Experimental changes in the alveolo-capillary barrier induced by artificial ventilation

Mechanical ventilation can have deleterious effects on the lungs. Extra-alveolar escape of air, such as pneumothorax or subcutaneous emphysema, are complications which have long been known. New experimental studies have clearly shown that mechanical ventilation can also result in pathologic changes to the air/blood barrier. Mechanical ventilation with high end-inspiratory pressure and high volume causes lung edema in whose origin abnormal permeability of the alveolo-capillary barrier plays a major role. The abnormalities are in fact the result of pulmonary distention and not of elevated air pressure; this justifies the term "volume traumatism". The presence of a previous acute pulmonary injury considerably increases the deleterious effects of mechanical ventilation on the lungs. Although the clinical implications of these experimental studies are difficult to assess, they have nevertheless resulted in major changes in ventilation strategy for acute lung diseases such as the acute respiratory distress syndrome of the adult.     

Volume reduction surgery in the native lung after single lung transplantation for emphysema

The natural history of emphysema suggests that progression of disease in the native lung may contribute to late deterioration in respiratory function after single lung transplantation. In this report, we describe our experience with unilateral volume reduction surgery in three single lung transplant recipients with emphysema. Each patient had had a late decline in lung function with a recurrence of symptoms. Chest radiographs demonstrated hyperinflation of the native lungs with encroachment on the grafts. Serial pulmonary function testing documented progressive reduction in expiratory flows with increases in residual volumes. Exercise testing confirmed severe intolerance to maximal exercise. Unilateral volume reduction surgery was undertaken at 36, 39, and 55 months after transplantation without incident. Radiographs obtained after the procedures demonstrated restoration of normal diaphragmatic contour, decreased aeration of the native lungs, and improved inflation of the allografts. Exercise testing at 3 months documented a mean improvement in maximal oxygen consumption of 35%. Expiratory flows improved by a mean of 60%. Quantitative ventilation and perfusion scans, however, were essentially unchanged. This experience suggests that unilateral volume reduction surgery may be considered as an alternative strategy in single lung transplant recipients with emphysema who exhibit clinically significant functional deterioration. Differentiation of the adverse effects of hyperinflation of the native lung from other potential causes of late deterioration might not be necessary but may be predictive of the degree of functional improvement after volume reduction. The relief of thoracic overdistention seems to play a primary role in the improvement pulmonary function.     

Bilateral pulmonary artery aneurysms in a patient with Behcet syndrome: evaluation with radionuclide angiography and V/Q lung scanning

The case of a 14-year-old girl with Behcet syndrome is described. Besides painful and recurrent oral ulcerations, the patient had a cough and intermittent hemoptysis. The initial chest roentgenogram revealed bilateral parahilar opacities. CT and MRI scans of the thorax showed bilateral thrombosing aneurysms of the pulmonary arteries. Pulmonary blood flow imaging was performed after technegas ventilation lung scanning and Tc-99m MAA injection using a first-pass radionuclide angiography procedure. Altered blood flow in the left pulmonary artery was shown. Bilateral and well-defined ventilation/perfusion mismatched areas suggested a high probability of pulmonary embolism. Little additional information was obtained on subsequent contrast pulmonary angiography. The high incidence of pulmonary artery hypertension and associated vascular injury risk makes pulmonary angiography an unsafe procedure in patients with pulmonary Behcet syndrome. The need for pulmonary angiography could be obviated in such cases with the use of high-precision MRI and ventilation/perfusion lung scanning, including radionuclide pulmonary angiography.     

Sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease): case report with nodal and diffuse muco-cutaneous involvement

