A Pilot Randomized Trial Comparing Weaning From Mechanical Ventilation on Pressure Support Versus Proportional Assist Ventilation.

OBJECTIVES: Despite protocols incorporating spontaneous breathing trials, 31% of ICU patients experience difficult or prolonged weaning from mechanical ventilation. Nonfatiguing modes such as pressure support ventilation are recommended. Proportional assist ventilation provides assistance in proportion to patient effort, which may optimize weaning. However, it is not known how proportional assist ventilation performs relative to pressure support ventilation over a prolonged period in the complex ICU setting. The purpose of this study was to compare the physiologic and clinical performance (failure rate), safety, and feasibility of protocols using daily spontaneous breathing trial plus pressure support ventilation versus proportional assist ventilation until ventilation discontinuation. DESIGN: Single-center, unblinded pilot randomized controlled trial. SETTING: Medical-surgical ICU of a tertiary-care hospital. PATIENTS: Adult patients intubated greater than 36 hours were randomized if they met eligibility criteria for partial ventilatory support, tolerated pressure support ventilation greater than or equal to 30 minutes, and either failed or did not meet criteria for a spontaneous breathing trial. INTERVENTIONS: Patients were randomized to the pressure support ventilation or proportional assist ventilation protocol (PAV+, Puritan Bennett 840; Covidien, Boulder, CO). Both protocols used progressive decreases in level of assistance as tolerated, coupled with daily assessment for spontaneous breathing trials. MEASUREMENTS AND MAIN RESULTS: Of 54 patients randomized, outcome data are available for 50 patients; 27 were randomized to receive proportional assist ventilation and 23 to receive pressure support ventilation. There were no adverse events linked to the study interventions, and protocol violations were infrequent. Recruitment was slower than projected (1.3 patients per month). The median (interquartile range) time from randomization to successful extubation was 3.9 days (2.8-8.4 d) on proportional assist ventilation versus 4.9 days (2.9-26.3 d) on pressure support ventilation (p = 0.39). Time to live ICU discharge was 7.3 days (5.2-11.4 d) on proportional assist ventilation versus 12.4 days (7.5-30.8 d) on pressure support ventilation (p = 0.03). CONCLUSION: This pilot study demonstrates the utility, safety, and feasibility of the weaning protocols and provides important information to guide the design of a future randomized controlled trial comparing weaning from mechanical ventilation on pressure support ventilation versus proportional assist ventilation.

[Comparative study between intermittent (Müller Reanimator) and continuous positive airway pressure in the postoperative period of coronary artery bypass grafting]. / Estudo comparativo entre a pressão positiva intermitente (Reanimador de Müller) e contínua no pós-operatório de cirurgia de revascularização do miocárdio.

OBJECTIVE: To compare the effect of the use of intermittent and continuous positive airway pressure in postoperative patients undergoing coronary artery bypass grafting. METHODS: This study included forty patients divided into two groups: one undergoing continuous positive airway pressure (CPAP Group), and the other undergoing intermittent pressure (Müller Resuscitator Group). The patients were evaluated in relation to the several study variables at the following time points: preoperative, 3rd, 24th, and 48th hours. RESULTS: The patient groups were homogeneous in relation to the several demographic and clinical variables. The values of pO2, pCO2 and sO2 were within normal limits and no significant differences were found between the groups. Regarding respirometry, the groups showed significant differences in the tidal volume and respiratory rate at the 48th postoperative hour. Dyspnea and use of accessory muscle in postoperative assessments were found with a significantly higher frequency in patients undergoing CPAP. Patients undergoing Müller Resuscitator had a normal chest radiograph more frequently than did patients undergoing CPAP. CONCLUSION: Both devices were shown to be able to keep pO2, pCO2, and sO2 values within normal limits. However, when the objective was pulmonary reexpansion with less imposed workload, the Müller Resuscitator was more effective because of its prompter action and consequently lower levels of dyspnea, respiratory rate (RR) and use of accessory muscle were observed.

Asthma mortality: an analysis of one years experience, review of the literature and assessment of current modes of therapy.

