Source of respiratory drive during periodic breathing in lambs

In order to investigate the mechanisms underlying periodic breathing (PB), we studied the initiation of breathing after passive hyperventilation in 14 anaesthetised 10-20 day old lambs. Eight of the lambs exhibited PB following post-hyperventilation apnea (PHA), with an epoch duration of 82.4 +/- 14.2 sec (mean +/- SEM), a cycle duration of 9.7 +/- 0.7 sec and a ratio of ventilatory duration to apnea duration (V-A ratio) of 1.24 +/- 0.32. The remaining lambs showed stable breathing patterns following PHA. The ventilatory response to isocapnic hypoxia was significantly greater in the group that had PB (-7.2 +/- 1.0 ml min-1% Sao2-1 kg-1) than in the animals that did not (-2.5 +/- 1.0 ml min-1%Sao2-1 kg-1). Using experimentally determined ventilatory response curves to O2 and CO2 we calculated that the swings in Sao2 and Paco2 during PB generated chemical drive that accounted for only 16.2% of the ventilatory oscillations observed during PB. Much of the remaining drive appeared to originate in the 'switch-on' characteristics of the respiratory controller, in lambs that exhibited periodic breathing, when breathing began after PHA ventilation jumped abruptly from zero to 55.1% of the eupneic ventilation. The magnitude of this jump in ventilation accounted for 51.9% of the amplitude of ventilatory oscillations that occur during PB. We speculate that this previously unrecognised feature of the respiratory controller, together with an elevated sensitivity to hypoxaemia, play crucial roles in generating PB in the infant.     

Influence of drive and timing mechanisms on breathing pattern and ventilation during mental task performance

Assessment of multiple respiratory measures may provide insight into how behavioral demands affect the breathing pattern. This is illustrated by data from a study among 44 subjects, in which tidal volume, respiration rate, minute ventilation and indices of central drive and timing mechanisms were assessed via inductive plethysmography, in addition to end-tidal PCO2. After a baseline, three conditions of a memory comparison task were presented. The first two conditions differed only with regard to the presence or absence of feedback of performance (NFB and FB). In the third 'all-or-nothing' (AON) condition, subjects only received a monetary bonus, if their performance exceeded that of the previous two conditions. Minute ventilation increased from baseline to all task conditions, and from NFB and FB to AON. Respiration rate increased in all task conditions, but there were no differences between task conditions. Tidal volume decreased during NFB, but was equal to baseline during FB and AON. Of the respiratory control indices, inspiratory flow rate covaried much more closely with minute ventilation than duty cycle. The task performance induced a minor degree of hyperventilation. The discussion focusses on how behavioral demands affect respiratory control processes to produce alterations in breathing pattern and ventilation.     

Effects of positive end-expiratory pressure on right ventricular function in COPD patients during acute ventilatory failure

OBJECTIVE: To examine the effects of external positive end-expiratory pressure (PEEP) on right ventricular function in chronic obstructive pulmonary disease (COPD) patients with intrinsic PEEP (PEEPi). DESIGN: Prospective study. SETTING: General intensive care unit in a university teaching hospital. PATIENTS: Seven mechanically ventilated flow-limited COPD patients (PEEPi = 9.7 +/- 1.3 cmH2O, mean +/- SD) with acute respiratory failure. INTERVENTION: Hemodynamic and respiratory mechanic data were collected at four different levels of PEEP (0-5-10-15 cmH2O). MEASUREMENTS AND RESULTS: Hemodynamic parameters were obtained by a Swan-Ganz catheter with a fast response thermistor. Cardiac index (CI) and end-expiratory lung volume (EELV) reductions started simultaneously when the applied PEEP was approximately 90% of PEEPi measured on 0 cmH2O (ZEEP). Changes in transmural intrathoracic pressure (PEEPi,cw) started only at a PEEP value much higher (120%) than PEEPi. The reduction in CI was related to a decrease in the right end-diastolic ventricular volume index (RVEDVI) (r = 0.61; p < 0.001). No correlation between CI and transmural right atrial pressure was observed. The RVEDVI was inversely correlated with PEEP-induced changes in EELV (r = -55; p < 0.001), but no with PEEPi,cw (r = -0.08; NS). The relationship between RVEDVI and right ventricular stroke work index, considered an index of contractility, was significant in three patients, i.e., PEEP did not change contractility. In the other patients, an increase in contractility seemed to occur. CONCLUSIONS: In COPD patients an external PEEP exceeding 90% of PEEPi causes lung hyperinflation and reduces the CI due to a preload effect. The reduction in RVEDVI seems related to changes in EELV, rather than to changes in transmural pressures, suggesting a lung/heart volume interaction in the cardiac fossa. Thus, in COPD patients, application of an external PEEP level lower than PEEPi may affect right ventricular function.     

