Chronic percutaneous pericardial drainage with modified pigtail catheters in children.

To determine the safety and efficacy of chronic percutaneous pericardial drainage in children, pigtail catheters were inserted over curved guidewires under fluoroscopic control into the pericardial space in 7 consecutive children with pericardial effusion. Pericardiocentesis was therapeutic (for tamponade) in 1 child, diagnostic in 4 and both therapeutic and diagnostic in 2. The children were 0.5 to 16 years old and weighed 5 to 65 kg. Underlying diagnoses included cancer (3 children), congenital heart disease (2 children) and immunodeficiency and hemolytic uremic syndrome (1 each). When unmodified pigtail catheters, designed for angiography, were used (as in the first 3 children), either the catheters clotted within 36 hours, necessitating operative pericardial drainage, or repeated heparin infusions were required to keep the catheter patent. However, when 8Fr catheters were modified by placing 0.050-inch side holes along the distal shaft, the catheters remained patent and effectively drained the pericardial space for 3 to 7 days. Heparin infusion was not required, no child managed with the modified catheters required subsequent drainage and no complications occurred. In conclusion, percutaneous pericardial drainage is safe, even in small children, and can be effective chronically if catheters with large drainage holes are used.

Management of congenital stenosis of a branch pulmonary artery with balloon dilation angioplasty. Report of 52 procedures.

Twenty-four children, aged 4 months to 16 years (nine patients 2 years old or younger), underwent balloon dilation angioplasty of hypoplastic or stenotic branch pulmonary arteries between July, 1981, and April, 1984. Most children had tetralogy of Fallot, with or without pulmonary atresia, or isolated peripheral pulmonary artery stenosis. Fifty-two dilations were attempted, 44 in the catheterization laboratory and eight in the operating room. Of these, 26 (50%) were judged successful; the average vessel diameter on angiogram increased from 4.1 +/- 0.3 to 7.2 +/- 0.3 mm (76%), the gradient across the narrowed segment fell from 60 +/- 10 to 36 +/- 5 mm (40%), pressure in the main pulmonary artery or right ventricle proximal to the obstruction decreased from 83 +/- 10 to 66 +/- 6 mm Hg (20%), and the radionuclide-determined fraction of cardiac output directed to the lung ipsilateral to the dilated pulmonary artery increased from 40 +/- 4 to 51 +/- 4 (28%). All changes were significant at the p less than 0.005 level. Reasons for failure included inadequate technique (balloon too small, inability to position balloon or wire) in 14 and the refractory nature of the lesion itself in 11. Technical failures were age independent. Nondilatable lesions were more common in children more than 2 years old (10/25 versus 1/10) or with isolated peripheral pulmonary artery stenosis (5/7). Five of seven stenoses near previous shunts were nondilatable. One child exsanguinated when the pulmonary artery ruptured during dilation, but other complications were few. Eight dilations, followed up for an average of 6 months after dilation, showed angiographic persistence of improvement; two of four lesions were successfully redilated to a larger size. Balloon dilation angioplasty appears beneficial, both short and long term, for some patients with hypoplastic or stenotic branch pulmonary arteries, especially if performed early in life.

Airway and alveolar pressures during perfluorocarbon breathing in infant lambs.

Previous studies exploring the utility of liquid breathing using perfluorocarbon have reported proximal airway pressures (Paw) as high as 70 Torr during inspiration, generating concern about the safety of this form of mechanical ventilation. Effects on the pulmonary capillary bed are, however, more likely related to alveolar pressure (PA) than to Paw, and data on PA during liquid breathing are limited. In this study in infant lambs, we reconstructed the pressure waveforms of PA during liquid breathing by using an occlusion technique and compared these with Paw waveforms. Peak PA (18.6 +/- 10.4 Torr) was significantly less than peak Paw (31.5 +/- 10.5 Torr, P less than 0.001), indicating a large resistive pressure drop (14.4 +/- 4.5 Torr) across the bronchial tree. Mean PA (mPA) was very similar to mean Paw (mPaw) [bias = -2.0 Torr, standard error of the average difference = 0.27 Torr, predictive value of mPaw for mPA (r2) = 0.978], suggesting that mPaw, which is easily measured, may be used to estimate mPA during perfluorocarbon liquid breathing. These data show that alveoli do not experience the same large swings in pressure as the proximal airway does during liquid breathing and that simple measurements of mPaw can be used to approximate mPA during liquid breathing.

