The effect of flash vacuum cooling on the flavor of ultrapasteurized milk.

Ultrapasteurization (UP) extends the shelf life of milk. Direct steam injection (DSI) is commonly used for UP because milk is quickly heated and cooled. During this process, steam is directly injected into milk and removed by a vacuum cooler. Consumers do not prefer the flavor of DSI-UP milk compared with traditional high temperature short time (HTST) milk due to the higher cooked and eggy flavors of DSI-UP milk. The objective of this research was to characterize the effect of the vacuum cooler on the flavor of DSI-UP milk. Raw skim milk was pasteurized at 140°C for 2.3 s by DSI and homogenized at 20.7 MPa. By using a liquid sample port, steam-infused pasteurized milk was sampled after heating but before reaching the vacuum chamber. A septum was installed in the vacuum chamber to allow sampling of the removed volatiles by solid-phase microextraction (SPME) fiber followed by gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) combined with a sulfur-selective flame photometric detector. Steam-infused milk and vacuum-cooled milk diluted to the same solids contents were evaluated by descriptive sensory analysis and volatile compound analysis. The entire experiment was replicated 3 times. Milks cooled by the vacuum cooler were lower in sweet aromatic, sulfur/eggy, and cooked flavors than milk sampled before the vacuum cooler. Volatile compounds removed by the vacuum cooler included the sweet aromatic flavor contributors furaneol, maltol, furfural, sotolon, 2-heptanone, γ-dodecalactone, γ-decalactone, and δ-decalactone, as well as the cooked and sulfur/eggy contributors hydrogen sulfide and dimethyl sulfide. The vacuum cooler applied during DSI-UP of milk is effective at removing steam and cooling UP milk, but this process may also remove important flavor compounds from fluid milk.

Effects of micellar casein concentrate purity and milk fat on sulfur/eggy flavor in ultrapasteurized milk-based beverages.

Our objectives were to determine the level of milk-derived whey protein (MDWP) removal necessary to achieve no detectable sulfur/eggy flavor in ultrapasteurized fat-free micellar casein concentrate (MCC) beverages (6.5% protein) and in the same beverages containing 1 and 2% milk fat. Micellar casein concentrate with 95% MDWP removal was produced from skim milk (50°C) with a 3×, 3-stage ceramic microfiltration (MF) process using 0.1-µm pore size graded permeability membranes (n = 3). In experiment 1, MCC-based beverages at about 6.5% (wt/wt) true protein were formulated at a fat content of 0.15% fat (wt/wt) at 4 different levels of MDWP removal percentages (95.2%, 91.0%, 83.2%, and 69.3%). In experiment 2, a similar series of beverages at 3 MDWP removal percentages (95.2%, 83.2%, and 69.3%) with 0.1, 1, and 2% fat content were produced. The purity (or completeness of removal of whey protein by MF) of MCC was determined by the Kjeldahl method and sodium dodecyl sulfate (SDS)-PAGE. Sensory properties of beverages were documented by descriptive sensory analysis, and volatile sulfur compounds were evaluated using solid-phase microextraction followed by gas chromatography-triple quadrupole mass spectrometry. The purity of MCC measured by the Kjeldahl method (casein as a percentage of true protein) was higher after thermal treatment than before, whereas MCC purity evaluated by SDS-PAGE was unchanged by heat treatment. The purity of MCC had an effect on the flavor profile of thermally processed beverages at 6.5% protein made with fresh liquid MCC. No sulfur/eggy flavor was detected in MCC beverages when 95% of the MDWP was removed (MCC purity about 93 to 94%) from skim milk by microfiltration at 0.1, 1, and 2% fat. As the fat content of 6.5% protein beverages produced with MCC increased, sulfur/eggy flavor intensity and hydrogen sulfide concentration decreased. However, the effect of increasing milk fat on reducing sulfur/eggy flavor in MCC-based beverages at 6.5% protein was less than that of increasing MDWP removal from MCC. Sulfur off-flavors in neutral-pH dairy protein beverages can be mitigated by use of high-purity MCC or by incorporation of fat in the beverage, or both.

Children's perceptions of fluid milk with varying levels of milkfat.

