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When the patient has rewarmed, cardiopulmonary bypass
is discontinued. Dopamine hydrochloride is routinely administered
at renal doses, and other inotropic agents and vasodila-tors
are titrated as necessary to sustain acceptable hemody-namics.
The cardiac output is generally high, with a low sys-temic
vascular resistance. Temporary atrial and ventricular
epi-cardial pacing wires are placed. Despite the duration
of extra-corporeal circulation, hemostasis is readily
achieved, and the administration of platelets or coagulation
factors is generally unnecessary. Wound closure is routine.
A vigorous diuresis is usual for the next few hours, also
a result of the previous sys-temic hypothermia.
Disease Classification:
Four Types
There are four broad types of pulmonary occlusive disease
relat-ed to thrombus that have been described by our group
15 :
- Type I disease (approximately 30% of cases of thromboem-bolic
pulmonary hypertension; Fig. 1) refers to the situation
in which major vessel clot is present and readily visible
on the opening of the pulmonary arteries. As mentioned
earli-er, all central thrombotic material has to be
completely removed before the endarterectomy
- In type II disease (approximately 60% of cases; Fig.
2), no major vessel thrombus can be appreciated. In
these cases only thickened intima can be seen, occasionally
with webs, and the endarterectomy plane is raised in
the main, lobar, or segmental vessels.
- Type III disease (approximately 10% of cases; Fig.
3) pres-ents the most challenging surgical situation.
The disease is very distal and confined to the segmental
and subsegmen-tal branches. No occlusion of vessels
can be seen initially. The endarterectomy plane must
be carefully and painstak-ingly raised in each segmental
and subsegmental branch. Type III disease is most often
associated with presumed repetitive thrombi from indwelling
catheters (such as pace-maker wires) or ventriculoatrial
shunts, and sometimes rep-resents “burnt out” disease,
where most of the embolic material has been reabsorbed.
- Type IV disease does not represent classic chronic
throm-boembolic pulmonary hypertension and is inoperable.
In this entity there is intrinsic small-vessel disease,
although secondary thrombus may occur as a result of
stasis. Small-vessel disease may be unrelated to thromboembolic
events (“primary” pulmonary hypertension) or occur in
relation to thromboembolic hypertension as a result
of a high flow or high-pressure state in previously
unaffected vessels similar to the generation of Eisenmenger’s
syndrome. We believe that there may also be sympathetic
“cross-talk” from an affected contralateral side or
stenotic areas in the same lung.
Postoperative Care
Meticulous postoperative management is essential to the
suc-cess of this operation. All patients are mechanically
ventilated for at least 24 hours, and all patients are
subjected to a main-tained diuresis with the goal of reaching
the patient’s preoper-ative weight within 24 hours. Although
much of the postopera-tive care is common to more ordinary
open-heart surgery patients, there are some important
differences. The electrocar-diogram, systemic and pulmonary
arterial and central venous pressures, temperature, urine
output, arterial oxygen saturation, chest tube drainage,
and fluid balance are moni-tored. A pulse oximeter is
used to continuously monitor peripheral oxygen saturation.
Management of cardiac arrhythmias and output and treatment
of wound bleeding are identical to other open-heart operations.
In addition, higher minute ventilation is often required
early after the operation to compen-sate for the temporary
metabolic acidosis that devel-ops after the long period
of circulatory arrest, hypothermia, and cardiopulmonary
bypass. Tidal volumes higher than those normally recommended
after cardiac surgery are therefore generally used to
obtain optimal gas exchange. The maximum inspi-ratory
pressure is maintained below 30 cm of water if possible.
Although we used to believe that prolonged sedation and
ventilation were beneficial and led to less pulmonary
edema, subsequent experience has shown this not to be
so. Extubation should be performed on the first postoperative
day, if possible.