Effects of static and fluctuating airway pressure on intact pulmonary circulation.

The direct effects on the pulmonary circulation of static and fluctuation airway pressure were compared in intact close-chest infant lambs with reactive pulmonary vasculature under alpha-chloralose anesthesia. A preparation developed to permit independent ventilation of right and left lungs and independent measurement of right and left lung blood flow was employed to separate direct from indirect effects of unilateral airway pressure changes on pulmonary vascular resistance (PVR). Both static and fluctuating unilateral airway pressure interventions directly elevated ipsilateral PVR. For purposes of comparison mean alveolar pressure (PA) was estimated for both static and fluctuating trials. Fluctuating interventions increased PVR more than did static trials at comparable levels of PA. Substantially less PA was needed to double ipsilateral PVR by fluctuating than by static interventions (16 vs. 26 mmHg, respectively). These data indicate that, in the intact animal with reactive pulmonary vasculature, both PA and the waveform of airway pressure applied can influence PVR.

Pulmonary vascular resistance after cessation of positive end-expiratory pressure.

This report describes the pulmonary vascular response of infant lamb lung to abrupt cessation of positive end-expiratory pressure (PEEP) during volume-regulated continuous positive-pressure breathing (CPPB). In an intact, endobronchially ventilated preparation, the increase in left lung blood flow (QL) after abrupt cessation of 11 Torr left lung PEEP was found to be gradual, although peak airway pressure (Pmax) fell promptly from 36 to 14 Torr; 49% of the increase in QL occurred greater than 10 s after cessation of PEEP. Recruitment of zone I vasculature that had been created by balloon occlusion of the left pulmonary artery was found to occur promptly after balloon deflation. Isolated neonatal lamb lungs, perfused at constant flow rate, showed similar persistent elevation of pulmonary vascular resistance after cessation of 15 Torr PEEP, although Pmax fell abruptly from 39 to 12 Torr. This hysteresis was eliminated by calcium channel blockade with verapamil, and the magnitude of the change in pulmonary arterial pressure after either application or cessation of PEEP was reduced (25 and 26%, respectively). These observations suggest that, during CPPB, lung stretch alters neonatal pulmonary vascular tone or, by causing calcium channel-dependent lung volume hysteresis, modulates pulmonary vascular resistance. This interaction exaggerates the effect of airway pressure changes on pulmonary vascular resistance during mechanical ventilation.

High-frequency partial liquid ventilation in respiratory distress syndrome: hemodynamics and gas exchange.

Partial liquid ventilation using conventional ventilatory schemes improves lung function in animal models of respiratory failure. We examined the feasibility of high-frequency partial liquid ventilation in the preterm lamb with respiratory distress syndrome and evaluated its effect on pulmonary and systemic hemodynamics. Seventeen lambs were studied in three groups: high-frequency gas ventilation (Gas group), high-frequency partial liquid ventilation (Liquid group), and high-frequency partial liquid ventilation with hypoxia-hypercarbia (Liquid-Hypoxia group). High-frequency partial liquid ventilation increased oxygenation compared with high-frequency gas ventilation over 5 h (arterial oxygen tension 253 +/- 21.3 vs. 17 +/- 1.8 Torr; P < 0.001). Pulmonary vascular resistance decreased 78% (P < 0.001), pulmonary blood flow increased fivefold (P < 0.001), and aortic pressure was maintained (P < 0.01) in the Liquid group, in contrast to progressive hypoxemia, hypercarbia, and shock in the Gas group. Central venous pressure did not change. The Liquid-Hypoxia group was similar to the Gas group. We conclude that high-frequency partial liquid ventilation improves gas exchange and stabilizes pulmonary and systemic hemodynamics compared with high-frequency gas ventilation. The stabilization appears to be due in large part to improvement in gas exchange.

Liquid ventilation attenuates pulmonary oxidative damage.