This analysis of asthma mortality has emphasized the roles played in its pathogenesis by different modes of therapy as reported in the literature. In addition attention was directed towards yet another potentially lethal therapeutic modality, IPPB, the efficacy and potential benefits of which are critically questioned. IPPB treatments were related to every fatal episode of asthma which made up the entire asthma mortality experience during a 12 month period at Morrisania Hospital. The adverse consequences of IPPB therapy were reviewed and it was further suggested that its use in acute asthma attacks was related to lethal episodes of hypoxia and pneumothorax. The patient must, in order to trigger an IPPB apparatus, create a pre-determined negative pressure to initiate inflation. The machine may, therefore, be ineffective in a patient with severe obstruction and greatly increased airway resistance either because of the inability to trigger it or with adequate triggering the subsequent delivery of an inadequate tidal volume at the pressure limitation set. Thus, severe hypercapnia and hypoxia may result especially if oxygen enriched gas mixtures are not used. This may occur even with the delivery of an adequate tidal volume since its distribution within the lungs is poor resulting in a worsening of ventilation-perfusion relationships as evidenced by an increase in the measured physiologic dead space. This experience and review of the literature suggests that IPPB treatment in asthma, especially during an acute attack, should always be administered with small doses of nebulized bronchodilators and oxygen with careful monitoring of arterial blood gases. This will allow for the detection of the adverse effects of this mode of therapy which may exceed the hoped for benefits, the most important being bronchodilatation and subsequent mobilization of secretions with continued treatment.

Airway resistance in infants after various treatments for hyaline membrane disease: special emphasis on prolonged high levels of inspired oxygen.

Thoracic gas volume, airway resistance (Raw), and dynamic lung compliance (CL) were measured in 48 infants surviving after hyaline membrane disease. Some infants were found to have a small reduction in CL after recovery from the acute phase of the illness but no other abnormalities were detected, irrespective of the type of treatment received. When studied again between the ages of 4 and 10 months, CL had returned to normal, but all infants who had been treated with intermittent positive pressure ventilation (IPPV) during the neonatal period were found to have developed a raised Raw. In contrast, all nonventilated infants, including those who had received up to five days of oxygen therapy in concentrations above 80%, had normal lung function. We conclude that IPPV, and not the increased inspired oxygen concentration, damaged the airways and interfered with their growth.

Chronic pulmonary disease in neonates with assisted ventilation.

Chronic lung disease in the form of stage III or IV bronchopulmonary dysplasia (BPD) was found to occur among nine of 188 infants receiving intermittent positive-pressure ventilation for respiratory insufficiency. None occurred in infants ventilated with a mask alone. The duration of endotracheal intubation was not significantly longer in patients developing BPD; however, the duration of exposure to inspired oxygen greater than 60 percent was significantly longer in that group (mean, 141 hours). A previously undescribed form of chronic lung disease was found to occur among nine of 150 infants ventilated because of underlying idiopathic respiratory distress syndrome. A radiographic appearance of diffuse haziness with loss of identifiable lung markings occurred at 5 to 15 days of age and was not associated with clinical signs or symptoms or increased oxygen needs. These changes disappeared in one to five days.

Pediatric noninvasive nasal ventilation.

Noninvasive nasal ventilation is an effective but underutilized method of chronic respiratory support for patients with respiratory insufficiency due to neuromuscular disease. Noninvasive nasal ventilation corrects nocturnal hypoxia and hypercapnia, resolving symptoms of chronic alveolar hypoventilation. Noninvasive nasal ventilation can allow selected patients with acute respiratory failure to avoid intubation and it can facilitate endotracheal extubation. Practical guidelines and the rationale for pediatric noninvasive nasal ventilation therapy will be discussed in this review.

Intermittent positive-pressure breathing. A critical appraisal.

There are relatively few valid indications for the use of intermittent positive-pressure breathing (IPPB). It is of limited or no value as prophylaxis of postoperative pulmonary problems (pneumonia, atelectasis) or as a means of delivering aerosol medications or treating stable chronic obstructive pulmonary disease. In these situations, IPPB has few if any advantages over voluntary hyperventilation or deep breathing.

Fatal air embolism after subclavian vein catheterization. Case report.

The authors describe a case of fatal air embolism in a patient with an endovenous catheter introduced into the subclavian vein through a supraclavicular way. The opening of pleura caused by the needle during the thrusting of the needle caused a subcutaneous supraclavicular and laterocervical emphysema during ventilation with intermittent positive pressure (IPPV). The authors suggest that IPPV, in the postoperative period following kidney removal, was the main ancillary reason of the air embolism since opening of pleura, in a patient who breathes spontaneously, only induces pneumothorax according to the majority of the authors.

Intermittent positive pressure breathing and the treatment of acute asthma.

Whether or not intermittent positive pressure breathing (IPPB) is beneficial in the treatment of asthma has been controversial for 30 years. IPPB is expensive and has been associated with pulmonary infection, pneumomediastinum, pneumothorax, and death. The exact factors involved in the observed effectiveness of IPPB remain undetermined. With evidence from a literature review, it is concluded that in cases of severe asthma failing to respond to other methods of beta-agonist inhalation, there is sufficient evidence for the use of IPPB.

Evaluation of manual and automatic manually triggered ventilation performance and ergonomics using a simulation model.

