A simple automated method for measuring pressure-volume curves during mechanical ventilation

Measurement of respiratory compliance is advocated for assessing the severity of acute respiratory failure (ARF). Recently, the administration of an automated constant flow of 15 L/min was proposed as a method easier to implement at the bedside than supersyringe or inspiratory occlusions methods. However, pressure-volume (P-V) curves were shifted to the right because of the resistive properties of the respiratory system. The aim of this study was to compare the P-V curves obtained using two constant flows-3 and 9 L/min-during volume-controlled mechanical ventilation with those obtained with the supersyringe and the inspiratory occlusions methods. Fourteen paralyzed patients with ARF were studied. The supersyringe and the inspiratory occlusions methods were performed according to usual recommendations. The new automated method was performed during volume-controlled mechanical ventilation by setting the inspiratory:expiratory ratio at 80%, the respiratory frequency at 5 breaths/min, and the tidal volume at 500 or 1,500 ml. These peculiar ventilatory settings were equivalent to administering a constant flow of 3 or 9 L/min during a 9.6-s inspiration. Esophageal and airway pressures were recorded. P-V curves obtained by the 3-L/min constant-flow method were identical to those obtained by the reference methods, whereas the P-V curve obtained by the 9-L/min constant flow was slightly shifted to the right. The slopes of the P-V curves and the lower inflection points were not different between all methods, indicating that the resistive component induced by administering a constant flow equal to or less than 9 L/min is not of clinical relevance. Because the 3-L/min constant-flow method is not artifacted by the resistive properties of the respiratory system and does not require any other equipment than a ventilator, it is an easy-to-implement, inexpensive, safe, and reliable method for measuring the thoracopulmonary P-V curve at the bedside.

Intravenous almitrine combined with inhaled nitric oxide for acute respiratory distress syndrome. The NO Almitrine Study Group

Inhaled nitric oxide (iNO), a selective pulmonary vasodilator and intravenously administered almitrine, a selective pulmonary vasoconstrictor, have been shown to increase PaO2 in patients with acute respiratory distress syndrome (ARDS). This prospective study was undertaken to assess the cardiopulmonary effects of combining both drugs. In 48 consecutive patients with early ARDS, cardiorespiratory parameters were measured at control, after iNO 5 ppm, after almitrine 4 micrograms. kg-1. min-1, and after the combination of both drugs. In 30 patients, dose response to 2, 4, and 16 micrograms. kg-1. min-1 of almitrine with and without NO was determined. Almitrine and lactate plasma concentrations were measured in 17 patients. Using pure O2, PaO2 increased by 75 +/- 8 mm Hg after iNO, by 101 +/- 12 mm Hg after almitrine 4 micrograms. kg-1. min-1, and by 175 +/- 18 mm Hg after almitrine combined with iNO (p < 0.001). In 63% of the patients, PaO2 increased by more than 100% with the combination of both drugs. Mean pulmonary artery pressure (Ppa) increased by 1.4 +/- 0.2 mm Hg with almitrine 4 micrograms/kg/ min (p < 0.001) and decreased by 3.4 +/- 0.4 mm Hg with iNO and by 1.5 +/- 0.3 mm Hg with the combination (p < 0.001). The maximum increase in PaO2 was obtained at almitrine concentrations <= 4 micrograms. kg-1. min-1, whereas almitrine increased Ppa dose-dependently. Almitrine plasma concentrations also increased dose-dependently and returned to values close to zero after 12 h. In many patients with early ARDS, the combination of iNO 5 ppm and almitrine 4 micrograms. kg-1. min-1 dramatically increases PaO2 without apparent deleterious effect allowing a rapid reduction in inspired fraction of O2. The long-term consequences of this immediate beneficial effect remain to be determined.

A computed tomography scan assessment of regional lung volume in acute lung injury. The CT Scan ARDS Study Group

The lobar and cephalocaudal distribution of aerated and nonaerated lung and of PEEP-induced alveolar recruitment is unknown in acute lung injury (ALI). Dimensions of the lungs and volumes of aerated and nonaerated parts of each pulmonary lobe were measured using a computerized tomographic quantitative analysis and compared between 21 patients with ALI and 10 healthy volunteers. Distribution of PEEP-induced alveolar recruitment along the anteroposterior and cephalocaudal axis and influence of the resting volume of nonaerated lower lobes were also assessed. Anteroposterior and transverse dimensions of the lungs of the patients were similar to those of healthy volunteers, whereas cephalocaudal dimensions were reduced by more than 15%. Total lung volume (aerated plus nonaerated lung) was reduced by 27%. Volumes of upper and lower lobes were 99 and 48% of normal values. In addition to an anteroposterior gradient in the distribution of aerated and nonaerated areas, a cephalocaudal gradient was also observed. Nonaerated areas were predominantly found in juxtadiaphragmatic regions. PEEP-induced alveolar recruitment was more pronounced in nondependent than in dependent regions and in cephalad than in caudal regions. A significant correlation between resting volume of nonaerated lower lobes and regional PEEP-induced alveolar recruitment was observed. In ALI, loss of lung volume involves predominantly lower lobes. The thorax shortens along its cephalocaudal axis. PEEP-induced alveolar recruitment predominates in nondependent and cephalad lung regions and is inversely correlated with the resting volume of nonaerated lung.

