Beta-mannosidosis in a domestic cat associated with a missense variant in MANBA

A 6-month-old cat of unknown ancestry presented for a neurologic evaluation due to progressive motor impairment. Complete physical and neurologic examinations suggested the disorder was likely to be hereditary, although the signs were not consistent with any previously described inherited disorders in cats. Due to the progression of disease signs including severely impaired motor function and cognitive decline, the cat was euthanized at approximately 10.5 months of age. Whole genome sequence analysis identified a homozygous missense variant c.2506G > A in MANBA that predicts a p.Gly836Arg alteration in the encoded lysosomal enzyme β -mannosidase. This variant was not present in the whole genome or whole exome sequences of any of the 424 cats represented in the 99 Lives Cat Genome dataset. β -Mannosidase enzyme activity was undetectable in brain tissue homogenates from the affected cat, whereas α-mannosidase enzyme activities were elevated compared to an unaffected cat. Postmortem examination of brain and retinal tissues revealed massive accumulations of vacuolar inclusions in most cells, similar to those reported in animals of other species with hereditary β -mannosidosis. Based on these findings, the cat likely suffered from β -mannosidosis due to the abolition of β -mannosidase activity associated with the p.Gly836Arg amino acid substitution. p.Gly836 is located in the C-terminal region of the protein and was not previously known to be involved in modulating enzyme activity. In addition to the vacuolar inclusions, some cells in the brain of the affected cat contained inclusions that exhibited lipofuscin-like autofluorescence. Electron microscopic examinations suggested these inclusions formed via an autophagy-like process.

A Homozygous MAN2B1 Missense Mutation in a Doberman Pinscher Dog with Neurodegeneration, Cytoplasmic Vacuoles, Autofluorescent Storage Granules, and an α-Mannosidase Deficiency

A 7-month-old Doberman Pinscher dog presented with progressive neurological signs and brain atrophy suggestive of a hereditary neurodegenerative disorder. The dog was euthanized due to the progression of disease signs. Microscopic examination of tissues collected at the time of euthanasia revealed massive accumulations of vacuolar inclusions in cells throughout the central nervous system, suggestive of a lysosomal storage disorder. A whole genome sequence generated with DNA from the affected dog contained a likely causal, homozygous missense variant in MAN2B1 that predicted an Asp104Gly amino acid substitution that was unique among whole genome sequences from over 4000 dogs. A lack of detectable α-mannosidase enzyme activity confirmed a diagnosis of a-mannosidosis. In addition to the vacuolar inclusions characteristic of α-mannosidosis, the dog exhibited accumulations of autofluorescent intracellular inclusions in some of the same tissues. The autofluorescence was similar to that which occurs in a group of lysosomal storage disorders called neuronal ceroid lipofuscinoses (NCLs). As in many of the NCLs, some of the storage bodies immunostained strongly for mitochondrial ATP synthase subunit c protein. This protein is not a substrate for α-mannosidase, so its accumulation and the development of storage body autofluorescence were likely due to a generalized impairment of lysosomal function secondary to the accumulation of α-mannosidase substrates. Thus, it appears that storage body autofluorescence and subunit c accumulation are not unique to the NCLs. Consistent with generalized lysosomal impairment, the affected dog exhibited accumulations of intracellular inclusions with varied and complex ultrastructural features characteristic of autophagolysosomes. Impaired autophagic flux may be a general feature of this class of disorders that contributes to disease pathology and could be a target for therapeutic intervention. In addition to storage body accumulation, glial activation indicative of neuroinflammation was observed in the brain and spinal cord of the proband.

Prostate Cancer Foundation-Department of Veterans Affairs Partnership: A Model of Public-Private Collaboration to Advance Treatment and Care of Invasive Cancers

BACKGROUND

Prostate cancer is the most frequently diagnosed and treated cancer in the US Department of Veterans Affairs (VA). As the leading philanthropic source for prostate cancer research, the Prostate Cancer Foundation (PCF) entered into a unique public-private biomedical research partnership with the VA with the goal of addressing the urgent health challenges faced by veterans with prostate cancer.

OBSERVATIONS

With a commitment of $50 million from PCF and the VA's vast medical center infrastructure, the PCF-VA partnership has established 12 precision oncology Centers of Excellence to date, forming a collaborative network called the Precision Oncology Program for Cancer of the Prostate (POPCaP) Network. A 4-year review reveals the importance of executive leadership, mission-driven advocacy, setting shared ambitious goals, maximizing existing infrastructure and human capital, recruiting talent and resources, and creating space for adaptation and iteration in the context of a learning health care system.

CONCLUSIONS

The PCF-VA partnership seeks to continue translating clinical research into national standards of care for veterans and serves as an innovative model of public-private collaborations for future health initiatives.

Outcomes associated with conventional versus lipid-based formulations of amphotericin B in propensity-matched groups

Background

Lipid-based formulations of amphotericin B (LF-AMB) are indicated for treatment of invasive fungal infections in patients intolerant to conventional amphotericin B (CAB) or with refractory infections. Physicians still may choose to administer CAB to such patients. We described the use of CAB and LF-AMB in this population and quantified differences in post-amphotericin B length of stay (LOS) among survivors and hospital mortality in matched patients.

Methods

Data were extracted from Health Facts (Cerner Corporation, Kansas City, MO, USA) for a retrospective cohort analysis. Inpatients aged ≥18 years with evidence of fungal infection and with orders for LF-AMB or CAB on ≥2 days from January 2001 to June 2010 were identified. Patients were required to have renal insufficiency or other relative contraindications to use of CAB, exposure to nephrotoxic agents, or evidence of a CAB-refractory infection. Multilevel (hierarchical) mixed-effects logistic regression was used to determine factors associated with initial exposure to LF-AMB versus CAB. Multivariate adjustment of outcomes was done using propensity score matching.

Results

655 patients were identified: 322 patients initiated therapy with CAB and 333 initiated treatment with LF-AMB. Compared to those initiating CAB, patients initiating LF-AMB had greater acuity and underlying disease severity. In unadjusted analyses, hospital mortality was significantly higher in the LF-AMB group (32.2% versus 23.7%; P = 0.02). After propensity score matching and covariate adjustment, mortality equalized and observed differences in LOS after amphotericin B initiation decreased.

Conclusion

Among patients at risk for amphotericin B toxicity, differences between CAB and LF-AMB seen in crude outcomes analyses relate to channeling of sicker patients to initiate treatment with LF-AMB. Failing to account for differences among patients that drive clinical decision-making will result in inaccurate conclusions about the real-world effectiveness of different amphotericin B formulations.

