MEDICAL GAS SYSTEMS
we obtain the design flow and diversified flow formulas for the operating theatre suite (see Table 1). So, in this case study, the total diversified flow for this operating theatre suite is 182 L/min. In practical terms the anaesthetic workstation in the anaesthetic or induction room will not be in use at the same time as the unit in the operating theatre; hence no addition is made in the diversified flow. Yet with adoption of low- flow techniques outlined above (flow rates of 0.2–0.4 L/min), and the technology of electrically-driven piston ventilators, the oxygen requirement will be significantly less. It is likely that the requirements for oxygen in the post- anaesthesia recovery area have not changed – essentially flowmeters with a standard vented mask. Turning to N2
Table 13,3 O from HTM 02-01 Part A Table 153 for operating theatres, the
diversified flow is given as: Q = 15+(nT–1)x6 So, for our case study: Q = 15+(4–1)x6 = 33 LPM
Changes in clinical practice Looking back to the changes in clinical practice, we can see that the N2
put on a ventilator, the gases specified in HTM 02-01 Part A Table 113
are four O is not
often used, and plans are ongoing to reduce or eliminate its use in anaesthetics. If we now consider that the patient is transferred to the Critical Care Unit and
Oxygen, Medical air, and Vacuum terminal units per bedspace, split between two circuits. Medical Air at 4 bar (MA4) and oxygen have traditionally been used for patient ventilators. In recent years we have seen a move to patient ventilators entraining air from the atmosphere via a High Efficiency Particulate Air (HEPA) filter. In order to draw in sufficient air for the high flow rates required for non- invasive ventilation, and the leaks around
the mask, a turbine is employed. On this basis, therefore, there may be little or no requirement for MA4 in a Critical Care Unit, and thus there is an opportunity for fewer terminal units.
Figure 3: A large animal ventilator.
Veterinary medical gases Veterinary practices use anaesthetic gases for surgical procedures on a range of animals – from the domestic cat to rear breeds of animals – in a similar way to the healthcare sector. Owners of thoroughbred racehorses, for example, are willing to invest in expensive surgery to keep their animals healthy. In larger veterinary practices or veterinary groups, and particularly those offering specialist orthopaedic surgery, medical gas pipeline systems are being installed based on the HTM guidance. However, the HTM, and much of the medical equipment, have been designed for human use, and the requirements of larger animals may differ dramatically. For example, a recent study7
found that the tidal volume (Vt) of an anesthetised horse was from 4 litres (8 mL/kg) to 10 litres (20 mL/kg), in comparison to an adult human, where the tidal volume is approx. 0.5 litres. Figure 3 shows a photograph of a large animal ventilator, which comprises a huge bellows capable of delivering a tidal volume of up to 20 litres. Clearly, this could dramatically influence the design
January 2022 Health Estate Journal 61
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