Comparison of high-flow nasal cannula versus oxygen face mask for environmental bacterial contamination in critically ill pneumonia patients: a randomized controlled crossover trial.

Whereas high-flow nasal cannula use is gaining prevalence, its high gas flow raises concerns about aerosolization of infectious particles and spread of infection. This randomized controlled crossover non-inferiority trial (N = 20) evaluated the degree of environmental contamination by viable bacteria associated with the use of high-flow nasal cannula compared with conventional oxygen mask for critically ill patients with Gram-negative pneumonia. The results show that high-flow nasal cannula use was not associated with increased air or contact surface contamination by either Gram-negative bacteria or total bacteria, suggesting that additional infection control measures are not required.

A randomized controlled trial of 2 protocols for weaning cardiac surgical patients receiving adaptive support ventilation.

PURPOSE: This study aims to compare the effectiveness of weaning with adaptive support ventilation (ASV) incorporating progressively reduced or constant target minute ventilation in the protocol in postoperative care after cardiac surgery. MATERIAL AND METHODS: A randomized controlled unblinded study of 52 patients after elective coronary artery bypass surgery was carried out to determine whether a protocol incorporating a decremental target minute ventilation (DTMV) results in more rapid weaning of patients ventilated in ASV mode compared to a protocol incorporating a constant target minute ventilation. RESULTS: Median duration of mechanical ventilation (145 vs 309 minutes; P = .001) and intubation (225 vs 423 minutes; P = .005) were significantly shorter in the DTMV group. There was no difference in adverse effects (42% vs 46%) or mortality (0% vs 0%) between the 2 groups. CONCLUSIONS: Use of a DTMV protocol for postoperative ventilation of cardiac surgical patients in ASV mode results in a shorter duration of ventilation and intubation without evidence of increased risk of adverse effects.

Performance of a new oxygen delivery device for potentially infectious critically ill patients.

In patients with highly contagious diseases that are spread by respiratory droplets or air-borne particles, the use of high-flow oxygen may carry a significant risk of nosocomial transmission. We tested a new oxygen delivery device designed to address these problems by simulating 108 patients with sepsis and respiratory failure. The device being tested consisted of an airtight mask, a bacterial and viral filter, a T-shaped reservoir (50 and 100 ml) and oxygen delivery tubing connected directly to the mask. When tested with a 50-ml reservoir, a high fractional oxygen concentration was achieved: mean (SD) 0.83 (0.11) at a flow of 15 l.min(-1) oxygen. The 50-ml reservoir, when compared with the 100-ml reservoir, was associated with reduced carbon dioxide rebreathing (mean (SD) inspired fractional carbon dioxide concentration 2.5 (1.0) vs 3.0 (1.1), respectively, p = 0.009) and reduced inspiratory resistive work of breathing (mean (SD) 1.0 (0.6) J.l(-1) vs 1.2 (0.5) J.l(-1), respectively, p = 0.028). However, rebreathing and work of breathing were relatively high if a high respiratory rate was simulated. We conclude that the novel oxygen device we describe, equipped with the 50-ml T-shaped reservoir, is suitable for potentially infectious patients with type-1 respiratory failure but without marked tachypnoea.

Bench performance of ventilators during simulated paediatric ventilation.

This study compares the accuracy and capabilities of various ventilators using a paediatric acute respiratory distress syndrome lung model. Various compliance settings and respiratory rate settings were used. The study was done in three parts: tidal volume and FiO2 accuracy; pressure control accuracy and positive end-expiratory pressure (PEEP) accuracy. The parameters set on the ventilator were compared with either or both of the measured parameters by the test lung and the ventilator. The results revealed that none of the ventilators could consistently deliver tidal volumes within 1 ml/kg of the set tidal volume, and the discrepancy between the delivered volume and the volume measured by the ventilator varied greatly. The target tidal volume was 8 ml/kg, but delivered tidal volumes ranged from 3.6-11.4 ml/kg and the volumes measured by the ventilator ranged from 4.1-20.6 ml/kg. All the ventilators maintained pressure within 20% of the set pressure, except one ventilator which delivered pressures of up to 27% higher than the set pressure. Two ventilators maintained PEEP within 10% of the prescribed PEEP. The majority of the readings were also within 10%. However, three ventilators delivered, at times, PEEPs over 20% higher. In conclusion, as lung compliance decreases, especially in paediatric patients, some ventilators perform better than others. This study highlights situations where ventilators may not be able to deliver, nor adequately measure, set tidal volumes, pressure, PEEP or FiO2.

A randomised controlled pilot study to compare filtration factor of a novel non-fit-tested high-efficiency particulate air (HEPA) filtering facemask with a fit-tested N95 mask.