Treatment of candidemia with echinocandins: data on hospital resource use from a real world setting

OBJECTIVE

Real-world data on patients treated with echinocandins for candidemia are limited. This study examined the effect of three echinocandin-based treatment regimens on resource utilization in patients with Candida infection.

RESEARCH DESIGN AND METHODS

A retrospective cohort study of patients hospitalized between 2005 and 2010 with a blood culture positive for Candida. Length of stay (LOS) following AF initiation (post-AF LOS) and total days with AF treatment were compared in patients treated with three different echinocandin regimens: patients with echinocandin only, patients who received fluconazole prior to an echinocandin (fluconazole-echinocandin), and patients who received an echinocandin prior to fluconazole (echinocandin-fluconazole). Generalized linear models were used to adjust for confounders.

RESULTS

A total of 647 patients met inclusion criteria. Patients treated with echinocandin only were more acutely ill, having more organ dysfunction and sepsis. Unadjusted post-AF LOS was significantly greater in the groups that received both echinocandin and fluconazole (mean, 13.1 days for echinocandin-only vs 25.5 and 21.2 days for fluconazole-echinocandin and echinocandin-fluconazole groups, respectively, p<0.001). These groups also had a higher total number of days with AF orders. These differences remained after multivariate adjustment and in survivor-only analyses. Compared with echinocandin-only treatment, the average marginal effect of fluconazole-echinocandin and echinocandin-fluconazole regimens were associated with significantly longer adjusted post-AF LOS (by 7.2 days and 9.3 days, respectively, p<0.001) and significantly more adjusted total AF days (by 5.3 days for fluconazole-echinocandin and 6.5 days for echinocandin-fluconazole patients, p<0.001). Limitations included lack of visibility to specific reasons for therapy changes.

CONCLUSIONS

Fluconazole before or after echinocandin was associated with significantly greater resource utilization than echinocandin use alone.

Compliance with biologic therapies for rheumatoid arthritis: do patient out-of-pocket payments matter?

OBJECTIVE

To assess the impact of patient out-of-pocket (OOP) expenditures on adherence and persistence with biologics in patients with rheumatoid arthritis (RA).

METHODS

An inception cohort of RA patients with pharmacy claims for etanercept or adalimumab during 2002-2004 was selected from an insurance claims database of self-insured employer health plans (n=2,285) in the US. Adherence was defined as medication possession ratio (MPR): the proportion of the 365 followup days covered by days supply. Persistence was determined using a survival analysis of therapy discontinuation during followup. Patient OOP cost was measured as the patient's coinsurance and copayments per week of therapy, and as the proportion of the total medication charges paid by the patient. Multivariate linear regression models of MPR and proportional hazards models of persistence were used to estimate the impact of cost, adjusting for insurance type and demographic and clinical variables.

RESULTS

Mean +/- SD OOP expenditures averaged $7.84+/-$14.15 per week. Most patients (92%) paid less than $20 OOP for therapy/week. The mean +/- SD MPR was 0.52+/-0.31. Adherence significantly decreased with increased weekly OOP (coeff= -0.0035, P<0.0001) and with a higher proportion of therapy costs paid by patients (coeff= -0.8794, P<0.0001), translating into approximately 1 week of therapy lost per $5.50 increase in weekly OOP. Patients whose weekly cost exceeded $50 were more likely to discontinue than patients with lower costs (hazard ratio 1.58, P<0.001).

CONCLUSION

Most patients pay less than $20/week for biologics, but a small number have high OOP expenses, associated with lower medication compliance. The adverse impact of high OOP costs on adherence, persistence, and outcomes must be considered when making decisions about increasing copayments.

Single Nucleotide Polymorphisms and Microarray Technology in Forensic Genetics - Development and Application to Mitochondrial DNA

Variations in the genome, due to base substitutions, insertions, or deletions at single positions, are known as single nucleotide polymorphisms (SNPs). Approximately 85% of human variation is based on such polymorphisms. Therefore, there is an abundance of human SNPs that are available for forensic identity testing purposes. SNP analyses also may be suitable for some forensic identity cases, because they can be detected in smallsized amplicons, allowing for genetic analysis of substantially degraded DNA. While SNP analysis is unlikely to replace short tandem repeat loci typing for routine casework, SNPs may prove useful for certain circumstances, for example, typing mitochondrial DNA (mtDNA). Although sequencing mtDNA enables detection of all SNPs contained within the region of interest, it is currently not a practical approach for simultaneously typing SNPs that reside throughout the entire mtDNA genome. A variety of alternate methods to detect SNPs are available that may facilitate mtDNA analysis. All the methods include amplification, typically by the polymerase chain reaction, of the region containing the SNP of interest. Most assays are based on either hybridization of a probe to amplified product or primer extension chemistry, and multiplexing is possible. Some of these methodologies are: chips, SNaP shot™, Luminex 100™, SNPstream® UHT, and Pyrosequencing™. SNP analysis of mtDNA, both in the noncoding and coding regions, has been demonstrated using a number of these formats.

Fully automated software to monitor wear in prosthetic knees using fluoroscopic images

Total knee arthroplasty is now a widely accepted treatment for late-stage arthritis. Wear of the polyethylene layer in prosthetic knees is a known cause of implant failure. Early detection of wear may allow prediction of device failure. In this paper we describe a fully automated image processing algorithm to measure the minimum tibiofemoral joint space width (mJSW) for monitoring prosthesis wear radiographically. The femoral portion and tibial plate were automatically delineated and mJSW was calculated in each compartment. The software also delineated the tip of the prosthesis pin in order to make a magnification correction. The algorithm was tested with a set of triplicate acquisitions of 18 fluoroscopic knee images. The RMS standard deviation (RMSSD) for the triplicate measurements was calculated as a figure of merit. The RMSSD was 0.077 and 0.087 mm for the lateral and medial compartments. The computer successfully found the minimum JSW for both compartments in all 54 images. A single case (2% of total) required user interaction to correct for an obvious failure to delineate the prosthesis pin. We document a robust and precise tool for quantifying mJSW to monitor prosthesis wear.

Surface temperature of two portable ventilators during simulated use under clinical conditions

During performance testing of portable ventilators, it was noted that an area on the case of one of the devices, the LTV 1000, was noticeably warm. This investigation examined the case temperatures of this portable ventilator and a portable ventilator currently in the Department of Defense inventory, the Uni-Vent 754, during simulated clinical conditions. Both have an integral method of producing compressed air. The hottest portion of the cases of the LTV 1000 and the Uni-Vent 754 reached temperatures of 39.9 to 46.7 degrees C and 35.4 to 35.9 degrees C, respectively, across a range of simulated clinical conditions. Investigations have found the risk of burns to increase with temperatures greater than 40 degrees C. The cases of these devices are not designed to be in contact with the skin. Personnel should properly position these and other devices during patient transport and not allow contact with the patient's skin.

