one lung ventilation

Physiological Aspects of Hypoxemia Physiological Aspects of Hypoxemia During One Lung VentilationDuring One Lung Ventilation

Stanford T. Prescott, MDStanford T. Prescott, MD

Staff AnesthesiologistStaff Anesthesiologist

Brooke Army Medical CenterBrooke Army Medical Center

Ventilation and Perfusion of the Ventilation and Perfusion of the Normal LungsNormal Lungs

Normal Distribution of PerfusionNormal Distribution of Perfusion– Mainly determined by gravityMainly determined by gravity– Other (non-gravity) determinantsOther (non-gravity) determinants

Normal Distribution of PerfusionNormal Distribution of Perfusionin the Lungsin the Lungs

Normal Distribution of Perfusion in Normal Distribution of Perfusion in the Lungsthe Lungs

Recruitment of pulmonary vessels when PRecruitment of pulmonary vessels when Ppapa and and

PPpvpv go from low to moderate go from low to moderate

Distention of pulmonary vessels when PDistention of pulmonary vessels when Ppapa and P and Ppvpv

go from moderate to highgo from moderate to high Transudation into ISF when PTransudation into ISF when Ppapa and P and Ppvpv go from go from

high to very highhigh to very high

Normal Distribution of Ventilation in Normal Distribution of Ventilation in the Lungsthe Lungs

Gravitational determinantsGravitational determinants Other (non-gravitational) determinantsOther (non-gravitational) determinants

Normal Distribution of Ventilation in Normal Distribution of Ventilation in the Lungsthe Lungs

The Ventilation to Perfusion RatioThe Ventilation to Perfusion Ratio

VVAA/Q best expresses the amount of ventilation /Q best expresses the amount of ventilation

relative to perfusion in any given lung regionrelative to perfusion in any given lung region At the base of the lung VAt the base of the lung VAA/Q approaches zero/Q approaches zero

At the apex of the lung VAt the apex of the lung VAA/Q approaches infinity /Q approaches infinity

(dividing by zero)(dividing by zero) PaOPaO22 gradients are much higher than PaCO gradients are much higher than PaCO2 2

gradients due to Vgradients due to VAA/Q mismatching/Q mismatching

Normal Distribution of Perfusion in Normal Distribution of Perfusion in the Lungsthe Lungs

Non-gravitational determinantsNon-gravitational determinants– Cardiac outputCardiac output– Alveolar hypoxiaAlveolar hypoxia– Lung volumesLung volumes– Alternate pathways of blood flowAlternate pathways of blood flow– Pulmonary compliancePulmonary compliance– Airway resistanceAirway resistance– Work of breathingWork of breathing

Non-Gravitational Determinants of Non-Gravitational Determinants of Distribution of PerfusionDistribution of Perfusion

Cardiac OutputCardiac Output– An increase in cardiac output causes an increase in An increase in cardiac output causes an increase in

pulmonary vascular pressurespulmonary vascular pressures– Distensible pulmonary vasculature causes a decrease Distensible pulmonary vasculature causes a decrease

in pulmonary vascular resistancein pulmonary vascular resistance– Opposite effect occurs with decreases in pulmonary Opposite effect occurs with decreases in pulmonary

vascular pressuresvascular pressures

Non-gravitational Determinants of Non-gravitational Determinants of Distribution of PerfusionDistribution of Perfusion

Alveolar hypoxiaAlveolar hypoxia– Alveolar hypoxia causes localized pulmonary Alveolar hypoxia causes localized pulmonary

vasoconstriction known as hypoxic pulmonary vasoconstriction known as hypoxic pulmonary vasoconstrictionvasoconstriction

» Due to release of vasoconstrictor substances?Due to release of vasoconstrictor substances?

» Direct effect of hypoxia on the pulmonary vasculature Direct effect of hypoxia on the pulmonary vasculature causes vasoconstriction?causes vasoconstriction?