Unfavorable mechanical effects of heat and moisture exchangers in ventilated patients

OBJECTIVE: To investigate the mechanical effects of artificial noses. SETTING: A general intensive care unit of a university hospital. PATIENTS: 10 patients in pressure support ventilation for acute respiratory failure. INTERVENTIONS: The following three conditions were randomly tested on each patient: the use of a heated humidifier (control condition), the use of a heat and moisture exchanger without filtering function (HME), and the use of a combined heat and moisture exchanger and mechanical filter (HMEF). The pressure support level was automatically adapted by means of a closed-loop control in order to obtain constancy, throughout the study, of patient inspiratory effort as evaluated from airway occlusion pressure at 0.1 s (P0.1). Patient's ventilatory pattern, P0.1, work of breathing, and blood gases were recorded. MEASUREMENTS AND MAIN RESULTS: The artificial noses increased different components of the inspiratory load: inspiratory resistance, ventilation requirements (due to increased dead space ventilation), and dynamic intrinsic positive end-expiratory pressure (PEEP). The additional load imposed by the artificial noses was entirely undertaken by the ventilator, being the closed-loop control of P0.1 effective to maintain constancy of patient inspiratory work by means of adequate increases in pressure support level. CONCLUSIONS: The artificial noses cause unfavorable mechanical effects by increasing inspiratory resistance, ventilation requirements, and dynamic intrinsic PEEP. Clinicians should consider these effects when setting mechanical ventilation and when assessing patients' ability to breathe spontaneously.     

A comparison of noninvasive positive-pressure ventilation and conventional mechanical ventilation in patients with acute respiratory failure

BACKGROUND AND METHODS: The role of noninvasive positive-pressure ventilation delivered through a face mask in patients with acute respiratory failure is uncertain. We conducted a prospective, randomized trial of noninvasive positive-pressure ventilation as compared with endotracheal intubation with conventional mechanical ventilation in 64 patients with hypoxemic acute respiratory failure who required mechanical ventilation. RESULTS: Within the first hour of ventilation, 20 of 32 patients (62 percent) in the noninvasive-ventilation group and 15 of 32 (47 percent) in the conventional-ventilation group had an improved ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2:FiO2) (P=0.21). Ten patients in the noninvasive-ventilation group subsequently required endotracheal intubation. Seventeen patients in the conventional-ventilation group (53 percent) and 23 in the noninvasive-ventilation group (72 percent) survived their stay in the intensive care unit (odds ratio, 0.4; 95 percent confidence interval, 0.1 to 1.4; P=0.19); 16 patients in the conventional-ventilation group and 22 patients in the noninvasive-ventilation group were discharged from the hospital. More patients in the conventional-ventilation group had serious complications (66 percent vs. 38 percent, P=0.02) and had pneumonia or sinusitis related to the endotracheal tube (31 percent vs. 3 percent, P=0.003). Among the survivors, patients in the noninvasive-ventilation group had shorter periods of ventilation (P=0.006) and shorter stays in the intensive care unit (P=0.002). CONCLUSIONS: In patients with acute respiratory failure, noninvasive ventilation was as effective as conventional ventilation in improving gas exchange and was associated with fewer serious complications and shorter stays in the intensive care unit.     