PURPOSE: Liquid perfluorochemicals reduce the production of reaction oxygen species by alveolar macrophages. We sought to determine whether the use of liquid perfluorochemicals in vivo during liquid ventilation would attenuate oxidative damage to the lung. MATERIALS AND METHODS: Healthy infant piglets (n = 16) were instrumented for mechanical ventilation and received intravenous oleic acid to create an acute lung injury. The animals were assigned to a nontreatment group receiving conventional mechanical ventilation or a treatment group receiving partial liquid ventilation with a liquid perfluorochemical. Following sacrifice, the bronchoalveolar lavage and lung parenchyma were analyzed for evidence of oxidative damage to lipids and proteins by determination of TBARS and carbonylated protein residues, respectively. RESULTS: Mortality in the control group was 50% at the completion of the study compared with no deaths in the partial liquid ventilation group (P = .025). The alveolar-arterial oxygen difference was more favorable following injury in the partial liquid ventilation group. The liquid ventilation group demonstrated a 32% reduction in TBARS (P = .043) and a 14% reduction in carbonylated protein residues (P = .061). CONCLUSION: These data suggest that partial liquid ventilation supports gas exchange and reduces mortality in association with a reduction in the production of reactive oxygen species and the concomitant attenuation of tissue damage during the early phase of acute lung injury.

Partial liquid ventilation influences pulmonary histopathology in an animal model of acute lung injury.

PURPOSE: The aim of this study was to assess the effect of partial liquid ventilation (PLV) and conventional mechanical ventilation (CMV) in the pattern of distribution of lung injury in a rabbit model of acute lung injury. MATERIALS AND METHODS: Animals (1.5 to 3.5 kg) were assigned to receive CMV (tidal volume of 10 mL/kg and a PEEP of 5 cm H2O) or PLV with 18 mL/kg of intratracheal perflubron (tidal volume of 10 mL/kg and a PEEP of 5 cm H2O). Lung injury was elicited by intravenous administration of Escherichia coliendotoxin. Uninjured animals ventilated as the CMV group served as controls. After 4 hours of mechanical ventilation, the lungs were removed and tissue injury was assessed by light microscopy using a scoring system. RESULTS: Animals in the CMV group had higher lung injury scores in comparison to the PLV group (10+/-4.5 vs. 5+/-3.3, respectively, P < .05). The injury scores were similar for nondependent lung regions (CMV: 8+/-4.3, PLV: 6+/-2.9) but significantly different for the dependent regions (CMV: 12+/-4.6, PLV: 5+/-3.8, P< .05). CONCLUSIONS: PLV is associated with significant attenuation of lung injury, in comparison to CMV. This effect is predominantly due to attenuation of injury in the dependent region of the lung.

Progress in pediatric extracorporeal membrane oxygenation.

Prolonged complete support of the circulation and of gas exchange can be achieved by extracorporeal membrane oxygenation (ECMO) in infants and children with potentially reversible, albeit life-threatening, disease. This allows lung rest or cardiac rest at times when dependence in those organs would be physiologically expensive. Although ECMO has no intrinsic healing powers, pediatric hearts and lungs exhibit tremendous recuperative power once the cycle of injury, inefficient performance, abuse, and secondary injury can be broken. Recent advances in technology, although impressive, do not explain the rapid growth of clinical interest in ECMO. Most recent progress in ECMO derives from refinement of clinical practices and the application of this technology to new patient populations. ECMO is not itself an experiment. It is the application of ECMO that is experimental.

Partial liquid ventilation and nitric oxide in congenital diaphragmatic hernia.

PURPOSE: In congenital diaphragmatic hernia (CDH) there is immature lung development with a resulting clinical picture of pulmonary hypoplasia, surfactant deficiency, and pulmonary hypertension. Pulmonary hypoplasia and surfactant deficiency both have been successfully treated using partial liquid ventilation (PLV). Pulmonary hypertension associated with CDH has proven difficult to treat, but inhaled nitric oxide, which is a potent highly selective pulmonary vasodilator, may have potential. The aim of this study was to assess PLV in CDH and to document the effect of nitric oxide when administered through perfluorocarbon. METHODS: This study using the lamb CDH model consisted of two groups; a conventional mechanically ventilated (CMV) group and a PLV group. At 1 and 3 hours, nitric oxide (80 ppm) was given for 15 minutes. Data collected included blood gases, pulmonary function tests, pulmonary and systemic blood pressure. RESULTS: After 30 minutes of ventilation, blood gases in the PLV group were all significantly improved (P < .001): pH, CMV 6.92 +/- 0.15 versus PLV 7.24 +/- 0.11; P(CO2), CMV 139 +/- 26 mmHg versus PLV 52 +/- 11 mmHg; P(O2), CMV 26 +/- 15 mmHg versus PLV 184 +/- 60 mmHg. In addition, there was a significant increase in dynamic compliance and a reduction in pulmonary hypertension. Nitric oxide was only efficacious in the PLV group, causing a further increase in oxygenation and a decrease in pulmonary hypertension. These effects were reversed when the nitric oxide was stopped. CONCLUSION: This study shows that PLV both improves gas exchange and pulmonary mechanics in CDH and allows the effective delivery of nitric oxide to reduce the pulmonary hypertension associated with CDH.

