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8361 Exam 4 > Mod XI - M&M25 - Miller66 - Thoracic: > Flashcards

Mod XI - M&M25 - Miller66 - Thoracic: Flashcards

1
Q

ANESTHESIA FOR THORACIC SURGERY

Don’t forget to go over the reading assignment for additional procedures not covered in this lecture

A

M&M25 - Miller66

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2
Q

ANESTHESIA FOR THORACIC SURGERY

OBJECTIVES

A
  • Describe indications, components, and preoperative assessment for thoracic surgeries
  • Identify potential anesthetic and surgical complications
  • State contraindications for OLV/DLT.
  • Be able to identify mispositioning of DLT based on case scenarios
  • Describe basic principles of postoperative pain management for thoracic surgery patients
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3
Q

ANESTHESIA FOR THORACIC SURGERY

lung isolation techniques have been in existence for as long as ET intubation itself - “Closed endobronchial anesthesia”, aka lung isolation technique, first performed in

A

1928

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4
Q

ANESTHESIA FOR THORACIC SURGERY

Closed endobronchial intubation, with the use of a bronchial blocker was 1st performed in

A

1936

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5
Q

ANESTHESIA FOR THORACIC SURGERY

First use of a double-lumen endotracheal tube (DLT) in

A

1950

DLT technology continuously evolving

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6
Q

ANESTHESIA FOR THORACIC SURGERY

DLT technology continuously evolving. However, what continues to be a its main concern?

A

Maintaining effective gas exchange in the face of ventilation perfusion mismatches

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7
Q

ANESTHESIA FOR THORACIC SURGERY

Two important anesthetic techniques for thoracic surgery

A

Lung isolation to facilitate surgical access within the thorax

Management of one-lung ventilation (OLV)

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8
Q

ANESTHESIA FOR THORACIC SURGERY

Benefits of OLV

A

Provides quiet surgical field

(This is very important in thoracoscopic surgeries)

Thoracic surgeons consider lung separation an absolute requirement for pulmonary surgery

Surgery can be performed on a lung while it’s being ventilated

Thoracic surgery alone is not an absolute indication for OLV

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9
Q

ABSOLUTE AND RELATIVE INDICATIONS FOR OLV

ABSOLUTE INDICATIONS FOR OLV

A

Lung isolation to prevent contamination/infection of health lung

Regulate distribution of ventilation to one lung

Unilateral lung lavage

Most common thoracic surgeries create relative indication for lung separation

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10
Q

ABSOLUTE AND RELATIVE INDICATIONS FOR OLV

RELATIVE INDICATIONS FOR OLV

A

Most common thoracic surgeries create relative indication for lung separation, in that they can safely accomplished without it

Surgical exposure for thoracic procedures- high Priority

•TAA

•Pneumonectomy

•Thoracoscopy

•Upper lobectomy

•Mediastinal exposure

Surgical exposure-medium (lower) priority

•Middle and lower lobectomies & segmental resections

•Esophageal resection

•Procedures on the thoracic spine

Severe hypoxemia r/t unilateral lung disease​

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11
Q

METHODS OF LUNG ISOLATION

A

1.DOUBLE-LUMEN TUBES

•Bifurcated tube with both an endotracheal and an endobronchial lumen

•Can be used to achieve isolation of either right or left lung

2.SINGLE-LUMEN TUBES

•Tube is advanced into the contralateral mainstem bronchus for ventilation while the surgical side is collapsed

3.BRONCHIAL BLOCKERS

•Blockade of a mainstem bronchus to allow lung collapse distal to the occlusion

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12
Q

METHODS OF LUNG ISOLATION

What the most common type of lung isolation?