PURPOSE: Based on a review of the background of MRI using inhaled hyperpolarized noble gases first experiences and perspectives for functional imaging in emphysema patients are presented. MATERIAL AND METHODS: In vonventional MRI, the spin density of protons, which is defined by the Boltzmann equilibrium, is the source of the imaging signal. Since proton density in the lungs is low and multiple air-tissue interfaces exist, MRI of the lung parenchyma is unsatisfactory. The possibility to artificially enrich the spin density (hyperpolarization) in noble gases (H3-3, Xe-129) by optical pumping results in a non-equilibrium polarization five orders of magnitude higher than the Boltzmann equilibrium. Hyperpolarized noble gases can then be applied as "inhaled contrast media" using a dedicated application device. At the MR unit several prerequisites must also be fulfilled: transmit-receive coil, boradband amplifier and fast sequences with low flip angles. These are essential for dynamic scans in breath-hold tecnique of the highly diffusible He-3 or the well soluble Xe-129. RESULTS: He-3 and Xe-129 have been successfully applied for imaging of the ventilated airspaces. Besides the well-known narcotic effects of Xenon no adverse effects were observed. A homogeneous distribution of signal intensity can be regarded as a normal findings in people without lung disease. Obstructive diseases and emphysematous changes lead to generalized or localized signal inhomogeneities. Most likely they are caused by disorders of the distribution of ventilation bases on a different functional vehavior of different alveolar regions. By making use of the paramagenetic properties of oxygen, He-3 can also be used for local measurements of oxygen partial pressure in the lung. Xe-129 exhibits a different chemical shift within alveoli, interstitial space and vessels which can be measured by MRI. CONCLUSIONS: MRI using inhaled hyperpolarized noble gases is a functional imaging modality with high spatial and/or temporal resolution. First studies for early detection of obstructive lung diseases and disorders of distribution of ventilation in emphysema are promising.     

Value of perfusion lung scan in the diagnosis of pulmonary embolism: results of the Prospective Investigative Study of Acute Pulmonary Embolism Diagnosis (PISA-PED)

To assess the value of perfusion lung scan in the diagnosis of pulmonary embolism, we prospectively evaluated 890 consecutive patients with suspected pulmonary embolism. Prior to lung scanning, each patient was assigned a clinical probability of pulmonary embolism (very likely, possible, unlikely). Perfusion scans were independently classified as follows: (1) normal, (2) near-normal, (3) abnormal compatible with pulmonary embolism (PE+: single or multiple wedge-shaped perfusion defects), or (4) abnormal not compatible with pulmonary embolism (PE-: perfusion defects other than wedge-shaped). The study design required pulmonary angiography and clinical and scintigraphic follow-up in all patients with abnormal scans. Of 890 scans, 220 were classified as normal/or near-normal and 670 as abnormal. A definitive diagnosis was established in 563 (84%) patients with abnormal scans. The overall prevalence of pulmonary embolism was 39%. Most patients with angiographically proven pulmonary embolism had PE+ scans (sensitivity: 92%). Conversely, most patients without emboli on angiography had PE- scans (specificity: 87%). A PE+ scan associated with a very likely or possible clinical presentation of pulmonary embolism had positive predictive values of 99 and 92%, respectively. A PE- scan paired with an unlikely clinical presentation had a negative predictive value of 97%. Clinical assessment combined with perfusion-scan evaluation established or excluded pulmonary embolism in the majority of patients with abnormal scans. Our data indicate that accurate diagnosis of pulmonary embolism is possible by perfusion scanning alone, without ventilation imaging. Combining perfusion scanning with clinical assessment helps to restrict the need for angiography to a minority of patients with suspected pulmonary embolism.     

The use of 99Tcm-Technegas in the investigation of patients with pulmonary thromboembolism

Pulmonary embolism remains a major cause of morbidity and mortality, being responsible for an estimated 200,000 deaths per annum in the USA and 21,000 per annum in the UK. Lung scintigraphy is in many instances the investigation of choice in suspected pulmonary thromboembolism. A normal perfusion lung scan excludes pulmonary embolism. An abnormal perfusion scan, while being sensitive, is of low specificity for the diagnosis of pulmonary embolism and needs to be complemented with a ventilation study. Lung ventilation has been studied using inert gases of radiolabelled aerosols. The new radiopharmaceutical 99Tcm-Technegas is a suspension of 99Tcm-labelled, ultrafine, carbon particles produced in an atmosphere of high-purity argon. The size of the particles is of the order of 0.005-0.2 microns, which assures good peripheral penetration and alveolar deposition. After inhalation, static images in multiple projections may be acquired. The resultant images are of excellent technical quality and several publications have shown the value of Technegas images as an adjunct to perfusion imaging in suspected pulmonary thromboembolism. Studies comparing Technegas images with other ventilatory radiopharmaceuticals have in the majority of instances reported comparable diagnostic qualities.     