Air trapping causes a Ca2(+)-channel-mediated increase in pulmonary vascular resistance in neonatal lambs.

Air trapping and alveolar hyperinflation may occur during mechanical ventilation in the presence of severe airway obstruction, during fast ventilator rates, and when expiratory time is compromised. Inadvertent positive end-expiratory pressure may occur with air trapping and increased mean airway pressure. The pulmonary artery pressure response to air trapping, produced during volume-regulated time-cycled ventilation, was studied in neonatal lamb lungs, isolated in situ, and perfused at a constant flow rate (50-75 ml.kg-1.min-1), both before and after Ca2(+)-channel blockade with verapamil (5 mg). The hub of the endotracheal tube was narrowed to a 1.5-mm orifice to produce fixed proximal airway obstruction. Air trapping was then produced by lengthening inspiratory time from 25 to 80%, at zero end-expiratory pressure. The magnitude of inadvertent positive end-expiratory pressure due to air trapping was estimated by end-expiratory occlusion pressure. End-expiratory occlusion pressure was 0.20 +/- 0.03 kPa (1.7 +/- 0.2 mm Hg) and 1.60 +/- 0.01 kPa (11.8 +/- 1.0 mm Hg), at 25 and 80% inspiratory times, respectively. On lengthening inspiratory time, mean pulmonary artery pressure (mPpa) increased briskly within 30 s followed by a gradual increase over the next 4 min. Verapamil blunted both the brisk and the gradual increase in mPpa on lengthening inspiratory time. Lengthening inspiratory time increased the mPpa by 2.0 +/- 0.1 kPa (14.7 +/- 0.8 mm Hg) from baseline, and verapamil reduced this increase to 1.3 +/- 0.1 kPa (10.1 +/- 0.6 mm Hg; p less than 0.05 by analysis of variance).(ABSTRACT TRUNCATED AT 250 WORDS)

Perfluorocarbon-associated gas exchange.

BACKGROUND AND METHODS: Liquid ventilation with oxygenated perfluorocarbon eliminates surface tension due to pulmonary air/fluid interfaces, and improves pulmonary function and gas exchange in surfactant deficiency. In liquid ventilation, perfluorocarbon is oxygenated, purged of CO2, and cycled into and out of the lungs using an investigational device. A new approach, perfluorocarbon-associated gas exchange, uses a conventional ventilator and combines features of liquid ventilation and continuous positive-pressure breathing. In 13 normal piglets, a volume of perfluorocarbon equivalent to the normal functional residual capacity (30 mL/kg) was instilled into the trachea, left in situ, and volume-regulated gas ventilation (FIO2 1.0) was resumed. For 1 hr, perfluorocarbon was continuously bubble-oxygenated within the lungs, where it directly participated in gas exchange. RESULTS: PaO2 and PaCO2 averaged 401 +/- 51 and 40 +/- 4 torr (53.6 +/- 6.8 and 5.3 +/- 0.5 kPa), respectively. Peak airway pressure during perfluorocarbon-associated gas exchange (22 +/- 2 cm H2O at 1 hr) and during continuous, positive-pressure breathing (23 +/- 4 cm H2O) were nearly identical. Venous oxygen saturation and pH were normal (73 +/- 8% and 7.43 +/- 0.05, respectively, at 1 hr). CONCLUSIONS: Perfluorocarbon-associated gas exchange was uniformly well tolerated, and its efficiency approached that of continuous positive-pressure breathing. Applications of perfluorocarbon technology to lung disease may not be limited by existing instrumentation.

Liquid ventilation: it's not science fiction anymore.

Liquid ventilation is, by all initial considerations, an unconventional concept. Decades of research, however, have found that by using perfluorocarbons, which are capable of holding high concentrations of critical gases such as oxygen and carbon dioxide, gas exchange optimal enough to support life is possible with no known toxic effects. The earliest method of liquid ventilation, tidal liquid breathing, involved infusion and active removal of tidal volumes of perfluorocarbons by a liquid ventilator for gas exchange. Recently, a new method of partial liquid breathing, called perfluorocarbon-associated gas exchange, makes the process of liquid ventilation simpler by using conventional gas ventilators. Current research is showing great promise in the use of liquid ventilation for patients with pulmonary pathology. Critical care nurses should become knowledgeable of this new mode of ventilation and be prepared to meet the special needs of this unique population.

