Central nervous system
Fluids ‘in’ vs. fluids ‘out’
Individual practices often have a standardised ‘minimum database’ of information that is gathered from emergency cases on admission. Where specific problems are suspected from physical examination, more specific monitoring can be performed and further laboratory information may be required, e.g. clotting times, slide saline auto-agglutination, blood gases, lactate levels.
Regular auscultation of the chest fields should be performed (see Practical techniques, Chapter 7) to detect any change in lung sounds. Lung sounds that have become muffled may indicate worsening pleural disease; an increase in lung sounds can indicate a worsening of lung or airway pathology.
Respiratory rate is useful as an indicator of respiratory disease. An increased rate could indicate a developing pneumothorax for instance, although an increase in respiratory rate (tachypnoea) can also be seen with pain, pyrexia, fear or abdominal distension.
An assessment of respiratory effort can be made by observation of the patient. Changes in posture can be indicative of increased effort: standing rather than sitting, extended neck, flared nostrils, open mouth breathing and increased abdominal movement may be seen.
Respiratory function can be considered adequate if partial pressures of both carbon dioxide and oxygen are within normal limits. The method of choice to monitor this is arterial blood gas analysis. Samples are usually obtained via an arterial catheter (see Chapter 3). Blood gas analysis measures the arterial partial pressure of oxygen (PaO2) (see Figure 2.2).
Pulse oximetery provides an estimate of the percentage of available haemaglobin that is carrying oxygen (oxygen saturation, SpO2) (see Figure 2.3). It does not reveal how the actual amount of oxygen is carried in the blood; this depends on the haemaglobin content. Oxygen saturation gives an idea of the efficiency of gaseous exchange from the inspired air in the alveoli into the body’s tissues. Care is required with the placement of the pulse oximetery probe, if left in place for too long it tends to compress tissue and give a false reading. Conscious animals can have the probe placed on toe webs, lips or ears rather than on the tongue.
Any animal with a reading of less than 95% SpO2 should receive oxygen supplementation. SpO2 values of 90% correspond to a PaO2 of 60 mmHg. Because of the nature of the oxygen saturation curve, below 60 mmHg there is a rapid drop in oxygen saturation, so aiming for an SpO2 of 95% or above gives some margin of safety.
Heart Rate and Rhythm
Heart rate can be measured by palpation of an apex beat, palpation of a pulse or auscultation with a stethoscope. Where abnormal rhythms are detected, a continuous electrocardiogram (ECG) should be carried out, and abnormalities recorded. While an ECG is useful to investigate rhythm disturbance, it only shows electrical activity. Just because there is a waveform does not mean there is an output at that point; it is always important to check pulses at the same time as auscultating the heart.
Pulses are commonly palpated on the femoral artery, but familiarity with palpating a metatarsal pulse is valuable. Much useful information is gathered from the rate, strength and characteristics of the palpable pulse.
A pulse should be present for each heart beat (see Figure 2.4). If this is not the case, or there are variations in pulse strength, then an ECG is necessary to identify rhythm disturbances.
Pulse rate and character are essential in detecting hypovolaemia and the response to treatment. Increasing pulse rate and decreasing amplitude are evidence of worsening hypovolaemia. The distal metatarsal pulse becomes non-palpable with moderate hypovolaemia, but should return if effective therapy is instituted (see Figure 2.5).
Importantly, what is palpated as the pulse amplitude is the difference between diastolic and systolic pressures (i.e. an animal with a systolic pressure of 100 mmHg and a diastolic pressure of 60 mmHg would have a similar pulse amplitude to an animal with 70/30 mmHg blood pressure); it cannot accurately measure actual blood pressure. Therefore the pulse needs to be considered in conjunction with measures of tissue perfusion and blood pressure readings.
Mucous Membranes and Capillary Refill Time
The mucous membrane colour (see Table 2.2) and capillary refill time (CRT) can help to give an idea of tissue perfusion and vasomotor tone. The oral mucosa is normally used as it is easiest to access. CRT tends to vary with an individual’s technique.
|Colour observed||Possible cause|
|Pale, white or grey||Poor perfusion, or anaemia|
|‘Brick red’ or ‘injected’||Vasodilation, systemic inflammatory response|
|Blue or purple||Cyanosis: low oxygen saturation of haemoglobin|
|Yellow||Increased blood bilirubin levels|
|Brown||Formation of methaemoglobin, e.g. paracetamol poisoning|
|Cherry red||Carbon monoxide poisoning|
A normal CRT is usually 1–1.75 s. A slower CRT suggests reduced blood flow in the tissue, often resulting from vasoconstriction with hypovolaemia, or heart failure. A more rapid CRT suggests increased blood present in the tissues; this may be due to vasodilation seen in sepsis.
Mucous membranes are normally pink, although healthy cats often have paler membranes than dogs.
The sole aim of the cardiovascular system is to deliver oxygenated blood to the tissues of the body. All tissues need a supply of oxygenated blood. Monitoring assesses the delivery of this blood to the capillary beds of the tissues. A range of parameters can help to form an overall picture of perfusion: