Natriuretic peptide-driven fluid management during ventilator weaning: a randomized controlled trial.

RATIONALE: Difficult weaning from mechanical ventilation is often associated with fluid overload. B-type natriuretic peptide (BNP) has been proposed as a tool for predicting and detecting weaning failure of cardiovascular origin. OBJECTIVES: To investigate whether fluid management guided by daily BNP plasma concentrations improves weaning outcomes compared with empirical therapy dictated by clinical acumen. METHODS: In a randomized controlled multicenter study, we allocated 304 patients to either a BNP-driven or physician-driven strategy of fluid management during ventilator weaning. To standardize the weaning process, patients in both groups were ventilated with an automatic computer-driven weaning system. The primary end point was time to successful extubation. MEASUREMENTS AND MAIN RESULTS: In the BNP-driven group, furosemide and acetazolamide were given more often and in higher doses than in the control group, resulting in a more negative median (interquartile range) fluid balance during weaning (-2,320 [-4,735, 738] vs. -180 [-2,556, 2,832] ml; P < 0.0001). Time to successful extubation was significantly shorter with the BNP-driven strategy (58.6 [23.3, 139.8] vs. 42.4 [20.8, 107.5] h; P = 0.034). The BNP-driven strategy increased the number of ventilator-free days but did not change length of stay or mortality. The effect on weaning time was strongest in patients with left ventricular systolic dysfunction. The two strategies did not differ significantly regarding electrolyte imbalance, renal failure, or shock. CONCLUSIONS: Our results suggest that a BNP-driven fluid management strategy decreases the duration of weaning without increasing adverse events, especially in patients with left ventricular systolic dysfunction. Clinical trial registered with www.clinicaltrials.gov (NCT00473148).

A new classification for sleep analysis in critically ill patients.

BACKGROUND: Patients in intensive care units (ICUs) experience severe sleep alterations and conventional sleep scoring rules are difficult to use in these patients. In a previous study, we showed that abnormal sleep EEG and wake EEG patterns could predict the outcome of noninvasive ventilation in a group of patients treated for acute respiratory failure. Our aims were to assess the prevalence of these abnormal sleep/wake EEG patterns in a larger group and search for objective parameters to help their identification. METHODS: We reviewed sleep studies previously performed with full polysomnography during 17-h in conscious nonsedated ICU patients receiving invasive ventilation during weaning or noninvasive ventilation for acute respiratory failure. RESULTS: We included 57 patients. Sleep scoring using conventional rules was not feasible in 16 (28%) patients due to the absence of stage-2 markers. Wake EEG in these 16 patients, although recognizable, showed abnormal features, including decreased reactivity to eye opening and slower peak EEG frequency compared to patients with normal sleep-wake EEGs. CONCLUSION: In almost one third of awake mechanically ventilated ICU patients, sleep cannot be classified with standard criteria. Two new states, atypical sleep and pathologic wakefulness, need to be added. We suggest rules for scoring these states. The origin and links with outcomes of these abnormal EEG patterns deserve investigation.

Comparison of the effects of two humidifier systems on endotracheal tube resistance.

