TAPVC defines the anomaly in which the pulmonary veins have no connection with the left atrium. Rather, the pulmonary veins connect directly to one of the systemic veins (TAPVC) or drain in to right atrium.
A PFO or ASD is present essentially in those who survive after birth
When pulmonary veins drain anomalously into the right atrium either because of complete absence of the interatrial septum or malattachment of the septum primum , then it is known as total anomalous pulmonary venous drainage.
When some or all of the pulmonary veins drain anomalously in to RA or its tributaries without being abnormally connected, the terms partially anomalous pulmonary venous drainage (PAPVD) or totally anomalous pulmonary venous drainage (TAPVD) with normal pulmonary venous connections are used.
2. DEFINITION
TAPVC defines the anomaly in which the pulmonary
veins have no connection with the left atrium. Rather,
the pulmonary veins connect directly to one of the
systemic veins (TAPVC) or drain in to right atrium.
A PFO or ASD is present essentially in those who
survive after birth
3. HISTORY
Wilson : 1st
description - case report in
1798.
Friedlowsky : 1st
description of TAPVC in
1868.
Muller : 1st
Successful open repair in
1951.
4. INCIDENCE
0.6 to 1.2 per 10,000 live births
0.7 and 1.5 percent of all CHD
5. A strong male preponderance of 3:1
Birth weight was less than 2500 g in 16.2%
Gestational age was less than 38 weeks in 18.9%
Intrauterine growth retardation occurred in 26.8%
68% of these patients were diagnosed as neonates
6. GENETICS
Mechanism of transmission – Not been elucidated
No known genetic pattern of transmission.
Associated with syndromes most notably Asplenia ,
Polysplenia .
10. TAPVC results from failure to establish a normal
connection between the pulmonary venous plexus
& the CPV before the connections with splanchnic
venous system have regressed .
12. CLASSIFICATION OF TAPVC
Smiths classification
Neills classification - Based on embryologic
basis
Burroughs and Edwards classification
Darlings classification
13. Smith classification
Supradiaphragmatic Type: Pulmonary veins are
connected to: the left innominate vein by the
characteristic vertical vein, or the coronary sinus,
the right atrium, or the SVC, without pulmonary
venous obstruction
Infradiaphragmatic Type: Pulmonary veins drain
into the portal vein or hepatic veins, with
pulmonary venous obstruction.
Smith et.al. Am J Dis Child 1961;101:41-51
14. Neills classification
Group having connection to the right atrium or
right common cardinal system (SVC and the
azygous veins)
Connections to the left common cardinal
system(left innominate vein, left SVC or the
coronary sinus)
Connections to the umbilicovitelline system
(portal vein, ductus venosus or hepatic veins)
Neill CA: Pediatrics 18:880,1956
15. Burroughs and Edwards classification
Suggested a classification with prognostic
implications based on the length of of the
anomalous channel (long, intermediate, or short)
However the prognostic implications suggested
are not always true.
Burroughs and Edwards.Am Heart J 1960;59:913-931
16. Darlings classification
The most common classification system was originally
described by Darling et al. in 1957. consists of four
types
Type I (Supracardiac TAPVC ): 45% of cases.
Both right and left pulmonary veins join a common
pulmonary venous confluence behind the heart that
drains via a vertical vein to the undersurface of the left
innominate vein and thence to the Right atrium.
Type II ( Cardiac TAPVC) : 25% of cases.
The pulmonary venous confluence connects to the
coronary sinus, & thence to the RA via the coronary
sinus ostium.
17. Type III (Infracardiac TAPVC) : 21% of cases.
The pulmonary venous confluence drains
inferiorly via a vertical vein to the portal vein
or hepatic veins & thence to the RA.
Type IV (Mixed Type ) : <10% of cases.
Left pulmonary veins drain to the LIV , &
right pulmonary veins to the coronary sinus
Darling RC et.al. Lab Invest.1957;6:44-64
18.
19.
20. THE FREQUENCIES OF THE
VARIOUS SITES OF TAPVC OR
DRAINAGE
More than one-third of the cases had the
anomalous connection to the left innominate
vein (LIV).
23. Similarly, the anomalous pulmonary vein in TAPVC
to the SVC may be obstructed by the right
pulmonary artery & trachea..