A

DOUBLE-LUMEN TUBES

  • Bifurcated tube with both an endotracheal and an endobronchial lumen
  • Can be used to achieve isolation of either right or left lung
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13
Q

METHODS OF LUNG ISOLATION

Placement options for Double-lumen tube (DLT)

A
  1. Direct laryngoscopy
  2. Via tube exchanger
  3. Fiberoptically
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14
Q

METHODS OF LUNG ISOLATION

Advantages of Double-lumen tube (DLT)

A

Easy to place successfully
Repositioning rarely required
Bronchoscopy to isolated lung
Suction to isolated lung
CPAP easily added
Can alternate one-lung ventilation to either lung easily
Placement still possible if bronchoscopy not available
Best device for absolute lung isolation

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15
Q

METHODS OF LUNG ISOLATION

Disadvantages of Double-lumen tube (DLT)

A

Size selection more difficult
Difficult to place in patients with difficult airways or abnormal tracheas
Not optimal for postoperative ventilation
Potential laryngeal trauma
Potential bronchial trauma

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16
Q

METHODS OF LUNG ISOLATION

Placement options for Bronchial Blockers (BB)

A
  1. Arndt
  2. Cohen
  3. Fuji
  4. EZ Blocker
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17
Q

METHODS OF LUNG ISOLATION

Advantages of Bronchial Blockers (BB)

A

Size selection rarely an issue
Easily added to regular ETT
Allows ventilation during placement
Easier placement in patients with difficult airways and in children
Postoperative two-lung ventilation by withdrawing blocker
Selective lobar lung isolation possible
CPAP to isolated lung possible

(Often used when lung isolation requirements were not anticipated at the begining of the case; so rather than switching out for a DLT, the decision was made to place a BB)

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18
Q

METHODS OF LUNG ISOLATION

Disadvantages of Bronchial Blockers (BB)

A

More time needed for positioning
Repositioning needed more often
Bronchoscope essential for positioning
Limited right lung isolation due to RUL anatomy
Bronchoscopy to isolated lung impossible
Minimal suction to isolated lung
Difficult to alternate one-lung ventilation to either lung

(Also have a higher incidence for being dislodged when compared to DLT)

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19
Q

METHODS OF LUNG ISOLATION

Which lung isolation technique is used when a DLT is not an option?

A. BB

B. SLT

A

A. BB

(These are not commonly used in the clinical setting, but are used moe often than single lumen tubes (SLT) when a DLT is not an option)

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20
Q

METHODS OF LUNG ISOLATION

The final option for lung isolation is to use either an SLT or an endobronchial tube that is advanced into the contralateral mainstem bronchus, protecting this lung while allowing collapse of the lung on the side of surgery

Why is this technique rarely used today in adult practice (except in some cases of difficult airways, carinal resection, or after a pneumonectomy),

A

Limited access to the surgical lung for bronchoscopy, suctioning or CPAP

owing to the limited access to the nonventilated lung and the difficulty in positioning a standard SLT in the bronchus

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21
Q

METHODS OF LUNG ISOLATION

Advantages of Endobrochial tube

A

Like regular ETTs, easier placement in patients with difficult airways
Longer than regular ETT
Short cuff designed for lung isolation

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22
Q

METHODS OF LUNG ISOLATION

Disadvantages of Endobrochial tube

A

Bronchoscopy necessary for placement
Does not allow for bronchoscopy, suctioning, or CPAP to isolated lung
Difficult one-lung ventilation (right lung)

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23
Q

METHODS OF LUNG ISOLATION

Advantages of Endotracheal tube advanced into bronchus

A

Easier placement in patients with difficult airways

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24
Q

METHODS OF LUNG ISOLATION

Disadvantages of Endotracheal tube advanced into bronchus

A

Does not allow for bronchoscopy, suctioning, or CPAP to isolated lung
Cuff not designed for lung isolation
Extremely difficult right one-lung ventilation

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25
Q

DOUBLE-LUMEN ENDOTRACHEAL TUBES

The DLT Consists of:

A

a single tube with two lumens

Bronchial lumen (blue cuff)

Tracheal lumen

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26
Q

DOUBLE-LUMEN ENDOTRACHEAL TUBES

Bronchial lumen (blue cuff)

A

Longer than the tracheal lumen

Designed to be inserted into the Right of Left main bronchus

Used to ventilate the lung that it is inserted into

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27
Q

DOUBLE-LUMEN ENDOTRACHEAL TUBES

Tracheal lumen

A

Terminates in the trachea (mid-trachea)

Corresponding port will ventilate the opposite lung

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28
Q

DOUBLE-LUMEN ENDOTRACHEAL TUBES

Why are Right and left DLT are manufactured?