PURPOSE: To compare the effects of two humidifier systems on endotracheal tube (ETT) resistance during mechanical ventilation, either an active heated humidifier (HH) or a passive heat and moisture exchanger (HME) was selected using current clinical recommendations. METHODS: This was a prospective clinical cohort study performed in an intensive care unit. Gas conditioning was performed using the HH in 22 patients and the HME in another 22. Patients were matched for endotracheal tube diameter, days of mechanical ventilation, simplified acute physiology score II (SAPS II), and fluid balance. RESULTS: Used-ETT resistance was measured immediately after extubation. Unused-ETT resistance was calculated with an identical, clean ETT. No differences were found between the HH and HME groups in ETT diameter (7.9 ± 0.4 vs. 7.9 ± 0.3 mm; p = 0.98), days of mechanical ventilation (11.3 ± 7.7 vs. 9.5 ± 4.5; p = 0.34), SAPS II (41.0 ± 13.6 vs. 42.0 ± 11.7; p = 0.79), or fluid balance (-2,552 ± 6,268 vs. -2,579 ± 5,422 mL; p = 0.98). ETT resistance increased from intubation to extubation: from 6.8 ± 1.1 to 10.6 ± 4.3 cmH(2)O L(-1) s(-1) in the HH group, (p < 0.001) and from 6.8 ± 1.1 to 10.2 ± 3.8 cmH(2)O L(-1) s(-1) in the HME group (p < 0.001), which is a 53% average increase in resistive load. CONCLUSIONS: We did not find differences between the two types of humidifiers in terms of airflow resistance during prolonged mechanical ventilation when the devices were selected on the basis of individual clinical needs. The increase in resistive load is physiologically relevant.

Physiological comparison of three spontaneous breathing trials in difficult-to-wean patients.

PURPOSE: To compare cardiovascular and respiratory responses to different spontaneous breathing trials (SBT) in difficult-to-wean patients using T-piece and pressure support ventilation (PSV) with or without positive end-expiratory pressure (PEEP). METHODS: Prospective physiological study. Fourteen patients who were monitored with a Swan-Ganz catheter and had failed a previous T-piece trial were studied. Three SBTs were performed in random order in all patients: PSV with PEEP (PSV-PEEP), PSV without PEEP (PSV-ZEEP), and T-piece. PSV level was 7 cmH(2)O, and PEEP was 5 cmH(2)O. Inspiratory muscle effort was calculated, and hemodynamic parameters were measured using standard methods. RESULTS [MEDIAN (AND INTERQUARTILE RANGE)]: Most patients succeeded in the PSV-PEEP (11/14) and PSV-ZEEP (8/14) trials, but all failed the T-piece trial. Patient effort was significantly higher during T-piece than during PSV with or without PEEP [esophageal pressure-time product was 292 (238-512), 128 (58-299), and 148 (100-465) cmH(2)O x s/min, respectively, p < 0.05]. Left ventricular heart failure was observed in 11 of the 14 patients during the T-piece trial. Pulmonary artery occlusion pressure and respiratory rate were significantly higher during T-piece than with PSV-PEEP [21 (18-24) mmHg versus 17 (14-22) mmHg, p < 0.05 and 27 (21-35) breaths/min versus 19 (16-29) breaths/min, p < 0.05 respectively]. Tidal volume was significantly lower during the T-piece trial. CONCLUSION: In this selected population of difficult-to-wean patients, PSV and PSV plus PEEP markedly modified the breathing pattern, inspiratory muscle effort, and cardiovascular response as compared to the T-piece. Caregivers should be aware of these differences in SBT as they may play an important role in weaning decision-making.

Poor sleep quality is associated with late noninvasive ventilation failure in patients with acute hypercapnic respiratory failure.

OBJECTIVE: To determine whether sleep quality helps to predict noninvasive ventilation outcome in patients with acute hypercapnic respiratory failure. Despite an initial clinical improvement, nearly one fourth of patients may fail noninvasive ventilation after several days. Because late intubation is associated with a poor prognosis, it may be useful to identify factors that may predict or explain late noninvasive ventilation failure. PATIENTS: We prospectively studied 27 hypercapnic patients in a medical intensive care unit who required noninvasive ventilation for >48 hrs. INTERVENTIONS: A 17-hr sleep polysomnography (3 PM-8 AM) was recorded 2 days to 4 days after noninvasive ventilation initiation. Late noninvasive ventilation failure was defined as death, endotracheal intubation, or persistent need for noninvasive ventilation on day 6. MEASUREMENTS AND MAIN RESULTS: An abnormal electroencephalographic pattern that eluded analysis by standard sleep-scoring criteria was noted in seven (50%) of the 14 patients with late noninvasive ventilation failure compared with one (8%) of the 13 patients successfully treated with noninvasive ventilation (p = .03). No clinical or laboratory variables explained the electroencephalographic differences. Patients failing noninvasive ventilation had poorer sleep quality with greater circadian sleep-cycle disruption and less nocturnal rapid eye movement sleep (6 mins [range, 0-12] vs. 26 mins [range, 6-49], p = .03), compared with patients successfully treated with noninvasive ventilation. Noninvasive ventilation failure was associated with delirium during the intensive care unit stay (64% vs. 0%). CONCLUSIONS: Late noninvasive ventilation failure in elderly patients with acute hypercapnic respiratory failure was associated with early sleep disturbances including an abnormal electroencephalographic pattern, disruption of the circadian sleep cycle, and decreased rapid eye movement sleep.

