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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3819_Библиотеки_им_академика_М_И_Перельмана
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Classification 57
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Fig. 1 DORV with antero-posterior (A) and «side-by-side» (B) infundibulums according to de la
Cruz et al. 1–anterior limb of the trabecula septomarginalis; 2–posterior limb of the trabecula
septomarginalis; 3–aortic valve; 4–pulmonary valve; LVFW–left ventricle free wall; RVFW–
right ventricle free wall; IVS–interventricular septum; MV–mitral valve; oIVS–outlet part of the
interventricular septum; TS–trabecula septomarginalis; TV–tricuspid valve; OS–outlet septum;
VIF–ventriculo-infundibular fold
DORV with side-by-side infundibulums is formed when the OS fuses with the
pTS, (i.e., DORV with subpulmonary VSD) and both infundibulums have contact
with atrioventricular valves (Fig. 1B).
The anatomical walls of the left (subpulmonary in D-malposition) infundibulum
are:
–OS;
– right ventricle free wall;
– left half of the VIF;
– on the left side, the left infundibulum opens to the left ventricle through
subpulmonary VSD located between the limbs of the TS.
The anatomical walls of the right (subaortic in D-malposition) infundibulum are:
–OS;
58 K. V. Shatalov and K. M. Dzhidzhikhiya
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– right ventricle free wall;
– right half of the VIF.
The practical value of this classification is backed by the fact that the knowledge of the anatomical boundaries of subaortic and subpulmonary infundibulums
in their different relationships allows to correctly recognize the intracardiac structures (mainly of the right ventricle) during the intracardiac revision as well as accurately differentiate anatomical structures responsible for subaortic or subpulmonary
stenosis which must be eliminated during the repair.
3 Anatamico-Hemodynamic Classification
Depending on the clinical, hemodynamic and anatomical features, the following
types of DORV may be distinguished:
•
«VSD» type (with subaortic/subarterial VSD). Features:
– no cyanosis due to direct flow of arterial blood from the left ventricle to the
ascending aorta;
– pulmonary overcirculation and hypertension.
•
«tetralogy» type (with subaortic/subarterial VSD) and pulmonary artery stenosis.
Features:
– cyanosis due to mixed arterio-venous blood in the ascending aorta;
– pulmonary undercirculation.
•
«TGA» type (with subpulmonary VSD). Features:
– severe cyanosis due to predominant flow of arterial blood from the left ventricle
to the pulmonary artery and venous blood from the right ventricle to the
ascending aorta;
– pulmonary overcirculation and hypertension.
•
«non-committed» type with or without pulmonary artery stenosis. Features:
– hemodynamics and clinical presentation depend on the proximity of VSD to
the arterial valves and presence or absence of pulmonary artery stenosis.
References
1. Neufeld HN, Dushane JW, Wood EH, Kirklin JW, Edwards JE. Origin of both great vessels from
the right ventricle I without pulmonary stenosis. Circulation. 1961;23:399–412.
2. Neufeld HN, Dushane JW, Edwards JE. Origin of both great vessels from the right ventricle II
without pulmonary stenosis. Circulation. 1961;23:603–12.
Classification 59
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3. Neufeld HN, Lucas RV, Lester RG, Adams P, Anderson RC, Edwards JE. Origin of both great
vessels from the right ventricle without pulmonary stenosis. Br Heart J. 1962;24:393–408.
4. Lev M, Bharati S, Meng CCL, Libethson RP, Paul MH, Idriss F. A concept of double outlet right
ventricle. J Thorac Cardiovasc Surg. 1972;64:271–81.
5. de la Cruz MV, Cayre R, Martinez OA, Sadowinski S, Serrano A. The infundibular interrela-
tionships and ventriculoarterial connection in double outlet right ventricle. Clinical and surgical
implications. Int J Cardiol 1992;5:153–164
6. Walters HL III, Mavroudis C, Tchervenkov CI, Jacobs JP, Lacour-Gayet F, Jacobs ML. Congen-
ital heart surgery nomenclature and database project: double outlet right ventricle. Ann Thorac
Surg. 2000;69:S249–63.