Finally, when the anomalous connection is to the
portal vein or one of its tributaries, the hepatic
sinusoids are interposed in the pulmonary venous
channel and result in increased resistance to
pulmonary venous return.
24. ASSOCIATED CARDIAC ANOMALI
ES
TAPVC occurs as an isolated anomaly in two third
cases.
It has been reported, however, to be associated wit
h TGA , TOF, PDA, single ventricle , truncus
arteriosus , tricuspid atresia , hypoplastic left heart
syndrome ,pulmonary atresia, multiple small
VSDs , COA , vascular sling, and other anomalies .
Asplenia & polysplenia syndromes.
25. SK Choudhary, A Bhan, R Sharma, B Airan, V Devagourou, A Saxena,
SS Kothari, Total-Anomalous-Pulmonary-Venous-Connection: Surgical Experience in Indians
Cardiothoracic Centre, All India Institute of Medical Sciences, New Delhi .
Indian Heart J 2001; 53: 754–760)
27. During fetal life, PBF is small & the combined
systemic and pulmonary venous return to the RA is
only minimally increased.
Hence, the stimulus for the development of a large
interatrial communication is minimal.
Some degree of restriction to fow across a patent
foramen ovale (found in 70% to 80% of cases) is
common.
In patients with a restrictive interatrial
communication , the amount of blood reaching the
LA is limited and systemic output is reduced.
28. As pulmonary vascular resistance gradually
decreases after birth and as demands for SBF
increase with the rapid growth of the infant, massive
pulmonary overcirculation ensues.
Pulmonary and systemic venous blood return is to
the RA , therefore, increased right atrial pressure
results in pressure elevation and congestion in both
venous circuits.
On the other hand, the presence of a widely patent
foramen ovale or ASD allows free communication
between the two atria.
29. In this circumstance, the distribution of mixed
venous blood depends on the relative compliance of
the atria and ventricles and the relative resistance
imposed by the pulmonary & systemic arterial
circuits.
The major variable is the state of the pulmonary
vascular bed , which initially depends on the
presence or absence of pulmonary venous
obstruction.
30. TAPVC without Pulmonary Venous Obstruction
At birth, the distribution of blood between the
pulmonary & systemic circuits is approximately
equal because the resistance in these two vascular
beds is nearly equal.
In the first few weeks of life , maturation of the
pulmonary vascular bed produces a decrease in
pulmonay vascular resistance , & a progressively
larger proportion of the mixed venous blood
traverses the pulmonary circuit.
PBF is three to five times SBF. SBF is usually
normal.
31. Progressive dilation and hypertrophy of RV and
dilation of the pulmonary artery usually occur.
Pulmonary artery pressure in infants ranges from
slightly elevated to systemic.
The state of the interatrial communication in
patients with TAPVC without pulmonary venous
obstruction has a major impact on PBF , pressure
and resistance.
In the few patients who survive to older childhood
or early adulthood , PA pressure is only slightly
elevated.
36. CLINICAL FEATURES
TAPVC without Pulmonary Venous Obstruction
Asymptomatic at birth.
Tachypnea and feeding difficulties - within
first few weeks of life.
Have recurrent resp.tract infections and
failure to thrive.
Mild cyanosis
Gradually they develop right heart failure
and pulmonary arterial hypertension
37. A prominent right ventricular heave .
A characteristic feature - multiple cardiac
sounds.
S1is Loud and often is often followed by a
systolic ejection click.
S2 widely split & does not vary with respiration,
The pulmonary component of the second sound
is accentuated.
S3 maximal at apex almost always ,is present.
S4 is frequently heard in older patients.
Characteristically, a grade 2/6 soft , blowing ,
systolic ejection murmur is heard in pulmonary
area .
39. TAPVC with Pulmonary Venous Obstruction
Tachypnea, tachycardia and cyanosis within few
hours of birth.
Dyspnea - pulmonary venous congestion and
cyanosis - reduced pulmonary flow.
If left untreated death may occur from pulmonary
edema and RV failure within few days or weeks of
life.
40. Once symptoms began- rapid progression to
dyspnea , feeding difficulties and cardiorespiratory
failure.
Age at death ranged from 2 days to 4.5 months .
When the anomalous connection is below the
diaphragm , cyanosis & dyspnea may be
accentuated by straining & swallowing as a
consequence of interference of pulmonary venous
outflow by increased intra-abdominal pressure or
impingement of the esophagus on the CPV as it
exits through the esophageal hiatus.
