Respiration is a process that is fundamental to life itself. In the absence of external respiration, oxygen is not absorbed into the circulation and carbon dioxide is not removed from it. Such a state is clearly incompatible with life and is of an importance few would fail to acknowledge. The process of respiration is considerably more complex than external respiration alone (Fig. 28.1). Respiration also takes place at a cellular level, known as internal respiration, where oxygen plays a fundamental part in cell energy production, or metabolism, with one of the by-products of this process being carbon dioxide. Internal and external respiration cannot sustain life without the existence of an adequate transport system that enables the oxygen absorbed by external respiration to be delivered to the cells to support internal respiration, and the removal of carbon dioxide produced by internal respiration to the lungs for excretion by means of external respiration.

Figure 28.1 Process involved in respiration. (After Hinchliff S, Montague S, Watson R (1996) Physiology for Nursing Practice, 2nd edn. London: Bailliére Tindall.)

It is essential that assessment of the respiratory system takes into account all of these processes, as the presence of one process does not ensure that other processes are functioning. It is equally important that an assessment evaluates the adequacy of these processes and not just their presence or absence. For example, readings of the patients’ respiratory rate, as well as assessment of depth of breathing, increased or decreased work of breathing, anxiety and skin colour and hydration are all markers that gas exchange is occurring and the patient is adequately respiring.

Oxygen is not available to haemoglobin in the red blood cells. This may occur when the patient is in an atmosphere which has a reduced oxygen content, although it is most likely to occur as a result of a decrease in respiratory rate and/or volume. If untreated, conditions such as pulmonary oedema or pneumonia lead to hypoxic hypoxia by preventing the diffusion of oxygen at the alveolar/capillary interface in the lungs.

Anaemic hypoxia

The oxygen-carrying capacity of the blood is reduced because of a lack of available haemoglobin. In the acute episode, this is likely to be due to hypovolaemia where haemoglobin is lost in proportion to the number of red cells lost. This type of hypoxia may also occur following chronic conditions where the number of red cells is normal but the haemoglobin is either reduced or not readily available, e.g., in iron deficiency anaemia and sickle cell anaemia. Following carbon monoxide poisoning, the carbon monoxide preferentially binds to the haemoglobin, preventing oxygen binding with the haemoglobin and thus resulting in anaemic hypoxia.

Stagnant hypoxia

This occurs as a result of failure of the circulatory system to transport oxygenated blood to the tissues. Normal diffusion occurs at the alveolar/capillary interface in the lungs, but inadequate circulation prevents the oxygen from being delivered to the tissues. This type of hypoxia is classically associated with physiological shock, be that cardiogenic, neurogenic, anaphylactic, etc. This type of hypoxia may also occur at a local level where vascular obstruction causes a reduction in blood flow distal to the obstruction.

Histotoxic hypoxia

In this case, adequate concentrations of oxygen are transported to the tissues, but the cells are unable to utilize the oxygen. This type of hypoxia usually results from certain types of poisoning, classically cyanide poisoning.

• hypoxic hypoxia

• anaemic hypoxia

• stagnant hypoxia

• histotoxic hypoxia.

Assessment of gas exchange

In recent years there has been an increased reliance upon pulse oximetry in respiratory assessment. In many cases, this technology is helpful in identifying hypoxia. However, pulse oximetry must be used with caution as it has the potential to mislead (Moyle 2002). Pulse oximetry gives an indication of the degree to which the available haemoglobin is saturated with oxygen. However, oximetry must only be trusted in situations where a correlation can be made to other assessments of hypoxia and it is strongly recommended to use an oximeter device that has ‘photoplethysmograph’ (PPG) capability (or ‘pleth’ as it is more commonly known). It can measure the change in the volume of arterial blood with each pulse beat and therefore can be useful in comparing to a peripheral pulse rate, and watching for signs of cardiac insufficiency (especially when ectopics occur) and, of course, prove that you have a strong enough signal and can trust the percentage reading. The relationship between oxygen saturation and the amount of oxygen within the circulation is illustrated in graphical format as the oxygen dissociation–haemoglobin dissociation curve. Assuming that the relationship on this curve is normal for a given patient, Gibson (2003) suggests that an oxygen saturation of 90 % represents a blood oxygen tension of 8 kPa. The normal range for arterial blood gases is shown in Box 28.2.

