A quantitative evaluation of aerosol generation during cardiopulmonary resuscitation.

It is unclear if cardiopulmonary resuscitation is an aerosol-generating procedure and whether this poses a risk of airborne disease transmission to healthcare workers and bystanders. Use of airborne transmission precautions during cardiopulmonary resuscitation may confer rescuer protection but risks patient harm due to delays in commencing treatment. To quantify the risk of respiratory aerosol generation during cardiopulmonary resuscitation in humans, we conducted an aerosol monitoring study during out-of-hospital cardiac arrests. Exhaled aerosol was recorded using an optical particle sizer spectrometer connected to the breathing system. Aerosol produced during resuscitation was compared with that produced by control participants under general anaesthesia ventilated with an equivalent respiratory pattern to cardiopulmonary resuscitation. A porcine cardiac arrest model was used to determine the independent contributions of ventilatory breaths, chest compressions and external cardiac defibrillation to aerosol generation. Time-series analysis of participants with cardiac arrest (n = 18) demonstrated a repeating waveform of respiratory aerosol that mapped to specific components of resuscitation. Very high peak aerosol concentrations were generated during ventilation of participants with cardiac arrest with median (IQR [range]) 17,926 (5546-59,209 [1523-242,648]) particles.l-1 , which were 24-fold greater than in control participants under general anaesthesia (744 (309-2106 [23-9099]) particles.l-1 , p < 0.001, n = 16). A substantial rise in aerosol also occurred with cardiac defibrillation and chest compressions. In a complimentary porcine model of cardiac arrest, aerosol recordings showed a strikingly similar profile to the human data. Time-averaged aerosol concentrations during ventilation were approximately 270-fold higher than before cardiac arrest (19,410 (2307-41,017 [104-136,025]) vs. 72 (41-136 [23-268]) particles.l-1 , p = 0.008). The porcine model also confirmed that both defibrillation and chest compressions generate high concentrations of aerosol independent of, but synergistic with, ventilation. In conclusion, multiple components of cardiopulmonary resuscitation generate high concentrations of respiratory aerosol. We recommend that airborne transmission precautions are warranted in the setting of high-risk pathogens, until the airway is secured with an airway device and breathing system with a filter.

A quantitative evaluation of aerosol generation during awake tracheal intubation.

Aerosol-generating procedures are medical interventions considered high risk for transmission of airborne pathogens. Tracheal intubation of anaesthetised patients is not high risk for aerosol generation; however, patients often perform respiratory manoeuvres during awake tracheal intubation which may generate aerosol. To assess the risk, we undertook aerosol monitoring during a series of awake tracheal intubations and nasendoscopies in healthy participants. Sampling was undertaken within an ultraclean operating theatre. Procedures were performed and received by 12 anaesthetic trainees. The upper airway was topically anaesthetised with lidocaine and participants were not sedated. An optical particle sizer continuously sampled aerosol. Passage of the bronchoscope through the vocal cords generated similar peak median (IQR [range]) aerosol concentrations to coughing, 1020 (645-1245 [120-48,948]) vs. 1460 (390-2506 [40-12,280]) particles.l-1 respectively, p = 0.266. Coughs evoked when lidocaine was sprayed on the vocal cords generated 91,700 (41,907-166,774 [390-557,817]) particles.l-1 which was significantly greater than volitional coughs (p < 0.001). For 38 nasendoscopies in 12 participants, the aerosol concentrations were relatively low, 180 (120-525 [0-9552]) particles.l-1 , however, five nasendoscopies generated peak aerosol concentrations greater than a volitional cough. Awake tracheal intubation and nasendoscopy can generate high concentrations of respiratory aerosol. Specific risks are associated with lidocaine spray of the larynx, instrumentation of the vocal cords, procedural coughing and deep breaths. Given the proximity of practitioners to patient-generated aerosol, airborne infection control precautions are appropriate when undertaking awake upper airway endoscopy (including awake tracheal intubation, nasendoscopy and bronchoscopy) if respirable pathogens cannot be confidently excluded.