Study on antifertility effect of a novel LHRH antagonist in male rats

The diagnosis of pulmonary embolism is even in contemporary clinical practice problematical. Pulmonary angiography is used in our departments very little due to its invasive character. The method of choice for diagnosis remains therefore perfusion scintigraphy of the lungs, in this country frequently without ventilation scintigraphy as it is not available in the majority of our departments of nuclear medicine. In recent years in the diagnostic algorithms also assessment of D-dimers was started, i.e. assessment of products of fibrinolysis assessed by monoclonal antibodies. The authors tried to find out how many patients admitted to the medical department for diagnosis of pulmonary embolization may have a false positive diagnosis on the basis of pulmonary scintigraphy. During the period III/96 to V/96 a total of 18 patients from the medical clinic with suspected pulmonary embolism were examined where the value of D-dimers(latex test) was assessed and at the same time perfusion scintigraphy was performed. With regard to the highly negative predictive value of D-dimer assessment the authors focused their attention on patients with a suspect or positive lung scan (i.e. treated on account of pulmonary embolism) while D-dimers were negative. Of 13 patients with suspect or possible pulmonary embolism, as assessed by scintigraphy, four had negative dimers(30%). With regard to the 90% reported negative predictive value, based on the literature, thus three of these patients were unnecessarily admitted to hospital and treated. The authors assume that assessment of D-dimers should be part of the examination protocol due to its non-pretentious character and low price as compared with costs of hospitalization.     

Latex hypersensitivity/glove component reaction as a contributing factor to osteomyelitis of the hand: a case report and review of the literature

High-resolution computed tomography (HRCT) can be used to diagnose and quantify emphysema noninvasively, as significant correlations have been found between the histological grade on resected lung specimens and quantified (q) computed tomography (CT). In this study, we performed thin section qHRCT in patients with severe hereditary alpha-1-antitrypsin (AAT) deficiency. AAT deficiency is the most common genetic cause of emphysema in adults, and exercise intolerance is the most disabling, distressing consequence of emphysema for the majority of patients. qHRCT was used to quantify precisely the alterations in the lung parenchyma due to pulmonary emphysema. Up until now, the important relationship between the severity of emphysema and the reduced exercise capacity has received little attention. Therefore the purpose of the study was to investigate the relationship between emphysema as displayed by qHRCT and cardiopulmonary exercise testing (CPX) in patients with severe cardiopulmonary impairment. - qHRCT was performed in 21 patients with homozygous AAT deficiency. CT scans were obtained at three spirometrically standardized levels at the carina and (5 cm above and below the carina). The mean lung density at 50% of vital capacity and a quantitative histogram analysis of the frequencies of CT values were determined. All patients underwent symptom-limited CPX to analyse simultaneously cardiovascular and ventilatory systems responses. - In all patients, qualitative CT assessment demonstrated panlobular emphysema with large and extensive areas of uniform low attenuation, characteristically with a lower-lobe distribution. Mean CT density values of the patients (-845 +/- 6.9 (mean +/- SEM)) were significantly correlated with work capacity (r = 0.55, p <0.01), oxygen-pulse (r = 0.54, p <0.01) and functional dead space ventilation (r = -0.54, p <0.01). Moreover, severe emphysema index (CT values below a threshold value of 950 HU) correlated positively with functional dead space ventilation (r = 0.60, p <0.01) and alveolar-arterial oxygen difference (r = 0.70, p <0.001). - These results clearly demonstrate that CPX parameters, indicating a disturbed pulmonary gas exchange and a ventilation-perfusion-mismatch during exercise, are significantly related to the extent of lung emphysema.     

Hyperlucent lung secondary to homocystinuria

At 23 months of age, one of a pair of monozygotic twins with radiographic unilateral hyperlucent lung was evaluated by radionuclide ventilation/perfusion pulmonary studies, which revealed a ventilation/perfusion mismatch of an entire lung. This twin died, and autopsy revealed pulmonary arterial thrombosis and histological changes compatible with homocystinuria, which was subsequently shown to be present in the surviving twin as well. A ventilation/perfusion lung scan of the surviving twin revealed multiple ventilation/perfusion mismatched defects, suggestive of pulmonary embolism. The presenting manifestation of homocystinuria in these patients was the pulmonary thrombotic disease. Neither twin had any other stigmata of homocystinuria at the time of initial presentation.     