Box 28.2 Normal arterial blood gas values

• pH – 7.35–7.45

• PCO₂ – 4.6–6.0 kPa

• PO₂ – 10.0–13.3 kPa

• Bicarbonate – 22–26 mmol/L

• Base excess – −2.4 to +2.2

A patient with carbon monoxide poisoning may well have an anaemic hypoxia whilst still presenting what appears to be a normal oxygen saturation on the pulse oximeter. Similarly, patients with other forms of hypoxic anaemia may have normal pulse oximetry readings because the pulse oximeter is a reflection of the degree of saturation of each red blood cell and not of the total oxygen content of the blood. Again pulse oximetry must be used with caution when there is probe movement or when peripheral perfusion is low, as recorded saturation may be inaccurate (Levine & Fromm 1995).

It must be remembered that pulse oximetry only provides information about the patient’s oxygen saturation; it is not able to offer information regarding carbon dioxide in the blood. Consider the patient who is having an acute asthma attack and who has been given oxygen therapy by facemask. They may well have what may be regarded as satisfactory oxygen saturation, yet have inadequate ventilation with high and increasing levels of blood carbon dioxide. The most accurate way to assess the gaseous content of the circulating volume is by arterial blood gas analysis. Not only does this investigation provide information regarding respiratory gases in the circulation, but it is also a vital tool in the assessment of acid−base balance.

Asthma

Asthma is a complex disorder characterized by variable and recurring symptoms, airflow obstruction, bronchial hyperresponsiveness, and an underlying inflammation (National Institutes of Health 2007). While many of the 10 % of children and 5 % of adults in the population who have asthma are asymptomatic or are well controlled with medication, approximately 1500 people per year die from asthma (Newman-Taylor 2003). Acute asthma is characterized by an acute attack of bronchospasm in which the airways become swollen, constricted and plugged with mucus. The airflow obstruction, which characteristically fluctuates markedly, causes a mismatch of alveolar ventilation and perfusion and increases the work of breathing. Being more marked during expiration it also causes air to be ‘trapped’ in the lungs.

Respiratory arrest may occur within a few minutes of the onset of a severe episode or death may occur from alveolar hypoventilation and severe arterial hypoxaemia in the patient exhausted by a prolonged attack. Severe airflow obstruction is manifested in the symptoms of shortness of breath, wheezing, chest tightness and a cough. Acute severe asthma may arise from absence of treatment or from inadequate or unsuccessful treatment and is life-threatening and should be considered a medical emergency.

In the non-asthmatic individual, there is a minimal reaction of the smooth muscle in the bronchial wall to stimulation by inhaled allergens such as the house dust mite, animal hair or pollen. Non-allergenic stimulants such as cold weather, cigarette smoke, anxiety and exercise also have a minimal effect on the reactivity of the smooth muscle. In the individual with asthma, reaction to such stimulation is exaggerated, a response termed bronchial hyperreactivity, which is thought to be associated with an inflammatory process.

Asthma can be broadly divided into two main types: allergic and non-allergic. Allergic asthma, as the name suggests, is triggered by allergens such as the house dust mite and others previously identified. This condition generally appears in childhood and may improve as the child reaches adolescence. Conversely, non-allergic asthma is triggered by factors such as anxiety or cold weather, first presenting in middle age. The symptoms of non-allergic asthma tend to intensify in both severity and frequency as the individual becomes older (Axford 1996).

Attendance at the ED is usually precipitated by one of two events:

1. an acute event in the individual who has episodic asthma, i.e., symptom-free between distinct acute episodes; or

2. an acute increase in the severity of symptoms in the individual who has chronic asthma, where tightness and wheezing are present most of the time, if not controlled by regular medication.