Autonomous control for miniaturized mobile robots in unknown pipe networks.

Despite recent advances in robotic technology, sewer pipe inspection is still limited to conventional approaches that use cable-tethered robots. Such commercially available tethered robots lack autonomy, and their operation must be manually controlled via their tethered cables. Consequently, they can only travel to a certain distance in pipe, cannot access small-diameter pipes, and their deployment incurs high costs for highly skilled operators. In this paper, we introduce a miniaturised mobile robot for pipe inspection. We present an autonomous control strategy for this robot that is effective, stable, and requires only low-computational resources. The robots used here can access pipes as small as 75 mm in diameter. Due to their small size, low carrying capacity, and limited battery supply, our robots can only carry simple sensors, a small processor, and miniature wheel-legs for locomotion. Yet, our control method is able to compensate for these limitations. We demonstrate fully autonomous robot mobility in a sewer pipe network, without any visual aid or power-hungry image processing. The control algorithm allows the robot to correctly recognise each local network configuration, and to make appropriate decisions accordingly. The control strategy was tested using the physical micro robot in a laboratory pipe network. In both simulation and experiment, the robot autonomously and exhaustively explored an unknown pipe network without missing any pipe section while avoiding obstacles. This is a significant advance towards fully autonomous inspection robot systems for sewer pipe networks.

Anaesthetists' current practice and perceptions of aerosol-generating procedures: a mixed-methods study.

The evidence base surrounding the transmission risk of 'aerosol-generating procedures' has evolved primarily through quantification of aerosol concentrations during clinical practice. Consequently, infection prevention and control guidelines are undergoing continual reassessment. This mixed-methods study aimed to explore the perceptions of practicing anaesthetists regarding aerosol-generating procedures. An online survey was distributed to the Membership Engagement Group of the Royal College of Anaesthetists during November 2021. The survey included five clinical scenarios to identify the personal approach of respondents to precautions, their hospital's policies and the associated impact on healthcare provision. A purposive sample was selected for interviews to explore the reasoning behind their perceptions and behaviours in greater depth. A total of 333 survey responses were analysed quantitatively. Transcripts from 18 interviews were coded and analysed thematically. The sample was broadly representative of the UK anaesthetic workforce. Most respondents and their hospitals were aware of, supported and adhered to UK guidance. However, there were examples of substantial divergence from these guidelines at both individual and hospital level. For example, 40 (12%) requested respiratory protective equipment and 63 (20%) worked in hospitals that required it to be worn whilst performing tracheal intubation in SARS-CoV-2 negative patients. Additionally, 173 (52%) wore respiratory protective equipment whilst inserting supraglottic airway devices. Regarding the use of respiratory protective equipment and fallow times in the operating theatre: 305 (92%) perceived reduced efficiency; 376 (83%) perceived a negative impact on teamworking; 201 (64%) were worried about environmental impact; and 255 (77%) reported significant problems with communication. However, 269 (63%) felt the negative impacts of respiratory protection equipment were appropriately balanced against the risks of SARS-CoV-2 transmission. Attitudes were polarised about the prospect of moving away from using respiratory protective equipment. Participants' perceived risk from COVID-19 correlated with concern regarding stepdown (Spearman's test, R = 0.36, p < 0.001). Attitudes towards aerosol-generating procedures and the need for respiratory protective equipment are evolving and this information can be used to inform strategies to facilitate successful adoption of revised guidelines.

Quantitative evaluation of aerosol generation from upper airway suctioning assessed during tracheal intubation and extubation sequences in anaesthetized patients.

