Anesthesia Circuit Research Articles

Adhesion of volatile propofol to breathing circuit tubing

Propofol in exhaled breath can be measured and may provide a real-time estimate of plasma concentration. However, propofol is absorbed in plastic tubing, thus estimates may fail to reflect lung/blood concentration if expired gas is not extracted directly from the endotracheal tube. We evaluated exhaled propofol in five ventilated ICU patients who were sedated with propofol. Exhaled propofol was measured once per minute using ion mobility spectrometry. Exhaled air was sampled directly from the endotracheal tube and at the ventilator end of the expiratory side of the anesthetic circuit. The circuit was disconnected from the patient and propofol was washed out with a separate clean ventilator. Propofol molecules, which discharged from the expiratory portion of the breathing circuit, were measured for up to 60 h. We also determined whether propofol passes through the plastic of breathing circuits. A total of 984 data pairs (presented as median values, with 95% confidence interval), consisting of both concentrations were collected. The concentration of propofol sampled near the patient was always substantially higher, at 10.4 [10.25–10.55] versus 5.73 [5.66–5.88] ppb (p < 0.001). The reduction in concentration over the breathing circuit tubing was 4.58 [4.48–4.68] ppb, 3.46 [3.21–3.73] in the first hour, 4.05 [3.77–4.34] in the second hour, and 4.01 [3.36–4.40] in the third hour. Out-gassing propofol from the breathing circuit remained at 2.8 ppb after 60 h of washing out. Diffusion through the plastic was not observed. Volatile propofol binds or adsorbs to the plastic of a breathing circuit with saturation kinetics. The bond is reversible so propofol can be washed out from the plastic. Our data confirm earlier findings that accurate measurements of volatile propofol require exhaled air to be sampled as close as possible to the patient.

Robotic-Assisted Thyroidectomy: A New Experience in Anaesthesia

This is our first experience in providing general anaesthesia for robotic-assisted thyroidectomy (RAT). It is rather a new experience for our anaesthetic team and few issues should be addressed. The conduct of RAT must be fully understood and familiarized as it may present with few challenges for the anaesthesiologists. The key point of success during this learning curve period is the importance of teamwork between the anaesthesiologists and the operating surgeons. The specific anaesthetic challenges include limited access to the patient post-docking of the robot, the need of extra precautions of the anaesthetic circuit and IV line connections, a vigilant anaesthesiologists and options for postoperative pain relief.

Humble Foley's catheter to the rescue in a case of T-tube insertion: a case report.

The Montgomery T-tube poses a challenge to anesthesiologists because of loss of anesthetic gases through the open proximal end of the vertical limb and lack of standard anesthesia circuit connectors. Here, we present a case of a 25-year-old woman with a reported history of accidental strangulation 18 months previously. The patient had a metallic tracheostomy tube in situ due to the development of tracheal stenosis. Computed tomography showed significant narrowing in a 7–8-mm segment, 2 cm proximal to the tracheostomy tube in situ. She was scheduled for tracheal reconstruction surgery and T-tube insertion due to persistent subglottic stenosis. In this case, the Foley's catheter, which was inserted into the glottis orally, not only aided easy insertion of the T-tube into the trachea through the tracheal stoma, but also enabled us to stop the loss of anesthetic gases through the proximal vertical limb of the T-tube.

Newer design, newer problems: Unusual complication with Limb-O anaesthesia circuit.

Newer design, newer problems: Unusual complication with Limb-O anaesthesia circuit.

Bacterial and viral contamination of breathing circuits after extended use - an aspect of patient safety?

In the past, anaesthetic breathing circuits were identified as a source of pathogen transmission. It is still debated, whether breathing circuits combined with breathing system filters can be safely used for more than 1 day. The aim of this study was to evaluate the transmission risk of bacteria and also viruses via breathing circuits after extended use. The inner and outer surface of 102 breathing circuits used for 1 day and of 101 circuits used for 7 days were examined for bacteria and viruses. Additionally, 10 and 20 breathing circuits each were examined after use on patients with pulmonary virus infection and with multidrug-resistant organism (MDRO) colonisation/infection respectively. Bacteria were detected by standard microbiological procedures; PCR techniques were applied for herpes simplex virus, cytomegalovirus, influenza, parainfluenza and respiratory syncytial virus. Endoluminal bacterial contamination of breathing circuits remained unchanged after 7-day vs. 1-day use (5.9% vs. 7.8%) [CI95%: -0.0886-0.0506, pnon-inferiority 0.0260]. Only outside surface contamination with bacteria belonging to environmental species or human flora increased (16.8 vs. 6.9%) [CI 95%: 0.0118 - 0.1876, pnon-inferiority 0.8660]. Viruses occurred on the patient side, but not in breathing circuits. No MDRO occurred in the 20 circuits after use on patients harbouring such germs. Endoluminal contamination of breathing circuits with bacteria did not increase after extended use. No viruses were detected in the breathing circuits using filters. Based on our results, the extended use of ABC without exceptions appears safe, if a high level of anaesthesia workplace cleaning is secured.