Initially, the most obvious sign of asthma may be noisy respiration in the form of a wheeze, which is generally expiratory but can also be inspiratory. One must be cautious not to make false assumptions based upon this symptom, for, as Axford (1996) notes, ‘all that wheezes is not asthma’. Wheezing is a sign of airway obstruction that may or may not be asthmatic in origin.

Assessment

A full and objective assessment is essential and should include a full history. It may not be possible to obtain this from the patient, if breathless. In cases of severe and life-threatening asthma, treatment should not be delayed in order to obtain a full history. The assessment should include the following:

medication history; beta blockers, aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) may precipitate a severe asthma attack in some patients with asthma

previous admissions, especially to intensive care units (British Thoracic Society 2012)

• observation

respiratory effort

use of accessory muscles

chest movement and symmetry

skin colour and appearance, such as sweating

respiratory rate, rhythm and depth

pulse

blood pressure

temperature (episode may have been precipitated by a chest infection)

anxiety

• Palpation

degree of chest expansion

temperature of the skin

• percussion – resonance of the chest

• auscultation

quality of breath sound

degree of air entry

silence

• peak expiratory flow rate

measured against predicted and actual normal for that individual

should not be done if the patient has signs of severe or life-threatening asthma (i.e., is unable to speak a complete sentence)

• pulse oximetry – use with caution; remember it will not tell you the amount of carbon dioxide the patient is retaining

• arterial blood gas analysis

• chest X-ray.

From the assessment it will be possible to identify those patients with severe and life-threatening asthma who need immediate intervention (Tables 28.1 and 28.2).

Table 28.1

Features of severe asthma

Adult	Child
Cannot complete sentences	Cannot talk or feed
Pulse >110 beats/min	Pulse >140 beats/min
Respiratory rate >25 min	Respiratory rate >50 min
Peak flow rate <50 % of predicted

(After Greaves I, Hodgetts T, Porter K (2005) Emergency Care: A Textbook for Paramedics, 2nd edn. London: WB Saunders.)

Table 28.2

Features of life-threatening asthma

Adult	Child
Exhaustion Cyanosis Bradycardia Hypotension Silent chest Peak flow <33 % of predicted Coma	Reduced conscious level Agitation Cyanosis Silent chest Coma

(After Greaves I, Hodgetts T, Porter K (2005) Emergency Care: A Textbook for Paramedics, 2nd edn. London: WB Saunders.)

Management

Position the patient to sit upright to maximize ventilation. Patients may need high concentrations of oxygen or medication nebulized by an oxygen-driven system. The drug regimen recommended by the British Thoracic Society and Scottish Intercollegiate Guidelines Network (British Thoracic Society 2012) includes nebulized or i.v. salbutamol, and oral or i.v. steroids depending upon the mechanism and severity of the attack. In life-threatening asthma, ipratropium should be added to the nebulizer and expert advice must be sought, which may include progression to non-invasive intermittent positive pressure ventilation (IPPV) with pressure support (PS) and positive end expiratory pressure (PEEP) (such as CPAP or BiPap). This can be done on the spontaneously breathing patient, via a face mask and a ventilator that is capable of delivering the non-invasive positive support safely, but is a skill that requires extra knowledge and training as there is risk of barotrauma. For children with moderate to severe exacerbation, bronchodilators can be given by inhaler using a spacer device. ED nurses must be familiar with the current British Thoracic Society and Scottish Intercollegiate Guidelines Network guidelines on asthma (British Thoracic Society 2012) and in particular the flow charts relating to the management of acute asthma in adults in ED and the management of acute asthma in children in ED. In addition to continued reassessment based upon the initial assessment, monitor the cardiac rhythm. Provide psychological care for patient and family in dealing with their stress and anxiety. The use of spacers for adult asthma patients as well as children is currently being evaluated.

