After WTG Morton's first public demonstration in 1846 of use of ether as an anaesthetic agent, for many years anaesthesiologists did not require a machine to deliver anaesthesia to the patients. After the introduction of oxygen and nitrous oxide in the form of compressed gases in cylinders, there was a necessity for mounting these cylinders on a metal frame. This stimulated many people to attempt to construct the anaesthesia machine. HEG Boyle in the year 1917 modified the Gwathmey's machine and this became popular as Boyle anaesthesia machine. Though a lot of changes have been made for the original Boyle machine still the basic structure remains the same. All the subsequent changes which have been brought are mainly to improve the safety of the patients. Knowing the details of the basic machine will make the trainee to understand the additional improvements. It is also important for every practicing anaesthesiologist to have a thorough knowledge of the basic anaesthesia machine for safe conduct of anaesthesia.
Anaesthesia machine; basic design; boyle machine; conventional flow meter; evolution and history; yoke assembly
Over the years, the conventional anaesthesia machine has evolved into an advanced carestation. The new machines use advanced electronics, software and technology to offer extensive capabilities for ventilation, monitoring, inhaled agent delivery, low-flow anaesthesia and closed-loop anaesthesia. They offer integrated monitoring and recording facilities and seamless integration with anaesthesia information systems. It is possible to deliver tidal volumes accurately and eliminate several hazards associated with the low pressure system and oxygen flush. Appropriate use can result in enhanced safety and ergonomy of anaesthetic delivery and monitoring. However, these workstations have brought in a new set of limitations and potential drawbacks. There are differences in technology and operational principles amongst the new workstations. Understand the principles of operation of these workstations and have a thorough knowledge of the operating manual of the individual machines.
Gas delivery; monitoring; ventilation; workstation
Vapourisers have evolved from rudimentary inhalers to the microprocessor controlled, temperature compensated and flow sensing devices, which are universal today. The improvements in the design was influenced by the development of potent inhalational anaesthetics, unique properties of some agents, a deeper understanding of their mechanism of action, inherent flaws in the older vapourisers, mechanical problems due to thymol deposition, factors influencing their output such as temperature and pressure variations. It is important to review the principles governing the design of the vapouriser to gain insight into their working. It is fascinating to know how some of the older vapourisers, popularly used in the past, functioned. The descendant of Oxford Miniature Vapourizer, the Triservice vapouriser is still a part of the military anaesthesia draw over equipment meant for field use whereas the Copper Kettle the first precision device is the fore-runner of the Tec 6 and Aladdin cassette vapouriser. Anaesthesia trainees if exposed to draw over techniques get a deeper understanding of equipment and improved skills for disaster situations. In the recent advanced versions of the vapouriser a central processing unit in the anaesthetic machine controls the operation by continuously monitoring and adjusting fresh gas flow through the vapouriser to maintain desired concentration of the vapour.
Anaesthesia equipment; history of vapouriser; principles of vapourisers; the development of vapourisers; understanding vapourisers; vapouriser
Inhalational anaesthetic agents are usually liquids at room temperature and barometric pressure and need to be converted to vapour before being used and this conversion is effected using a vapouriser. Vapourisers have evolved from very basic devices to more complicated ones. Anaesthetists should understand the basic principles of anaesthetic vapouriser, including the principles that affect vapouriser output and how they influence vapouriser design. Most of the modern vapourisers in use are designed to be used between the flow meter and the common gas outlet on the anaesthesia machine. Modern vapourisers are flow and temperature compensated, concentration calibrated, direct reading, dial controlled and are unaffected by positive-pressure ventilation. Safety features include an anti-spill and a select-a-tec mechanism and a specific vapouriser filling device. Desflurane has unique physical properties requiring the use of a specific desflurane vapouriser. The most recently designed vapourisers are controlled by a central processing unit in the anaesthetic machine. The concentration of vapour is continuously monitored and adjusted by altering fresh gas flow through the vapouriser. This article looks at the basic design and functioning of the modern vapourisers.
Aladin cassettes; desflurane vapouriser; direct injection of volatile anesthetic; measured flow vapouriser; plenum vapouriser
Anaesthesia is one of the few sub-specialties of medicine, which has quickly adapted technology to improve patient safety. This application of technology can be seen in patient monitoring, advances in anaesthesia machines, intubating devices, ultrasound for visualisation of nerves and vessels, etc., Anaesthesia machines have come a long way in the last 100 years, the improvements being driven both by patient safety as well as functionality and economy of use. Incorporation of safety features in anaesthesia machines and ensuring that a proper check of the machine is done before use on a patient ensures patient safety. This review will trace all the present safety features in the machine and their evolution.
Anaesthesia machine; hypoxia prevention; safety features
The technical advancement in the anaesthesia workstations has made the peri-operative anaesthesia more safer. Apart from other monitoring options, respiratory gas analysis has become an integral part of the modern anaesthesia workstations. Monitoring devices, such as an oxygen analyser with an audible alarm, carbon dioxide analyser, a vapour analyser, whenever a volatile anaesthetic is delivered have also been recommended by various anaesthesia societies. This review article discusses various techniques for analysis of flow, volumes and concentration of various anaesthetic agents including oxygen, nitrous oxide and volatile anaesthetic agents.
Anaesthesia machine; gas analyser; gas flows; gas volumes; oxygen analyser; volatile agent analyser
The anaesthesia gas supply system is designed to provide a safe, cost-effective and convenient system for the delivery of medical gases at the point of-use. The doctrine of the anaesthesia gas supply system is based on four essential principles: Identity, continuity, adequacy and quality. Knowledge about gas supply system is an integral component of safe anaesthetic practice. Mishaps involving the malfunction or misuse of medical gas supply to operating theatres have cost many lives. The medical gases used in anaesthesia and intensive care are oxygen, nitrous oxide, medical air, entonox, carbon dioxide and heliox. Oxygen is one of the most widely used gases for life-support and respiratory therapy besides anaesthetic procedures. In this article, an effort is made to describe the production, storage and delivery of anaesthetic gases. The design of anaesthesia equipment must take into account the local conditions such as climate, demand and power supply. The operational policy of the gas supply system should have a backup plan to cater to the emergency need of the hospital, in the event of the loss of the primary source of supply.
Cylinders; manifolds; medical gases; pipelines; vacuum-insulated evaporators
Invention of oxygen cylinder was one of the most important developments in the field of medical practice. Oxygen and other gases were compressed and stored at high pressure in seamless containers constructed from hand-forged steel in1880. Materials technology has continued to evolve and now medical gas cylinders are generally made of steel alloys or aluminum. The filling pressure as well as capacity has increased considerably while at the same time the weight of cylinders has reduced. Today oxygen cylinder of equivalent size holds a third more oxygen but weighs about 20 kg less. The cylinders are of varying sizes and are color coded. They are tested at regular intervals by the manufacturer using hydraulic, impact, and tensile tests. The top end of the cylinder is fitted with a valve with a variety of number and markings stamped on it. Common valve types include: Pin index valve, bull nose, hand wheel and integral valve. The type of valve varies with cylinder size. Small cylinders have a pin index valve while large have a bull nose type. Safety features in the cylinder are: Color coding, pin index, pressure relief device, Bodok seal, and label attached etc., Safety rules and guidelines must be followed during storage, installation and use of cylinders to ensure safety of patients, hospital personnel and the environment.
Cylinders; installation of cylinders; medical and anaesthetic gases; pin index safety system; safety devices; testing; valves
Mapleson breathing systems are used for delivering oxygen and anaesthetic agents and to eliminate carbon dioxide during anaesthesia. They consist of different components: Fresh gas flow, reservoir bag, breathing tubes, expiratory valve, and patient connection. There are five basic types of Mapleson system: A, B, C, D and E depending upon the different arrangements of these components. Mapleson F was added later. For adults, Mapleson A is the circuit of choice for spontaneous respiration where as Mapleson D and its Bains modifications are best available circuits for controlled ventilation. For neonates and paediatric patients Mapleson E and F (Jackson Rees modification) are the best circuits. In this review article, we will discuss the structure of the circuits and functional analysis of various types of Mapleson systems and their advantages and disadvantages.