Adaptive support ventilation

Adaptive support ventilation (ASV) is a newer form of closed-loop ventilation control available on the Galileo ventilator (Hamilton Medical). ASV provides automated selection of initial ventilator parameters based on measurements of patient lung mechanics and breathing effort. After initiation, ASV will "titrate" ventilator output (mandatory breath rate, tidal volume, inspiratory pressure, inspiratory time, and I to E ratio) to maintain a calculated optimal breathing pattern that ensures delivery of a clinician selected minute ventilation target. ASV may be thought of as an "electronic" ventilator management protocol that may improve the safety and efficacy of mechanical ventilation. Additional clinical investigations regarding the effect of ASV on outcome, ventilator days, and so forth are forthcoming.

Work of breathing characteristics of seven portable ventilators

Portable ventilators (PVs) are used for patient transport with increasingly frequency. Due to design differences it would not be unexpected to find differences among these ventilators in the imposed work of breathing (WOBI) during spontaneous respiratory efforts. The purpose of this investigation was to compare the WOBI characteristics during spontaneous breathing of seven PVs; Bird Avian, Bio-Med Crossvent 4, Pulmonetics LTV 1000, Hamilton Max, Drägerwerk Oxylog 2000, Impact Uni-Vent 750, and Impact Uni-Vent 754 using a model of spontaneous breathing. Differences between the PVs in regards to the measured parameters increased with increases in simulated breathing demand. WOBI, peak inspiratory pressure, and pressure-time product were consistently less with the LTV 1000 over the range of simulated breathing conditions. During pressure support ventilation these parameters were significantly less with the LTV 1000 compared with the Crossvent 4. Only the WOBI produced by the LTV was consistently lower than the physiologic work of breathing across the simulated spontaneous breathing conditions. Based on these results it is predicted PVs with flow triggering and positive end-expiratory pressure compensation will consistently offer the least WOBI. Clinicians should be aware of these characteristics when using PVs with spontaneous breathing patients.

Prone positioning and inhaled nitric oxide: synergistic therapies for acute respiratory distress syndrome

BACKGROUND

Inhaled nitric oxide (INO) and prone positioning have both been advocated as methods to improve oxygenation in patients with acute respiratory distress syndrome (ARDS). This study was designed to evaluate the relative contributions of INO and prone positioning alone and in combination on gas exchange in trauma patients with ARDS.

METHODS

Sixteen patients meeting the consensus definition of ARDS were studied. Patients received mechanical ventilation in the supine position, mechanical ventilation plus INO at 1 part per million in the supine position, mechanical ventilation in the PP, and mechanical ventilation in the prone positioning plus INO at 1 part per million. A stabilization period of 1 hour was allowed at each condition. After stabilization,hemodynamic and gas exchange variables were measured.

RESULTS

INO and prone positioning both increased PaO2/FIO2 compared with ventilation in the supine position. PaO2/FIO2 increased by 14% during use of INO, and 10 of 16 patients (62%) responded to INO in the supine position. PaO2/FIO2 increased by 33%, and 14 of 16 patients (87.5%) responded to the prone position. The combination of INO and prone positioning resulted in an improvement in PaO2/FIO2 in 15 of 16 patients(94%), with a mean increase in PaO2/FIO2 of 59%. Pulmonary vascular resistance was reduced during use of INO, with a greater reduction in pulmonary vascular resistance seen with INO plus prone positioning (175 +/- 36 dynes x s/cm5 vs. 134 +/- 28 dynes x s/cm5) compared with INO in the supine position (164 +/- 48 dynes x s/cm5 vs.138 +/- 44 dynes x s/cm5). There were no significant hemodynamic effects of INO or prone positioning and no complications were seen during this relative short duration of study.

CONCLUSIONS

INO and prone positioning can contribute to improved oxygenation in patients with ARDS. The two therapies in combination are synergistic and may be important adjuncts to mechanical ventilation in the ARDS patient with refractory hypoxemia.

Current concepts in imaging of tendinopathy

With the rising popularity of recreational sports, radiologists are being asked to image tendons with increasing frequency. Recognition of the critical link tendons provide between muscle and bone has also led to a better understanding of the processes leading to tendon damage. While plain radiography and CT have only a limited role to play in the diagnosis of tendon abnormality, the improvements in ultrasound and MRI technology mean that tendons can now be demonstrated in exquisite detail and previously undetectable abnormalities are readily demonstrated. This article reviews the structure and pathological processes affecting tendons and discusses the role of imaging in their assessment with an emphasis on ultrasound and MRI.

The acute effects of body position strategies and respiratory therapy in paralyzed patients with acute lung injury

BACKGROUND

Routine turning of critically ill patients is a standard of care. In recent years, specialized beds that provide automated turning have been introduced. These beds have been reported to improve lung function, reduce hospital-acquired pneumonia, and facilitate secretion removal. This trial was designed to measure the physiological effects of routine turning and respiratory therapy in comparison with continuous lateral rotation (CLR).

METHODS

The study was a prospective, quasi-experimental, random assignment, trial with patients serving as their own controls. Paralyzed, sedated patients with acute respiratory distress syndrome were eligible for study. Patients were randomized to receive four turning and secretion management regimens in random sequence for 6 h each over a period of 24 h: (1) routine turning every 2 h from the left to right lateral position; (2) routine turning every 2 h from the left to right lateral position including a 15-min period of manual percussion and postural drainage (P&PD); (3) CLR with a specialized bed that turned patients from left to right lateral position, pausing at each position for 2 min; and (4) CLR with a specialized bed that turned patients from left to right lateral position pausing at each position for 2 min, and a 15-min period of percussion provided by the pneumatic cushions of the bed every 2 h.

RESULTS

Nineteen patients were entered into the study. There were no statistically significant differences in the measured cardiorespiratory variables. There was a tendency for the ratio of partial pressure of arterial oxygen to fractional inspired oxygen concentration (PaO2/FIO2) to increase (174 +/- 31 versus 188 +/- 36; P = 0.068) and for the ratio of deadspace to tidal volume (Vd/Vt) to decrease (0.62 +/- 0.18 versus 0.59 +/- 0.18; P = 0.19) during periods of CLR, but these differences did not achieve statistical significance. There were statistically significant increases in sputum volume during the periods of CLR. The addition of P&PD did not increase sputum volume for the group as a whole. However, in the four patients producing more than 40 ml of sputum per day, P&PD increased sputum volume significantly. The number of patient turns increased from one every 2 h to one every 10 min during CLR.

