Intraoperative Intraoperative Hypoxia During Hypoxia During Thoracic Surgery Thoracic Surgery Tarek Ashoor Tarek Ashoor
Mar 26, 2015
Intraoperative Intraoperative Hypoxia During Hypoxia During
Thoracic SurgeryThoracic Surgery
Intraoperative Intraoperative Hypoxia During Hypoxia During
Thoracic SurgeryThoracic Surgery
Tarek AshoorTarek Ashoor
ObjectivesObjectives• 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.
Introduction Introduction •Shunting is :• Shunting is simply the passage of
venous blood (Venous admixture) to the left side of the heart .
So What?
Introduction (cont.)Introduction (cont.)
The venous admixture causes dilution of the PaO2 in the arterial blood ending in
Introduction (cont.)Introduction (cont.) The venous admixture causes
dilution of the PaO2 in the arterial blood ending in
HypoxiaHypoxia
Introduction (cont.)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
Introduction (cont.)Introduction (cont.)• Transpulmonary shunt occur due
to continued perfusion of the atelectatic lung (or part of it).atelectatic lung (or part of it).
•Perfused Non-ventilated part of the lung
Introduction (cont.)Introduction (cont.) Dead space: Space in the respiratory
tract that doesn’t share in gas exchange.
This accounts for the normal difference between PaCO2 and ETCO2 (5 mmHg).
Introduction (cont.)Introduction (cont.)Alveolar dead space: Parts in the lungs that are
ventilated but not perfused.Ex: Pulmonary embolism
V-Q relationships in the anesthetized, open-chest and paralyzed patients in LDP
V-Q relationships in the anesthetized, open-chest and paralyzed patients in LDP (cont.)
Physiology of the LDPPhysiology of the LDP
• Upright LDP, lateral decubitus Upright LDP, lateral decubitus
Physiology of OLVPhysiology 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.
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
Two-lung Ventilation and OLV
Factors Affecting Regional HPVFactors Affecting Regional HPV
Factors Affecting Factors Affecting Regional HPVRegional 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
Hypoxemia in OLV Causes of hypoxemia in OLV:Causes of hypoxemia in OLV:
– Mechanical failure of 02 supply or airway blockade
– Hypoventilation– Factors that decrease Sv02 (CO,
02 consumption)
Hypoxemia in OLV
• If severe hypoxemia occurs: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?
Hypoxemia in OLV
• If severe hypoxemia occurs: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.
Right Robert Shaw – FOB Internal View from Tracheal
Lumen
Left Robert Shaw –FOB Internal View
Broncho-Cath CPAP Broncho-Cath CPAP SystemSystem
Rich Man’sRich Man’s* * CPAPCPAP
*Guageguided CPAP system
*Permits measuring actual pressure applied
Adjust to 5-10 cmsH2O
POOR MAN’sCPAP (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)
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
•X = Don’t place tight sealed catheter in
endotracheal tube to try and deliver
CPAP!!! It can lead to……………… .→
•1 - Mediastinal Air
•2- Pneumothorax on side opposite
sugery
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.
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.
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.
Questions(cont.)• Single lung ventilation cause 50%
shunting.• High dose of inhalational
anaesthetic is appropriate in controlling hypertension during single lung ventilation.
Questions(cont.)• Hypotension increase the alveolar
dead space.• Physiological shunting accounts
for the normal difference between the alveolar and the pulmonary end capillary PO2.
•THANKS