Pre-oxygenation using a mouthpiece

Several authors have previously published studies on pre-oxygenation using a mouthpiece 1, 2. We would like to remind readers of the utility of this technique for pre-oxygenating patients who find close-fitting facemasks alarmingly claustrophobic. Using a standard mouthpiece (Intersurgical Ltd, Wokingham, UK) routinely used in obstetric patients for inhaling oxygen/nitrous oxide mixtures, which is detached from the filter it is usually supplied with and attached to the catheter mount of an anaesthetic breathing circuit (Fig. 3), allows for suitable pre-oxygenation when the patient forms a seal around the mouthpiece with their lips and inspires normal tidal ventilations with a fresh gas flow of 10 l.min−1 and an FiO2 of 1.0. The mouthpiece is changed to a standard anaesthetic mask following induction of general anaesthesia, once pre-oxygenation is complete.

Oxygen Reserve Index: A Novel Noninvasive Measure of Oxygen Reserve--A Pilot Study.

Pulse oximetry provides no indication of downward trends in PaO2 until saturation begins to decrease. The Oxygen Reserve Index (ORI) is a novel pulse oximeter-based nondimensional index that ranges from 1 to 0 as PaO2 decreases from about 200 to 80 mmHg and is measured by optically detecting changes in SvO2 after SaO2 saturates to the maximum. The authors tested the hypothesis that the ORI provides a clinically important warning of impending desaturation in pediatric patients during induction of anesthesia. After preoxygenation, anesthesia induction, and tracheal intubation, the anesthesia circuit was disconnected and oxygen saturation was allowed to decrease to 90% before ventilation recommenced. The ORI and SpO2 values were recorded from a Masimo Pulse Co-Oximeter Sensor at the beginning of apnea, beginning and end of intubation, beginning and end of the ORI alarm, and 2 min after reoxygenation. Data from 25 healthy children, aged 7.6 ± 4.6 yr, were included in the analysis. During apnea, the ORI slowly and progressively decreased over a mean of 5.9 ± 3.1 min from 0.73 ± 0.16 at the beginning of apnea to 0.37 ± 0.11. SpO2 remained 100% throughout this initial period. Concurrently with alarm activation, the ORI began to decrease rapidly, and in median of 31.5 s (interquartile range, 19 to 34.3 s), saturation decreased to 98%. In this pilot study, the ORI detected impending desaturation in median of 31.5 s (interquartile range, 19-34.3 s) before noticeable changes in SpO2 occurred. This represents a clinically important warning time, which might give clinicians time for corrective actions.

Assessment of Common Preoxygenation Strategies Outside of the Operating Room Environment.

Preoxygenation prior to intubation aims to increase the duration of safe apnea by causing denitrogenation of the functional residual capacity, replacing this volume with a reservoir of oxygen. In the operating room (OR) the criterion standard for preoxygenation is an anesthetic circuit and well-fitting face mask, which provide a high fractional inspired oxygen concentration (FiO2 ). Outside of the OR, various strategies exist to provide preoxygenation. The objective was to evaluate the effectiveness of commonly used preoxygenation strategies outside of the OR environment. This was a prospective randomized unblinded study of 30 healthy staff volunteers from a major trauma center emergency department (ED) in Sydney, Australia. The main outcome measure is fractional expired oxygen concentration (FeO2 ) measured after a 3-minute period of tidal volume breathing with seven different preoxygenation strategies. The mean FeO2 achieved with the anesthetic circuit was 81.0% (95% confidence interval [CI] = 78.3% to 83.6%), bag-valve-mask (BVM) 80.1% (95% CI = 76.5% to 83.6%), BVM with nasal cannula (NC) 74.8% (95% CI = 72.0% to 77.6%), BVM with positive end-expiratory pressure valve (PEEP) 78.9% (95% CI = 75.4% to 82.3%), BVM + NC + PEEP 75.5% (95% CI = 72.2% to 78.9%), nonrebreather mask (NRM) 51.6% (95% CI = 48.8% to 54.4%), and NRM + NC 57.1% (95% CI = 52.9% to 61.2%). Preoxygenation efficacy with BVM strategies was significantly greater than NRM strategies (p < 0.01) and noninferior to the anesthetic circuit. In healthy volunteers, the effectiveness of BVM preoxygenation was comparable to the anesthetic circuit (criterion standard) and superior to preoxygenation with NRM. The addition of NC oxygen, PEEP, or both did not improve the efficacy of the BVM device.

