Inaccuracies of Nitric Oxide Delivery Systems during Adult Mechanical Ventilation

Background: Various systems to administer inhaled nitric oxide (NO) have been used in patients and experimental animals. We used a lung model to evaluate five NO delivery systems during mechanical ventilation with various ventilatory patterns.

Methods: An adult mechanical ventilator was attached to a test lung configured to separate inspired and expired gases. Four injection systems were evaluated with NO injected either into the inspiratory circuit 90 cm proximal to the Y piece or directly at the Y piece and delivered either continuously or only during the inspiratory phase. Alternatively, NO was mixed with air using a blender and delivered to the high-pressure air inlet of the ventilator. Nitric oxide concentration was measured from the inspiratory limb of the ventilator circuit and the tracheal level using rapid- and slow-response chemiluminescence analyzers. The ventilator was set for constant-flow volume control ventilation, pressure control ventilation, pressure support ventilation, or synchronized intermittent mandatory ventilation. Tidal volumes of 0.5 l and 1 l were evaluated with inspiratory times of 1 s and 2 s.

Results: The system that premixed NO proximal to the ventilator was the only one that maintained constant NO delivery regardless of ventilatory pattern. The other systems delivered variable NO concentration during pressure control ventilation and spontaneous breathing modes. Systems that injected a continuous flow of NO delivered peak NO concentrations greater than the calculated dose. These variations were not apparent when a slow-response chemiluminescence analyzer was used.     

Performance characteristics of five new anesthesia ventilators and four intensive care ventilators in pressure-support mode: a comparative bench study

BACKGROUND: During the past few years, many manufacturers have introduced new modes of ventilation in anesthesia ventilators, especially partial-pressure modalities. The current bench test study was designed to compare triggering and pressurization of five new anesthesia ventilators with four intensive care unit ventilators. METHODS: Ventilators were connected to a two-compartment lung model. One compartment was driven by an intensive care unit ventilator to mimic "patient" inspiratory effort, whereas the other was connected to the tested ventilator. The settings of ventilators were positive end-expiratory pressures of 0 and 5 cm H2O, and pressure-support ventilation levels of 10, 15, and 20 cm H2O with normal and high "patient" inspiratory effort. For the anesthesia ventilators, all the measurements were obtained for a low (1 l/min) and a high (10 l/min) fresh gas flow. Triggering delay, triggering workload, and pressurization at 300 and 500 ms were analyzed. RESULTS: For the five tested anesthesia ventilators, the pressure-support ventilation modality functioned correctly. For inspiratory triggering, the three most recent anesthesia machines (Fabius, Dr?gerwerk AG, Lübeck, Germany; Primus, Dr?gerwerk AG; and Avance, GE-Datex-Ohemda, Munchen, Germany) had a triggering delay of less than 100 ms, which is considered clinically satisfactory and is comparable to intensive care unit machines. The use of positive end-expiratory pressure modified the quality of delivered pressure support for two anesthesia ventilators (Kion, Siemens AG, Munich, Germany; and Felix, Taema, Antony, France). Three of the five anesthesia ventilators exhibited pressure-support ventilation performance characteristics comparable to those of the intensive care unit machines. Increasing fresh gas flow (1 to 10 l/min) in the internal circuit did not influence the pressure-support ventilation performance of the anesthesia ventilators. CONCLUSION: Regarding trigger sensitivity and the system's ability to meet inspiratory flow during pressure-supported breaths, the most recent anesthesia ventilators have comparable performances of recent-generation intensive care unit ventilators.     

Inspiratory work imposed by demand valve ventilator circuits

The inspiratory work (WI) imposed by three commonly used demand valve ventilator circuits was studied using a lung model to simulate spontaneous ventilation. The CPU-1 and Engstrom Erica circuits recorded WI of 379 mJ/l and 190 mJ/l respectively. A negative WI of -32 mJ/l was recorded for the Servo 900C, denoting that the circuit performed work on the lung. The demand valves recorded a time delay between inspiratory effort and onset of gas flow, of 300 ms (CPU-1), 190 ms (Servo 900c) and 160 ms (Engstrom Erica). Both the Servo 900C and Engstrom Erica demand valves were able to generate a high inspiratory gas flow response, but the CPU-1 lacked such a flow compensation. Expiratory work was also greatest with the CPU-1 (156 mJ/l) with 141 mJ/l and 90 mJ/l recorded for the Servo 900C and Engstrom Erica. Of the three ventilators studied, the Servo 900C appears to be the ventilator circuit of choice for spontaneous ventilation.     