– It is now thought that both of these theories are related It is now thought that both of these theories are related to nitric oxide mediated vasoconstrictionto nitric oxide mediated vasoconstriction

Non-gravitational Determinants of Non-gravitational Determinants of Distribution of PerfusionDistribution of Perfusion

Alveolar hypoxia (continued)Alveolar hypoxia (continued)– Three mechanisms of HPV in humansThree mechanisms of HPV in humans

» High altitude (decreased PoHigh altitude (decreased Po22) or decreased Fio) or decreased Fio22

» Hypoventilation or atelectasis (as in one lung ventilation)Hypoventilation or atelectasis (as in one lung ventilation)

» COPD, asthma, pneumoniaCOPD, asthma, pneumonia

Oxygen Transport and Causes of Oxygen Transport and Causes of HypoxemiaHypoxemia

Oxygen Dissociation CurveOxygen Dissociation Curve– Shifts of curve have little effect when PShifts of curve have little effect when PO2O2 is in normal is in normal

rangerange– Shifts of curve have a greater effect on saturation when Shifts of curve have a greater effect on saturation when

PPO2O2 is on steep portion of curve is on steep portion of curve

– When PWhen P5050 is less than 27mm = Left shift is less than 27mm = Left shift

– When PWhen P5050 is more than 27mm = Right shift is more than 27mm = Right shift» Decreases cause left shiftDecreases cause left shift

» Increases cause right shiftIncreases cause right shift

Oxygen Transport and Causes of HypoxemiaOxygen Transport and Causes of Hypoxemia


Shunt fraction (QShunt fraction (Qss/Q/QTT))

– Shunt refers to right to left diversion of pulmonary blood Shunt refers to right to left diversion of pulmonary blood flowflow

– Blood does not get oxygenatedBlood does not get oxygenated» Perfusion of underventilated alveoliPerfusion of underventilated alveoli» Bronchial blood flowBronchial blood flow» Intra-arterial and intra-cardiac shuntsIntra-arterial and intra-cardiac shunts

– Increasing FiOIncreasing FiO22 when Q when Qss/Q/QT T is greater than 50% is not is greater than 50% is not

helpfulhelpful


Calculation of Shunt FractionCalculation of Shunt Fraction– Fick EquationFick Equation

» QQss/Q/Qtt=[Cco=[Cco2 2 - Cao- Cao22] / [Cco] / [Cco2 2 - Cvo- Cvo22]]

» CaoCao2 2 = (1.39)(Hb)(%sat) + (0.003)(Pao= (1.39)(Hb)(%sat) + (0.003)(Pao22))

– Estimation using P(A-a)Estimation using P(A-a)O2O2

» P(A-a)P(A-a)O2O2 / 20 / 20

» If cardiac output is normal and PaoIf cardiac output is normal and Pao22 is > 175 is > 175

Causes of Hypoxemia During Causes of Hypoxemia During AnesthesiaAnesthesia

Equipment malfunctionEquipment malfunction HypoventilationHypoventilation HyperventilationHyperventilation Decreased FRCDecreased FRC Decreased cardiac outputDecreased cardiac output Inhibition of HPVInhibition of HPV Increased right to left shuntIncreased right to left shunt

Physiology of One Lung VentilationPhysiology of One Lung Ventilation

Effects of anesthetics on HPVEffects of anesthetics on HPV– Inhaled anesthetics inhibit HPV experimentallyInhaled anesthetics inhibit HPV experimentally– Nitrous Oxide has only a small effect on HPVNitrous Oxide has only a small effect on HPV– Injectable anesthetics have no effectInjectable anesthetics have no effect– Variability of effects experimentally likely related to Variability of effects experimentally likely related to

the mechanism of HPV which is unknownthe mechanism of HPV which is unknown» Mechanism of HPV probably due to reaction of individual Mechanism of HPV probably due to reaction of individual

arterial smooth muscle cells to local Oarterial smooth muscle cells to local O2 2 conditionsconditions

