2) Consider an operating system capable of loading and executing a single sequential user process at a time. The disk head scheduling algorithm used is First Come First Served (FCFS). If FCFS is replaced by Shortest Seek Time First (SSTF), claimed by the vendor to give 50% better benchmark results, what is the expected improvement in the I/O performance of user programs? (GATE CS 2004) (A) 50% (B) 40% (C) 25% (D) 0% See this for solution.
Factors causing surgical site infection are multifarious. Several studies have identified the main patient-related (endogenous risk factors) and procedure-related (external risk factors) factors that influence the risk of SSI. The rate of surgical wound infections is strongly influenced by operating theatre quality, too. A safe and salubrious operating theatre is an environment in which all sources of pollution and any micro-environmental alterations are kept strictly under control. This can be achieved only through careful planning, maintenance and periodic checks, as well as proper ongoing training for staff.
operating system notes in hindi pdf 134
Many international scientific societies have produced guidelines regarding the environmental features of operating theatres (positive pressure, exchanges of filtered air per hour, air-conditioning systems with HEPA filters, etc.) and issued recommendations on healthcare-associated infection, including SSI, concerning surveillance methods, intervention to actively prevent SSI and approaches to monitoring the implementation of such strategies.
Occasionally, the pathogenic microorganisms are acquired from an exogenous source, such as the operating theatre environment, surgical personnel [23] and all tools, instruments, and materials brought to the sterile field during an operation.
The design of the operating unit is complex and requires that different areas be correctly integrated. In addition to keeping clean and dirty areas separate, it is important to ensure that patient flow, from arrival to discharge, is orderly and logical.
The operating unit should be arranged in progressively less contaminated areas, from the reception area to the operating theatres. Moreover, organisational/functional and/or structural intervention must be implemented in order to ensure that "dirty" and "clean" pathways be kept separate. The size of storage areas for dirty material, clean material, supplies, instruments, equipment and drugs must be determined in accordance with the type and volume of activity of the operating unit [29].
Moreover, in designing an operating unit, the choice of surface finishes, as well as structural features, is of great importance; surfaces should be easy to clean in order to facilitate infection control. Design, layouts, fittings, furnishings, floor coverings and finishes will have a significant impact on the cleaning of the unit. Ledges, corners and all other surfaces that are difficult to clean should be minimized.
The surfaces of floors should be impervious to moisture, easily cleaned, stain resistant, comfortable for long periods of standing and suitable for wheeled traffic. In the operating theatres the colour should be such that small items can easily be found, if dropped [30].
Therefore, maintaining a high quality of the air in the operating theatre is essential to controlling the risk of surgical infections. To reduce the morbidity and healthcare costs associated with these infections, airborne bacteria and other sources of contamination must be minimised.
In the operating theatre, the specific features of the airflow system which enable SSIs to be contained are ventilation (dilution), air distribution, room pressurization (infiltration barrier) and filtration (contaminant removal) [33].
The air in operating theatres should be kept at a higher pressure than in corridors and adjacent areas. This positive pressure prevents the flow of air from less sterile areas into more sterile ones [18].
With regard to ventilation, various international scientific organisations recommend a minimum of 15 air exchanges per hour. Specifically, the "Guidelines for environmental infection control in health-care facilities" issued by the CDC [34] recommend a minimum of about 15 exchanges of filtered air per hour, three (20%) of which must be fresh air. The 2008 edition of ANSI/ASHRAE/ASHE Standard 170 ("Ventilation of Health-care Facilities") [35], recommends a minimum of 20 total air exchanges per hour and a minimum of 4 exchanges of outdoor air per hour in operating theatres.
The main types of airflow systems are: turbulent-flow, unidirectional-flow and mixed-flow. Turbulent flow directly involves the whole environment, the concentration of airborne contaminants being controlled by means of dilution. This type of system increases the effectiveness of air exchange and distribution. However, it has the disadvantage of speeding up microbial dispersion [33]. In several countries, this type of airflow is generally considered adequate for operating theatres in which general surgery or similar operations are performed [29].
