Predictors and outcomes of withholding and withdrawal of life-sustaining treatments in intensive care units in Singapore: a multicentre observational study

BACKGROUND

Clinical practice guidelines on limitation of life-sustaining treatments (LST) in the intensive care unit (ICU), in the form of withholding or withdrawal of LST, state that there is no ethical difference between the two. Such statements are not uniformly accepted worldwide, and there are few studies on LST limitation in Asia. This study aimed to evaluate the predictors and outcomes of withholding and withdrawal of LST in Singapore, focusing on the similarities and differences between the two approaches.

METHODS

This was a multicentre observational study of patients admitted to 21 adult ICUs across 9 public hospitals in Singapore over an average of three months per year from 2014 to 2019. The primary outcome measures were withholding and withdrawal of LST (cardiopulmonary resuscitation, invasive mechanical ventilation, and vasopressors/inotropes). The secondary outcome measure was hospital mortality. Multivariable generalised mixed model analysis was used to identify independent predictors for withdrawal and withholding of LST and if LST limitation predicts hospital mortality.

RESULTS

There were 8907 patients and 9723 admissions. Of the former, 80.8% had no limitation of LST, 13.0% had LST withheld, and 6.2% had LST withdrawn. Common independent predictors for withholding and withdrawal were increasing age, absence of chronic kidney dialysis, greater dependence in activities of daily living, cardiopulmonary resuscitation before ICU admission, higher Acute Physiology and Chronic Health Evaluation (APACHE) II score, and higher level of care in the first 24 h of ICU admission. Additional predictors for withholding included being of Chinese race, the religions of Hinduism and Islam, malignancy, and chronic liver failure. The additional predictor for withdrawal was lower hospital paying class (with greater government subsidy for hospital bills). Hospital mortality in patients without LST limitation, with LST withholding, and with LST withdrawal was 10.6%, 82.1%, and 91.8%, respectively (p < 0.001). Withholding (odds ratio 13.822, 95% confidence interval 9.987-19.132) and withdrawal (odds ratio 38.319, 95% confidence interval 24.351-60.298) were both found to be independent predictors of hospital mortality on multivariable analysis.

CONCLUSIONS

Differences in the independent predictors of withholding and withdrawal of LST exist. Even after accounting for baseline characteristics, both withholding and withdrawal of LST independently predict hospital mortality. Later mortality in patients who had LST withdrawn compared to withholding suggests that the decision to withdraw may be at the point when medical futility is recognised.

Individualised, short-course antibiotic treatment versus usual long-course treatment for ventilator-associated pneumonia (REGARD-VAP): a multicentre, individually randomised, open-label, non-inferiority trial

BACKGROUND

Ventilator-associated pneumonia (VAP) is associated with increased mortality, prolonged hospitalisation, excessive antibiotic use and, consequently, increased antimicrobial resistance. In this phase 4, randomised trial, we aimed to establish whether a pragmatic, individualised, short-course antibiotic treatment strategy for VAP was non-inferior to usual care.

METHODS

We did an individually randomised, open-label, hierarchical non-inferiority-superiority trial in 39 intensive care units in six hospitals in Nepal, Singapore, and Thailand. We enrolled adults (age ≥18 years) who met the US Centers for Disease Control and Prevention National Healthcare Safety Network criteria for VAP, had been mechanically ventilated for 48 h or longer, and were administered culture-directed antibiotics. In culture-negative cases, empirical antibiotic choices were made depending on local hospital antibiograms reported by the respective microbiology laboratories or prevailing local guidelines. Participants were assessed until fever resolution for 48 h and haemodynamic stability, then randomly assigned (1:1) to individualised short-course treatment (≤7 days and as short as 3-5 days) or usual care (≥8 days, with precise durations determined by the primary clinicians) via permuted blocks of variable sizes (8, 10, and 12), stratified by study site. Independent assessors for recurrent pneumonia and participants were masked to treatment allocation, but clinicians were not. The primary outcome was a 60-day composite endpoint of death or pneumonia recurrence. The non-inferiority margin was prespecified at 12% and had to be met by analyses based on both intention-to-treat (all study participants who were randomised) and per-protocol populations (all randomised study participants who fulfilled the eligibility criteria, met fitness criteria for antibiotic discontinuation, and who received antibiotics for the duration specified by their allocation group). This study is registered with ClinicalTrials.gov, number NCT03382548.

FINDINGS

Between May 25, 2018, and Dec 16, 2022, 461 patients were enrolled and randomly assigned to the short-course treatment group (n=232) or the usual care group (n=229). Median age was 64 years (IQR 51-74) and 181 (39%) participants were female. 460 were included in the intention-to-treat analysis after excluding one withdrawal (231 in the short-course group and 229 in the usual care group); 435 participants received the allocated treatment and fulfilled eligibility criteria, and were included in the per-protocol population. Median antibiotic treatment duration for the index episodes of VAP was 6 days (IQR 5-7) in the short-course group and 14 days (10-21) in the usual care group. 95 (41%) of 231 participants in the short-course group met the primary outcome, compared with 100 (44%) of 229 in the usual care group (risk difference -3% [one-sided 95% CI -∞ to 5%]). Results were similar in the per-protocol population. Non-inferiority of short-course antibiotic treatment was met in the analyses, although superiority compared with usual care was not established. In the per-protocol population, antibiotic side-effects occurred in 86 (38%) of 224 in the usual care group and 17 (8%) of 211 in the short-course group (risk difference -31% [95% CI -37 to -25%; p<0·0001]).

INTERPRETATION

In this study of adults with VAP, individualised shortened antibiotic duration guided by clinical response was non-inferior to longer treatment durations in terms of 60-day mortality and pneumonia recurrence, and associated with substantially reduced antibiotic use and side-effects. Individualised, short-course antibiotic treatment for VAP could help to reduce the burden of side-effects and the risk of antibiotic resistance in high-resource and resource-limited settings.

FUNDING

UK Medical Research Council; Singapore National Medical Research Council.

TRANSLATIONS

For the Thai and Nepali translations of the abstract see Supplementary Materials section.

Point-of-care ultrasound for critically-ill patients: A mini-review of key diagnostic features and protocols

Point-of-care ultrasonography (POCUS) for managing critically ill patients is increasingly performed by intensivists or emergency physicians. Results of needs surveys among intensivists reveal emphasis on basic cardiac, lung and abdominal ultrasound, which are the commonest POCUS modalities in the intensive care unit. We therefore aim to describe the key diagnostic features of basic cardiac, lung and abdominal ultrasound as practised by intensivists or emergency physicians in terms of accuracy (sensitivity, specificity), clinical utility and limitations. We also aim to explore POCUS protocols that integrate basic cardiac, lung and abdominal ultrasound, and highlight areas for future research.

Molecular simulation of linear octacosane via a CG10 coarse grain scheme

Following our previous work on the united-atom simulation on octacosane (C₂₈H₅₈) (Dai et al., Phys. Chem. Chem. Phys., 2021, 23, 21262-21271), we developed a coarse grain scheme (CG10), which is able to reproduce the pivotal phase characteristics of octacosane with highly improved computational efficiency. The CG10 octacosane chain was composed of 10 consecutive beads, maintaining the fundamental zigzag chain morphology. When the potential functions were set up and the coefficients were parameterized, our CG10 models yielded solid phase diagrams and transitions during an annealing process. We also detected the melting point by various means: direct observation, bond order, density tracking, and an enthalpy plot. Furthermore, our CG10 successfully reproduced the liquid density with only 2% underestimation, indicating its applicability across the solid and liquid phases. Therefore, with the ability to reproduce critical structure and property characteristics, our CG10 scheme provides an effective means of numerically modelling octacosane with highly improved computational efficiency.

Separation from mechanical ventilation and survival after spinal cord injury: a systematic review and meta-analysis

Background

Prolonged need for mechanical ventilation greatly impacts life expectancy of patients after spinal cord injury (SCI). Weaning outcomes have never been systematically assessed. In this systematic review and meta-analysis, we aimed to investigate the probability of weaning success, duration of mechanical ventilation, mortality, and their predictors in mechanically ventilated patients with SCI.

