:
-Alkalosis
-Excessive tidal volume or PEEP
-Hemodilution
-Hypervolemia (LAP >25 mm Hg), atrial natriuretic peptide
-Hypocapnia
-Hypothermia
-Prostacyclin
-Shunt fraction <20% or >80%
-Vasodilators, phosphodiesterase inhibitors, and calcium channel blockers
-Volatile anesthetics >1.5 MAC

Question 6

What is the effect of vasoconstrictive drugs like Neosynephrine on HPV?

Answer 6

Vasoconstrictive drugs, including dopamine, epinephrine, and phenylephrine, may preferentially constrict normally oxygenated pulmonary vessels and reestablish the shunt flow.
-Increase CO and PVR, causing further shunting (partial reversal of HPV)

Question 7

Why do vasodilators inhibit HPV?

Answer 7

-Dependent lung is maximally dilated.
-Can’t dilate it anymore, so these will work in non-dependent lung, inhibiting HPV.
-Opening up blood flow to an area of no ventilation.
-Cardene is the best to use, because will still inhibit HPV but not as much as others.
-Treat pain before treating HTN.

Question 8

What is Dead Space?

Answer 8

The fraction of inspired volume that does not contribute to gas exchange
-V/Q= infinity
-Increased with circuit and ETT

Question 9

What is Shunt?

Answer 9

Perfused alveoli that are unventilated and do not contribute to gas exchange.
-V/Q = 0

Question 10

How does blood flow change when you convert from two-lung to one-lung ventilation?

Answer 10

HPV response will decrease the blood flow in the isolated lung by 50%. (Never goes to 0%, have to keep tissue alive).
-This shunts remaining blood flow to the other lung.
-This prevents PaO2 from dropping dramatically.
-Review slide 32

Question 11

Can you use Nitrous Oxide in thoracic surgery?

Answer 11

-Usually avoided as it increases PVR (patients already have elevated PVR so this effect is significantly worse)
-Avoid use in patients with bullous and emphysematous lungs (Avoid in expandable spaces - will increase pressure and potential rupture)

Question 12

What is the most effective way of reducing inhibition of HPV?

Answer 12

CPAP 5-10 cm to the non-ventilated lung. (!!!)
-Can’t get blood flow to 0% to non-ventilated lung, so if we can get some air in there, will have less of a V/Q mismatch.
-Seldom used because it lengthens surgical time and surgeons want lung completely deflated.

Question 13

What are Anesthetic methods that reduce the inhibition of HPV (good)?

Answer 13

1) Narcotic anesthesia or nerve blocks (reduce volatile needed)
2) CPAP 5-10 cm to the non-ventilated lung (most effective!!!)
3) PEEP 5-10 cm to the ventilated lung
4) Early ligation of pulmonary artery (pneumonectomy only- eliminates flow, changing HPV proportions)
5) Periodic inflation of non-ventilated lung (SpO2 is low, EtCO2 is high = pt not tolerating OLV)
6) Insufflation of oxygen into collapsed lung (Can do NC blow-by)
7) Limit MAC of inhaled anesthetic to less than 1 MAC
8) Reduce vasodilator concentrations (use narcs to control BP)
9) TIVA - Does not inhibit HPV

Question 14

What are Absolute indications for One Lung Ventilation (OLV)?

Answer 14

-Video-assisted thoracoscopic surgeries
-Purulent secretions (infection)
-Massive pulmonary hemorrhage
-Bronchopleural fistula
-Blebs
-Bullae/cysts ( blood, air, pus)
-Unilateral Bronchopulmonary lavage

Question 15

What are Relative indications for One Lung Ventilation (OLV)?

Answer 15

To facilitate surgical exposure. Highest to lowest priority:
-Thoracic aortic aneurysms
-Pneumonectomy
-Upper lobectomies
-Minimally invasive cardiac surgery
-Esophageal resections
-Middle and lower lobe resections
-Bilateral sympathectomies

Question 16

Describe the different types of Double Lumen Tubes?

Answer 16

-Robertshaw: Most common.
-Carlens: Left-sided tube with a carinal hook to stabilize tube (higher risk of vocal cord damage)
-White: Right-sided Carlens tube (Carinal hook)

Question 17

How does a Double-Lumen tube work?

Answer 17

Gold standard for OLV.
-Most effective, most control in the lungs.
-Can suction and remove secretions.
-Tracheal limb ventilates like a regular ETT into the trachea. If the bronchial cuff is not up, will inflate both lungs. Once bronchial cuff is up (2-3 ccs of air), need to ventilate through bronchial limb to get to that side.

Nagelhout:
The bronchial lumen is identified by its blue cuff and is designed to be inserted into either the left or right mainstem bronchus. The bronchial lumen will be used to initially ventilate the corresponding lung. The tracheal lumen is positioned midtrachea, and the corresponding port will ventilate the opposite lung. The bronchial lumen does not necessarily have to be placed within the bronchus of the operative lung.

Question 18

What is different with a Right-sided tube?

Answer 18

The right mainstem is very short, only about 2 cm past carina.
-Little port needs to sit right on opening, risk of not ventilating right upper lobe if that port isn’t in right place.
-Left lung is further distance, about 5 cm so not as much of a risk.

Question 19

How do you size a Double Lumen Tube (DLT)?

Answer 19

Correlates with height.
-Average male 37 or 39 F (67 in)
-Tall male 41 F
-Average female 35 (63 in) or 37 F

General rule of thumb for depth of insertion:
-27 cm (F) or 29 cm (M) +/- 1 cm for each 10 cm of height above or below 170 cm.