Effect of inspiratory time on tidal volume delivery in anesthesia and intensive care unit ventilators operating in pressure control mode

STUDY OBJECTIVE: To compare the effect of inspiratory time and lung compliance on tidal volume (Vt) delivery in anesthesia and intensive care unit (ICU) ventilators operating in pressure control mode. SETTING: Respiratory research laboratory of a tertiary care medical center. DESIGN: Two anesthesia ventilators with pressure control capability (Narkomed 6000, Drager Medical, Inc, Telford, Pa, and the Datex-Ohmeda Aestiva 5, Datex-Ohmeda, Inc, Madison, Wis) and one critical care ventilator (Puritan Bennett 7200, Puritan-Bennett, Pleasanton, Calif) were studied under varying inspiratory time and lung compliance conditions using a mechanical lung model. INTERVENTION: Each ventilator was set to pressure control mode at a fixed inspiratory/expiratory (I/E) ratio. The respiratory rate (RR) was varied between 6 and 28 breaths per minute. Lung compliance and inspiratory time settings were set to simulate clinical conditions known to affect anesthesia ventilator performance. MEASUREMENTS: Inspiratory flow, Vts, and peak airway pressures were measured using the on-board monitor for each ventilator, and confirmed with the Bicore CP-100 pulmonary mechanics monitor (Bicore Monitoring Systems, Inc, Irvine, Calif). To assess differences in inspiratory flow between ventilators, airway pressures were continuously monitored during inspiration. MAIN RESULTS: Increasing RRs caused delivered Vts to decrease for all ventilators. However, decreases in Vts were significantly larger for anesthesia than for ICU ventilators. At a lung compliance of 0.02 L/cm H(2)O and set Vt of 700 mL, Vt delivery for the Puritan Bennett 7200 ventilator remained at 88% of baseline, but decreased to 76% for the Aestiva 5 when RRs were increased from 6 to 28 breaths per minute (P < .0025). Airway pressure tracings demonstrated a slower increase in inspiratory airway pressure for the Aestiva 5 than for the other ventilators. CONCLUSION: Differences in inspiratory flow delivery between ICU and anesthesia ventilators can cause differences in Vt delivery when the pressure control mode is used at high RRs. These differences can significantly impact the perioperative care of critically ill patients requiring ventilatory support.     

Performance Characteristics of Five New Anesthesia Ventilators and Four Intensive Care Ventilators in Pressure-support Mode: A Comparative Bench Study

Background: During the past few years, many manufacturers have introduced new modes of ventilation in anesthesia ventilators, especially partial-pressure modalities. The current bench test study was designed to compare triggering and pressurization of five new anesthesia ventilators with four intensive care unit ventilators.

Methods: Ventilators were connected to a two-compartment lung model. One compartment was driven by an intensive care unit ventilator to mimic "patient" inspiratory effort, whereas the other was connected to the tested ventilator. The settings of ventilators were positive end-expiratory pressures of 0 and 5 cm H2O, and pressure-support ventilation levels of 10, 15, and 20 cm H2O with normal and high "patient" inspiratory effort. For the anesthesia ventilators, all the measurements were obtained for a low (1 l/min) and a high (10 l/min) fresh gas flow. Triggering delay, triggering workload, and pressurization at 300 and 500 ms were analyzed.

Results: For the five tested anesthesia ventilators, the pressure-support ventilation modality functioned correctly. For inspiratory triggering, the three most recent anesthesia machines (Fabius, Dragerwerk AG, Lubeck, Germany; Primus, Dragerwerk AG; and Avance, GE-Datex-Ohemda, Munchen, Germany) had a triggering delay of less than 100 ms, which is considered clinically satisfactory and is comparable to intensive care unit machines. The use of positive end-expiratory pressure modified the quality of delivered pressure support for two anesthesia ventilators (Kion, Siemens AG, Munich, Germany; and Felix, Taema, Antony, France). Three of the five anesthesia ventilators exhibited pressure-support ventilation performance characteristics comparable to those of the intensive care unit machines. Increasing fresh gas flow (1 to 10 l/min) in the internal circuit did not influence the pressure-support ventilation performance of the anesthesia ventilators.     

