, Amy Gospel2, Andrew Griffiths3 and Jeremy Henning4
Intensive Care Unit, James Cook University Hospital, Middlesbrough, UK
Tyne and Wear, UK
The York Hospital, Middlesbrough, UK
James Cook University Hospital, Middlesbrough, UK
By the end of this chapter you should know:
What constitutes minimum monitoring standards.
The equipment required to safely carry out pre-hospital anaesthesia (PHA).
How to set a ventilator.
How to perform an oxygen requirement calculation.
As with all forms of anaesthesia the most important monitor of patient well-being is the close attention of the clinician delivering it. Simple, but essential clinical measurement and monitoring should include:
Pulse, rate and character (weak or strong); this may include distal pulses
Pupil size and reactivity
Presence or absence of muscular activity and limb movement
In addition to this, electro-medical monitors markedly improve the safety of anaesthesia, especially in austere and confined environments. For this reason the minimum monitoring standard to undertake PHA and onward patient transfer must be the same as in-hospital anaesthesia, and this is outlined in the Association of Anaesthetists and the Intensive Care Society safety guidance on Pre-hospital Anaesthesia (2000, 2009) (Whiteley et al. 2002) (Box 6.1).
Box 6.1: Minimum Monitoring Standards (Fig. 6.1)
Lifepak 15 monitor with SpO2, ECG, NIBP & ETCO2
Continuous ECG monitoring
Non-invasive blood pressure (NIBP)
End-Tidal Carbon dioxide (ETCO2) measurement
Exceptionally it may be necessary to reduce this level of monitoring during the extrication of trapped patients, but full monitoring must be re-established at the earliest opportunity. A small battery powered pulse oximeter that clips onto a finger will at least provide heart rate and pulse oximetry. The absence of monitoring equipment is a strong contra-indication to pre-hospital anaesthesia. In the case of equipment failure a risk-benefit analysis should be undertaken to determine whether anaesthesia is still appropriate and the decision clearly written in the patient’s notes.
NIBP measurements should be taken at least every 3 min during and following pre-hospital anaesthesia. It is important to be aware that frequent NIBP cycling may be a significant drain on a monitor battery. Batteries should be conditioned and maintained as per the manufacturers instructions and at least one spare should always be carried. Invasive arterial pressure monitoring uses far less energy, however this is impractical in most circumstances due to the additional time required to perform and set-up.
In addition to manual documentation of monitoring measurements, most monitors should now provide the ability to record, review and either download or print readings for future reference.
ETCO2 measurement must be quantitative (i.e. provide an accurate numeric value). A capnograph is the gold standard, as this provides a reassuring visual display of each breath and can be an additional sign of ventilator disconnection. Lightweight, battery powered, portable monitors are commercially available (e.g. Capnocheck® (Fig. 6.2)), although most pre-hospital defibrillator monitors now include waveform capnography as one of their functions. They use infra-red absorbance spectroscopy to determine the presence and quantity of CO2 in the exhaled breath. Monitors generally display this information as a figure and as a waveform. The waveforms can be useful for the recognition of trends in ventilation and diagnosing ventilatory problems. The shape of the trace can indicate problems such as a patient starting to breathe against the ventilator, or obstructive breathing (kinked tubing or bronchospasm (Fig. 5.1)). Some devices may need regular calibration.
Capnocheck II battery powered capnograph
A capnometer (e.g. EMMATM (Fig. 6.3)) is the next best option. This will give an accurate figure to guide ventilation, but no waveform. The final option is a qualitative ETCO2 device. These only provide evidence of the presence of CO2 and usually an idea of whether this is high or low, typically by colour change (e.g. Easy Cap®(Figs. 6.4 and 6.5)). They are disposable and consist of a filter paper impregnated with a pH-sensitive, non-toxic chemical indicator that reversibly changes colour on contact with CO2. The Easy Cap® provides a breath to breath colour change from purple on inspiration to yellow on expiration, confirming the presence of CO2 in the exhaled breath. Qualitative devices are only really suitable for confirmation of tracheal placement of a tube in the absence or failure of a quantitative device, and should be replaced as soon as possible.
Easy Cap II – CO2 present
Easy Cap II – CO2 absent
6.2 Other Equipment
All equipment used in the pre-hospital setting must be fit for purpose. It should be designed to allow it to be clinically effective, whilst meeting the demands of the operator. Of particular importance in pre-hospital use, it must be portable, robust and functional in a range of weather and environmental conditions. Visualisation of monitor screens must be possible from bright sunlight to darkness, and controls need to be both intuitive and easy to operate. Measurements should not be disturbed by vibration during transport; this is particularly relevant when travelling by helicopter. Alarm functions should involve multimodal alerting (e.g. noise and flashing lights) to overcome high ambient noise levels during transfer and bright light on scene. It should be noted that too many ‘nuisance’ alarms may distract from critical problems, and alarm limits may need amending to prevent this.