Effects of support pressure ventilation with facial mask in patients with chronic respiratory failure in acute decompensation

BACKGROUND: In previous nonrandomized studies the efficacy of ventilation with back up pressure with face mask (BUPM) in the treatment of patients with chronic obstructive pulmonary disease (COPD) in acute decompensation has been demonstrated. This study analyzes the acute effects and the clinical efficacy of BUPM in a group of patients with COPD in acute respiratory failure comparing the same with conventional therapy (CONV). METHODS: A prospective randomized study including patients with COPD in acute decompensation was carried out comparing treatment with BUPM (n = 9) with CONV treatment (n = 9). Back up pressure was fixed at 20 cmH2O. Acute gasometric effects were analyzed as well as the need for intratracheal intubation, mortality and hospital stay. RESULTS: No clinical or gasometric differences were found between either group of patients upon admission. Only the patients of the BUPM group presented a significant improvement from gaseous exchange and respiratory frequency from the first hour of treatment. Three of the nine patients (33%) of the BUPM group and nine of the CONV group of patients (100%) required intubation and mechanical ventilation (p = 0.001). CONCLUSIONS: Back up pressure face mask is the technique of choice in patients with chronic obstructive pulmonary disease in acute decompensation given that this technique leads to a rapid and significant improvement of gaseous exchange and avoids the need for intubation and mechanical ventilation in most of these patients.     

Breathing pattern and additional work of breathing in spontaneously breathing patients with different ventilatory demands during inspiratory pressure support and automatic tube compensation

OBJECTIVE: To identify predictors of hypoglycemic and hyperglycemic episodes in hospitalized patients with diabetes with special attention to the effectiveness of sliding scale insulin regimens. DESIGN: Prospective cohort study. SETTING: Urban university hospital. PARTICIPANTS: One hundred seventy-one adults with diabetes mellitus as a comorbid condition admitted consecutively to medical inpatient services during a 7-week period. MEASUREMENTS: Demographic, clinical, and laboratory data from inpatient medical records. MAIN OUTCOMES: Rates of hypoglycemic (capillary blood glucose, < or = 3.3 mmol/L [< or = 60 mg/dL]) and hyperglycemic (capillary blood glucose, > or = 16.5 mmol/L [> or = 300 mg/ dL]) episodes. RESULTS: Of the patients, 23% experienced hypoglycemic episodes, and 40% experienced hyperglycemic episodes. The overall rates of hypoglycemic and hyperglycemic episodes were 3.4 and 9.8 per 100 capillary blood glucose measurements, respectively. Independent predictors of hypoglycemic episodes included African American race (relative risk [RR], 2.13) and low serum albumin level (RR, 1.92 per 100-g/L decrease); corticosteroid use was associated with a reduced risk of hypoglycemic episodes (RR, 0.32; P < .05). Independent predictors of hyperglycemic episodes included female gender (RR, 1.67), severity of illness (RR, 1.22 per 10 Acute Physiology and Chronic Health Evaluation III units), severe diabetic complications (RR, 2.32), high admission glucose level (RR, 1.33 per 5.5 mmol/L), admission for infectious disease (RR, 2.14), and corticosteroid use (RR, 3.74; P < .05). Of 171 patients, 130 (76%) were placed on a sliding scale insulin regimen. When used alone, sliding scale insulin regimens were associated with a 3-fold higher risk of hyperglycemic episodes compared with individuals following no pharmacologic regimen (RRs, 2.85 and 3.25, respectively; P < .05). CONCLUSIONS: Suboptimal glycemic control is common in medical inpatients with diabetes mellitus. The risk of suboptimal control is associated with selected demographic and clinical characteristics, which can be ascertained at hospital admission. Although sliding scale insulin regimens are prescribed for the majority of inpatients with diabetes, they appear to provide no benefit; in fact, when used without a standing dose of intermediate-acting insulin, they are associated with an increased rate of hyperglycemic episodes.     

Effects of inhaled nitric oxide during permissive hypercapnia in acute respiratory failure in piglets