Schools participating in federal meal programs are limited to serving skim or low-fat (≤1%) flavored and unflavored milk. Few studies have directly addressed child perceptions and preferences for milk containing different amounts of milkfat. The objective of this study was to determine whether children can differentiate between flavored and unflavored fluid milk containing varying levels of milkfat and whether preferences for certain levels of milkfat exist. Flavored and unflavored milks containing 4 different percentages of milkfat (≤0.5, 1, 2, and 3.25%) were high-temperature, short-time processed, filled into half-gallon light-shielded milk jugs, and stored at 4°C in the dark. Milks were evaluated by children (ages 8-13 yr) following 7 d at 4°C. Acceptance testing and tetrad difference testing were conducted on flavored and unflavored milks with and without visual cues to determine if differences were driven by visual or flavor or mouthfeel cues. Child acceptance testing (n = 138 unflavored; n = 123 flavored) was conducted to evaluate liking and perception of selected attributes. Tetrad testing (n = 127 unflavored; n = 129 flavored) was conducted to determine if children could differentiate between different fat levels even in the absence of a difference in acceptance. The experiment was replicated twice. When visual cues were present, children had higher overall liking for 1% and 2% milks than skim for unflavored milk and higher liking for chocolate milks containing at least 1% milk fat than for skim. Differences in liking were driven by appearance, viscosity, and flavor. In the absence of visual cues, no differences were observed in liking or flavor or mouthfeel attributes for unflavored milk but higher liking for at least 1% milk fat in chocolate milk compared with skim was consistent with the presence of visual cues. From tetrad testing, children could visually tell a difference between all unflavored pairs except 2% versus whole milk and could not detect consistent differences between milkfat pairs in the absence of visual cues. For chocolate milk, children could tell a difference between all milk fat pairs with visual cues and could tell a difference between skim versus 2% and skim versus whole milk without visual cues. These results demonstrate that in the absence of package-related flavors, school-age children like unflavored skim milk as well as milk with higher fat content in the absence of visual cues. In contrast, appearance as well as flavor and mouthfeel attributes play a role in children's liking as well as their ability to discriminate between chocolate milks containing different amounts of fat, with chocolate milk containing at least 1% fat preferred. The sensory quality of school lunch milk is vital to child preference, and processing efforts are needed to maximize school milk sensory quality.

Ready-to-drink protein beverages: Effects of milk protein concentration and type on flavor.

This study evaluated the role of protein concentration and milk protein ingredient [serum protein isolate (SPI), micellar casein concentrate (MCC), or milk protein concentrate (MPC)] on sensory properties of vanilla ready-to-drink (RTD) protein beverages. The RTD beverages were manufactured from 5 different liquid milk protein blends: 100% MCC, 100% MPC, 18:82 SPI:MCC, 50:50 SPI:MCC, and 50:50 SPI:MPC, at 2 different protein concentrations: 6.3% and 10.5% (wt/wt) protein (15 or 25 g of protein per 237 mL) with 0.5% (wt/wt) fat and 0.7% (wt/wt) lactose. Dipotassium phosphate, carrageenan, cellulose gum, sucralose, and vanilla flavor were included. Blended beverages were preheated to 60°C, homogenized (20.7 MPa), and cooled to 8°C. The beverages were then preheated to 90°C and ultrapasteurized (141°C, 3 s) by direct steam injection followed by vacuum cooling to 86°C and homogenized again (17.2 MPa first stage, 3.5 MPa second stage). Beverages were cooled to 8°C, filled into sanitized bottles, and stored at 4°C. Initial testing of RTD beverages included proximate analyses and aerobic plate count and coliform count. Volatile sulfur compounds and sensory properties were evaluated through 8-wk storage at 4°C. Astringency and sensory viscosity were higher and vanillin flavor was lower in beverages containing 10.5% protein compared with 6.3% protein, and sulfur/eggy flavor, astringency, and viscosity were higher, and sweet aromatic/vanillin flavor was lower in beverages with higher serum protein as a percentage of true protein within each protein content. Volatile compound analysis of headspace vanillin and sulfur compounds was consistent with sensory results: beverages with 50% serum protein as a percentage of true protein and 10.5% protein had the highest concentrations of sulfur volatiles and lower vanillin compared with other beverages. Sulfur volatiles and vanillin, as well as sulfur/eggy and sweet aromatic/vanillin flavors, decreased in all beverages with storage time. These results will enable manufacturers to select or optimize protein blends to better formulate RTD beverages to provide consumers with a protein beverage with high protein content and desired flavor and functional properties.

