Caring for the Seriously Ill Patient 2E

Michael Macintosh, Tracey Moore, Michael Macintosh, Tracey Moore, Michael Macintosh, Tracey Moore

• Publisher: Routledge
• Year: 2011
• ISBN:
  9781482213249
• Edition: 2
• Topic: Medicina
• Subtopic: Infermieristica

As more critically ill patients are cared for on acute general wards rather than in ICUs, many nurses are having to cope with the particular problems of very sick patients without the specialist knowledge of an ICU trained nurse. This book considers the key issues surrounding the critical patient's care in the acute general hospital. The anatomy an

CHAPTER 1

CARDIOVASCULAR ASSESSMENT AND MANAGEMENT

Mike Macintosh

Introduction

Anatomy and physiology

Assessment of the cardiovascular system

Assessing the cardiac rhythm

Acute coronary syndrome

Heart failure

Acute left ventricular failure

Shock (circulatory failure)

Cardiogenic shock

Inotropic drugs

Hypovolaemia

Conclusion

References

LEARNING OUTCOMES

On completion of this chapter the reader will:

1. have a good understanding of the underlying physiology and pathophysiology of the cardiovascular system

2. be able to discuss assessment of the cardiovascular system

3. have an understanding of the assessment and management of acute coronary syndromes

4. understand the underlying physiology, assessment and management of acute heart failure

5. be able to discuss the physiology, assessment and management of cardiogenic and hypovolaemic shock.

Introduction

An understanding of the cardiovascular system, including assessment and management of common cardiovascular problems, is at the core of safe, effective acute care. Most, if not all, serious illnesses will impact on the cardiovascular system in some way. More specifically, cardiovascular disease remains the most common cause of mortality in the developed world. This chapter explores normal and altered physiology, discusses cardiovascular assessment, and introduces common cardiovascular problems.

Anatomy and physiology

Oxygen delivery

The cardiovascular system is a transport system with continuous responsibility for the delivery of oxygen and nutrients to the cells of the body, and for the removal of the waste products of metabolism. The quantity of oxygen that is supplied to the tissues depends on three factors:

• the arterial oxygen saturation;

• the haemoglobin content of the blood;

• the cardiac output.

Expressed as an equation, this is:

To maintain adequate delivery of oxygen to all the tissues of the body, and to be able to increase delivery when demands dictate, the body needs to be able to increase the value of one or all of these physiological parameters. For the cardiovascular system this means being able to increase cardiac output in relation to the resistance in the vessels to maintain perfusion. This section will focus on the maintenance of adequate cardiac output and tissue perfusion and go on to consider the conditions that may threaten effective cardiovascular function.

Parts of the cardiovascular system

The cardiovascular system (CVS) can be thought of as having three parts:

• a pump (the heart);

• volume (the blood);

• pipes (the veins and arteries).

Each of these three parts is constantly being adjusted in response to demand, and a problem with one of the three must be compensated for by one or both of the other two. The aim of the CVS in continually making these adjustments is to maintain perfusion. To ensure adequate delivery of oxygen to the cells there has to be adequate tissue perfusion. In other words, there needs to be an acceptable level of pressure maintained at the delivery end of the CVS. When this perfusion pressure falls, the delivery of oxygenated blood will fall.

Continuing with this simple model, the cardiovascular system can be likened to any system that delivers fluid under pressure, such as a garden hose. The purpose of a garden hose is to deliver a jet of water under sufficient pressure to supply the flowers with enough fluid to prevent them from dying.

Consider for a moment the pump (heart) to be represented by the tap. The tap can be turned up, or the hosepipe (the blood vessels) can be made to have a narrower diameter. Provided there is a sufficient and constant supply of water (the blood), then either of these measures will result in the jet of water at the end of the pipe increasing – that is, perfusion. If, however the pump starts to fail by the tap being turned down, the jet of water will fall. Similarly, if the hosepipe is changed for one that has a larger diameter, a fire hose for example, the jet of water will again fall. In each of these examples there must be compensation – either the tap is turned up to increase the pressure drop caused by the larger diameter hose, or the hose must be made smaller to increase the pressure drop caused by the turning down of the tap.

