Page 320 - ACCCN's Critical Care Nursing

Cardiac Surgery and Transplantation 297

new ischaemia or infarction should be made, which if of Rhythm monitoring and postoperative
significant size, may warrant surgical re-exploration arrhythmias
or angiographic investigation. Pericardial tamponade Continuous rhythm monitoring is necessary while in
is also a cause of hypotension (covered later in this intensive care, and telemetry monitoring is usually con-
chapter).
tinued until discharge from hospital. Lead selection is
A fourth common postoperative profile is hypotension often haphazard, but a chest lead in the V1 position (or
with normal or elevated cardiac output in the presence lead MCL1) generally provides best information on atrial
27
of low SVR. This may occur with excess vasodilator and ventricular activity. Unlike many leads, these two
administration, the use of postoperative epidural infu- leads reliably demonstrate normal rhythms, bundle
27
sions, and vasodilation from a systemic inflammatory branch block and ventricular rhythms, and may be
response to cardiopulmonary bypass and other factors useful in confirming pulmonary artery catheter irritation
such as reinfusion of collected operative site blood. The as the cause of ventricular arrhythmias. 28
24
inotrope milrinone hydrochloride is popular in the post- A 12-lead ECG is performed on admission to the ICU
operative phase because of its dilating effect on radial and should be compared with the preoperative ECG. It
artery grafts, but often contributes to hypotension should be assessed for signs of new ischaemia or infarc-
25
through its systemic vasodilator properties. When hypo- tion, new bundle branch block and arrhythmias or con-
tension is attributable to vasodilation, metaraminol or duction disturbances. Pericarditis, a frequent complication
19
noradrenaline may be used. Arginine vasopressin, by of surgery, appears as ST segment elevation (often, but
infusion, has more recently emerged as an effective alter- not always, in many leads), and may mask or mimic
native vasoconstrictor for cardiac surgical patients. 26 myocardial infarction. The nurse should look for the
classic concave upward, or ‘saddle-shaped’ ST segment, to
A mean arterial pressure of 70–80 mmHg is generally
21
targeted in the postoperative period. This can some- distinguish pericardial changes from the more convex
times be reduced if there has been ventriculotomy or if upward ST segment of infarction. Worsening of pain on
20
there is concern about the status of the aorta. The cardiac inspiration and a pericardial rub help to confirm
27
2
index should be maintained above 2.2 L/min/m , as pericarditis.
hypoperfusion develops below these values. When at Atrial fibrillation is the most common postoperative
these levels, additional assessments are often undertaken, arrhythmia and contributes significantly to postoperative
29
such as mixed venous oxygen saturation measurement morbidity and hospital length of stay. It occurs in up
(to assess oxygen delivery deficits) and arterial pH and to 30–50% of patients, most often on days 2 to 3 post-
lactate measurements (to detect metabolic acidosis from operatively. 15,29 Many patients revert without treatment,
19
anaerobic metabolism). but when treatment becomes necessary beta-blockers and
amiodarone appear the most successful agents for cor-
In addition to assessment of preload, contractility and rection. Digitalis is effective for rate control and IV
29
afterload, heart rate and rhythm should be assessed for magnesium is often used, although further evidence for
their input into cardiac output and blood pressure. its use is needed. Atrial pacing to prevent atrial fibrilla-
Extremes of rate and arrhythmias alter ventricular filling tion is being increasingly explored but a clear recom-
and may need correction. If temporary pacing wires are mendation on pacing sites and protocols has yet to
present, pacing strategies for haemodynamic improve- emerge. By contrast, atrial overdrive pacing can be an
ment include rate rises (even if already in the normal effective means to immediately and safely interrupt atrial
range) and the provision of dual-chamber or atrial flutter. 29
21
pacing as alternatives to just ventricular pacing. Alterna-
tively, if ventricular pacing is present, reducing the rate to Ventricular ectopic beats are common and by themselves
permit expression of a slower sinus rhythm may, with the do not require treatment unless they accompany isch-
19
provision of atrial kick, improve cardiac output and aemia or biochemical disturbance, in which case they
blood pressure (refer to Chapter 11 for more information may progress to more complex arrhythmias. Consider-
on pacing). ation should always be given to the pulmonary artery
catheter as the cause (including both correctly and
malpositioned catheters), as this is an easily corrected
28
influence. Ventricular tachycardia and fibrillation are
uncommon and usually denote myocardial disturbance
Practice tip such as ischaemia or infarction, shock, electrolyte distur-
bance, hypoxia, or increased excitation by high circulat-
Be aware of an apparent paradox: hypertension may occur even ing catecholamine levels. Standard approaches to
17
if there is hypovolaemia. The intense vasoconstriction often resuscitation according to protocols in Chapter 24 apply,
seen postoperatively not only raises blood pressure but aids including standard CPR over the recent sternotomy.
venous return so that right atrial pressure is normal. It may not When ventricular fibrillation cannot be corrected, consid-
be until the patient has warmed and dilated that the true filling eration is often given to re-exploration of the chest to
status becomes revealed. When the patient is cold and with examine graft patency and/or provide internal cardiac
normal filling pressures, be prepared for possible hypotension, massage. The cardiac surgical intensive care unit should
and the need for significant fluid resuscitation, on rewarming. be equipped to enable emergency re-exploration for such
purposes.