A

DLT can be used to achieve isolation of either right or left lung

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29
Q

DOUBLE-LUMEN ENDOTRACHEAL TUBES

What’s the most widely used DLT?

A

Left DLT

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30
Q

DOUBLE-LUMEN ENDOTRACHEAL TUBES

Sizing of DLT is determined by:

A

Patient’s gender and height

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31
Q

DOUBLE-LUMEN ENDOTRACHEAL TUBES

Which DLT size is used for females? which size is used for males?

A

Females: 35-37

Males: 39-41

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32
Q

DOUBLE-LUMEN ENDOTRACHEAL TUBES

What are the charateristics of internal vs external diameters of DLTs?

A

Internal diameter of DLT are reduced b/c of the double-lumen

External diameters of DLT are large

Size 37 Fr = 11 mm external diameter

Smallest DLT 25 Fr = 7.5 mm external diameter

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33
Q

DOUBLE-LUMEN ENDOTRACHEAL TUBES

Why are DLTs are not typically used in children?

A

Large external diameters

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34
Q

DOUBLE-LUMEN ENDOTRACHEAL TUBES

Which method is suggested by some books to determine proper positioning/size of the DLT? Typically DLT size is simply based on:

A

CT-scan with a superimposed DLT to predict proper positioning/size

This is actually never done in practice

Typically DLT size is simply based on gender and height

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35
Q

Comparative Diameters of Single- and Double-Lumen Tubes

How do external diameters of SLTs and DLTs compared? Why should DLTs never be advanced againts resistance?

A

Compared with SLTs, DLTs have a large external diameter

This is why DLTs should not be advanced against significant resistance

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36
Q

Selection of Double-Lumen Tube Size Based on Adult Patient—s Sex and Height

What the appropriate Size of Double-Lumen Tube (Fr) for Female <160 (63 in)* vs Female >160 cm in height?

A

35 Fr. vs 37 Fr

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37
Q

Selection of Double-Lumen Tube Size Based on Adult Patient—s Sex and Height

What the appropriate Size of Double-Lumen Tube (Fr) for Male <170 (67 in)* vs Male >170 cm in height?

A

39 Fr. vs 41 Fr

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38
Q

Comparative Diameters of Single- and Double-Lumen Tubes

Photograph of the cut cross sections of several SLTs and DLTs.

A

Note that:

The external diameter of a 35-Fr DLT is larger than that of an 8.0-mm (internal diameter) SLT, and a 41-Fr DLT is larger than a 10-mm SLT.

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39
Q

ANATOMIC CONSIDERATIONS

Why are Right and left-sided DLTs designed differently?

A

To accommodate differences in bronchial anatomy between left and right side must be taken into acount

Right side main bronchus is shorter than the left side

Distance from carinal bifurcation to right upper lobe takeoff = 1.5-2 cm

Distance from carinal bifurcation to left upper lobe takeoff = 4.5-5 cm

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40
Q

ANATOMIC CONSIDERATIONS

Which main bronchus is shorter?

A

Right side main bronchus is shorter than the left side

Distance from carinal bifurcation to right upper lobe takeoff = 1.5-2 cm

Distance from carinal bifurcation to left upper lobe takeoff = 4.5-5 cm

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41
Q

ANATOMIC CONSIDERATIONS

Right-sided DLTs are made to reduce the chance of obstruction of the orifice of the right upper lobe - Such differences include:

A

Modifications in the R DLT => slot in the endobronchial cuff for ventilation of right upper lobe

Note view If FO scope is passed at the end of the endobrochial lumen

Note view if FO scope is passed at the tracheal lumen

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42
Q

RIGHT VERSUS LEFT SIDED DLT

PROS of the RIGHT SIDED DLT

A

Distorted anatomy of the entrance of left mainstem bronchus (tumor or TAA)

Site of surgery involving left mainstem bronchus

Left lung transplant, L-pneumonectomy

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43
Q

RIGHT VERSUS LEFT SIDED DLT

CONS of the RIGHT SIDED DLT

A

More difficult to use

More easily mispositioned

Not stocked by many places to reduce the cost of purcahsing an item that is rarely used