So it is with the cardiovascular system. However, this ability to compensate has limits. Just as the tap has a limit beyond which it cannot be increased, so the heart has a limit to its output. Just as the hose has a limit to which it can be made to have a smaller diameter, so the blood vessels have a limit beyond which further constriction will not help. This, then, is the model of perfusion that will be used to describe the normal physiology and abnormal pathology, and to discuss assessment and management of the individual with an actual or potential problem with the CVS.

Chapter 3 explains how the oxygen saturation of haemoglobin maybe compromised, and how it can be optimized by appropriate nursing and medical interventions. The aim of this chapter is to help the practitioner understand the factors that determine cardiac output and its role in oxygen delivery, to consider the possible situations that may contribute to failure of the cardiovascular system, and to help meet the needs of these seriously ill individuals.

Oxygenation of blood

The cardiovascular system is essentially a closed transport circuit, comprising a double pump and a network of blood vessels. The unidirectional flow of blood is ensured by valves, which are positioned at the entrance and exit to each ventricular chamber. Here the normal blood flow through this system is described (Fig. 1.1).

• The right atrium receives deoxygenated blood from the inferior and superior vena cava. This blood has drained from the systemic venous circulation and from the coronary sinus.

• This blood then flows through the tricuspid valve and into the right ventricle.

• From here it is pumped up through the pulmonary valve and into the pulmonary artery, which takes the blood to the lungs for oxygenation.

• The reoxygenated blood then flows back to the heart via the four pulmonary veins that empty into the left atrium.

• The blood then passes through the mitral valve into the left ventricle. From there it is pumped out through the aortic valve into the aorta, and so into the systemic arteries where it is distributed to the peripheral circulation.

This simple description follows the passage of blood around the system. It is also important to understand the events that comprise the cardiac cycle.

Figure 1.1 Frontal section of the heart, showing the direction of blood flow

The cardiac cycle

The following description of the stages of the cardiac cycle begins at the point immediately following ventricular contraction. Remember that the two sides of the heart operate simultaneously rather than in tandem (Fig. 1.2).

The heart has just emptied its contents into the two arteries that leave the ventricles. On the left is the aorta, taking oxygenated blood to the organs and peripheral circulation. On the right is the pulmonary artery, taking deoxygenated blood back to the lungs. The two ventricles then relax. This begins the phase of diastole. During this phase, blood flows into the atria and the ventricles, from the pulmonary veins on the left and the vena cava on the right; the atria now are resting and acting as passive conduits to the flow of blood. Between 60 and 70 per cent of ventricular filling is achieved in this way, the blood flowing along its pressure gradient from the venous system into the relaxed ventricles.

Next is the phase of atrial contraction. Both atria contract and effectively ‘top up’ the ventricles, giving the volume that is in the ventricle at the end of the diastolic phase – the end-diastolic volume. This volume represents preload stress (discussed later) and plays an important part in the cardiac output. In the seriously ill patient the loss of the atrial component can reduce cardiac output, and this can be seen in atrial fibrillation or ventricular pacing.

At the end of the atrial contraction the phase of ventricular contraction or systole begins. Tension increases in the muscular walls of the ventricles and pressure within the ventricular chambers rises rapidly. The valves of the heart are at this point all closed. The rising pressure in the ventricles causes the atrioventricular valves to close against the relatively low pressure in the atria. The aortic and pulmonary valves are still shut at this point.

This phase is called isovolumetric contraction – that is, pressure is increasing but the volume has not yet changed. This phase consumes the most energy and therefore oxygen. It can be seen that the greater the pressure that has to be overcome the more work the heart must do. For example, a hypertensive patient with a high diastolic pressure will have an increase in myocardial oxygen demand during this phase because of the extra pressure that must be generated.

Once the pressure in the ventricles overcomes the pressure in the aorta and pulmonary artery, the valves will open and the contents of the ventricles ...

Table of contents

• Cover
• Title Page
• Copyright
• Contents
• List of contributors
• Preface
• CHAPTER 1 Cardiovascular assessment and management
• CHAPTER 2 Supporting respiration
• CHAPTER 3 Caring for the renal system
• CHAPTER 4 Neurological assessment and management
• CHAPTER 5 Infection control and sepsis
• CHAPTER 6 Acute care and management of diabetes
• CHAPTER 7 Nutrition
• CHAPTER 8 Acute pain
• CHAPTER 9 The patient and family: support and decision-making
• CHAPTER 10 Systems of care
• Appendix: Malnutrition Universal Screening Tool (MUST)
• Index