Improved flow and pressure capabilities of the Datex-Ohmeda SmartVent anesthesia ventilator

STUDY OBJECTIVE: To compare the flow and pressure capabilities of the Datex-Ohmeda SmartVent (Ohmeda 7900, Datex-Ohmeda, Madison, WI) to previous Ohmeda (7810 and 7000, Datex-Ohmeda, Madison, WI) anesthesia ventilators. To determine airway pressure and minute ventilation thresholds for intraoperative use of a critical care ventilator. DESIGN: Three anesthesia ventilators and one critical care ventilator (Siemens Servo 900C, Siemens, Solna, Sweden) were studied in a lung model. Retrospective medical record review. SETTING: Research Laboratory and Critical Care Unit of a Level I Trauma Center. PATIENTS: 145 mechanically ventilated patients treated for acute respiratory failure who underwent 200 surgical procedures. INTERVENTIONS: The effect of increasing pressure on mean inspiratory flow was determined by cycling each ventilator through increasing restrictors. Maximum minute ventilation was measured at low compliance (10-30 mL/cm H2O), positive end-expiratory pressure (PEEP) (0-20 cm H2O), and increased airway resistance (approximately 19 and approximately 36 cm H2O/L/sec) in a mechanical lung model. MEASUREMENTS AND MAIN RESULTS: Flow, volume, and pressure were measured with a pulmonary mechanics monitor (BICORE CP-100, Thermo Respiratory Group, Yorba Linda, CA). Preoperative peak airway pressure and minute ventilation (VE) were extracted from the medical record. Mean inspiratory flow declined with increasing pressure in all anesthesia ventilators. The SmartVent and the 7810 produced greater mean inspiratory flow than did the 7000 ventilator. As compliance progressively decreased, the Siemens, the SmartVent, and the 7810 ventilators maintained VE compared to the 7000 ventilator. The Siemens and the SmartVent maintained VE with PEEP, compared to the 7810 and 7000 ventilators. During increased airway resistance, maximal VE was lower for all ventilators. The SmartVent met the ventilation requirements in 90% of the patients compared to 67% of patients with the 7000 ventilator. CONCLUSION: The improved pressure and flow capabilities of the SmartVent increase the threshold for using a critical care ventilator intraoperatively to a peak airway pressure > 65 cm H2O and/or VE > 18 L/min.     

A pressure-controlled rat ventilator with electronically preset respirations

Major experimental surgery on laboratory animals requires adequate anesthesia and ventilation to keep the animal alive throughout the procedure. A ventilator is a machine that helps the anesthesized animal breathe through an endotracheal tube by pumping a volume of gas (oxygen, air, or other gaseous mixtures), comparable with the normal tidal volume, into the animal's lungs. There are two main categories of ventilators for small laboratory rodents: volume-controlled and pressure-controlled ones. The volume-controlled ventilator injects a preset volume into the animal's lungs, no matter the airways' resistance (with the peak inspiratory pressure allowed to vary), while the pressure ventilator controls the inspiratory pressure and allows the inspiratory volume to vary. Here we show a rat pressure ventilator with a simple expiratory valve that allows gas delivery through electronic expiration control and offers easy pressure monitoring and frequency change during ventilation.     

Distribution of Expiratory Gas and Rebreathing in a T-piece Modification Combined with a PEEP Valve

T-piece modifications with PEEP valves are often used in weaning from mechanical ventilation or for intubated patients not requiring ventilatory support. Distribution of expiratory gas and the extent of rebreathing in a T-piece modified with an inspiratory reservoir (ICR) and with a PEEP valve were studied in a model with various fresh gas flows (FGF), tidal volumes and frequencies at three valve settings: 0 cmH2O (ZEEP) and PEEP of 5 and 10 cmH2O (0.490-0.981 kPa). Two types of distribution of expiratory gas were delineated: type one with expiratory gas in the inspiratory limb (IL) and a high ratio of the maximum CO2 content and corresponding end-expiratory CO2 concentration in the expiratory limb (EL) (FmaxCO2/FECO2) and a type 2 with no detectable alveolar gas in the IL and a low ratio of FmaxCO2/FECO2. The use of PEEP did not increase the amount of alveolar gas in the system, and no increase occurred in the end-expiratory CO2 concentration. The investigated system is in fact a Mapleson A system. The ratio of FGF to minute ventilation just preventing rebreathing during spontaneous ventilation is approximately 1, in contrast to 3 in other modifications. These advantages minimize the risk of rebreathing, even when the minute ventilation rises to that of the fresh gas flow. The T-system with a compliant inspiratory reservoir and a PEEP valve can, in most clinical weaning situations, satisfy the inspiratory peak flow of different respiratory patterns with a standard FGF of 15 l X min-1.     