A lung computed tomographic assessment of positive end-expiratory pressure-induced lung overdistension

The aim of this study was to assess positive end-expiratory pressure (PEEP)-induced lung overdistension and alveolar recruitment in six patients with acute lung injury (ALI) using a computed tomographic (CT) scan method. Lung overdistension was first determined in six healthy volunteers in whom CT sections were obtained at FRC and at TLC with a positive airway pressure of 30 cm H2O. In patients, lung volumes were quantified by the analysis of the frequency distribution of CT numbers on the entire lung at zero end-expiratory pressure (ZEEP) and PEEP. In healthy volunteers at FRC, the distribution of the density histograms was monophasic with a peak at -791 +/- 12 Hounsfield units (HU). The lowest CT number observed was -912 HU. At TLC, lung volume increased by 79 +/- 35% and the peak CT number decreased to -886 +/- 26 HU. More than 70% of the increase in lung volume was located below -900 HU, suggesting that this value can be considered as the threshold separating normal aeration from overdistension. In patients with ALI, at ZEEP the distribution of density histograms was either monophasic (n = 3) or biphasic (n = 3). The mean CT number was -319 +/- 34 HU. At PEEP 13 +/- 3 cm H2O, lung volume increased by 47 +/- 19% whereas mean CT number decreased to -538 +/- 171 HU. PEEP induced a mean alveolar recruitment of 320 +/- 160 ml and a mean lung overdistension of 238 +/- 320 ml. In conclusion, overdistended lung parenchyma of healthy volunteers is characterized by a CT number below -900 HU. This threshold can be used in patients with ALI for differentiating PEEP-induced alveolar recruitment from lung overdistension.

Factors influencing indoor concentrations of nitric oxide in a Parisian intensive care unit

In low concentrations, inhaled nitric oxide (NO) increases arterial oxygenation in patients with severe acute respiratory distress syndrome. When present in the ambient atmosphere, NO and its oxidative derivate, nitrogen dioxide (NO2), are considered pollutants. The aim of this study was to assess whether the administration of inhaled NO to mechanically ventilated patients was associated with an increased risk of exposure to NO and NO2 for medical and paramedical staff. During a 1-yr period, indoor and outdoor NO and NO2 concentrations were measured using chemiluminescence in a 14-bed intensive care unit (ICU) to assess the possible influence of therapeutic NO administration on indoor pollution. Ambient concentrations of NO within the ICU were 237 +/- 147 parts per billion (ppb) during periods of NO administration and 289 +/- 147 ppb during periods without NO administration (mean +/- SD, NS). Indoor concentrations of NO and NO2 were entirely dependent on outdoor concentrations and were mainly influenced by climatic conditions such as atmospheric pressure, mass of clouds, and speed of the wind. Therapeutic administration of concentrations of inhaled NO < or = 5 ppm to critically ill patients did not affect the ambient concentration of NO and NO2 within the ICU, which was mainly dependent on the outdoor air pollution. As a consequence, scavenging of exhaust NO from the breathing circuit in the ventilator does not appear mandatory in ICUs located in areas with significant urban pollution when NO concentrations < or = 5 ppm are administered.

Factors influencing the tracheal fluctuation of inhaled nitric oxide in patients with acute lung injury

BACKGROUND

Inhaled nitric oxide (NO) improves arterial oxygenation in patients with acute lung injury (ALI) by selectively dilating pulmonary vessels perfusing ventilated lung areas. It can be hypothesized that NO uptake from the lung decreases with increasing ventilation perfusion mismatch. This study was undertaken to determine the factors influencing the fluctuation of tracheal NO concentration over the respiratory cycle as an index of NO pulmonary uptake in patients with ALI.

METHODS

By using a prototype system (Opti-NO) delivering a constant flow of NO only during the inspiratory phase, 3 and 6 ppm of NO were administered during controlled mechanical ventilation into a lung model and to 11 patients with ALI. All patients had a thoracic computed tomography (CT) scan. Based on an analysis of tomographic densities, lungs were divided into three zones: normally aerated (-1.000 to -500 Hounsfield units [HU]), poorly aerated (-500 to -100 HU), and nonaerated (-100 to +100 HU), and the volume of each zone was computed. Concentrations of NO in the inspiratory limb and trachea were continuously measured by a fast-response chemiluminescence apparatus.