OBJECTIVE: To look for the effects of inhaled nitric oxide on oxygenation and pulmonary hemodynamics during acute hypercapnia in acute respiratory failure. DESIGN: Prospective, randomized, experimental study. SETTING: University research laboratory. SUBJECTS: Ten piglets, weighing 9 to 13 kg. INTERVENTIONS: Acute respiratory failure was induced by oleic acid infusion and repeated lung lavages with 0.9% sodium chloride. The protocol consisted of three randomly assigned periods with different PaCO2 levels. Tidal volume was reduced to induce hypercapnia. Inspiratory time was prolonged to achieve similar mean airway pressures. During permissive hypercapnia, pH was not corrected. At each PaCO2 period, the animals were ventilated with inhaled nitric oxide of 10 parts per million and without nitric oxide inhalation. MEASUREMENTS AND MAIN RESULTS: Continuous hemodynamic monitoring included right atrial, mean pulmonary arterial, and mean systemic arterial pressures, arterial and mixed venous oxygen saturations, and continuous flow recording at the pulmonary artery. In addition, airway pressures, tidal volumes, dynamic lung compliance and airway resistance, end-tidal CO2 concentrations, and arterial and mixed venous blood gases were measured. Data were obtained at baseline and after lung injury, at normocapnia, at two levels of hypercapnia with and without nitric oxide inhalation. Acute hypercapnia resulted in a significant decrease in blood pH and a significant increase in mean pulmonary arterial pressure. There was no significant change in PaO2 during normocapnia and hypercapnia. Inhaled nitric oxide significantly decreased the mean pulmonary arterial pressure during both hypercapnic periods. It significantly improved oxygenation during both normocapnia and hypercapnia. CONCLUSIONS: Acute hypercapnia resulted in a significant increase in pulmonary arterial pressure without influencing oxygenation and cardiac output. Inhaled nitric oxide significantly reduced the pulmonary hypertension induced by acute permissive hypercapnia but did not influence the flow through the pulmonary artery. Inhaled nitric oxide significantly improved oxygenation in this model of acute lung injury during normocapnia and acute hypercapnia.     

Effects of partial liquid ventilation on lung injury in a model of acute respiratory failure: a histologic and morphometric analysis

OBJECTIVE: To compare the histopathologic changes observed in a sheep model of oleic acid-induced acute respiratory failure during partial liquid ventilation with perflubron with gas ventilation. DESIGN: Randomized, controlled study. SETTING: Animal laboratory and pathology laboratories of a university hospital. SUBJECTS: Fourteen healthy adult sheep, weighing 64.9 +/- 6.4 kg. INTERVENTIONS: Lung injury was induced with oleic acid (0.15 mL/kg). A tracheostomy tube was inserted, along with systemic and pulmonary artery monitoring catheters. Animals were randomized to undergo either partial liquid ventilation (n = 7) or gas ventilation (n = 7). Animals underwent euthanasia at the end of the 90-min study period, after which the endotracheal tube was clamped with the lungs in expiratory hold at a positive end-expiratory pressure of 5 cm H2O. En bloc excision of the heart and lungs was performed by thoracotomy. Perfusion of the isolated lung vasculature with 2.5% paraformaldehyde and 0.25% glutaraldehyde in a 0.1-M phosphate buffer was performed. Histologic analysis followed. MEASUREMENTS AND MAIN RESULTS: Gas exchange increased markedly in the animals that underwent partial liquid ventilation compared with the gas-ventilated animals (PaO2 at 90 mins: gas ventilation-treatment group, 40 +/- 8 torr [5.3 +/- 1.1 kPa]; partial liquid ventilation-treatment group, 108 +/- 60 torr [14.4 +/- 8.0 kPa]; p = .004). Lung histologic analysis demonstrated a better overall diffuse alveolar damage score (partial liquid ventilation-treatment group, 12.4 +/- 1.4; gas ventilation-treatment group, 15.0 +/- 1.7; p = .01). In the partial liquid ventilation-treatment group, we observed an increase in mean alveolar diameter (partial liquid ventilation-treatment group, 82.4 +/- 2.9 microm; gas ventilation-treatment group, 67.7 x 3.9 microm; p = .0022) and a decrease in the number of alveoli per high-power field (partial liquid ventilation-treatment group, 25.7 +/- 0.9, gas ventilation-treatment group, 31.4 +/- 2.5; p = .0022), in septal wall thickness (partial liquid ventilation-treatment group, 6.0 +/- 0.6 microm; gas ventilation-treatment group, 8.3 +/- 1.0 microm; p = .0033), and in mean capillary diameter (partial liquid ventilation-treatment group, 13.0 +/- 0.8 microm; gas ventilation-treatment group, 19.9 +/- 1.4 microm; p = .0022). CONCLUSIONS: Partial liquid ventilation is associated with notable improvement in gas exchange and with a reduction in the histologic and morphologic changes observed in an oleic acid model of acute lung injury.     