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44
Q

RIGHT VERSUS LEFT SIDED DLT

PROS of the LEFT SIDED DLT

A

•Most commonly used

  • Quickest/most successfully placed
  • Repositioning rarely required
  • Best for absolute lung separation
  • Large lumen easy for suctioning
  • Placement still possible w/o bronchoscopy
45
Q

RIGHT VERSUS LEFT SIDED DLT

CONS of the LEFT SIDED DLT

A
  • Can be difficult to select proper size
  • Tear in tracheal cuff during intubation
  • Potential for laryngeal, tracheal, and bronchial injuries
46
Q

RIGHT VERSUS LEFT SIDED DLT

It is also typical to manage some cases that would require a Right side DLT w/ a Left side DLT - (e.g.

A

Left pneumonectomy

In this case a Left DLT can be used, but it would to be removed prior to stappling the left maintsem bronchus

47
Q

LEFT SIDED DOUBLE-LUMEN TUBES

Blue cuff = ? lumen going where?

Blue cuff volume? (mL)

A

Blue = Bronchial = B

Bronchial cuff volume = ( 3 mL)

48
Q

LEFT SIDED DOUBLE-LUMEN TUBES

White cuff = ? lumen going where?

White cuff volume ?(mL)

A

White cuff = portion of the tube that will sit in the trachea, just above the carina

White cuff volume = 5 mL

49
Q

LEFT SIDED DOUBLE-LUMEN TUBES

Why is it important to never over inflate either of the cuffs (Bronchial vs tracheal cuffs?

A

Cuff can rupture, which reduces chances of maintaining OLV

Tissue corrosion to surrounding the tube can occur

50
Q

LEFT SIDED DOUBLE-LUMEN TUBES

Suction can be placed in either of the lumens - for what purpose?

A

To help facilitate collapse of the lung during surgery

Suction that can be placed in either lumen to help facilitate complete lung collapse

51
Q

LEFT SIDED DOUBLE-LUMEN TUBES

What the purpose of the Connector?

A

Connector that allows for ventilation of both lungs together

52
Q

PLACEMENT OF A DOUBLE-LUMEN TUBE

Describe inertion of the the DLT:

A

DLT is passed by direct laryngoscopy, with the stylet in place, just beyond the vocal cords

DLT is advanced until endobronchial cuff has passed beyond the vocal cords

Remove stylet and turn DLT 90 degrees counterclockwise (for a left-sided DLT placement)

Finally, tube is advanced to appropriate depth or until resistance is met, which is usually around 27 to 29 cm at the lip

53
Q

PLACEMENT OF A DOUBLE-LUMEN TUBE

Representation of when the Remove stylet and turn DLT 90 degrees counterclockwise (for a left-sided DLT placement)

A

the Remove stylet and turn DLT 90 degrees counterclockwise (for a left-sided DLT placement)

54
Q

PLACEMENT OF A DOUBLE-LUMEN TUBE

Finally, tube is advanced to appropriate depth or until resistance is met, which is usually around 27 to 29 cm at the lip

A

Finally, tube is advanced to appropriate depth or until resistance is met, which is usually around 27 to 29 cm at the lip

55
Q

PLACEMENT OF A DOUBLE-LUMEN TUBE

Based on the Average anatomy of 170 cm patient, optimal depth strongly correlates with

A

Patient’s height

56
Q

PLACEMENT OF A DOUBLE-LUMEN TUBE​

As previously noted, the tube is typically inserted to 27 to 29 cm at the teeth/lip - Optional technique - The correct depth can also be calculated by:

A

Depth = (patient’s height/10) cm + 12

57
Q

PLACEMENT OF A DOUBLE-LUMEN TUBE​

What should you do if you meet resistance before the tube had reached the calculated depath?