41. The clinical course in patients with severely
obstructed infradiaphragmatic TAPVC might be
stormy with rapid development of severe respiratory
distress and acidosis in the first hours of life.
Despite the alarming symptoms, the cardiovascular
findings may be minimal.
No significant right ventricular heave.
S1 loud, S2 split, P2 loud
A cardiac murmur often is absent, but, when
present, it is usually a soft blowing systoloic
ejection murmur in the pulmonary area.
Moist rales - lung bases.
Hepatomegaly and peripheral edema.
44. CRITERIA OF RVH IN NEWBORNS
Pure R wave 10 mm (with no S waves )in V1.˃
R wave in V1 25 mm or R wave in aVR 8 mm.˃ ˃
S wave in lead I 12 mm or greater.
A qR pattern in V1.(also seen in10% of normal
newborns).
Extreme RAD.
Upright T waves in V1 after 1 week of age.
Normally T wave upright until 4 to 7 days of
age. Between 1 week to adolescence it is negative
and then reverts to upright.
49. To image the course of the pulmonary venous
channel (usually the vertical vein ), its connection
with systemic vein & its relation to neighboring
structures (i.e., pulmonary arteries and airways);
To determine whether there is obstruction to
pulmonary venous flow ;
To evaluate the interatrial communication for
obstruction; and
To perform a complete anatomic and functional
survey of all cardiovascular structures & to exclude
additional structural cardiac anomalies.
These goals are achieved by performing
a complete step by step
echocardiographic examination from multiple
windows.
50. The features common to all forms of TAPVC are
Signs of Rright ventricular volume overload.
The right-sided heart structures are dilated.
The RA is enlarged, and the atrial septum
bows toward the left.
The right ventricle appears to compress
the left ventricle, the interventricular septum
deviates leftward,and left ventricular volume is
decreased.
The IVS septum may move paradoxically.
The pulmonary arteries are dilated.
52. Once the pulmonary venous confluence is characte
rized, the venous channel that connects with the
systemic vein is followed by 2-D imaging
and color Doppler flow mapping.
The venous channel in
Supracardiac TAPVC - precordial windows
Infradaiphragmatic TAPVC - subcostal view.
In supracardiac TAPVC, the venous channel
should be examined for its relation with the branch
pulmonary arteries and the bronchi.
53.
54. In TAPVC to coronary sinus, the sinus is
dilated and bulges anterosuperiorly into the
LA.
Imaging of the pulmonary veins draining into
the coronary sinus is important for diagnosis
because CS may be dilated in other conditions
also like persistent LSVC to CS.
Descending anomalous vein is characterized
by the venous flow pattern and direction of
flow is away from the heart towards abdomen.
55.
56. An increased flow velocity, turbulent flow pattern
and loss of phasic variations characterize
obstructed pulmonary venous flow. (normal venous
flow is low velocity, phasic laminar pattern with
brief flow reversal during atrial systole)
63.
Interpretation of atrial pressures – adequacy of
the interatrial communication, is difficult.
The presence of equal pressures in the two atria -
nonobstructive intera-trial communication.
A RA pressure >2 mm Hg in excess of LA pressure -
restrictive interatrial communication.
64. TAPVC with Pulmonary Venous Obstruction
Difficult in patients with obstructed TAPVC
Must be avoided – May aggravate already
compromised clinical condition of these patients
and delay operation.
Right ventricular pressures usually are systemic or
higher.
Pressures in the RA usually are normal.
LA pressure is normal.
68. NATURAL HISTORY
Among patients of TAPVC of all types, 50% die at 3
months and almost 80% die by the age of 1 year
Asymptomatic at birth
56% symptomatic at 1st
month of life
Failure at 6 months of age
Severe obstruction pulmonary edema 1st
few hrs
Cyanosis mild, more with failure & pulm vascular
changes
69. Death – 1st
few wks/months of life in most neonates
80% death – 1st
year of life
Survivors of 1st
few wks of life – ↑pulm bld flow mild
cyanosis, PHTN
50% survive beyond 3 months
Median survival 3wks (obst) & 2.5 months in (non
obstr)
Infracardiac- worse prognosis- 3wks survival
70. MANAGEMENT
Corrective surgery - definitive treatment.
Infants presenting with obstructed TAPVC
represent surgical emergency. They need require
intensive resuscitation before going for definitive
surgery.
