Usefulness of technetium-99m hexamethylpropylene amine oxime lung scan to detect inhalation lung injury of patients with pulmonary symptoms/signs but negative chest radiograph and pulmonary function test findings after a fire accident--a preliminary report

OBJECTIVE

In this study, we employed technetium-99m hexamethylpropylene amine oxime (99mTc HMPAO) lung scan to detect inhalation lung injury of patients after a fire accident.

METHODS

Ten healthy men for controls and 10 male patients with pulmonary symptoms/signs from a fire accident were enrolled in this study for comparison. 99mTc HMPAO lung scan was performed in each control and patient, as well as the degree of pulmonary vascular endothelium damage was represented as lung/liver uptake ratios (L/L ratio). All of the controls and patients had no smoking histories. None of the controls and patients had positive findings of plain chest radiograph (CXR) and pulmonary function test (PFT).

RESULTS

The results showed that significantly higher L/L ratio in the 10 patients (0.53 +/- 0.07) than in the 10 controls (0.30 +/- 0.07) (the p value < 0.05). Using a cut-off value of 0.40, all of the 10 patients had abnormally increased L/L ratios.

CONCLUSIONS

We conclude that 99mTc HMPAO lung scan has the potential to be a sensitive, objective and noninvasive method to detect inhalation lung injury of patients with pulmonary symptoms/signs but negative CXR and PFT findings after a fire accident.

Radiological manifestation of pulmonary complications in deceased intensive care burn patients

The chest radiographs of 46 burn patients who died in the burn intensive care unit (BICU) were retrospectively analyzed to study the spectrum of pulmonary complications and their contribution to patient's mortality. There were 25 male and 21 female patients and their mean ages were 34 and 30 years, respectively. Forty-three patients had flame burns, two chemical, and one scald with a mean total burn surface area (TBSA) of 71%. Thirty-six of them had inhalation injury and of these 25 patients developed septicaemia. Out of these 46 patients, 39 had a total of 60 pulmonary complications on various postburn days. The commonest complications were consolidation (28.3%) and adult respiratory distress syndrome (ARDS) (26.7%) mainly due to inhalation injury and/or following septicaemia. The majority of these complications (46.7%) occurred in the late phase (postburn day 5 onwards). Forty-one (89.2%) patients died due to multi-organ failure (MOF) and a good number of them had secondary respiratory failure. The flame burn patients with large TBSA, presence of inhalation injury, and occurrence of septicaemia, are at risk for pulmonary complications that equally affect adult males and females. Pulmonary complications irrespective of the cause significantly contribute to the mortality. This study suggests that serial chest X-rays done in BICU form an important diagnostic tool for pulmonary complications from postburn day 1 onwards, and is useful for subsequent monitoring of the treatment. All burn intensive care units may not be privileged to have a full time radiologist, and intensivist. Therefore, the burn surgeon needs to metamorphose into an intensivist and double as a burn radiologist for early detection and quick treatment if his surgical skills are to be adequately rewarded.

[Intrabronchial surfactant administration in inhalation trauma of severely burned patients with ARDS. Initial case reports]

Damage to the respiratory system caused by inhalation of toxic products of combustion and the subsequent development of adult respiratory distress syndrome (ARDS) are the main lethal factors in burns patients. Treatment with exogenous surfactant is one of the therapeutic options. However, no clinical reports have yet been published about this therapy. We report on two patients with burn injuries of second to third degree affecting 42% and 48% respectively of the total body surface plus inhalation injury complicated by ARDS. Both patients were treated with bovine surfactant (Alveofact). The therapeutic effects on oxygenation and pulmonary function were monitored. Intrabronchial application of surfactant by bronchoscopy during exhaustive conventional mechanical ventilation resulted in improved gas exchange with an increase in arterial O2 pressure (paO2); inspired O2 concentration (FiO2) was lowered and there was an improvement in lung compliance. Both patients survived this critical situation. We conclude that treatment with exogenous surfactant in postburn victims with ARDS is a promising therapeutic approach to improve the survival rate of these high-risk patients.

