One-Lung Ventilation: physiology and practical approach

1
One-Lung Ventilation physiology and practical
approach

• Konstantin Balonov
• Department of Anesthesiology
• Boston Medical Center

2
Objectives

• Indication/contraindication of OLV
• Physiology changes of OLV
• Selection of the methods for OLV
• Management of common problems associated with
  OLV, especially hypoxemia

3
Introduction

• One-lung ventilation, OLV, means separation of
  the two lungs and each lung functioning
  independently by preparation of the airway
• OLV provides
• Protection of healthy lung from infected/bleeding
  one
• Diversion of ventilation from damaged airway or
  lung
• Improved exposure of surgical field
• OLV causes
• More manipulation of airway, more damage
• Significant physiologic change and easily
  development of hypoxemia

4
Absolute indication for OLV

• Isolation of one lung from the other to avoid
  spillage or contamination
• Infection
• Massive hemorrhage
• Control of the distribution of ventilation
• Bronchopleural / - cutaneous fistula
• Surgical opening of a major conducting airway
• giant unilateral lung cyst or bulla
• Tracheobronchial tree disruption
• Life-threatening hypoxemia due to unilateral lung
  disease
• Unilateral bronchopulmonary lavage

5
Relative indication

• Surgical exposure ( high priority)
• Thoracic aortic aneurysm
• Pneumonectomy
• Upper lobectomy
• Mediastinal exposure
• Thoracoscopy
• Surgical exposure (low priority)
• Middle and lower lobectomies and subsegmental
  resections
• Esophageal surgery
• Thoracic spine procedure
• Minimal invasive cardiac surgery (MID-CABG, TMR)
• Postcardiopulmonary bypass status after removal
  of totally occluding chronic unilateral pulmonary
  emboli
• Severe hypoxemia due to unilateral lung disease

6
Physiology of the LDP

• Upright position LDP, lateral decubitus
  position

7
Physiology of LDP

• Awake/closed chest Anesthetized
  .
• V Q V Q V Q
• ND ? ? ? ? ? ?
• D ? ? ? ? ? ?

8
Summary of V-Q relationships in the anesthetized,
open-chest and paralyzed patients in LDP
9
Physiology of OLV

• The principle physiologic change of OLV is the
  redistribution of lung perfusion between the
  ventilated (dependent) and blocked (nondependent)
  lung
• Many factors contribute to the lung perfusion,
  the major determinants of them are hypoxic
  pulmonary vasoconstriction (HPV) and gravity.

10
Hypoxic pulmonary vasoconstriction

• HPV is a physiological response of the lung to
  alveolar hypoxia, which redistributes pulmonary
  blood flow from areas of low oxygen partial
  pressure to areas of high oxygen availability.
• The mechanism of HPV is not completely
  understood. Vasoactive substances released by
  hypoxia or hypoxia itself (activating K, Ca
  and TRP channels) cause pulmonary artery smooth
  muscle contraction

11
HPV oxygen sensors
12
HPV

• HPV aids in keeping a normal V/Q relationship by
  diversion of blood from underventilated areas,
  responsible for the most lung perfusion
  redistribution in OLV
• HPV is graded and limited, of greatest benefit
  when 30 to 70 of the lung is made hypoxic.
• HPV is effective only when there are normoxic
  areas of the lung available to receive the
  diverted blood flow

13
Factors affecting regional HPV

• HPV is inhibited directly by volatile anesthetics
  (not N20), vasodilators (NTG, SNP, NO,
  dobutamine, many ß2-agonist), increased PVR (MS,
  MI, PE) and hypocapnia
• HPV is indirectly inhibited by PEEP
  vasoconstrictor drugs (epinephrine,
  norepinephrine, phenylephrine, dopamine)
  constrict normoxic lung vessels preferentially

14
Gravity and V-Q

• Upright LDP

15
Shunt and OLV

• Physiological (postpulmonary) shunt
• About 2-5 CO,
• Accounting for normal A-aD02, 10-15 mmHg
• Including drainages from
• Thebesian veins of the heart
• The pulmonary bronchial veins
• Mediastinal and pleural veins
• Transpulmonary shunt increased due to continued
  perfusion of the atelectatic lung and A-aD02 may
  increase

16
Two-lung ventilation and OLV
17
Cardiac output and OLV

• Decreased CO may reduce SvO2 and thus impair SpO2
  in presence of significant shunt
• Hypovolemia
• Compression of heart or great vessels
• Thoracic epidural sympathetic blockade
• Air trapping and high PEEP
• Increased CO increases PA pressures which
  increases perfusion of the non-ventilated lung ?
  increase of shunt fraction

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Methods of OLV

• Double-lumen endotracheal tube, DLT
• Single-lumen ET with a built-in bronchial
  blocker, Univent Tube
• Single-lumen ET with an isolated bronchial
  blocker
• Arndt (wire-guided) endobronchial blocker set
• Balloon-tipped luminal catheters
• Endobronchial intubation of a single-lumen ET