Nonobstructed TAPVC patient are relatively stable
and can be taken for elective corrective surgery
within few days of diagnosis irrespective of patients
age and weight.
72. ADDITIONAL INTERVENTIONS INCLUDE
Extracorporeal membrane oxygenation (ECMO) may
be used in infants with severe pulmonary
hypertension or refractory cardiac failure.
Balloon or blade atrial septostomy may be used as a
palliative procedure.
It is not appropriate because it delays the definitive
procedure and is of no value in obstructed venous
channel.
73. SURGERY
The goal of the surgery is
To create a communication between LA and
the pulmonary venous.
Closure of the anomalous pulmonary
venous connections to systemic circulation
Closure of ASD
74. The surgical approach is via a median sternotomy
and is performed under cardiopulmonary bypass
with circulatory arrest. The surgical procedure
varies depending upon the anatomy of the TAPVC
lesion.
In supra- and infracardiac TAPVC with a common
vertical vein, a normal pulmonary venous
pathway is created by opening and forming an
anastomosis between the pulmonary venous
confluence and the left atrium. The vertical vein is
then ligated and divided.
77. CARDIAC TAPVC:
In intracardiac TAPVC to the coronary sinus, the
sinus and the partition between the sinus and right
atrium are incised, and connected to the left
atrium.
78. MIXED TYPE TAPVC
The repair of mixed type TAPVC involves a
combination of the above approaches as
dictated by the specific anatomy of the
lesion
80. SURGICAL OUTCOMES
Surgical mortality has decreased from approx. 50%
in 1960 to 5% recently.˂
Risk factors for mortality included earlier age at
surgery, hypoplastic/stenotic pulmonary veins,
associated cardiac lesions, postoperative pulmonary
hypertension, postoperative PVO , Small pulmonary
vein and confluence size & Increased total bypass
and circulatory arrest time .
81. SURGICAL OUTCOMES RISK FACTORS
377 patients of operated TAPVC were followed
retrospectively.pulmonary venous obstruction was in 48% of
patients.
82.
83. SURGICAL OUTCOMES IN NEONATES
112 patient were followed retrospectively who were
operated for simple TAPVC in first month of life
from 1973 to 2008.
Preoperative pulmonary venous obstruction in 89
pts (80%).
84. There were 12 (10.7%) early deaths. Significant risk
factors were bypass time 65 minutes and emergent˃
surgery.
Survival at 20 years was 83.4%.Risk factors for late
death were operative weight 2.5 kg or less and
postoperative pulmonary hypertensive crisis.
Re-operation for recurrent PVO was in 13 patients
(11.9%).
85. SURGICAL OUTCOMES IN INDIA
73 pts, were operated on for TAPVC from Jan 1987 to Oct
1997.
35 patients had obstructed drainage.
Operative mortality was 23.3% (17 out of 73).
88. Pulmonary edema- noncompliant left heart and
increased left atrial pressure leads to pulmonary
arteriolar vasoconstriction. Diuretics are useful for
treatment.
Pulmonary hypertensive crisis-hyperventilation with
100% oxygen and inhaled nitric oxide is the treatment of
choice. Infusion of prostacyclin may also be useful.
Rhythm disorders- junctional rhythms and various
types of heart blocks are common in cardiac type TAPVC
repair.
89. Pulmonary venous obstruction
This is most significant cause of late morbidity and
mortality after corrective surgery.
It develops in 5-15% of patients within first
postoperative year where TAPVC is corrected using
standard technique.
Anastomotic fibrotic strictures, intimal proliferation
and diffuse fibrosis are pathogenic mechanisms.
90. REOPERATION
Based upon a number of case series, the rate
for reoperation is between 10 and 15 percent
in patients with isolated TAPVC (11 percent) .
Stenosis of individual pulmonary vein and
surgical anastomosis are the primary reasons
for reoperation.
If restenosis does not occur within one year
after surgical repair, then reoperation is rarely
required.
91. MORBIDITY
Although long-term follow-up data are limited, one
case series reported a poorer perception of health
and school performance in survivors of TAPVC
correction.
In addition, several case series noted an increased
risk of arrhythmias, especially sinus node
dysfunction .
This may be due to disruption of the conduction
system by the atrial incision used to repair TAPVC.