Sleep in the intensive care unit.

Intensive care unit (ICU) environment is not propitious for restoring sleep. Alterations in sleep have potential detrimental consequences explaining increasing interest in the field over the last years. Methods to study sleep in ICU meets some limitations. Accurate sleep analysis requires full polysomnography, but polysomnographic patterns of normal sleep are frequently lacking in these patients and conventional scoring rules may be inadequate. Patients experience severe alterations of sleep with sleep loss, sleep fragmentation and sleep-wake cycle disorganization. Many factors may contribute to these abnormalities, including patient-related factors (e.g., disease severity) environmental factors (e.g., continuous exposure to light and noise, around-the-clock care, and medications). Health support techniques such as mechanical ventilation and sedation may also contribute to sleep disruption. The impact of sleep disturbances on morbidity and mortality in ICU patients remains unknown but inferences from experimental studies or indirect evidence suggest possible immune function alterations and neuropsychological dysfunction that could hamper weaning from assisted ventilation. Whether sleep disruption in ICU patients is independently associated with adverse outcomes or merely constitutes a marker for cerebral dysfunction remains to be determined. However, whatever signification and mechanisms of these alterations, now specific measures are recommended to protect sleep and circadian rhythm in ICU.

Sleep quality in mechanically ventilated patients: comparison of three ventilatory modes.

OBJECTIVES: To compare the influence of three ventilatory modes on sleep. DESIGN: Prospective, comparative, crossover study. SETTING: Medical intensive care unit in a university hospital. PATIENTS: Fifteen conscious, nonsedated, mechanically ventilated patients. INTERVENTIONS: Patients were successively ventilated with assist-control ventilation, clinically adjusted pressure support ventilation (cPSV), and automatically adjusted pressure support ventilation (aPSV). Sleep polysomnography was performed during three consecutive 6-hr periods, one with each mode in random order. Airway pressure and thorax and abdomen plethysmography were used to diagnose central apneas and ineffective efforts. MEASUREMENTS AND MAIN RESULTS: The main abnormalities were a low percentage of rapid eye movement (REM) sleep counting, for a median (25th-75th percentiles) of 10% (3.5-12.5) of total sleep, and a highly fragmented sleep with 29 arousals and awakenings per hour of sleep. REM sleep duration was similar in the three ventilatory modes, 7% in assist-control, 4% in aPSV, and 1% during cPSV (p = .54), as well as in the fragmentation index, 31 arousals and awakenings per hour in assist-control, 32 in aPSV, and 34 during cPSV (p = .62). Ineffective efforts occurred similarly with the three modes (seven per hour of sleep in assist-control, 16 in aPSV, and 12 during cPSV) or central apneas during PSV (five in aPSV, seven during cPSV). Minute ventilation was similar with the three modes. CONCLUSIONS: In conscious, mechanically ventilated patients, sleep architecture was highly abnormal, with a short REM stage and a high degree of fragmentation. The ventilatory mode did not influence sleep pattern, arousals, awakenings, and ineffective efforts.