BACKGROUND: Open respiratory suctioning is defined as an aerosol generating procedure (AGP). Laryngopharyngeal suctioning, used to clear secretions during anaesthesia, is widely managed as an AGP. However, it is uncertain whether upper airway suctioning should be designated as an AGP due to the lack of both aerosol and epidemiological evidence. AIM: To assess the relative risk of aerosol generation by upper airway suctioning during tracheal intubation and extubation in anaesthetized patients. METHODS: This prospective environmental monitoring study was undertaken in an ultraclean operating theatre setting to assay aerosol concentrations during intubation and extubation sequences, including upper airway suctioning, for patients undergoing surgery (N=19). An optical particle sizer (particle size 0.3-10 µm) sampled aerosol 20 cm above the patient's mouth. Baseline recordings (background, tidal breathing and volitional coughs) were followed by intravenous induction of anaesthesia with neuromuscular blockade. Four periods of laryngopharyngeal suctioning were performed with a Yankauer sucker: pre-laryngoscopy, post-intubation, pre-extubation and post-extubation. FINDINGS: Aerosol was reliably detected {median 65 [interquartile range (IQR) 39-259] particles/L} above background [median 4.8 (IQR 1-7) particles/L, P<0.0001] when sampling in close proximity to the patient's mouth during tidal breathing. Upper airway suctioning was associated with a much lower average aerosol concentration than breathing [median 6.0 (IQR 0-12) particles/L, P=0.0007], and was indistinguishable from background (P>0.99). Peak aerosol concentrations recorded during suctioning [median 45 (IQR 30-75) particles/L] were much lower than during volitional coughs [median 1520 (IQR 600-4363) particles/L, P<0.0001] and tidal breathing [median 540 (IQR 300-1826) particles/L, P<0.0001]. CONCLUSION: Upper airway suctioning during airway management was not associated with a higher aerosol concentration compared with background, and was associated with a much lower aerosol concentration compared with breathing and coughing. Upper airway suctioning should not be designated as a high-risk AGP.

Quantitative evaluation of aerosol generation during manual facemask ventilation.

Manual facemask ventilation, a core component of elective and emergency airway management, is classified as an aerosol-generating procedure. This designation is based on one epidemiological study suggesting an association between facemask ventilation and transmission during the SARS-CoV-1 outbreak in 2003. There is no direct evidence to indicate whether facemask ventilation is a high-risk procedure for aerosol generation. We conducted aerosol monitoring during routine facemask ventilation and facemask ventilation with an intentionally generated leak in anaesthetised patients. Recordings were made in ultraclean operating theatres and compared against the aerosol generated by tidal breathing and cough manoeuvres. Respiratory aerosol from tidal breathing in 11 patients was reliably detected above the very low background particle concentrations with median [IQR (range)] particle counts of 191 (77-486 [4-1313]) and 2 (1-5 [0-13]) particles.l-1 , respectively, p = 0.002. The median (IQR [range]) aerosol concentration detected during facemask ventilation without a leak (3 (0-9 [0-43]) particles.l-1 ) and with an intentional leak (11 (7-26 [1-62]) particles.l-1 ) was 64-fold (p = 0.001) and 17-fold (p = 0.002) lower than that of tidal breathing, respectively. Median (IQR [range]) peak particle concentration during facemask ventilation both without a leak (60 (0-60 [0-120]) particles.l-1 ) and with a leak (120 (60-180 [60-480]) particles.l-1 ) were 20-fold (p = 0.002) and 10-fold (0.001) lower than a cough (1260 (800-3242 [100-3682]) particles.l-1 ), respectively. This study demonstrates that facemask ventilation, even when performed with an intentional leak, does not generate high levels of bioaerosol. On the basis of this evidence, we argue facemask ventilation should not be considered an aerosol-generating procedure.

Multisite silicon probes enable simultaneous recording of spontaneous and evoked activity in multiple isolated C-fibres in rat saphenous nerve.