CONCLUSION

The acute effects of CLR are undoubtedly different in other patient populations (spinal cord injury and unilateral lung injury). The link between acute physiological changes and improved outcomes associated with CLR remain to be determined.

Routine thin slice MRI effectively demonstrates the lumbar pars interarticularis

Campbell, R. S. D. and Grainger, A. J. (2000). Clinical Radiology55, 984.

Prone positioning for acute respiratory distress syndrome in the surgical intensive care unit: who, when, and how long?

BACKGROUND

We evaluated the effects of prone positioning (PP) on surgery and trauma patients with acute respiratory distress syndrome (ARDS).

METHODS

Patients with ARDS were studied. Exclusion criteria were contraindications to PP. Patients were evaluated in the supine position and after being turned to the PP. After 6 hours, patients were returned to the supine position for 3 hours. One hour after each position change, arterial and mixed venous blood was drawn and analyzed for blood gases and pH, and hemodynamics were measured.

RESULTS

Over 20 months, 27 patients met the criteria, and 20 of the patients were entered into the study. On day 1, 18 of 20 patients (90%) responded with an increase in PaO(2) during PP. On day 2, 16 of 17 patients (94%) responded; on day 3, 15 of 16 patients responded (94%); on day 4, 11 of 13 patients responded (85%); on day 5, 8 of 8 patients responded (100%); and on day 6, 4 of 5 patients responded (80%). Pao(2)/Fio(2) and Qs/Qt were significantly improved (P<.05) during PP. There were 91 periods of PP, lasting 10.3+/-1.2 hours. Of 91 changes to PP, 78 changes (86%) resulted in an improvement in Pao(2)/Fio(2) of more than 20%.

CONCLUSIONS

PP improves oxygenation in ARDS for 6 days with few complications.

MR appearances of the locked knee

This review illustrates the MR appearances of commonly encountered problems that can present as a "locked knee", as well as several unusual causes. Internal derangement of menisci, particularly bucket handle tears, predominate. Loose bodies as a result of trauma/degeneration and lesions such as cysts of the cruciate ligaments and focal pigmented villonodular synovitis are also illustrated. While meniscal tears are the major cause of "locked knee" in clinical practice, interference with normal knee kinematics is non-specific with regard to the diagnosis. Emphasis is therefore given to less frequently seen abnormalities that lead to a mechanical block of knee extension.

A radiological technique for the assessment of wear in prosthetic knee replacements

OBJECTIVE

Wear of the polyethylene insert is a well-recognised cause of implant failure in total knee replacements. The purpose of this study was to evaluate a simple, digital fluoroscopic technique for the assessment of wear in knee prostheses.

DESIGN

Fluoroscopic images of knee prostheses were produced both of a phantom and in a patient group. Joint space thickness was measured by reference to a known diameter. Measurements were made to assess repeatability of positioning, inter-and intra-observer variance and the effect of angulation.

RESULTS

Standard phantom images showed small variation between measurements, high inter-reader correlation (Pearson's correlation coefficient, r=0.98, P<0.001; coefficient of variation=0.53%) and low intra-reader variation (coefficient of variation=0.57%). Inter- and intra-imager variation were low (coefficient of variation=1.05% and 0.88%, respectively). In the patient group, the range of joint space measurements was 1.9-8.9 mm. The coefficient of variation in insert measurements on repeated images was 2.0%. Repeatability of measurements was 0.2 mm with 99% confidence interval.

CONCLUSIONS

This technique allows repeatable, precise measurement of insert thickness. The technique may be adapted to any implant where a reliable calibrating distance is present.

Diagnoses, demographics, and utilization of care as encountered by three U.S. Navy general medical officers

U.S. Navy general medical officers (GMOs) are physicians serving as general practitioners. Although exceptions exist, most GMOs are not board-certified in a specialty. They are post-graduate year 1 (PGY-1)-trained, state-licensed physicians analogous to civilian general practitioners. We conducted a retrospective study using data generated from patient visits with active duty males and females from June 1 to 30, 1998, to describe diagnoses, demographics, and utilization of care patterns encountered by three PGY-1-trained GMOs at an ambulatory clinic. A total of 781 patient encounters with 123 diagnoses from a patient population of 3,178 were recorded. This is an average of 260 patient encounters per GMO, at a rate of 2.52 patients seen per patient-care hour. Fifty-seven consultations/referrals were requested (7.3% of encounters, 1.8% of the patient population). Personnel assigned to the clinic accounted for 4.2% of visits (2% of the patient population). Patient satisfaction was rated as "excellent" to "satisfactory," and no significant morbidity was observed at 1.5-year follow-up. With PGY-1 training, GMOs provide primary care to a substantial volume of prescreened patients and treat patients with a majority of diagnoses without referral or unacceptable complications. The role of GMOs, and perhaps other physicians without specialty training (i.e., general practitioners), in selected settings seems valid and may have advantageous medicoeconomic implications for military and civilian managed care systems.

Prolonged use of heat and moisture exchangers does not affect device efficiency or frequency rate of nosocomial pneumonia

OBJECTIVE

To determine whether use of a single heat and moisture exchanger (HME) for < or =120 hrs affects efficiency, resistance, level of bacterial colonization, frequency rate of nosocomial pneumonia, and cost compared with changing the HME every 24 hrs.

DESIGN

Prospective, controlled, randomized, unblinded study.

SETTING

Surgical intensive care unit at a university teaching hospital.

PATIENTS

A total of 220 consecutive patients requiring mechanical ventilation for >48 hrs.

INTERVENTIONS

Patients were randomized to one of three groups: a) hygroscopic HME (Aqua+) changed every 24 hrs (HHME-24); b) hydrophobic HME (Duration HME) changed every 120 hrs (HME-120); and c) hygroscopic HME (Aqua+) changed every 120 hrs (HHME-120). Devices in all groups could be changed at the discretion of the staff when signs of occlusion or increased resistance were identified.