Anaesthesia breathing systems; anaesthesia circuits; bain's circuit; magill's circuit; mapleson breathing systems; jackson-rees modification
A breathing system is defined as an assembly of components, which delivers gases from the anesthesia machine to the patients’ airways. When the components are arranged as a circle, it is termed a circle system. The flow of exhaled gases is unidirectional in the system. The system contains a component (absorber), which absorbs exhaled carbon dioxide and it is not necessary to give high fresh gas flows as in Mapleson systems. When the adjustable pressure limiting (APL) valve is closed and all the exhaled gases without carbon dioxide are returned to the patient, the system becomes a totally closed one. Such a circle system can be used with flows as low as 250 to 500 mL and clinically can be termed as low-flow systems. The components of the circle system can be arranged in different ways with adherence to basic rules: (1) Unidirectional valve must be present between the reservoir bag and the patient on both inspiratory and expiratory sides; (2) fresh gas must not enter the system between the expiratory unidirectional valve and the patient; and (3) the APL valve must not be placed between the patient and the inspiratory unidirectional valve. The functional analysis is explained in detail. During the function, the arrangement of components is significant only at higher fresh gas flows. With the introduction of low resistance valves, improved soda lime canisters and low dead space connectors, the use of less complicated pediatric circle systems is gaining popularity to anesthetize children. There are bidirectional flow systems with carbon dioxide absorption. The Waters to and fro system, a classic example of bidirectional flow systems with a canister to absorb carbon dioxide, is valveless and portable. It was widely used in the past and now is only of historical importance.
Anesthesia; circle system; closed system; low flow
Anaesthesia ventilators are an integral part of all modern anaesthesia workstations. Automatic ventilators in the operating rooms, which were very simple with few modes of ventilation when introduced, have become very sophisticated with many advanced ventilation modes. Several systems of classification of anaesthesia ventilators exist based upon various parameters. Modern anaesthesia ventilators have either a double circuit, bellow design or a single circuit piston configuration. In the bellows ventilators, ascending bellows design is safer than descending bellows. Piston ventilators have the advantage of delivering accurate tidal volume. They work with electricity as their driving force and do not require a driving gas. To enable improved patient safety, several modifications were done in circle system with the different types of anaesthesia ventilators. Fresh gas decoupling is a modification done in piston ventilators and in descending bellows ventilator to reduce th incidence of ventilator induced volutrauma. In addition to the conventional volume control mode, modern anaesthesia ventilators also provide newer modes of ventilation such as synchronised intermittent mandatory ventilation, pressure-control ventilation and pressure-support ventilation (PSV). PSV mode is particularly useful for patients maintained on spontaneous respiration with laryngeal mask airway. Along with the innumerable benefits provided by these machines, there are various inherent hazards associated with the use of the ventilators in the operating room. To use these workstations safely, it is important for every Anaesthesiologist to have a basic understanding of the mechanics of these ventilators and breathing circuits.
Anaesthesia ventilators; circle system changes; classification; hazards; working principle
From a simple pneumatic device of the early 20th century, the anaesthesia machine has evolved to incorporate various mechanical, electrical and electronic components to be more appropriately called anaesthesia workstation. Modern machines have overcome many drawbacks associated with the older machines. However, addition of several mechanical, electronic and electric components has contributed to recurrence of some of the older problems such as leak or obstruction attributable to newer gadgets and development of newer problems. No single checklist can satisfactorily test the integrity and safety of all existing anaesthesia machines due to their complex nature as well as variations in design among manufacturers. Human factors have contributed to greater complications than machine faults. Therefore, better understanding of the basics of anaesthesia machine and checking each component of the machine for proper functioning prior to use is essential to minimise these hazards. Clear documentation of regular and appropriate servicing of the anaesthesia machine, its components and their satisfactory functioning following servicing and repair is also equally important. Trace anaesthetic gases polluting the theatre atmosphere can have several adverse effects on the health of theatre personnel. Therefore, safe disposal of these gases away from the workplace with efficiently functioning scavenging system is necessary. Other ways of minimising atmospheric pollution such as gas delivery equipment with negligible leaks, low flow anaesthesia, minimal leak around the airway equipment (facemask, tracheal tube, laryngeal mask airway, etc.) more than 15 air changes/hour and total intravenous anaesthesia should also be considered.