Newer modes of mechanical ventilatory support

Recent modes of ventilatory support aim to facilitate weaning and minimise the physiological disadvantages of intermittent positive pressure ventilation (IPPV). Intermittent mandatory ventilation (IMV) allows the patient to breathe spontaneously in between ventilator breaths. Mandatory minute volume ventilation (MMV) ensures that the patient always receives a preset minute volume, made up of both spontaneous and ventilator breaths. Pressure supported (assisted) respiration is augmentation of a spontaneous breath up to a preset pressure level, and is different from 'triggering', which is a patient-initiated ventilator breath. Other modes or refinements of IPPV include high frequency ventilation, expiratory retard, differential lung ventilation, inversed ratio ventilation, 'sighs', varied inspiratory flow waveforms and extracorporeal membrane oxygenation. While these techniques have useful applications in selective situations, IPPV remains the mainstay of managing respiratory failure for most patients.     

Trigger sensitivity of Servo 300 (Siemens Elema) for pressure support ventilation in an infant

The trigger sensitivity for pressure support ventilation (PSV) with a Servo 300 ventilator was evaluated in a 6-month-old male infant ventilated with synchronized intermittent mandatory ventilation (SIMV) of 14 c.min^?1 and PSV of 4 cmH₂O. The delay time between onset of inspiration and the trigger signal was 42 and 139 msec for trigger sensitivity of –2 and –4 cmH₂O, respectively. On the former sensitivity, the inspiration was sensed by a decrease of expiratory bias flow before the airway pressure decreased to the set level. The time between the trigger signal and the flow delivery was 7 msec. The supplied volume exceeded the spontaneous breath on both trigger sensitivities. Using Servo 300, the constant expiratory bias flow, the use of a flow trigger and the mechanical improvement of the inspiratory valve contribute to reduced delay time in the trigger function, making the ventilator well suited, set in the PSV mode, even at high spontaneous respiratory rates for infants.     

High-frequency artificial respiration. II. Intratracheal high-frequency pressure changes with a rotation-valve catheter

From the history of ventilatory support, the early studies of Auer und Meltzer only now seem to find a functional explanation. A rotating valve mounted on the tip of an endotracheal tube delivers a widespread gas bolus. The turbulent flow acts as a stirring device on the intrapulmonary gas volume. The method reduces the directional selectivity that typically limits the efficiency of jet ventilation. Systematically changing the rotational frequency between 10 and 80 Hz allows sequential stimulation, compartment by compartment, of the entire lung, which also gives rise to frequency-dependent local air-trapping that sequentially inflates different compartments. Jet ventilation and high-frequency oscillation were compared in dogs with the rotating valve tube by taking blood gas samples from 4-6 intrapulmonary veins: jet ventilation is characterized by preponderant ventilation of lung compartments opposite the lower aperture of the endotracheal tube. High-frequency oscillation induces a frequency dependent repartition of alveolar ventilation. The rotating valve tube definitely contributes to the homogenisation of alveolar ventilation in a manner that is less dependant upon segmental compliance than conventional ventilation.     

Pressure characteristics of the Ambu CPAP system and the Servo Ventilator 900C in CPAP mode

Spontaneous breathing was stimulated in the Ambu continuous positive airway pressure (CPAP) system and the Servo Ventilator 900C by means of a lung model programmed to mimic the respiratory flow patterns of a healthy volunteer and a patient in severe respiratory distress. Changes in airway pressure, flow and volume were recorded during "breathing" with CPAP at 0.5, 1.0 and 1.5 kPa. In the Ambu system, the airway pressure decreased during inspiration and increased during expiration, while the mean airway pressure was close to the pre-set CPAP value. The pressure changes were minimal when the fresh gas flow was increased from 15 to 25 1 X min-1. The higher fresh gas flow is recommendable during deep or rapid breathing. In the Servo ventilator 900C, there was a short initial inspiratory pressure drop, succeeded by a pressure rise above the CPAP value. The expiratory airway pressure was somewhat higher than CPAP. Both systems were found to be recommendable for clinical use.     