Radionuclide lung scanning in the management of respiratory burns

Soluble radioaerosols such as technetium-99m diethylene triamine pentacetate (DTPA) permit simple quantitative studies of alveolar-capillary permeability to be performed, since the submicronic aerosols are deposited mainly at the lung periphery and are cleared across the alveolar-capillary membrane. Regional alterations in permeability can also be noted using this radionuclide technique. We have measured the alteration in pulmonary epithelial permeability in normal subjects and in patients with inhalation burns using a computer-linked gamma-camera. In the normal volunteers, the time taken for 50% of inhaled Tc-99m DTPA to be cleared from the lungs (T1/2) was 66 minutes +/- 1sd of 12 minutes. In the 42 patients with inhalation burns, besides the T1/2, retention images of uncleared Tc-99m DTPA in the lungs were obtained to note regional differences, if any, in lung clearance arising from pulmonary epithelial damage; these patients showed increased rate of clearance (short T1/2) with mean T1/2 of 36 minutes +/- 1sd of 11 minutes, while the retention images revealed regional lung damage in moderately severe inhalation burns. In 18 patients with abnormal T1/2, 16 (89%) had abnormal bronchoscopy findings. Fifteen patients also had lung perfusion scans with Tc-99m MAA (macroaggregated albumin). The regional defects in perfusion when present were generally matched with the defects seen on ventilation scans. The Tc-99m DTPA lung clearance measurement and imaging has clinical usefulness in suspected inhalation burns.

Clearance of aerosolized 99mTc-diethylenetriaminepentacetate before and after smoke inhalation

The pulmonary clearance of aerosolized 99mTc-diethylenetriaminepentacetate (DTPA) was studied in mongrel dogs immediately after exposure to wood smoke to see if a sensitive, objective way of assessing the degree of pulmonary injury might be found. Animals were studied in four groups as follows: control, following five minutes, two minutes, and 15 seconds of smoke exposure. Chest roentgenograms and 133Xe scans were taken before and after smoke exposure. The DTPA clearance was more sensitive in detecting injury than either of these imaging techniques. The DTPA clearance rates increased in a dose responsive way following smoke inhalation: 2.4 percent and 12.1 percent excreted per minute for control animals and those exposed to five minutes of smoke, respectively. Seven patients in a clinical trial of DTPA following smoke exposure are described; their DTPA clearance rates were all normal, although five were active cigarette smokers. Despite encouraging results in animal experiments, DTPA clearance studies may be of little practical value in the clinical setting of acute inhalation injury.

[Lung densitometry in radiologic follow-up diagnosis in burn patients]

Chest x-ray films obtained by means of a portable x-ray apparatus were reviewed in 101 patients with skin burns and/or burns of the airways. The densitometric difference between measurements at a specific area in the sixth intercostal space lateral to the right hilus, and another measurement area in the mediastinum at the level of the sixth thoracic vertebral body correlated inversely with a radiographic adult respiratory distress syndrome score as suggested by Rommelsheim and Thelen. Our findings suggest that the densitometric difference between mediastinum and lung may aid in the evaluation of ARDS, especially if x-rays have different exposure parameters.

The plain chest radiograph after acute smoke inhalation

Serial chest radiographs of 45 patients from a major fire disaster were assessed for the effects of smoke inhalation injury. Thirty-three had abnormal chest radiographs on admission. Bronchial wall thickening was present in a total of 29 patients, subglottic oedema in 13, pulmonary oedema in seven, and patchy consolidation in three. Seven patients developed pulmonary oedema following initial exposure. This was the cause of death in two patients. Serial chest radiographs were useful in monitoring this very severe complication. Bronchial wall thickening and subglottic oedema were common early findings and thus may herald more serious subsequent respiratory embarrassment. Subglottic oedema is a previously undescribed finding. It not only indicates damage to the upper airways but may also indicate damage to the lung parenchyma. It may also make endotracheal intubation difficult. Therefore, the initial chest radiograph is an important predictor of significant smoke inhalation injuries enabling selection of patients likely to need ventilatory support.