Arterial Hypoxemia
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A. K. Kade , P. P. Polyakov ,S.A.Zanin , and Z. M. Dzhidzhikhiya
Abstract Arterial hypoxemia is a leading clinical syndrome, especially in DORV
with subpulmonary and non-committed VSD. The syndrome develops as a result
of blood mixing at the ventricular level and significantly affects quality of life. It
this chapter we describe arterial hypoxemia from pathophysiological standpoint
as a non-specific syndrome associated with all cyanotic CHDs, in particular with
DORV. Acute episodes of severe arterial hypoxemia are potentially life-threatening
conditions and require urgent care. In patients with long standing arterial hypoxemia, hypoxia-inducible factor initiates different mechanisms (molecular, cellular,
etc.) of adaptation which play crucial role in supporting relatively stable clinical
condition. Despite its direct influence arterial hypoxemia is also responsible for
secondary erythrocytosis and coagulation abnormalities as well as angiogenesis and
osteoarthropathy which complicate medical and surgical treatment.
Keywords Double-outlet right ventricle
· Cyanotic congenital heart defects ·
Arterial hypoxemia · Coagulation · Hypoxia-inducible factor
Complex and at the same time diverse intracardiac anatomy of the entire spectrum
of DORV determines the existence of a wide range of hemodynamic scenarios of the
disease. Intracardiac hemodynamics, specific for each morphological type of DORV,
triggers pathophysiological mechanisms, by which the adverse effects of the disease
occur and which determine the clinical symptoms. Knowledge of the main pathophysiological processes as well as the mechanisms of their manifestation at different
levels of the organism contributes to a more thorough planning for both therapeutic
and surgical treatment. For example, in cyanotic patients with DORV, hypoxemia
triggers a number of pathological processes in almost all tissues, which must be
taken into account not only during the hospital period, but also in the long-term after
A. K. Kade · P. P. P o l ya k ov (B) · S. A. Zanin
Departement of Pathophisiology, Kuban State Medical University, Krasnodar, Russia
e-mail: palpal.p@yandex.ru
Z. M. Dzhidzhikhiya
Research Institute – Ochapovsky Regional Clinical Hospital
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024
K. V. Shatalov and K. M. Dzhidzhikhiya (eds.), Double-Outlet Right Ventricle,
https://doi.org/10.1007/978-3-031-49707-0_4
№1, Krasnodar, Russia
61
62 A. K. Kade et al.
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surgical correction, which can significantly reduce the incidence of complications
and improve the effectiveness of treatment and patients’ quality of life.
The main pathophysiological syndromes accompanying DORV are:
– arterial hypoxemia;
– myocardial remodeling and heart failure;
– pulmonary hypertension.
Pulmonary hypertension in CHDs is widely discussed in a literature. The pathophysiological mechanisms and influence on the organism of arterial hypoxemia
and remodeling of the heart, which are characteristic of all cyanotic CHDs, will
be described below.
Partial pressure of O
in dry atmospheric air at sea level is 0.21 (FiO2—21%)
2
× 760 mmHg = 156 mmHg (21.2 kPa). In upper airways at 37 °C, taking into
account humidification (and partial pressure of water vapor equal to 47 mmHg), the
partial pressure of O
alveolar level, the partial pressure (P
(PiO2) is 150 mmHg (0.21 × (760–47)) or 20 kPa. At the
2
) decreases, in particular, due to the dilution
AO2
with carbon dioxide. This indicator can be calculated using the simplified alveolar
gas equation: P
in arterial blood (can be measured in the laboratory), RQ is the respiratory
CO
2
= PiO2—(PaCO2/RQ), where PaCO2is the partial pressure of
AO2
coefficient, which approaches 0.8 (characterizes tissue metabolism, namely the ratio
of CO
P
produced to O2consumed). Thus, this formula can be written as follows:
2
= 150 mmHg—(PaCO2/0.8) [1].
AO2
The difference between the oxygen content in the alveoli and pulmonary arteries
(in other words, in venous blood, which is 32 mmHg or 4.3 kPa), the so-called
pressure gradient, ensures the diffusion of oxygen into the blood, an increase in the
oxygen pressure in the pulmonary veins (denoted as P
100 mmHg or 10–13.3 kPa) and arterial blood. In an «ideal» lung, P
, the normal value is 75–
aO2
AO2
and PaO
are equal, but in a real situation, there is a limited diffusion rate and an imperfect
ventilation-perfusion ratio in different parts of the lungs (in other words, change of
the V/Q ratio–an increase in dead space and an increasing shunt fraction) [1].