BACKGROUND: Recordings of electrical activity in nerves have provided valuable insights into normal function and pathological behaviours of the nervous system. Current high-resolution techniques (e.g. teased fibre recordings) typically utilise electrodes with a single recording site, capturing the activity of a single isolated neuron per recording. NEW METHOD: We conducted proof-of-principle C-fibre recordings in the saphenous nerve of urethane-anaesthetised adult Wistar rats using 32-channel multisite silicon electrodes. Data was acquired using the OpenEphys recording system and clustered offline with Kilosort 2.5. RESULTS: In single recordings in 5 rats, 32 units with conduction velocities in the C-fibre range (< 1 m/s) were identified via constant latency responses and classified using activity dependent slowing. In two animals, 6 C-fibres (5 classified as nociceptors) were well isolated after clustering. Their activity could be tracked throughout the recording - including during periods of spontaneous activity. Axonal conduction velocities were calculated from spontaneous activity and/or low frequency electrical stimulation using only the differences in action potential latency as it propagated past multiple probe sites. COMPARISON WITH EXISTING METHODS: Single electrode approaches have a low data yield and generating group data for specific fibre types is challenging as it requires multiple experimental subjects and recording sessions. This is particularly true when the experimental targets are the small, unmyelinated C-fibres carrying nociceptive information. CONCLUSIONS: We demonstrate that multisite recordings can greatly increase experimental yields and enhance fibre identification. The approach is of particular utility when coupled with clustering analysis. Multisite probes and analysis approaches constitute a valuable new toolbox for researchers studying the peripheral nervous system.

A quantitative evaluation of aerosol generation during supraglottic airway insertion and removal.

Many guidelines consider supraglottic airway use to be an aerosol-generating procedure. This status requires increased levels of personal protective equipment, fallow time between cases and results in reduced operating theatre efficiency. Aerosol generation has never been quantitated during supraglottic airway use. To address this evidence gap, we conducted real-time aerosol monitoring (0.3-10-µm diameter) in ultraclean operating theatres during supraglottic airway insertion and removal. This showed very low background particle concentrations (median (IQR [range]) 1.6 (0-3.1 [0-4.0]) particles.l-1 ) against which the patient's tidal breathing produced a higher concentration of aerosol (4.0 (1.3-11.0 [0-44]) particles.l-1 , p = 0.048). The average aerosol concentration detected during supraglottic airway insertion (1.3 (1.0-4.2 [0-6.2]) particles.l-1 , n = 11), and removal (2.1 (0-17.5 [0-26.2]) particles.l-1 , n = 12) was no different to tidal breathing (p = 0.31 and p = 0.84, respectively). Comparison of supraglottic airway insertion and removal with a volitional cough (104 (66-169 [33-326]), n = 27), demonstrated that supraglottic airway insertion/removal sequences produced <4% of the aerosol compared with a single cough (p < 0.001). A transient aerosol increase was recorded during one complicated supraglottic airway insertion (which initially failed to provide a patent airway). Detailed analysis of this event showed an atypical particle size distribution and we subsequently identified multiple sources of non-respiratory aerosols that may be produced during airway management and can be considered as artefacts. These findings demonstrate supraglottic airway insertion/removal generates no more bio-aerosol than breathing and far less than a cough. This should inform the design of infection prevention strategies for anaesthetists and operating theatre staff caring for patients managed with supraglottic airways.

A quantitative evaluation of aerosol generation during tracheal intubation and extubation.

The potential aerosolised transmission of severe acute respiratory syndrome coronavirus-2 is of global concern. Airborne precaution personal protective equipment and preventative measures are universally mandated for medical procedures deemed to be aerosol generating. The implementation of these measures is having a huge impact on healthcare provision. There is currently a lack of quantitative evidence on the number and size of airborne particles produced during aerosol-generating procedures to inform risk assessments. To address this evidence gap, we conducted real-time, high-resolution environmental monitoring in ultraclean ventilation operating theatres during tracheal intubation and extubation sequences. Continuous sampling with an optical particle sizer allowed characterisation of aerosol generation within the zone between the patient and anaesthetist. Aerosol monitoring showed a very low background particle count (0.4 particles.l-1 ) allowing resolution of transient increases in airborne particles associated with airway management. As a positive reference control, we quantitated the aerosol produced in the same setting by a volitional cough (average concentration, 732 (418) particles.l-1 , n = 38). Tracheal intubation including facemask ventilation produced very low quantities of aerosolised particles (average concentration, 1.4 (1.4) particles.l-1 , n = 14, p < 0.0001 vs. cough). Tracheal extubation, particularly when the patient coughed, produced a detectable aerosol (21 (18) l-1 , n = 10) which was 15-fold greater than intubation (p = 0.0004) but 35-fold less than a volitional cough (p < 0.0001). The study does not support the designation of elective tracheal intubation as an aerosol-generating procedure. Extubation generates more detectable aerosol than intubation but falls below the current criterion for designation as a high-risk aerosol-generating procedure. These novel findings from real-time aerosol detection in a routine healthcare setting provide a quantitative methodology for risk assessment that can be extended to other airway management techniques and clinical settings. They also indicate the need for reappraisal of what constitutes an aerosol-generating procedure and the associated precautions for routine anaesthetic airway management.

