++
When it is clear that the patient needs restoration of
perfusion, vascular access must be established (see Chapter 107). The route of catheter placement is dictated by the urgency
for care. It is often quite difficult to place a percutaneous catheter
in a peripheral vein when the patient’s intravascular volume
is decreased, so alternative approaches may be needed. Techniques such
as intraosseous cannulation, percutaneous cannulation (Seldinger
technique) of a large central vein, or venisection are appropriate when
the patient is in shock and there is no means for fluid and medication
administration.
++
Supplemental oxygen should be provided (by face
mask, nasal cannulae, or head box in the infant) to maximize oxygen
delivery and to keep the lungs filled with oxygen, even if arterial
oxygen saturation is normal. If, however, oxygen administration
worsens the patient’s perfusion, as can occur in the infant with
critical left-heart obstruction in whom the ductus arteriosus constricts,
then it should be stopped immediately (as with any other drug that
causes an adverse outcome).
+++
Improvement
of Cardiac Output
++
Physical assessment should identify factors—heart
rate, cardiac ejection, or cardiac filling—responsible
for poor perfusion, and therapy should be targeted accordingly.
With prolonged or severe shock, it is likely that circulatory function
is impaired by more than one of these factors. For example, with
sepsis, a child can have poor contractile function, diminished intravascular
volume, vasodilation, maldistribution of blood flow, and increased
metabolic demands. However, in any child with poor perfusion, it
is essential to start restoring circulatory function before there
is further deterioration. If there are no signs of venous congestion
(ie, liver not enlarged or jugular veins distended), perfusion will
likely improve with rapid and repetitive infusion of crystalloid
fluid in an isotonic mixture (eg, isotonic saline or Ringer’s
lactate) in aliquots of 5 to 20 mL/kg over 5 to 20 minutes. The
precise amount in an aliquot is less important than the need for
continued reassessment of the intervention’s effect.
++
After assessing serum glucose concentration, glucose should be given
with the initial fluid if there is hypoglycemia. Routine glucose
administration is not indicated, as hyperglycemia has been associated
with worse outcomes following resuscitation from traumatic shock
and cardiac arrest. Although there is a long-standing and unresolved
controversy about the merits of colloid versus crystalloid in resuscitation,
crystalloid remains a practical initial therapy.15,16 Following
initial attempts at restoring perfusion with crystalloid, the subsequent
choice of fluid should be based on the type of deficits and specific
problems identified. For example, if there is anemia or hemorrhage,
packed red blood cells are needed.
++
The quantity of fluid required for restoring perfusion
might be quite large and can exceed normal blood volume, which is
70 to 80 mL/kg. Often, the fluid volume has been lost over
an extended period of time, such that the interstitial or cellular
compartments are also likely to be depleted. Much of the isotonic
fluid will leave the intravascular compartment and distribute rapidly
into extravascular spaces during the resuscitation. In addition,
when capillary integrity is damaged, fluid may readily extravasate
from the plasma into the interstitium, even though the effective
circulating plasma volume is inadequate. For these reasons, some
clinicians prefer to use colloid-containing fluid, although it,
too, can extravasate rapidly from the vascular compartment if there
is capillary injury.
++
If, during the course of fluid infusion, venous congestion
develops before perfusion is near normal, then impaired ejection
of blood or impedance to filling of the heart is likely. Inotropic support
should be provided whenever there is direct evidence of depressed
myocardial function (eg, venous congestion, cardiomegaly in the
presence of a gallop rhythm) or when there is a progressive increase
in venous engorgement without improvement in perfusion during fluid administration.
Even with the risks of venous congestion, when myocardial function
is depressed, it is appropriate to provide sufficient intravascular
volume so that inotropic medications will be effective in increasing stroke
volume (for any given ejection fraction, the stroke volume will
increase when the filling of the heart is increased). Although peripheral edema
is unsightly, it is unlikely to compromise the patient’s
vital functions. Pulmonary edema, on the other hand, will increase
the work of breathing and can impair gas exchange, thereby necessitating
tracheal intubation and assisted ventilation.