Use of a fit-tested N95 or FFP2 mask is recommended to protect against transmission of airborne pathogens. This poses considerable logistic problems when preparing for, or dealing with, an epidemic. Some of these problems might be overcome by use of a compact reusable high-efficiency particulate air filtering mask that can be cut to size. We carried out a randomised controlled cross-over study to compare the efficacy of such a mask (Totobobo, Dream Lab One Pte Ltd, Singapore) with fit-tested N95 masks (1860 or 1860s or 1862; 3M, St Paul, MN, USA) in 22 healthy volunteers. The median (interquartile range) reduction in airborne particle counts was significantly higher [193-fold (145-200)] for N95 masks than for Totobobo masks [135-fold (83-184)] (P<0.05). There was no statistically significant difference between the proportion of subjects achieving a reduction of > or =100-fold between N95 (19/22) and Totobobo (16/22) masks. We conclude that use of the Totobobo mask without fit testing cannot be recommended, but its performance is sufficiently promising to warrant further investigation.

Can learning to sustain life be BASIC? Teaching for the initial management of the critically ill in Australia and New Zealand.

Commonly in Australia and New Zealand, initial intensive care support of critically ill patients is by non-intensive care trained medical and nursing staff Basic Assessment and Support in Intensive Care (BASIC) is an internationally run short course to assist practitioners to gain knowledge and skills to manage the early hours of critical illness. The aim of this study was to assess the performance and acceptance of the BASIC course as conducted in an Australian metropolitan teaching hospital and a major regional centre in New Zealand. Performance on pre- and post-course multiple choice examinations and the overall course assessment by all participants attending between 2005 and 2009 was analysed. Of 796 participants, 338 (42%) were in Australia and 458 (58%) in New Zealand. Compared to New Zealand, Australian non-intensive care consultants and junior medical staff attended more commonly at 9% vs 4% and 62% vs 42% respectively, while nurses more frequently attended in New Zealand (47% compared to 12%, P < 0.001). The pre-course open book examination result averaged 79% (95% confidence interval 78 to 80) and the post-course closed book examination was 64% (95% confidence interval 63 to 65). The post-course examination score was predicted by pre-course examination score (beta = 0.22, 95% confidence interval 0.17 to 0.27), nursing occupation, (beta = -3.96, 95% confidence interval -5.03 to -2.90) and the availability of a scenario-based simulation module (beta = 0.22, 95% confidence interval 0.17 to 0.27, R2 = 0.38, P < 0.001). Participants generally found they had learned a great deal from the program and that the course material was of an appropriate level. The BASIC course was found to be a positive learning experience for health care practitioners inexperienced in the management of the critically ill.

A systematic review of antibiotic dosing regimens for septic patients receiving continuous renal replacement therapy: do current studies supply sufficient data?

BACKGROUND: Drug dosing for septic patients with acute renal failure receiving continuous renal replacement therapy (CRRT) is complicated, and failure to correctly dose may result in either drug toxicity or treatment failure and development of antibiotic resistance. The aim of this study was to establish an ideal dataset that needs to be reported when presenting pharmacokinetic data for these patients and review current literature for completeness of this dataset. METHODS: An ideal dataset was established of the parameters that should be reported when calculating a drug dosing regimen from first principles. A Medline search was performed of relevant literature producing 64 citations from which completeness of the specified criteria was examined. RESULTS: None of the studies analysed presented the full dataset that we established as necessary. Of concern, basic pharmacokinetic parameters such as volume of distribution (V(d)) and clearance (CL) were specified in only 79% and 81% of studies, respectively. CONCLUSIONS: A large proportion of current studies do not report key information necessary to devise a rational dosing regimen for patients with acute renal failure receiving CRRT, and we hope this dataset will be a useful guide when reporting future pharmacokinetic data.

Outcome of patients receiving high dose vasopressor therapy: a retrospective cohort study.

The aim of this study was to determine the hospital survival of patients receiving high doses of catecholamines. A retrospective observational study was conducted in a 22-bed multidisciplinary adult intensive care unit of a tertiary referral university hospital. All patients (n = 64) receiving > 100 microg/min of adrenaline or noradrenaline or adrenaline and noradrenaline combined over a one-year period were studied to determine survival to intensive care unit and hospital discharge. Four patients survived to intensive care unit discharge and hospital discharge (6.25%, 95% CI 0.3 to 12.2%). Survival was 3.3% (95% CI 0 to 7.9%) in the subgroup of 60 patients who received > 100 microg/min noradrenaline and 3.6% (95% CI 0 to 8.6%) in the 55 patients who received > 2 microg/kg/min noradrenaline. None of the 32 patients who received > 200 microg/min noradrenaline survived. We conclude that the survival of patients requiring high doses of catecholamines is poor but the use of such doses is probably not futile. It remains for individual clinicians, patients and their surrogates to decide whether use of high doses of vasopressor is appropriate, given the low probability of survival.

