Adjustable Pressure-limiting Valve Research Articles

A threshold of 100 or more colony-forming units on the anesthesia machine predicts bacterial pathogen detection: a retrospective laboratory-based analysis.

Preventing the spread of pathogens in the anesthesia work area reduces surgical site infections. Improved cleaning reduces the percentage of anesthesia machine samples with ≥ 100 colony-forming units (CFU) per surface area sampled. Targeting a threshold of < 100CFU when cleaning anesthesia machines may be associated with a lower prevalence of bacterial pathogens. We hypothesized that anesthesia work area reservoir samples returning < 100CFU would have a low (< 5%) prevalence ofpathogens. In this retrospective cohort study of bacterial count data from nine hospitals, obtained between 2017 and 2022, anesthesia attending and assistants' hands, patient skin sites (nares, axilla, and groin), and anesthesia machine (adjustable pressure-limiting valve and agent dials) reservoirs were sampled at case start and at case end. The patient intravenous stopcock set was sampled at case end. The isolation of ≥ 1CFU of Staphylococcus aureus, methicillin-resistant Staphylococcusaureus, Enterococcus, vancomycin-resistant Enterococcus, gram-negative (i.e., Klebsiella, Acinetobacter, Pseudomonas, and Enterobacter spp.) or coagulase-negative Staphylococcus was compared for reservoir samples returning ≥ 100CFU vs those returning < 100CFU. Bacterial pathogens were isolated from 24% (7,601/31,783) of reservoir samples, 93% (98/105) of operating rooms, and 83% (2,170/2,616) of cases. The ratio of total pathogen isolates to total CFU was < 0.0003%. Anesthesia machine reservoirs returned ≥ 100CFU for 44% (2,262/5,150) of cases. Twenty-three percent of samples returning ≥ 100CFU were positive for ≥ 1 bacterial pathogen (521/2,262; 99% lower confidence limit, 22%) vs 3% of samples returning < 100CFU (96/2,888; 99% upper limit, 4%). Anesthesia machine reservoir samples returning < 100CFU were associated with negligible pathogen detection. This threshold can be used for assessment of terminal, routine, and between-case cleaning of the anesthesia machine and equipment. Such feedback may be useful because the 44% prevalence of ≥ 100CFU was comparable to the 46% (25/54) reported earlier from an unrelated hospital.

Pressure-controlled versus manual facemask ventilation for anaesthetic induction in adults: A randomised controlled non-inferiority trial.

Pressure-controlled face mask ventilation (PC-FMV) with positive end-expiratory pressure (PEEP) after apnoea following induction of general anaesthesia prolongs safe apnoea time and reduces atelectasis formation. However, depending on the set inspiratory pressure, a delayed confirmation of a patent airway might occur. We hypothesised that by lowering the peak inspiratory pressure (PIP) when using PC-FMV with PEEP, confirmation of a patent airway would not be delayed as studied by the first return of CO2 , compared with manual face mask ventilation (Manual FMV). This was a single-centre, randomised controlled non-inferiority trial. Seventy adult patients scheduled for elective day-case surgery under general anaesthesia with body mass index between 18.5 and 29.9 kg m-2 , American Society of Anesthesiologists (ASA) classes I-III, and without anticipated difficult FMV, were included. Before the start of pre-oxygenation and induction of general anaesthesia, participants were randomly allocated to receive ventilation with either PC-FMV with PEEP, at a PIP of 11 and a PEEP of 6 cmH2 O or Manual FMV, with the adjustable pressure-limiting valve set at 11 cmH2 O. The primary outcome variable was the number of ventilatory attempts needed until confirmation of a patent airway, defined as the return of at least 1.3 kPa CO2 . The return of ≥1.3 kPa CO2 on the capnography curve was observed after mean ± SD, 3.6 ± 4.2 and 2.5 ± 1.9 ventilatory attempts/breaths with PC-FMV with PEEP and Manual FMV, respectively. The difference in means (1.1 ventilatory attempts/breaths) had a 99% CI of -1.0 to 3.1, within the accepted upper margin of four breaths for non-inferiority. Following induction of general anaesthesia, PC-FMV with PEEP was used without delaying a patent airway as confirmed with capnography, if moderate pressures were used.