A Non-Blinded, Case Controlled Pilot Study to Evaluate a Novel Mask Ventilation Technique in Patients with Established Risk Factors for Difficult Mask Ventilation

Traditionally, there are two main methods of mask placement during face mask ventilation: one handed (CE) grip and two handed grip (THT). One handed grip is limited by air leaks between mask and patients face on the side opposite to stabilizing hand. Two handed grips provide protection against air leak but require second provider to deliver tidal volumes when using a self inflating bag or anesthesia circuit on manual ventilation. This study introduces modified CE grip which creates a firm seal at patient’s face on both sides of mask, enabling adequate tidal volume delivery with provider’s second hand. Using left hand, provider places the fifth digit along inferior border of body of left mandible. The fourth digit is placed along inferior border of body right mandible. Standing 6 inches to the left and immediately behind a supine patient on an OR table, provider rotates clockwise 45 degrees at hip, keeping elbow against their body, and lifts patient’s chin to 45 degrees. Rotational force at hip augments hand strength while tilting chin. The thumb applies pressure along left border of facemask, and the second and third digits apply pressure to right border of facemask. Methods: Patients with known predictors of difficult mask ventilation (Edentulous, bearded, Obstructive sleep apnea (OSA), mallampati 3 or 4) were in experimental group. Normal patients assigned as Controls. After induction of general anesthesia, provider ventilated patient using adult sized facemask. The anesthesia ventilator delivered standardized tidal volumes. TV, airway pressures, HR and O2 saturation were recorded after each breath. Results: All groups, except OSA, showed improvement, in tidal volumes with the novel technique compared to the traditional CE grip. Conclusion: The novel submandibular technique, an important skill, increases tidal volumes during mask ventilation for certain high risk patients.

Defective heat moisture exchange filter causing 'block' in anaesthesia breathing circuit.

Sir, We describe a case where a blocked heat moisture exchange (HME) filter was missed in the pre-anaesthesia machine check leading to a potentially life-threatening situation. An American Society of Anaesthesiologists physical status I, female patient was scheduled for exploratory laparotomy. Anaesthesia Machine (Datex Ohmeda S/5 Avance®) with disposable anaesthesia breathing circuit from “Airway Surgicals®,” was used for the case. Anaesthesia machine was checked as per the Association of Anaesthetists of Great Britain and Ireland (AAGBI) recommendations, and standard monitoring recommended by AAGBI was attached to the patient.[1] The patient was pre-oxygenated and administered glycopyrrolate 0.2 mg, fentanyl 100 μg and propofol 120 mg intravenously. Once the patient stopped breathing, mask ventilation was attempted which was unsuccessful even after insertion of an oral airway. The immediate concern was that this was an unanticipated difficult airway. As the patient was apnoeic and adequately relaxed under the effect of propofol, the airway was quickly secured by endotracheal intubation. The airway resistance remained high after intubation and auscultation revealed a silent chest. Considering bronchospasm as a likely cause, intravenous hydrocortisone and vecuronium were administered and the depth of anaesthesia was increased with sevoflurane. There was no change in the resistance to ventilation, but the capnography showed a trace of low amplitude. As the reservoir bag felt different, some malfunction of the anaesthesia equipment was suspected. A non-rebreathing (AMBU) bag was connected with the filter and catheter mount in the circuit, but the air entry did not improve. The catheter mount and filter were removed immediately, and the AMBU bag was directly connected to the tube and the lungs could be ventilated easily. Air entry was bilaterally equal. ETCO2 trace was normal and airway pressure was also reduced. Auscultation of the chest showed clear breath sounds. It was evident that the problem was due to blocked filter which was immediately replaced. The surgery was completed and the patient made an uneventful recovery from anaesthesia. The oxygen saturation did not drop below 96% at any point during the episode. Possibly, there was some air entry in the lungs through the blocked filter, and the actions described above were carried out swiftly with the help of other anaesthetists who were in the theatre complex. On subsequent investigation, it was discovered that the two bag test was completed without connecting the HME filter and catheter mount.[2] Probably, the obstruction in the breathing system would have been picked up, had the circuit been completely assembled while checking. Obstructions in the anaesthesia breathing circuits have been reported due to various foreign bodies.[3] We concluded that the HME filter had a manufacturing defect on the basis of elimination. The filter was dismantled and assessed. It consisted of two discs, one of green foam and another thin white papery disc. On using individual components of the filter, it was evident that the green foam of the filter was blocked. On pressing the oxygen flush, the blast could not be felt at the tube connector end. As there was no possible technique to confirm the structural defect in the foam, one possibility that can be considered is compression of the disc in the filter making them impermeable. This report adequately delineates the importance of anticipating problems and finding prompt solutions by stepwise exclusion of apparatus failure. Anticipating trouble, innovating and learning from the experience of others are inherent in the anaesthesia community. An important learning point from this case is, in the event of ‘Tight Bag’ during anaesthesia, the anaesthesia circuit should be immediately replaced by the AMBU bag at the end of the endotracheal tube.[4] This will ensure that the patient is safely oxygenated while the equipment issues are resolved. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Threshold valves to create positive end-expiratory pressure (PEEP) in conventional large animal anaesthesia ventilators and circuits