Hospital and 28-day mortality amongst 'high risk' surgical patients. A retrospective cohort study.

The likely mortality benefit from pre-optimisation of high risk surgical patients depends on the baseline risk of death. The baseline risk estimated from the control groups of studies of pre-optimisation may not reflect the risk in other institutions. We determined the 28-day mortality of 'high risk' adult surgical patients in our institution by performing a retrospective cohort study of 554 patients undergoing major or ultra-major general or vascular surgery lasting more than two hours. Patients were identified as being high risk based on the presence of risk factors used in previous studies of pre-optimisation. The 28-day mortality (95% CI) was 0% for patients with no risk factors and 2.3 (0.8 to 3.7)% for patients with at least one risk factor. These data indicate that the risk of death amongst high risk surgical patients may vary considerably between institutions.

Protecting staff against airborne viral particles: in vivo efficiency of laser masks.

Laser masks are used to prevent inhalation of viral particles during laser surgery. A crossover trial was performed in eight volunteers to compare the ability of a surgical mask and a laser mask with that of an FFP2 respirator to filter airborne dust particles. The surgical and laser masks were tested when worn normally and when they were taped to the face. The mean reductions in particle counts were 3.0 fold [95% confidence interval (95% CI) 1.8-4.2] for the untaped surgical mask, 3.8 fold (95% CI 2.9-4.6) for the untaped laser mask, 7.5 fold (95% CI 6.5-8.5) for the taped surgical mask, 15.6 fold (95% CI 13.5-17.8) for the taped laser mask, and 102.6 fold (95% CI 41.2-164.1) for the FFP2 half-face respirator. The laser mask provided significantly less protection than the FFP2 respirator (P=0.02), and only marginally more protection than the surgical mask. The continued use of laser masks for respiratory protection is questionable. Taping masks to the face only provided a small improvement in protection.

Dynamic airflow limitation after topical anaesthesia of the upper airway.

This prospective before-and-after observational study investigated the effect of upper airway anaesthesia on dynamic airflow. Six consenting ASA 1 adults, all authors of this study, underwent a series of spirometric measurements before and after topical anaesthesia of the upper airway using lignocaine. Peak inspiratory flow rate, forced inspiratory flow between 25% and 75% of the maximum inhaled volume, forced expiratory volume at 1 second, and forced vital capacity in the supine and sitting positions were measured. The measured inspiratory parameters were significantly reduced after lignocaine topical anaesthesia of the upper airway. Expiratory flow parameters were not affected. We conclude that topical anaesthesia of the upper airway leads to dynamic inspiratory airflow limitation.

Impact of severe acute respiratory syndrome (SARS) on pulmonary function, functional capacity and quality of life in a cohort of survivors.

OBJECTIVE: To examine the impact of severe acute respiratory syndrome (SARS) on pulmonary function, exercise capacity, and health-related quality of life (HRQoL) among survivors. METHODS: 110 survivors with confirmed SARS were evaluated at the Prince of Wales Hospital, HK at the end of 3 and 6 months after symptom onset. The assessment included lung volumes (TLC, VC, RV, FRC), spirometry (FVC, FEV1), carbon monoxide transfer factor (TLCO adjusted for haemoglobin), inspiratory and expiratory respiratory muscle strength (Pimax and Pemax), 6 minute walk distance (6MWD), chest radiographs, and HRQoL by SF-36 questionnaire. RESULTS: There were 44 men and 66 women with a mean (SD) age of 35.6 (9.8) years and body mass index of 23.1 (4.8) kg/m2. Seventy (64%) were healthcare workers. At 6 months 33 subjects (30%) had abnormal chest radiographs; four (3.6%), eight (7.4%), and 17 (15.5%) patients had FVC, TLC, and TLCO below 80% of predicted values; and 15 (13.9%) and 24 (22.2%) had Pimax and Pemax values below 80 cm H2O, respectively. The 6MWD increased from a mean (SD) of 464 (83) m at 3 months to 502 (95) m (95% CI 22 to 54 m, p<0.001), but the results were lower than normal controls in the same age groups. There was impairment of HRQoL at 6 months. Patients who required ICU admission (n = 31) had significantly lower FVC, TLC, and TLCO than those who did not. CONCLUSION: The exercise capacity and health status of SARS survivors was considerably lower than that of a normal population at 6 months. Significant impairment in surface area for gas exchange was noted in 15.5% of survivors. The functional disability appears out of proportion to the degree of lung function impairment and may be related to additional factors such as muscle deconditioning and steroid myopathy.