The importance of post marketing quality control

BACKGROUND A previously published study reported on the nonlinear behaviour for airway pressure and tidal volume of the adjustable pressure-limiting (APL) valve of the Aisys CS2 anaesthesia machine (GE Healthcare, Madison, Wisconsin, USA) during manual bag ventilation. In co-operation with the manufacturer, an adapted APL valve was developed. OBJECTIVE To test and characterise the performance of an adapted APL valve and assess its clinical usability. DESIGN Two-stage study, consisting of an in-vitro testing of an adapted APL valve in a baby and adolescent lung model, followed by a clinical experience survey of anaesthesia personnel after the official implementation of the new APL valve into clinical routine. SETTING Anaesthesia Department at the University Children's Hospital Zurich. MAIN OUTCOME MEASURES Airway pressures and inspiratory tidal volumes during opening and closure of the APL valve at different settings. Likert scale assessment of performance expectance, effort expectance, behavioural intention and safety of the APL valve during clinical use. RESULTS In contrast to the original APL valve of the GE Aisys CS2, the adapted APL valve showed a nearly linear increase in airway pressures as well as in the tidal volumes measured. Most importantly, the measured pressures never exceeded the set pressures. Based on the experimental findings, all original APL valves of the GE Aisys CS2 were replaced by the adapted APL valve. Two months later, an anonymised and standardised questionnaire was handed out to all employees working with the adapted APL valve. Analysis of the questionnaire indicated that the adapted APL valve is easier and more precise to handle in the daily routine than the original one. CONCLUSION The newly adapted APL valve for the GE Aisys CS2 has considerably improved its linearity at lower pressures and supports our institution's bag mask ventilation practices.

Response to comments on 'Hypertension and tachycardia following high spinal anaesthesia during LSCS: An unusual presentation'.

Dear Editor, We read with interest the comments[1] to our published article,[2] and we would like to address the queries raised on a point-to-point basis. With regard to the timeline of events during the episode of hypotension, we would like to reiterate that, as mentioned in the article,[2] the blood pressure (BP) of the patient fell to 78/40 mmHg immediately after the administration of the subarachnoid block, and that following this vasopressors and intravenous (IV) fluids were given. After one minute, her BP had improved. However, after five minutes of our having administered the subarachnoid block, she complained of breathlessness. Closed breathing circuits have myriad advantages, such as providing a constant and higher fraction of inspired oxygen (FiO2), removing carbon dioxide from the expired gases, and offering lesser resistance when compared to an endotracheal tube. The work of breathing may increase when the adjustable pressure-limiting (APL) valve is partially or fully closed, providing an obstacle to the egress of gases, or when the set flow is not enough to meet the patient’s peak inspiratory flows.[3] However, the APL valve was kept open when applying the closed circuit on our patient, and a flow of 15 L/min was ensured, thereby thwarting any possibility of increased work of breathing. Our patient presented with breathlessness stemming from hypoventilation, which was more a cause rather than a symptom of probable hypercarbia. She exhibited mild agitation at that time but did not appear confused or flushed. We were unable to corroborate our clinical findings with a blood gas, as stabilizing the mother and baby took precedence over the former. However, the tidal volume and end-tidal capnography were suggestive of hypoventilation and resultant hypercarbia. We again reiterate that, as mentioned in our article,[2] other possible causes of hypertension, such as distended urinary bladder, patient anxiety, inappropriately sized non-invasive BP cuff, and pre-existing hypertensive disorders, were ruled out. Informed consent The patient has given informed consent. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Effect of different ventilation strategies during cardiopulmonary bypass on cardiac de-airing in congenital cardiac surgery: A trans-esophageal echocardiography comparative study