Reduction of patient-ventilator asynchrony by reducing tidal volume during pressure-support ventilation.

OBJECTIVE: To identify ventilatory setting adjustments that improve patient-ventilator synchrony during pressure-support ventilation in ventilator-dependent patients by reducing ineffective triggering events without decreasing tolerance. DESIGN AND SETTING: Prospective physiological study in a 13-bed medical intensive care unit in a university hospital. PATIENTS AND PARTICIPANTS: Twelve intubated patients with more than 10% of ineffective breaths while receiving pressure-support ventilation. INTERVENTIONS: Flow, airway-pressure, esophageal-pressure, and gastric-pressure signals were used to measure patient inspiratory effort. To decrease ineffective triggering the following ventilator setting adjustments were randomly adjusted: pressure support reduction, insufflation time reduction, and change in end-expiratory pressure. MEASUREMENTS AND RESULTS: Reducing pressure support from 20.0 cm H(2)O (IQR 19.5-20) to 13.0 (12.0-14.0) reduced tidal volume [10.2ml /kg predicted body weight (7.2-11.5) to 5.9 (4.9-6.7)] and minimized ineffective triggering events [45% of respiratory efforts (36-52) to 0% (0-7)], completely abolishing ineffective triggering in two-thirds of patients. The ventilator respiratory rate increased due to unmasked wasted efforts, with no changes in patient respiratory rate [26.5 breaths/min (23.1-31.9) vs. 29.4 (24.6-34.5)], patient effort, or arterial PCO(2). Shortening the insufflation time reduced ineffective triggering events and patient effort, while applying positive end-expiratory pressure had no influence on asynchrony. CONCLUSIONS: Markedly reducing pressure support or inspiratory duration to reach a tidal volume of about 6 ml/kg predicted body weight eliminated ineffective triggering in two-thirds of patients with weaning difficulties and a high percentage of ineffective efforts without inducing excessive work of breathing or modifying patient respiratory rate.

Mechanical ventilation: let us minimize sleep disturbances.

PURPOSE OF REVIEW: This review provides a background in mechanical ventilation and sleep. RECENT FINDINGS: Sleep pattern in mechanically ventilated patients differs largely from physiological sleep. The ventilatory mode and the ventilatory settings could have an influence on the sleep quality and quantity. Pressure support ventilation can increase the sleep fragmentation and decrease the sleep quantity, due to central apneas when compared with assist control ventilation. An excessive level of ventilatory assistance during sleep promotes central apneas and ineffective efforts. These two respiratory events can trigger arousals and awakenings, thus altering the sleep quality and quantity in mechanically ventilated patients. Ventilatory settings adjusted according to the patient's effort during pressure support allow reducing the number of ineffective efforts and improve sleep quality when compared with a clinical adjustment. A physiological approach to set the ventilator and the ventilatory mode may improve sleep quality and quantity. SUMMARY: Minimizing the sleep alterations in mechanically ventilated patients could be obtained by setting the ventilator in such a way to avoid hyperventilation during the sleep stage. The impact of sleep derangements in patient outcomes is, however, unknown.

Patient-ventilator asynchrony during assisted mechanical ventilation.

