Anesthetic Equipment

Gas Supplies Bulk Supply of Anesthetic Gases In the majority of modern hospitals, piped medical gases and vacuum (PMGV) systems have been installed only a few cylinders are kept in reserve, attached usually to the anesthetic machine The PMGV services comprise five sections: bulk store distribution pipelines in the hospital terminal outlets, situated usually on the walls or ceilings of the operating theatre suite and other sites flexible hoses connecting the terminal outlets to the anesthetic machine connections between flexible hoses and anesthetic machines Responsibility for the first three items lies with the engineering and pharmacy departments. Within the operating theatre, it is partly the anesthetist’s responsibility to check the correct functioning of the last two items

Bulk Store: Oxygen In small hospitals: Oxygen cylinder manifolds consist of two groups of large cylinders (size J)

Bulk Store: Oxygen In large hospitals: Liquid oxygen store Liquid oxygen is stored at a temperature of approximately −165 °C at 10.5 If the pressure increases above 17 bar (1700 kPa), a safety valve opens and oxygen runs to waste Liquid oxygen plants are housed some distance away from hospital buildings because of the risk of fire Even when a hospital possesses a liquid oxygen plant, it is still necessary to hold reserve banks of oxygen cylinders in case of supply failure

Other Gases Nitrous Oxide Medical Compressed Air Piped Medical Vacuum Nitrous oxide and Entonox may be supplied from banks of cylinders connected to manifolds similar to those used for oxygen Medical Compressed Air Compressed air is supplied from a bank of cylinders into the PMGV system Air of medical quality is required, as industrial compressed air may contain fine particles of oil Piped Medical Vacuum Piped medical vacuum is provided by large vacuum pumps

Terminal Outlets Six types of terminal outlet are found commonly in the operating theatre The terminals are color-coded and also have non-interchangeable connections specific to each gas: Vacuum (colored yellow) – a vacuum of at least 53 kPa (400 mmHg) should be maintained at the outlet, which should be able to take a free flow of air of at least 40 L min–1 Compressed air (colored white/black) at 4 bar – this is used for anesthetic breathing systems and ventilators Air (colored white/black) at 7 bar – this is to be used only for powering compressed air tools and is confined usually to the orthopedic operating theatre Nitrous oxide (colored blue) at 4 bar Oxygen (colored white) at 4 bar Scavenging designed to accept a standard 30-mm connection

Outlet of central oxygen supply system

Gas Cylinders Modern cylinders are constructed from molybdenum steel They are checked at intervals by the manufacturer to ensure that they can withstand hydraulic pressures considerably in excess of those to which they are subjected in normal use The cylinders are provided in a variety of sizes (A to J), and color-coded according to the gas supplied Cylinders attached to the anesthetic machine are usually size E The cylinders comprise a body and a shoulder

Gas Cylinders Cylinder valves should be opened slowly to prevent sudden surges of pressure The color codes used for medical gas cylinders in the United Kingdom are shown in Table 15.2. Different colors are used for some gases in other countries Cylinder sizes and capacities are shown in Table 15.3. Oxygen, air and helium are stored as gases in cylinders and the cylinder contents can be estimated from the cylinder pressure Nitrous oxide and carbon dioxide cylinders contain liquid and vapor The cylinder pressure cannot be used to estimate its contents because the pressure remains relatively constant until after all the liquid has evaporated and the cylinder is almost empty The contents of nitrous oxide and carbon dioxide cylinders can be estimated from the weight of the cylinder

The anesthetic machine comprises: A means of supplying gases either from attached cylinders or from piped medical supplies via appropriate unions on the machine Methods of measuring flow rate of gases Apparatus for vaporizing volatile anesthetic agents Breathing systems and a ventilator for delivery of gases and vapors from the machine to the patient Apparatus for scavenging anesthetic gases in order to minimize environmental pollution.

ventilator Flow meter bellow vaporizer Corrugated tube APL valve Scavenging system Soda lime

The Anesthesia Machine High Intermediate Low Pressure Circuit Mention how the machine is divided into high, intermediate, and low pressure systems

Oxygen Supply Failure Alarm The machine standard specifies that whenever the oxygen supply pressure falls below a manufacturer-specified threshold (usually 30 psig) a medium priority alarm shall blow within 5 seconds

Oxygen Flush Valve (O2+) Receives O2 from pipeline inlet or cylinder reducing device and directs high, unmetered flow directly to the common gas outlet (downstream of the vaporizer) Machine standard requires that the flow be between 35 and 75 L/min The ability to provide jet ventilation Hazards May cause barotrauma Dilution of inhaled anesthetic