A

If you ever meet resistance, you wanna stop advancing the tube

You may not actually reach the correctly calculated depth before you meet Resistance

58
Q

PLACEMENT OF A DOUBLE-LUMEN TUBE​

Once the tube is in place you must check correct placement - During bilateral lung ventilation, the tracheal cuff is inflated, and auscultation should occur to

A

Confirm bilateral ventilation

59
Q

PLACEMENT OF A DOUBLE-LUMEN TUBE​​

Once bilateral breath sounds and chest rise are confirmed, the tracheal lumen is clamped, and the port distal to that clamp is opened

The Bronchial cuff is then inflated and auscultation should occur

A

over the side of the lung being ventilated by the bronchial lumen

In the case of this picture, no chest rise would be expected over the right side

Chest rise and lung sounds would be expected over the left side

60
Q

PLACEMENT OF A DOUBLE-LUMEN TUBE​​

Auscultation alone should not be used to confirm placement of a DLT - What’s more?

A

A fiber optic scope should be inserted into the tracheal lumen for inittial positioning, and for any subsequent time the pt’s position changes

61
Q

PLACEMENT OF A DOUBLE-LUMEN TUBE​​

Through the tracheal view, the blue or bronchial cuff should not herniated out of the left bronchus, and it should be seen at

A

approximately 5 mm below the tracheal carina in the left bronchus

62
Q

PROBLEMS RELATED TO DOUBLE-LUMEN TUBES

The most commonly occuring problem with positioning of the of a DLT is

A

Mispositioning, whereby the tube is either

Tip of tube

Too proximal,

Too distal, or

Placed in the incorrect bronchus

Any of these could be the reason why the intended lung is not collapsing

Fiberoptic broncoscopy should be used to reconfirm and repostition the tube

63
Q

PROBLEMS RELATED TO DOUBLE-LUMEN TUBES

Any of the causes of malpositioning could be the reason why the intended lung is not collapsing - What should be used to reconfirm and repostition the tube?

A

Fiberoptic broncoscopy

64
Q

PROBLEMS RELATED TO DOUBLE-LUMEN TUBES​

Tracheal and bronchial injuries can occur, and is typically seen when

A

DLT is too small

Undersized DLT migrates too distally than anticipated causing the main body of the DLT to be positioned into a bronchus

65
Q

PROBLEMS RELATED TO DOUBLE-LUMEN TUBES​

Hoarseness can occur with

A

Traumatic intubations

Too large DLT causing pressure on surrounding tissue

Movement of DLT with inflated cuffs

66
Q

BRONCHIAL BLOCKER PLACEMENT

OLV w/ a BB may be desired if DLT cannot be placed, eg. :

A

Previous oral or neck surgery

Difficult intubation

Anticipated need for mechanical ventilation post op

May be used preferentially in patients with previous oral or neck surgery

Used for patients with anticipated postoperative mechanical ventilation

67
Q

BRONCHIAL BLOCKER PLACEMENT

How are BB placed

A

Through a SLT, with the assistance of a bronchoscopy

Blockade of a mainstem bronchus

Collapse distal to the occlusion

Requires the use of a bronchoscopy for correct placement

68
Q

VENTILATORY SETTINGS FOR OLV

What are the GOALS of mechanical ventilation for OLV?

A

Maintain adequate arterial oxygen saturation,

Protect the lung, and

Optimize surgical field for adequate visualization and manipulation

69
Q

VENTILATORY SETTINGS FOR OLV

•Tidal volumes, •Historically

A

Large TV used

Thought behing 10-15 mL/kg of TV was that this will prevent atelectasis

70
Q

VENTILATORY SETTINGS FOR OLV

Now understood that high volume predispose the dependent lung to

A

Volutrauma

Which causes the release of local mediators (cytokine inflammatory mediators)

Could lead to Acute Lung Injury (ALI)

It is now Recommended to keep TV 5-6 mL/kg

71
Q

VENTILATORY SETTINGS FOR OLV

It also recommended to keep Peak Inspiratory Pressures (PIP) < 25 cm H2O - Peak airway pressures > 40 cmH2O may contribute to:

A

“Hyper-inflation injury”

72
Q

VENTILATORY SETTINGS FOR OLV

It’s important to determine An appropriate air-oxygen mixture - This value will vary from pt to pt - Be sure to leave room for “reserve” - why?