Invited review: Microfiltration-derived casein and whey proteins from milk.

Milk, a rich source of nutrients, can be fractionated into a wide range of components for use in foods and beverages. With advancements in filtration technologies, micellar caseins and milk-derived whey proteins are now produced from skim milk using microfiltration. Microfiltered ingredients offer unique functional and nutritional benefits that can be exploited in new product development. Microfiltration offers promise in cheesemaking, where microfiltered milk can be used for protein standardization to improve the yield and consistency of cheese and help with operation throughputs. Micellar casein concentrates and milk whey proteins could offer unique functional and flavor properties in various food applications. Consumer desires for safe, nutritious, and clean-label foods could be potential growth opportunities for these new ingredients. The application of micellar casein concentrates in protein standardization could offer a window of opportunity to US cheese makers by improving yields and throughputs in manufacturing plants.

The role of heat treatment in light oxidation of fluid milk.

Light-oxidized flavor (LOF) resulting from photooxidation of riboflavin following light exposure is one of the most common off-flavors in fluid milk. The sensory perception of LOF has been studied extensively in high temperature, short time pasteurized (HTST) milk, but few studies have evaluated ultrapasteurized (UP) milk. The objective of this study was to evaluate the role of heat treatment in the development of LOF in UP fluid skim milk. Skim milk was processed by HTST or by direct steam injection (DSI-UP) and subsequently exposed to 2,000-lx light-emitting diode light for various times. Sensory properties were monitored by descriptive analysis and threshold tests, and volatile compounds were evaluated by solid phase microextraction with gas chromatography-mass spectrometry. Dissolved oxygen and riboflavin were determined at each time point using an oxygen meter and ultra-performance liquid chromatography with a fluorescence detector, respectively. The entire experiment was performed in triplicate. Typical cardboard and mushroom flavors (LOF) were detected by trained panelists in HTST milk after 3.5 h of light exposure. In contrast, LOF was not detected by trained panelists in UP milk until 36 h of light exposure. Similarly, the best estimate threshold for LOF from untrained consumers (n = 101) was higher for DSI-UP milk (61.0 h) than for HTST milk (15.2 h). Milks with LOF were characterized by higher relative abundance of the lipid oxidation compounds hexanal and heptanal. Dissolved oxygen (DO) and riboflavin concentrations decreased with increased light exposure time, and the decrease was slower in UP milk compared with HTST milk. Initial DO concentration was investigated as a possible influence in LOF development because DSI-UP milks had lower initial DO concentrations than HTST milks. However, follow-up evaluations of deaerated HTST milks suggested that DO was not a significant factor in LOF development. These results demonstrate that UP milk is less sensitive to LOF than HTST milk, possibly due to sensory masking effects or antioxidant effects of volatile sulfur compounds. An enhanced understanding of light and storage effects on milks will assist with best practices when transporting and displaying fluid milk products for sale.

Invited review: Astringency in whey protein beverages.

Astringency is the sensation of mouth drying and puckering, and it has also been described as a loss of lubrication in the mouth. Astringency is perceived as an increase in oral friction or roughness. Astringency caused by tannins and other polyphenols has been well documented and studied. Whey proteins are popular for their functional and nutritional quality, but they exhibit astringency, particularly under acidic conditions popular in high acid (pH 3.4) whey protein beverages. Acids cause astringency, but acidic protein beverages have higher astringency than acid alone. Whey proteins are able to interact with salivary proteins, which removes the lubricating saliva layer of the mouth. Whey proteins can also interact directly with epithelial tissue. These various mechanisms of astringency limit whey protein ingredient applications because astringency is undesirable to consumers. A better understanding of the causes of whey protein astringency will improve our ability to produce products that have high consumer liking and deliver excellent nutrition.

Identification of the source of volatile sulfur compounds produced in milk during thermal processing.