Low Pressure System Consists of: Flow meters Vaporizer mounting device Check valve Common gas outlet

Flowmeter assembly When the flow control valve is opened the gas enters at the bottom and flows up the tube elevating the indicator The indicator floats freely at a point where the downward force on it (gravity) equals the upward force caused by gas molecules hitting the bottom of the float

Vaporizers A vaporizer is an instrument designed to change a liquid anesthetic agent into its vapor and add a controlled amount of this vapor to the fresh gas flow

Factors That Influence Vaporizer Output Flow Rate: The output of the vaporizer is generally less than the dial setting at very low (< 200 ml/min) or very high (> 15 L/min) flows Temperature: Automatic temperature compensating mechanisms in bypass chambers maintain a constant vaporizer output with varying temperatures Back Pressure: Intermittent back pressure (eg positive pressure ventilation causes a higher vaporizer output than the dial setting) C’ = concentration at the new atmospheric pressure C = the concentration at the old atmospheric pressure (ie the concentration dialed into the vaporizer) P’ = the barometric pressure for which c’ is being established P = the barometric pressure for which the vaporizer is calibrated (ie at the old atmospheric pressure)

Factors That Influence Vaporizer Output Atmospheric Pressure: Changes in atmospheric pressure affect variable bypass vaporizer output as measured by volume % concentration, but not (or very little) as measured by partial pressure (lowering atmospheric pressure increases volume % concentration and vice versa) Carrier Gas: Vaporizers are calibrated for 100% oxygen Carrier gases other than this result in decreased vaporizer output

The Circuit: Circle System Arrangement is variable, but to prevent re-breathing of CO2, the following rules must be followed: Unidirectional valves between the patient and the reservoir bag Fresh-gas-flow cannot enter the circuit between the expiratory valve and the patient Adjustable pressure-limiting valve (APL) cannot be located between the patient and the inspiratory valve

The carbon dioxide absorber Sodalime (CaOH2 + NaOH + KOH + silica) or Baralyme (Ba[OH] 2 + Ca[OH]2) contained in the absorber combines with carbon dioxide, forming CaCO2 and liberating heat and moisture (H2O) A pH-sensitive dye changes to a blue-violet color, indicating exhaustion of the absorbing capacity The canister should be changed when 25% to 50% of the contents has changed color, although it should continue to absorb satisfactorily until at least the contents of the top canister have changed color

Circle System Advantages: Relative stability of inspired concentration Conservation of respiratory moisture and heat Prevention of operating room pollution PaCO2 depends only on ventilation, not fresh gas flow Low fresh gas flows can be used Disadvantages: Complex design = potential for malfunction High resistance (multiple one-way valves) = higher work of breathing The final three points of the advantages section are meant to contrast with the Bain circuit

The reservoir bag The reservoir bag is located on the expiratory limb The reservoir bag accumulates gas between inspirations It is used to visualize spontaneous ventilation and to assist ventilation manually Adults require a 3-L bag Children a 2-L bag Most new machines have a valve used to switch between the reservoir bag and the ventilator Older machines may require that the bag be removed and a hose to the ventilator be connected The final three points of the advantages section are meant to contrast with the Bain circuit

The Adjustable Pressure Limiting (APL) Valve User adjustable valve that releases gases to the scavenging system and is intended to provide control of the pressure in the breathing system Bag-mask Ventilation: Valve is usually left partially open During inspiration the bag is squeezed pushing gas into the inspiratory limb until the pressure relief is reached, opening the APL valve Mechanical Ventilation: The APL valve is excluded from the circuit when the selector switch is changed from manual to automatic ventilation

Scavenging Systems A scavenging system channels waste gases away from the operating room to a location outside the hospital building The ambient concentration of anesthetic gases in the operating room should not exceed 25 ppm for nitrous oxide and 2 ppm for halogenated agents Specific anesthetic gas-scavenging systems should be used routinely These systems consist of a collecting system, a transfer system, a receiving system, and a disposal system

Scavenging Systems The disposal system may be passive or active, although passive systems are inadequate for modern hospitals A passive system consists of wide-bore tubing that carries gases directly to the exterior or into the exhaust ventilation ducts Active systems can be powered by vacuum systems, fans, pumps, or Venturi systems

Scavenging Systems The disposal system may be passive or active, although passive systems are inadequate for modern hospitals A passive system consists of wide-bore tubing that carries gases directly to the exterior or into the exhaust ventilation ducts Active systems can be powered by vacuum systems, fans, pumps, or Venturi systems Mention that the ventilator relief valve is the same thing as the overflow valve mentioned in the previous slides