FACTORS AFFECTING CARBON DIOXIDE HOMEOSTASIS DURING CONTROLLED VENTILATION WITH CIRCLE SYSTEMS

An experimental lung model was used, with controlled ventilation,to determine the effect of different circle arrangements andvarying ventilatory frequencies on the efficiency of carbondioxide removal from a circle system without carbon dioxideabsorption. Greater efficiency was found when fresh gas enteredthe system between the unidirectional inspiratory valve andthe subject than when the fresh gas inlet was on the ventilatorside of this valve. At any fresh gas flow and minute volume,efficiency was greater at low respiratory frequencies. Goodcorrelations existed between carbon dioxide concentration inthe model lung, fresh gas flow and minute ventilation when respiratoryfrequency was constant. Paradoxical results were obtained whenminute volume was varied by changes in frequency at a constanttidal volume. The major cause of the various differences inperformance has been ascribed to variations in the degree ofmixing of fresh and expired gas within the system.     

Predictable normocapnia [correction of normocapnoea] in controlled ventilation of infants with Jackson Rees or Bain system

We have devised a formula for ventilator settings which provide normal minute ventilation without rebreathing during controlled ventilation using a Jackson Rees or Bain system. As VT = VS + VF- VL, where VT = delivered tidal volume, VS = set tidal volume, VF = the volume of fresh gas entering during the inspiratory phase and VL = the lost volume due to the compliance of the system, VS was derived: VS = VL + VT x [1-b/(1 + a)] where a = expiratory-to-inspiratory ratio and b = the ratio of fresh gas flow to the minute ventilation. It was evaluated in 62 infants. Arterial partial pressure of carbon dioxide (mean (SD)) was 4.6 (0.5) kPa (35 (4) mmHg) with a range of 3.42-5.78 kPa (26-44 mmHg). The 90th percentile was 5.1 kPa (39 mmHg). It is concluded that predictable normocapnia [corrected] can be conveniently achieved in infants in controlled ventilation with Jackson Rees or Bain system if our formula is applied.     

Laboratory evaluation of the I-NOvent nitric oxide delivery device

The "I-NOvent delivery system" (Ohmeda Inc., Madison, WI, USA) is a device designed to add nitric oxide to a ventilator breathing system so that the inspired nitric oxide concentration remains constant in spite of changes in minute ventilation. In a laboratory study the device maintained the inspired nitric oxide concentration delivered to a model lung in the range 10.2-10.7 parts per million (ppm) when set to deliver 10 ppm, and in the range 40.5-42 ppm when set to deliver 40 ppm, for tidal volumes of 500, 700 and 900 ml, ventilator rates of 10, 15 and 20 bpm, peak inspiratory flow rates of 30, 40 and 50 litre min-1, and square, sine and decelerating ramp flow waveforms.      

Capnographic detection of anaesthesia circle valve malfunctions

To determine whether capnographic waveforms can characterize valve malfunction of the anaesthesia circle, which would enable such problems to be identified and rectified immediately, we monitored capnographic respiratory waveforms during anaesthesia with simulated circle valve malfunctions. Ten mongrel dogs were anaesthetized with pentobarbitone, 25 mg.kg-1 IV, and halothane, 0.5 to 1 per cent. Respiratory gas was sampled from the elbow of the circle system for capnographic monitoring. At fresh gas flow rates of 2.5 or 5 L.min-1 during consecutive periods of controlled and spontaneous ventilation, the inspiratory valve, the expiratory valve, or both valves of the circle system were opened for 15 min. Inspired CO2 concentration increased significantly every time a valve was opened, except during spontaneous breathing at 5 L.min-1. At 2.5 L.min-1, inspired CO2 increased from baseline to 0.41 +/- 0.28 per cent with the inspiratory valve opened and to 2.22 +/- 1.72 per cent with the expiratory valve opened during controlled ventilation and to 0.43 +/- 0.20 per cent and 2.02 +/- 1.28 per cent, respectively, during spontaneous ventilation. Inspired CO2 increased to almost 1 per cent when the inspiratory valve was open and to greater than or equal to 1.89 per cent when the expiratory valve was open. The effects with the expiratory valve open and with both valves open were similar. Capnograms were affected in characteristic ways by the valve malfunctions.     

