Noninvasive pressure support ventilation in COPD patients with postextubation hypercapnic respiratory insufficiency

Patients with chronic obstructive pulmonary disease (COPD) who have been intubated and mechanically ventilated may prove difficult to wean. Noninvasive ventilation may be used in an attempt to avoid new endotracheal intubation. The efficacy of administration of noninvasive pressure support ventilation was evaluated in 30 COPD patients with postextubation hypercapnic respiratory insufficiency, compared with 30 historically matched control patients who were treated conventionally. Patients were included in the study if, within 72 h postextubation, they presented with respiratory distress, defined as the combination of a respiratory frequency >25 breaths x min(-1), an increase in the arterial carbon dioxide tension (Pa,CO2) of at least 20% compared with the value measured after extubation, and a pH <7.35. Noninvasive pressure support ventilation was effective in correcting gas exchange abnormalities. The use of noninvasive ventilation significantly reduced the need for endotracheal intubation: 20 of the 30 patients (67%) in the control group required endotracheal intubation, compared with only six of the 30 patients (20%) in the noninvasive-ventilation group (p<0.001). In-hospital mortality was not significantly different between the two groups, but the mean duration of ventilatory assistance for the treatment of the postextubation distress, and the length of intensive care unit stay related to this event, were both significantly shortened by noninvasive ventilation (p<0.01). In conclusion, noninvasive ventilation may be used in the management of patients with chronic obstructive pulmonary disease and postextubation hypercapnic respiratory insufficiency.     

Clinical characteristics, respiratory functional parameters, and outcome of a two-hour T-piece trial in patients weaning from mechanical ventilation

The discrepancy in results from different studies regarding outcome of weaning from mechanical ventilation may be due to several factors such as the differences in patient populations and weaning indexes used. In order to analyze the clinical characteristics and weaning indexes in patients undergoing a 2-h T-piece weaning trial and the relationship between the etiology of acute respiratory failure (ARF) and the outcome of this weaning trial, we prospectively studied 217 patients receiving mechanical ventilation who met standard weaning criteria. Successful weaning occurred in 57.6% (125 of 217) of patients: 13 of 33 (39.4%) patients with chronic obstructive pulmonary disease (COPD), 27 of 46 (58.7%) neurologic patients, and 85 of 138 (61.6%) patients with ARF. Ventilatory support was reinstituted in 31.8% (69 of 217) patients: 20 of 33 (60.6%) of patients with COPD, four of 46 (8.7%) neurologic patients, and 45 of 138 (32.6%) patients with ARF (p < 0.001). Reintubation was required in 23 of 148 (15.5%) patients: 15 of 42 (35.7%) neurologic patients, and eight of 93 (8.6%) patients with ARF, whereas no patient with COPD was reintubated (p < 0.001). Using a discriminant analysis, the following variables were selected as the best predictors of outcome: (1) in the whole population, days of mechanical ventilation before weaning trial (DMV), frequency-to-tidal volume ratio (f/VT), maximal inspiratory pressure (MIP), airway occlusion pressure (P0.1), maximal expiratory pressure (MEP), and vital capacity (VC); (2) in patients with ARF, DMV, P0.1/MIP, MIP, f/VT, and age; (3) in patients with COPD, f/VT, P0.1, P0.1/MIP, MIP, age, and DMV; (4) in neurologic patients, MIP, MEP, and f/VT.P0.1. Using these predictors, 74.6% of the whole population, 76.1% of patients with ARF, 93.9% of patients with COPD, and 73.9% of neurologic patients were accurately classified as weaning successes or failures. The highest rate of reintubation occurred in neurologic patients. In this group, the ability to cough and clear respiratory secretions, objectively reflected by MEP, may help in clinical decision-making.     

A randomized, controlled trial of aminophylline in ventilatory weaning of premature infants