Using the above-mentioned formula and results of the analysis of arterial blood
gases, it is possible to calculate the value of A-a gradient, that is, the difference
between the oxygen pressure in the alveolar air (P
in arterial blood (P
, measured in the laboratory). A-a gradient is a convenient tool
aO2
, estimated by the equation) and
AO2
for differential diagnosis of the etiology of hypoxemia. The A-a gradient increases
within lung diseases and remains normal within extrapulmonary pathologies with
the exception of right-to-left shunt, which also increases the A-a gradient [2].
The intracellular oxygen pressure is 8–10 mmHg in the cytoplasm and 6–8 mmHg
in the mitochondria [3]. The gradual decrease in oxygen pressure in the alveoli, blood,
cytoplasm and mitochondria is known as «oxygen cascade».
Oxygen delivery (DO
by the following formula: DO
in arterial blood (CaO
volume, while CaO
) to tissues depends on two factors and can be expressed
2
= cardiac output (liter per min.) × oxygen content
2
, ml/dl). Cardiac output depends on the heart rate and stroke
2
depends on the amount of oxygen combined with Hb (98.5%),
2
as well as dissolved in blood plasma (1.5%). Thus, the total oxygen content in arterial
2
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Fig. 1 Oxyhemoglobin
dissociation curve
blood can be expressed as follows: CaO2= Hb(g/l) × 1.34 × SaO2(%) + PaO2×
0.003, where 1.34 is Hüfner’s constant, reflecting the oxygen-binding capacity of
hemoglobin [1, 4].
depends on PaO2, which is graphically expressed as oxygen-hemoglobin
S
aO2
dissociation curve (Fig. 1). The initial nonlinear part of the curve is explained
by the phenomenon of positive cooperation—when one of the four hemoglobin
subunits binds oxygen, the affinity of the others increases. The middle ascending part
reflects the direct linear dependence of S
of hemoglobin. At a level of about 60 mmHg, S
on PaO2, while the plateau-saturation
aO2
approaches the level of plateau
aO2
(> 94%).
The dissociation curve of oxyhemoglobin shifts to the right with a decrease in
the affinity of hemoglobin to oxygen, which can be observed with an increase in the
level of 2,3-diphosphoglycerate (a natural regulator of the affinity of hemoglobin
to oxygen produced during glycolysis in the erythrocyte), hyperthermia, acidosis
(Bohr effect) and high carbon dioxide content. An increase in affinity and a shift
of the curve to the left, on the contrary, is observed with a decrease in the level of
2,3-diphosphoglycerate, hypothermia, alkalosis and low carbon dioxide content [3].
Indicators of S
oximeter) and P
clinical context. So, in a patient on oxygen therapy (e.g., with FiO
value equal to 100 mmHg (saturation is close to 100%) reflects the pres-
P
aO2
ence of a serious pathology. The oxygenation index (P
(measured by CO-oximeter), SpO2(measured by pulse
aO2
are not informative enough without taking into account the
aO2
= 0.5), the
2
/FiO2), which depends
aO2
on numerous factors, in this case is much less than it should be [5]. At the same
time, SpO
> 94% can be observed in a patient who is in a state of hypoxia [6].
2
This may be due to a shift in the dissociation curve of oxyhemoglobin to the left
in alkalosis, low carbon dioxide content, hypophosphatemia (lowers the level of
2,3-diphosphoglycerate), sepsis (lowers the level of 2,3-diphosphoglycerate) etc.
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Incorrect results of pulse oximetry can be explained by the presence of endogenous and exogenous pigments in the blood, the patient’s motor activity (trembling,
convulsions, screaming, crying of a child, etc.), reduced perfusion of peripheral
tissues (circulatory insufficiency, inflating of the cuff for measuring blood pressure), increased venous pulsation (tricuspid regurgitation), carboxyhemoglobinemia,
methemoglobinemia, sulfhemoglobinemia, and possibly a significant amount of fetal
hemoglobin (HbF). Devices that have protection against interference and artifacts,
as well as the use of CO-oximetry that recognizes inactivated forms of hemoglobin,
allow to avoid false results [7, 8].
The capabilities of pulse oximetry in detecting «normal» forms of hemoglobin are
apparently comparable to those of CO-oximetry at S
with more pronounced hypoxemia, pulse oximetry may overestimate (S
greater than 91%. However,
aO2
pO2>SaO2
the amount of oxygenated hemoglobin (false negative result) [8]. This is due to the
fact that the calibration of devices is carried out on healthy volunteers under normal
conditions, as well as with some other causes [7, 9]. This problem, in particular, has
been studied in newborn children with heart defects and patients after surgery with
cardiopulmonary bypass [10–12].