RESULTS

In the lung model, tracheal NO concentration was stable with minor fluctuation. In contrast, in patients, tracheal NO concentration fluctuated widely during the respiratory cycle (55 +/- 10%). Because uptake of NO from the lungs was absent in the lung model but present in the patients, this fluctuation was considered as an index of pulmonary uptake of NO. This was further substantiated by (1) the coincidence of the peak and minimum tracheal NO concentration with the end-inspiratory and end-expiratory phases, respectively, and (2) continued decrease of tracheal NO concentration during prolonged expiratory phase. In patients with ALI, the fluctuation of tracheal NO concentration expressed as the difference between inspiratory and expiratory NO concentrations divided by inspiratory NO concentration was greater at 6 ppm than at 3 ppm (P < 0.01), was linearly correlated with normally aerated lung volume, inversely correlated with alveolar dead space and with poorly aerated lung volume.

CONCLUSION

In patients with ALI, fluctuation of tracheal NO concentration over the respiratory cycle can be considered as an index of NO uptake from the lungs that depends on aerated lung volume and perfusion of ventilated lung areas. At bedside, it may be used to follow the evolution of ventilation-perfusion mismatch.

Distribution of inhaled nitric oxide during sequential and continuous administration into the inspiratory limb of the ventilator

OBJECTIVES

The concentrations of nitric oxide (NO) in the ventilatory circuits and the patient's airways were compared between sequential (SQA) and continuous (CTA) administration during inspiratory limb delivery.

DESIGN

Prospective controlled study.

SETTING

14-bed Surgical Intensive Care Unit of a teaching University hospital.

PATIENTS AND PARTICIPANTS

Eleven patients with acute lung injury on mechanical ventilation and two healthy volunteers.

INTERVENTIONS

A prototype NO delivery device (Opti-NO) and César ventilator were set up in order to deliver 1, 3 and 6 parts per million (ppm) of NO into the bellows of a lung model in SQA and CTA. Using identical ventilatory and Opti-NO settings, NO was administered to the patients with acute lung injury.

MEASUREMENTS AND RESULTS

NO concentrations measured from the inspiratory limb [INSP-NOMeas] and the trachea [TRACH-NOMeas] using fast response chemiluminescence were compared between the lung model and the patients using controlled mechanical ventilation with a constant inspiratory flow. INSP-NOMeas were stable during SQA and fluctuated widely during CTA (fluctuation at 6 ppm = 61% in the lung model and 58 +/- 3% in patients). In patients, [TRACH-NOMeas] fluctuated widely during both modes (fluctuation at 6 ppm = 55 +/- 3% during SQA and 54 +/- 5% during CTA). The NO flow requirement was significantly lower during SQA than during CTA (74 +/- 0.5 vs 158 +/- 2.2 ml.min-1 to attain 6 ppm, p = 0.0001). INSP-NOMeas were close to the values predicted using a classical formula only during SQA (bias = -0.1 ppm, precision = +/-1 ppm during SQA; bias = 2.93 ppm and precision = +/-3.54 ppm during CTA). During SQA, INSP-NOMeas varied widely in healthy volunteers on pressure support ventilation.

CONCLUSIONS

CTA did not provide homogenous mixing of NO with the tidal volume and resulted in fluctuating INSP-NOMeas. In contrast, SQA delivered stable and predictable NO concentrations during controlled mechanical ventilation with a constant inspiratory flow and was economical compared to CTA. However, SQA did not provide stable and predictable NO concentrations during pressure support ventilation.

[Pharmacologic treatment of hypoxemia in adult respiratory distress syndrome]

New drugs that improve arterial oxygenation (nitric oxide, almitrine, inhaled prostacyclin and cyclooxygenase inhibitors) are useful in the treatment of severe hypoxemia unresponsive to conventional treatment that is mainly seen in patients with acute respiratory distress syndrome (ARDS). By acting selectively on pulmonary blood flow and redistributing it, these drugs achieve effects unattainable until now. Thus, they decrease perfusion in non-ventilated zones (V/Q = O) responsible for shunt, or increase perfusion in well ventilated zones, guaranteeing adequate oxygenation. To apply these drugs the physician must understand their mechanism of action, guidelines for dosing, constraints on their use and side effects.

Permissive hypercapnia with and without expiratory washout in patients with severe acute respiratory distress syndrome

BACKGROUND

Permissive hypercapnia is a ventilatory strategy aimed at avoiding lung volutrauma in patients with severe acute respiratory distress syndrome (ARDS). Expiratory washout (EWO) is a modality of tracheal gas insufflation that enhances carbon dioxide removal during mechanical ventilation by reducing dead space. The goal of this prospective study was to determine the efficacy of EWO in reducing the partial pressure of carbon dioxide (PaCO2) in patients with severe ARDS treated using permissive hypercapnia.