OBJECTIVES: To determine whether maximal inspiratory force predicts successful neonatal extubation, and whether aminophylline affects maximal inspiratory force or the success rate of extubation. DESIGN: Double-blind, prospective, randomized, placebo-controlled trial. SETTING: Tertiary level neonatal intensive care unit. PATIENTS: A total of 20 ventilated, preterm, newborn infants: birth weight < 2.5 kg; gestation < 35 wks. INTERVENTIONS: Intravenous aminophylline 4 mg/kg bolus followed by 2.5 mg/kg every 6 hrs x three doses, then 1.5 mg/kg every 6 hrs; or placebo. Drug administration began when infants were receiving an FIO2 of < 0.4 and were progressively weaning from assisted mechanical ventilation. A standardized weaning protocol was instituted, and patients were extubated when they were able to tolerate a mechanical ventilatory rate of < 5 cycles/min. MEASUREMENTS AND MAIN RESULTS: Occlusion pressures, including maximal inspiratory force, were measured before aminophylline and daily until endotracheal extubation. Arterial blood gases were measured every 3 hrs, and 24-hr cardiac and respiratory recordings were performed postextubation. Three of ten aminophylline-treated patients failed extubation compared with two of ten placebo infants (p = nonsignificant). Mean apnea frequency postextubation was 0.02/hr in the aminophylline group compared with 0.3/hr in the placebo group (p < .05). Aminophylline had no effect on successful extubation or on maximal inspiratory force. Maximal inspiratory force was not correlated with the success of extubation. Apnea frequency postextubation was significantly reduced by aminophylline. CONCLUSIONS: Aminophylline is an effective prophylaxis for postextubation apnea in the preterm infant but does not affect maximal inspiratory force or increase the success rate of extubation in this patient population.     

Contribution of bronchoalveolar lavage and transbronchial biopsy to diagnosis and prognosis of drug-induced pneumopathies

OBJECTIVE: The purpose of this study was to evaluate three ventilator weaning strategies and to evaluate whether the use of continuous positive airway pressure (CPAP) via a nasopharyngeal or endotracheal tube would increase the likelihood of extubation failure in very low birth weight (VLBW) infants. STUDY DESIGN: We studied prospectively 87 preterm infants (mean +/- SD; birth weight: 1078 +/- 188 g; gestational age: 28.8 +/- 2.2 weeks) who were in the process of being weaned from intermittent mandatory ventilation (IMV). Infants were assigned by systematic sampling to one of the following three treatment groups: (1) direct extubation from IMV (D.EXT) (n = 30); (2) preextubation endotracheal CPAP (ET-CPAP) for 12-24 hr (n = 28); or (3) postextubation nasopharyngeal CPAP (NP-CPAP) for 12-24 hr (n = 29). Failure was defined as the need for resumption of mechanical ventilation within 72 hr of extubation due to frequent or severe apnea and/or respiratory failure (pH < 7.25, PaCO2 > 60 mm Hg, and/or requirement for oxygen FiO2 > 60%). RESULTS: There were no significant differences in failure rates among the three procedures. Failures were 2/30 (7%) in D.EXT; 4/28 (14%) in ET-CPAP; and 7/29 (24%) in the NP-CPAP. There were also no differences in FiO2, PaO2, and respiratory rates before and after discontinuation of IMV among the three groups. PaCO2 values were slightly higher in the NP-CPAP group 12-24 hr after weaning from IMV. CONCLUSION: We were unable to demonstrate a clear difference in extubation outcome by use of CPAP administered via an endotracheal or nasopharyngeal tube when compared to direct extubation from low-rate IMV in VLBW infants.     

Gastric intramucosal pH: an indicator of weaning outcome from mechanical ventilation in COPD patients

The aim of this study was to determine whether gastric intramucosal pH (pHim) and/or gastric intramucosal carbon dioxide tension (PCO2,im) measured by tonometry can be used to predict the success of weaning in chronic obstructive pulmonary disease (COPD) patients. Twenty six consecutive COPD patients, undergoing mechanical ventilation for acute respiratory failure and satisfying the criteria of weaning from mechanical ventilation with nasogastric tonometer in place, were studied. Arterial blood gas values and PCO2,im were measured 24 h before (H-24), just before (H0), and after 20 min of a weaning trial on T-piece (H20min). Weaning failure was defined as the development of respiratory distress and/or arterial blood gas impairments during the first 2 h of spontaneous breathing on T-piece, or reintubation within 24 h after extubation. Between the weaning failure (n = 6) and weaning success (n = 20) groups, there were no differences in blood gas analysis readings at H-24 and H0 before the weaning period, age, Simplified Acute Physiology Score (SAPS) on admission, SAPS on the day of weaning trial, and duration of ventilation. Clinical status, tonometric and arterial gasometric data were similar at H-24 and H0 in all patients. During mechanical ventilation, pHim was < or = 7.30 in patients who failed weaning and > 7.30 in patients who were successfully weaned (p < 0.001; 100% sensitivity and specificity). The threshold value for PCO2,im of 8.0 kPa (60 mmHg) represents a clear demarcation with respect to outcome before the weaning trial. PCO2,im values during mechanical ventilation are significantly different (p < 0.001) between patients who were successfully weaned and those who were not (6.9 +/- 0.9 vs 9.9 +/- 1.1 kPa (51.9 +/- 6.7 vs 74.3 +/- 8.0 mmHg, respectively)). At H20min, pHim and PCO2,im were still statistically different between the weaning failure and the weaning success group. We conclude that measurement of gastric intramucosal pH (or gastric intramucosal carbon dioxide tension) represents a simple and accurate index to predict weaning outcome in chronic obstructive pulmonary disease patients before attempting weaning.     

