Wednesday, 09 October 2013
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Dear all, I hope this is a place where I can ask a question in the forum. WHO PQS-qualified refrigerators used frequently at the health facility level (E003) have a holding capacity measured by a particular WHO testing process. However, most fridges also have certain limitations on that holding capacity when used in practice. For example, the spatial geometry of the refrigerator or the ice-pack linings may result in unusuable dead space in the corners and edges. Also, shelf placement creates dead space in between vaccine carton packages. These conditions make it difficult to estimate the number of vials or doses of a particular vaccine that can fit in a fridge (including when given the secondary packaging's "dose-per-cc of cold chain space" measurements). What is a reasonable estimate for the number of vials that can fit in a fridge with a payload storage volume of x liters? What might be a variance on this value, and what does the variance depend on? Put another way, what is an estimate for the amount of so-called "dead space" in a fridge of volume x liters? Thanks very much in advance for this discussion.
10 years ago
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#2712
The issue raised is a relevant one. In addition to the inside geometry of the refrigerator, the configuration of vaccine packaging boxes also influences the effective use of storage space. The geometry and dimensions of packaging are different from different manufacturers. Since the vaccines have to be kept with the vial septum up, different boxes with different shapes (with same number of vials) will occupy different space in the same same fridge. The exact figures of the number of vials that can fit in a fridge with a specific inside layout, can be estimated based on a given configuration of vaccine packaging boxes. In the lack of these precise data, we use 2/3 as an indicative reduction factor of the net space stated for a fridge. So 1/3 of volume may be an empty space that includes dead space. Using this opportunity to call for more field feedback on this interesting subject. Souleymane Kone, World Health Organization
10 years ago
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#2714
Ryan raises a very important question. WHO PQS believes, but cannot yet give a figure, that the appropriate utilization factor should be different (and lower) in health facility refrigerators. In these settings, easy access to vaccines, storage of diluent, and the need to segregate opened and unopened vials, means that the close packing found in district and higher level refrigerators cannot be achieved with current refrigerator designs. Another major reason is that vaccine cartons frequently contain too many doses for them to be operationally useful in smaller health facilities - this is especially true of cartons containing multi-dose presentations. Consequently HF refrigerators frequently store vaccines and diluents as individual vials and countries adopt ad-hoc solutions by storing them in plastic boxes or trays; the attached photograph (from Anthony Battersby) shows one of these approaches (Kenya). Note also the presence of Oxytocin in a segregated area of this refrigerator (see parallel postings on this topic). The efficient use of space in HF refrigerators is an outstanding design problem that WHO PQS has identified as part of an on-going review of refrigerator specifications. As part of this review, we need to gather systematic field data on actual usage at sub-national and health facility level; any suggestions on how to do this would be welcome. Denis http://www.technet-21.org/images/agorapro/attachments/2489/mini_Kenya-fridge.jpg
10 years ago
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#2715
Thanks for bringing this topic. on 18 Nov 2012 I posted 'Operational way of calculating cold space requirement at a Planning unit level where all vaccines are to be kept in the Ice-Lined Refrigerator (ILR) between 2 to 8 degree C. In all workshops cold space required was expressed as ml/child for full vaccination which varied from 55 ml to 78 ml excluding/including HepB/diluent. As per this it was estimated that a planning unit with one lakh population at 25 birthrate (2500 live births per yr, average of 208 children per month, @ 78 ml per child-cold space required was calculated as 16 liter viz one basket space in the ILR with an assumption that all children come to one place at one time in a month). But in reality the cited planning unit with about 98000 population conducts 131 sessions per month requiring minimum of one vial per session + 25% buffer stalk. Thus there is a huge gap between theory and (practical) reality. Details are in the post.
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