Volatile sulfur compounds in ultra-pasteurized (UP) milk are the major contributors to sulfur/burnt and eggy flavors, and these flavors are disliked by consumers. Previous research has established distinct differences in flavor profiles of fluid milk processed by high temperature, short time pasteurization (HTST) and UP by direct steam injection (DSI-UP) or indirect heat (IND-UP). An understanding of the contribution of the individual milk proteins to sulfur off-flavors would clarify the source of sulfur flavors in UP milks. The objective of this study was to determine the source of volatile sulfur compounds in fluid milk with a specific focus on the comparison of heat treatment effects on milks by HTST and UP. Formulated skim milks (FSM) were manufactured by blending micellar casein concentrate and serum protein isolate (SPI). Three different caseins as a percentage of true protein (FSM95, FSM80, and FSM60) were formulated to determine the source of sulfur/burnt and eggy flavors. Freshly processed micellar casein concentrate or SPI were blended to achieve a true protein content of about 3.2%. Raw skim milk served as a control. Skim milk and FSM were pasteurized at 78°C for 15 s (HTST) or 140°C for 2.3 s by IND-UP or DSI-UP. The experiment was replicated twice. Sensory properties of milks and FSM were documented by descriptive sensory analysis. Volatile sulfur compounds in milks and FSM were evaluated using solid-phase microextraction followed by gas chromatography-triple quadrupole mass spectrometry combined with a sulfur selective flame photometric detector. The FSM with higher SPI as a percent of true protein had higher sensory sulfur/burnt and eggy flavors along with elevated concentrations of hydrogen sulfide and carbon disulfide compared with skim milk or FSM with lower proportions of SPI. Sulfur compounds including dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, dimethyl sulfoxide, and methional were not associated with sulfur/burnt and eggy flavors, which suggests that these compounds may not specifically contribute to the sulfur/burnt and eggy off-flavors of UP milks. Sensory panelists found higher overall aroma impact, and cooked, sulfur/burnt, and eggy flavors for DSI-UP, followed by IND-UP and HTST. The combination of sensory and instrumental methods used in the current study effectively identified that milk serum proteins are the source of sulfur compounds in milk, and further confirmed the contribution of hydrogen sulfide and carbon disulfide to eggy and sulfur/burnt flavors, respectively.

Invited review: The effects of processing parameters on the flavor of whey protein ingredients.

Whey protein ingredients are used in a wide variety of products and are added primarily for nutritional benefits or functionality, not for flavor. However, the processes used to further refine fluid whey produce and encourage development of off-flavors that carry through to the final product. From the milk source to spray drying, each step contributes to the oxidation of lipids, which negatively affects flavor. An understanding of the sources of these flavor constituents and volatile compounds, as well as how they are formed during processing and handling, are important to eliminate or reduce undesirable flavors and for understanding how to best incorporate these ingredients into high-quality finished products.

Effects of fat content, pasteurization method, homogenization pressure, and storage time on the mechanical and sensory properties of bovine milk.

Fluid milk may be pasteurized by high-temperature short-time pasteurization (HTST) or ultrapasteurization (UP). Literature suggests that UP increases milk astringency, but definitive studies have not demonstrated this effect. Thus, the objective of this study was to determine the effects of pasteurization method, fat content, homogenization pressure, and storage time on milk sensory and mechanical behaviors. Raw skim (<0.2% fat), 2%, and 5% fat milk was pasteurized in duplicate by indirect UP (140°C, 2.3 s) or by HTST pasteurization (78°C, 15 s), homogenized at 20.7 MPa, and stored at 4°C for 8 wk. Additionally, 2% fat milk was processed by indirect UP and homogenized at 13.8, 20.7, and 27.6 MPa and stored at 4°C for 8 wk. Sensory profiling, instrumental viscosity, and friction profiles of all milk were evaluated at 25°C after storage times of 1, 4, and 8 wk. Sodium dodecyl sulfate PAGE and confocal laser scanning microscopy were used to determine protein structural changes in milk at these time points. Fresh HTST milk was processed at wk 7 for wk 8 evaluations. Ultrapasteurization increased milk sensory and instrumental viscosity compared with HTST pasteurization. Increased fat content increased sensory and instrumental viscosity, and decreased astringency and friction profiles. Astringency, mixed regimen friction profiles, and sensory viscosity also increased for UP versus HTST. Increased storage time showed no effect on sensory viscosity or mechanical viscosity. However, increased storage time generally resulted in increased friction profiles and astringency. Sodium dodecyl sulfate PAGE and confocal laser scanning microscopy showed increased denatured whey protein in UP milk compared with HTST milk. The aggregates or network formed by these proteins and casein micelles likely caused the increase in viscosity and friction profiles during storage. Homogenization pressure did not significantly affect friction behaviors, mechanical viscosity, or astringency; however, samples homogenized at 13.8 MPa versus 20.7 and 27.6 MPa showed higher sensory viscosity. Astringency was positively correlated with the friction coefficient at 100 m/s sliding speed (R2 = 0.71 for HTST milk and R2 = 0.74 for UP milk), and sensory viscosity was positively correlated with the mechanical viscosity at a shear rate of 50 s-1 (R2 = 0.90). Thus, instrumental testing can be used to indicate certain sensory behaviors of milk.