Extended operation for T4 lung carcinoma

PURPOSE: The study objective was to determine an "optimal" individual pressure support (PS) level for beginning weaning with PS ventilation in patients with chronic obstructive pulmonary disease (COPD). MATERIALS AND METHODS: Eleven COPD patients intubated and ventilated for acute respiratory failure and judged ready for weaning were studied. The technique consisted of lowering the PS level from a point that was characteristic for each patient and measurable under controlled mechanical ventilation, after setting the ventilator as recommended for COPD patients judged ready for weaning, that is, peak inflation pressure (PIP). This determination was based mainly on exploring the diaphragm with an electromyographic technique by defining the optimal PS level as the lowest PS level associated with no EMG evidence of diaphragmatic stress. Diaphragmatic electromyographic activity (diEMG) was recorded by a bipolar esophageal electrode (Disa-Denmark), and the high-frequency electrical component/low-frequency ratio (H/L) was calculated. The reference H/L was determined during a few spontaneous ventilatory cycles. Muscle stress was defined as a greater than 20% reduction in H/L compared with the reference value. RESULTS: Optimal PS levels ranged from 4 to 24 cm H2O with a mean of 14+/-6 cm H2O. Two patients with optimal PS level at 4 cm H2O did not require weaning and were quickly extubated. For the nine other patients, optimal PS levels were found to be 70% of PIP; in none was it necessary during weaning to use PS levels higher than individual optimal PS levels. CONCLUSIONS: Optimal PS level established with diEMG monitoring seems to be a useful index for beginning weaning in the PS ventilation mode in COPD patients. The hypothesis of beginning weaning with a PS level equal to 70% of PIP needs to be tested.     

Effects of nasal continuous positive airway pressure on breathing pattern and respiratory drive in patients with obstructive sleep apnea syndrome

To examine the influence of continuous positive airway pressure (CPAP) therapy on respiratory center drive in patients with obstructive sleep apnea syndrome (OSAS), 20 normocapnic OSAS patients (group 0) and 20 simple snoring patients were studied. In the first night, diagnostic polysomnography (PSG) was performed. Before and after PSG monitoring, mouth occlusion pressure (P0.1), tidal volume (VT), minute ventilation (VE), respiratory rate (RR), inspiratory time (Ti), expiratory time (Te), total cycle duration (Ttot), inspiratory duty cycle (Ti/Ttot), mean inspiratory flow (VT/Ti) and effective inspiratory impedance (P0.1/VT/Ti, Ieff) were measured while they were breathing room air. In the following night the OSAS patients were treated with nasal CPAP and PSG monitoring and the above mentioned measurements were repeated. The results showed that pre-PSG values of P0.1, RR and P0.1/VT/Ti in the OSAS patients were significantly higher than those in the snoring patients, while VT, Ti, Te and Ttot values were lower. In the first night, the post-PSG P0.1 value in the OSAS patients increased markedly as compared with the pre-PSG. After overnight nasal CPAP therapy, the respiratory disorder index in the OSAS patients decreased markedly, the nadir SaO2 increased markedly, but the post-PSG P0.1 value did not increase significantly. It is concluded that, before sleep, OSAS patients exhibit a higher respiratory drive and a shallow and frequent breathing pattern as compared with simple snoring patients. After nocturnal sleep, the respiratory drive of OSAS patients increases significantly, the breathing pattern becomes more shallow and frequent. Nasal CPAP may effectively relieve the sleep apnea and hypopnea as well as the resulting hypoxemia and therefore correct the changes in breathing pattern and respiratory drive through nocturnal sleep in patients with OSAS.     