A

Some facilities will keep the pt at an FiO2 of 1.0 the entire procedure

This can cause atelectasis, and eliminate the reserve intervention in the face of a declining oxygenation

If FiO2 less than 1.0 is used, and the pt experiences hypoxemia, increasing the FiO2 to 1.0 would buy the practitionner time to plan another intervention

However, if the FiO2 starts out at 1.0, there is no “reserve”

Also, on 1.0 FiO2, by the time the SpO2 is falling, the insult that’s causing the hypoxiawould be more advanced and the saturation will continue to decline during diagnosis and management of the issue

73
Q

VENTILATORY SETTINGS FOR OLV

Volume Control versus Pressure control

A

Pressure control will curtail sudden increases in PAP,

however must watch for rapid changes in tidal volumes

74
Q

PHYSIOLOGY OF TWO-LUNG VENTILATION - AFFECT OF POSITION ON GAS EXCHANGE

Effect of positioning on ventilation - Pts are typically placed in which position for thoracic surgery?

A

Lateral decubitus position

Gravitational effects on gas and blood flow => Result of differences in ventilation and perfusion in different lung segments

75
Q

PHYSIOLOGY OF TWO-LUNG VENTILATION - AFFECT OF POSITION ON GAS EXCHANGE

Normal V/Q ratio =

A

0.8 (ventilation 4L/min; perfusion 5L/min)

76
Q

PHYSIOLOGY OF TWO-LUNG VENTILATION - AFFECT OF POSITION ON GAS EXCHANGE

Position changes can result in changes in ventilation/perfusion, especially in the anesthetized and paralyzed pt

When the anesthetized pt is placed in the lateral decubitus position, the ventilation/perfusion ration is

A

DECREASED V/Q ratio

So there is physiologic shunting increased to 20-30%

vs normal shunt = 3-5%

77
Q

PHYSIOLOGY OF TWO-LUNG VENTILATION - AFFECT OF POSITION ON GAS EXCHANGE

Why is V/Q ratio DECREASED in the lateral decubitus position?

A

Increased of the compliance of the Nondependent lung, It becomes easier to ventilate

Aslo noted is decreased perfusion of the Nondependent lung

The displacement of the relaxed diaphragm by abdominal viscera, and the downward gravity of the mediastinum result in DECREASED compliance of the Dependent lung

Perfusion the Dependent lung is increased

78
Q

PHYSIOLOGY OF TWO-LUNG VENTILATION - AFFECT OF POSITION ON GAS EXCHANGE

Further reduction in movement of dependent hemithorax in lateral decubitus position d/t:

A

Utilization of bean bag or axillary roll

79
Q

PHYSIOLOGY OF TWO-LUNG VENTILATION - AFFECT OF POSITION ON GAS EXCHANGE

During Two-lung ventilation, when the pt is in the lateral decubitus position, the Distribution of blood flow between nondependent and dependent lung is:

A

40%:60%

80
Q

PHYSIOLOGY OF TWO-LUNG VENTILATION - AFFECT OF POSITION ON GAS EXCHANGE

When One-lung ventilation is initiated, lateral decubitus, the Distribution of blood flow between nondependent and dependent becomes:

A

20%:80%

81
Q

PHYSIOLOGY OF TWO-LUNG VENTILATION - AFFECT OF POSITION ON GAS EXCHANGE

During Two-lung ventilation, when the pt is in the lateral decubitus position, the Distribution of blood flow between nondependent and dependent lung is 40%:60%

When One-lung ventilation is initiated, lateral decubitus, the Distribution of blood flow between nondependent and dependent is reduced to 20%:80%

Why?

A

Hypoxic pulmonary vasoconstriction (HPV)

HPV reduces blood flow to the non-dependent lung by 50% in an effort to reduce the physiologic shunting

Without autoregulation of pulmonary blood flow, (aka without HPV), a large physiologic shunt of 40% would occur

82
Q

The Reflex intrapulmonary feedback mechanism that improves gas exchange and arterial oxygenation is known as:

A

HYPOXIC PULMONARY VASOCONSTRICTION (HPV)

It is Present in most mammals

83
Q

HYPOXIC PULMONARY VASOCONSTRICTION (HPV)

In response to Hypoxia, normal tissue will vasodilate - With HPV, Alveolar hypoxia leads to:

A

Increased pulmonary vascular resistance (PVR) and vasoconstriction to reduce blood flow to nonventilated lung (non-dependent lung)

This reduces perfusion during OLV

Blood is then redirected towards the dependent, more perfused lung

84
Q

HYPOXIC PULMONARY VASOCONSTRICTION (HPV)

When is HPV initiated? When does its maximum effect occur? when does it return to baseline?