In unidirectional-flow systems ("laminar airflow or LAF"), the air travels in parallel lines and contaminants are carried away at the same velocity as the airflow. Low-velocity unidirectional flow tends to minimize the spread of airborne contaminants and direct them towards the exhaust outlets. This system, as opposed to turbulent flow, allows airborne particles to pass the operating area and prevents them from landing in the wound area [33].
Unidirectional airflow is designed to move particle-free air (called "ultraclean air") over the aseptic operating field at a uniform velocity (0.3 to 0.5 μm/sec), sweeping away particles in its path [18].
From a purely technical standpoint, systems that provide laminar flow regimes constitute the best option for an operating theatre, in terms of contamination control, as they result in the smallest percentage of particles impacting the surgical site.
Laminar airflow through HEPA filters, which display 99.97% efficiency in removing airborne particles of 0.3 μm and above, can be supplied to the operating area by ceiling-mounted (vertical flow) or wall-mounted (horizontal flow) units. It has been suggested [37, 38] that improper positioning of personnel in operating theatres with a horizontal and vertical laminar airflow may increase the risk of infection.
Charnley [39] evaluated 5,800 surgical operations; he showed that intraoperative contamination was a major threat to the success of total joint replacements, and revealed that the rate of SSI fell dramatically from 7 to 0.5% when unidirectional airflow regimes with a high number of hourly air exchanges were adopted and surgical staff wore special suits that covered the whole body. Subsequently, other studies [40-42] have shown that fewer infections arise when orthopaedic surgery is performed in operating theatres with ultra-clean air facilities.
Immunocompromised patients are particularly susceptible to infection by waterborne microorganisms, which can cause bacteraemia, pneumopathy, meningitis, urinary tract infections and surgical site infections [49-51]. Apart from water used in dental surgery, another area of environmental control in operating theatres is the bacteriological quality of water used for surgical handscrubs for which there are no standardized limits at present.
In general, the strategy for reducing intra-operative contamination involves a systemic and behavioural approach. As already seen, a systemic approach consists of improving the airflow system. A behavioural approach aims to reduce the number of airborne particles in the operating theatre through disciplinary measures. Simple and cheap measures include limiting the number of personnel in the operating theatre and restricting the movements of personnel in the operating theatre to a minimum, as it has been shown that increased activity facilitates the dispersion of bacteria [54].
In addition to the number and movements of personnel in the operating theatre, adverse surgical events may be due to poor communication, bad operative technique, malfunctioning or improperly used equipment, and cognitive errors due to stress or inattention, all compounded by resource and organizational problems. Communication in the operating suite is often poor and may contribute to adverse outcomes [55].
Knobben et al. [56] found that, in patients undergoing orthopaedic implant surgery, adopting a range of measures in the operating theatre had a significantly positive effect on outcomes during the postoperative period. In that study, the measures adopted involved limiting needless activity, correct use of plenum (area of laminar flow), work-up in the preparation room rather than in the operating theatre, and the wearing of proper attire. These Authors observed that the combination of systemic and behavioural measures in the operating theatre led to a reduction in the incidence of intra-operative bacterial contamination and, consequently, of prolonged wound discharge and superficial surgical site infection. Moreover, after one-year follow-up, fewer deep periprosthetic infections were recorded. While it is difficult to determine the relative influence of each individual measure on the final result, the combination of all these parameters evidently creates the most effective weapon against infections. To maintain low bacterial counts, both the airflow system and behaviour have to be monitored by an infection committee. Both positive and negative feedback helps to maintain the reduction in bacterial dispersal.
Finally, it is important to emphasize that all personnel working in operating theatres, including surgeons, operating theatre assistants, anaesthesiologists and cleaning personnel, must follow hygiene protocols very strictly.
Basically, the checklist includes three moments of formalized briefings and safety checks: a 'sign in' before induction of anaesthesia, a 'time out' before skin incision and a 'sign out' before the patient leaves the operating room. 2ff7e9595c
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