MEASUREMENTS AND MAIN RESULTS

Daily measurements of inspired gas temperature, inspired relative humidity, and device resistance were made. Additionally, daily cultures of the patient side of the device were accomplished. The frequency rate of nosocomial pneumonia was made by using clinical criteria. Ventilatory support variables, airway care, device costs, and clinical indicators of humidification efficiency (sputum volume, sputum efficiency) were also recorded. Prolonged use of both hygroscopic and hydrophobic devices did not diminish efficiency or increase resistance. There was no difference in the number of colony-forming units from device cultures over the 5-day period and no difference between colony-forming units in devices changed every 24 hrs compared with devices changed after 120 hrs. The average duration of use was 23+/-4 hrs in the HHME-24 group, 73+/-13 hrs in the HME-120 group, and 74+/-9 hrs in the HHME-120 group. Mean absolute humidity was greater for the hygroscopic devices (30.4+/-1.1 mg of H2O/L) compared with the hydrophobic devices (27.8+/-1.3 mg of H2O/L). The frequency rate of nosocomial pneumonia was 8% (8:100) in the HHME-24 group, 8.3% (5:60) in the HME-120 group, and 6.6% (4:60) in the HHME-120 group. Pneumonia rates per 1000 ventilatory support days were 20:1000 in the HHME-24 group, 20.8:1000 in the HME-120 group, and 16.6:1000 in the HHME-120 group. Costs per day were $3.24 for the HHME-24 group, $2.98 for the HME-120 group, and $1.65 for the HHME-120 group.

CONCLUSIONS

Changing the hydrophobic or hygroscopic HME after 3 days does not diminish efficiency, increase resistance, or alter bacterial colonization. The frequency rate of nosocomial pneumonia was also unchanged. Use of HMEs for >24 hrs, up to 72 hrs, is safe and cost effective.

Effects of body temperature on accuracy of continuous cardiac output measurements

Intermittent measurement of cardiac output is routine in the critically ill surgical patient. A new catheter allows real-time continuous measurement of cardiac output. This study evaluated the impact of body temperature variation on the accuracy of these measurements compared to standard intermittent bolus thermodilution technique. This prospective study in a university hospital surgical intensive care unit included 20 consecutive trauma patients. Data were collected with pulmonary artery catheters, which allowed both continuous (COC) and bolus (COB) thermodilution measurements. The catheter was placed through either the subclavian or internal jugular vein. Measurements for COB were performed using a bolus (10 cm3) of ice-cold saline with a closed-injectate delivery system at end-expiration. Computer-generated curves were created on a bedside monitor, and the average of three measurements within 10% of one another was used as COB. COC was determined as the average of the displayed CO before and after thermodilution CO measurements. Body temperature was measured from the pulmonary artery catheter and was grouped as < or =36.5 degrees C, 36.6-38.4 degrees C, and > or =38.5 degrees C. COB and COC were compared for agreement by plotting the mean of the differences (COB - COC) between the methods. The differences were plotted against the average of each pair and analyzed with linear regression. One hundred seventy-eight paired measurements were made over a period of 1 to 3 days. CO ranged from 3.7 to 15.5 L/min. Eighty-one percent of measurements were at a temperature of 36.5-38.4 degrees C. Approximately 7% of measurements were at a temperature below 36.5 degrees C and 11.2% were in patients with a core temperature above 38.5 degrees C. Correlation between the two techniques was 0.96, 0.91, and 0.82 for temperatures of < or =36.5 degrees C, 36.6-38.4 degrees C, and > or = 38.5 degrees C, respectively. In conclusion, the COC measurements correlate well with COB in trauma patients with a core temperature < or =38.5 degrees C. The accuracy degraded at higher temperatures, which may be related to the smaller signal-to-noise ratio at elevated body temperatures.

Positive end-expiratory pressure and response to inhaled nitric oxide: changing nonresponders to responders

BACKGROUND

Inhaled nitric oxide (INO) has been shown to improve oxygenation in two thirds of patients with acute respiratory distress syndrome (ARDS). Failure to respond to INO is multifactorial. We hypothesized that the addition of positive end expiratory pressure (PEEP) might modify the response to INO in patients who had previously failed to respond to INO.

METHODS

Patients with ARDS who failed to respond to INO at 1 ppm (PaO2 increase of < 20%) were selected. Each patient underwent a PEEP trial using an improvement in static lung compliance as the end point. One hour after the new PEEP level was reached, hemodynamic and blood gas values were obtained. INO was then reinstituted at 1 ppm, and hemodynamic and blood gas variables were obtained 1 hour later.

RESULTS

Six of nine patients demonstrated an increase in PaO2/FIO2 (161 +/- 27 to 186 +/- 29) with a mean increase in PEEP of 3.7 cm H2O. Each patient responding to PEEP further improved PaO2/FIO2 (186 +/- 29 to 223 +/- 36) with INO at 1 ppm. The three patients who failed to improve after the PEEP increase also failed to respond to a second trial of INO. There were no changes in cardiac output or systemic vascular resistance. Pulmonary artery pressures decreased slightly (39 +/- 5 vs 38 +/- 7 vs 35 +/- 9 mm Hg). Pulmonary vascular resistance decreased significantly after reintroduction of INO (298 +/- 131 vs 310 +/- 122 vs 249 +/- 105 dynes/sec/cm-5) in patients who responded positively.

CONCLUSIONS

The response of ARDS patients to INO can be improved if optimum alveolar recruitment is achieved by the addition of PEEP. PEEP and INO have a synergistic effect on PaO2/FIO2. Patients who fail to respond to INO may benefit from an optimum PEEP trial.

The effects of passive humidifier dead space on respiratory variables in paralyzed and spontaneously breathing patients

BACKGROUND

Passive humidifiers have gained acceptance in the intensive care unit because of their low cost, simple operation, and elimination of condensate from the breathing circuit. However, the additional dead space of these devices may adversely affect respiratory function in certain patients. This study evaluates the effects of passive humidifier dead space on respiratory function.

METHODS

Two groups of patients were studied. The first group consisted of patients recovering from acute lung injury and breathing spontaneously on pressure support ventilation. The second group consisted of patients who were receiving controlled mechanical ventilation and were chemically paralyzed following operative procedures. All patients used 3 humidification devices in random order for one hour each. The devices were a heated humidifier (HH), a hygroscopic heat and moisture exchanger (HHME) with a dead space of 28 mL, and a heat and moisture exchanger (HME) with a dead space of 90 mL. During each measurement period the following were recorded: tidal volume, minute volume, respiratory frequency, oxygen consumption, carbon dioxide production, ratio of dead space volume to tidal volume (VD/VT), and blood gases. In the second group, intrinsic positive end-expiratory pressure was also measured.