Methods

We searched six databases from inception until August 2021 for randomized-controlled trials and observational studies enrolling adult patients (≥ 16 years) with SCI from any cause requiring mechanical ventilation. Titles and abstracts were screened independently by two reviewers. Full texts of the identified articles were then assessed for eligibility. Data were extracted independently and in duplicate by pairs of authors, using a standardized data collection form. Synthetic results are reported as meta-analytic means and proportions, based on random effects models.

Results

Thirty-nine studies (14,637 patients, mean age 43) were selected. Cervical lesions were predominant (12,717 patients had cervical lesions only, 1843 in association with other levels’ lesions). Twenty-five studies were conducted in intensive care units (ICUs), 14 in rehabilitative settings.

In ICU, the mean time from injury to hospitalization was 8 h [95% CI 7–9], mean duration of mechanical ventilation 27 days [20–34], probability of weaning success 63% [45–78] and mortality 8% [5–11]. Patients hospitalized in rehabilitation centres had a greater number of high-level lesions (C3 or above), were at 40 days [29–51] from injury and were ventilated for a mean of 97 days [65–128]; 82% [70–90] of them were successfully weaned, while mortality was 1% [0–19].

Conclusions

Although our study highlights the lack of uniform definition of weaning success, of clear factors associated with weaning outcomes, and of high-level evidence to guide optimal weaning in patients with SCI, it shows that around two-thirds of mechanically ventilated patients can be weaned in ICU after SCI. A substantial gain in weaning success can be obtained during rehabilitation, with additional duration of stay but minimal increase in mortality. The study is registered with PROSPERO (CRD42020156788).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-021-00938-x.

Clinical characteristics and outcomes of myocardial infarction with nonobstructive coronary arteries

Background

Myocardial infarction with nonobstructive coronary arteries (MINOCA) is caused by a heterogenous group of conditions with clinically significant sequelae.

Purpose

This study aims to compare the clinical characteristics and prognosis of MINOCA with myocardial infarction with obstructive coronary artery disease (MICAD).

Methods

Data was obtained from the Singapore Cardiac Longitudinal Outcomes Database (SingCLOUD), a national multicenter registry of patients with cardiovascular disease. Patients with a first presentation of acute myocardial infarction who underwent coronary angiography between 1 January 2011 and 31 December 2014 were extracted from the database. Follow up was conducted until 31 December 2017. Subjects were classified as having either MICAD or MINOCA based on angiographic findings. The primary outcomes were all-cause mortality and major adverse cardiac events (MACE) defined as a composite of all-cause mortality, recurrent myocardial infarction, hospitalization for heart failure and ischemic stroke.

Results

All 4124 patients who met the inclusion criteria were included in this study, of which 159 (3.9%) were diagnosed with MINOCA. Patients with MINOCA were more likely to be female, present with a non-ST elevation myocardial infarction (NSTEMI), have a higher left ventricular ejection fraction and less likely to have diabetes mellitus, previous ischemic stroke or smoking history. Over a mean follow-up duration of 4.5 years, MINOCA patients had a lower incidence of all-cause mortality (10.1% vs. 16.5%, p=0.030) and MACE (20.8% vs. 35.5%, p&lt;0.0001) compared to patients with MICAD. On multivariable analysis, patients with MINOCA had a significantly lower risk of all-cause mortality (HR 0.42; 95% CI 0.21–0.82; p=0.011), MACE (HR 0.42; 95% CI 0.26–0.69; p=0.001) and recurrent myocardial infarction (HR 0.35; 95% CI 0.15–0.85; p=0.021). Within the MINOCA group, older age, higher creatinine, a STEMI presentation and the absence of antiplatelet use predicted all-cause mortality and MACE.

Conclusions

While patients with MINOCA had better clinical outcomes compared to MICAD patients, MINOCA is not a benign entity with about one in five patients experiencing a major adverse cardiovascular event in the mid-term.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Medical Research Council Project Grant

Molecular dynamics simulation of octacosane for phase diagrams and properties via the united-atom scheme

We used the united-atom scheme to build three types of crystalline structures for octacosane (C₂₈H₅₈) and carried out molecular dynamics simulations to investigate their phase properties. By gradually heating the three polymorphs, we managed to reproduce the sequence of experimentally reported crystalline phases and rotator phases. By studying the system density, molecule morphology, chain tilt angle and cell anisotropy, we hypothesized three mechanisms behind the observed system deformations and phase transformations during the annealing process. Furthermore, our model successfully predicted the melting temperature and heat of fusion. We also reproduced the characteristics of the rotator phases and the liquid phase, validating the transferability of the united-atom scheme among the different condensed phases of octacosane. Our methodology represents an effective and efficient means of numerical study for octacosane and may be used for other members of the n-alkane family.

