Chapter 13. Assessment and monitoring
Clinical assessment
Colour
• Pallor: very pale appearance, best visualised in the conjunctivae or the mouth. Usually a sign of anaemia but may also be seen in vasoconstriction due to hypotension, hypothermia or severe pain
• Flushing or redness of the skin is caused by vasodilation and may be a sign of fever, extreme exertion or superficial burns
• Cyanosis refers to bluish-grey discolouration of skin or mucous membranes caused by an excess of deoxygenated haemoglobin:
Central cyanosis – imperfect oxygenation of the blood by the lungs or where deoxygenated blood bypasses the lungs for example in congenital heart defects.
Peripheral cyanosis – where slow blood flow leads to increased deoxygenation of the haemoglobin in the peripheries. May be a normal finding for example in patients who are cold.
Pulse
• In the collapsed patient, palpate for a pulse at the carotid or the femoral artery
• The brachial pulse is recommended for palpation in cardiac arrest in infants
• Consider the rate, strength and character of the pulse
• Heart rate can also be documented by the ECG or the pulse oximeter.
Respiratory rate
• Always measure the respiratory rate in breaths per minute
• Neonates have the highest normal respiratory rate and it falls progressively up to the adult range of 12–18 breaths/minute
• A rapid respiratory rate is known as tachypnoea. Rates >30 breaths/minute are usually a sign of serious illness
• Conscious patients may be using their accessory muscles of respiration, e.g. in severe asthma
• A low respiratory rate is bradypnoea, sometimes caused by opiate use
• Some patients with heart failure, neurological disease or drug intoxication demonstrate varying respiratory rate and depth known as Cheyne–Stokes respiration.
Blood pressure
• Accurate blood pressure measurement is important and allows successive readings to be compared to allow monitoring of the patient’s progress and response to treatment
• Most portable monitors now provide automatic blood pressure monitoring
• Anaeroid sphygmomanometers are used if electronic devices fail or are unavailable
• Where possible the patient should be seated comfortably, with the upper arm at the level of the heart
• The cuff must be correctly sized to the patient – small cuffs for children and large cuffs for the obese adult
• The ideal size of cuff is equal in width to approximately two-thirds of the length of the upper arm
• The blood pressure cuff is applied to the upper arm, in the absence of intervening clothing. Most modern cuffs have a method of indicating the correct position of the cuff over the brachial artery
• Portable monitors usually allow the interval between blood pressure measurements to be adjusted depending on the patient’s requirements
• Systematic errors are often seen when the pulse is irregular, such as in atrial fibrillation.
Intra-arterial blood pressure monitoring
Intra-arterial measurement is performed when continuous monitoring of arterial pressure is required, most often in the operating theatre or intensive therapy unit. A catheter is inserted directly into an artery and the pressure wave is monitored by a transducer connected to the catheter. Such intra-arterial monitoring lines may be in situ when a patient is transferred between hospitals; paramedics should be aware of their presence and clarify any precautions necessary during the journey with the appropriate staff.
Pulse oximetry
• Pulse oximetry is the most convenient non-invasive method of monitoring arterial oxygen saturation and is presented in percentage terms
• Oxygenated and deoxygenated haemoglobin absorbs or attenuates differing wavelengths of light. The probe emits rapid bursts of red light which are picked up by a photodetector on the other side of the probe
• The probe can be used on any digit or earlobe or especially in children, the forehead
• Pulsatile blood flow is required so reading may be difficult if the patient is shocked or peripherally shut-down
• Rapid fluctuations in ambient light levels may produce false signals and movement during patient transport may also cause inaccurate readings. Other causes of inaccurate readings include:
• Poor circulation
• Fluctuating light levels
• Carbon monoxide poisoning
• Skin, dirt and grease
• Nail varnish (dark and metallic colours only)
• Carbon monoxide poisoning may cause a pulse oximeter to overestimate the true oxygen saturation: the pulse oximeter will measure the total percentage saturation of haemoglobin with oxygen (oxyhaemoglobin) and carbon monoxide (carboxyhaemoglobin)
• The relationship between arterial oxygen tension ( PaO 2) and arterial oxygen saturation is described by the oxyhaemoglobin dissociation curve
Pulse oximetry does not measure carbon dioxide.
• Because pulse oximetry cannot measure carbon dioxide levels, it does not give a complete picture of ventilation. Inadequate ventilation may give rise to hypercarbia in the present of normal oxygen saturations
• Anaemia or blood loss will not be picked up by pulse oximetry. The patient may have lost a significant proportion of their blood volume but they can continue to have 100% oxygen saturation of the haemoglobin that is left.