Threshold valves to create positive end-expiratory pressure (PEEP) in conventional large animal anaesthesia ventilators and circuits

消毒机程序与不同定时消毒对消毒效果的比较

目的：观察消毒机程序消毒与定时消毒对较高值2类医用品的消毒效果。方法：利用麻醉机呼吸回路消毒机对医用品进行程序消毒，与定时45 min、60 min两种不同时间对医用品进行消毒，检验三种方法的消毒效果，进行临床对比。结果：消毒机程序消毒与单项定时60 min进行医用品消毒，两种方法均达到高水平的消毒效果，细菌培养均阴性。单项定时45 min消毒时间，医用品消毒表面有细菌生长。结论：使用消毒机自身设计的程序消毒和单项定时60 min进行医用品消毒，均能达到高水平的消毒效果，安全可靠。单项定时45 min消毒时间，医用品消毒表面有细菌生长，达不到高水平的消毒效果。 Aim: To observe the disinfection effect of disinfection machine procedure and regular disinfection on 2 kinds of high-value medical supplies. Methods: The anesthetic machine breathing circuit disinfector in terms of program, and two different time of 45 min as well as 60 min were used in disinfection of medical supplies; the disinfection effect of these above three methods was tested and compared clinically. Result: Disinfection using disinfection machine procedure and single timing of 60 min all reached high-level effect, and bacterial cultures were negative. While when the single timing was 45 min, bacteria grew on the medical supplies’ disinfection surface. Conclusion: Using disinfection machine procedure and single timing of 60 min for disinfection of medical supplies can reach high-level disinfection effect, and these two methods are safe and reliable. Nevertheless disinfection of 45 min single timing results in bacteria growth on medical supplies’ disinfection surface, which cannot get high-level disinfection effect.

Difficult bag mask ventilation: Catheter mount cap, a cause for concern.