A

Within second of hypoxia

Maximum effect after ~15 minutes

May not return to baseline for several hours following prolonged OLV

85
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

Can be caused by:

A

•Volatile anesthetics inhibit HPV in dose-dependent fashion

•Higher doses = more inhibition

•Halothane > Enflurane > Isoflurane

•Doses < 1 MAC = weak inhibition of HPV

•Nonventilated lung à reduced delivery of inhalational agents to alveoli àless inhibition of HPV

•Vasodilators

•Nitroglycerin, Nitroprusside, Phosphodiesterase inhibitors, beta blockers, calcium channel blockers

•Nitrous Oxide

Very high/very low pulmonary artery pressures

Hypocapnia = Vasodilation

High mixed venous PaO2

Also low PaO2, why?

Excessive PEEP

Pulmonary infection

Increased cardiac output

86
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

How do volatile anesthetics inhibit HPV

A

in dose-dependent fashion

•Higher doses = more inhibition

87
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

Which volatile anesthetics inhibit HPV the most?

A

Older agents

•Halothane > Enflurane > Isoflurane

88
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

How do Modern volatile anesthetics inhibit HPV?

A

At Doses < 1 MAC = modern agents are weak inhibition of HPV

Cause only a 4% increase in the shunt that would be expected with a normal HPV response

•Nonventilated lung => reduced delivery of inhalational agents to alveoli àless inhibition of HPV

89
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

How do Vasodilators such as Nitroglycerin, Nitroprusside, etc affect HPV

(Phosphodiesterase inhibitors, beta blockers, calcium channel blockers)

A

Can reduce HPV by causing the opposite effect

Which is vasodilation in the non ventilated pulomonary vasculature

90
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

Why is Nitrous Oxide generally avoided?

A

Nitrous Oxide can cause an increase in PVR

Which can either cause or exacerbate Pulm HTN, thus opposing HPV

91
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

Why does low PaO2 inhinbits HPV?

A

…

92
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

How to Very high/very low pulmonary artery pressures affect HPV?

A

Low PAP as in those seen with hypovolemic pts can trigger an adrenergic vasoconstriction, which reduces blood flow to the well ventilated lung

Increase PAP will increase PVR, which will vasoconstrict the pulmonary vasculature, potentially reducing flow to ventilated lung and exacerbating hypoxemia

93
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

How does Hypocapnia affect HPV?

A

Hypocapnia causes vasodilation

Hypocapnia causes reduced pulmonary vascular resistance and vasodilation, which oppose HPV

94
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

How does High PaO2 affect HPV?

A

High PaO2 can cause atelectasis which further induces hypoxemia

95
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

How does Excessive PEEP affect HPV?

A

Excessive PEEP can potentially reduce perfusion into well ventilated areas

This can cause zone 1 ventilation/perfusion ratio, where more of the lung enters into a death space ventilatory pattern

96
Q

INHIBITION OF HYPOXIC PULMONARY VASOCONSTRICTION

How does Increased cardiac output inhibits HPV?

A

Increased cardiac output is an interesting inhibitor of HPV

Thought to potentially recruit constricted vessels, thereby increasing the shunt

97
Q

HYPOXEMIA DURNG ONE-LUNG VENTILATION

Hypoxemia during OLV is defined as:

A

PaO2 < 90%

Acceptable saturation = >90%

Brief periods of saturation in high 80% acceptable in patients without significant comorbidities

Lower acceptable saturations will be higher in pts with organs that are highly susceptible to hypoxemia, including those with CV or cerbrovascular disease

98
Q

HYPOXEMIA DURING ONE-LUNG VENTILATION

Hypoxemia is set to now occur in about what % of pts under OLV?