Reducing antibiotic treatment duration for ventilator-associated pneumonia (REGARD-VAP): a trial protocol for a randomised clinical trial

INTRODUCTION

Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in intensive care units (ICUs). Using short-course antibiotics to treat VAP caused by Gram-negative non-fermenting bacteria has been reported to be associated with excess pneumonia recurrences. The "REducinG Antibiotic tReatment Duration for Ventilator-Associated Pneumonia" (REGARD-VAP) trial aims to provide evidence for using a set of reproducible clinical criteria to shorten antibiotic duration for individualised treatment duration of VAP.

METHODS AND ANALYSIS

This is a randomised controlled hierarchical non-inferiority-superiority trial being conducted in ICUs across Nepal, Thailand and Singapore. The primary outcome is a composite endpoint of death and pneumonia recurrence at day 60. Secondary outcomes include ventilator-associated events, multidrug-resistant organism infection or colonisation, total duration of antibiotic exposure, mechanical ventilation and hospitalisation. Adult patients who satisfy the US Centers for Disease Control and Prevention National Healthcare Safety Network VAP diagnostic criteria are enrolled. Participants are assessed daily until fever subsides for >48 hours and have stable blood pressure, then randomised to a short duration treatment strategy or a standard-of-care duration arm. Antibiotics may be stopped as early as day 3 if respiratory cultures are negative, and day 5 if respiratory cultures are positive in the short-course arm. Participants receiving standard-of-care will receive antibiotics for at least 8 days. Study participants are followed for 60 days after enrolment. An estimated 460 patients will be required to achieve 80% power to determine non-inferiority with a margin of 12%. All outcomes are compared by absolute risk differences. The conclusion of non-inferiority, and subsequently superiority, will be based on unadjusted and adjusted analyses in both the intention-to-treat and per-protocol populations.

ETHICS AND DISSEMINATION

The study has received approvals from the Oxford Tropical Research Ethics Committee and the respective study sites. Results will be disseminated to patients, their caregivers, physicians, the funders, the critical care societies and other researchers.

TRIAL REGISTRATION NUMBER

NCT03382548.

Point-of-Care Ultrasound Training Among Intensivists in Singapore: A Multicentre Survey

INTRODUCTION

Point of care ultrasound (POCUS) has become essential in the management of critically ill patients. Multiple POCUS training courses exist, but are not widely adopted in Singapore. Given the discordance between training supply and demand, we aimed to uncover the learning needs and barriers among intensive care medicine (ICM) doctors locally.

MATERIALS AND METHODS

An anonymous online survey was carried out from January to April 2019 among ICM doctors from 6 major teaching hospitals in Singapore.

RESULTS

66 out of 160 ICM specialists and trainees responded (41.3%). Although only 6% of respondents had current formal POCUS accreditation, the majority were already using critical care echocardiography (CCE) and pleural/ lung ultrasound. 93% supported having a local training programme. More than 50% of trainees wanted training in CCE, diaphragm/muscle ultrasound, airway ultrasound and ultrasound for neurological disease. More than 50% of specialists wanted training in diaphragm/muscle ultrasound, with mixed interests in other topics. The top 2 obstacles hindering POCUS training were lack of supervisors and locally based programmes.

CONCLUSIONS

ICM doctors who responded were supportive of a local POCUS training programme. The programme's curriculum should address the learning needs of the majority of learners, with diaphragm/muscle ultrasound being the top unmet need. The programme would need to develop supervisors and be as affordable as possible.