Routine fecal occult blood testing does not predict necrotizing enterocolitis in very low birth weight neonates.

OBJECTIVE: To determine sensitivity, specificity, predictive value of routine fecal occult blood (FOB) testing on the identification of Bell's Stage II or III necrotizing enterocolitis (NEC) in very low birth weight (VLBW) infants. METHODS: Retrospective medical record review of VLBW infants from 2012- 2013 evaluating FOB results and clinical and demographic risk factors. We determined predictive values of positive FOB testing within 48 hours of definite NEC diagnosis. We performed logistic regression analyses for predictors of NEC and for predictors of having positive FOB during NICU admission. RESULTS: The incidence of NEC in our cohort of 203 infants was 3.9% (n = 8). None had positive FOB results within 48 hours of diagnosis, and only 12.5% had any positive FOB within 7 days. Sensitivity of positive FOB for predicting definite NEC = 0%, specificity = 34.4%, and positive predictive value = 0%. A majority of VLBWs (67.0%) had > one positive FOB result during their NICU course. On logistic regression, intrauterine growth restricted (IUGR) infants had significantly higher odds of both developing NEC and of having positive FOB. Positive FOB was not a significant predictor of NEC. Those with lower birth gestational ages had higher odds of positive FOB. CONCLUSIONS: Positive FOB testing occurred in a majority of VLBW infants, with higher odds in the more preterm and IUGR. However, the sensitivity, specificity, and predictive value of routine FOB testing for identifying NEC were all very poor. Our data demonstrates that this test offers no advantages in the early diagnosis of NEC.

The cost-effectiveness of diagnostic management strategies for children with minor head injury.

AIM: To estimate the cost-effectiveness of diagnostic management strategies for children with minor head injury and identify an optimal strategy. METHODS: A probabilistic decision analysis model was developed to estimate the costs and quality-adjusted life years (QALYs) accrued by each of six potential management strategies for minor head injury, including a theoretical 'zero option' strategy of discharging all patients home without investigation. The model took a lifetime horizon and the perspective of the National Health Service. RESULTS: The optimal strategy was based on the Children's Head injury Algorithm for the prediction of Important Clinical Events (CHALICE) rule, although the costs and outcomes associated with each strategy were broadly similar. CONCLUSIONS: Liberal use of CT scanning based on a high sensitivity decision rule is not only effective but also cost saving, with the CHALICE rule being the optimal strategy, although there is some uncertainty in the results. Incremental changes in the costs and QALYs are very small when all selective CT strategies are compared. The estimated cost of caring for patients with brain injury worsened by delayed treatment is very high compared with the cost of CT scanning. This analysis suggests that all hospitals receiving children with minor head injury should have unrestricted access to CT scanning for use in conjunction with evidence-based guidelines.

Endogenous analgesic action of the pontospinal noradrenergic system spatially restricts and temporally delays the progression of neuropathic pain following tibial nerve injury.