METHODS

Seven critically ill patients with severe ARDS (lung injury severity score, 3.1 +/- 0.3) and no contraindications for permissive hypercapnia were studied. On the first day, hemodynamic and respiratory parameters were measured and the extent of lung hyperdensities was assessed using computed tomography. A positive end-expiratory pressure equal to the opening pressure identified on the pressure-volume curve was applied. Tidal volume was reduced until a plateau airway pressure of 25 cm H2O was reached. On the second day, after implementation of permissive hypercapnia, EWO was instituted at a flow of 15 l/min administered during the entire expiratory phase into the trachea through the proximal channel of an endotracheal tube using a ventilator equipped with a special flow generator. Cardiorespiratory parameters were studied under three conditions: permissive hypercapnia, permissive hypercapnia with EWO, and permissive hypercapnia.

RESULTS

During permissive hypercapnia, EWO decreased PaCO2 from 76 +/- 4 mmHg to 53 +/- 3 mmHg (-30%; P < 0.0001), increased pH from 7.20 +/- 0.03 to 7.34 +/- 0.04 (P < 0.0001), and increased PaO2 from 205 +/- 28 to 296 +/- 38 mmHg (P < 0.05). The reduction in PaCO2 was accompanied by an increase in end-inspiratory plateau pressure from 26 +/- 1 to 32 +/- 2 cm H2O (P = 0.001). Expiratory washout also decreased cardiac index from 4.6 +/- 0.4 to 3.7 +/- 0.3 l.min-1.m-2 (P < 0.01), mean pulmonary arterial pressure from 28 +/- 2 to 25 +/- 2 mmHg (P < 0.01), and true pulmonary shunt from 47 +/- 2 to 36 +/- 3% (P < 0.01).

CONCLUSIONS

Expiratory washout is an effective and easy-to-use ventilatory modality to reduce PaCO2 and increase pH during permissive hypercapnia. However, it significantly increases airway pressures and lung volume through expiratory flow limitation, reexposing some patients to a risk of lung volutrauma if the extrinsic positive end-expiratory pressure is not substantially reduced.

Histology and microbiology of ventilator-associated pneumonias

A good knowledge of histological and bacteriological characteristics of experimental and human ventilator-associated bronchopneumonias (BPN) is of critical importance for the intensivist. BPN can be experimentally produced by intratracheal inoculation of microorganisms in high concentrations and ventilator-associated BPN by ventilating baboons with oleic-acid lung injury. Experimental ventilator-associated BPN is frequently polymicrobial, and bacterial lung burden increases with the severity of lung infection. In human ventilator-associated BPN, gross examination is of poor value for diagnosing lung infection. Four histologic categories of increasing severity have been described: bronchiolitis, focal bronchopneumonia, confluent bronchopneumonia, and lung abscess. Nonspecific inflammatory lesions are always associated with histologic lung infection: primary lung infection causes secondary inflammatory lung damage, whereas non-specific alveolar injury is rapidly superinfected when the lungs are mechanically ventilated. Infectious pulmonary lesions are disseminated within all pulmonary segments but preferentially found in the dependent segments. This fact suggests that ventilator-associated BPN has a bronchogenic origin and that gravity plays an important role in the dissemination of microorganisms within lung parenchyma. Ventilator-associated BPN is a nosocomial infection with a predominance of gram-negative bacteria, staphylococci species, and yeasts. It is frequently polymicrobial, and the lung bacterial burden depends on the histologic grade, the administration of topical and intravenous antibiotics, and the host's local antibacterial defenses. The bacterial complexity of human lung infection does not support the concept of a threshold for the diagnosis of nosocomial BPN. Intensivists should always keep in mind that human ventilator-associated BPN is a complex and rapidly changing entity.

Posttransfusion purpura-like syndrome associated with CD36 (Naka) isoimmunization

BACKGROUND

CD36 deficiency, which could lead to CD36 isoimmunization, has been reported in the Japanese population. CD36 isoantibody has been involved in platelet transfusion refractoriness.

CASE REPORT

A 50-year-old woman originally from Corsica developed severe acute thrombocytopenia after massive transfusion. She was found to be CD36 deficient, and platelet immunoassays revealed a CD36 (Naka) platelet isoantibody. Although the involvement of another mechanism could not be entirely ruled out, the thrombocytopenia was attributed to posttransfusion purpura-like syndrome. The antibody was also involved in platelet transfusion refractoriness. CD36 deficiency was present in two members of the patient's family as well. Flow cytometry studies demonstrated the absence of CD36 expression on the surface of blood monocytes and cultured erythroblasts and megakaryocytes from one of the two CD36-deficient family members studied, but, in the absence of previous immunization, these CD36-deficient patients were not isoimmunized. In contrast, CD36 deficiency was not found in a population of 808 healthy blood donors in the Paris, France, area.