Smoke inhalation: radiologic manifestations

The medical records and radiographs of 62 patients admitted for smoke inhalation were reviewed to determine the value of the plain chest radiograph in the early detection of inhalation injury. Pulmonary edema resulting from the inhalation injury often leads to pulmonary insufficiency, and its early diagnosis is crucial to the management of patients with this condition. In addition to the usual presentation of pulmonary edema, subtle radiographic findings of interstitial edema such as perivascular fuzziness and peribronchial "cuffing" were observed. Of 56 patients with significant inhalation injury, 35 (62.5%) had radiographic findings attributed only to smoke inhalation. These abnormalities often had a characteristic distribution in the lungs, and in the majority of patients they appeared in the first 24 hours after the injury. The radiologic diagnosis of inhalation injury may be made at a time when findings of other diagnostic tests are still equivocal or mildly abnormal, thus alerting the clinician to impending pulmonary failure.

Radionuclide evaluation of lung trauma

Nuclear medicine imaging procedures can play a significant role in evaluating the pulmonary complications that are seen in trauma patients. A quantitative method for measuring increased pulmonary capillary permeability that uses Tc-99m HSA allows early diagnosis of acute respiratory distress syndrome (ARDS) and accurately differentiates this condition from pneumonia or cardiogenic pulmonary edema. This technique may be of great value in following the response to therapy. The use of 133Xe to diagnose inhalation injury remains an important diagnostic tool, particularly at hospitals with specialized burn units. Regional decreases in ventilation-perfusion images reliably localize aspirated foreign bodies. Radionuclide techniques that are used to demonstrate gastropulmonary aspiration remain controversial and require further clinical evaluation. Pulmonary perfusion imaging, although nonspecific, may provide the earliest clue for correct diagnosis of fat embolism, air embolism, contusion, or laceration. Furthermore, the possibility of perfusion abnormality due to these uncommon conditions must be remembered whenever trauma patients are evaluated for pulmonary thromboembolism with scintigraphy. Occasionally, liver or spleen scintigraphy may be the most appropriate procedure when penetrating chest trauma also involves these subdiaphragmatic organs.

Radionuclide imaging in the assessment of lung injury

Nuclear medicine imaging techniques are being more widely applied to study a variety of lung injuries. Ventilation and perfusion imaging is often superior to other roentgenographic techniques for establishing the diagnosis and demonstrating the extent of such injuries. At several large burn centers, the Xe-133 washout technique has become the cornerstone for diagnosing early inhalation injury. The overall accuracy of this procedure is 92%. Regional decreases in ventilation and perfusion can reliably localize aspirated radiolucent foreign bodies. Disproportionate perfusion changes are often the earliest indicator of radiation pneumonitis and other forms of vascular injury. Other types of injury, such as gastropulmonary aspiration, blunt trauma, and near-drowning, require further evaluation before the ultimate role of nuclear imaging is defined. An imaging technique to assess capillary permeability in the adult respiratory distress syndrome would be of great clinical benefits.

Xenon ventilation-perfusion lung scans. The early diagnosis of inhalation injury

The use of xenon Xe 133 ventilation-perfusion lung scans for the early diagnosis of inhalation injury was evaluated in 67 patients with acute thermal burns. Study results were interpreted as normal if there was complete pulmonary clearance of the radioactive gas by 150 seconds. Thirty-two scans were normal, 32 abnormal, and three technically inadequate. There were three true false-positive study results and one false-negative study result. Good correlation was found between the scan results and various historical, physical, and laboratory values currently used to evaluate inhalation injury. The scans appeared to be the most sensitive method for the detection of early involvement, often being abnormal several days before the chest roentgenogram. Xenon lung scanning is a safe, easy, accurate, and sensitive method for the early diagnosis of inhalation injury and has important therapeutic and prognostic implications as well.