Blood and plasma volumes are markedly influenced by the physical activity, hydration status and posture of the subject prior to sample collection. The sampling site and method can also affect the haemoglobin concentration, as arterial, capillary and venous samples differ in a number of respects due to fluid exchange between the vascular and extravascular spaces and to differences in the distribution of red blood cells (Harrison, 1985).
The venous plasma to red cell ratio is higher than that of arterial blood, although the total body haemoglobin content is clearly not acutely affected by these factors. Haemodynamic changes caused by postural shifts will alter the fluid exchange across the capillary bed, leading to plasma volume changes that will cause changes in the circulating concentration. On going from a supine position to standing, plasma volume falls by about 10% and whole blood volume by about. This corresponds to a change in the measured haemoglobin concentration of about
SAFETY ISSUES
Whatever method is used for the collection of blood samples, the safety of the subject and of the investigator is paramount. Strict safety precautions must be followed at all times in the sampling and handling of blood. It is wise to assume that all samples are infected and to treat them accordingly. This means wearing gloves and appropriate protective clothing and following guidelines for handling of samples and disposal of waste material.
Appropriate antiseptic procedures must be followed at all times, including ensuring cleanliness of the sampling environment, cleaning of the puncture site and use of clean materials to staunch bleeding after sampling. Blood sampling should be undertaken only 28 RON MAUGHAN ET AL. by those with appropriate training and insurance cover, and a qualified first-aider should be available at all times. All contaminated materials must be disposed of using appropriate and clearly identified waste containers
REFERENCES AND FURTHER READING
What is it to behave in an ethical manner as a researcher? The term ‘ethics’ suggests a set of standards by which behaviour is regulated, and these standards help us to decide what is acceptable in terms of pursuing our aims, as well as helping us to distinguish between right and wrong acts.
The principal question of ethics is ‘What ought I do? Broadly speaking ethical actions are derived from principles and values, which are in turn derived from ethical theories. The major ethical theories are briefly introduced here for two reasons: to enable researchers to identify where principles are derived from, and to facilitate deeper thought on how potential actions may be justified.
INFORMED CONSENT
A central feature of modern biomedical research ethics is the notion of obtaining first person, written, voluntary informed consent from research participants. Given that it is a required element of most projects, researchers need to be aware of what the concept involves.
First informed implies that potential participants (or their legal representatives) obtain sufficient information about the project. This information must be presented in such a way that it is matched to the appropriate comprehension level (see Olivier and Olivier, 2001. and Cardinal, 2000, for further details on establishing comprehension levels), enabling participants to evaluate and understand the implications of what they are about to agree to. Second, consent implies free, voluntary agreement to participation, without coercion or unfair inducement.