Sir, Use of disposable products is common in anaesthesia practice. Occasionally, aberrations can occur in this type of equipment. Failure to check equipment properly is an important factor leading to potential critical events. Proper checking of equipment before use may help prevent equipment-related morbidity and mortality, improve preventive maintenance and educate the provider about equipment.[1] Unfortunately, failure to perform a proper check before use is common.[2] A 54-year-old female patient was posted for examination under anaesthesia and a cervical biopsy in the minor operation theatre. Prior to induction of general anaesthesia, the oxygen saturation was 99%. Following induction with fentanyl and propofol, we encountered a tight bag situation while using the face mask and could not ventilate the patient. There was no chest rise and no air entry on auscultation. We increased the depth of anaesthesia, optimised mask holding and used an oral airway. On visual inspection, the anaesthesia circuit assembly appeared appropriate. The bag continued to remain tight with no chest expansion, with no obvious reason for difficult mask ventilation. Post-induction, the oxygen saturation was 98%. The mask was disconnected from the circuit to connect to a self-inflating reservoir bag for ventilation, anticipating desaturation due to the lapsed time. The patient could be ventilated easily using the self-inflating reservoir bag. Much to our surprise, we saw a red-coloured cap occluding the mask, which was completely concealed when connected to the catheter mount [Figure 1a]. The red-coloured catheter mount cap was not removed before connecting to the mask and had resulted in the complete circuit obstruction [Figure 1b]. Once recognized, the cap was removed, the patient could be ventilated easily and the anaesthesia proceeded uneventfully. Figure 1 (a) Catheter mount cap concealed in the mask, (b) complete obstruction of the mask with cap (viewed from above), (c) complete obstruction of the mask with cap (viewed from below), (d) catheter mount covered with cap The red cap covering the catheter mount connected to the mask if not noticed on time could have led to potentially dangerous consequences. This was not a manufacturing defect, and interestingly, the cap fitted perfectly well into the mask [Figure 1c]. This was not detected through the mask as it was semi-opaque. These caps may often be transparent and may not be picked up even through a transparent mask. The catheter mount with the cap [Figure 1d] was connected to the mask by a new operating room technician who was unaware of the consequences. In a busy place like the minor operation theatre with a rapid turnover, due to paucity of time, things are often hurried leading to failure to perform a proper equipment check. A visual check may well have picked up the fault.[3] On doing a root cause analysis, we discovered that the circuit had been checked by the provider; however, the disposable catheter mount was attached in the circuit and fitted to the mask by the technician just prior to induction of anaesthesia and the cap thus went unnoticed. The anesthesia apparatus check-out recommendations[4] clearly states that though the technician may have a role in checking the equipment, the ultimate responsibility for ensuring that the equipment functions properly lies with the anaesthesia provider. Thus, failure to check the complete breathing system assembly may account for serious negligence on the part of the anaesthesia provider. This case reaffirms the importance of a complete cockpit drill before conducting anaesthesia. Financial support and sponsorship We have no financial support and sponsorship Conflicts of interest There are no conflicts of interest.

Airway management in a child with partial mandibulo-maxillary fusion.

Sir, Syngnathia, bony maxilla-mandibular fusion, is a rare anomaly and usually associated with cleft palate or other systemic anomalies. We herewith describe a method to maintain adequate depth of anaesthesia while managing airway by fibre-optic (FO) intubation. A 4-month-old female child weighing 3.5 kg with congenital complete fusion of left mandible and maxilla with 0.2 cm opening on right side [Figure 1] presented to the hospital. History revealed that the patient was more comfortable in either of the lateral positions. Her routine haematological, biochemical and radiological workup was normal. Reconstructed three-dimensional computed tomography scan images of the skull showed complete left-sided mandibulo-maxillary fusion, with opening seen on the right [Figure 2]. She was scheduled for left maxilla-mandibular release. An FO nasal intubation while maintaining spontaneous ventilation was planned. Nebulisation with lignocaine spray (2%, 10.5 mg) was started 20 min before surgery. Nasal packing with 1:100,000 adrenaline was done. Intravenous glycopyrrolate (4 μg/kg) was administered. Anaesthesia induction was started with O2, N2O and sevoflurane (gradually increased to 8% and maintained at 2%), with gradually increasing concentration of inhalational agent, following which size 2.5 mm (internal diameter [ID]) of endotracheal tube (ETT) was passed through right nostril up to nasopharynx. Jackson Rees’ circuit was connected; bag movements corresponded with chest expansion and end-tidal CO2; FO bronchoscope (FOB) with size 2.5 mm ID of ETT loaded was over it and was passed through the left nostril and cords were negotiated in the first attempt. After confirming ventilation, muscle relaxant (injection atracurium, 0.5 mg/kg) was administered and surgical procedure started. Peri-operatively, the patient was maintained on O2, N2O, sevoflurane (2%) and intermittent doses of muscle relaxant. Surgical procedure lasted for approximately 90 min. Bony release of the left maxilla and mandible was done. Blood loss was around 25 ml, which was replaced by crystalloids. Infra-orbital, greater palatine and postero-superior alveolar block were given for post-operative pain relief. At the end of procedure, immediate extubation was circumvented to avoid airway compromise from soft tissue oedema during the post-operative period. The patient was shifted to intensive care unit with T-piece and extubated after 12 h.Figure 1: Complete fusion of the left mandible and maxilla with 0.2 cm opening on the right sideFigure 2: Reconstructed volume rendered three-dimensional computed tomography images of skull showing complete left-sided mandibulo-maxillary fusion, with opening seen on the rightMaxillo-mandibular fusion is a rare group of anomalies varying in severity from simple mucosal adhesions (synechiae) to extensive bony fusion (syngnathia), depending on the amount of mesodermal penetration. True bony fusion is a very rare anomaly, and only a handful of case reports exist in literature.[1] Adhesion can be complete or incomplete, unilateral or bilateral, with an anterior opening. Problems associated with syngnathia include maintenance and protection of the airway, feeding difficulties and particularly when surgical correction is planned – difficulty in induction of anaesthesia.[2] Securing airway is the biggest challenge in patients. With history of airway obstruction, our aim was to maintain spontaneous ventilation. Adequate preparation of upper airway is important as even the slightest bleeding leads to aspiration and complications such as laryngospasm, bronchospasm or difficulty in ventilation; readiness for emergency tracheostomy is therefore important. Meier et al. showed that continuous positive airway pressure (CPAP) in addition to chin lift and jaw thrust nearly doubled the size of the glottic opening by working as a pneumatic splint, as visualised by FOB.[3] An elegant way of providing CPAP/positive end-expiratory pressure while simultaneously handling a difficult airway with an FOB through one nostril is by inserting an ETT (3.0–3.5) as a nasopharyngeal airway approximately 8 cm into the contralateral nostril attached to an anaesthetic circuit.[4] This helps in giving CPAP, provides passive flow of O2 and inhalational agents, providing stable plane of anaesthesia; at the same time, bag movements assess breathing pattern. Thus, use of FOB can be facilitated using an endotracheal tube, connected to an anaesthetic circuit and passed till nasopharynx. However, utmost care is required to avoid mucosal bleeding and oedema due to airway manipulation. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