Diuresis. Patients have considerable
positive fluid balance after operation. After hypothermic
circulatory arrest, patients initiate an early spontaneous
aggressive diuresis for unknown reasons, but this may,
in part, be related to the increased car-diac output related
to a now lower PVR level. This should be augmented with
diuretics, however, with the aim of returning the patient
to the preoperative fluid balance within 24 hours of operation.
Because of the increased cardiac output, some degree of
systemic hypotension is readily tolerated. Fluid administration
is minimized, and the patient’s hematocrit level should
be maintained above 30% to increase oxygen carrying capacity
and mitigate the pulmonary reperfusion phenomenon.
Arrhythmias. The development of atrial
arrhythmias, at approximately 10%, is no more common than
that encountered in patients who undergo other types of
nonvalvular heart sur-gery. The small, inferior atrial
incision, away from the conduc-tion system of the atrium
or its blood supply, may be helpful in the reduction of
the incidence of these arrhythmias.
Transfusion. Despite the requirement
for the maintenance of an adequate hematocrit level, with
careful blood conserva-tion techniques used during operation,
transfusion is required in a minority of patients.
Anticoagulation. A Greenfield filter
is usually inserted before operation, to minimize recurrent
pulmonary embolism after pul-monary endarterectomy. However,
if this is not possible, it can also be inserted at the
time of operation. If the device is to be placed at operation,
radiopaque markers should be placed over the spine that
correspond to the location of the renal veins to allow
correct positioning. Postoperative venous thrombosis pro-phylaxis
with intermittent pneumatic compression devices is used,
and the use of subcutaneous heparin is begun on the evening
of surgery. Anticoagulation with warfarin is begun as
soon as the pacing wires and mediastinal drainage tubes
are removed, with a target international normalized ratio
of 2.5 to 3.
Complications
Patients are subject to all complications associated with
open heart and major lung surgery (arrhythmias, atelectasis,
wound infection, pneumonia, mediastinal bleeding, etc.)
but also may develop complications specific to this operation.
These include persistent pulmonary hypertension, reperfusion
pulmonary response, and neurologic disorders related to
deep hypothermia.
Persistent Pulmonary Hypertension. The
decrease in PVR level usually results in an immediate
and sustained restoration of pulmonary artery pres-sures
to normal levels, with a marked increase in cardiac output.
In a few patients, an immediately normal pulmonary vascular
tone is not achieved, but an additional substantial reduction
may occur over the next few days because of the subsequent
relax-ation of small vessels and the resolution of intraoperative
factors such as pulmonary edema. In such patients, it
is usual to see a large pulmonary artery pulse pressure,
the low diastolic pressure indicating good runoff, and
yet persistent pulmonary arterial inflexibility still
resulting in a high systolic pressure.
There are a few patients in whom the pulmonary artery
pres-sures do not resolve substantially. We do operate
on some patients with severe pulmonary hypertension but
equivocal embolic disease. Despite the considerable risk
of attempted endarterectomy in these patients, since transplantation
is the only other avenue of therapy, there may be a point
when it is unlikely that a patient will survive until
a donor is found. In our most recent 500 patients, more
than one third of perioperative deaths were directly attributable
to the problem of inadequate relief of pulmonary artery
hypertension. This was a diagnostic rather than an operative
technical problem. Attempts at phar-macologic manipulation
of high residual PVR levels with sodi-um nitroprusside,
epoprostenol sodium, or inhaled nitric oxide are generally
not effective. Because the residual hypertensive defect
is fixed, it is not appropriate to use mechanical circula-tory
support or extracorporeal membrane oxygenation in these
patients if they deteriorate subsequently.
The Reperfusion Response. A specific
complication that occurs in most patients to some degree
is localized pulmonary edema, or the reperfusion response.
Reperfusion injury is defined as a radiologic opacity
seen in the lungs within 72 hours of pulmonary endarterectomy.