Respiratory failure based on pulmonary tuberculosis sequelae and its management

According to the complexity of pathological change of pulmonary tuberculosis sequelae (TB seq), on which respiratory failure based shows the higher incidence of marked degree of hypoxemia and hypercapnia than that based on chronic pulmonary emphysema (CPE). In TB seq, pulmonary artery mean pressure is higher, nocturnal oxyhemoglobin desaturation is much lower than in CPE. Also hypoxemia on exercise is lower, and oxygen inhalation for this hypoxemia is more effective than in CPE. The most effective therapy is continuous oxygen therapy. Home oxygen therapy has improved the prognosis and quality of life (QOL) of patients with respiratory failure based on TB seq. Artificial positive pressure ventilation (TIPPV) with intubation or tracheotomy is carried out for patients with severe hypercapnia and respiratory acidosis. Recently, early application of nasal mask ventilation (NPPV) on patients with TB seq has prohibited acute exacerbation of chronic respiratory failure. And also for patients with severe hypercapnia, NPPV with BIPAP method is effective for their QOL. Comprehensive respiratory rehabilitation is also successfully applied for their management.     

Quantitative pO2 imaging in vivo with perfluorocarbon F-19 NMR: tracking oxygen from the airway through the blood to organ tissues

The physiological redistribution of perfluorocarbon (PFC) compounds to liver, spleen, bone marrow, and lung after intravenous (i.v.) or intraperitoneal (IP) administration of PFC emulsions affords the unique opportunity for non-invasive monitoring of oxygenation status of these organs and tissues utilizing fluorine (F-19) nuclear magnetic resonance (NMR) imaging techniques. PFCs also may be introduced directly into the pulmonary airways by procedures such as liquid ventilation, intratracheal instillation, or aerosol inhalation. Considerations of importance when establishing methodology for accurate quantitation of oxygen partial pressure (pO2) in vivo using F-19 NMR include: 1.) error analysis of the calibration curves which relate pO2 to the measured PFC F-19 relaxation rate, 2.) optimization of the NMR pulse sequence for efficient oxygen sensitive data acquisition and, 3.) fluorine signal independence from emulsion aqueous phase bioconstituents. The porcine model was investigated at 0.14T following i.v. or IP administration of the PFC emulsion containing perfluorotributylamine (FC-43) to demonstrate the capability for tracking oxygen with F-19 NMR from the lung through the blood to selected organ tissues. Quantitative pO2 projection images and isobaric contour graphs were derived for the liver, spleen, and lungs as a function of inspired oxygen. Blood pO2 levels in aorta, pulmonary artery, and hepatic vein were monitored simultaneously with NMR imaging for correlative analysis.     

Cadaver lungs for transplantation. Effect of ventilation with alveolar gas

In an effort to increase the donor pool for lung transplantation (LTX), we have demonstrated the feasibility of LTX from circulation-arrested cadavers in a canine LTX model. We hypothesized that ventilation of the cadaver lung with alveolar gas (20% O2, 5% CO2, balance N2) (AG) would be superior to ventilation with 100% oxygen (O2) after circulatory arrest of the donor. Twelve mongrel dogs were intubated, heparinized and euthanized by pentothal injection and ventilated with AG (n=6) or O2 (n=6). Four hours later, donor animals underwent sternotomy, and the lungs were flushed with cold modified Euro-Collins solution, harvested, and stored inflated in ice slush. Left lung allotransplantation was performed, and recipients were made dependent o n the transplanted lung by occlusion of the contralateral bronchus and pulmonary artery. Recipient animals were ventilated with an FiO2 of 0.4 and followed for 8 hr. Total ischemic time was 7.9 hr for both groups. Pulmonary edema developed in all recipients of AG lungs; one recipient survived the 8-hr observation period with poor oxygenation. In contrast, three of six recipients of O2-ventilated lungs survived for 8-hr with excellent gas exchange. Specimens of donor lungs before and after transplant were evaluated histologically utilizing trypan blue exclusion as an indicator of cell viability. At the time of organ retrieval 4 hr after death, 6% of cells were nonviable in the O2-ventilated cadaver lungs. Circulation-arrested cadaver lungs ventilated with 100% O2 prior to organ retrieval have superior pulmonary function after transplant compared with lungs ventilated with AG. Ventilation of cadaver lungs with AG induces pulmonary injury in this model. retrieval of donor lungs from circulation-arrested cadavers has potential for increasing the pulmonary donor pool.     