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DLT

• Type
• Carlens, a left-sided a carinal hook
• White, a right-sided Carlens tube
• Bryce-Smith, no hook but a slotted cuff/Rt
• Robertshaw, most widely used
• All have two lumina/cuffs, one
  terminating in the trachea and the other in the
  mainstem bronchus
• Right-sided or left-sided available
• Available size 41,39, 37, 35, 28 French (ID6.5,
  6.0, 5.5, 5.0 and 4.5 mm respectively)

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Left DLT

• Most commonly used
• The bronchial lumen is longer, and a simple round
  opening and symmetric cuff? Better margin of
  safety than Rt DLT
• Easy to apply suction and/or CPAP to either lung
• Easy to deflate lung
• Lower bronchial cuff
  volumes and pressures
• Can be used
• Left lung isolation
• clamp bronchial
• ventilate/ tracheal lumen
• Right lung isolation
• clamp tracheal
• ventilate/bronchial lumen

21
Left DLT

• More difficult to insert (size and curve, cuff)
• Risk of tube change and airway damage if kept in
  position for post-op ventilation
• Contraindication
• Presence of lesion along DLT pathway
• Difficult/impossible conventional direct vision
  intubation
• Critically ill patients with single lumen tube in
  situ who cannot tolerate even a short period of
  off mechanical ventilation
• Full stomach or high risk of aspiration
• Patients, too small (lt25-35kg) or too young (lt
  8-12 yrs)

22
Right DLT bronchoscopic view
23
Another indication for DLT Reexpansion pulmonary
edema
24
Univent Tube...

• Developed by Dr. Inoue
• Movable blocker shaft in external lumen of a
  single-lumen ET tube
• Easier to insert and properly position than DLT
  (diff airway, C-s injury, pedi or critical pts)
• No need to change the tube for postop ventilation
• Selective blockade of some lobes of the lung
• Suction and delivery CPAP to the blocked lung

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...Univent Tube

• Slow deflation (need suction) and inflation
  (short PPV or jet ventilation)
• Blockage of bronchial blocker lumen
• Higher endobronchial cuff volumes pressure
  (just-seal volume recommended)
• Higher rate of intraoperative leak in the
  blocker cuff
• Higher failure rate if the blocker advanced
  blindly

26
Univent Tube
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Arndt Endobronchial Blocker set

• Invented by Dr. Arndt, an anesthesiologist
• Ideal for diff intubation, pre-existing ETT and
  postop ventilation needed
• Requires ETT gt or 8.0 mm
• Similar problems as Univent
• Inability to suction or ventilate the blocked lung

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Other methods of OLV

• Single-lumen ETT with a balloon-tipped catheter
• Including Fogarty embolectomy catheter, Magill or
  Foley, and Swan-Ganz catheter (children lt 10 kg)
• Not reliable and may be more time-consuming
• Inability to suction or ventilate the blocked
  lung
• Endobronchial intubation of single-lumen ETT
• The easiest and quickest way of separating one
  lung from the other bleeding one, esp. from left
  lung
• More often used for pedi patients
• More likely to cause serious hypoxemia or severe
  bronchial damage

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Management of OLV...

• Maintain two-lung ventilation as long as possible
• Start OLV with 100 O2 then start backing off the
  FiO2 if saturations are OK
• Manual ventilation for the first few minutes of
  OLV to get a sense of pulmonary compliance /
  resistance
• Be attentive to inspiratory pressures and tidal
  volumes and adjust the ventilator to optimize
  oxygenation and alveolar ventilation, with
  minimal barotrauma
• Look at the surgical field to see if the
  non-dependent lung is collapsed

30
...Management of OLV

• Tidal volume 8-10 ml/kg
• Adjust RR (increasing 20-30) to keep PaCO2 40
  mmHg
• No PEEP (or very low PEEP, lt 5 cm H2O)
• Continuous monitoring of oxygenation and
  ventilation (SpO2, ABG and ET CO2)

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Management of hypoxemia during OLV

• FiO2 1.0
• Manual ventilation
• Check DLT position with FOB
• Check hemodynamic status
• CPAP (5-10 cm H2O, 5 L/min) to nondependent lung,
  most effective
• PEEP (5-10 cm H2O) to dependent lung, least
  effective
• Intermittent two-lung ventilation
• Clamp pulmonary artery

32
Other causes of hypoxemia in OLV

• Mechanical failure of O2 supply or airway
  blockade
• Hypoventilation
• Resorption of residual O2 from the clamped lung
• Factors that decrease SvO2 (?CO, ?O2 consumption)

33
Broncho-Cath CPAP system
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Summary

• OLV widely used in cardiothoracic surgery
• Many methods can be used for OLV. Optimal methods
  depends on indication, patient factors,
  equipment, skills and level of training
• FOB is the key equipment for OLV
• Principle physiologic change of OLV is the
  redistribution of pulmonary blood flow to keep an
  appropriate V/Q match
• Management of OLV is a challenge for the
  anesthesiologist, requiring knowledge, skill,
  vigilance, experience, and practice