The effect of erythrocytosis on pulse oximetry is not entirely clear. According
to Schmidt et al., erythrocytosis does not distort the measurement result in children
with CHD and saturation less than 80% [10].
A striking clinical sign of an increase in the amount of deoxyhemoglobin and
a decrease in S
is central cyanosis, which is clinically manifested at a deoxy-
aO2
hemoglobin level of 50 g/l. At the same time, a decrease or increase in the total
hemoglobin content affects the occurrence of this symptom. For example, with
anemia and a hemoglobin concentration of 60 g/l, even the presence of 60% deoxyhemoglobin (36 g/l) will not be accompanied by cyanosis, while with erythrocytosis
and a hemoglobin concentration of 180 g/l, already 28% of deoxyhemoglobin will
manifest as cyanosis [13].
The oxygen delivered is consumed by tissues, the intensity of which can be represented as oxygen extraction ratio using the following formula: O
)/CaO2, where CaO2is the oxygen content in arterial blood and CvO2is the
CvO
2
ER = (CaO2—
2
oxygen content in venous blood. Normally, the extraction coefficient is 20–30%
ER = 0.2–0.3). This indicator varies depending on the metabolic needs of tissues
(O
2
(e.g., myocardial O
ER is 0.6). Witha decrease in oxygen delivery(Fig. 2), organs can
2
compensatorily increase its extraction, but this mechanism works up to a certain limit,
after which aerobic metabolism is no longer possible and lactic acidosis develops.
Organs with high metabolic needs cannot significantly increase oxygen uptake from
the blood, since O
ER is normally high enough [4].
2
Oxygen consumption may increase with excitation, convulsions, hyperventilation, fever, sepsis, etc., and decreases with sedation, muscle relaxation, hypothermia,
inactivation of electron transport chain respiratory enzymes, etc. [4].
At each of the above-mentioned levels, from the external environment to the
mitochondria, disturbances are possible that lead to the development of hypoxia.
Hypoxia is a typical pathophysiological process, in which all (generalized form) or
)
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Fig. 2 Decrease in oxygen
consumption can be
compensated by its enhanced
extraction ratio (dotted
lines), e.g., from 30 to 40%,
but up to a certain limit after
which lactate acidosis
develops
some (local form) organs and tissues of the body do not receive or are unable to use
oxygen in an amount sufficient for normal intracellular metabolism.
According to the etiology, hypoxia can be divided into:
– exogenous: hypobaric, normobaric;
– endogenous: respiratory, hemic, circulatory, tissue.
Depending on the type of hypoxia, the indicators of FiO
and DO2may differ (Table 1).
S
aO2
2,PaO2
, A-a gradient,
Hypoxemia is characterized by a decrease in partial oxygen pressure in arterial
blood. As follows from the CaO
calculation equation, the partial oxygen pressure
2
is not identical to the oxygen content in the blood and even more so to the delivery
and consumption of it by tissues. The partial pressure determines the solubility of
oxygen in the blood (according to Dalton’s law of partial pressures) and S
not the amount of hemoglobin. A patient with severe anemia may have normal P
aO2
,but
aO2
and SpO2values.
The main mechanisms of hypoxemia include:
– low-pressure oxygen in the inhaled air;
– hypoventilation not related to lung diseases;
– ventilation, perfusion and diffusion in the lungs;
– venoarterial (right-left) blood shunt.
The last two groups are characterized by an increase in the A-a gradient.