Pontospinal noradrenergic neurons form part of an endogenous analgesic system that suppresses acute pain, but there is conflicting evidence about its role in neuropathic pain. We investigated the chronology of descending noradrenergic control during the development of a neuropathic pain phenotype in rats following tibial nerve transection (TNT). A lumbar intrathecal cannula was implanted at the time of nerve injury allowing administration of selective α-adrenoceptor (α-AR) antagonists to sequentially assay their effects upon the expression of allodynia and hyperalgesia. Following TNT animals progressively developed mechanical and cold allodynia (by day 10) and subsequently heat hypersensitivity (day 17). Blockade of α2-AR with intrathecal yohimbine (30 µg) revealed earlier ipsilateral sensitization of all modalities while prazosin (30 µg, α1-AR) was without effect. Established allodynia (by day 21) was partly reversed by the re-uptake inhibitor reboxetine (5 µg, i.t.) but yohimbine no longer had any sensitising effect. This loss of effect coincided with a reduction in the descending noradrenergic innervation of the ipsilateral lumbar dorsal horn. Yohimbine reversibly unmasked contralateral hindlimb allodynia and hyperalgesia of all modalities and increased dorsal horn c-fos expression to an innocuous brush stimulus. Contralateral thermal hyperalgesia was also reversibly uncovered by yohimbine administration in a contact heat ramp paradigm in anaesthetised TNT rats. Following TNT there is an engagement of inhibitory α2-AR-mediated noradrenergic tone which completely masks contralateral and transiently suppresses the development of ipsilateral sensitization. This endogenous analgesic system plays a key role in shaping the spatial and temporal expression of the neuropathic pain phenotype after nerve injury.

The legal status of the fetus in New South Wales.

The issue of how to define the legal status of the fetus is complex. Three clinical cases with fetal losses following motor vehicle accidents raise important issues regarding the legal status of the unborn child. Legislation was submitted to the New South Wales Parliament in the form of the Crimes Amendment (Grievous Bodily Harm) Bill 2005 (NSW) but was subsequently repealed. Medical technological advances make the viability of a fetus a shifting standard and encourage the comparison between newborns and late-term fetuses, offer increased fetal health status information and provide greater capacity to maintain the life of babies born prematurely. In view of the sophisticated state of medical care available in New South Wales, the three cases reviewed highlight the discrepancy between the medical recognition of the fetus as a patient and its lack of legal recognition.

The cost-effectiveness of diagnostic management strategies for adults with minor head injury.

STUDY OBJECTIVE: To estimate the cost-effectiveness of diagnostic management strategies for adults with minor head injury. METHODS: A mathematical model was constructed to evaluate the incremental costs and effectiveness (Quality Adjusted Life years Gained, QALYs) of ten diagnostic management strategies for adults with minor head injuries. Secondary analyses were undertaken to determine the cost-effectiveness of hospital admission compared to discharge home and to explore the cost-effectiveness of strategies when no responsible adult was available to observe the patient after discharge. RESULTS: The apparent optimal strategy was based on the high and medium risk Canadian CT Head Rule (CCHRhm), although the costs and outcomes associated with each strategy were broadly similar. Hospital admission for patients with non-neurosurgical injury on CT dominated discharge home, whilst hospital admission for clinically normal patients with a normal CT was not cost-effective compared to discharge home with or without a responsible adult at £39 and £2.5 million per QALY, respectively. A selective CT strategy with discharge home if the CT scan was normal remained optimal compared to not investigating or CT scanning all patients when there was no responsible adult available to observe them after discharge. CONCLUSION: Our economic analysis confirms that the recent extension of access to CT scanning for minor head injury is appropriate. Liberal use of CT scanning based on a high sensitivity decision rule is not only effective but also cost-saving. The cost of CT scanning is very small compared to the estimated cost of caring for patients with brain injury worsened by delayed treatment. It is recommended therefore that all hospitals receiving patients with minor head injury should have unrestricted access to CT scanning for use in conjunction with evidence based guidelines. Provisionally the CCHRhm decision rule appears to be the best strategy although there is considerable uncertainty around the optimal decision rule. However, the CCHRhm rule appears to be the most widely validated and it therefore seems appropriate to conclude that the CCHRhm rule has the best evidence to support its use.