OAA Small Project Grant
The performance of leucocyte filters for the safe retransfusion of unwashed blood salvaged at caesarean section in resource-poor situations
Dr Jeremy Campbell
Background: This is the second of a multi-part study to determine if a leucocyte filter may provide benefit for the safe re-transfusion of salvaged blood in obstetrics in the resource-poor situation. In global terms, haemorrhage remains one of the most important causes of maternal mortality, accounting for 11% of all maternal deaths. The World Health Organization (WHO) estimates a 1% case fatality rate for the 14 million annual cases of obstetric haemorrhage. In developing countries, the problem of haemorrhage is compounded by a lack of access to safe donated blood. In order to reduce the transfusion of donated blood and its associated risks (transfusion reactions, transmission of infection), cell salvage is being used increasingly in many surgical specialties. In obstetrics, cell salvage has previously been contraindicated because of concerns over contamination of
salvaged blood with amniotic fluid, leading to the syndrome of amniotic fluid embolism (AFE) when this blood is re-transfused. Components of amniotic fluid which have been postulated to cause AFE include lamellar bodies (phospholipids derived from fetal lung), fetal squames, meconium, trophoblastic tissue, fetal hair and mucin, tissue factor, alpha-fetoprotein and endothelin I, although the actual role of amniotic fluid components in the syndrome is uncertain and has been questioned. In a recent pilot study, we have shown that using a leucocyte filter alone (i.e. without the expensive cell washing process) is efficient at removing these components from pure amniotic fluid. However, we do not know to what extent a leucocyte filter alone would remove these same components from unwashed blood which is contaminated with amniotic fluid.
Aims: This project will investigate the efficacy of a leucocyte filter alone (without the expensive cell washing process) on blood contaminated with amniotic fluid which has been salvaged during caesarean section.
Methodology: This will be an observational study, with unfiltered samples of blood acting as controls and filtered samples as test samples. Samples of blood contaminated with amniotic fluid, each of 150ml, will be taken in 10 cases of planned caesarean section after delivery of the fetus. Each sample will then be divided into two. One half will be a control (pre-filtered sample) and the other half will be passed through a leucocyte filter (post-filtered sample). The pre-filtered samples will then be compared to the post-filtered samples, and appropriate statistical tests will be used to determine the efficacy of the filter in removing various components of amniotic fluid from the samples.
Implications:
If the study shows that leucocyte filters are efficient at removing components of amniotic fluid from unwashed blood, it could have massive implications for parturients in the developing world, where local resources cannot provide a safe supply of stored donated blood. A further study would then be performed to investigate the potential for leucocyte filters to provide lifesaving benefit in the developing world.
Does a 30° head up position in term parturients with a BMI >= 35kg/m2 increase FRC?
Dr Roshan Fernando
Every 3 years in the UK, a report is published looking in depth at the number of deaths and the reasons why women die in pregnancy and childbirth. Obesity, or being overweight during pregnancy, is repeatedly highlighted as being associated with a much higher risk of complications. It is also associated with a significantly higher chance of needing a caesarean section (an operation for the delivery of the baby), compared to other patients who are not overweight. In the emergency situation, when there is an immediate risk to the wellbeing of the mother or baby, it is sometimes necessary to perform a caesarean section under general anaesthesia. Although general anaesthesia for caesarean section is usually very safe, the risks associated with it are higher if you are overweight or obese. The reason for this is that when the anaesthetist delivers the general anaesthetic, there is a period of time after you go to sleep, before the anaesthetist is able to take over the breathing. This period of time is usually very short and insignificant. However, in the pregnant patient who is overweight or obese, even this short period of time may result in lowering of oxygen levels to mother and the baby. Therefore it is important to try and increase the reserve of oxygen in the body before sending pregnant patients off to sleep. It is well known that by keeping patients in an upright sitting position prior to sending them off to sleep, we can increase this reserve of oxygen. This reserve of oxygen in the lungs is called the functional residual capacity (FRC), and it can be measured very easily. The method we will be using is called the helium dilution method. This technique is routinely used in pregnant patients who need tests of their lung function. It is an extremely safe and accurate technique. The technique requires the patient to breathe normally into a piece of apparatus via a mouthpiece, very similar to that of a snorkel. The test is complete when the concentration of helium in the apparatus is the same as in the lungs, and from this we can get a value for the volume of the FRC. We will be measuring this lung volume in 3 positions, lying flat, slightly head up, and erect sitting positions. We have previously done an identical study that has demonstrated this benefit in healthy term pregnant patients. We are now hoping to repeat the same study, but in obese pregnant patients, to see if by maintaining a more upright position we can increase the FRC to the same extent. In this way we will be able to assess whether there is any benefit in delivering oxygen prior to a general anaesthetic in either of the more upright positions in the obese pregnant patient. If the volume of FRC measured is higher in the more upright position, this may enable additional oxygen to be stored in the lungs prior to general anaesthesia. This would improve the safety of women undergoing general anaesthesia for caesarean section, in the future.
Changes in cytokines and neurotrophins in cerebrospinal fluid during labour pain
Dr Kevin McCarthy
Background: The experience of pain can vary significantly for different people and is difficult to predict. Pain is transmitted along a chain of neurons to the conscious brain, like cables carrying electricity. This transmission can be amplified by other cells called glia, which were thought to act as the insulation around neurons but are now known to amplify the signals that neurons carry. There is strong experimental evidence that glia have a role in maintaining persistent chronic pain long after any tissue injury. Cytokines and neurotrophins are two classes of messengers that neurons and glia use to communicate with each other. These are akin to e-mails or text messages that cells send and respond to. By looking at the patterns of expression, we hope to decode this language to see which signals are associated with severe pain, both in labour and in women undergoing elective caesarean section.
Methods: We intend to look at the levels of these markers in the spinal fluid of women in labour and those undergoing caesarean section. By comparing these two groups we can distinguish which changes are due to pregnancy and which are specific to being in labour. We will also compare levels of these markers to questionnaires which record pain, pain-related anxiety and sleep disturbance to see if there are relationships between these messengers and clinical findings.