Effects of physical training on ventilatory equivalent and respiratory exchange ratio during weight supported, steady-state exercise

Thirty-three college men participated in a 9-week endurance training program. An equal number of subjects served as controls. Pre- and post-test metabolic measurements were made during 10 min of submaximal exercise (1080 kpm/min at 60 rpm) and 15 min of recovery. Measurements included oxygen consumption, CO2 production, ventilatory equivalent (Ve/VO2 ratio) and respiratory exchange ratio (R). A three factor design variance analysis was used to analyze the effects of training on min-by-min exercise and recovery Ve/VO2 ratio and R. For the experimental group training resulted in a significant improvement in ventilatory efficiency during exercise, as well as a significant decrease in R. During recovery, Ve/VO2 and R decreased significantly for both groups although the magnitude of change was greater for the group that trained. Apparently, there was a significant habituation effect due to test procedures for the control group. The results are discussed in terms of lactate production and substrate utilization during exercise.     

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.     

Comparative physiologic effects of noninvasive assist-control and pressure support ventilation in acute hypercapnic respiratory failure

STUDY OBJECTIVE: To compare the effects of noninvasive assist-control ventilation (ACV) and pressure support ventilation (PSV) by nasal mask on respiratory physiologic parameters and comfort in acute hypercapnic respiratory failure (AHRF). DESIGN: A prospective randomized study. SETTING: A medical ICU. PATIENTS AND INTERVENTIONS: Fifteen patients with COPD and AHRF were consecutively and randomly assigned to two noninvasive ventilation (NIV) sequences with ACV and PSV mode, spontaneous breathing (SB) via nasal mask being used as control. ACV and PSV settings were always subsequently adjusted according to patient's tolerance and air leaks. Fraction of inspired oxygen did not change between the sequences. MEASUREMENTS AND RESULTS: ACV and PSV mode strongly decreased the inspiratory effort in comparison with SB. The total inspiratory work of breathing (WOBinsp) expressed as WOBinsp/tidal volume (VT) and WOBinsp/respiratory rate (RR), the pressure time product (PTP), and esophageal pressure variations (deltaPes) were the most discriminant parameters (p<0.001). ACV most reduced WOBinsp/VT (p<0.05), deltaPes (p<0.05), and PTP (0.01) compared with PSV mode. The surface diaphragmatic electromyogram activity was also decreased >32% as compared with control values (p<0.01), with no difference between the two modes. Simultaneously, NIV significantly improved breathing pattern (p<0.01) with no difference between ACV and PSV for VT, RR, minute ventilation, and total cycle duration. As compared to SB, respiratory acidosis was similarly improved by both modes. The respiratory comfort assessed by visual analog scale was less with ACV (57.23+/-30.12 mm) than with SB (75.15+/-18.25 mm) (p<0.05) and PSV mode (81.62+/-25.2 mm) (p<0.01) in our patients. CONCLUSIONS: During NIV for AHRF using settings adapted to patient's clinical tolerance and mask air leaks, both ACV and PSV mode provide respiratory muscle rest and similarly improve breathing pattern and gas exchange. However, these physiologic effects are achieved with a lower inspiratory workload but at the expense of a higher respiratory discomfort with ACV than with PSV mode.     

Preservation of humidity and heat of respiratory gases in spontaneously breathing, tracheostomized patients

BACKGROUND: Ventilation with endotracheal intubation bypasses the upper airway and the normal heat and moisture exchanging process of inspired gases. A continuous loss of moisture and heat occurs and predisposes patients to serious airway damage. We therefore prospectively studied one heated humidifier system, one cold humidifier system and one heat and moisture exchanger in spontaneously breathing, tracheostomized intensive care unit patients to determine the ability to preserve patients' heat and water. METHODS: Following a randomized order, 10 patients were spontaneously ventilated for 24-h periods with the Nam 35 humidifier (Europe Medical, France, a cold water humidifier), the heat and moisture exchange Trach-Vent (Gibeck, Sweden), and the Aerodyne humidifier (Kendall USA). In each patient, during the inspiration phase, the following measurements were performed: mean values of temperature and relative humidity of inspired gases. The absolute humidity was calculated. Values were obtained in each patients after 40 min and 24 h. RESULTS: The Trach-Vent filter and the Aerodyne humidifier had better humidification and thermic capacities than the Nam 35 humidifier (P < 0.001). With the Nam 35 humidifier, no patient had temperature of inspired gas > 29 degrees C. Concerning absolute humidity of inspired gases, the Nam 35 humidifier achieved a lower performance than the other two tested systems (P < 0.001). CONCLUSION: In spontaneously breathing, tracheostomized intensive care unit patients, the Trach-Vent heat and moisture exchanger and the Aerodyne heated system achieved satisfactorily preservation of heat and humidity of inspired gases.     