In the less severe episodes, it is important to check out the patient’s understanding of the illness and management. It is not uncommon for some individuals with asthma to have a poor understanding of the purpose of their medication, when it should be taken and how to take it correctly. This can lead to poor compliance and leave the patient in a brittle state, with decreased reserve to cope with any triggering episodes. It is important to make use of such opportunities to provide some preventive care. It is also essential that appropriate follow-up is arranged to continue patient education and monitoring in the primary healthcare setting. Patients with little understanding of their condition and medication regimen will continue to attend EDs where their symptoms will be treated without resolving the underlying issues.

It is important to differentiate asthma from hyperventilation, as the presenting symptoms of both are dramatic and can easily be confused by the inexperienced nurse (Yeh & Schwartzstein 2010). A hyperventilating patient will be tachypnoeic but not tachycardic and will usually have oxygen saturation levels of 100 %. Hyperventilation is associated with anxiety and responds quickly to rebreathing through a paper bag. Hyperventilating patients generally do not have a history of asthma.

Chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a collective term for a number of chronic respiratory diseases, the most common of which are chronic bronchitis and emphysema and is characterized by airflow obstruction that is not fully reversible (National Institute for Health and Clinical Excellence 2010). Airflow obstruction has profound effects on cardiac function and gas exchange with systemic consequences (Barnes & Celli 2009, MacNee 2011).

Chronic bronchitis

Chronic bronchitis is most frequently seen in adults of middle age and beyond. It is characterized by a productive cough resulting from increased mucus secretion from hypertrophied mucus-secreting glands in the bronchi. The patency of the smaller bronchi is further compromised by inflammation of the mucosa. The cough and associated inflammation last for several months each year and occur on consecutive years.

Assessment

When the individual with chronic bronchitis attends the ED, it is usually because of an acute exacerbation of symptoms associated with a superimposed upper respiratory tract infection. Assessment of the individual will include:

• a full history, including past history as well as the history of the current episode

signs of chronic respiratory disease, e.g., clubbing of the fingers, barrel chest

respiratory effort

use of accessory muscles

chest movement and symmetry

skin colour

respiratory rate, rhythm and depth

degree of chest expansion

temperature of the skin

• percussion – resonance of the chest

• auscultation

quality of breath sound

degree of air entry

• pulse oximetry – use with caution; remember many of these patients retain carbon dioxide which can result in fatal respiratory acidosis, even in the presence of adequate oxygen saturation. Pulse oximetry will not provide any information about elevated levels of carbon dioxide

• arterial blood gas analysis – will be abnormal given the chronic respiratory disease and should be viewed in the light of the individual’s actual or predicted normal

• sputum sample – for microbiological examination (microscopy, culture and sensitivity)

• chest X-ray.

Assessment of the patient is likely to reveal the following clinical features:

• purulent productive cough

• increased sputum volume

• dyspnoea

• tachypnoea

• wheezing

• respiratory distress and use of accessory muscles

• poor chest expansion

• cyanosis.

Management

Position the patient sitting upright to maximize ventilation. Oxygen should be given at a low concentration, initially no more than 28 %; increased concentrations may be necessary if improvement does not occur, but this should be based on the results of arterial blood gas analysis. Whilst on oxygen the patient must be closely monitored for signs of respiratory depression. Antibiotics, bronchodilators and steroids should be given if asthma is an element in the acute episode. Where nebulized medication is indicated the British Thoracic Society (2012) recommend that a compressed air nebulizer should be used and the patient given supplemental oxygen by nasal prongs. In addition to continued reassessment based upon the initial assessment, the cardiac rhythm should be monitored. Arterial blood gas analysis must be carried out within the first hour of admission to the ED and results used to inform on-going management of the patient. Psychological care for patient and family should be provided in dealing with their stress and anxiety. Progression to invasive, or non-invasive positive pressure ventilation may also be needed if the condition deteriorates and there is a clinical need, however the medical staff will need to take into consideration all aspects of the individual’s medical history including their normal functioning state and any advanced health directives. Discussions with family members will also be valuable in deciding the next appropriate step in resuscitation.