Impact of thrombelastography in paediatric intensive care.

We assessed the clinical impact of thrombelastography (TEG®) results (TEG® 5000, Haemonetics Corporation, Braintree, MA, USA) by measuring their ability to cause changes in a theoretical treatment plan and contribute to the understanding of haemostasis. We prospectively included paediatric intensive care unit (PICU) patients who had standard tests of haemostasis and TEG ordered and had an arterial catheter or extracorporeal access port in situ. Blood for standard tests and TEG was taken simultaneously. Independent of patient care, general patient information and results of standard laboratory tests were presented to five clinicians who were asked to document their theoretical treatment plan. Clinicians were then shown TEG results and asked if they caused a change in their plan, if they confirmed initial standard laboratory test results, if they enabled a better understanding of haemostasis and if they provided additional information. Inter-rater agreement between the clinicians was determined. Forty-two TEG results were obtained from 34 patients. Overall, the inclusion of TEG results led to a change in treatment plan in 97 of 207 occasions (47%), confirmed standard laboratory test results in 177 of 204 occasions (87%), enabled a better understanding of haemostasis in 140 of 204 occasions (69%) and provided additional information in 131 of 204 occasions (64%). Variation existed between clinicians, seemingly due to individual differences, with poor inter-rater agreement. We conclude that TEG results led to changes in treatment plans almost half the time, confirmed findings of standard tests and provided a better understanding of haemostasis, but randomised controlled trials are required to determine the role and influence of TEG results on patient outcome.

Short communication: Sensitive detection of norbixin in dried dairy ingredients at concentrations of less than 1 part per billion.

Norbixin is the water-soluble carotenoid in annatto extracts used in the cheese industry to color Cheddar cheese. The purpose of norbixin is to provide cheese color, but norbixin is also present in the whey stream and contaminates dried dairy ingredients. Regulatory restrictions dictate that norbixin cannot be present in dairy ingredients destined for infant formula or ingredients entering different international markets. Thus, there is a need for the detection and quantification of norbixin at very low levels in dried dairy ingredients to confirm its absence. A rapid method for norbixin evaluation exists, but it does not have the sensitivity required to confirm norbixin absence at very low levels in compliance with existing regulations. The current method has a limit of detection of 2.7 µg/kg and a limit of quantification of 3.5 µg/kg. The purpose of this study was to develop a method to extract and concentrate norbixin for quantification in dried dairy ingredients below 1 µg/kg (1 ppb). A reverse-phase solid-phase extraction column step was applied in the new method to concentrate and quantify norbixin from liquid and dried WPC80 (whey protein concentrate with 80% protein), WPC34 (WPC, 34% protein), permeate, and lactose. Samples were evaluated by both methods for comparison. The established method was able to quantify norbixin in whey proteins and permeates (9.39 µg/kg to 2.35 mg/kg) but was unable to detect norbixin in suspect powdered lactose samples. The newly developed method had similar performance to the established method for whey proteins and permeates but was also able to detect norbixin in powdered lactose samples. The proposed method had a >90% recovery in lactose samples and a limit of detection of 28 ppt (ng/kg) and a limit of quantification of 94 ppt (ng/kg). The developed method provides detection and quantification of norbixin for dairy ingredients that have a concentration of <1 ppb.

ICP and CPP: excellent predictors of long term outcome in severely brain injured children.

OBJECTIVE: To determine the predictive powers of intracranial pressure (ICP) and cerebral perfusion pressure (CPP) amongst severely brain injured children. MATERIALS AND METHODS: ICP and CPP were recorded from thirty-five severely brain injured children who were prospectively recruited after admission to paediatric intensive care. Twenty-five suffered traumatic brain injury (TBI) and ten suffered non-TBI. Peak ICP and minimum CPP recorded for each patient during their admission were related to 5 year Glasgow Outcome Scale outcome. Receiver operator characteristic curves determined that the optimum threshold for unfavourable outcome prediction was >or=40 mmHg for ICP and

Bilaterally absent pupillary responses: not always a bad sign.