92. Children with TAPVC should undergo appropriate
surveillance, screening, and or referral for
neurodevelopmental impairment as recommended
in a 2012 scientific statement from the American
Heart Association.
93. follow-up care should be individually planned through
the primary caregiver in collaboration with a pediatric
cardiologist
In the absence of residual pulmonary vein stenosis or
pulmonary hypertension, exercise tolerance is generally
normal in children with repaired TAPVC regardless of
the anatomic subtype.
Physical activities and sports participation should not be
restricted. Infective endocarditis prophylaxis precautions
should be considered within the first six months after
surgical repair, after which it is no longer required.
FOLLOW-UP CARE
94. Periodic screening for arrhythmias is not routinely
recommended in asymptomatic children with
repaired TAPVC.
Because of the known association between
intracardiac surgical repairs and atrial arrhythmias,
however, periodic Holter monitoring may be
considered in asymptomatic adolescents
95. CONCLUSION
TAPVC is a rare congenital heart anomaly but
presents as a surgical emergency in neonatal
periods.
Echocardiography is the diagnostic modality of
choice.
Cardiac catheterization is rarely needed for
diagnosis.
Surgical correction is the definitive treatment.
96. Improved surgical techniques and hospital care
have led to significantly better outcomes of TAPVC
surgery.
Suturless repair is safe and effective method to deal
with post operative pulmonary venous obstruction.
97. DIFFERENTIAL DIAGNOSIS
Non obstructive TAPVC -
Conditions producing high pulmonary flow
with cyanosis like TGA ,Taussig Bing anomaly,
persistent truncus arteriosus and common atrium.
Obstructive type of TAPVC-
Conditions producing PAH without shunt
lesion like congenital mitral stenosis, cor-
triatriatum, pulmonary venous stenosis and
persistent fetal circulation.
A monogenic pattern of inheritance has been suggested from the number of reported family cases in the literature among siblings
TAPVR: Anatomy- Supracardiac 1
Gross anatomy of supracardiac total anomalous pulmonary venous return. Pulmonary veins (PV) drain to a vertical vein that connects to the right atrium (RA) via the innominate vein and superior vena cava (SVC). Other abbreviation: RV right ventricle
TAPVC: Anatomy- Coronary Sinus
Posterior view of gross anatomy of total anomalous pulmonary venous return to the coronary sinus. The coronary sinus has been opened longitudinally. The right forceps is grasping one side of the coronary sinus wall. The left forceps is grasping the left atrial appendage (LAA). The left (LPV) and right (RPV) pulmonary veins enter the coronary sinus. Through the opened coronary sinus, a patch can be seen that covers the coronary sinus os in the right atrium.
TAPVR: Anatomy- Infradiaphragmatic 2
Posterior view of gross anatomy of infradiaphragmatic total anomalous pulmonary venous return. The right (RPV) and left (LPV) pulmonary veins enter a vertical vein that courses through the esophageal hiatus to connect to the portal venous system.
Obstruction in the anomalous venous channel may be caused by several factors.
Tapvc as isolated lesion in two third cases , remaining one third pda,sv,avcd,tga
In the last 15 years, 248 patients (168 boys, 80 girls)
Pulmonary edema results when the hydrostatic pressure in the capillaries exceeds the osmotic pressure of the blood.
Mechanisms that tend to prevent pulmonary edema include increased pulmonary lymphatic flow, alternative pulmonary venous bypass channels, altered permeability of the pulmonary capillary wall and reflex pulmonary arteriolar constriction.
Dyspnea, tachypnea, tachycardia, and poor feeding are almost always present.
This murmur often is heard well over the xiphoid and at the lower left sternal border; in this case, it is SI coincident secondary to tricuspid regurgitation.
Turbulence in the pulmonary outflow tract or tricuspid valve insufficiency, or both, account for the systolic murmurs.
S1is loud and distinct and often is often followed by a systolic ejection click.
S2 widely split & does not vary with respiration,The pulmonary component of the second sound is accentuated.
S3 maximal at the apex almost always, is present.
S4 is frequently heard in older patients.
Characteristically, a grade 2/6 soft , blowing , systolic ejection murmur is heard in pulmonary area .
A diastolic tricuspid flow murmur at the lower left sternal border occurs frequently.
Unlike the &quot;innocent&quot; venous hum, this murmur is not louder during diastole and is not altered by change in position or pressure on the neck veins.