Effect of step duration during incremental exercise on breathing pattern and mouth occlusion pressure

We compared the effects of two step durations on breathing pattern, mouth occlusion pressure and "effective" impedance of the respiratory system during incremental exercise. Nine normal subjects (mean age: 27.8+/-1.21 years) performed two incremental exercise tests in randomized order: one test with step increments every 1 min 30s and the other, every 4 min. After a warm-up at 25 W for the 1 min 30 s test, the power was increased by 50 W from 50 W to exhaustion. During the last minute at each power, we measured ventilation (VE), tidal volume (VT), breathing frequency (fR), inspiratory and expiratory time (TI and TE), total time of the respiratory cycle (TTOT), TI/TTOT, mean inspiratory flow (VT/TI), mouth occlusion pressure (P0.1), "effective" impedance of the respiratory system (P0.1/(VT/ TI)) and venous blood lactate concentration ([La]). Our result showed that at maximal exercise the power was significantly higher (p < 0.01) and [La] lower (p < 0.01) in the 1 min 30 s test. At 100, 150 and 200 W, the 4 min test showed significantly higher oxygen uptake (VO2), carbon dioxide output (VCO2), VE, P0.1, fR, VT/TI and HR (p <0.001) and significantly lower TI, TE and TTOT (p<0.01). [La] was significantly higher at 150 W (p<0.05) and 200 W (p<0.001). At the same VCO2, P0.1 was not significantly different between the two tests, whereas VE showed a tendency to be higher (p = 0.08) and P0.1/(VT/TI) was significantly lower during the 4 min test. In conclusion, this study allowed us to quantify the difference in inspiratory neuromuscular output and ventilatory response between 1 min 30s and 4 min tests and showed that different step durations alter the relationship between inspiratory neuromuscular output and mean inspiratory flow.     

Criteria for extubation and tracheostomy tube removal for patients with ventilatory failure. A different approach to weaning

The purpose of this study was to prospectively compare parameters that might predict successful translaryngeal extubation and tracheostomy tube decannulation. Irrespective of ventilatory function, 62 extubation/decannulation attempts were made on 49 consecutive patients with primarily neuromuscular ventilatory insufficiency who satisfied criteria. Thirty-four patients required 24-h ventilatory support. Noninvasive intermittent positive pressure ventilation (IPPV) was substituted as needed for IPPV via translaryngeal or tracheostomy tubes. Successful decannulation was defined as extubation or decannulation and site closure with no consequent respiratory symptoms or blood gas deterioration for at least 2 weeks. Failure was defined by the appearance of respiratory distress and decreases in vital capacity and oxyhemoglobin saturation despite use of noninvasive IPPV and assisted coughing. The independent variables of age, extent of predecannulation ventilator use, vital capacity, and peak cough flows (PCF) were studied to determine their utility in predicting successful extubation and decannulation. Only the ability to generate PCF greater than 160 L/min predicted success, whereas inability to generate 160 L/min predicted the need to replace the tube. All 43 attempts on patients with PCF greater than 160 L/min succeeded; all 15 attempts on patients with PCF below 160 L/min failed; and of 4 patients with PCF of 160 L/min, 2 succeeded and 2 failed. We conclude that the ability to generate PCF of at least 160 L/min is necessary for the successful extubation or tracheostomy tube decannulation of patients with neuromuscular disease irrespective of ability to breathe.     

Wortmannin-sensitive activation of p70S6-kinase and MAP-kinase by the G protein-coupled receptor, G/CCKB

OBJECTIVE: To determine whether emergency rigid bronchoscopic intervention, including Nd-YAG laser resection or stenting, immediately affected the need for continued mechanical ventilation or intensive care level of support in critically ill patients with acute respiratory failure from malignant or benign central airways obstruction. DESIGN: Retrospective review of medical records of all patients with acute respiratory failure and malignant or benign tracheobronchial obstruction necessitating intubation, mechanical ventilation, or hospitalization in the ICU prior to referral for therapeutic bronchoscopy. SETTING: University of California San Diego, a tertiary care institution specialized in airway management. PATIENTS: Medical records of 32 patients with malignant or benign central airways obstruction requiring admission to the ICU prior to rigid bronchoscopic intervention between January 1994 and April 1996. INTERVENTIONS: Emergent rigid bronchoscopy with dilatation, Nd-YAG laser resection, or silicone stent insertion performed in the operating room under general anesthesia. RESULTS: Thirty-two patients with central airways obstruction requiring emergent hospitalization in the ICU were referred for therapeutic rigid bronchoscopy. Airway strictures were caused by benign disease in 18 patients, and by primary bronchogenic lung cancer in 14. Of the 19 patients who were mechanically ventilated, bronchoscopic intervention allowed immediate discontinuation of mechanical ventilation in 10 (52.6%). Twenty-five patients had indwelling artificial airways (12 endotracheal tubes, 13 tracheotomy tubes). Two, however, were considered tracheotomy-dependent because of neuromuscular disease. Of the remaining 23 patients, immediate extubation or decannulation was possible in seven (30.4%). Of seven patients with no indwelling airway, five (71.4%) were immediately transferred to a lower level of care after intervention. Of the 32 total patients, 20 (62.5%) were immediately transferred to a lower level of care immediately after intervention. CONCLUSIONS: Emergency laser resection or stent insertion can favorably affect health-care utilization in patients with acute respiratory distress from central airways obstruction. Treatment may be lifesaving and allows successful withdrawal from mechanical ventilation, hospitalization in a lower level of care environment, relief of symptoms, and extended survival in critically ill patients. In patients with regionally advanced cancer, the palliative nature of this procedure postpones death by respiratory distress and may prompt consideration for institution of conservative comfort measures to reduce patient suffering.     