Protecting healthcare staff from severe acute respiratory syndrome: filtration capacity of multiple surgical masks.

Guidelines issued by the Centers for Disease Control and Prevention and the World Health Organisation state that healthcare workers should wear N95 masks or higher-level protection during all contact with suspected severe acute respiratory syndrome (SARS). In areas where N95 masks are not available, multiple layers of surgical masks have been tried to prevent transmission of SARS. The in vivo filtration capacity of a single surgical mask is known to be poor. However, the filtration capacity of a combination of masks is unknown. This was a crossover trial of one, two, three and five surgical masks in six volunteers to determine the in vivo filtration efficiency of wearing more than one surgical mask. We used a Portacount to measure the difference in ambient particle counts inside and outside the masks. The best combination of five surgical masks scored a fit factor of 13.7, which is well below the minimum level of 100 required for a half face respirator. Multiple surgical masks filter ambient particles poorly. They should not be used as a substitute for N95 masks unless there is no alternative.

Predictive value of the user seal check in determining half-face respirator fit.

Guidelines issued by the Centers for Disease Control and Prevention and the World Health Organization state that healthcare workers should wear N95 masks or higher-level protection during all contact with suspected cases of severe acute respiratory syndrome. Before use, the manufacturer recommends performing a user seal check to ensure that the mask is fitted correctly. This study aimed to test the ability of the user seal check to detect poorly fitting masks. This study is a retrospective review of a mask-fitting programme carried out in the intensive care unit of the Prince of Wales Hospital in Hong Kong. In this programme, all staff were tested with two types of N95 mask and one type of N100 mask. The results of the documented user seal check were then compared with the formal fit-test results from a PortaCount. Using a PortaCount reading of 100 as the criterion for a correctly fitted mask, the user seal check wrongly indicated that the mask fitted on 18-31% of occasions, and wrongly indicated that it did not fit on 21-40% of occasions. These data indicate that the user seal check should not be used as a surrogate fit test. Its usefulness as a pre-use test must also be questioned.

Ethical attitudes of intensive care physicians in Hong Kong: questionnaire survey.

OBJECTIVES: To examine the practice and ethical attitudes of intensive care doctors in Hong Kong and to compare findings with those from European studies. DESIGN: Structured questionnaire survey, modified from a similar questionnaire used in Europe. SETTING: Eleven publicly funded intensive care units in Hong Kong. PARTICIPANTS: Ninety-five doctors practising in intensive care units. RESULTS: Of the sixty-five respondents, sizeable proportions indicated that the admission of patients to the intensive care unit is often (25%) or sometimes (51%) limited by bed availability. About 69% to 86% of doctors admit patients with limited prognosis or poor quality of life, although all felt that these admissions should be more restricted. 'Do-not-resuscitate' orders are applied by almost all respondents, and 52% and 89% of respondents would discuss such orders with the patient or with the family, respectively. The withholding and withdrawal of therapy from patients with no chance of recovery to a meaningful life is common in Hong Kong (99% and 89%, respectively). A total of 83% respondents involved patients or families in the decision to limit therapy, compared with less than half in Europe overall. When the family wanted aggressive life-support despite doctors' recommendations to limit therapy, 62% of the respondents would still withhold therapy while only 9% would withdraw therapy. More than 60% of doctors feel comfortable talking to patients' relatives about limitation of therapy. Approximately 75% felt that euthanasia is unacceptable. Most respondents (94%) reported that medical programmes should include more extensive discussion on ethical issues. CONCLUSION: The ethical attitudes of intensive care doctors in Hong Kong are similar to those of counterparts in Europe. However, Hong Kong doctors tend to involve families more often in the discussion of end-of-life issues.

Performance of an oxygen delivery device for weaning potentially infectious critically ill patients.

Oxygen delivery via a heat and moisture exchange filter with an attached T-shaped reservoir satisfies infection control requirements of high efficiency bacterial and viral filtration and low gas flows. In order to assess the performance of such a device in critically ill patients being weaned from mechanical ventilation, we simulated 16 patients using a human patient simulator, measuring fractional inspired oxygen and carbon dioxide concentrations and work of breathing at three oxygen flow rates. Oxygen concentration was dependent on peak inspiratory flow rate, tidal volume and oxygen flow rate. Rebreathing, as indicated by inspired carbon dioxide concentration, was greatest at high respiratory rates and low tidal volumes. Imposed inspiratory work of breathing was relatively high (mean 0.88 J.l(-1)[SD 0.30]). We conclude that this method of oxygen delivery is only suitable for patients in whom rapid extubation is anticipated.