ABSTRACT Objectives This study was conducted to evaluate the efficacy of using either low tidal ventilation or continuous positive pressure ventilation on the quality of de-airing procedure during cardiopulmonary bypass (CPB) surgery for correction of congenital heart diseases. Patients and methods This study was conducted on 48 children under the age of 6 years scheduled for elective correction of congenital heart diseases. Patients were randomly allocated into three groups. In the low tidal volume (LTV) group, ventilator was set to a respiratory rate of 5 breaths per minute with tidal volume of 2–3 ml/kg of ideal body weight and a positive end-expiratory pressure of 3–5 cmH2O. In continuous positive airway pressure (CPAP) group, oxygen flow was maintained at 0.5 L/min during CPB, ventilator was shut off and the adjustable pressure-limiting valve (APL) was set at a pressure of 10 cmH2O. In the no ventilation (NV) group, ventilator was shut off, fresh flow air was completely stopped and APL was adjusted on spontaneous position. The primary outcome was the total de-airing time using transesophageal echocardiography. Results The total de-airing time was significantly decreased in CPAP group, with the shortest duration of 246.88 ± 5.40 sec in comparison to both LTV group with 284.25 ± 6.52 sec and NV group with 452.12 ± 26.6 sec with p-value 0.001. Conclusion Use of CPAP 10 cmH2O ventilation during CPB surgery for correction of congenital heart diseases could improve the process of de-airing by decreasing the total time needed to de-air heart chambers.

A closed ‘pop‐off’ valve and patient safety incident: A human factors approach to understanding error

AbstractA 3‐month‐old, 1.4 kg, female domestic short hair cat was scheduled for ovariohysterectomy surgery during a final‐year veterinary student clinical rotation. Shortly after transfer to the operating room (OR) and connection to the anaesthetic machine, signs consistent with high gas pressure build up in the anaesthetic breathing system were observed. Because a clear view of the anaesthetic machine was obscured, the cat was immediately disconnected from the breathing system and transferred to a different anaesthetic machine. Inspection of the OR anaesthetic machine revealed that the adjustable pressure limiting (APL) (‘pop‐off') valve was closed, despite completion of a machine checkout procedure at the start of the day. The valve was opened, the cat returned to the OR, and surgery completed. Recovery was uneventful. Investigation of the incident revealed several contributing factors leading to the APL valve being left closed.

A recurring case of ‘no trace, right place’ during emergency tracheal intubations in the critical care setting

We wish to highlight a safety issue concerning the use of the Mapleson C circuit along with high fresh gas flows and the potential impact this could have on capnography. The authors have encountered a situation where despite successful tracheal intubation, there can be continued failure to detect carbon dioxide. This issue became apparent during the undertaking of a large number of emergency tracheal intubations in the current COVID-19 pandemic. The cases involved patients with uneventful airway management and clear placement of a tracheal tube between the vocal cords using videolaryngoscopy. This was followed in all cases by the clinical confirmation of successful tracheal intubation but the absence of a capnographic trace. A commonly identified feature in all events was very high fresh gas flow to the Mapleson C circuit. This high flow was unintentional and frequently had been commenced by a clinician assisting with the tracheal intubation, before the arrival of the intubator. Furthermore, the high flow was initially unrecognised due to the urgent nature of the situation and the impact of personal protective equipment. The standard oxygen flowmeter present in most wards or resuscitation bays displays flow graduations of up to 15 l.min-1. The authors found that while often the last graduation marked is 15 l.min-1, these devices are not flow-limited and when the valve is opened fully can generate flows much higher than this. Further investigation of the technical data supplied by the manufactures of several flowmeters reveals that the high flows produced when the valve is opened fully are referred to as ‘flush’ or ‘flood’ flows and can be as high as 90 l.min-1 [1]. The authors confirmed this by testing the flows generated from oxygen flowmeters encountered throughout their hospital including the auxiliary oxygen outlet present on the anaesthetic machine which produced 84 l.min-1 oxygen while a standard ward oxygen flowmeter achieved 75 l.min-1. When the situation was encountered again and the high flows identified, a capnographic trace could be produced by turning down the oxygen flow to the Mapleson C circuit. The exact cause of this phenomenon is yet to be determined but correspondence with the manufacturer of the Mapleson C circuit suggests that carbon dioxide washout is the likely cause. However, a number of confounders may also contribute and they include the flowmeters flush rate, the composition of the circuit, the type of heat and moisture exchange filter, the behaviour of the adjustable pressure limiting (APL) valve, the adequacy of the tracheal tube cuff and the patient's pulmonary compliance. A review of the technical data provided by the manufacturers of the Mapleson C circuit, revealed that with the APL valve set in the semi-closed position, a fresh gas flow of 50 l.min-1 will generate a resistance of 32 cmH2O (Technical document, Armstrong Medical, Coleraine). The authors will explore these concepts further in a laboratory setting. The current pandemic has seen oxygen capacity in hospitals come under strain due to the large number of COVID-19 patients [2, 3]. It is, therefore, imperative that we reduce the wastage of oxygen wherever possible.