Anaesthesia machine; anaesthesia workstation; checklist; hazards; scavenging
The main purpose of this review article is to bring up what has been known (practiced) about decontamination, disinfection, and sterilisation of anaesthetic equipment. It also discusses how this evidence-based information on infection prevention and control impacts care of patient in routine anaesthesia practice. This review underscores the role played by us, anaesthetists in formulating guidelines, implementing the same, monitoring the outcome and training post-graduate trainees and coworkers in this regard. The article re-emphasises that certain guidelines when followed strictly will go a long way in reducing transmission of hospital acquired infection between patient and anaesthetist or between patients. Anaesthetists do not restrict their work to operating room but are involved in disaster management, interventional radiological procedures and in trauma care. They should ensure that the patients are cared for in clean and safe environment so as to reduce healthcare associated infections (HCAIs) simultaneously taking preventive measures against the various health hazards associated with clinical practice. They should ensure that the coworkers too adopt all the preventive measures while delivering their duties. For this review, we conducted literature searches in Medline (PubMed) and also searched for relevant abstracts and full texts of related articles that we came across. There is much to be learned from the western world where, health care organisations now have legal responsibility to implement changes in accordance with the newer technology to reduce health care associated infection. There is a need to develop evidence-based infection prevention and control programs and set national guidelines for disinfection and sterilisation of anaesthesia equipment which all the institutions should comply with.
Anaesthetic equipment; decontamination; disinfection; sterilisation
The advantages of video assisted thoracoscopic surgery (VATS) in children have led to its increased usage over the years. VATS, however, requires an efficient technique for one lung ventilation. Today, there is an increasing interest in developing the technique for lung isolation to meet the anatomic and physiologic variations in infants and children. This article aims to provide an updated and comprehensive review on one-lung ventilation strategies for infants and children undergoing VATS. Search of terms such as ‘One lung ventilation for infants and children’, ‘Video assisted thoracoscopic surgery for infants and children’, and ‘Physiologic changes during one lung ventilation for infants and children’ were used. The search mechanics and engines for this review included the following: Kandang Kerbau Hospital (KKH) eLibrary, PubMed, Ovid Medline, Cochrane Central Register of Controlled Trials, and Cochrane Database of Systematic Reviews. During the search the author focused on significant current and pilot randomized control trials, case reports, review articles, and editorials. Critical decision making on what device to use based on the age, weight, and pathology of the patient; and how to use it for lung isolation are discussed in this article. Furthermore, additional information regarding the advantages, limitations, techniques of insertion and maintenance of each device for one lung ventilation in infants and children were the highlights in this article.
Balloon-tipped bronchial blockers; double lumen endobronchial tubes; infants and children; one lung ventilation; univent tubes; video assisted thoracoscopic surgery
During the inhalation of anaesthesia use of low fresh gas flow (0.35-1 L/min) has some important advantages. There are three areas of benefit: pulmonary - anaesthesia with low fresh gas flow improves the dynamics of inhaled anaesthesia gas, increases mucociliary clearance, maintains body temperature and reduces water loss. Economic - reduction of anaesthesia gas consumption resulting in significant savings of > 75% and Ecological - reduction in nitrous oxide consumption, which is an important ozone-depleting and heat-trapping greenhouse gas that is emitted. Nevertheless, anaesthesia with high fresh gas flows of 2-6 L/min is still performed, a technique in which rebreathing is practically negligible. This special article describes the clinical use of conventional plenum vaporizers, connected to the fresh gas supply to easily perform low (1 L/min), minimal (0.5 L/min) or metabolic flow anaesthesia (0.35 L/min) with conventional Primus Draeger® anaesthesia machines in routine clinical practice.