Effects of body temperature on ventilatory response to hypoxia and breathing pattern in man

The ventilatory response to hypoxia (PAO2 55 and 45 Torr) at each of four levels of PACO2 was studied in five healthy subjects before and after a rise in rectal temperature of 1.4 degrees C had been induced by means of a heated flying suit. At a given level of chemical drive both ventilation and mean inspiratory flow increased after heating, frequency relatively more than tidal volume. In isoventilation comparisons mean inspiratory flow was identical in normo- and hyperthermia, whereas the durations of inspiration (TI) and expiration (TE) were proportionately shortened. It is suggested that a rise in temperature shortens TI by affecting a central "clock" and that TE changes are secondary to changes in end-inspiratory volume. The euoxic CO2 response in hyperthermia was suggestive of multiplication between CO2 and temperature. Hypoxic sensitivity was significantly increased, indicating a temperature effect on the arterial chemoreceptors. The breathing pattern was in either temperature condition identical in euoxia and in hypoxia.     

Safety of combined heat and moisture exchanger filters in long-term mechanical ventilation

Immediate breast reconstruction with the tissue expander is now established as an accepted procedure after mastectomy, and large series have been published concerning the technique and its complications. Unfortunately, only scarce information is available regarding the long-term aesthetic results and patient satisfaction achieved by immediate reconstruction using tissue expansion. In this study, we reviewed 52 patients who had undergone immediate breast reconstruction using the tissue expander with a follow-up of at least 1 year after completion of the reconstruction. We developed an objective assessment of patient satisfaction, aesthetic results, and the factors affecting them. The results show remarkable concordance of assessment by patient, surgeon, and independent observer: All gave good scores for aesthetic appearance (6.4 to 7.4 on a scale of 1 to 10). A total of 92.3 percent of patients rated their satisfaction as good to excellent. Symmetry was the main parameter influencing the patients' score, while the surgeon's score also was affected by the quality of the inframammary fold and capsular contracture. Breast size, chemotherapy, complications, time interval, and additional procedures had no relation to either scoring or patient satisfaction.     

Comparing two heat and moisture exchangers, one hydrophobic and one hygroscopic, on humidifying efficacy and the rate of nosocomial pneumonia