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Tabl e 1 Variants and mechanisms of hypoxia development [2, 14]
Hypoxia and hypoxemia
(Reduction of P
AO2,SPO2
) with normal A-a gradient
Exogenous hypobaric hypoxia − Reduced atmospheric pressure;
− Normal FiO
;
2
− Hypocapnia, respiratory alkalosis
Exogenous normobaric hypoxia − Normal atmospheric pressure;
− Decrease in FiO
(<0.21);
2
− Hypercapnia, respiratory acidosis
Endogenous respiratory hypoxia associated
with extrapulmonary causes
− Pathology of the nervous system,
neuromuscular transmission, respiratory
muscles, pleura, thorax;
− Hypercapnia, respiratory acidosis (type II
respiratory failure)
Hypoxia and hypoxemia
(Reduction of P
AO2,SPO2
Endogenous respiratory hypoxia associated
with pulmonary pathology
) with increased A-a gradient
− Ventilation, perfusion and/or diffusion
disorders;
− Normocapnia/hypocapnia and respiratory
alkalosis in type I respiratory failure,
hypercapnia and acidosis in type II
Endogenous circulatory hypoxia with
venoarterial shunt
− Cyanotic CHD, pulmonary arteriovenous
malformations (e.g., Osler-Weber-Rendu
disease), etc
Hypoxia without hypoxemia
(Normal P
Endogenous circulatory hypoxia without
, normal or falsely normal SPO2)
AO2
− Ischemia, venous hyperemia
venoarterial shunt
Endogenous hemic hypoxia − Anemia
− Inactivation of hemoglobin by carbon
monoxide, methemoglobinemia,
sulfhemoglobinemia
Endogenous tissue hypoxia − Inactivation of electron transport chain
enzymes (cyanides, carbon monoxide,
barbiturates, rotenone), uncouplers of oxidative
phosphorylation (salicylates, dinitrophenol);
− Hyperoxia, which increases free radical
oxidation and mitochondrial dysfunction;
− Normal DO
.value
2
Thus, the terms hypoxia and hypoxemia are not synonymous. For example, conditions in which tissues do not consume oxygen due to mitochondrial dysfunction
(tissue hypoxia) are not accompanied by a decrease in P
Table 1 combines both presented classifications.
aO2
and SaO2.
Arterial Hypoxemia 67
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1 Hemodynamic Bases of Hypoxemia in DORV
In patients with DORV «VSD» type arterial hypoxemia is not typical. Due to
subaortic/subarterial location of VSD and absence of pulmonary artery stenosis,
blood from the left ventricle predominantly goes to the ascending aorta minimally
mixing with venous blood in the right ventricule.
In DORV «tetralogy» type, hypoxemia develops as a result of limited pulmonary
circulation due to multilevel RVOT and pulmonary artery stenosis (Q
leads to an increase in proportion of venous blood (coming from venae cavae)
compared with arterial blood (coming from the pulmonary veins) when two flows
are mixed at the ventricular level. In addition, pulmonary artery stenosis contributes
to a greater mixing of arterial and venous blood in the right ventricle.
In DORV «TGA» type hypoxemia is caused by predominant flow of venous blood
from the right ventricle into the aorta and arterial blood from the left ventricle into
the pulmonary artery.
In DORV with non-committed VSD hypoxemia develops because arterial blood
from the left ventricle does not enter the aorta directly, but only after shunting to the
right ventricle and significantly mixing with venous blood. Additional pulmonary
artery stenosis leads to greater mixing of flows in the right ventricle.
Thus, two general mechanisms of arterial hypoxemia can be distinguished in
DORV: limited pulmonary blood flow and venoarterial shunting (Table 2).
Hypoxemia in patients with DORV (with the exception of «VSD» type) takes
place from the moment of transition from placental to pulmonary respiration starting
from the first breath of the child. The most severe clinical manifestations of hypoxemia that occur immediately after birth are seen in DORV «TGA» type without
pulmonary artery stenosis (Taussig-Bing anomaly). In such cases, balloon atrioseptostomy is urgently performed to stabilize the child’s condition and results in greater
mixing of systemic and pulmonary venous flows at the atrial level, so the more
oxygenated blood enters the right ventricle and aorta (see Chap. 10). In TaussigBing anomaly surgical intervention is indicated in the first weeks of life due to
the risk of pulmonary hypertension. However, in some cases, such patients may
undergo pulmonary artery banding as a first stage of surgical treatment. In DORV
s>Qp
) which
Tabl e 2 Mechanisms and severity of arterial hypoxemia in various types of DORV
DORV type Hypovolemia of
«VSD» − − −
«Tetralogy» +/++/+++ +/++/+++ +/++/+++
«TGA» (without pulmonary artery
stenosis-Taussig-Bing anomaly)
«Non-committed»:
without pulmonary artery stenosis
with pulmonary artery stenosis
pulmonary blood flow
− +++ +++
−
+
Venoarterial
shunting
+/++
++/+++
Cyanosis
+/++
++/+++
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