Physiology of One Lung Ventilation and the Physiology of One Lung Ventilation and the Lateral Decubitus PositionLateral Decubitus Position

Blood flow distribution in both lungs in the lateral Blood flow distribution in both lungs in the lateral decubitus position (LDP)decubitus position (LDP)– Gravity causes a vertical gradient as in the upright Gravity causes a vertical gradient as in the upright

positionposition– Blood flow is greater to the dependent lungBlood flow is greater to the dependent lung

Physiology of One Lung Ventilation in the Physiology of One Lung Ventilation in the Lateral Decubitus PositionLateral Decubitus Position

Physiology of One Lung Ventilation and the Physiology of One Lung Ventilation and the Lateral Decubitus PositionLateral Decubitus Position

During one lung ventilation blood flow to the non-During one lung ventilation blood flow to the non-dependent lung is decreased by 50 percent due to HPVdependent lung is decreased by 50 percent due to HPV

Blood flow to the dependent lung is increased by 33 Blood flow to the dependent lung is increased by 33 percent (from 60% to 80%)percent (from 60% to 80%)

Ratio of non-dependent to dependent lung blood flow is Ratio of non-dependent to dependent lung blood flow is 20% : 80%20% : 80%

Shunt flow is therefore 20% and PaOShunt flow is therefore 20% and PaO22 is 280mm Hg is 280mm Hg

(100% O(100% O22))

Physiology of One Lung Ventilation and Physiology of One Lung Ventilation and the Lateral Decubitus Positionthe Lateral Decubitus Position


Effects of anesthetics on HPVEffects of anesthetics on HPV– Inhibition of HPV by 1 MAC isoflurane is about 21%Inhibition of HPV by 1 MAC isoflurane is about 21%

– Inhibition of HPV causes an increase in blood flow to the non-Inhibition of HPV causes an increase in blood flow to the non-dependent lung of about 4% of total blood flowdependent lung of about 4% of total blood flow

– This 4% increase in shunt causes PaOThis 4% increase in shunt causes PaO22 to drop from 280 to 205 to drop from 280 to 205

– This 4% increase in shunt flow is not usually clinically This 4% increase in shunt flow is not usually clinically detectabledetectable

– Inhaled anesthetics actually have little clinical effect on HPVInhaled anesthetics actually have little clinical effect on HPV


Other inhibitors of HPVOther inhibitors of HPV– Factors that increase PAP antagonize the effect of Factors that increase PAP antagonize the effect of

increased resistance caused by HPVincreased resistance caused by HPV» Indirect inhibitors: MS, volume overload, thromboembolism, Indirect inhibitors: MS, volume overload, thromboembolism,

hypothermia, vasoconstrictors, and large hypoxic lung hypothermia, vasoconstrictors, and large hypoxic lung segmentsegment

» Direct inhibitors: Infection, vasodilators, hypocarbia, and Direct inhibitors: Infection, vasodilators, hypocarbia, and metabolic alkalemiametabolic alkalemia

» These actually have more of an effect on HPV than anesthetic These actually have more of an effect on HPV than anesthetic agentsagents


Potentiators of HPVPotentiators of HPV– Almitrine, a respiratory stimulant drugAlmitrine, a respiratory stimulant drug

» Improves PaoImproves Pao22 in patients with COPD in patients with COPD

» Actually non-specifically increases pulmonary vascular Actually non-specifically increases pulmonary vascular pressurespressures

– Prostaglandin inhibitorsProstaglandin inhibitors» Prostaglandins may inhibit HPVProstaglandins may inhibit HPV

» Found to reverse HPV inhibition in dogsFound to reverse HPV inhibition in dogs

» Value in humans undeterminedValue in humans undetermined


Potentiators of HPVPotentiators of HPV– Nitric OxideNitric Oxide

» Conflicting studies have shown either no improvement of Conflicting studies have shown either no improvement of oxygenation or has shown improvement of oxygenation with oxygenation or has shown improvement of oxygenation with nitric oxide in OLVnitric oxide in OLV