Gas Analysis Several methods are used to monitor concentrations of oxygen, carbon dioxide, and anesthetic gases in the breathing system The oxygen analyzer is the single most important monitor for detection of a hypoxic gas mixture Capnometry, the measurement of carbon dioxide, has many uses, including monitoring the adequacy of ventilation and detection of breathing system faults Breath-to-breath monitoring of anesthetic concentrations provides tracking of anesthetic uptake and distribution Most gas analyzers incorporate alarms. Among the techniques for measurement are the following: Mass spectrometry, infrared analysis and oxygen concentrations analysis

Anesthesia Ventilators Most modern anesthesia machines are fitted with a mechanical ventilator that uses a collapsible bellows within a closed chamber The bellows is compressed intermittently when oxygen or air is directed into the chamber, thereby pressurizing it The ventilators are time cycled flow (as opposed to pressure) generators, controlled both mechanically and electronically, and pneumatically driven (requiring 10 to 20 L of driving gas per minute) Ventilator controls vary among makes and models. Some ventilators require setting of minute ventilation, rate, and inspiratory-expiratory (I:E) ratio to produce the desired tidal volume; other ventilators allow direct adjustment of tidal volume, with I : E ratio being dependent on the inspiratory flow rate, which is set independently

Anesthesia Ventilators Ventilator controls vary among makes and models Some ventilators require setting of minute ventilation, rate, and inspiratory-expiratory (I:E) ratio to produce the desired tidal volume; other ventilators allow direct adjustment of tidal volume, with I : E ratio being dependent on the inspiratory flow rate, which is set independently Although gas-driven ventilators can be safely driven with either oxygen or air, most often oxygen is chosen and is supplied by pipeline. Whether or not cylinder gases are used to drive the ventilator in the event of pipeline failure is usually determined by the user. If the machine is set up to drive the ventilator using cylinder oxygen, mechanical ventilation should be discontinued in the event of pipeline failure to conserve oxygen supplies

Flow Generator Ventilators Flow generators deliver a set tidal volume regardless of changes in patients' compliance ( unlike pressure generators ) but will not compensate for system leaks and may produce barotrauma because high pressures can be generated They reliably deliver the preset tidal volume (even in the presence of a small leak). The risk o f barotrauma is minimal because most patients presenting to the operating room have healthy normally compliant lungs.

Pressure Generator Ventilators For infants and patients with diseased lungs, the maintenance of preset tidal volumes may produce unacceptably high airway pressures and increased risk of barotrauma Pressure generators are more appropriate in these situations, because airway pressure is controlled and barotrauma risk minimized

Checking Anesthesia Machines Emergency ventilation equipment High-Pressure system Low-Pressure system Scavenging system Breathing system Manual and automatic ventilation system Monitors

Basic Anesthetic Monitoring ASA Standards for Basic Anesthesia Monitoring Prepared by Dr. Mahmoud Abdel-Khalek

Basic Anesthetic Monitoring The primary goal of anesthesia is to keep the patient as safe as possible in the perioperative period Anesthesia and surgery are serious invasions on the physiologic stability of the human body Careful monitoring of the patient during and after surgery allows the anesthesiologist to identify problems early, when they can still be corrected Proper monitoring of the patient can reduce the risks involved in anesthesia and surgery Some of the physiologic disturbances that occur in the perioperative period include: apnea, respiratory depression, airway obstruction, cardiac depression, hypertension, hypotension, hypervolemia, hypovolemia, arrhythmias, blood loss, fluid shifts, weakness, bradycardia, tachycardia, hyperthermia, and hypothermia

Standards of Care Proper monitoring standards are well-defined The most widely accepted current anesthesia monitoring standards are those that have been published by the by the American Society of Anesthesiologists (ASA) The ASA standards were initially published in 1986, and were updated afterwards

The ASA Standards for Basic Anesthetic Monitoring Standard I states that a qualified anesthesia provider will be present with the patient throughout the anesthetic Standard II states that the patient's oxygenation, ventilation, circulation, and temperature will be continually monitored Assessment of oxygenation involves two parts: measurement of inspired gas with an oxygen analyzer and assessment of hemoglobin saturation with a pulse oximeter and observation of skin color Assessment of ventilation is by clinical assessment and preferably capnography