CONCLUSION

CD36 isoantibody might be involved in some cases of posttransfusion purpura and platelet transfusion refractoriness. These findings also confirm the extremely low frequency of CD36 deficiency among whites.

Systemic gas embolism complicating pulmonary contusion. Diagnosis and management using transesophageal echocardiography

Systemic air embolism has been frequently reported after penetrating thoracic trauma. In blunt thoracic trauma, systemic air embolism has been rarely diagnosed, and then only after an invasive procedure such as thoracotomy. Transesophageal echocardiography has been recently introduced for the early assessment of trauma patients and is considered a sensitive noninvasive procedure to diagnose air embolism. We report three cases of systemic air embolism in patients with pulmonary contusion secondary to a blunt thoracic trauma requiring controlled ventilation. Transesophageal echocardiography was performed for evaluation of hemodynamic instability, and it showed air bubbles in the left atrium and left ventricle during the insufflation phase, which disappeared during apnea. A decrease in airway pressure (release of PEEP, low tidal volume, high frequency jet ventilation) significantly reduced the systemic air embolism. We concluded that systemic air embolism can occur after blunt thoracic trauma, and transesophageal echocardiography enables a rapid and accurate diagnosis that may be useful for therapeutic management.

Inhibition of platelet aggregation by inhaled nitric oxide in patients with acute respiratory distress syndrome

BACKGROUND

Nitric oxide inhibits platelet adhesion and aggregation in vitro. The aim of this prospective study was to assess the platelet antiaggregating activity of nitric oxide administered to patients with acute respiratory distress syndrome (ARDS) at increasing concentrations.

METHODS

In six critically ill patients (mean age 37 +/- 16 yr) with ARDS (lung injury severity score > or = 2.2), the lungs were mechanically ventilated with inhaled nitric oxide (1, 3, 10, 30, and 100 ppm) randomly administered. Patients with cardiac dysrhythmias, septic shock, an underlying hemostasis disorder (constitutive or acquired), a platelet count less than 100 Giga/l, or a decreased platelet aggregation and those treated with antiplatelet or anticoagulant agents were excluded. Platelet aggregation was measured without nitric oxide and at each nitric oxide concentration in platelet-rich plasma issued from radial artery. Ivy bleeding time using a horizontal incision was simultaneously performed.

RESULTS

After nitric oxide, a non-dose-dependent but statistically significant decrease in ex vivo platelet aggregation induced by three aggregating agents was observed: adenosine diphosphate = -56 +/- 18%, collagen = -37 +/- 18%, and ristocetin = -45 +/- 18% (P < 0.05). In each individual, Ivy bleeding time remained within normal values measured in healthy volunteers, and variations after nitric oxide did not correlate with changes in platelet aggregation. Simultaneously, arterial oxygenation improved significantly and pulmonary artery pressure decreased significantly.

CONCLUSIONS

In patients with ARDS and without preexisting coagulation disorders, the beneficial effects of inhaled nitric oxide on arterial oxygenation and pulmonary circulation are associated with a significant inhibition of platelet aggregation. This antithrombotic effect is not associated with a significant prolongation of the bleeding time.

Factors influencing cardiopulmonary effects of inhaled nitric oxide in acute respiratory failure

The aim of this prospective study was to determine factors influencing effects of inhaled nitric oxide (NO) on the pulmonary circulation and on gas exchange in critically ill patients with acute lung injury. Twenty-one hypoxemic patients with acute respiratory failure (PaO2 = 127 +/- 69 mm Hg during intermittent positive pressure ventilation, FiO2 = 1), were mechanically ventilated with 2 ppm NO and pure oxygen. The effect of positive end-expiratory pressure (PEEP) on alveolar recruitment was assessed on an anatomic basis using a high-resolution and spiral thoracic computed tomographic (CT) scan. Four conditions were studied in random order: zero end-expiratory pressure (ZEEP), ZEEP + 2 ppm NO, 10 cm H2O PEEP, 10 cm H2O PEEP + 2 ppm NO. During ZEEP and PEEP, NO significantly decreased pulmonary vascular resistance index (PVRI), mean pulmonary arterial pressure (MPAP), true pulmonary shunt (Qs/QT), and alveolar dead space (VDA/VT) and significantly increased PaO2 (p < 0.01). During ZEEP, NO-induced decreases in PVRI (delta PVRI) and MPAP (delta MPAP) were significantly correlated to baseline PVRI and MPAP (delta PVRI = -0.5 PVRI + 125, r = 0.97, p < 0.01 and delta MPAP = -0.28 MPAP + 4.8, r = 0.69, p < 0.05). These changes were not potentiated by PEEP-induced alveolar recruitment. The NO-induced increase in PaO2 (delta PaO2) was not significantly correlated with baseline PaO2 but was correlated with baseline PVRI (delta PaO2 = 0.11 PVRI + 30, r = 0.67, p < 0.05). In patients in whom PEEP was associated with alveolar recruitment, NO increased PaO2 by 66 +/- 24 mm Hg during ZEEP and by 104 +/- 26 mm Hg during PEEP (p < 0.01). In patients in whom PEEP did not induce alveolar recruitment, the NO-induced increase in PaO2 was similar during ZEEP and PEEP conditions (+70 +/- 15 mm Hg versus +76 +/- 12 mm Hg, NS). In patients with adult respiratory distress syndrome, factors determining NO-induced improvement in arterial oxygenation and pulmonary vascular effects are PEEP-induced alveolar recruitment and the baseline level of pulmonary vascular resistance.