Closed-circuit anaesthesia; inhalation anaesthesia; quantitative closed circuit anaesthesia
Correlation between the clinical and electroencephalogram-based monitoring has been documented sporadically during the onset of sedation. Propofol and midazolam have been studied individually using the observer's assessment of awareness/sedation (OAA/S) score and Bispectral index score (BIS). The present study was designed to compare the time to onset of sedation for propofol and midazolam using both BIS and OAA/S scores, and to find out any correlation.
A total of 46 patients (18-60 years, either sex, American Society of Anesthesiologists (ASA) I/II) posted for infraumbilical surgeries under spinal anaesthesia were randomly allocated to receive either injection propofol 1 mg/kg bolus followed by infusion 3 mg/kg/h (Group P, n=23) or injection midazolam 0.05 mg/kg bolus followed by infusion 0.06 mg/kg/h (Group M, n=23). Spinal anaesthesia was given with 2.5 ml to 3.0 ml of 0.5% bupivacaine heavy. When sensory block reached T6 level, sedation was initiated. The time to reach BIS score 70 and time to achieve OAA/S score 3 from the start of study drug were noted. OAA/S score at BIS score 70 was noted. Data from 43 patients were analyzed using SPSS 12 for Windows.
Time to reach BIS score 70 using propofol was significantly lower than using the midazolam (P<0.05). Time to achieve OAA/S score 3 using propofol was comparable with midazolam (P=0.358).
A divergence exists between the time to reach BIS score 70 and time to achieve OAA/S score 3 using midazolam, compared with propofol, during the onset of sedation.
Bispectral index score; midazolam; observer's assessment of awareness/sedation score; propofol; sedation
Maintenance of adequate depth of anaesthesia in spine surgery is vital to prevent awareness, to reduce stress response and possible autonomic instability frequently associated with spine surgery. Dexmedetomidine, a α2-adrenoceptor agonist with analgesic and sedative adjuvant property has been found to reduce dose requirement of multiple anaesthetic agents both for induction and during the maintenance of anaesthesia.
The aim of this study is to observe the effect of dexmedetomidine, on the requirement of propofol for induction and maintenance of adequate depth of anaesthesia during spine surgery.
It was a prospective, randomised, double-blinded, parallel group, placebo controlled and open-lebel study in tertiary care hospital. A total of 70 patients aged 20-60 years, American Society of Anaesthesiologists GradeI and II, scheduled for elective spine surgery were randomly allocated into two groups. Each patient of Group D (n=35) received an initial loading dose of dexmedetomidine at 1 μg/kg over 10 min, started 15 min before induction of anaesthesia followed by an infusion at a rate of 0.2 μg/kg/h. Patients of Group P (n=35) received the same volume of 0.9% normal saline solution as placebo. Requirement of propofol at induction and during maintenance was calculated maintaining bispectral index between 40 and 60. P<0.05 was considered to be statistically significant.
Mean requirement of propofol was found to be lessened by 48.08% and 61.87% for induction and maintenance of anaesthesia respectively while using dexmedetomidine.
Administration of dexmedetomidine significantly reduces the requirement of propofol while maintaining desired depth of anaesthesia without any significant complication.
Bispectral index monitor; dexmedetomidine; propofol; spine surgery
Although different techniques have been developed for administering combined spinal epidural (CSE) anaesthesia, none can be described as an ideal one.
We performed a study to compare two popular CSE techniques: Double segment technique (DST) and single segment (needle through needle) technique (SST) with another alternative technique: Paramedian epidural and midline spinal in the same intervertebral space (single space dual needle technique: SDT).
After institutional ethical clearance, 90 consenting patients undergoing elective lower limb orthopaedic surgery were allocated to receive CSE into one of the three groups (n=30 each): Group I: SST, Group II: SDT, Group III: DST using computerized randomization. The time for technique performance, surgical readiness, technical aspects of epidural and subarachnoid block (SAB) and morbidity were compared.