Pupillary responses are a simple test commonly used as a predictor of outcome after severe brain injury. It is also common for clinicians to associate bilaterally absent pupillary responses with very poor prognosis. We report a series of cases of severely brain injured children with bilaterally absent pupillary responses who had favourable outcomes. From a group of 89 patients with brain injury, 32 had bilaterally absent pupillary responses and six (four with traumatic brain injury and two with infective brain injury) subsequently had favourable outcomes. This represents 18.8% of patients and should be a reminder to clinicians that the clinical sign of bilaterally absent pupillary responses is not always associated with a hopeless outcome.

ICU staffing: identification and survey of staff involved in providing technical support services to Australian and New Zealand intensive care units.

We conducted a survey of all (200) Australian and New Zealand intensive care units to determine the presence and nature of staff employed in a technical support role. Specifically, we attempted to identify staff who are formally employed in a role where they are directly responsible for the equipment used in intensive care. Of 130 returned surveys, 80 units (62%) reported not having any personnel in this role. In these units technical tasks were most commonly performed by registered nurses (79%) but were also performed by a variety of other personnel. Fifty units (38%), consisting of approximately 105 individuals providing a total of 84.3 EFTs and most commonly in public (84%) or metropolitan (70%) hospitals or level 3 (64%) intensive care units, did have one or more staff acting in a formal technical support role. The most common groups filling the technical support role were nurses (42%), technicians (24%), biomedical engineers (10%) and technologists (6%). The most common duties performed were equipment troubleshooting (92%), training (80%), equipment evaluation (80%), ordering supplies (77%), consumable evaluation (75%), equipment cleaning (73%), delivery of supplies (70%), handling product recalls (65%), equipment maintenance (65%) and sitting on hospital committees (52%). This is the first attempt to identify and understand the technical support role in Australian and New Zealand intensive care units. Numerous issues remain and future work will hopefully add to our findings, with the possibility of formal recognition of the role, training and/or accreditation and its extension into other hospital departments.

A prospective study of outcome predictors after severe brain injury in children.

OBJECTIVE: To directly compare the predictive powers of somatosensory evoked potentials (SEPs) to those of motor and pupillary responses. DESIGN AND SETTING: Prospective clinical study in a paediatric intensive care unit. PATIENTS AND PARTICIPANTS: 102 severely brain-injured children less than 15 years of age. MEASUREMENTS AND RESULTS: SEPs and motor and pupillary responses were serially recorded during the first 9 days after admission. Initial, last and those tests performed on or after day 2 were analysed. Outcome was assessed 5 years after injury. SEPs had equal or superior predictive statistics and ROC curves compared to the other tests with few exceptions. Pupillary responses had higher sensitivity for favourable outcome prediction while for unfavourable outcome prediction the last motor responses had higher sensitivity, and the last pupillary responses had slightly higher specificity. Combining SEPs and motor responses provided the best combination for predicting unfavourable outcome. CONCLUSIONS: SEPs are the best overall predictor of outcome while motor and pupillary responses have advantages in some specific areas. The routine use of SEPs should be considered in the prediction of outcome of severely brain-injured patients.

Are somatosensory evoked potentials the best predictor of outcome after severe brain injury? A systematic review.

OBJECTIVE: Many tests have been used to predict outcome following severe brain injury. We compared predictive powers of clinical examination (pupillary responses, motor responses and Glasgow Coma Scale, GCS), electroencephalography (EEG) and computed tomography (CT) to that of somatosensory evoked potentials (SEPs) in a systematic review. MATERIALS AND METHODS: Medline (1976-2002) and Embase (1980-2002) were searched, manual review of article reference lists was conducted, and authors were contacted. We selected 25 studies addressing the prediction of outcome after severe brain injury using SEPs and either GCS, EEG, CT, pupillary or motor responses. Outcomes were determined for patients with normal or bilaterally absent SEPs and graded measures of GCS, EEG, CT, pupillary responses or motor responses. For favourable outcome prediction SEPs were superior in sensitivity, specificity and positive and negative predictive values, except for pupillary responses which had superior sensitivity and GCS which had higher specificity. SEPs had superior summary receiver operating characteristic curves, with the exception of motor responses, and superior ratio of odds ratios. For unfavourable outcome prediction SEPs were superior to the other tests in sensitivity, specificity and positive and negative predictive values, except for motor and pupillary responses, GCS and CTs which had superior sensitivity. All SEP summary receiver operating characteristic curves and pooled ratio of odds ratios were superior. CONCLUSIONS: Although imperfect, SEPs appear to be the best single overall predictor of outcome. There is sufficient evidence for clinicians to use SEPs in the prediction of outcome after brain injury.