This unfortunately loose definition may therefore encompass
many causes, such as fluid overload and infection. True
reperfusion injury that directly adversely impacts the
clinical course of the patient now occurs in approximately
10% of patients. In its most dramatic form, it occurs
soon after operation {within a few hours) and is associ-ated
with profound desaturation. Edema-like fluid, sometimes
with a bloody tinge, is suctioned from the endotracheal
tube. Frank blood from the endotracheal tube, however,
signifies a mechanical violation of the blood-airway barrier
that has occurred at operation and stems from a technical
error. This complication should be managed, if possible,
by identification of the affected area by bronchoscopy
and balloon occlusion of the affected lobe until coagulation
can be normalized.
One common cause of the reperfusion pulmonary edema is
persistent high pulmonary artery pressures after operation
when a thorough endarterectomy has been performed in certain
areas, but there remains a large part of the pulmonary
vascular bed affected by type IV change. However, the
reperfusion phe-nomenon is often encountered in patients
after a seemingly technically perfect operation with complete
resolution of high pulmonary artery pressures. In these
cases the response may be one of reactive hyperemia, after
the revascularization of segments of the pulmonary arte-rial
bed that have long experienced no flow. Other contributing
factors may include perioperative pul-monary ischemia
and conditions associated with high permeability lung
injury in the area of the now denuded endothelium. Fortunately,
the incidence of this complication is very much less common
now in our series, probably as a result of the more complete
and expeditious removal of the endarterectomy spec-imen
that has come with the large experience over the last
few years.
Management of the Reperfusion Response.
Early measures should be taken to minimize the develop-ment
of pulmonary edema with diuresis, mainte-nance of the
hematocrit levels, and the early use of peak end-expiratory
pressure. Once the capillary leak has been established,
treatment is supportive because reperfusion pul-monary
edema will eventually resolve if satisfactory hemody-namics
and oxygenation can be maintained. Careful manage-ment
of ventilation and fluid balance is required. The hemat-ocrit
is kept high (32%-36%), and the patient undergoes aggressive
diuresis, even if this requires ultrafiltration. The patient’s
ventilatory status may be dramatically position sensi-tive.
The FIO 2 level is kept as low as is compatible with an
oxy-gen saturation of 90%. A careful titration of positive
end-expi-ratory pressure is carried out, with a progressive
transition from volume-limited to pressure-limited inverse
ratio ventilation and the acceptance of moderate hypercapnia.
Infrequently, inhaled nitric oxide at 20 to 40 parts per
million can improve the gas exchange. On occasion we have
used extracorporeal perfusion support (extracorporeal
membrane oxygenator or extracorporeal carbon dioxide removal)
until ventilation can be resumed satis-factorily, usually
after 7 to 10 days.
Delirium. Early in the pulmonary endarterectomy
experience (before 1990), there was a substantial incidence
of postopera-tive delirium. A study of 28 patients who
underwent pulmonary endarterectomy showed that 77% experienced
the development of this complication.18 Delirium appeared
to be related to an accumulated duration of circulatory
arrest time of more than 55 minutes; the incidence fell
to 11% with significantly shorter periods of arrest time.19
With the more expeditious operation that has come with
our increased experience, postoperative confusion is now
encountered no more commonly than with ordinary open-heart
surgery.
Results
More than 1575 pulmonary thromboembolism operations have
been performed at UCSD Medical Center since 1970. Nearly
1400 have been completed since 1990, when the surgical
pro-cedure was modified as described earlier. The mean
patient age in the last 1300 patients was 52 years, with
a range of 8 to 85 years. There was a very slight male
predominance. In nearly one third of these cases, at least
one additional cardiac procedure was performed at the
time of operation. Most commonly, the adjunct procedure
was closure of a persistent foramen ovale or atrial septal
defect (26%) or coronary artery bypass grafting (8%).
Hemodynamic Results.