Cardiac failure occurs in most patients prior to 6 months of age.
D/D Respiratory distress syndrome-symptoms within 12 hours of life.
Certain features are common to all cases.
The lung fields reflect increased In addition, the specific site of anomalous connection may result in characteristic signs.
PBF.
The upper portion of the figure-of 8 Is Composed Of the Anomalous Vertical Vein on the left, the LIV superiorly & SVC on the right.
This diagnostic sign usually is not present in the first few months of life but often is present in the older child and adult.
When the anomalous connection is to the right SVC, dilation of this structure results in a prominence at the upper right cardiac border
The cardiac size is normal or nearly so.
The lung fields have abnormal pulmonary vascular markings, characterized by diffuse, stippled densities that form a reticular pattern that fans out from the hilar regions.
The cardiac borders often are obscured.
Kerley B lines have been described, and prominence of the superior pulmonary veins is usual.
The radiographic appearance is not diagnostic of TAPVC with obstruction because it also is associated with other causes of pulmonary venous obstruction.
Next, the individual pulmonary veins are sought.
Once identified, each individual pulmonary vein is imaged by 2-D and is interrogated by color Doppler flow mapping.
The course and diameter of each vein then should be determined. Jenkins et al. (45) showed that the size of the individual pulmonary veins at the time of initial diagnosis is a strong, independent predictor of survival in TAPVC.
Smaller pulmonary veins were associated with poorer prognosis.
Based upon a recent multicenter study from Europe investigators similarly found hypoplastic/stenotic pulmonary veins to be an independent risk factor for death (46).
In supracardiac TAPVC, the site of connection with systemic vein (most frequently the left innominate vein) is a common site of narrowing.
In infradiaphragmatic TAPVC, the most common site of obstruction is its connection with the portal or hepatic vein
The 2D and Doppler findings are as described in the previous section on TAPVC without obstruction.
Angio CT examination with coronal MIP reformat and 3D reconstruction. Infradiaphragmatic type of total anomalous pulmonary venous connection. The four pulmonary veins join together and drain downwards, connecting to the liver&apos;s portal vein system
Angio CT examination. Infradiaphragmatic type of total anomalous pulmonary venous connection (reconstruction)
In the uncommon circumstance when echocardiography cannot provide all diagnostic information required for surgical planning, MRI provides an excellent complementary option.
The accuracy of 2-D and Doppler echocardiography in identifying the presence and type of TAPVC nearly has eliminated the need for diagnostic cardiac catheterization and angiography in the diagnosis of TAPVC.
Ninety-seven percent sensitivity and 99% specificity have been reported in the echocardiographic diagnosis of TAPVC, even before color Doppler became available (48).
Diagnostic cardiac catheterization now rarely is performed to clarify problems unresolved by 2-D and Doppler echocardiography.
The advent of MRI in recent years may obviate the need for diagnostic catheterization even further.
When TAPVC is to the LIV or right SVC , SVC blood preferentially flows in to the tricuspid orifice and IVC blood preferentially shunts into the LA, resulting in a pulmonary artery oxygen saturation that may be higher than that in the systemic artery.
particularly in an attempt to determine the
This phenomenon is most likely attributable to the fact that the compliances of the two ventricles are usually comparable, and their filling pressures are thus equal even in the face of a restrictive interatrial communication.
Interpretation of oximetry must be cautious , however On the one hand, PBF is decreased and its volume may not be sufficient to allow a high oxygen saturation when mixed with systemic venous blood.
Selective pulmonary arteriography usually is diagnostic.
Following injection and passage of opaque dye through the pulmonary fields, the dye collects in the pulmonary venous channels and clearly outlines the anomalous connection (Fig. 35.20).
In TAPVC to the LIV, the vertical vein can be seen to originate from the area of the&apos; common pulmonary vein and to ascend to join the LIV.
The latter is outlined in its course to the SVC.
In infracardiac type, anomalous connection of pulmonary veins via descending vertical vein to portal vein is characteristic and it is termed as TREE IN WINTER.
The counterclockwise frontal vector loop identifies common AVSD, as does the murmur of MR.
Immediate endotracheal intubation and hyperventilation with 100% oxygen to a PaCO2 of ˂ 30 mm Hg and correction of pH. Induced respiratory alkalosis decreases pulmonary vascular resistance and improves oxygenation