Evaluation of emphysema progression as measured by computed tomography in patients with chronic obstructive pulmonary disease

It has been difficult to assess the progression of pulmonary emphysema since accurate quantification of the extent of this condition has only previously been possible on post mortem or resected lungs. Previously we have shown that measurements of CT lung density correlated with the degree of emphysema, measured morphometrically in resected lungs. We have therefore employed this technique to assess the progression of emphysema in 17 patients (12M, 5F) with wide range of chronic airflow limitation (FEV1 15-68% predicted). There was little change in the degree of airflow limitation, hyperinflation or arterial blood gas values over 30 +/- 4 months of follow up (p > 0.05). However during this period there was a significant decrease in the lowest 5th percentile of CT density, which fell from -920 +/- 32 to -940 +/- 36 Hounsfield units (p < 0.005) associated with significant fall in the diffusing capacity for carbon monoxide. We believe that these data show the ability of CT scanning to assess the progression of emphysema in patients with chronic obstructive pulmonary disease.     

Modern concepts in the management of emphysema in the aged and infirm

The haphazard method of treating patients seriously ill with emphysema is gradually being replaced by modern, well organized cardiopulmonary therapeutic and rehabilitation programs. This evolution is the result of a further expansion in our knowledge of cardiopulmonary physiology and biochemistry; an additional factor is the recent public awareness of the seriousness of the problem, brought about by public educational programs. Emphysema is chiefly a disease of old age. It develops as a result of a degenerative process in which the alveolar walls become thinner and the lungs less elastic. Senile emphysema per se may not be disabling, but it is often associated with a severe chronic pulmonary disorder and thus can become the most distressing disease of old age, with shortness of breath even on such slight exertion as dressing or talking. Disturbances in cardiopulmonary physiology due to obstruction in the free flow of air and to superimposed infections require the use of all available procedures designed to obtain maximal pulmonary ventilation. The magnitude, the difficulty and the many controversial aspects of this problem are evident. The eventual solution will come gradually with continued interest and research.     

Extended preservation of ischemic pulmonary graft by postmortem alveolar expansion

BACKGROUND: If lungs could be retrieved for transplantation from non-heart-beating cadavers, the shortage of donors might be significantly alleviated. METHODS: Peak airway pressure, mean pulmonary artery pressure, pulmonary vascular resistance, and wet to dry weight ratio were measured during delayed hypothermic crystalloid flush in rabbit lungs (n = 6) at successive intervals after death comparing cadavers with lungs left deflated (group 1), inflated with room air (group 2) or 100% oxygen (group 4), or ventilated with room air (group 3), or 100% nitrogen (group 5), or 100% oxygen (group 6). RESULTS: There was a gradual increase in mean pulmonary artery pressure and pulmonary vascular resistance with longer postmortem intervals in all study groups (p = not significant, group 1 versus group 2 versus group 3). There was also a gradual increase in peak airway pressure and wet-to-dry weight ratio over time in all groups, which reflected edema formation during flush (airway pressure, from 14.5 +/- 1.0 cm H2O to 53.7 +/- 12.2 cm H2O, and wet-to-dry weight ratio, from 3.6 +/- 0.1 to 11.5 +/- 1.2, in group 1 at 0 and 6 hours postmortem, respectively; p < 0.05). Compared with group 1, however, the increase in groups 2 and 3 was much slower (airway pressure, 20.9 +/- 0.5 cm H2O and 18.8 +/- 1.2 cm H2O, and wet-to-dry weight ratio, 5.2 +/- 0.3 and 4.6 +/- 0.4 at 6 hours postmortem, respectively; p < 0.05 versus group 1 and p = not significant, group 2 versus group 3). Airway pressure and wet-to-dry weight ratio did not differ between groups 2 and 4 or between groups 3, 5, and 6. CONCLUSIONS: These data suggest that (1) pulmonary edema will develop in atelectatic lungs if hypothermic flush is delayed for 2 hours after death, (2) postmortem inflation is as good as ventilation in prolonging warm ischemic tolerance, (3) inflation with oxygen or ventilation with nitrogen or oxygen is no different from that with room air, and (4) therefore, prevention of alveolar collapse appears to be the critical factor in protecting the lung from warm ischemic damage independent of continued oxygen delivery.     