RESULTS

Addition of either of the passive humidifiers was associated with increased VD/VT. In spontaneously breathing patients, VD/VT increased from 59 +/- 13 (HH) to 62 +/- 13 (HHME) to 68 +/- 11% (HME) (p < 0.05). In these patients, constant alveolar ventilation was maintained as a result of increased respiratory frequency, from 22.1 +/- 6.6 breaths/min (HH) to 24.5 +/- 6.9 breaths/min (HHME) to 27.7 +/- 7.4 breaths/min (HME) (p < 0.05), and increased minute volume, from 9.1 +/- 3.5 L/min (HH) to 9.9 +/- 3.6 L/min (HHME) to 11.7 +/- 4.2 L/min (HME) (p < 0.05). There were no changes in blood gases or carbon dioxide production. In the paralyzed patient group, VD/VT increased from 54 +/- 12% (HH) to 56 +/- 10% (HHME) to 59 +/- 11% (HME) (p < 0.05) and arterial partial pressure of carbon dioxide (PaCO2) increased from 43.2 +/- 8.5 mm Hg (HH) to 43.9 +/- 8.7 mm Hg (HHME) to 46.8 +/- 11 mm Hg (HME) (p < 0.05). There were no changes in respiratory frequency, tidal volume, minute volume, carbon dioxide production, or intrinsic positive end-expiratory pressure.

DISCUSSION

These findings suggest that use of passive humidifiers with increased dead space is associated with increased VD/VT. In spontaneously breathing patients this is associated with an increase in respiratory rate and minute volume to maintain constant alveolar ventilation. In paralyzed patients this is associated with a small but statistically significant increase in PaCO2.

CONCLUSION

Clinicians should be aware that each type of passive humidifier has inherent dead space characteristics. Passive humidifiers with high dead space may negatively impact the respiratory function of spontaneously breathing patients or carbon dioxide retention in paralyzed patients. When choosing a passive humidifier, the device with the smallest dead space, but which meets the desired moisture output requirements, should be selected.

MRI screening for acoustic neuroma: a comparison of fast spin echo and contrast enhanced imaging in 1233 patients

Gadolinium enhanced MRI is the gold standard investigation for the detection of acoustic neuroma. Non-contrast MRI sequences have been suggested as an alternative for screening examinations. In order to determine the utility of fast spin echo imaging, both gadolinium enhanced T1 weighted images and fast spin echo T2 weighted images were acquired in 1233 consecutive patients referred for exclusion of acoustic neuroma. Two radiologists independently recorded their findings. Fast spin echo T2 weighted images were evaluated with respect to the visibility of nerves within the internal auditory canals and allocated a confidence score for the presence or absence of acoustic neuroma. 33 acoustic neuromas were identified. Only 56% were confidently identified on fast spin echo T2 weighted images alone; gadolinium enhanced T1 weighted images were required to confirm the diagnosis in 44% of the cases, including 9 of the 10 intracanalicular tumours. However, when identification of two normal intracanalicular nerves is employed as the criterion of normality, the single fast spin echo T2 weighted sequence excluded acoustic neuroma in 59% of this screened population. It is concluded that an imaging strategy intended to identify small intracanalicular acoustic neuromas cannot rely on fast spin echo T2 weighted imaging alone. Gadolinium enhanced T1 weighted imaging could be restricted to patients where fast spin echo images do not exclude acoustic neuroma but this strategy requires continuous supervision by an experienced radiologist. In most practices the screening examination should continue to include a gadolinium enhanced sequence in order to optimize the detection of small acoustic neuromas.

Sonographic findings in the anterior interosseous nerve syndrome

This report details previously undescribed sonographic findings in the anterior interosseous nerve syndrome. Loss of muscle bulk, increased reflectivity, reduced perfusion on Doppler sonography, and lack of active contraction of the affected muscles were observed. These findings can aid in the localization of the pathologic process and in the exclusion of tendon rupture. Dynamic observation of muscle function and Doppler changes after exercise can also help identify the muscles involved. Both sonography and MRI may be useful in the evaluation of patients with the anterior interosseous nerve syndrome and other peripheral neuropathies.

Optimization of MRI pulse sequences to visualize the normal pars interarticularis

Magnetic resonance imaging (MRI) is a potentially useful means of detecting acute pars stress fractures. However, recent publications have highlighted the deficiencies of routine MRI in evaluating the pars interarticularis. Twenty-nine volunteers underwent thin section, multi-planar MR examinations of the lumbar spine to evaluate whether the normal pars could be more reliably demonstrated. MRI examinations were performed with sagittal and reserve angle oblique axial T1W images, and also 3D sagittal gradient echo images with reverse angle reconstructions. Sagittal STIR images were also acquired in 14 cases. Two hundred and ninety pars were evaluated, of which 66% were deemed definitely intact (type I) on the sagittal T1W images alone (continuous marrow throughout the pars). However 93% were deemed intact when all images were reviewed together. The majority of pars defects occur at L4/L5, and 74% of these were intact on the sagittal T1W sequence alone, and 90% on combined sequences. Eighteen pars (6%) were considered to be hypointense (type II) after review of all sequences, but appeared otherwise intact. One volunteer had bilateral definite pars defects (type IV) at L5 on all sequences. This study indicates that improved visualization of the normal pars interarticularis can be achieved with optimized MRI.

Changes in respiratory mechanics after tracheostomy

OBJECTIVE

To determine the effects of tracheostomy on respiratory mechanics and work of breathing (WOB).

DESIGN

A before-and-after trial of 20 patients undergoing tracheostomy for repeated extubation failure.

SETTING

Surgical intensive care unit at a university teaching hospital and a level I trauma center.

PATIENTS

A consecutive sample of 20 patients who met extubation criteria (Pa(O2), >55 mm Hg; pH >7.30; and respiratory rate, <30/min on room air continuous positive airway pressure after 20 minutes) but failed extubation on 2 occasions were eligible for the study.

INTERVENTIONS

Respiratory mechanics, lung volumes, and WOB were measured before and after tracheostomy.

MAIN OUTCOME MEASURES

Patients in whom extubation fails often progress to unassisted ventilation after tracheostomy. The study hypothesis was that tracheostomy would result in improved pulmonary function through changes in respiratory mechanics.

RESULTS

Data are given as means +/- SDs. After tracheostomy, WOB per liter of ventilation (0.97+/-0.32 vs. 0.81+/-0.46 J/L; P<.09), WOB per minute (8.9+/-2.9 vs. 6.6+/-1.4 J/min; P<.04), and airway resistance (9.4+/-4.1 vs. 6.3+/-4.5 cm H20/L per second; P<.07) were reduced compared with breathing via an endotracheal tube. These findings, however, do not fully explain the ability of patients to be liberated from mechanical ventilation after tracheostomy. In 4 patients who were extubated before tracheostomy, WOB was significantly greater during extubation than when breathing through an endotracheal or tracheostomy tube (1.2+/-0.19 vs. 0.81+/-0.24 vs. 0.77+/-0.22 J/L).