Compensating for the effect of inlet gas temperature on heated humidifier performance.

The humidity output of heated humidifiers may be compromised by inlet gas temperatures exceeding approximately 26 degrees C, with humidity dropping below the recommended levels for intubated patients. A new version of the Fisher & Paykel MR850 humidifier claims to deal with this problem by offering a humidity compensation option. The present study tested this feature by measuring humidity output using the gravimetric method and a hygrometer at different inlet gas temperatures (16.6 degrees C to 40.0 degrees C) with compensation on and off. It was found that the compensation is effective in maintaining humidity levels despite high inlet gas temperatures.

An evaluation of nitric oxide and nitrogen dioxide absorbers and filters.

The absorbance of NO (5-90 ppm) and NO2 (0.5-4 ppm) by a number of absorbers and filters was assessed via bench testing. All absorbers (Sodasorb, Purafil CP, Purafil Select, Sofnolime, Sofnofil and 50/50 mix of Sofnolime/Sofnofil) except Sodasorb absorbed NO almost completely. Only Sofnolime absorbed NO2 completely while Sodasorb and the Sofnolime/Sofnofil 50/50 mix had absorbances between 47% and 90%. The absorbance of four filters (ILF100, ILF150, ILF200 and HgCONO) as well as Sofnolime and the Sofnolime/Sofnofil 50/50 mix was tested in the expiratory port of a Servo 900C ventilator All absorbers and filters produced a change in ventilator pressures. The HgCONO filter Sofnolime and the Sofnolime/Sofnofil 50/50 mix all absorbed NO. At 80 ppm NO, the HgCONO filter had 100% absorbance for four hours while Sofnolime's absorbance was significantly reduced after one hour. All filters and absorbers tested on the ventilator except the Sofnolime/Sofnofil 50/50 mix and the ILF150 filter absorbed NO2 completely for a period ranging from 90 minutes to four hours. We recommend the HgCONO filter and Sofnolime to absorb both NO and NO2. If absorption of NO2 only is required we recommend the HgCONO, ILF100 or ILF200 filters or the Sofnolime absorber.

Performance of transcutaneous PCO2 and pulse oximetry monitors in newborns and infants after cardiac surgery.

We examined the effect of core and skin temperature on the accuracy of two pulse oximeters (Nellcor Symphony and Hewlett Packard saturation module, M1020A) and a transcutaneous PCO2 monitor (Fastrac Transcutaneous monitor) immediately after cardiac surgery in a group of newborns and infants. Seventy-nine sets of data were collected from 46 patients. Core temperatures ranged from 35.3 degrees C to 39.4 degrees C, skin temperatures ranged from 27.0 degrees C to 37.4 degrees C and core-skin temperature gradients ranged from 0.1 degree C to 10.1 degrees C. Data analysis consisted of comparing the difference between transcutaneous PCO2 and arterial PCO2 and the differences between oxygen haemoglobin saturation measured by both pulse oximeters and oxygen haemoglobin saturation measured by co-oximeter to core temperature, skin temperature and core-skin temperature gradients. The mean differences +/- standard deviations and limits of agreement for transcutaneous PCO2 and oxygen haemoglobin saturation measured by the Hewlett Packard and Nellcor pulse oximeters were 0.95 +/- 4.10 mmHg (-7.09 mmHg to 8.99 mmHg), -1.07 +/- 1.84% (-4.68% to 2.54%) and -1.23 +/- 2.23% (-5.60% to 3.14%) respectively. Analysis of correlation coefficients showed that the accuracy of the transcutaneous PCO2 monitor and the pulse oximeters were not affected by core temperature, skin temperature or core-skin temperature gradient in the ranges encountered. We therefore conclude that these devices are acceptably accurate and suitable for use in infants when core and skin temperatures and core-skin temperature gradient are in the range normally found after cardiac surgery.