Experimentally induced nasal hypersecretion does not reduce the efficacy of intranasal levocabastine

Pulmonary tumor embolism is an often missed antemortem diagnosis in patients with cancer and respiratory failure. Although rare, this complication is an important cause of additional morbidity. Referred for radionuclide pulmonary perfusion and ventilation scintigraphy, a typical pattern of multiple subsegmental peripheral defects on perfusion lung scanning without matching ventilation defects, suggesting a high probability of pulmonary thromboembolism, often leads to false conclusions. We present a case of bilateral multiple subsegmental mismatched defects in lung ventilation perfusion scintigraphy, where autopsy confirmed the diagnosis of pulmonary tumor embolism, secondary to an undifferentiated ductal type adenocarcinoma of the pancreas. Pulmonary tumor embolism is an entity to keep in mind in patients treated for carcinoma presenting with (sub) acute dyspnea.     

Consequences of a small decrease of air temperature from thermal equilibrium on thermoregulation in sleeping neonates

PURPOSE: To evaluate macromolecular contrast-enhanced MR-angiography for the detection of experimentally induced pulmonary artery embolism and to determine the size of the smallest detectable embolised vessel. METHODS: Pulmonary artery embolism was artificially induced in eight isolated perfused sheep lungs by injecting room air into the main pulmonary artery. The pulmonary vascular system enhanced by macromolecular gadolinium-DTPA-polylysine was imaged with a flow-sensitive gradient-echo technique. RESULTS: Pulmonary artery embolism was demonstrated in all eight lungs by an obvious cut-off phenomenon in the contrast-enhanced arteries proximal to the pulmonary air emboli. The smallest detectable embolised artery measured 1.6 mm in diameter and was located in the 6th generation of the pulmonary vascular system. CONCLUSIONS: In this experimental study MR angiography enhanced by a macromolecular contrast agent allowed noninvasive diagnosis of pulmonary artery embolism.     

A clinical method to determine the effectiveness of dental handpiece sterilization

The interaction of ventilation and hemodynamics in the posttraumatic period has been studied in 131 patients with severe craniocerebral trauma. Indexes of respiratory function, central and pulmonary hemodynamics were determined over the first week and on days 10, 14, 21 and 28 after trauma. The data obtained have shown that respiratory function and circulation damages during brain trauma are predetermined by the reduction in pulmonary volume and capacity, impaired alveolar ventilation and bronchial patency, followed by development of atelectasis of the lungs and pulmonary shunt. Patients with severe brain injury more often develop bronchospasm and disorders of central and pulmonary hemodynamics, as compared to patients with moderate injury.     

Acute median nerve compression associated with tumescent fluid administration

A 13 yr old male with acute lymphoblastic leukaemia who received bilevel positive airway pressure ventilation via a face mask for post-transplant pneumonitis developed subcutaneous emphysema, radiographic evidence of pulmonary interstitial emphysema, pneumomediastinum and 6 h later, right hemiparesis and focal livedo reticularis. This case illustrates that severe barotrauma may complicate noninvasive bilevel positive airway pressure ventilation.     

Helium pneumoperitoneum for laparoscopic cholecystectomy: ventilatory and blood gas changes

Laparoscopic cholecystectomy with carbon dioxide pneumoperitoneum may result in hypercarbia and acidosis in patients with cardiorespiratory disease. The aim of the present study was to assess helium as an alternative to carbon dioxide for creating the pneumoperitoneum. Ventilation requirements and carbon dioxide levels were assessed at the beginning and end of laparoscopic cholecystectomy using helium (n = 30) and carbon dioxide (n = 30) pneumoperitoneum. Insufflation with helium did not result in an increase in ventilation requirement although, like carbon dioxide pneumoperitoneum, it was associated with a mean rise in peak airway pressure (of 7 cmH2O; P < 0.001). There was also a 3.2-kPa increase in the alveolar-arterial oxygen gradient with helium (P = 0.006). Carbon dioxide pneumoperitoneum was associated with a significant rise in arterial carbon dioxide levels, despite increasing ventilation. Four patients with helium pneumoperitoneum had surgical emphysema for 5 days. Helium may be a suitable alternative to carbon dioxide for creating pneumoperitoneum in patients with severe cardiorespiratory disease. However, because of its low water solubility helium has a lower safety margin than carbon dioxide in the rare event of gas embolism.