A simple method for isocapnic hyperventilation evaluated in a lung model.

Isocapnic hyperventilation (IHV) has the potential to increase the elimination rate of anaesthetic gases and has been shown to shorten time to wake-up and post-operative recovery time after inhalation anaesthesia. In this bench test, we describe a technique to achieve isocapnia during hyperventilation (HV) by adding carbon dioxide (CO2) directly to the breathing circuit of a standard anaesthesia apparatus with standard monitoring equipment. Into a mechanical lung model, carbon dioxide was added to simulate a CO2 production (V(CO2)) of 175, 200 and 225 ml/min. Dead space (V(D)) volume could be set at 44, 92 and 134 ml. From baseline ventilation (BLV), HV was achieved by doubling the minute ventilation and fresh gas flow for each level of V(CO2), and dead space. During HV, CO2 was delivered (D(CO2)) by a precision flow meter via a mixing box to the inspiratory limb of the anaesthesia circuit to achieve isocapnia. During HV, the alveolar ventilation increased by 113 ± 6%. Tidal volume increased by 20 ± 0.1% during IHV irrespective of V(D) and V(CO2) level. D(CO2) varied between 147 ± 8 and 325 ± 13 ml/min. Low V(CO2) and large V(D) demanded a greater D(CO2) administration to achieve isocapnia. The FICO2 level during IHV varied between 2.3% and 3.3%. It is possible to maintain isocapnia during HV by delivering carbon dioxide through a standard anaesthesia circuit equipped with modern monitoring capacities. From alveolar ventilation, CO2 production and dead space, the amount of carbon dioxide that is needed to achieve IHV can be estimated.

The CO2 Absorber Based on LiOH

Abstract Carbon dioxide absorbers have been used in anesthesiology for many years. However, this process is not limited to this field of medicine. Removing carbon dioxide from human environment is used in other areas as well: mining industry, submarines, scuba diving, space travel and many others. The rationale to remove carbon dioxide from confined spaces is that cannot be eliminated otherwise. Anesthesia practitioners are well aware of this component of the circle system, the carbon dioxide absorber. In daily practice the clinician is less concerned with what kind of substance fills the dedicated canister, as this is usually in the care of the maintenance personnel. The appearance of Sevoflurane and Desflurane, with their own chemical characteristics, prompted the clinician to dedicate new attention to these absorbents. The classical substances used for this purpose are different combinations of limes. The practical concern of the anesthesiologist is to notice when the absorbent is consumed and call for its replacement. Still, many other aspects remain: compound A formation with Sevoflurane, carbon monoxide formation with Desflurane and dry absorbent for instance. The latest member of these products in the medical field is the LiOH carbon dioxide absorbent. Although used for many years in the space exploration, its way into the operating room is a rather recent achievement. Special chemical properties and high absorptive capacity make this new type of absorbent an attractive option for modern anesthesia practice. The article below invites the reader through a short journey on the history of the CO2 absorbents and anesthesia circuits, Lithiumas a chemical element and, finally, to this new type of absorbent.