OBJECTIVE: Many heat and moisture exchangers with filter (HMEF) have been developed. In-house data from companies provide some information about their performances; unfortunately, to our knowledge, no comparative evaluation in clinical conditions has been undertaken of these newer products. The aim of this study was to compare the efficiency of two HMEFs, one hydrophobic and one hygroscopic, on humidifying capacity and the rate of bronchial colonization and ventilator-associated pneumonia in ICU patients. DESIGN: Prospective, randomized study. SETTING: ICU of a university hospital. PATIENTS: All patients who required mechanical ventilation for > or = 24 h during the study period. INTERVENTIONS: On admission to the ICU, patients were randomly assigned to one of two groups. In one group, the patients were ventilated with a hygroscopic device (Humid-Vent Filter Light HMEF; Gibeck; Upplands Vaesby, Sweden). The condensation surface was made of paper (Microwell) impregnated with CaCl2. The filter membrane was made of polypropylene. In the other group, the patients were ventilated with a hydrophobic device (Pall BB100 HMEF). The condensation surface was made of a hydrophobic resin with a hydrophylic layer. The filter membrane was made of ceramic fibers. In both groups, HMEFs were changed daily. MEASUREMENTS AND RESULTS: Both groups of patients were similar for the tested characteristics, including parameters of mechanical ventilation. Sixty-six patients were ventilated for 11.7+/-11 days with the Humid-Vent Filter Light HMEF and 70 patients for 12.2+/-12 days with the Pall BB 100. Patients ventilated with the Humid-Vent Filter Light underwent 6.0+/-3.0 tracheal aspirations and 1.7+/-2.0 instillations per day, and those with the Pall BB 100, 6.0+/-3.0 and 1.6+/-2.0 per day, respectively (not significant [NS]). Abundance of tracheal secretions, presence of blood, and viscosity, evaluated by semiquantitative scales, were similar in both groups. No difference in the rate of atelectasis was observed between the two groups (7.5% and 7.1%, NS). One episode of tracheal tube occlusion was observed with the Humid-Vent Filter Light HMEF, and one with the other HMEF (NS). One patient in each group (NS) was switched to an active heated humidifier because of very tenacious bronchial secretions despite repeated instillations. Tracheal colonization was observed at a rate of 67% with the Humid-Vent Filter Light and 58% with the Pall BB 100 (NS). A small, but NS difference was observed in the rate of ventilator-associated pneumonia: Humid-Vent Filter Light, 32% (27.1 per 1000 ventilator days); and Pall BB 100, 37% (30.4 per 1000 ventilator days). Bacteria responsible for tracheal colonization and pneumonia were similar in both groups. Three patients in each group died from their nosocomial pneumonia. CONCLUSION: Despite differences in their components, the two HMEFs tested achieved similar performances in terms of humidification and heating of inspired gases. Only one episode of endotracheal tube occlusion was detected and very few patients (one in each group) had to be switched to an active heated humidifier. No difference was observed either in the rate of tracheal colonization or of ventilator-associated pneumonia. These data show that the hygroscopic HME (Humid-Vent Filter Light) and the hydrophobic HME (Pall BB 100) are suited for use in ICU patients.     

Comparison of noninvasive positive pressure ventilation with standard medical therapy in hypercapnic acute respiratory failure

STUDY OBJECTIVE: To compare the efficacy of standard medical therapy (ST) and noninvasive mechanical ventilation additional to standard medical therapy in hypercapnic acute respiratory failure (HARF). DESIGN: Single center, prospective, randomized, controlled study. SETTING: Pulmonary medicine directed critical care unit in a university hospital. PATIENTS: Between March 1993 and November 1996, 30 HARF patients were randomized to receive ST or noninvasive positive pressure ventilation (NPPV) in addition to ST. INTERVENTIONS: NPPV was given with an air-cushioned face via a mechanical ventilator (Puritan Bennett 7200) with initial setting of 5 cm H2O continuous positive airway pressure and 15 cm H2O pressure support. RESULTS: At the time of randomization, patients in the ST group had (mean+/-SD) PaO2 of 54+/-13 mm Hg, PaCO2 of 67+/-11 mm Hg, pH of 7.28+/-0.02, and respiratory rate of 35.0+/-5.8 breaths/min. Patients in the NPPV group had PaO2 of 55+/-14, PaCO2 of 69+/-15, pH of 7.27+/-0.07, and respiratory rate of 34.0+/-8.1 breaths/min. With ST, there was significant improvement of only respiratory rate (p < 0.05). However, with NPPV, PaO2 (p < 0.001), PaCO2 (p < 0.001), pH (p < 0.001), and respiratory rate (p < 0.001) improved significantly compared with baseline. Six hours after randomization, pH (p < 0.01) and respiratory rate (p < 0.01) in NPPV patients were significantly better than with ST. Hospital stay for NPPV vs ST patients was, respectively, 11.7+/-3.5 and 14.6+/-4.7 days (p < 0.05). One patient in the NPPV group required invasive mechanical ventilation. The conditions of six patients in the ST group deteriorated and they were switched to NPPV; this was successful in four patients, two failures were invasively ventilated. CONCLUSION: This study suggests that early application of NPPV in HARF patients facilitates improvement, decreases need for invasive mechanical ventilation, and decreases the duration of hospitalization.     