Unexpected APL Valve Failure During Bag Mask Ventilation

Unexpected APL Valve Failure During Bag Mask Ventilation

Audit of Anesthetic Equipment in Veterinary Clinics in Spain and Portugal

The objective of this retrospective study was to review the results of a 4-year audit performed on anesthetic machines and vaporizers used in veterinary clinics in Spain and Portugal. Data was collected between July 2016 and April 2020. Inspections were carried out by a team of seven veterinarians, using a human-modified system of checks that was adapted to a veterinary practice. The evaluation of each item was noted as “correct” or “incorrect”. The vaporizers' performance was evaluated using a self-calibrating gas analyzer. The vaporizer was classified as “correct” or “incorrect” when the vaporization error was less than or equal to, or more than 20%, respectively. The anesthetic machine was classified as “conforming” if all its components were noted as “correct” and no leaks were detected, or as “non-conforming” if any of the components was noted as “incorrect” or if a leak was detected. If the inspector was able to repair on-site the item malfunctions detected and the machine was fit for use, they issued a final report as “conforming.” On the contrary, if such malfunctions persisted, the final report was “non-conforming,” and a recommendation to remove the machine from service until its final repair was provided. To perform statistical analysis, each inspected item was used as predictor, classification and regression trees were built, and a random forest analysis was performed. A total of 2,001 anesthetic machines and 2,309 vaporizers were studied. After inspection, 42.7 and 26.4% of the machines were non-conforming and conforming, respectively, whereas 30.9% could be repaired in situ. A total of 27.1% of the isoflurane vaporizers and 35.9% of the sevoflurane vaporizers were incorrect. Machine learning techniques showed that the most important variables in the classification of the anesthetic machines as conforming or non-conforming were mostly the scavenger system and the canister, followed some way behind by the APL valve, source of oxygen, reservoir bag, vaporizer, and connections.

Quantification of reservoir bags as airway pressure-limiting devices in a nonrebreathing system

ObjectiveTo evaluate the influence of reservoir bag types, volumes and previous use on the peak pressures (Pmax) and the times to develop 30 cmH2O pressure (P30) within a nonrebreathing system with a closed adjustable pressure-limiting (APL) valve. Study designIn vitro study using three-way factorial design with repeated measure on one factor. SubjectsA total of 75 new anesthesia reservoir bags (five types, three volumes, five bags from each type × volume). The bag types were reusable latex (RL), disposable latex (DL) and three disposable neoprene (DN-1, DN-2 and DN-3). MethodsEach bag was tested three times (treatments): new, after prestretching and 1 week later. The bags were attached to a Bain system and anesthesia machine with closed APL valve and patient port with O2 flow 2 L minute–1 until Pmax was reached. The Pmax and time to reach P30 values were determined from recorded pressure traces. General linear mixed model analysis was used to examine the effects of bag type, volume and treatment. One-sided 95% upper prediction limits of Pmax were calculated to test the null hypothesis that predicted Pmax of new bags would be ≥ 50 cmH2O for each factor combination. ResultsRL bags were the least and DN-3 bags were the most compliant. Prestretching increased compliance in all bag types. Smaller bags of RL, DL and DN-1 were less compliant than larger ones. The predicted Pmax values were < 50 cmH2O only for DN-3 bags after prestretching. The time to reach P30 was critically low when using 0.5 L bags (median 17 seconds). Conclusions and clinical relevanceTo minimize the risk of barotrauma, highly compliant reservoir bags (e.g. DN-3) are recommended and reusable bags should be avoided. Bags should be prestretched before first use, 0.5 L bags should be avoided and fresh gas flow minimized.