++
The inotropic drugs that are most appropriate are given by intravenous
route and are rapidly metabolized, and the dose can be adjusted
as conditions change. The most commonly used drugs (see Table 103-3) are the direct-
and indirect-acting β agonists, including epinephrine, isoproterenol,
dopamine, and dobutamine, and phosphodiesterase inhibitors such
as milrinone. Because these drugs also have important effects on
the peripheral vasculature, it is worth considering whether some
degree of vasoconstriction is needed to increase blood pressure
(eg, dopamine, epinephrine) or whether vasodilation would be beneficial
(eg, dobutamine, milrinone, amrinone, isoproterenol). Generally,
the former group of drugs is most useful initially until it is clear
whether blood pressure is sufficient to support perfusion. More
invasive approaches to supporting circulation, such as left-ventricular
assist devices and balloon counterpulsation, are not widely available
and are appropriate only in specialized settings (see Chapter 109).
++
++
If the heart rate is not appropriately increased, there
should be immediate concern that there is severe hypoxemia or asphyxia
or that the myocardium is intrinsically injured. In this circumstance,
oxygen should be given immediately, cardiac rhythm should be checked
closely, and use of an inotropic drug with chronotropic properties
or use of a pacemaker if the rhythm is not sinus should be considered.
In addition, chest compressions should be started if severe bradycardia
is associated with poor perfusion.
++
The response to therapy must be evaluated with
repetitive physical examinations and measurements of vital signs.
In particular, if cardiac output is improving, one should expect
to find a decreasing heart rate, enhanced peripheral perfusion,
and possibly increasing blood pressure or pulse pressure as the
circulation is improved, as well as warming extremities. If, on
the other hand, signs of pulmonary congestion or edema (eg, tachypnea,
crackles, wheezing, retractions) develop or worsen, or signs of
systemic venous congestion (eg, enlarged liver or fontanel) develop
without appropriate restoration of peripheral perfusion, it is necessary
to consider more invasive monitoring and more extensive evaluation of
cardiac function by echocardiography. Placement of a central venous
catheter can be useful for measuring the filling pressure of the
right side of the heart and for monitoring oxygen extraction. When
there is reason to believe that the right and left ventricles have
markedly different filling pressures or disparate function, a balloon
flotation catheter can be passed into the pulmonary artery to measure
wedge pressure and cardiac output and to assist in evaluating cardiac
function and response to therapy.
+++
Reduction in
Demands and Adjuncts to Treatment
++
When shock is present, the goal of therapy is to
maximize oxygen delivery and minimize demand for oxygen and blood
flow. Anemia, hypoxemia, and fever should be corrected whenever
possible. It is important to recognize, however, that fever may
not abate until perfusion is restored, because the vasoconstriction
interferes with heat dissipation. This is in keeping with a common
finding of an increased core temperature in the presence of cold
extremities.
++
An important adjunct to therapy can be using positive-pressure
ventilation in the patient with shock, even when there are no overt
signs of respiratory distress. Supplanting the work of breathing
can decrease overall metabolic rate and can divert blood flow from
respiratory muscles to other vital tissues.17 Tracheal
intubation and initiation of assisted ventilation is not without
risk, so it should be performed in a controlled environment with
appropriate personnel; tube placement should always be verified
using physical examination and, if possible a confirmation device
(eg, exhaled CO2 detector) at the time of insertion, when
the patient is moved, and whenever the intubated patient deteriorates.
Positive-pressure ventilation can reduce venous return and decrease
cardiac output.18Therefore, it is important to
be prepared to restore cardiac filling if this occurs.
++
There are some special considerations related
to the neonate with left-heart obstruction, coarctation, aortic
stenosis, or atresia that merit discussion because of the frequency
with which these conditions occur and the potential for improvement
with infusion of prostaglandin E1 (see Chapters 56, 60, and 483). These conditions commonly produce circulatory shock
within the first week after birth; there will be little, if any,
improvement in perfusion by using the conventional approaches described
above, but dilation of a constricted ductus arteriosus after the
administration of a prostaglandin can provide a dramatic increase in
perfusion until more definitive therapy is initiated.
++
After therapy for poor perfusion begins, it is incumbent
to search for an underlying etiology to treat (eg, antibiotics for
suspected sepsis), to consider additional strategies for improving
circulatory function, and to plan a transfer to a facility that
can provide extended monitoring and management. eFigure 103.2 summarizes many of the manifestations of circulatory
shock described in this chapter, including hypotension, marked vasoconstriction,
the inability to dissipate heat, the decline in metabolic rate,
the increase in O2 extraction, the increase in lactate concentration,
and progressive acidosis. It also shows the types of responses expected
as the circulation is restored.14
++