SDT is comparable with SST and DST in time for technique performance (13.42±2.848 min, 12.18±6.092 min, 11.63±3.243 min respectively; P=0.268), time to surgical readiness (18.28±3.624 min, 17.64±5.877 min, 16.87±3.137 min respectively; P=0.42) and incidence of technically perfect block (70%, 66.66%, 76.66%; respectively P=0.757). Use of paramedian route for epidural catheterization in SDT group decreases complications and facilitates catheter insertion. There was a significant number of cases with lack of dural puncture appreciation (SST=ten, none in SDT and DST; P=0.001) and delayed cerebrospinal fluid reflux (SST=five, none in SDT and DST; P=0.005) while performance of SAB in SST group. The incidence of nausea, vomiting, post-operative backache and headache was comparable between the three groups.
SDT is an acceptable alternative to DST and SST.
Combined spinal epidural; double segment; needle through needle; paramedian
Anaesthesia for spine surgeries is not only concerned with relieving pain during surgeries but also during the post-operative period. A prospective randomised study was carried out to evaluate the efficacy of epidural route and to compare the efficacy and clinical profile of dexmedetomidine and clonidine as an adjuvant to ropivacaine, in epidural analgesia with special emphasis on their quality of analgesia and the ability to provide the smooth post-operative course.
A total of 60 subjects, 33 were men and 27 were women between the age of 18 and 65 years of American Society of Anaesthesiologists (ASA) I/II class who underwent spine surgeries were randomly allocated into two groups, ropivacaine + dexmedetomidine (RD) and ropivacaine + clonidine (RC), comprising 30 patients each. Group RD received 20 ml of 0.2% ropivacaine and 1 μg/kg of dexmedetomidine while group RC received 20 ml of 0.2% ropivacaine and 2 μg/kg of clonidine through the epidural catheter. Onset of analgesia, time of peak effect, duration of analgesia, cardiorespiratory parameters, side-effects and need of rescue intravenous (IV) analgesics were observed.
The demographic profile and ASA class were comparable between the groups. None of the patients needed rescue analgesics in either group. Group RD had early onset, early peak effect, prolonged duration and stable cardiorespiratory parameters when compared with group RC. The side-effects profile was also comparable with a little higher incidence of nausea and dry mouth in both groups.
Epidural route provided acceptable analgesia in spine surgeries and avoided the need of IV analgesics in either group. Dexmedetomidine is a better neuraxial adjuvant compared with clonidine for providing early onset and prolonged post-operative analgesia and stable cardiorespiratory parameters.
Anaesthesia technique; clonidine; dexmedetomidine; epidural analgesia; ropivacaine; spine surgeries
During paediatric cleft surgeries intraoperative heat loss is minimal and hence undertaking all possible precautions available to prevent hypothermia and use of active warming measures may result in development of hyperthermia. This study aims to determine whether there will be hyperthermia on active warming and hypothermia if no active warming measures are undertaken. The rate of intraoperative temperature changes with and without active warming was also noted.
This study was conducted on 120 paediatric patients undergoing cleft lip and palate surgeries. In Group A, forced air warming at 38°C was started after induction. In Group B, no active warming was done. Body temperature was recorded every 30 min starting after induction until 180 min or end of surgery. Intragroup comparison of variables was done using Paired sample test and intergroup comparison using independent sample t-test.
In Group A, all intraoperative temperature readings were significantly higher than baseline. In Group B, there was a significant reduction in temperature at 30 and 60 min. Temperature at 90 min did not show any significant difference, but further readings were significantly higher. Maximum rise in temperature occurred in Group A between 120 and 150 min and maximum fall in temperature in Group B was seen during first 30 min.
In pediatric cleft surgeries, we recommend active warming during the first 30 minutes if the surgery is expected to last for <2h, and no such measures are required if the expected duration is >2h.
Active warming; hyperthermia; hypothermia; paediatric cleft surgeries