Page 263 - ACCCN's Critical Care Nursing

240 P R I N C I P L E S A N D P R A C T I C E O F C R I T I C A L C A R E

have both inotropic and chronotropic actions, so that cardiopulmonary bypass and left ventricular assist devices
cardiac contractility and heart rate are both increased to (LVADs) may be used. In appropriate candidates, cardiac
improve cardiac output. Continuous ambulatory infu- transplant may also be an option. These procedures are
sion of inotropic agents such as dobutamine are admini- covered under cardiac surgery.
stered in patients with severe heart failure as a bridge to
transplantation which allows these patients to be dis- Acute Exacerbations of Heart Failure
charged home with support from a home visit nurse. Acute exacerbations of CHF usually occur as episodes of
Cardiac glycosides decompensation due to progression of the disease or
87
non-adherence to their management plan. Acute epi-
Cardiac glycosides such as digitalis inhibit the sodium sodes usually present as congestive heart failure with
pump such that the exchange between sodium and associated pulmonary oedema, cardiogenic shock (see
calcium is impaired. This results in calcium stores being Chapter 21) or decompensated CHF. Patients with
55
released and intracellular calcium levels rising. As more severe dyspnoea due to pulmonary congestion should be
calcium is available for contraction, contractility and administered oxygen therapy. If their hypoxaemia does
cardiac output increase. These changes in ion movement not improve then they may benefit from bilevel positive
and additional affects, which enhance parasympathetic airway pressure (BiPAP) to support ventilation and gas
stimulation, result in decreased impulse generation by exchange. The use of continuous positive airway pressure
the sinoatrial (SA) node. This is known as a negative ventilation (CPAP) or BiPAP in acute pulmonary oedema
chronotropic effect. Conduction is also slowed through will reduce the need for intubation and mechanical
the atrioventricular (AV) node and ventricles, allowing ventilation.
more filling time, and therefore having a positive effect
on cardiac output. The negative chronotropic effects are The mainstay of treatment of an acute exacerbation is
particularly beneficial in patients with the atrial fibrilla- pharmacological, so a combination of the medications
tion that is so common in CHF. Digitalis may also affect is given, usually comprising diuretics, morphine and
cardiopulmonary baroreceptors to reduce sympathetic nitrates. The nitrates and morphine cause vasodilatation.
tone, which may be a valuable offset to excessive sympa- Morphine also reduces the respiratory drive and respira-
thetic stimulation in CHF. tory workload. Nitrates also cause epicardial artery dilata-
tion and reduce preload which also helps to relieve
The most important adverse effects of digoxin are caused symptoms of pulmonary congestion particularly at night
by changes in conduction: tachycardia, fibrillation and AV when filling pressures are increased due to the recumbent
block. Digoxin may also cause nausea and vomiting by position of sleeping. Diuretics should be administered
55
direct brain effects and gastrointestinal irritation. Digi- intravenously to optimise the excretion of intra and extra-
talis has a narrow margin of safety, a long half-life, and vascular cellular fluid to reduce circulating blood volume
side effects can be fatal, so assay of plasma drug levels to reduce cardiac workload. Fluid restriction, usually to
must be conducted regularly and at initiation and change 1–1.5 L in 24 hours, is begun. A urinary catheter may need
of treatment. Excessive digoxin causes disorientation, hal- to be inserted so that accurate, continuous measures of
lucinations and visual disturbances. Potassium levels urine output can be gained and an accurate fluid balance
directly alter the effect of digoxin, so that low levels calculated. This is necessary, along with consistent daily
enhance effects and high levels reduce effects. weighing, to determine the effectiveness of diuretic therapy
Arrhythmias are common in heart failure and need to be and renal status. Various positive inotropes may be admin-
treated. The agent must be carefully selected, as chronic istered (e.g. IV dobutamine causes vasodilatation; IV
heart failure patients often have complex medication regi- dopamine to improve renal function) to improve contrac-
mens and interactions may occur. Also, some ventricular tility and reduce systemic venous return. Various mechani-
antiarrhythmics, like class 1 agents (e.g. flecainide), are cal devices are also available, e.g. intra-aortic balloon
associated with sudden death in CHF. Implantable pump, LVAD (discussed in Chapter 12). CRT with or
cardioverter-defibrillator (ICD) therapy may be more without an ICD may be implanted. CRT is recommended
effective in treating ventricular arrhythmias. ICDs reduce in NYHA class III–IV patients on optimal pharmacologi-
86
mortality by 20–30% and are first-line therapy in patients cal therapy, LVEF ≤35%, QRS duration > 120 ms, and
55
with a history of VF or sustained VT, LVEF ≤30% at least sinus rhythm. All of these criteria must be fulfilled. Cri-
one month post myocardial infarction or three months teria for implantation of an ICD include: symptomatic
post CABGs and symptomatic heart failure and LVEF patients (NYHA class II–IV) and LVEF ≤35%, LVEF <30%
55
≤35%. Cardiac resynchronisation therapy (CRT) (also one month post AMI or three months post CABGs, spon-
known as biventricular pacing) is also indicated in patients taneous VT with structural CHD, or survived a cardiac
with symptomatic heart failure to reduce asynchronous arrest due to VT or VF which was not due to a reversible
pacing of the left ventricle (QRS duration > 150 ms). cause. If a patient is to have an ICD implanted then exten-
Systolic function is improved when the left and right sive counselling pre- and post-implantation must be
ventricles are paced simultaneously. Often patients with undertaken with the patient and carer to ensure they are
a prolonged QRS will have a combination of an ICD with aware of the painful and unexpected shocks that may be
55
CRT therapy. ICDs and CRT are discussed in more detail delivered. Figure 10.15 provides an overview of the esca-
in Chapter 11. lation of treatment for acute heart failure. 55
In severe heart failure, when patients do not respond to Most patients in acute heart failure have poor perfusion
pharmacological treatment, mechanical measures such as of the gastrointestinal system and, combined with