Risk factors and clinical relevance of nosocomial maxillary sinusitis in the critically ill

The incidence of infectious maxillary sinusitis (IMS) and its clinical relevance was prospectively studied in 162 consecutive critically ill patients who were mechanically ventilated for a period longer than 7 d. All had a paranasal computed tomographic (CT) scan within 48 h of admission and were divided into three groups according to the radiologic aspect of their maxillary sinuses: Group 1 = normal maxillary sinuses (n = 40), Group 2 = maxillary mucosal thickening (n = 26), Group 3 = radiologic maxillary sinusitis (RMS) defined as the presence of an air fluid level and/or opacification of maxillary sinuses (n = 96). Group 1 patients were randomized between nasal and oral endotracheal intubation with a gastric intubation performed via the same route and had a second paranasal CT scan 7 d later. Endotracheal and gastric tubes were left in their original position in Group 2 patients and a second paranasal CT scan was performed 7 d later. All patients of Group 3 underwent a transnasal puncture for bacteriologic analysis of maxillary sinus content. Forty-five spontaneously breathing patients served as a control group. In all patients with RMS, the occurrence of bronchopneumonia (BPN) was prospectively assessed for 7 d following the initial CT scan. Upon inclusion, only 25% of the patients had normal maxillary sinuses whereas all patients in the control group had normal paranasal CT scans. After 7 d, 46% of Group 2 patients had evidence of RMS. Risk factors for RMS were nasal placement and duration of endotracheal and gastric intubation.(ABSTRACT TRUNCATED AT 250 WORDS)

High-frequency jet ventilation vs continuous positive airway pressure for differential lung ventilation in patients undergoing resection of thoracoabdominal aortic aneurysm

Twenty patients, scheduled for surgical resection of thoracoabdominal aortic aneurysm were divided into two groups according to the type of differential lung ventilation used during graft replacement of the descending thoracic aorta. In the high-frequency jet ventilation (HFJV) group of ten patients, HFJV was applied to the left lung once collapsed and retracted by the surgeon, the patient lying in the right lateral decubitus and being intubated by a Carlens' tube. In the continuous positive airway pressure (CPAP) group of ten patients, CPAP was applied to the left lung at the same mean airway pressure as HFJV (1 kPa). Before anaesthetic induction, an arterial and a Swan-Ganz catheter were inserted for cardiovascular monitoring. The same anaesthetic technique using fentanyl 6 micrograms.kg-1, flunitrazepam 0.02 mg.kg-1 and pancuronium 0.1 mg.kg-1 was used for each patient. Haemodynamic and respiratory measurements were made; 15 min after positioning the patients in the right lateral decubitus using two-lung ventilation; 15 min after collapse and retraction of the left lung using one-lung ventilation and 15 min after using differential lung ventilation with CPAP or HFJV. Left lung collapse with conventional one-lung ventilation induced a dramatic decrease in arterial oxygenation: PaO2/FIO2 ratio decreased from 43 +/- 6 kPa to 20 +/- 8 kPa, alveolo-arterial oxygen difference increased from 24 +/- 7 kPa to 72 +/- 11 kPa and pulmonary shunt increased from 17 +/- 2% to 37 +/- 3%. Whereas differential lung ventilation with CPAP did not improve any of the respiratory parameters measured, differential lung ventilation with HFJV, significantly increased PaO2/FIO2 ratio to 41 +/- 14 kPa.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhaled nitric oxide reverses the increase in pulmonary vascular resistance induced by permissive hypercapnia in patients with acute respiratory distress syndrome

BACKGROUND

The aim of this prospective study was to determine if inhaled nitric oxide (NO) would reverse the increase in pulmonary arterial pressures and in pulmonary vascular resistance induced by acute permissive hypercapnia in patients with acute respiratory distress syndrome.

