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Intraoperative Hypoxia During Thoracic Surgery

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... the respiratory tract that doesn t share in gas exchange. This accounts for the normal difference between PaCO2 and ETCO2 (5 mmHg). Introduction ... – PowerPoint PPT presentation

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Title: Intraoperative Hypoxia During Thoracic Surgery


1
Intraoperative Hypoxia During Thoracic Surgery
  • Tarek Ashoor

2
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.

3
Introduction
  • Shunting is
  • Shunting is simply the passage of venous blood
    (Venous admixture) to the left side of the heart
    .
  • So What?

4
Introduction (cont.)
  • The venous admixture causes dilution of the PaO2
    in the arterial blood ending in

5
Introduction (cont.)
  • The venous admixture causes dilution of the PaO2
    in the arterial blood ending in
  • Hypoxia

6
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

7
Introduction (cont.)
  • Transpulmonary shunt occur due to continued
    perfusion of the atelectatic lung (or part of
    it).
  • Perfused Non-ventilated part of the lung

8
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).

9
Introduction (cont.)
  • Alveolar dead space
  • Parts in the lungs that are ventilated
    but not perfused.
  • Ex Pulmonary embolism

10
V-Q relationships in the anesthetized,
open-chest and paralyzed patients in LDP
11
V-Q relationships in the anesthetized,
open-chest and paralyzed patients in LDP (cont.)
12
Physiology of the LDP
  • Upright LDP, lateral
    decubitus

13
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.

14
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

15
Two-lung Ventilation and OLV
16
Factors Affecting Regional HPV
17
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

18
Hypoxemia in OLV
  • Causes of hypoxemia in OLV
  • Mechanical failure of 02 supply or airway
    blockade
  • Hypoventilation
  • Factors that decrease Sv02 (?CO, ?02 consumption)

19
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?

20
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.

21
Right Robert Shaw FOB Internal View from
Tracheal Lumen
22
Left Robert Shaw FOB Internal View
23
Broncho-Cath CPAP System
24
Rich Mans CPAP
  • Guageguided CPAP system
  • Permits measuring actual pressure applied
  • Adjust to 5-10 cmsH2O

25
(No Transcript)
26
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)

27
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

28
  • X Dont place tight sealed catheter in
    endotracheal tube to try and deliver CPAP!!! It
    can lead to . ?

29
  • 1 - Mediastinal Air
  • 2 -Pneumothorax on side opposite sugery

30
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.

31
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.

32
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.

33
Questions(cont.)
  • Single lung ventilation cause 50 shunting.
  • High dose of inhalational anaesthetic is
    appropriate in controlling hypertension during
    single lung ventilation.

34
Questions(cont.)
  • Hypotension increase the alveolar dead space.
  • Physiological shunting accounts for the normal
    difference between the alveolar and the pulmonary
    end capillary PO2.

35
  • THANKS
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