Cardiopulmonary resuscitation in a pediatric ICU.

A 30-month, retrospective study of CPR was undertaken in a 10-bed, medical/surgical pediatric ICU (PICU). The 121 episodes of CPR reviewed represented 81 of 1357 admissions and 7537 cumulative days of PICU care. Of the 121 CPR attempts, 64% were initially successful, 48% were associated with at least 24-h survival, and 31% were followed by discharge from PICU. Unlike pediatric arrests outside the hospital or on general pediatric wards, PICU arrests were seldom unanticipated, were commonly nonrespiratory in origin, and generally occurred in spite of aggressive support. Of 118 PICU deaths during the study period, 45 (38%) were associated with CPR. In the 73 remaining PICU deaths, CPR had been withheld because of an order not to resuscitate. CNS status before arrest was the most important factor influencing outcome. In this pediatric population, 29% were noncomatose survivors 24 h after more than 30 min of resuscitation.

Balloon occlusion of atrial septal defect to assess right ventricular capability in hypoplastic right heart syndrome.

Early surgery for forms of hypoplastic right heart syndrome may increase right ventricular size but could leave the patient with a residual right-to-left atrial shunt. Previous attempts to assess the capability of the right ventricle to accept systemic venous return have relied on angiographic estimates of tricuspid valve and right ventricular sizes. Since the minimum adequate sizes have not been established, we used a more physiologic technique of temporarily occluding the interatrial communication with a balloon-tipped catheter at cardiac catheterization in six consecutive patients. Five patients tolerated complete occlusion, although the tricuspid valve anulus diameter was less than the fifth percentile in all, and right ventricular volume was less than the fifth percentile in four. These five underwent surgical closure of an interatrial communication without evidence of postoperative systemic venous hypertension. Attempted occlusion in the sixth patient caused profound systemic venous hypoxia and surgical closure was not attempted. Temporary balloon occlusion may improve selection of patients for definitive operation.

Cardiopulmonary effects of unilateral airway pressure changes in intact infant lambs.

Direct effects of airway pressure changes on the pulmonary vascular bed of the intact infant lamb were studied under chloralose anesthesia using a preparation developed to permit independent ventilation of right and left lungs and independent measurement of right and left lung blood flow. A specially designed endobronchial tube eliminated the need for thoracotomy the day of study. Unilateral changes in positive end-expiratory pressure (PEEP) during volume-regulated ventilation increased ipsilateral but not contralateral airway pressure, confirming adequate separation of right and left lungs and suggesting rigidity of the mediastinum. Such interventions ( UPEEP ) at levels of 5, 10, and 15 cmH2O reduced ipsilateral but not contralateral pulmonary blood flow (by 10, 25, and 46%, respectively) but did not alter end-tidal PCO2 of either lung. UPEEP had less effect on cardiac output, stroke volume, right atrial, left atrial, esophageal, and pulmonary arterial pressures than did PEEP applied to both lungs. Because this preparation separates the predominantly direct effects of UPEEP on the ipsilateral lung from its indirect effects on the contralateral lung, it is well suited to studies of direct pulmonary vascular effects of airway pressure changes in an intact closed-chest preparation with reactive pulmonary vasculature.

Perfluorocarbon-associated gas exchange (partial liquid ventilation) in respiratory distress syndrome: a prospective, randomized, controlled study.