BACKGROUND: In the absence of endotracheal intubation, the manual bag-valve-mask (BVM) is the most frequently used ventilation technique during resuscitation. The efficiency of other devices has been poorly studied. The bench-test study described here was designed to evaluate the effectiveness of an automatic, manually triggered system, and to compare it with manual BVM ventilation. METHODS: A respiratory system bench model was assembled using a lung simulator connected to a manikin to simulate a patient with unprotected airways. Fifty health-care providers from different professional groups (emergency physicians, residents, advanced paramedics, nurses, and paramedics; n = 10 per group) evaluated manual BVM ventilation, and compared it with an automatic manually triggered device (EasyCPR). Three pathological situations were simulated (restrictive, obstructive, normal). Standard ventilation parameters were recorded; the ergonomics of the system were assessed by the health-care professionals using a standard numerical scale once the recordings were completed. RESULTS: The tidal volume fell within the standard range (400-600 mL) for 25.6% of breaths (0.6-45 breaths) using manual BVM ventilation, and for 28.6% of breaths (0.3-80 breaths) using the automatic manually triggered device (EasyCPR) (P < .0002). Peak inspiratory airway pressure was lower using the automatic manually triggered device (EasyCPR) (10.6 ± 5 vs 15.9 ± 10 cm H2O, P < .001). The ventilation rate fell consistently within the guidelines, in the case of the automatic manually triggered device (EasyCPR) only (10.3 ± 2 vs 17.6 ± 6, P < .001). Significant pulmonary overdistention was observed when using the manual BVM device during the normal and obstructive sequences. The nurses and paramedics considered the ergonomics of the automatic manually triggered device (EasyCPR) to be better than those of the manual device. CONCLUSIONS: The use of an automatic manually triggered device may improve ventilation efficiency and decrease the risk of pulmonary overdistention, while decreasing the ventilation rate.

Massive air embolism in a neonate with respiratory distress.

The occurrence of massive air embolism in a neonate during treatment with intermittent positive-pressure respiration and positive end expiratory pressure is reported as a note of caution. It is possible that this complication may indeed be more common. Careful post-mortem examinations (including radiological examinations) are advocated in order that the true incidence of this devastating event shall be known.

Insidious onset of acute alveolar hypoventilation following intermittent positive-pressure breathing (IPPB).

2 patients developing acute alveolar hypoventilation following IPPB therapy are presented. The hypoventilation occurred insidiously following therapy. It is hypothesized that respiratory center depression from excessive oxygen administration caused the hypoventilation. When the IPPB machines were driven by compressed air instead of oxygen, this complication was revealed in 1 of the patients.

Effects of inspiratory support upon breathing in humans during wakefulness and sleep.

We have compared the effects on breathing of inspiratory mechanical support during wakefulness and sleep in healthy subjects. Nine awake volunteers breathed through a nose mask connected to a machine supplying variable levels of inspiratory positive airway pressure (IPAP). Tidal volume (VT), breath duration (TTOT) and end-tidal PCO2 (PETCO2) were measured over 1 min steady state periods with IPAP set at a minimal level (approx. 2 cmH2O) and at approx. 10 cmH2O. This protocol was repeated in 6 of the subjects during non-REM sleep. When awake, "10 cmH2O IPAP" caused a significant increase in mean VT from 513 to 842 ml and a significant fall in PETCO2 from 39.7 to 32.7 mmHg. During sleep, "10 cmH2O IPAP" caused no significant changes in VT (388 to 390 ml) or PETCO2 (41.8 to 39.8 mmHg). In each state, "10 cmH2O IPAP" had no significant effect on TTOT. Three subjects repeated the protocol with diaphragmatic surface EMG recorded as an index of efferent inspiratory activity. "10 cmH2O IPAP" had no consistent effect on EMG when awake but caused a reduction in each subject during sleep. We conclude that during non-REM sleep, inspiratory mechanical support is associated with a compensatory decrease in efferent inspiratory activity to achieve a similar tidal volume with maintenance of arterial PCO2. When awake, a "wakefulness drive to breathe" may be associated with maintained inspiratory activity such that mechanical support results in an increased tidal volume despite a fall in arterial PCO2.

Diagnosis of pneumothorax complicating mechanical ventilation.

Pneumothorax developed in 4 patients as a complication of mechanical ventilation and the manifestations were different in each case. The first patient had had a previous pneumomediastinum with symptoms of chest pain and rise in blood pressure. The second became restless and "fought" the ventilator. The third had pneumothorax previously and developed tachycardia and arrhythmias, and the level of end-expiratory pressure in the manometer of the ventilator rose above the present level. In the fourth patient, subcutaneous and submucous emphysema were apparent before pneumothorax was diagnosed. Pneumothorax was diagnosed promptly in all these patients, permitting adequate management without additional complications.