Pressure support ventilation in adult respiratory distress syndrome: short-term effects of a servocontrolled mode

PURPOSE: To assess the short-term effects of pressure support ventilation in adult respiratory distress syndrome (ARDS), we studied 17 patients with moderate to severe ARDS using mandatory rate ventilation (MRV), a servocontrolled mode of PSV having respiratory rate as the targeted parameter. MATERIALS AND METHODS: Based on the duration of ARDS, the patients were divided into two groups: Group 1, early ARDS (duration up to 1 week), 10 patients; Group 2, intermediate ARDS (duration between 1 and 2 weeks). The patients were initially ventilated with assisted mechanical ventilation then with MRV, and finally with controlled mechanical ventilation. After a 20-minute period allowed for stabilization in each mode, ventilatory variables, gas exchange, hemodynamics, and patient's inspiratory effort were evaluated. RESULTS: During MRV blood gases, airway pressures and hemodynamic variables remained within acceptable limits in all patients. Compared with assisted mechanical ventilation, during MRV, patients of group 1 decreased their VT and V (from 0.64 +/- 0.04 to 0.42 +/- 0.03 L/sec) and increased their TI/TT (from 0.39 +/- 0.03 to 0.52 +/- 0.03). f did not change. PAO2 - PaO2 and QS/QT decreased (from 306 +/- 16 to 269 +/- 15 mm Hg, and from 20.2 +/- 1.4 to 17.5 +/- 1.1, respectively), while PaCO2 increased (from 44 +/- 3 to 50 +/- 3 mm Hg). On the contrary, patients of group 2 increased their VT (from 0.69 +/- 0.02 to 0.92 +/- 0.09 L), decreased their f (from 22.3 +/- 0.5 to 19.3 +/- 0.3 b/min), although they did not change their V and TI/TT. PAO2 - PaO2 and QS/QT remained stable. PaCO2 diminished (from 39 +/- 3 to 34 +/- 3 mm Hg). Pressure support level was higher in group 2 than in group 1 (29.4 +/- 3.0 v 19.8 +/- 2.9 cm H2O). CONCLUSIONS: We conclude that (1) PSV delivered by MRV may adequately ventilate patients with moderate to severe ARDS, preserving gas exchange and hemodynamics, at least for the short period tested; (2) early and intermediate ARDS respond in a different manner to MRV in terms of breathing pattern, gas exchange, and level of pressure assistance; and (3) patients with early ARDS are those who have an improvement in intrapulmonary oxygenation probably due, at least in part, to alveolar recruitment augmented by active diaphragmatic contraction.     

Respiration during emergence from anaesthesia with desflurane/N2O vs. desflurane/air for gynaecological laparoscopy

BACKGROUND: The complications related to anaesthesia usually occur in the early postoperative period. Hypercapnia and hypoxaemia may result from any persistent depression of the respiratory drive relative to the metabolic demand. The purpose of this study was to compare the respiratory effects of desflurane anaesthesia with or without nitrous oxide during the period of emergence. METHODS: Twenty patients scheduled for a standardised surgical procedure, laparoscopic hysterectomy, were randomly allocated to anaesthesia with 1.3 MAC of desflurane/N2O (Group 1) or desflurane alone (Group 2), with 10 patients in each group. Times of resumption of spontaneous breathing and extubation were recorded and elimination rates of carbon dioxide, end-tidal concentrations of desflurane and N2O, and blood gases were measured. RESULTS: Spontaneous breathing was resumed in both groups when pH had decreased by about 0.07 and PaCO2 increased by about 1.4 kPa compared with the values at the end of 1.3 MAC anaesthesia with controlled normoventilation. There were no significant differences between the groups with regards to extubation time, 6 vs. 13 min, or total MAC value at extubation, 0.20 vs. 0.19 in Group 1 and 2, respectively. Neither did the groups differ in minute ventilation, end-tidal carbon dioxide, oxygen concentrations, or blood gases. CO2 elimination decreased in both groups from about 220 ml 70 kg-1 min-1 at the end of anaesthesia to a lowest value of about 160 ml 70 kg-1 min-1. CONCLUSION: The respiratory profiles during recovery from gynaecological laparoscopy with either desflurane/N2O or desflurane anaesthesia were similar with fast resumption of spontaneous breathing, short time to extubation, and no signs of CO2 retention.     