Cardiovascular function during maintenance of anaesthesia with isoflurane or alfaxalone infusion in greyhounds experiencing blood loss

ObjectiveTo compare adequacy of oxygen delivery and severity of shock during maintenance of anaesthesia with isoflurane or alfaxalone infusion in greyhounds experiencing blood loss. Study designProspective, randomised study. AnimalsTwenty-four greyhounds (ASA I). MethodsAll greyhounds were premedicated with methadone (0.2 mg kg−1) intramuscularly. Anaesthesia was induced with alfaxalone 2.5 mg kg−1intravenously. Following endotracheal intubation, the dogs were connected to an anaesthetic circle circuit delivering oxygen. Dogs were allocated to receive inhaled isoflurane or an intravenous infusion of alfaxalone for maintenance of anaesthesia. Isoflurane was initially administered to achieve an end-tidal concentration of 1.4% and alfaxalone was initially administered at 0.13 mg kg−1 minute−1. The dose of isoflurane or alfaxalone was adjusted during instrumentation to produce a clinically equivalent depth of anaesthesia. All dogs were mechanically ventilated to normocapnia (PaCO2 35–40 mmHg; 4.67–5.33 kPa). Passive warming maintained core body temperature between 37 and 38 °C. Measured and calculated indices of cardiovascular function, including mean arterial blood pressure (MAP), cardiac index (CI), systemic vascular resistance index (SVRI), oxygen delivery index ( D˙O2I), oxygen consumption index ( V˙O2I) and oxygen extraction ratio (OER), were determined at baseline (60 minutes after start of anaesthesia) and after removal of 32 mL kg−1and 48 mL kg−1of blood. ResultsIn all dogs, blood loss resulted in a significant decrease in MAP, CI, D˙O2, and a significant increase in SVRI, V˙O2I, and OER. The changes in each of the indices did not differ significantly between dogs receiving isoflurane and dogs receiving alfaxalone. Conclusion and clinical relevanceNo difference in oxygen delivery or severity of shock was observed when either inhaled isoflurane or intravenous alfaxalone infusion was used for maintenance of anaesthesia in greyhounds experiencing blood loss. There appears to be no clinical advantage to choosing one anaesthetic agent for maintenance of anaesthesia over the other in a dog experiencing blood loss.

Anaesthetic in the garb of a propellant.

Anaesthetic in the garb of a propellant.

Foregut reduplication cyst: Anaesthetic implications of the rare anomaly.