OBJECTIVE: To determine the efficacy of perfluorocarbon-associated gas exchange (partial liquid ventilation) in respiratory distress syndrome. DESIGN: Prospective, randomized, controlled study. SETTING: State University of New York at Buffalo, School of Medicine and Biomedical Sciences. SUBJECTS: Eleven premature lambs with respiratory distress syndrome, delivered by cesarean section. INTERVENTIONS: Five lambs were supported by conventional mechanical ventilation alone. Six lambs were switched to perfluorocarbon-associated gas exchange after 60 to 90 mins of conventional mechanical ventilation. Perfluorocarbon-associated gas exchange was accomplished by instilling a volume of liquid perfluorocarbon equivalent to normal functional residual capacity (30 mL/kg) into the trachea, performing 3 to 4 mins of tidal liquid ventilation, and, at end-expiration, with liquid functional residual capacity of 30 mL/kg remaining in the lung, reconnecting the animal to the volume ventilator for gas tidal volumes. MEASUREMENTS AND MAIN RESULTS: Serial arterial blood gases and lung mechanics were measured. While receiving conventional ventilation, all animals developed progressive hypoxemia, hypercarbia, and acidosis. However, in the perfluorocarbon-associated gas exchange group, within 5 mins of the initiation of perfluorocarbon-associated gas exchange, mean PaO2 increased four-fold, from 59 +/- 6 torr (7.9 +/- 0.8 kPa) during conventional ventilation to 250 +/- 28 torr (33.3 +/- 3.7 kPa; p < .05) during perfluorocarbon-associated gas exchange, and this increase was sustained at 60 mins of perfluorocarbon-associated gas exchange (268 +/- 38 torr; 35.7 +/- 5.1 kPa; p < .05). Mean PaCO2 decreased progressively from 62 +/- 4 torr (8.3 +/- 0.5 kPa) during conventional ventilation to 38 +/- 3.3 torr (5.1 +/- 0.4 kPa) at 60 mins of perfluorocarbon-associated gas exchange (p < .05). Mean pH concomitantly increased. Dynamic compliance increased three-fold within 15 mins of instituting perfluorocarbon-associated gas exchange, from 0.31 +/- 0.02 mL/cm H2O during conventional ventilation to 0.90 +/- 0.11 mL/cm H2O during perfluorocarbon-associated gas exchange, and this increase was sustained at 60 mins of perfluorocarbon-associated gas exchange (p < .05). Mean peak expiratory flow and mean expiratory resistance were essentially unchanged during perfluorocarbon-associated gas exchange as compared with conventional ventilation in the same group. CONCLUSIONS: We conclude that perfluorocarbon-associated gas exchange, which employs liquid functional residual capacity and gas tidal volumes delivered by a conventional ventilator, can facilitate oxygenation and CO2 removal, and dramatically improve lung mechanics in the premature lamb with respiratory distress syndrome.

Positive end-expiratory pressure-induced, calcium-channel-mediated increases in pulmonary vascular resistance in neonatal lambs.

OBJECTIVES: a) To study the dose response of the calcium-channel-mediated increases in pulmonary vascular resistance with different levels of positive end-expiratory pressure; b) to study the reversibility of the calcium-channel mediated increases in pulmonary vascular resistance after discontinuation of positive end-expiratory pressure; and c) to study the effect of cyclooxygenase and lipoxygenase inhibition on the calcium-channel mediated increases in pulmonary vascular resistance. DESIGN: A prospective, multiexperimental, dose response study. SETTING: Laboratory setting in a university hospital. SUBJECTS: Twenty-three 4- to 10-day-old neonatal lambs. INTERVENTIONS AND MEASUREMENTS: Lungs of neonatal lambs were isolated in situ, and perfused at a constant flow rate, and ventilated at a fixed tidal volume and rate. Mean pulmonary arterial pressure responses to the application and discontinuation of four levels (3.7, 7.4, 11, and 14.7 mm Hg) of positive end-expiratory pressure were studied before and after calcium-channel blockade with verapamil (5 mg) (n = 12). In addition, the mean pulmonary arterial pressure response to 11 mm Hg of positive end-expiratory pressure was studied before and after inhibition of cyclooxygenase with indomethacin (10 mg/kg) (n = 6) and lipoxygenase with diethylcarbamazine (100 mg/kg) (n = 5). RESULTS: The magnitude of the calcium-channel-dependent mean pulmonary arterial pressure response 4 mins after the application of positive end-expiratory pressure was dose related (2.1, 3.0, 4.1, and 5.5 mm Hg with 3.7, 7.4, 11.0, and 14.7 mmHg positive end-expiratory pressure, respectively) and entirely reversible on discontinuation of positive end-expiratory pressure with a time course of 2 to 4 mins. Neither indomethacin nor diethylcarbamazine affected the pulmonary arterial pressure responses to positive end-expiratory pressure. Airway pressure changes with positive end-expiratory pressure were not affected by verapamil, indomethacin, or diethylcarbamazine. CONCLUSIONS: The calcium-channel-mediated pulmonary arterial pressure responses with positive end-expiratory pressure, applied during continuous positive pressure breathing, occur even at low levels of positive end-expiratory pressure, are dose dependent, and are not abolished by treatment with indomethacin or diethylcarbamazine.