A

5-10%

99
Q

HYPOXEMIA DURING ONE-LUNG VENTILATION

Previously, hypoxemia occurred frequently, 20-30% of cases. Now 5% - Improvement is the result of:

A

Improvement in lung isolation

Anesthetic agents

Better understanding of the physiology behind OLV

100
Q

HYPOXEMIA DURING ONE-LUNG VENTILATION

What are anesthetic goals of OLV?

A

Maximize pulmonary vascular resistance in nonventilated lung (or non-dependent lung) while minimize PVR in ventilated or dependent lung

Thinking about the physiology behind this will help you remember

101
Q

HYPOXEMIA DURING ONE-LUNG VENTILATION

First step if hypoxemia occur during OLV is to

A

Check for tube malpositioning

A large portion of hypoxemic episodes are remedied by tube repositioning

102
Q

HYPOXEMIA DURING ONE-LUNG VENTILATION

Beside tube malpositioning, other causes of hypoxemia during OLV include:

A

Bronchospasm

Decreased cardiac output

Hypoventilation

Low FiO2

Pneumothorax of dependent lung

103
Q

PREDICTION OF HYPOXEMIA DURING OLV

Factors That Correlate with an Increased Risk of Desaturation and hypoxemia During One-Lung Ventilation include:

A
  1. High percentage of ventilation or perfusion to the operative lung on preoperative scan
  2. Poor PaO2 during two-lung ventilation, particularly in the lateral position intraoperatively
  3. Right-sided thoracotomy
  4. Normal preoperative spirometry (FEV1 or FVC) or restrictive lung disease
  5. Supine position during one-lung ventilation

In these pts, it could be anticipated that prophylactic measures would need to be employed

104
Q

PREDICTION OF HYPOXEMIA DURING OLV

The most important predictor of hypoxemia during OLV is:

A

the PaO2 during Two-Lung Ventilation, specifically in the lateral position

105
Q

PREDICTION OF HYPOXEMIA DURING OLV

Normal preoperative spirometry (FEV1 or FVC) or restrictive lung disease

A

Perfusion scans and spirometry can be used to help predict the potential for hypoxemia during OLV

Perfusion to the operative lung is inversely proportional to the physiologic shunting

Pts with a lower FEV1 such as those with obstructive lung disease have be shown to experience less hypoxemia than pts with normal spirometry or pts with restrictive lung disease

This is thought the be the result of intrincic or auto-peep that helps keep the pt airway patent during OLV

106
Q

PREDICTION OF HYPOXEMIA DURING OLV

Right sided thoracotomy are also a/w higher incidences of hypoxemia - why?

A

This is b/c the right lung is larger than the left, so perfusion is higher to the right

107
Q

PREDICTION OF HYPOXEMIA DURING OLV

Supine position with OLV has also been show to have less favorable outcomes than the lateral position - why?

A

This is d/t to the gravitational changes that occur with ventilation and perfusion

108
Q

Therapies for Desaturation during One-Lung Ventilation

A

Severe or precipitous desaturation: resume two-lung ventilation (if possible).

Gradual desaturation

Ensure that delivered FiO2 is 1.0.

Check position of double-lumen tube or blocker with fiberoptic bronchoscopy.

Ensure that cardiac output is optimal; decrease volatile anesthetics to <1 MAC.

Apply a recruitment maneuver to the ventilated lung (this will transiently make the hypoxemia worse).

Apply PEEP 5 cm H2O to the ventilated lung (except in patients with emphysematous pathology).

Apply CPAP 1-2 cm H2O to the nonventilated lung (apply a recruitment maneuver to this lung immediately before CPAP).

Use intermittent reinflation of the nonventilated lung.

Partial ventilation techniques of the nonventilated lung:

Lung oxygen insufflation

Lobar insufflation

Lobar collapse (using a bronchial blocker)

Use mechanical restriction of the blood flow to the nonventilated lung

PEEP, positive end-expiratory pressure; CPAP, continuous positive airway pressure.

109
Q

Therapies for Desaturation during One-Lung Ventilation

Re-inflation of the non-ventilated lung can cause HPV to

A

be more effective

HPV has a pre-conditionning effect

HPV response to a second hypoxic challenge after re-expansion will be greater than the first

8361 Exam 4 (16 decks)

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