Verify placement with bronchoscope

Question 20

How do you insert a DLT?

Answer 20

-Preferred blade is Macintosh
-Deflate both cuffs
-Lubricate distal end
-DLT bronchial balloon passed cords , then remove stylet, then rotated 90 degrees while advancing.
-Inflate tracheal cuff (5-10 cc of air) then inflate the bronchial cuff (1-2 cc of air).
-Confirm fiber optically and auscultation. (Confirm again after turning laterally)

Question 21

How do you auscultate breath sounds for proper placement of a DLT?

Answer 21

-Bilateral breath sounds with both cuffs inflated.
-Clamp tracheal side and open to air, should only have breath sound on bronchial side.
-Close port and unclamp.
-Repeat with bronchial side, should only have breath sounds on tracheal side.

Question 22

What are complications associated with DLTs?

Answer 22

Nagelhout:
-Malpositioning is most common
-Damage to vocal cords/arytenoids due to carinal hook
-Hoarseness/vocal cord lesions due to large size of tube
-If inserted too deeply, can give entire tidal volume to a single lung (barotrauma)
-Rupture of thoracic aneurysm if it’s compressing left mainstem bronchus

Question 23

What are indications for a Right-sided DLT?

Answer 23

-Tumor in left mainstem bronchus
-Left sided pneumonectomy
-Left sided lung transplant
-Distorted or sharp angled left mainstem bronchus
-Left sided tracheobronchial disruption

Nagelhout:
-Many practitioners have resolved to use left-sided DLTs for all right and left thoracotomies unless a left-sided tube is contraindicated by internal lesions of the airway, compression of the trachea or main bronchi by an external mass, or the presence of a descending thoracic aortic aneurysm, which can compress or erode the left main bronchus.

Question 24

What are complications that are frequently associated with thoracotomy?

Answer 24

-Hypoxemia: Intrapulmonary shunt during OLV
-Sudden, severe hypotension: Surgical compression of the heart or great vessels
-Sudden changes in ventilating pressure or volume: Movement of endobronchial tube/blocker, air leak
-Arrhythmias: Direct mechanical irritation of the heart
-Bronchospasm: Direct airway stimulation, increased frequency of reactive airway disease
-Massive Hemorrhage: Surgical blood loss from great vessels or inflamed pleura
-Hypothermia: Heat loss from the open hemithorax (less occurs with thorascopic, but still some does occur)

Question 25

Describe the clinical approach to OLV Management?

Answer 25

-FIO2 of 1.0 is controversial (FiO2 will need to be higher due to HPV)
-Ventilate with a TV of 5-7 mL/kg for ideal body weight
-PIP less than 35mmHG (ideally)
-Respiratory rate to maintain PaCO2 between 35 and 40 mm Hg
-Check the DLT/endobronchial blocker position subsequent to the lateral decubitus positioning
-If peak airway pressure exceeds 40 mm Hg during OLV, DLT/endobronchial blocker malposition should be excluded.
-For hypoxemia, apply CPAP 10 cm H2O to the nondependent lung (Limited during VAT)
-If additional correction of hypoxemia is necessary add PEEP 5–10 cm H2O to the ventilated lung
-Frequent recruiting maneuvers
-Avoid fluid overload
-TIVA may be preferable to inhalation anesthetics (Think HPV)
-If necessary, intermittently inflate and deflate the operated lung

Question 26

What are recommendations for avoiding hypoxemia and ALI during OLV?

Answer 26

Nagelhout:
-Fi o 2 <1.0: Fi o 2 of 1.0 can facilitate atelectasis, inducing atelectotrauma and, paradoxically, hypoxemia.
-Low Vt (e.g., 6 mL/kg) (or low pressures): High Vt (or high pressures) can lead to volutrauma (or barotrauma).
-Routine use of PEEP: PEEP is beneficial for oxygenation and for lung protection.
-Recruitment maneuvers: Recruitment maneuvers improve oxygenation and achieve a better distribution of aeration.
-Routine use of CPAP to nondependent lung: CPAP is beneficial for both oxygenation and lung protection.
-Permissive hypercapnia: High P co 2 can be beneficial in avoiding ALI.
-Inhalational anesthetics + TEA: TEA does not inhibit HPV allowing a lower inhalational anesthetic MAC value; Inhalational anesthetics can reduce the potential for ALI.

Question 27

What is the Univent Tube?

Answer 27

-A tube with a Bronchial blocker fused to it.
-Can determine which side the blocker goes down.
-Requires bronchoscope for placement
-With any bronchial blocker, wherever the blocker is, that is the isolated (non-ventilated) lung. Can’t ventilate through it.
-May be used for right or left lung isolation
-Balloon inserted into mainstem of lung to be deflated
-Can be used for post-op ventilation without replacement

Question 28

What are Arndt Tubes?

Answer 28

Endobronchial Blockers.
-Inserted through a regular 8 French or greater endotracheal tube
-Must be inserted fiberoptically
-Can be used of right or left lung isolation
-Balloon inserted into mainstem of lung to be deflated
-Removed at end of case thus ETT can remain for post operative ventilation.

Question 29

What is the EZ Blocker?

Answer 29

-Similar to Arndt bronchial blocker. Can do right or left. Has 2 balloons.
-Can’t suction through it though. Have to deflate it to suction.
-Has Y-shaped distal extensions that go into each mainstem.
-Manufacturing issues allowing small amounts of air to transfer between the two balloons. Can end up isolating both lungs. If you need to add air to balloon, assess balloon of other tube.