Blood transfusion and lung function in chronically anemic patients with severe chronic obstructive pulmonary disease

OBJECTIVE: To study in anemic patients with chronic obstructive pulmonary disease (COPD) whether blood transfusion reduces minute ventilation and work of breathing (WOB). DESIGN: We prospectively evaluated the minute ventilation and WOB in 20 anemic adults (hemoglobin of <11 g/dL). Ten patients had severe COPD and ten patients were without lung disease. Measurements were made before and after receiving red blood cell transfusion; post-transfusion measurements were made 24 to 36 hrs after the last transfusion. SETTING: The study was performed in the intensive care unit of a tertiary referral center for home mechanical ventilation and for patients considered difficult to wean from mechanical ventilation. PATIENTS: Twenty clinically stable patients (12 female, eight male) with chronic anemia were studied. Ten patients with COPD (mean forced expiratory volume in 1 sec: 0.55+/-0.1 [SD] L) were compared with ten patients without lung disease. All participants had adequate renal and left ventricular function. INTERVENTIONS: Patients received 1 unit of packed red blood cells for each g/dL that their hemoglobin value was less than an arbitrarily defined target value of 11.0 to 12.0 g/dL. Each unit was transfused over 2 hrs and < or =3 units in total was given. MEASUREMENTS AND MAIN RESULTS: Esophageal pressure was measured from a catheter which was positioned in the middle of the esophagus. Flow was measured using a pneumotachygraph connected to a mouthpiece while a nose clip closed the nostrils during the measurements. From these data, respiratory rate, minute ventilation, and inspiratory resistive WOB were computed. Arterial blood gas values, oxygen saturation, hemoglobin, and hematocrit were also measured, and oxygen content was calculated before and 24 to 36 hrs after transfusion. In patients with COPD, hemoglobin increased from 9.8+/-0.8 to 12.3+/-1.1 g/dL due to a mean transfusion of 2.2+/-0.4 (SD) units of red blood cells. There was a reduction in the mean minute ventilation from 9.9+/-1.0 to 8.2+/-1.2 L/min (p < .0001); correspondingly, WOB decreased from 1.03+/-0.24 to 0.85+/-0.21 WOB/L (p< .0001). The capillary P(CO2) increased from 38.1+/-6.0 to 40.7+/-6.8 torr (5.1+/-0.8 to 5.8+/-0.9 kPa) (p < .05). Similarly, capillary P(O2) changed from 56.9+/-8.9 to 52.8+/-7.0 torr (7.6+/-1.2 to 7.0+/-0.9 kPa) (p < .05). In anemic patients without lung disease, minute ventilation, WOB, and the capillary blood gas values did not change after increase of the hemoglobin by a similar degree. CONCLUSIONS: We conclude that red blood cell transfusion in anemic patients with COPD leads to a significant reduction of both the minute ventilation and the WOB. In these patients, transfusion may be associated with unloading of the respiratory muscles, but it may also result in mild hypoventilation.     

Instillation of calf lung surfactant extract (calfactant) is beneficial in pediatric acute hypoxemic respiratory failure. Members of the Mid-Atlantic Pediatric Critical Care Network