METHODS

In 11 critically ill patients (mean age 59 +/- 22 yr) with acute respiratory distress syndrome (Murray Score > or = 2.5), the lungs were mechanically ventilated with NO 2 ppm during both normocapnic and hypercapnic conditions. Four phases were studied: normocapnia (arterial carbon dioxide tension 38 +/- 6 mmHg, tidal volume (655 +/- 132 ml); normocapnia plus inhaled NO 2 ppm; hypercapnia (arterial carbon dioxide tension 65 +/- 15 mmHg, tidal volume 330 +/- 93 ml); and hypercapnia plus inhaled NO 2 ppm. Continuous recordings were made of heart rate, arterial pressure, pulmonary artery pressure, tracheal pressure, and tidal volume (by pneumotachograph). At the end of each condition, arterial pressure, pulmonary artery pressure, cardiac filling pressures, and cardiac output were measured. Simultaneous arterial and mixed venous blood samples were obtained to measure arterial oxygen tension, arterial carbon dioxide tension, mixed venous oxygen tension, arterial hemoglobin oxygen saturation, mixed venous hemoglobin oxygen saturation, pH, and blood hemoglobin and methemoglobin concentrations (by hemoximeter). In addition, plasma concentrations of catecholamines were measured with a radioenzymatic assay. In 5 patients, end-tidal carbon dioxide tension was measured with a nonaspirative infrared capnometer. Calculations were made of pulmonary vascular resistance index, systemic vascular resistance index, true pulmonary shunt, and alveolar dead space.

RESULTS

During hypercapnia, NO decreased pulmonary vascular resistance index from 525 +/- 223 to 393 +/- 142 dyn.s.cm-5.m-2 (P < 0.01), a value similar to that measured in normocapnic conditions (391 +/- 122 dyn.s.cm-5.m-2). It also reduced mean pulmonary artery pressure from 40 +/- 9 to 35 +/- 8 mmHg (P < 0.01). NO increased arterial oxygen tension (inspired oxygen fraction 1) from 184 +/- 67 to 270 +/- 87 mmHg during normocapnia and from 189 +/- 73 to 258 +/- 101 mmHg during hypercapnia (P < 0.01). NO decreased true pulmonary shunt during normocapnia (from 34 +/- 3% to 28 +/- 4%, P < 0.001) but had no significant effect on it during hypercapnia (39 +/- 7% vs. 38 +/- 8.5%). In five patients, NO resulted in a decrease in alveolar dead space from 34 +/- 7% to 28 +/- 10% in normocapnic conditions and from 30 +/- 9% to 22 +/- 10% in hypercapnic conditions (P < 0.05).

CONCLUSIONS

Inhaled NO completely reversed the increase in pulmonary vascular resistance index induced by acute permissive hypercapnia. It only partially reduced the pulmonary hypertension induced by acute permissive hypercapnia, probably because the flow component of the increase in pulmonary pressure (i.e., the increase in cardiac output) was not reduced by inhaled NO. A significant increase in arterial oxygenation after NO administration was observed during normocapnic and hypercapnic conditions. A ventilation strategy combining permissive hypercapnia and inhaled NO may reduce the potentially deleterious effects that permissive hypercapnia alone has on lung parenchyma and pulmonary circulation.

Inhaled nitric oxide in acute respiratory failure: dose-response curves

OBJECTIVE

To determine the dose-response curve of inhaled nitric oxide (NO) in terms of pulmonary vasodilation and improvement in PaO2 in adults with severe acute respiratory failure.

DESIGN

Prospective randomized study.

SETTING

A 14-bed ICU in a teaching hospital.

PATIENTS

6 critically ill patients with severe acute respiratory failure (lung injury severity score > or = 2.5) and pulmonary hypertension.

INTERVENTIONS

8 concentrations of inhaled NO were administered at random: 100, 400, 700, 1000, 1300, 1600, 1900 and 5000 parts per billion (ppb). Control measurements were performed before NO inhalation and after the last concentration administered. After an NO exposure of 15-20 min, hemodynamic parameters obtained from a fiberoptic Swan-Ganz catheter, blood gases, methemoglobin blood concentrations and intratracheal NO and nitrogen dioxide (NO2) concentrations, continuously monitored using a bedside chemiluminescence apparatus, were recorded on a Gould ES 1000 recorder. In 2 patients end-tidal CO2 was also recorded.

RESULTS

The administration of 100-2000 ppb of inhaled NO induced: i) a dose-dependent decrease in pulmonary artery pressure and in pulmonary vascular resistance (maximum decrease--25%); ii) a dose-dependent increase in PaO2 via a dose-dependent reduction in pulmonary shunt; iii) a slight but significant decrease in PaCO2 via a reduction in alveolar dead space; iv) a dose-dependent increase in mixed venous oxygen saturation (SVO2). Systemic hemodynamic variables and methemoglobin blood concentrations did not change. Maximum NO2 concentrations never exceeded 165 ppb. In 2 patients, 91% and 74% of the pulmonary vasodilation was obtained for inhaled NO concentrations of 100 ppb.