Cardiopulmonary resuscitation-from the patient's perspective

With increasing emphasis on patient autonomy, patients are encouraged to be more involved in end-of-life issues, including the use of extraordinary efforts to prolong their lives. Being able to make anticipatory decisions is seen to promote autonomy, empower patients and optimise patient care. To facilitate shared decision-making, patients need to have a clear and accurate understanding of cardiopulmonary resuscitation (CPR). This study aims to understand the knowledge and perspectives of the local community regarding resuscitation options and end-of-life decision-making and to explore ways to improve the quality of end-of-life discussions. An interviewer-administered survey was conducted with a prospectively recruited group of surgical patients admitted postoperatively to the day surgery ward of a single tertiary institution in Singapore from April to May 2015. The survey, modelled after two validated questionnaires, measured patients' knowledge, attitudes and preferences regarding CPR in a series of 18 questions. Fifty-one out of 67 (76.1%) patients completed the survey. Results indicated that 80.4% (n=41) of participants correctly understood the purpose of CPR, but 64.7% (n=33) did not know of any possible complications of CPR. Less than half (n=21, 41.2%) of participants had thought about life support measures they wanted for themselves. Most of the participants agreed that they should personally be involved in making end-of-life decisions (n=44, 86.3%). Many patients had a poor knowledge of CPR and other resuscitation measures and the majority overestimated the success rate of CPR. However, a majority were receptive to improving their knowledge and keen to discuss end-of-life issues with physicians.

Recall of discharge advice given to patients with minor head injury presenting to a Singapore emergency department

INTRODUCTION

Most patients presenting to the emergency department (ED) with minor head injury (HI) can be discharged, provided a caregiver is present and careful discharge instructions are given. The study ED uses an advice leaflet with verbal reinforcement to patients and caregivers detailing post-discharge instructions and warning symptoms of worsening HI. We aim to evaluate local patients' and caregivers' compliance to discharge instructions and their ability to recall HI advice.

METHODS

A prospective study was conducted in an adult ED between April 10, 2006 and May 1, 2006. All patients with minor HI discharged from the ED or its 24-hour observation ward were included in the study. A telephone survey was conducted within 48 hours of discharge using a standardised questionnaire.

RESULTS

During the study period, 292 patients had HI, of which 182 were eligible for the study. 71 were uncontactable and one refused to participate, leaving 110 patients in the study. Patients' age ranged between 7 and 109 years (median 41 years). 100 confirmed receiving HI advice (57 percent received by patients, 26 percent caregivers, 16 percent both patients and caregivers). 29 percent of respondents reported non-compliance to discharge advice. Mean HI-symptom recall score was 1.9 (SD 1.6) (total 9 symptoms). 30 percent cited other symptoms not part of the HI advice, which they believed necessitated a return to the ED. Recall scores were not statistically different, regardless of mode of instruction (verbal or printed) or the recipient (patient, caregiver or both).

CONCLUSION

Our study raises concerns about the reliability of discharge advice for minor HI patients.

Non-rigid image registration using a median-filtered coarse-to-fine displacement field and a symmetric correlation ratio

Conventional approaches to image registration are generally limited to image-wide rigid transformations. However, the body and its internal organs are non-rigid structures that change shape due to changes in the body's posture during image acquisition, and due to normal, pathological and treatment-related variations. Inter-subject matching also constitutes a non-rigid registration problem. In this paper, we present a fully automated non-rigid image registration method that maximizes a local voxel-based similarity metric. Overlapping image blocks are defined on a 3D grid. The transformation vector field representing image deformation is found by translating each block so as to maximize the local similarity measure. The resulting sparsely sampled vector field is median filtered and interpolated by a Gaussian function to ensure a locally smooth transformation. A hierarchical strategy is adopted to progressively establish local registration associated with image structures at diminishing scale. Simulation studies were carried out to evaluate the proposed algorithm and to determine the robustness of various voxel-based cost functions. Mutual information, normalized mutual information, correlation ratio (CR) and a new symmetric version of CR were evaluated and compared. A T1-weighted magnetic resonance (MR) image was used to test intra-modality registration. Proton density and T2-weighted MR images of the same subject were used to evaluate inter-modality registration. The proposed algorithm was tested on the 2D MR images distorted by known deformations and 3D images simulating inter-subject distortions. We studied the robustness of cost functions with respect to image sampling. Results indicate that the symmetric CR gives comparable registration to mutual information in intra- and inter-modality tasks at full sampling and is superior to mutual information in registering sparsely sampled images.