Electrocardiographic monitoring
Electrocardiographic (ECG) monitoring is undertaken to define the cardiac rhythm. Accurate rhythm monitoring and interpretation are especially important in the management of cardiac arrest. Manual defibrillators and cardiac monitors feature a screen for displaying the cardiac rhythm and usually incorporate an arrangement for obtaining a printout of the ECG. Automated external defibrillators (AEDs) often store the ECG electronically and a hard copy is obtained from the appropriate playback device. Many cardiac monitors incorporate a heart rate meter which is triggered by the QRS complex of the ECG. An alarm will sound automatically should the heart rate fall outside preset limits; lights and audible signals may also provide additional indications of the heart rate.
Monitoring electrodes
• ECG monitoring requires the attachment of adhesive electrodes to the patient’s chest
• The monitor will interpret the signals to provide records that approximate to leads I, II or III of the conventional ECG
• Lead II normally allows for the best evaluation of the P wave and QRS complex
• Occasionally, hair will need to be shaved to allow electrode placement
• Muscle movement will create artefact waveforms – keep the patient warm and ask the patient to remain still
• Monitoring can be achieved through adhesive defibrillation pads to allow prompt treatment of VT or VF. The monitor/defibrillator may require changing from displaying the monitor leads to the defibrillator pads and vice versa.
Diagnosis from cardiac monitors
The printout of the ECG should be inspected carefully to diagnose the cardiac rhythm and retained for transfer to the patient’s records on arrival at hospital. The time when the trace is recorded is essential information and should be added manually at the start of the record if this is not done automatically by the monitor. It is also good practice to write on the printed rhythm strip other relevant clinical information such as symptoms or blood pressure. Some monitors allow this information to be entered electronically.
Defibrillators
During defibrillation sufficient electrical energy is delivered to the surface of the chest to enable a current of electricity to depolarise a critical mass of the fibrillating myocardium, in the hope that orderly cardiac depolarisation ensues. Most defibrillators deliver a predetermined energy, measured in joules (J).
‘Hands-free’ defibrillation via adhesive pads is now standard across all models.
Types of defibrillator:
• Manual
• Semi-automatic (advisory)
• Fully automated.
• Manual Defibrillators: the operator interprets the cardiac rhythm, decides whether a defibrillatory countershock is required, charges the machine and administers the shock. Experience in ECG interpretation is required and training in the use of such devices is therefore more prolonged
• Semi-automatic defibrillator: the processes of rhythm recognition and charging for defibrillation are automated. All that is required of the operator is to recognise that cardiac arrest may have occurred, to attach two electrodes to the patient’s chest and to follow the instructions from the defibrillator if these seem appropriate. During the analysis period (which in most models is less than 10 seconds), no contact must be made with the patient to avoid the chance of movement artefact. Many models incorporate written on-screen instructions and some models also feature synthesised voice instructions to guide the operator
• Automated external defibrillators (AED) are accurate in the interpretation of shockable rhythms and only rarely is a DC shock advised inappropriately. An override key can be used to convert an automated external defibrillator into a manual one.
All prehospital defibrillators will run off batteries. Monitors that incorporate blood pressure monitoring will tend to use battery power quicker. Batteries should always be checked at the beginning of a shift and spares should be carried where possible. Biphasic defibrillators use less power and achieve more successful defibrillation. These are gradually replacing the older monophasic devices. Lower energy requirements are sometimes recommended – consult the manufacturer’s instructions.
Defibrillator safety
• It is essential that no part of the operator or any assistant is in electrical contact with the patient when the shock is administered
• The operator must shout ‘Stand clear! Shocking!’ and visually check that no person is touching the patient
• Intravenous fluid giving sets may act as a potential conductor and helpers should not be holding these while a shock is administered
• Defibrillation in the rain is normally safe, providing the chest is wiped dry first
• Patients lying in a pool of water should be moved before defibrillation and the carers must ensure they are not connected to the patient by standing in water
• Nitrate patches should be removed to reduce the risk of them igniting and causing severe burns
• Any oxygen source (e.g. bag-valve-mask) should be removed from the patient before administering each shock
• Patients with pacemakers should still be defibrillated – however, do not place the adhesive pad directly over the pacemaker box.
For further information, see Ch. 13 in Emergency Care: A Textbook for Paramedics.