CONCLUSIONS

We believe that the rigid nature of the tracheostomy tube represents reduced imposed WOB compared with the longer, thermoliable endotracheal tube. The clinical significance of this effect is small, although as respiratory rate increases, the effects are magnified. In patients in whom extubation failed, WOB may be elevated because of incomplete control of the upper airway. Future studies should evaluate the cause of increased WOB after extubation.

Ultrasonic heel pad thickness measurements: a preliminary study

The heel pad has an important role in pain-free locomotion due to its shock-attenuation function. Various diagnostic techniques are available to measure heel pad thickness. Ultrasonic measurement of the heel pad is inexpensive, involves no ionizing radiation and is portable, making it an ideal screening technique. Measurement errors may occur between different ultrasonic techniques used to measure heel pad thickness. A new standardized ultrasonic technique was performed on 15 healthy volunteers. The ultrasonic measurements were compared with the measurement obtained from a normal non-weightbearing heel pad thickness ultrasonic assessment. The results demonstrated a significant mean difference (p < 0.001) between the two techniques. The 95% confidence interval of the heel pad thickness difference indicated values between 7.68 and 9.13 mm. These results suggest that a standardized technique reduces the variability of measurement error when using weightbearing ultrasound, allowing a more reproducible diagnostic technique for assessing heel pad function, and improving patient management.

Anterior interosseous nerve syndrome: appearance at MR imaging in three cases

Three patients with symptoms attributable to anterior interosseous nerve syndrome underwent forearm magnetic resonance (MR) imaging. In all patients, short inversion time inversion-recovery, or STIR, images depicted increased signal intensity from some or all muscle groups innervated by the anterior interosseous nerve. In one patient, atrophy was depicted in these muscles. MR imaging may serve as a useful adjunct to electromyography in the investigation of anterior interosseous nerve syndrome.

Post-traumatic bone cyst: a case of the floating fragment

We report a case of an intraosseous foreign body leading to the formation of a bone cyst. The cyst was identified 20 years after the initial injury and was found to contain the foreign body. No infection was found.

Humidification in the intensive care unit

In summary, current data indicate that body temperature cannot be controlled efficiently by changing inspired gas temperature. Inspired gas temperature should therefore be maintained at 32 degrees C to 34 degrees C for intubated patients and other efforts should be made to optimize body temperature.

Anaesthesia circuits, humidity output, and mucociliary structure and function

We compared the effects of humidity delivered by the circle system at low fresh gas flows (FGF) with a conventional two-limb and coaxial circuit on the structure and function of the tracheobronchial epithelium in dogs. Animals were anaesthetized and mechanically ventilated using an anaesthesia ventilator to maintain normocarbia. Group I (control) animals received a FGF equal to the required minute ventilation mimicking an open circuit technique. Group II and III animals had FGF set at 20% of the required minute ventilation. Group II used a two-limb circuit and Group III used a coaxial circuit. Relative humidity and temperature of inspired gases were measured at baseline and hourly afterwards. In the first experiment, biopsies of the tracheobronchial tree were obtained bronchoscopically at baseline and then hourly for six hours. Microscopic examination of these samples allowed calculation of mean ciliary length. In the second experiment, tracheal mucus flow velocity (TMFV) was measured at baseline and hourly afterward, using a cinebroncho-fibrescopic method. Delivered absolute humidity was greatest with low FGF and the coaxial circuit, followed by low FGF and a conventional circuit, and high FGF (15 +/- 1.4 vs 9 +/- 0.8 vs 5 +/- 0.4 mg H2O, P < 0.01) after two hours. Mean cilia length (micron) and TMFV (mm/min) fell during the first hour in all three groups. At hour two TMFV returned to baseline in Group III and was significantly greater than Groups I and II (0.8 +/- 0.4 vs 8.6 +/- 1.1 vs 15.4 +/- 2.1, P < 0.001). Mean ciliary length demonstrated a similar pattern with reductions from baseline in all three groups for the first two hours. Groups II and III had an increase in cilia length beginning at hour three and were both significantly greater than Group I at hours 3 through 6 (1.3 +/- 0.5 vs 3.2 +/- 1.1 vs 4.2 +/- 0.8, P < 0.001). Alterations in tracheobronchial structure and function result from exposure to dry gases and are amplified by the duration of exposure. Our findings suggest a minimum of 12 to 15 mg H2O/l is necessary to prevent these alterations. In this study, the combination of low FGF and a coaxial anaesthesia circuit reached this minimum threshold more quickly than a conventional two-limb circuit.

Inhaled nitric oxide in acute respiratory distress syndrome

BACKGROUND

Inhaled nitric oxide has been shown to improve oxygenation in select patients with acute respiratory distress syndrome (ARDS).

OBJECTIVE

The purpose of this study was to evaluate the clinical response to four concentrations of inhaled nitric oxide (NO) in 20 patients with ARDS.

METHODS

All patients with ARDS were eligible for the study. ARDS was defined as (1) the presence of a predisposing factor; (2) a PaO2/FiO2 ratio < 200; (3) bilateral infiltrates on chest radiograph; and (4) absence of evidence of congestive heart failure and pulmonary artery wedge pressure < 18 mm Hg. Patients received each of four doses (1, 15, 30, and 60 ppm) in random order, each for a 3-hour period. Cardiovascular variables were continuously monitored, and arterial and mixed venous blood gas measurements were obtained at 30 minutes and 3 hours.

RESULTS

Thirteen of the 20 patients demonstrated a significant increase in their PaO2/FiO2 (> 20% increase) when treated with inhaled NO. The administration of inhaled NO was associated with an increase in oxygenation at doses of 1, 15, and 30 ppm, but not 60 ppm. Increasing NO dose to more than 1 ppm did not significantly improve response. Mean pulmonary artery pressure decreased with increasing NO concentration, but this did not reach statistical significance. Nine of the 13 responding patients and 2 of the 7 nonresponding patients survived.

CONCLUSION

Inhaled NO was successful in increasing PaO2/FiO2 by > 20% in 65% of the surgical patients in this trial. Response to NO could not be predicted by initial PaO2/FiO2 or pulmonary artery pressures. A trial of inhaled NO at a dose of < 10 ppm may be helpful in ARDS patients requiring increasing FiO2 and positive end-expiratory pressure.

Use of the rapid/shallow breathing index as an indicator of patient work of breathing during pressure support ventilation

BACKGROUND

Measuring patient work of breathing (WOBpt) has been suggested to provide safe, aggressive weaning from mechanical ventilation. We compared WOBpt and pressure-time-product (PTP) to routine weaning parameters [breath rate (f), tidal volume (VT), frequency/tidal volume ratio (f/VT)] at different levels of pressure support ventilation (PSV).

