Intraoperative Hypoxia During Thoracic Surgery

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Intraoperative Hypoxia During Thoracic Surgery

• Tarek Ashoor

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Objectives

• Shunting and its significance.
• Alveolar dead space .
• Physiology of LDP.
• HPV and the factors affecting it.
• Causes of hypoxia in one lung ventilation.
• How to manage them.

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Introduction

• Shunting is
• Shunting is simply the passage of venous blood
  (Venous admixture) to the left side of the heart
  .
• So What?

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Introduction (cont.)

• The venous admixture causes dilution of the PaO2
  in the arterial blood ending in

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Introduction (cont.)

• The venous admixture causes dilution of the PaO2
  in the arterial blood ending in
• Hypoxia

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Introduction (cont.)

• This occur physiologically due to
• Thebesian veins of the heart
• The pulmonary bronchial veins
• Mediastinal and pleural veins
• Accounting for normal A-aD02, 10-15 mmHg

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Introduction (cont.)

• Transpulmonary shunt occur due to continued
  perfusion of the atelectatic lung (or part of
  it).
• Perfused Non-ventilated part of the lung

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Introduction (cont.)

• Dead space
• Space in the respiratory tract
  that doesnt share in gas exchange.
• This accounts for the normal difference between
  PaCO2 and ETCO2 (5 mmHg).

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Introduction (cont.)

• Alveolar dead space
• Parts in the lungs that are ventilated
  but not perfused.
• Ex Pulmonary embolism

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V-Q relationships in the anesthetized,
open-chest and paralyzed patients in LDP
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V-Q relationships in the anesthetized,
open-chest and paralyzed patients in LDP (cont.)
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Physiology of the LDP

• Upright LDP, lateral
  decubitus

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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, and gravity.

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HPV

• HPV, a local response of pulmonary artery smooth
  muscle, decreases blood flow to the area of lung
  where a low alveolar oxygen pressure is sensed.
• HPV aids in keeping a normal V/Q relationship by
  diversion of blood from underventilated areas.
• HPV is graded and limited, of greatest benefit
  when 30 to 70 of the lung is made hypoxic.
• But effective only when there are normoxic
  areas of the lung available to receive the
  diverted blood flow

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Two-lung Ventilation and OLV
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Factors Affecting Regional HPV
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Factors Affecting Regional HPV

• HPV is inhibited directly by volatile anesthetics
  (not N20), vasodilators (NTG, SNP, dobutamine,
  many ß2-agonist), increased PVR (MS, MI, PE) and
  hypocapnia
• HPV is indirectly inhibited by PEEP,
  vasoconstrictor drugs (Epi, dopa) by
  preferentially constrict normoxic lung vessels

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Hypoxemia in OLV

• Causes of hypoxemia in OLV
• Mechanical failure of 02 supply or airway
  blockade
• Hypoventilation
• Factors that decrease Sv02 (?CO, ?02 consumption)

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Hypoxemia in OLV

• If severe hypoxemia occurs
• -Am I using FiO2 1?
• Is my tube in correct position?
• Is the tube clear (no secretions)
• Am I using vasodilator?

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Hypoxemia in OLV

• If severe hypoxemia occurs
• After asking those Questions consider
• 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.

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Right Robert Shaw FOB Internal View from
Tracheal Lumen
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Left Robert Shaw FOB Internal View
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Broncho-Cath CPAP System
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Rich Mans CPAP

• Guageguided CPAP system
• Permits measuring actual pressure applied
• Adjust to 5-10 cmsH2O

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(No Transcript)
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POOR MANsCPAP (DLETT)

• 1 BABYSAFEUnit
• 2 Attached to surgical DLETT lumen
• 3 O2 tubing to aux. O2port on anesthesia
  machine
• 4 adjust flow so bag is just full(not
  quantitative)

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CPAP with Arndt

• 1 BABYSAFE system
• 2 special connector (in kit) for Arndt CPAP
  administration through blocker lumen
• 3 adjuster valve
• 4 standard anesthesia circuit

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• X Dont place tight sealed catheter in
  endotracheal tube to try and deliver CPAP!!! It
  can lead to . ?

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• 1 - Mediastinal Air
• 2 -Pneumothorax on side opposite sugery

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Questions

• The increase in alveolar PCO2 decrease alveolar
  PO2
• Pulmonary embolism increase the difference
  between the PaCO2 and ED CO2.
• Shunting cause mainly hypercarbia
• Pulmonary oedema may occur in the nondependent
  lung during single lung ventilation.

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Questions(cont.)

• Application of CPAP to the nondependent lung is
  the least effective way to guard against hypoxia
  during single lung ventilation.
• The use of vasodilator is the appropriate way to
  manage hypertension during single lung
  ventilation.
• Valvular lesions of the heart have no impact on
  PO2 during single lung ventilation.

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Questions(cont.)

• HPV is an all or non reflex.
• Decrease in FiO2 than 1 is important to guard
  against absorption collapse in the ventilated
  lung during single lung ventilation.
• Patients under single lung ventilation should
  receive below average IV fluids.

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Questions(cont.)

• Single lung ventilation cause 50 shunting.
• High dose of inhalational anaesthetic is
  appropriate in controlling hypertension during
  single lung ventilation.

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Questions(cont.)

• Hypotension increase the alveolar dead space.
• Physiological shunting accounts for the normal
  difference between the alveolar and the pulmonary
  end capillary PO2.

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• THANKS