» A potent vasodilatorA potent vasodilator

» One theory suggests use of almitrine (non-specific One theory suggests use of almitrine (non-specific vasoconstrictor in pulmonary vasculature) and nitric oxide to vasoconstrictor in pulmonary vasculature) and nitric oxide to dependent lungdependent lung

» As yet unproven to be of benefitAs yet unproven to be of benefit


Distribution of perfusionDistribution of perfusion– Two lung ventilationTwo lung ventilation– One lung ventilationOne lung ventilation

Distribution of ventilationDistribution of ventilation– Two lung ventilationTwo lung ventilation– One Lung ventilationOne Lung ventilation

Physiology of the Lateral Decubitus Physiology of the Lateral Decubitus PositionPosition

Physiology of One Lung Ventilation and Physiology of One Lung Ventilation and Causes of HypoxemiaCauses of Hypoxemia

The non-dependent lung is not ventilated which The non-dependent lung is not ventilated which causes mismatch of ventilation and perfusion causes mismatch of ventilation and perfusion (V(VAA/Q)/Q)

Blood flow to the non-dependent lung is shunt flowBlood flow to the non-dependent lung is shunt flow Causes an obligatory right to left shuntCauses an obligatory right to left shunt P(A-a)OP(A-a)O22 gradient is larger and PaO gradient is larger and PaO22 is lower than is lower than

in two lung ventilationin two lung ventilation


Factors that decrease blood flow distribution to Factors that decrease blood flow distribution to the non-dependent lungthe non-dependent lung– Surgical compressionSurgical compression– RetractionRetraction– Ligation of pulmonary vesselsLigation of pulmonary vessels– Amount of disease in the non-dependent lungAmount of disease in the non-dependent lung– Hypoxic pulmonary vasoconstrictionHypoxic pulmonary vasoconstriction


Factors that increase blood flow distribution to the Factors that increase blood flow distribution to the dependent lungdependent lung– Gravitational effects (zones of perfusion)Gravitational effects (zones of perfusion)– Hypoxic pulmonary vasoconstriction in the non-Hypoxic pulmonary vasoconstriction in the non-

dependent lungdependent lung

One Lung Ventilation and Causes of One Lung Ventilation and Causes of HypoxemiaHypoxemia

Factors that decrease ventilation to the dependent Factors that decrease ventilation to the dependent lunglung– Reduced lung volumesReduced lung volumes– Absorption atelectasisAbsorption atelectasis– Difficulty of secretion removalDifficulty of secretion removal– LDP for long period can increase transudationLDP for long period can increase transudation– Increases in HPVIncreases in HPV

Treatment of Hypoxemia During One Lung Treatment of Hypoxemia During One Lung VentilationVentilation

Conventional managementConventional management– Increase FiOIncrease FiO22 to dependent lung to dependent lung

» Helps to increase the PaOHelps to increase the PaO22

» Causes vasodilation which increases blood flow to dependent lungCauses vasodilation which increases blood flow to dependent lung

– Tidal volume of 10ml/kg and RR to keep COTidal volume of 10ml/kg and RR to keep CO22 at at

40mm Hg40mm Hg» Lower tidal volume can cause atelectasisLower tidal volume can cause atelectasis

» Greater tidal volume may increase airway pressuresGreater tidal volume may increase airway pressures

– Selective dependent lung PEEPSelective dependent lung PEEP

Treatment of Hypoxemia During One Lung Treatment of Hypoxemia During One Lung VentilationVentilation

Differential management of one lung ventilationDifferential management of one lung ventilation

– Intermittent inflation of the non-dependent lungIntermittent inflation of the non-dependent lung

– Selective dependent lung PEEPSelective dependent lung PEEP

– Selective non-dependent lung CPAPSelective non-dependent lung CPAP

one lung ventilation

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