The Munich Valsalva Implantation Technique (MuVIT) for Cardiac Output Reduction During TEVAR: Vena Cava Occlusion With the Valsalva Maneuver

Purpose To demonstrate a physiologically induced alternative to the typical methods of reducing cardiac output during deployment of stent-grafts in the aortic arch and proximal aorta. Technique A modified Valsalva maneuver, the Munich Valsalva implantation technique (MuVIT), to raise the intrathoracic pressure, minimize backflow, and reduce the cardiac output is illustrated in a patient undergoing a triple-branch thoracic endovascular aortic repair (TEVAR). During manual mechanical ventilation, the adjustable pressure-limiting valve is carefully closed to 25 mm Hg, creating “manual bloating” of the lungs and sustained apnea. The increased intrathoracic pressure causes compression of the vena cava and pulmonary veins, reducing the venous backflow and gradually decreasing the arterial pressure. Once the desired pressure is obtained, the stent-graft is accurately deployed. The airway pressure is thereupon slowly reduced, and the patient is taken back to normal ventilation. The procedure is then finished following standard practice. Conclusion The MuVIT is a simple, noninvasive technique for cardiac output reduction during aortic arch TEVAR, eliminating the need for other invasive techniques.

A practical method to improve preoxygenation: Using the APL valve

Aim: After induction of anesthesia hypoxemia may rapidly develop due to hypoventilation, apnea and decrease in functional residual capacity. Thus, preoxygenation should be administered to every patient before anesthesia induction since airway management may unexpectedly be difficult. Applying positive airway pressure is reported to improve preoxygenation. In this study, we aimed to investigate the effect of applying positive pressure via the adjustable pressure limiting valve (APL) on preoxygenation. Material and Methods: 40 patients aged from 18 to 80 years to be operated under general anesthesia were included in this prospective randomized controlled study. The patients were randomly divided into two groups and preoxygenation was administered with anesthesia facemask in the supine position using two different techniques. In both techniques, the anesthesia circuit was flushed with O2 flush for 30 seconds and then preoxygenation was performed with 100% oxygen and 12 L/min of fresh gas flow for 3 min in spontaneous breathing. In Group APL the APL valve was set at 5 cmH2O pressure position. In Group SB, the APL valve was set at open (spontaneous) position. Results: The percentage of patients with an FeO2 of ≥ 90% at 3rd min was higher in Group APL than in Group SB (75% vs 40%, p=0.006). The mean FeO2 value at 3rd min was statistically significantly higher in Group APL (89.6 vs 88.2, p=0.001). The degree of the difficulty of the technique was reported to be higher in Group APL. Conclusion: In conclusion, we have shown that applying 5 cmH2O positive pressure by APL valve improved preoxygenation compared with spontaneous breathing.

Catheterization of the subclavian vein and the risk of pneumothorax : Mechanical ventilation increases the risk of pneumothorax during infraclavicular landmark-guided subclavian vein puncture: aprospective randomized study

Infraclavicular subclavian vein (SCV) catheterization is astandard procedure in anesthesia and intensive care. There is alack of evidence on how mechanical ventilation during venipuncture of the SCV influences pneumothorax rates. Primary hypothesis: non-inferiority of continuing vs. discontinuing mechanical ventilation during infraclavicular puncture of the SCV with respect to the pneumothorax rate. This prospective, randomized and single-blinded study was approved by the local ethics committee. Atotal of 1021 eligible patients who underwent cranial neurosurgery in 2 different university hospitals were assessed between August 2014 and October 2017. Patients were randomly assigned to two groups directly before induction of anesthesia. Intervention groups for venipuncture of the SCV were mechanical ventilation: tidal volume 7 ml/kg ideal body weight, positive end expiratory pressure (PEEP) ideal body weight/10, n = 535, or apnea: manual/spontaneous, APL valve 0 mbar, n = 486. Patients and the physicians who assessed pneumothorax rates were blinded to the intervention group. Venipuncture was carried out by both inexperienced and experienced physicians. The pneumothorax rate was significantly higher in the mechanical ventilation group (2.2% vs. 0.4%; p = 0.012) with an odds ratio (OR) of 5.63 (95% confidence interval, CI: 1.17-27.2; p = 0.031). Alower body mass index (BMI) was associated with ahigher pneumothorax rate, OR 0.89 (95% CI: 0.70-0.96; p = 0.013). In this study landmark-guided infraclavicular SCV catheterization was associated with asignificantly higher rate of pneumothorax when venipuncture was performed during mechanical ventilation and not in apnea. If ashort phase of apnea is justifiable in the patient, mechanical ventilation should be discontinued during the venipuncture procedure.