CONCLUSION

In hypoxemic patients with pulmonary hypertension and severe acute respiratory failure, therapeutic inhaled NO concentrations are in the range 100-2000 ppb. The risk of toxicity related to NO inhalation is therefore markedly reduced. Continuous SVO2 monitoring appears useful at the bedside for determining optimum therapeutic inhaled NO concentrations in a given patient.

Prevention of gram negative nosocomial bronchopneumonia by intratracheal colistin in critically ill patients. Histologic and bacteriologic study

OBJECTIVE

To evaluate the efficiency of intratracheal colistin in preventing nosocomial bronchopneumonia (BPN) in the critically ill.

DESIGN

Study evaluating the clinical incidence of nosocomial BPN in 2 groups of critically ill patients who receive or did not receive intratracheal colistin. BPN was assessed clinically in survivors and histologically in non-survivors.

SETTING

A 14-bed surgical intensive care unit.

PATIENTS

598 consecutive critically ill patients were studied during a prospective non-randomized study over a 40-month period.

INTERVENTIONS

251 patients--31 non-survivors and 220 survivors--did not receive intratracheal colistin and 347-42 non-survivors and 305 survivors--received intratracheal colistin for a 2-week period (1,600,000 units per 24 h).

MEASUREMENTS AND RESULTS

The incidence of nosocomial BPN was evaluated clinically in survivors, using repeated protected minibronchoalveolar lavages, and histologically in non-survivors via an immediate postmortem pneumonectomy (histologic and semi-quantitative bacteriologic analysis of one lung). The clinical incidence of nosocomial BPN was of 37% in coli (-) survivors and of 27% in coli (+) survivors (p < 0.01). This result was histologically confirmed in non-survivors, where the incidence of histologic BPN was of 61% in coli (-) patients and of 36% in coli (+) patients (p < 0.001). Emergence of BPN due to colistin-resistant micro-organisms was not observed. Because colistin was successful in preventing Gram-negative BPN and did not change the absolute number of Gram-positive BPN, the proportion of BPN caused by staphylococcus species was higher in group coli (+) patients (33% vs 16%). Mortality was not significantly influenced by the administration of colistin.

CONCLUSION

This study suggests that the administration of intratracheal colistin during a 2-week period significantly reduces the incidence of Gram-negative BPN without creating an increasing number of BPN due to colistin-resistant micro-organisms.

Histologic aspects of pulmonary barotrauma in critically ill patients with acute respiratory failure

OBJECTIVE

To describe histologically pulmonary barotrauma in mechanically ventilated patients with severe acute respiratory failure.

DESIGN

Assessment of histologic pulmonary barotrauma.

SETTING

A 14-bed surgical intensive care unit (SICU) PATIENTS: The lungs of 30 young critically ill patients (mean age 34 +/- 10 years) were histologically examined in the immediate post-mortem period. None of them were suspected of pre-existing emphysema.

MEASUREMENTS AND RESULTS

Clinical events and ventilatory settings used during mechanical ventilation were compared with lung histology. Airspace enlargement, defined as the presence of either alveolar overdistension in aerated lung areas or intraparenchymal pseudocysts in nonaerated lung areas, was found in 26 of the 30 lungs examined (86%). Patients with severe airspace enlargement (2.6-40 mm internal diameter) had a significantly greater incidence of pneumothorax (8 versus 2, p < 0.05), were ventilated using higher peak airway pressures (56 +/- 18 cmH2O versus 44 +/- 10 cmH2O, p < 0.05) and tidal volumes (12 +/- 3 ml/kg versus 9 +/- 2 ml/kg, p < 0.05), were exposed significantly longer to toxic levels of oxygen (8.6 +/- 9.4 days versus 1.9 +/- 2 days at FIO2 > 0.6, p < 0.05) and lost more weight (6.3 +/- 9.2 kg versus 0.75 +/- 5.8 kg, p < 0.05) than patients with mild airspace enlargement (1-2.5 mm internal diameter).

CONCLUSION

Underlying histologic lesions responsible for clinical lung barotrauma consist of pleural cysts, bronchiolar dilatation, alveolar overdistension and intraprenchymal pseudocysts. Mechanical ventilation appears to be an aggravating factor, particularly when high peak airway pressures and large tidal volumes are delivered by the ventilator.

Combined severe myocardial and pulmonary contusion: early diagnosis with transesophageal echocardiography and management with high-frequency jet ventilation: case report

We report the case of a 27-year-old patient with blunt thoracic trauma in whom transesophageal echocardiography enabled an early diagnosis of severe myocardial contusion. Conventional mechanical ventilation dramatically enhanced cardiogenic shock because of myocardial contusion, requiring increasing doses of catecholamine. High-frequency jet ventilation produced an immediate improvement in hemodynamic status, permitting a decrease in catecholamine administration.