Outcomes of noninvasive positive-pressure ventilation in patients with acute hypercapnia complicating chronic respiratory failure]

We used noninvasive positive-pressure ventilation to treat hypercapnea due to acute exacerbations of chronic respiratory failure (21 episodes in 19 patients; COPD, 4; pulmonary tuberculosis sequelae, 4; silicosis, 3; silicotuberculosis, 3; bronchiectasis, 3; others, 2). All patients had acute onsets of severe hypercapnea (PaCO2 > 45 Torr), acute decreases in pH (< 7.35), and tachypnea, paradoxical breathing or both. During the first 2 to 4 hours of bi-level positive airway pressure, PaCO2 decreased from 72 to 61 Torr (p < 0.0005), pH increased from 7.26 to 7.31 (p < 0.001), and respiratory rate decreased from 30 to 25 breaths/min (p < 0.005). In three cases leakage of air through the mouth prevented improvement in the patients' conditions, but in two of those a face mask was then used successfully. In 17 of the 21 episodes (81%) gas exchange improved and intubation was not necessary. In those 17, the mean duration of noninvasive positive-pressure ventilation was 6.3 days. We conclude that noninvasive positive-pressure ventilation can improve gas exchange in patients with acute hypercapnea complicating chronic respiratory failure.     

Effect of noninvasive positive pressure ventilation on mortality in patients admitted with acute respiratory failure: a meta-analysis

Changes in angiogenesis and expression of extracellular matrix-degrading enzymes have been substantiated during progression of solid tumours, whereas information on haematological tumours remains circumstantial. In this study, 57 biopsies of mycosis fungoides (MF), a haematological tumour of T-cell lineage, were investigated immunohistochemically for the extent of angiogenesis, and by in situ hybridisation for the expression of matrix metalloproteinases 2 (MMP-2, collagenase A) and 9 (MMP-9, collagenase B). The biopsies we grouped according to the stage of progression: patch-->plaque-->nodular (most advanced). The extent of angiogenesis, as microvessel area, of MF lesions as a whole was significantly higher than that of normal uninjured skin, used as a control. When the stages of MF progression were compared, the values of MF patch stage overlapped that of control skin, while values were significantly higher in the plaque stage and even higher in the nodular stage. In these stages, microvessels were widely scattered in the tumour tissue, in close association with tumour cells, and they frequently displayed arborisation and microaneurysmatic dilation. In contrast, in the patch stage microvessels were irregularly distributed around the tumour aggregates, and arborisation or dilated structures were only rarely seen. The expression of MMP-2 and MMP-9 mRNAs underwent significant upregulation in relation to advancing stage. Indeed, the upstaging was significantly associated with higher proportions of lesions positive for each mRNA or for both, and with lesions with the greatest intensity of expression for each mRNA. Besides tumour cells, the MMP-2 mRNA was expressed by microvascular endothelial cells of intratumour and peri-tumour vessels, and by fibroblasts which were especially abundant in the stroma adjacent to the tumour nodules. The MMP-9 mRNA was found to be present in a subset of tissue macrophages which were more frequently located in close vicinity to the tumour nodules. In contrast, in control skin, a weak positivity for the MMP-2 mRNA in very few microvascular endothelial cells and no signal for the MMP-9 mRNA were observed. These in situ data suggest that angiogenesis and degradation of the extracellular matrix occur simultaneously during MF progression. They imply that interaction between tumour cells and their microvasculature are all the more likely to occur during progression, occasionally with the contribution of tumour-associated stromal cells.     

Effects of negative pressure assisted ventilation on dyspnoeic sensation and breathing pattern

Although negative pressure assisted ventilation with an assist-control mode may have a potential therapeutic role in the treatment of severe dyspnoea, the effects of negative pressure assisted ventilation with the assist-control mode on dyspnoea and breathing patterns have not been examined. We examined the effects of negative pressure assisted ventilation with the assist-control mode on dyspnoea and breathing patterns produced by a combination of resistive loading and hypercapnia in nine healthy subjects breathing spontaneously. Subjects were asked to rate their sensation of respiratory discomfort using a visual analogue scale. Negative pressure assisted ventilation caused a significant reduction in sensation of respiratory discomfort from a visual analogue scale score of 74 (55-91) (median (range)) before negative pressure assisted ventilation to 34 (15-53) during negative pressure assisted ventilation (p<0.01). During negative pressure assisted ventilation, there were significant changes in breathing patterns characterized by an increase in tidal volume and a decrease in respiratory frequency, while neither minute ventilation nor end-tidal carbon dioxide tension changed. Our results indicate that negative pressure assisted ventilation with the assist-control mode is effective in relief of dyspnoea and that negative pressure assisted ventilation influences the control of breathing to minimize respiratory discomfort.