OBJECTIVE: Prospective study of the efficacy of calf lung surfactant extract in pediatric respiratory failure. DESIGN: Multi-institutional, prospective, randomized, controlled, unblinded trial. SETTING: Eight pediatric intensive care units (ICU) of tertiary medical centers. PATIENTS: Forty-two children with acute hypoxemic respiratory failure characterized by diffuse, bilateral pulmonary infiltrates, need for ventilatory support, and an oxygenation index of >7. INTERVENTION: Instillation of intratracheal surfactant (80 mL/m2). MEASUREMENTS AND MAIN RESULTS: Ventilator parameters, arterial blood gases, and derived oxygenation and ventilation indices were recorded before and at intervals after surfactant administration. Complications and outcome measures, including mortality, duration of mechanical ventilation, and length of pediatric ICU and hospital stay, were also examined. Patients who received surfactant demonstrated rapid improvement in oxygenation and, on average, were extubated 4.2 days (32%) sooner and spent 5 fewer days (30%) in pediatric intensive care than control patients. There was no difference in mortality or overall hospital stay. Surfactant administration was associated with no serious adverse effects. CONCLUSIONS: Administration of calf lung surfactant extract, calfactant, appears to be safe and is associated with rapid improvement in oxygenation, earlier extubation, and decreased requirement for intensive care in children with acute hypoxemic respiratory failure. Further study is needed, however, before widespread use in pediatric respiratory failure can be recommended.     

High-pressure destruction kinetics of Listeria monocytogenes on pork

OBJECTIVE: To define the incidence of complications of endotracheal intubation and the factors associated with these complications. STUDY DESIGN: During a 22-month period, 227 intubated infants weighing <1,501 g were followed prospectively in a neonatal intensive care unit. Detailed records of events associated with airway management were kept after every intubation, in addition to clinical data. RESULTS: Eleven infants (4.8%) developed respiratory stridor after extubation which was treated with either systemic corticosteroids, racemic epinephrine and/or reintubation for respiratory failure. Four infants were submitted for bronchoscopy, mild subglottic stenosis with tracheal edema was found in 1 patient, granulation tissue and airway edema were noted in 3 infants. Traumatic intubation, prolonged ventilation, multiple intubations and bacterial colonization of the endotracheal tube were the factors associated with postextubation stridor. CONCLUSIONS: Subglottic stenosis is an infrequent complication of endotracheal intubation with current airway management of very-low-birth-weight infants. Less severe complications are still common, but they are usually amenable to clinical treatment. Bronchoscopy should be performed selectively only in infants with clinical evidence of airway obstruction after extubation.     

Effect of spontaneous breathing trial duration on outcome of attempts to discontinue mechanical ventilation. Spanish Lung Failure Collaborative Group

The duration of spontaneous breathing trials before extubation has been set at 2 h in research studies, but the optimal duration is not known. We conducted a prospective, multicenter study involving 526 ventilator-supported patients considered ready for weaning, to compare clinical outcomes for trials of spontaneous breathing with target durations of 30 and 120 min. Of the 270 and 256 patients in the 30- and 120-min trial groups, respectively, 237 (87.8%) and 216 (84.8%), respectively, completed the trial without distress and were extubated (p = 0.32); 32 (13.5%) and 29 (13.4%), respectively, of these patients required reintubation within 48 h. The percentage of patients who remained extubated for 48 h after a spontaneous breathing trial did not differ in the 30- and 120-min trial groups (75.9% versus 73.0%, respectively, p = 0.43). The 30- and 120-min trial groups had similar within-unit mortality rates (13 and 9%, respectively) and in-hospital mortality rates (19 and 18%, respectively). Reintubation was required in 61 (13.5%) patients, and these patients had a higher mortality (20 of 61, 32.8%) than did patients who tolerated extubation (18 of 392, 4.6%) (p < 0.001). Neither measurements of respiratory frequency, heart rate, systolic blood pressure, and oxygen saturation during the trial, nor other functional measurements before the trial discriminated between patients who required reintubation from those who tolerated extubation. In conclusion, after a first trial of spontaneous breathing, successful extubation was achieved equally effectively with trials targeted to last 30 and 120 min.     

Occlusion pressure in the first 100 ms of inspiration (P0.1) as an index of the possibility of decreasing respiratory support in acute respiratory failure

The need in making the process of transfer of patients to spontaneous respiration using ventilation of the lungs with inspiratory pressure support (VLIPS) after prolonged mechanical ventilation of the lungs prompted the authors to analyze the prognostic value of criteria traditionally used by the physician to cease or decrease the respiratory support (vital capacity of the lungs, peak spontaneous flow, PaO2, etc.) and the P0.1 occlusion pressure in the airways at the end of the first 100 msec of inhalation. This latter value proved to be the most sensitive (88%), specific (86%), positive (95%) and negative (67%) prognostic value in predicting the results of decrease of respiratory support under conditions of VLIPS. The P0.1 value determining the result of decrease of respiratory support in patients with parenchymatous pulmonary diseases under conditions of VLIPS is 3.8 cm H2O.     