Flow‐pressure characteristics of an Intersurgical adjustable pressure‐limiting valve

Flow‐pressure characteristics of an Intersurgical adjustable pressure‐limiting valve

Performance of adjustable pressure‐limiting (APL) valves in two different modern anaesthesia machines

The ability to gently ventilate a patient's lungs using a self-inflating bag requires a properly working adjustable pressure-limiting (APL) valve. We compared the performance of the APL valves of the GE Aisys CS2 and the Draeger Fabius anaesthetic machines during closure and opening from 1-20 and from 20-1 cmH2 O, using standardised experimental baby and adolescent patient lung models. Airway pressures and inspiratory tidal volumes were measured using an ASL-5000 test lung and a GE Aisys CS2 near-patient spirometry sensors. In both lung models, the GE Aisys CS2 APL valves demonstrated non-linear behaviours for airway pressures and for inspiratory tidal volumes, with a sharp increase at set APL pressure levels of 8-10cmH2 O. With further closure of the GE Aisys CS2 APL valves up to 20cmH2 O, inspiratory tidal volumes decreased to ~50% of the highest values measured. Airway pressures in the Draeger Fabius APL valves demonstrated a near linear increase and decrease. Airway pressure values measured in the Draeger Fabius were never higher than those set by the APL valves, whereas in the GE Aisys CS2 , they considerably exceeded set pressures (by up to 27cmH2 O). We conclude that the performance of the GE Aisys CS2 APL valve does not allow safe bag-assisted ventilation of a patient's lungs.

The dynamics of Enterococcus transmission from bacterial reservoirs commonly encountered by anesthesia providers.

Enterococci, the second leading cause of health care-associated infections, have evolved from commensal and harmless organisms to multidrug-resistant bacteria associated with a significant increase in patient morbidity and mortality. Prevention of ongoing spread of this organism within and between hospitals is important. In this study, we characterized Enterococcus transmission dynamics for bacterial reservoirs commonly encountered by anesthesia providers during the routine administration of general anesthesia. Enterococcus isolates previously obtained from bacterial reservoirs frequently encountered by anesthesiologists (patient nasopharynx and axilla, anesthesia provider hands, and the adjustable pressure-limiting valve and agent dial of the anesthesia machine) at 3 major academic medical centers were identified as possible intraoperative bacterial transmission events by class of pathogen, temporal association, and phenotypic analysis (analytical profile indexing). They were then subjected to antibiotic disk diffusion sensitivity for transmission event confirmation. Isolates involved in confirmed transmission events were further analyzed to characterize the frequency, mode, origin, location of transmission events, and antibiotic susceptibility of transmitted pathogens. Three hundred eighty-nine anesthesia reservoir isolates were previously identified by gross morphology and simple rapid tests as Enterococcus. The combination of further analytical profile indexing analysis and temporal association implicated 43% (166/389) of those isolates in possible intraoperative bacterial transmission events. Approximately, 30% (49/166) of possible transmission events were confirmed by additional antibiotic disk diffusion analysis. Two phenotypes, E5 and E7, explained 80% (39/49) of confirmed transmission events. For both phenotypes, provider hands were a common reservoir of origin proximal to the transmission event (96% [72/75] hand origin for E7 and 89% [50/56] hand origin for E5) and site of transmission (94% [16/17] hand transmission location for E7 and 86% [19/22] hand transmission location for E5). Anesthesia provider hand contamination is a common proximal source and transmission location for Enterococcus transmission events in the anesthesia work area. Future work should evaluate the impact of intraoperative hand hygiene improvement strategies on the dynamics of intraoperative Enterococcus transmission.

Transmission dynamics of gram-negative bacterial pathogens in the anesthesia work area.