A reduction in pulmon-ary pressures and resistance to
normal levels and a corresponding improvement in pulmonary
blood flow and cardiac output are generally immediate
and sustained. In general, these changes can be assumed
to be permanent. Before the operation, more than 95% of
the patients are in NYHA func-tional class III or IV;
at 1 year after the operation, 95% of patients remain
in NYHA functional class I or II.20, 21 In addition, echocardiographic
studies have demonstrated that, with the elimination of
chronic pressure overload, right ventricular geome-try
rapidly reverts toward normal. Right atrial and right
ventricular enlargement regresses. Tricuspid valve function
returns to normal within a few days as a result of restoration
of tricuspid annular geometry after the remodeling of
the right ventricle, and tri-cuspid repair is not therefore
part of the operation.
Operative Morbidity. Severe reperfusion
injury was the sin-gle most frequent complication in the
UCSD series, occurring in 10% of patients. Some of these
patients did not survive, and other patients required
prolonged mechanical ventilatory sup-port. A few patients
were salvaged only by the use of extracor-poreal support
and blood carbon dioxide removal. Neurologic complications
from circulatory arrest appear to have been elim-inated,
probably as a result of the shorter circulatory arrest
peri-ods now experienced, and perioperative confusion
and stroke are now no more frequent than with conventional
open-heart surgery. Early postoperative hemorrhage required
reexploration in 2.5% of patients, and only 50% of patients
required intra-or postoperative blood transfusion. Despite
the prolonged oper-ation, wound infections are relatively
infrequent. Only 1.8% experienced the development of sternal
wound complications, including sterile dehiscence or mediastinitis.
Deaths. In our experience, the overall
mortality rate (30 days or in-hospital if the hospital
course is prolonged) was 9% for the entire patient group,
which encompasses a time span of 30 years. The mortality
rate was 9.4% in 1989 and has been 5% to 7% for the more
than 1300 patients who have under-gone the operation since
1990. In the most recent series of 500 patients (June
1998 to July 2002), the mortality rate was 4.4%. We generally
quote an operative risk of approximately 5%, but some
patients predictably fall within a much higher risk. With
our increasing experience and many referrals, we con-tinue
to accept the occasional patient who, in retrospect, was
unsuitable for the procedure. We also accept patients
in whom we know that the entire degree of pulmonary hypertension
can-not be explained by the occlusive disease detected
by angiog-raphy but feel that they will be benefited by
operation, albeit at higher risk. Residual causes of death
are operation on patients in whom thromboembolic disease
was not the cause of the pul-monary hypertension (50%)
and the rare case of reperfusion pulmonary edema that
progresses to a respiratory distress syn-drome of long
standing, which is not reversible (25%).
Summary
It is increasingly apparent that pulmonary hypertension
caused by chronic pulmonary embolism is a condition that
is under-rec-ognized and carries a poor prognosis. Medical
therapy is ineffective in prolonging life and only transiently
improves the symptoms. The only therapeutic alternative
to pulmonary thromboendarterectomy is lung transplantation.
The advantages of thromboendarterectomy include a lower
operative mortality and excellent long-term results without
the risks associated with chronic immunosuppression and
chronic allograft rejec-tion. The mortality for thromboendarterectomy
at our institution is now in the range of 4.5%, with sustained
benefit. These results are clearly superior to those for
transplantation both in the short and long term.
Although pulmonary thromboendarterectomy is technically
demanding for the surgeon, and requires careful dissection
of the pulmonary artery planes and the use of circulatory
arrest; excellent short- and long-term results can be
achieved. Successive improvements in operative technique
developed over the last four decades allow pulmonary endarterectomy
to be offered to patients with an acceptable mortality
rate and excellent anticipation of clinical improvement.
With this grow-ing experience, it has also become clear
that unilateral opera-tion is obsolete and that circulatory
arrest is essential. The pri-mary problem remains that
this is an under-recognized condi-tion. Increased awareness
of both the prevalence of this condi-tion and the possibility
of a surgical cure should avail more patients of the opportunity
for relief from this debilitating and ultimately fatal
disease.
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