Microwave a-Dipole Transitions of CH2DOH and CHD2OH in Excited Torsional States

We have previously shown (Am. J. Respir. Crit. Care Med. 1995;152:1248-1255) that in patients needing mechanical ventilation, the load imposed on the inspiratory muscles is excessive relative to their neuromuscular capacity. We have therefore hypothesized that weaning failure may occur because at the time of the trial of spontaneous breathing there is insufficient reduction of the inspiratory load. We therefore prospectively studied patients who initially had failed to wean from mechanical ventilation (F) but had successful weaning (S) on a later occasion. Compared with S, during F patients had greater intrinsic positive end-expiratory pressure (6. 10 +/- 2.45 versus 3.83 +/- 2.69 cm H2O), dynamic hyperinflation (327 +/- 180 versus 213 +/- 175 ml), total resistance (Rmax, 14.14 +/- 4.95 versus 11.19 +/- 4.01 cm H2O/L/s), ratio of mean to maximum inspiratory pressure (0.46 +/- 0.1 versus 0.31 +/- 0.08), tension time index (TTI, 0.162 +/- 0.032 versus 0.102 +/- 0.023) and power (315 +/- 153 versus 215 +/- 75 cm H2O x L/min), less maximum inspiratory pressure (42.3 +/- 12.7 versus 53.8 +/- 15.1 cm H2O), and a breathing pattern that was more rapid and shallow (ratio of frequency to tidal volume, f/VT 98 +/- 38 versus 62 +/- 21 breaths/min/L). To clarify on pathophysiologic grounds what determines inability to wean from mechanical ventilation, we performed multiple logistic regression analysis with the weaning outcome as the dependent variable. The TTI and the f/VT ratio were the only significant variables in the model. We conclude that the TTI and the f/VT are the major pathophysiologic determinants underlying the transition from weaning failure to weaning success.     

A comparative study of human immunodeficiency virus culture, polymerase chain reaction and anti-human immunodeficiency virus immunoglobulin A antibody detection in the diagnosis during early infancy of vertically acquired human immunodeficiency virus infection

Asynchrony of delivered and spontaneous breaths in mechanically ventilated infants may impair gas exchange and prolong the need for assisted ventilation. We conducted a randomized, controlled trial of a patient-triggered, flow-synchronized ventilator on 30 preterm infants with respiratory distress syndrome who weighed between 1100 and 1500 gm at birth. Entry criteria included radiographic evidence of respiratory distress syndrome and the need for mechanical ventilation and surfactant replacement therapy. Patients were assigned to either conventional time-cycled, pressure-limited ventilation or patient-triggered, flow-synchronized ventilation in an assist/control mode. Otherwise clinical management was identical. Time to extubation was the primary outcome measure. Patients treated with flow-synchronized ventilation were weaned more rapidly and had a significantly shorter mean time to extubation than those treated with time-cycled, pressure-limited ventilation, 119 versus 271 hours, p = 0.0152. In addition, there was no difference in the rate of complications between the two groups. There were, however, considerable reductions in patient charges of $4344 per patient in the flow-synchronized ventilation group.     

Physiologically based indices of volumetric capnography in patients receiving mechanical ventilation

Several indices of ventilatory heterogeneity can be identified from the expiratory CO2 partial pressure or CO2 elimination versus volume curves. The aims of this study were: 1) to analyse several computerizable indices of volumetric capnography in order to detect ventilatory disturbances; and 2) to establish the relationship between those indices and respiratory system mechanics in subjects with normal lungs and in patients with acute respiratory distress syndrome (ARDS), both receiving mechanical ventilation. We studied six normal subjects and five patients with early ARDS mechanically ventilated at three levels of tidal volume (VT). Respiratory system mechanics were assessed by end-expiratory and end-inspiratory occlusion methods, respectively. We determined Phase III slopes, Fletcher's efficiency index, Bohr's dead space (VD,Bohr/VT), and the ratio of alveolar ejection volume to tidal volume (VAE/VT) from expiratory capnograms, as a function of expired volume. Differences between normal subjects and ARDS patients were significant both for capnographic and mechanical parameters. Changes in VT significantly altered capnographic indices in normal subjects, but failed to change ventilatory mechanics and VAE/VT in ARDS patients. After adjusting for breathing pattern, VAE/VT exhibited the best correlation with the mechanical parameters. In conclusion, volumetric capnography, and, specifically, the ratio of alveolar ejection volume to tidal volume allows evaluation and monitoring of ventilatory disturbances in patients with adult respiratory distress syndrome.