Choice of collimator for cardiac SPET when resolution compensation is included in iterative reconstruction

In clinical cardiac single-photon emission tomography (SPET) studies, collimators of different spatial resolution and geometric efficiency are available for imaging. In selecting the appropriate collimator for clinical use, there is a trade-off between spatial resolution, which can limit the contrast of the reconstructed image, and detection efficiency, which determines the noise in the image. Our objective was to assess which collimator is best suited for cardiac SPET when reconstruction is performed with and without compensation for distance-dependent resolution (CDR). The dynamic MCAT thorax phantom was used to simulate 180 degree technetium-99m cardiac data, acquired using either a general-purpose (GP) or high-resolution (HR) collimator. For GP and HR, the resolution at 15 cm was 11.5 mm and 9.5 mm respectively, and the corresponding relative efficiency was 1.0 and 0.52 respectively. Distance-dependent resolution, attenuation and noise were included in the projection data; scatter was not included. Ordered subsets expectation maximisation reconstruction (subset size 4) was performed with and without CDR. Results were evaluated by comparing the myocardial recovery coefficient and contrast between myocardium and ventricle relative to the original phantom, each plotted for different noise levels corresponding to increasing iteration number. The study demonstrated that, without CDR, HR gave the best results. However, for any given noise level with CDR, GP gave superior recovery and contrast. These findings were confirmed in a physical phantom study. Results suggest that improved reconstruction can be achieved using a GP collimator in combination with resolution compensation.

Improved efficiency for MRI-SPET registration based on mutual information

Mutual information has been proposed as a criterion for image registration. The criterion is calculated from a two-dimensional grey-scale histogram of the image pair being registered. In this paper we study how sparse sampling can be used to increase speed performance using the registration algorithm of Maes et al. (IEEE Trans Med Imaging 1997; 16: 187-198) with a focus on registration of MRI-SPET brain images. In particular we investigate how sparse sampling and parameters such as the number of bins used for the grey-scale histograms and smoothing of the data prior to registration affect accuracy and robustness of the registration. The method was validated using both simulated and human data. Our results show that sparse sampling introduced local maxima into the mutual information similarity function when the number of bins used for the histograms was large. To speed up registration while retaining robustness, smoothing of the data prior to registration was used and a coarse to fine subsampling protocol, where the number of bins in the histograms were dependent on the subsampling factor, was employed, For the simulated data, the method was able to recover known transformations with an accuracy of about 1 mm. Using the human data, there were no significant differences in the recovered transformation parameters when the suggested subsampling scheme was used compared with when no subsampling was used, but there was a more than tenfold increase in speed. Our results show that, with the appropriate choice of parameters, the method can accurately register MRI-SPET brain images even when very efficient sampling protocols are used.

Application of distance-dependent resolution compensation and post-reconstruction filtering for myocardial SPECT

Compensation for distance-dependent resolution can be directly incorporated in maximum likelihood reconstruction. Our objective was to examine the effectiveness of this compensation using either the standard expectation maximization (EM) algorithm or an accelerated algorithm based on use of ordered subsets (OSEM). We also investigated the application of post-reconstruction filtering in combination with resolution compensation. Using the MCAT phantom, projections were simulated for 360 degrees data, including attenuation and distance-dependent resolution. Projection data were reconstructed using conventional EM and OSEM with subset size 2 and 4, with/without 3D compensation for detector response (CDR). Also post-reconstruction filtering (PRF) was performed using a 3D Butterworth filter of order 5 with various cutoff frequencies (0.2-1.2 cycles cm(-1)). Image quality and reconstruction accuracy were improved when CDR was included. Image noise was lower with CDR for a given iteration number. PRF with cutoff frequency greater than 0.6 cycles cm(-1) improved noise with no reduction in recovery coefficient for myocardium but the effect was less when CDR was incorporated in the reconstruction. CDR alone provided better results than use of PRF without CDR. Results suggest that using CDR without PRF, and stopping at a small number of iterations, may provide sufficiently good results for myocardial SPECT. Similar behaviour was demonstrated for OSEM.