Sir, Congenital duplications can occur anywhere in the gastrointestinal tract and one-third of all duplications are foregut duplications.[1] A 6-month-old male child weighing 4 kg was admitted in our hospital with the history of recurrent productive cough with intermittent fever for 4 months. He was born full term by normal vaginal delivery. The child was apparently well till 2 months of age after which he started developing repeated episodes of cough and cold with fever. Child was febrile (102° F), lethargic with respiratory rate of 28-30/min. Breath sounds were markedly decreased on the right side of the chest. X-ray chest showed a homogenous opacity in mid-thoracic region compressing the right lung. The computed tomography [Figure 1] scan of chest revealed a large cystic mass (7 cm × 4 cm × 4 cm) in posterior mediastinum extending from the lung apex to base and reaching the opposite mediastinum posterior to oesophagus causing displacement of oesophagus and bronchus anteriorly. It also showed mild pleural effusion on the right side. A provisional diagnosis of foregut duplication cyst was made, and cyst excision via right thoracotomy was planned. Figure 1 Computed tomography scan of the thorax showing the cyst His pre-operative blood investigations were all normal. Once the patient arrived, monitors including electrocardiography (ECG), oxygen saturation (SpO2) and non-invasive blood pressure were placed. No sedative premedication was given. After pre-oxygenation, anaesthesia was induced with sevoflurane in graded concentration and an intravenous line secured. Intubation was performed under sevoflurane with a 4 mm uncuffed flexometallic endotracheal tube. Injection fentanyl 10 μg and injection vecuronium 0.4 mg were then given, and anaesthesia maintained with isoflurane and O2/N2O (50:50). Right internal jugular and right radial arterial cannulation were performed. Intraoperative monitoring included ECG, intra-arterial blood pressure, SpO2, nasopharyngeal temperature, end-tidal carbon dioxide, airway pressures, urine output, central venous pressure and intermittent arterial blood gas (ABG) analysis. The cyst was removed after mobilization that took 3 h. Warming mattress and radiant warmer were used to maintain normothermia. The estimated blood loss was around 300 ml, which was replaced with packed cells. Intercostal block was given with 6 ml of injection bupivacaine 0.125% and rectal suppository of paracetamol 80 mg inserted for post-operative analgesia. The patient was extubated uneventfully in the end and shifted to post-operative care unit. The post-extubation ABG was normal with pH - 7.4; pCO2-38 mmHg; HCO3-20 mmol/L; PaO2-98 mm Hg and SpO2-97% on oxygen by mask at 4 L/min. The post-operative course was uneventful, and the child was discharged after 15 days. The biopsy report later confirmed the diagnosis. Foregut malformation cysts are the second most common cause of posterior mediastinal mass after the neural tumours.[2] An embryonic defect in vacuolization of the oesophagus results in duplication and normally occurs in the 6th week of gestation.[1] The fusion anomalies of cervical and upper thoracic vertebral bodies are encountered in 80% of these cases due to the defect in their embryological development.[2] Although the mean age of onset of symptoms was 49.4 months in a study by Cohen et al., it ranges from 1 month to 18 years.[2] Most cases present with respiratory distress, which may be present from birth. Sometimes the symptoms may be delayed with sudden onset cough, wheeze or recurrent respiratory infections. In rare cases the cyst may perforate into the bronchial tree.[1] Extension of the cyst into the infradiaphragmatic area may cause gastrointestinal symptoms and extension into the neural canal can cause signs of spinal cord compression.[3] Cysts require total excision, to prevent cancer development or recurrence of symptoms.[2] The incidence of complications with the induction of anaesthesia in patients with mediastinal masses has been reported to be 7-18% including refractory cardio-respiratory collapse.[4,5] Inhalational induction with sevoflurane was chosen with a hope that the spontaneous ventilation will preserve the diaphragmatic movements in a caudal direction, and a normal transpleural pressure gradient will be maintained preventing airway collapse. Intubation was also carried out without muscle relaxants with a flexometallic tube to cause splinting of the trachea beyond the obstruction.[6,7] Successful use of femoro-femoral cardiopulmonary bypass (CPB) has been described in patients with mediastinal masses to restore the oxygenation in the event of severe life-threatening hypoxia.[4] Tempe et al. have recommended femoral vessel cannulation under local anaesthesia and CPB circuit primed and kept ready before induction of GA in symptomatic patients with a mediastinal mass.[8] Invasive haemodynamic monitoring is mandatory in these cases as severe cardiorespiratory embarrassments are noted. Good post-operative analgesia is a must after thoracotomy to hasten recovery. We used intercostal block, and rectal acetaminophen as thoracic epidural in infants is not a technique that is commonly practiced in our institution. We could successfully extubate the patient on the table after end of surgery, and he had an uneventful recovery.

Time course of end-tidal desflurane concentration during delivery and elimination according to the type and location of filters in a semi-closed circuit system.

BackgroundThe aim of this study was to determine whether the end-tidal concentration of desflurane would be affected by a breathing circuit system filter attached at two different positions in anesthetic breathing circuit systems.MethodsAn artificial lung was ventilated under five different conditions. The first group was without any filter or desflurane (n = 5, sham), the second was with desflurane but without any filter (n = 10, control), the third group had a bacterial filter on the expiratory limb (n = 10), and the fourth and fifth groups had a viral/bacterial filter added on the expiratory limb (n = 10) or at the Y-piece of the breathing circuit (n = 10), respectively. In all groups except the sham, administration of 10% desflurane was performed for 5 minutes and then stopped for 5 minutes.ResultsThe mean (SD) end-tidal concentration of desflurane for the groups described above peaked at 0 (0), 9.8 (0.1), 9.8 (0.1), 8.5 (0.1), and 6.7% (0.1) (P < 0.001), respectively. There was no difference in the desflurane concentrations and the expired tidal volume over time between the control and bacterial group, but there was a significant difference between the control and the fourth and fifth groups (P < 0.001).ConclusionsFilters can affect the expiratory desflurane concentration during anesthesia.