Gram-negative organisms are a major health care concern with increasing prevalence of infection and community spread. Our primary aim was to characterize the transmission dynamics of frequently encountered gram-negative bacteria in the anesthesia work area environment (AWE). Our secondary aim was to examine links between these transmission events and 30-day postoperative health care-associated infections (HCAIs). Gram-negative isolates obtained from the AWE (patient nasopharynx and axilla, anesthesia provider hands, and the adjustable pressure-limiting valve and agent dial of the anesthesia machine) at 3 major academic medical centers were identified as possible intraoperative bacterial transmission events by class of pathogen, temporal association, and phenotypic analysis (analytical profile indexing). The top 5 frequently encountered genera were subjected to antibiotic disk diffusion sensitivity to identify epidemiologically related transmission events. Complete multivariable logistic regression analysis and binomial tests of proportion were then used to examine the relative contributions of reservoirs of origin and within- and between-case modes of transmission, respectively, to epidemiologically related transmission events. Analyses were conducted with and without the inclusion of duplicate transmission events of the same genera occurring in a given study unit (first and second case of the day in each operating room observed) to examine the potential effect of statistical dependency. Transmitted isolates were compared by pulsed-field gel electrophoresis to disease-causing bacteria for 30-day postoperative HCAIs. The top 5 frequently encountered gram-negative genera included Acinetobacter, Pseudomonas, Brevundimonas, Enterobacter, and Moraxella that together accounted for 81% (767/945) of possible transmission events. For all isolates, 22% (167/767) of possible transmission events were identified by antibiotic susceptibility patterns as epidemiologically related and underwent further study of transmission dynamics. There were 20 duplicates involving within- and between-case transmission events. Thus, approximately 19% (147/767) of isolates excluding duplicates were considered epidemiologically related. Contaminated provider hand reservoirs were less likely (all isolates, odds ratio 0.12, 95% confidence interval 0.03-0.50, P = 0.004; without duplicate events, odds ratio 0.05, 95% confidence interval 0.01-0.49, P = 0.010) than contaminated patient or environmental sites to serve as the reservoir of origin for epidemiologically related transmission events. Within- and between-case modes of gram-negative bacilli transmission occurred at similar rates (all isolates, 7% between-case, 5.2% within-case, binomial P value 0.176; without duplicates, 6.3% between-case, 3.7% within-case, binomial P value 0.036). Overall, 4.0% (23/548) of patients suffered from HCAIs and had an intraoperative exposure to gram-negative isolates. In 8.0% (2/23) of those patients, gram-negative bacteria were linked by pulsed-field gel electrophoresis to the causative organism of infection. Patient and provider hands were identified as the reservoirs of origin and the environment confirmed as a vehicle for between-case transmission events linked to HCAIs. Between- and within-case AWE gram-negative bacterial transmission occurs frequently and is linked by pulsed-field gel electrophoresis to 30-day postoperative infections. Provider hands are less likely than contaminated environmental or patient skin surfaces to serve as the reservoir of origin for transmission events.

P183 An off-line end-tidal breath sampling method in anaesthetised patients with analysis by selected ion flow tube mass spectrometry

IntroductionMonitoring of breath volatiles could provide non-invasive rapid assessment of metabolic stress, inflammation and intravenous anaesthetic drug concentrations in anaesthetised patients. This study was designed to validate an off-line single...

Disconnection Technique With a Bronchial Blocker for Improving Lung Deflation: A Comparison With a Double-Lumen Tube and Bronchial Blocker Without Disconnection

One-lung ventilation (OLV) is accomplished with a double-lumen tube (DLT) or a bronchial blocker (BB). The authors compared the effectiveness of lung collapse using DLT, BB, and BB with the disconnection technique. Prospective, randomized, blind trial. A university hospital. Fifty-two patients undergoing elective pneumothorax surgery. Patients were assigned randomly to 1 of 3 groups: The DLT group (group 1), the BB group (group 2), and the BB with the disconnection technique group (group 3). The authors modified the disconnection technique in group 3 as follows: (1) turned off the ventilator and opened the adjustable pressure-limiting valve, allowing both lungs to collapse and (2) after loss of the CO2 trace on the capnograph, inflated the blocker cuff and turned on the ventilator, allowing only dependent-lung ventilation. Five and ten minutes after OLV, the degree of lung collapse was assessed by the surgeon, who was blinded to the isolation technique. The quality of lung collapse at 5 and 10 minutes was significantly better in groups 1 and 3 than in group 2. No significant differences were observed for the degree of lung collapse at any time point between groups 1 and 3. The average time for loss of the CO2 trace on the capnograph was 32.3±7.0 seconds in group 3. A BB with spontaneous collapse took longer to deflate and did not provide equivalent surgical exposure to the DLT. The disconnection technique could be helpful to accelerate lung collapse with a BB.

The closed circuit and the low flow systems

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.