Impaired permeability in radiation-induced lung injury detected by technetium-99m-DTPA lung clearance

This study evaluates the use of the 99mTc-DTPA aerosol lung clearance method to investigate radiation-induced lung changes in eight patients undergoing radiotherapy for lung or breast carcinoma. The sensitivity of the method was compared with chest radiography for detecting radiation-induced changes in the lung, regional alterations within (irradiated region) and outside (shielded region) the treatment ports, effect of irradiated lung volume, and dependence on time after radiotherapy.

METHODS

Serial DTPA lung clearance studies were performed before the first radiation treatment (baseline), then weekly during a 5- to 7-wk course, and up to 12 times post-therapy over periods of 56-574 days. The total activity deposited in the lungs for each study was approximately 150 microCi (approximately 5.6 MBq). DTPA clearance, expressed in terms of the biological half-time, t 1/2, was computed from the slopes of the least-squares fit regression lines of the time-activity curves for the first 10 min for irradiated and shielded lung regions.

RESULTS

Major findings include: (a) significant and early DTPA t 1/2 changes were observed in all patients during and after radiotherapy; (b) changes in DTPA t 1/2 values were observed in both irradiated and shielded lung regions in all patients suggesting a radiation-induced systemic reaction; (c) changes in DTPA t 1/2 values were correlated (p < 0.05) with the irradiated lung volumes; (d) significantly reduced DTPA t 1/2 values were observed in three patients who subsequently presented with clinical symptoms and/or radiographic changes consistent with radiation pneumonitis (t1/2 felt to 19% +/- 6% of baseline values, compared with 64% +/- 17% in the remaining patients [p < 0.01]); (e) the onset of decreased DTPA t 1/2 values in these three patients occurred 35-84 days before clinical symptoms and/or radiographic changes; and (f) DTPA t 1/2 tended to approach baseline values with time after radiotherapy, suggesting a long-term recovery in lung injury.

CONCLUSION

These observations show significant and early alterations in DTPA lung clearance during and after radiotherapy that may provide a sensitive assay to monitor changes in radiation-induced lung injury and may facilitate early therapeutic intervention.

Glucose metabolic changes in nontumoral brain tissue of patients with brain tumor following radiotherapy: a preliminary study

PURPOSE

Our goal was to measure the effect of radiotherapy on the brain glucose metabolism of tumoral and nontumoral tissue of patients with brain malignancies.

METHOD

Fifteen patients with primary or metastatic brain tumors were studied with 2-deoxy-2-[18F]fluoro-D-glucose and PET prior to radiotherapy, and nine of them were rescanned 1 week after completing radiotherapy.

RESULTS

Brain metabolism in patients (all brain regions except for tumoral and edematous tissue) was lower than that of matched controls (34.0 +/- 8.3 vs. 46.5 +/- 6.4 mumol/100 g/min; p < or = 0.0001). Five of the nine patients retested after radiotherapy showed decrements in tumor metabolism (47 +/- 10%; p < or = 0.05) and increases in brain metabolism (10 +/- 4%; p < or = 0.004), and the other four showed no changes in tumor or in brain metabolism. Radiotherapy-induced changes in tumor metabolism were negatively correlated with changes in brain metabolism (r = 0.85, p < or = 0.004), but not with changes in tumor volume (assessed with MR images).

CONCLUSION

The study indicates that radiotherapy-induced increases in metabolism of nontumoral tissue are secondary to decreased tumor metabolic activity and not just due to volume reduction.

Effects of adenosine diphosphate on Ca2+ fluxes and Ca2+ accumulation of sarcoplasmic reticulum