OBJECTIVE: The incidence, pathophysiology, and consequences of patient-ventilator asynchrony are poorly known. We assessed the incidence of patient-ventilator asynchrony during assisted mechanical ventilation and we identified associated factors. METHODS: Sixty-two consecutive patients requiring mechanical ventilation for more than 24 h were included prospectively as soon as they triggered all ventilator breaths: assist-control ventilation (ACV) in 11 and pressure-support ventilation (PSV) in 51. MEASUREMENTS: Gross asynchrony detected visually on 30-min recordings of flow and airway pressure was quantified using an asynchrony index. RESULTS: Fifteen patients (24%) had an asynchrony index greater than 10% of respiratory efforts. Ineffective triggering and double-triggering were the two main asynchrony patterns. Asynchrony existed during both ACV and PSV, with a median number of episodes per patient of 72 (range 13-215) vs. 16 (4-47) in 30 min, respectively (p=0.04). Double-triggering was more common during ACV than during PSV, but no difference was found for ineffective triggering. Ineffective triggering was associated with a less sensitive inspiratory trigger, higher level of pressure support (15 cmH(2)O, IQR 12-16, vs. 17.5, IQR 16-20), higher tidal volume, and higher pH. A high incidence of asynchrony was also associated with a longer duration of mechanical ventilation (7.5 days, IQR 3-20, vs. 25.5, IQR 9.5-42.5). CONCLUSIONS: One-fourth of patients exhibit a high incidence of asynchrony during assisted ventilation. Such a high incidence is associated with a prolonged duration of mechanical ventilation. Patients with frequent ineffective triggering may receive excessive levels of ventilatory support.

A multicenter randomized trial of computer-driven protocolized weaning from mechanical ventilation.

RATIONALE AND OBJECTIVES: Duration of weaning from mechanical ventilation may be reduced by the use of a systematic approach. We assessed whether a closed-loop knowledge-based algorithm introduced in a ventilator to act as a computer-driven weaning protocol can improve patient outcomes as compared with usual care. METHODS AND MEASUREMENTS: We conducted a multicenter randomized controlled study with concealed allocation to compare usual care for weaning with computer-driven weaning. The computerized protocol included an automatic gradual reduction in pressure support, automatic performance of spontaneous breathing trials (SBT), and generation of an incentive message when an SBT was successfully passed. One hundred forty-four patients were enrolled before weaning initiation. They were randomly allocated to computer-driven weaning or to physician-controlled weaning according to local guidelines. Weaning duration until successful extubation and total duration of ventilation were the primary endpoints. MAIN RESULTS: Weaning duration was reduced in the computer-driven group from a median of 5 to 3 d (p=0.01) and total duration of mechanical ventilation from 12 to 7.5 d (p=0.003). Reintubation rate did not differ (23 vs. 16%, p=0.40). Computer-driven weaning also decreased median intensive care unit (ICU) stay duration from 15.5 to 12 d (p=0.02) and caused no adverse events. The amount of sedation did not differ between groups. In the usual care group, compliance to recommended modes and to SBT was estimated, respectively, at 96 and 51%. CONCLUSIONS: The specific computer-driven system used in this study can reduce mechanical ventilation duration and ICU length of stay, as compared with a physician-controlled weaning process.

Computer-driven management of prolonged mechanical ventilation and weaning: a pilot study.

OBJECTIVE: To evaluate the ability of a computer-driven system (CDS) to manage pressure-support ventilation over prolonged periods and to predict weaning readiness compared to intensivists. The system continuously adapts pressure support, gradually decreases ventilatory assistance when possible, and indicates weaning readiness. DESIGN AND SETTING: A two-center, prospective, open, clinical, pilot study in medical ICUs of two university hospitals. PATIENTS AND PARTICIPANTS: 42 consecutive mechanically ventilated patients (60+/-14 years, SAPS II 39+/-15), 9 of whom were excluded. INTERVENTIONS: As soon as patients could tolerate pressure support, they were ventilated with the CDS. The times of weaning readiness determined by the intensivists and CDS were compared. MEASUREMENTS AND RESULTS: Weaning was successful in 25 patients and failed in 7; unplanned extubation occurred in 1 patient. Time on CDS ventilation was 3+/-3 days (maximum, 12 days). The CDS detected weaning readiness earlier than the intensivists in 17 patients, and intensivists earlier than the CDS in 4; in 11 patients detection times coincided. CONCLUSIONS: A CDS was successful in fully managing pressure-support ventilation over prolonged periods and often proposed weaning readiness earlier than the intensivists did. Use of this CDS may reduce the duration of mechanical ventilation.