Pressure and flow limitations of anesthesia ventilators

The effect of increasing airway pressure on the mean inspiratory flow and maximum minute ventilation (VE) capabilities of five anesthesia ventilators (Ohio Anesthesia, Airshields Ventimeter, Ohmeda 7000, Draeger AV-E and Siemens 900D) was compared to identify mechanical factor(s) limiting intraoperative ventilation of the lungs of patients with acute respiratory failure. The effect of increasing airway pressure on mean inspiratory flow was determined by cycling each ventilator through increasing restrictors. Maximum VE was measured under three study conditions using a test lung: 1) low compliance (10-30 ml/cmH2O) and minimal airflow resistance; 2) positive end-expiratory pressure (PEEP) of 0, 10, and 20 cmH2O at a compliance of 20 ml/cmH2O with minimal airflow resistance; and 3) increased resistance (19 +/- 11 cmH2O.1(-1).s-1) and compliance of 30 ml/cmH2O. As airway pressure increased from 0 to 80 cmH2O, mean inspiratory flow decreased markedly for all ventilators except the Siemens. The Siemens ventilator delivered the greatest VE under all three conditions and maintained VE when airway pressure increased due to decreased compliance or the application of PEEP; all other ventilators markedly decreased VE under these conditions. The addition of airway resistance reduced maximal VE for all ventilators by limiting the maximal inspiratory duty cycle (T1/TTOT). Thus, mean inspiratory flow of conventional anesthesia ventilators decreases with increasing airway pressure. The decreased inspiratory flow limits maximum VE when airway pressure is elevated because of decreased lung-thorax compliance and/or increased airway resistance, such as that characterizing patients with acute respiratory failure. Significant airway resistance further limits maximum VE by limiting the maximal T1/TTOT that can be used without increasing end-expiratory lung pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tracheal tube resistance and airway and alveolar pressures during mechanical ventilation in the neonate

The relationship between peak airway pressure, alveolar pressure and respiratory frequency was calculated for the range of compliances and airway resistances which might be encountered during mechanical ventilation of a 3-kg neonate. The pressure/flow relationships of 2.5, 3.0, 3.5 and 4-mm tracheal tubes were determined at a series of flows from 0.5 to 4 litres/minute. Peak airway and alveolar pressures were then measured at various frequencies and inspiratory:expiratory ratios with the tubes incorporated in a model lung. Large differences between peak airway and alveolar pressures developed when frequency was increased or inspiratory time decreased; the differences were greatest with the smaller tubes. Shortening expiratory time by increasing the frequency or altering the inspiratory:expiratory ratio resulted in increased end-expiratory pressure because of incomplete emptying of the lung.     

An unusual cause of anesthetic ventilator malfunction]

We report a case of malfunction of an anesthetic ventilator by an unusual cause. A 48-year-old male with gastric cancer was scheduled for gastrectomy. Anesthesia was maintained with enflurane, N2O, O2 and epidural blockade using a semiclosed circuit system. The patient was ventilated using AV1 anesthetic machine (Dr?ger Co.). Forty minutes after induction of anesthesia, chest movement of the patient suddenly stopped. There was no gas flow to the patient during inspiratory phase. Air leak was not found in anesthetic respiratory circuit and at the bellows of the ventilator. The supply of oxygen and air to the anesthetic machine was sufficient. Since we could not find any cause of the ventilator failure, anesthesia was maintained with manual ventilation by using another anesthetic machine until completion of the surgery. After the surgery, we recognized that the controller unit of expiratory valve of the ventilator was obstructed by a Tamper Proof Film, which seals the outlet of a commercial bag of lactated Ringer's solution (Solulact, Terumo Co.). It seems that the film dropped accidentally between the main part and the ventilator system of anesthetic machine when the bellows was exchanged before the surgery, and moved on to the controller unit of the expiratory valve of the ventilatory system during surgery. In conclusion, it is necessary for anesthetists to understand the inner structure and system of the anesthetic machine and to check the anesthetic machine to avoid the troubles and accidents related to anesthetic machine.     

A circle system with a rotating wick vaporizer

The humidity output of a circle system was raised to 28 mgH₂O/l by the use of a modified rotating wick vaporizer placed in the center of the soda lime canister and coaxial inspiratory and expiratory limbs. Both the fresh gas inflow and the expired gases passed through the lime and reached a compartment below it. The bag/ventilator connector, bearing a pressure relief valve, opened on the lateral wall of that compartment. Gases returning to the inspiratory valve passed: (1) through a tube in the canister connecting the inferior compartment to the vaporizer above water level, (2) through the upper portion of the vaporizer and around the rotating wick, and (3) through a tube emerging from the top of the vaporizer to reach the inspiratory valve. Thus inspired gases were humidified by the rotating wick constantly replenishing its water content warmed by the reaction of neutralization. The use of coaxial inspiratory and expiratory limbs reduced water condensation outside the canister.