Ca2+ transport by sarcoplasmic reticulum vesicles was examined by incubating sarcoplasmic reticulum vesicles (0.15 mg/ml) at 37 degrees C in, either normal medium that contained 0.15 M sucrose, 0.1 M KCl, 60 microM CaCl2, 2.5 mM ATP and 30 mM Tes at pH 6.8, or a modified medium for elimination of ADP formed from ATP hydrolysis by including, in addition, 3.6 mM phosphocreatine and 33 U/ml of creatine phosphokinase. In normal medium, Ca2+ uptake of sarcoplasmic reticulum vesicles reached a plateau of about 100 nmol/mg. In modified medium, after this phase of Ca2+ uptake, a second phase of Ca2+ accumulation was initiated and reached a plateau of about 300 nmol/mg. The second phase of Ca2+ accumulation was accompanied by phosphate uptake and could be inhibited by ADP. Since, under these experimental conditions, there was no significant difference of the rates of ATP hydrolysis in normal medium and modified medium, extra Ca2+ uptake in modified medium but not in normal medium could not be explained by different phosphate accumulation in the two media. Unidirectional Ca2+ influx of sarcoplasmic reticulum near steady state of Ca2+ uptake was measured by pulse labeling with 45Ca2+. The Ca2+ efflux rate was then determined by subtracting the net uptake from the influx rate. At the first plateau of Ca2+ uptake in normal medium, Ca2+ influx was balanced by Ca2+ efflux with an exchange rate of 240 nmol/mg per min. This exchange rate was maintained relatively constant at the plateau phase. In modified medium, the Ca2+ exchange rate at the first plateau of Ca2+ uptake was about half of that in normal medium. When the second phase of Ca2+ uptake was initiated, both the influx and efflux rates started to increase and reached a similar exchange rate as observed in normal medium. Also, during the second phase of Ca2+ uptake, the difference between the influx and efflux rates continued to increase until the second plateau phase was approached. In conditions where the formation of ADP and inorganic phosphate was minimized by using a low concentration of sarcoplasmic (7.5 micrograms/ml) and/or using acetyl phosphate instead of ATP, the second phase of Ca2+ uptake was also observed. These data suggest that the Ca2+ load attained by sarcoplasmic reticulum vesicles during active transport is modulated by ADP accumulated from ATP hydrolysis. ADP probably exerts its effect by facilitating Ca2+ efflux, which subsequently stimulates Ca2+ exchange.

Ouabain binding and coupled sodium, potassium, and chloride transport in isolated transverse tubules of skeletal muscle

The affinity and number of binding sites of [3H]ouabain to isolated transverse (T) tubules were determined in the absence and presence of deoxycholate. In both conditions the KD was approximately 53 nM while deoxycholate increased the number of binding sites from 3.5 to 37 pmol/mg protein. We concluded that the ouabain binding sites were located primarily on the inside of the isolated vesicle and that the vesicles were impermeable to ouabain. ATP induced a highly active Na+ accumulation by the T tubules which increased Na+ in the T tubular lumen by almost 200 nmol/mg protein. The accumulation had an initial fast phase lasting 2-3 min and a subsequent slow phase which continued for at least 40 min. The rate of the initial fast phase indicated a turnover number of 20 Na+/s. The Na+ accumulation was prevented by monensin but was unaffected by valinomycin. Ouabain did not influence Na+ uptake, but digitoxin inhibited it. At low K+ the accumulation of Na+ was reduced 3.7-fold below the value at 50 mM K+. 86Rb, employed as a tracer to detect K+, showed a first phase of K+ release while Na+ was accumulated. After 2-3 min, K+ was reaccumulated while Na+ continued to increase in the lumen. T tubules accumulated Cl- on addition of ATP. This suggested that ATP initiated an exchange of Na+ for K+ followed by uptake of Na+ and K+ accompanied by Cl-.

Electrophysiological effects of mexiletine (Kö1173) on ovine cardiac Purkinje fibers

To clarify the electrophysiological mechanisms of the antiarrhythmic effects of mexiletine, we examined the actions of mexiletine (0.1--30 mg/l) on action potential characteristics (phase 0 amplitude, overshoot, maximum upstroke velocity, maximum diastolic and activation voltages, duration at 50% and 90% repolarization) of cardiac Purkinje fibers using standard microelectrode techniques. In fibers stimulated at constant rate, mexiletine decreased phase 0 amplitude and Vmax and shortened the action potential. Mexiletine shortened action potential duration at lower concentrations than those which altered phase 0 depolarization. The effect of mexiletine on normal automaticity in cardiac Purkinje fibers was studied in fibers made automatic either by hypokalemia or by isoproterenol. Mexiletine suppressed normal automaticity by shifting activation voltage, so that spontaneous phase 4 depolarization reached a stable resting voltage without triggering regenerative phase 0 depolarization. The effects of mexiletine on abnormal automaticity were studied in Purkinje fibers intoxicated by ouabain. Mexiletine decreased the amplitude of or abolished either early or delayed after depolarizations induced by ouabain.