METHODS

Fifteen patients in the surgical intensive care unit requiring prolonged weaning (more than 3 days) were entered in the study. A balloon-tipped esophageal catheter was placed and position confirmed by inspection of pressure and flow waveforms. Each patient was randomly assigned to breathe with 5, 10, 15, and 20 cm H2O of PSV. After 30 minutes, 40 breaths were recorded and analyzed. Measurement of WOBpt PTP, f, VT, and f/VT were made using the Bicore CP-100 monitor. Mean values for each parameter were calculated. PTP and WOBpt were plotted against f/VT to determine correlation coefficient.

RESULTS

PTP, WOBpt and f/VT decreased in a stepwise fashion as PSV was increased. The f/VT correlated most closely with WOBpt (r = 0.983) and PTP (r = 0.972). Monitoring f alone also correlated with WOBpt (r = 0.894) and PTP (r = 0.881). All patients were weaned from the ventilator (mean duration, 22 +/- 5.9 days). Nine patients required tracheostomy before final liberation from the ventilator (mean duration, 22 +/- 5.9 days). Nine patients required tracheostomy before final liberation from the ventilator.

CONCLUSIONS

Direct measurement of WOBpt is invasive, expensive, and' may be confusing to clinicians. Monitoring f/VT may be useful when changing PSV during weaning.

Late presentation of solitary jejunal metastasis from renal cell carcinoma

Haematogenous metastases to the small bowel are a rare occurrence, usually from malignant melanoma or bronchogenic carcinoma. There are occasional reports of other primary tumours presenting with small bowel involvement as the first evidence of metastases. We describe a case of intraluminal jejunal metastasis from a renal cell carcinoma, occurring 10 years after the original nephrectomy.

Respiratory support of the head-injured patient

Approximately 500,000 patients present with a CHI annually in the United States alone. Up to 20% of these injuries are classified as severe. Appropriate and aggressive intensive care of CHI patients will certainly reduce both the morbidity and mortality rates. Early therapy includes provision of adequate ventilation and oxygenation and definitive care based on clinical assessment. Once the acute phase of the injury has passed, supportive therapy should be maintained as long as secondary injury or complications are avoided. Respiratory care of CHI patients is important though different in each phase of the disease. Proper placement of and maintenance of airways, efficient use of and withdrawal from the mechanical ventilator, and providing adequate pulmonary toilet in order to treat or avoid pneumonia are but a few of the very important respiratory care practices necessary to provide optimal outcomes in patients with CHI.

Combined differential lung ventilation and inhaled nitric oxide therapy in the management of unilateral pulmonary contusion

Unilateral pulmonary contusion after blunt thoracic trauma can prove to be a devastating injury. Regional disturbances in blood flow and alveolar ventilation can significantly alter pulmonary function. We present a case report of unilateral pulmonary contusion that resulted in significant pulmonary dysfunction. This patient was successfully managed with multimodality therapy consisting of differential lung ventilation and inhaled nitric oxide. The effect of nitric oxide applied to the "normal" lung, the "injured" lung, and both lungs is described. The use of inhaled nitric oxide was associated with an increase in oxygenation when applied to the normal or both lungs. The use of nitric oxide in conjunction with differential lung ventilation appeared to offer benefit in this patient with severe unilateral pulmonary contusion.

Comparison of volume control and pressure control ventilation: is flow waveform the difference?

OBJECTIVE

To examine the hypothesis that a decelerating inspiratory flow waveform is responsible for improvements in gas exchange during pressure control ventilation for acute lung injury.

DESIGN

Prospective, controlled, crossover study.

MEASUREMENTS AND MAIN RESULTS

Twenty-five patients with acute lung injury requiring mechanical ventilation with a positive-end expiratory pressure > or = 10 cm H2O, ventilator frequency of > or = 8 bpm, inspired oxygen concentration of > or = 0.50, peak inspiratory pressure > or = 40 cm H2O, and requiring sedation and paralysis were studied. Patients were ventilated at a tidal volume of 10 mliters/kg, respiratory frequency was set to maintain a pH > 7.30 and PaCO2 < 50 mm Hg, and positive end-expiratory pressure (PEEP) set to maintain Pao2 > 70 mm Hg or Sao2 > 93% with an Fio2 < or = 0.50. In random sequence, ventilator mode was changed from volume control with a square flow waveform, pressure control ventilation with a decelerating flow waveform, or volume control ventilation with a decelerating flow waveform. Tidal volume, minute ventilation, and airway pressures were continuously measured at the proximal airway. After 2 hours of ventilation in each mode, arterial and mixed venous blood gases were drawn and cardiac output determined by thermodilution. Dead space to tidal volume ratio was determined from mixed expired gas concentrations and Paco2. During volume control ventilation with a square flow waveform, Pao2 was decreased (75 +/- 11 mm Hg vs. 85 +/- 9 mm Hg and 89 +/- 12 mm Hg), p < 0.05, and peak inspiratory pressure was increased (50 +/- 9 cm H2O vs. 42 +/- 7 cm H2O and 39 +/- 9 cm H2O) p < 0.05 compared to volume control with a decelerating flow waveform and pressure control ventilation. Mean airway pressure was also lower with volume control with a square flow waveform (17 +/- 4 cm H2O vs. 20 +/- 4 cm H2O and 21 +/- 3 cm H2O) compared to volume control with a decelerating flow waveform and pressure control ventilation. There were no differences in hemodynamic parameters.

CONCLUSIONS

Both pressure control ventilation and volume control ventilation with a decelerating flow waveform provided better oxygenation at a lower peak inspiratory pressure and higher mean airway pressure compared to volume control ventilation with a square flow waveform. The results of our study suggest that the reported advantages of pressure control ventilation over volume control ventilation with a square flow waveform can be accomplished with volume control ventilation with a decelerating flow waveform.

The pathologist in virology

While the study of a virus may be the domain of a virologist or molecular biologist, an understanding of the pattern and dynamics of a viral disease in the animal requires a multidisciplinary attack by a team that includes a pathologist. This balance is particularly needed in the field where natural disease can be subject to influential variables such as duration of infection, immune status of the population and the presence of intercurrent infectious agents that may be latent or superimposed. Complicating agents vary widely from region to region, e.g. Africa compared with South-east Asia. Accurate diagnosis of a field outbreak may therefore be difficult in the absence of a full battery of diagnostic tools. The design of investigations is critical to the proper interpretation of findings.