The ASA Standards for Basic Anesthetic Monitoring Tracheal intubation must be verified clinically and by detection of exhaled CO2 Mechanical ventilation must be monitored with an audible disconnect monitor Assessment of circulation involves continuous ECG monitoring, blood pressure measurement at least every five minutes, and continuous monitoring of peripheral circulation by such means as palpation, ausculation, plethysmography, or arterial pressure monitoring The patient's temperature must be measured if changes are anticipated, intended, or suspected

Oxygen analyzers Oxygen Analyzers Oxygen analyzers are an integral part of the newer anesthesia machines The purpose of the oxygen analyzer is to confirm that oxygen is being delivered to the patient and that concentration of oxygen in the gas mixture is adequate The oxygen analyzer provides one last check before the gas mixture is delivered to the patient For the analyzer to be useful, it must be calibrated and the low-limit alarm must be working The two main types of oxygen analyzers are galvanic (fuel cell), and the polarographic

Pulse Oximeters Pulse oximetry have been a major advance in improving the safety of anesthesia The pulse oximeter provides continuous monitoring of hemoglobin saturation using a two-wavelength light absorption technique The monitor filters out the effects of ambient light, tissue, skin pigment, tissue, and venous blood It focuses on the pulsatile absorption which due to pulsatile arterial blood Pulse oximeters were developed in the early 1980's and rapidly proved their value in anesthesia Pulse oximetry allows rapid, beat-by-beat, noninvasive monitoring of blood oxygenation Disadvantages of pulse oximetry are that it is motion sensitive, and that substances like carbon monoxide, methemoglobin, and some dyes like nail polish affect the readings

Capnography The most common method of exhaled CO2 measurement is sidestream infrared (IR) capnography Gas from the circuit is drawn into an infrared measurement chamber CO2, N2O, H20, and inhaled anesthetic agents all absorb infrared light, but at slightly different frequencies Newer monitors have precise light sources and filters that specifically measure the individual gases These monitors provide breath-by-breath gas analysis Problems with IR capnographs are that moisture can cause blockage of the gas path, and that they can't measure oxygen or nitrogen

Abnormalities: Complete absence of waveform Circuit disconnection Cardiac arrest Esophageal intubation Complete respiratory obstruction

Automatic blood pressure monitors Current automatic noninvasive blood pressure monitors work on the oscillometric technique The cuff inflates well above the systolic pressure and then deflates slowly The monitor first senses oscillations as the cuff drops to systolic pressure The point at which the oscillations are the strongest is read as the mean pressure Most of these devices calculate the diastolic pressure after they measure the systolic and mean pressures The system is normally very reliable and accurate, but motion (especially shivering) on the part of the patient or the surgeon leaning against the cuff will cause false readings or failure to get a reading Patient injury is possible if the tubing becomes kinked Values may be in error if the cuff is not the proper size

ECG Monitor The ECG monitor can provide a lot of information to the anesthesiologist Arrhythmia detection and identification of tachycardia and bradycardia are important uses The ECG monitor may also provide the first indication of myocardial ischemia However the absence of ST depression does not guarantee that ischemia is not present Lead placement is important in ischemia detection The most sensitive lead is lead V5, detecting about 75% of ischemic episodes Lead II plus lead V5 raise the detection rate to 80%, whereas leads II, V4, and V5 together detect 98% of ischemic events Current top-of-the line monitors do automated ST analysis which is more reliable than individual practitioner assessment as long as the measurement points are correct

Ventilation Monitors Current anesthesia machines have ventilator disconnect alarms and built-in spirometers The spirometers have high and low limit alarm settings Continuous measurement of exhaled tidal volume can detect circuit leaks and hypoventilation The spirometers on the anesthesia machines may give false readings if moisture blocks the inner workings Current anesthesia machines also have overpressure alarms and overpressure "pop-off" valves

Temperature Monitors Monitoring of skin temperature is nearly useless Upper esophageal and nasopharyngeal temperature are affected by airway temperature Lower esophageal temperature is normally a good reflection of core or blood temperature Tympanic membrane temperature is also a good indication of core temperature but it is not practical in the operating room environment

Peripheral Nerve Stimulators Peripheral nerve stimulation (PNS) monitoring is not required by the ASA standards However, it is an important safety monitor in patients who a receiving neuromuscular blocking drugs Train-of-four monitoring assesses the level of nondepolarizer blockade and double-burst stimulation assesses return of strength at the end of the case Clinical monitoring of neuro- muscular blockade during an anesthetic is difficult without a PNS monitor Clinical assessment of strength is important, however, at the conclusion of an anesthetic before a final decision is made to extubate the patient

Thank You