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Critical Care Medicine  |   January 2016
New versus Conventional Helmet for Delivering Noninvasive Ventilation: A Physiologic, Crossover Randomized Study in Critically Ill Patients
Author Notes
  • From Anesthesia and Intensive Care, “Maggiore Della Carità” Hospital, Novara, Italy (C.O., G.C., R.V., A.M., P.B., F.D.C.); Anesthesia and Intensive Care, Sant’Andrea Hospital, ASL VC, Vercelli, Italy (F.L., P.N.); the Medical Statistics and Cancer Epidemiology Unit, Eastern Piedmont University “A. Avogadro,” Novara, Italy (T.C., C.M.); the Department of Translational Medicine, Eastern Piedmont University “A. Avogadro,” Novara, Italy (F.D.C., P.N.); and CRRF Mons. L. Novarese, Moncrivello (VC), Italy (P.N.).
  • The first two authors contributed equally to this study.
    The first two authors contributed equally to this study.×
  • Part of the results of this study were presented in abstract form at the European Society of Intensive Care Medicine Congress in Paris, France, on October 8, 2013.
    Part of the results of this study were presented in abstract form at the European Society of Intensive Care Medicine Congress in Paris, France, on October 8, 2013.×
  • Submitted for publication February 16, 2015. Accepted for publication August 26, 2015.
    Submitted for publication February 16, 2015. Accepted for publication August 26, 2015.×
  • Address correspondence to Dr. Navalesi: Via Solaroli 17, 28100, Novara, Italy. paolo.navalesi@med.unipmn.it. Information on purchasing reprints may be found at www.anesthesiology.org or on the masthead page at the beginning of this issue. Anesthesiology’s articles are made freely accessible to all readers, for personal use only, 6 months from the cover date of the issue.
Article Information
Critical Care Medicine / Clinical Science / Airway Management / Critical Care / Respiratory System / Technology / Equipment / Monitoring
Critical Care Medicine   |   January 2016
New versus Conventional Helmet for Delivering Noninvasive Ventilation: A Physiologic, Crossover Randomized Study in Critically Ill Patients
Anesthesiology 1 2016, Vol.124, 101-108. doi:10.1097/ALN.0000000000000910
Anesthesiology 1 2016, Vol.124, 101-108. doi:10.1097/ALN.0000000000000910
Abstract

Background: The helmet is a well-tolerated interface for noninvasive ventilation, although it is associated with poor patient–ventilator interaction. A new helmet (NH) has proven to attenuate this limitation of the standard helmet (SH) in both bench study and healthy volunteers. The authors compared a NH and a SH in intensive care unit patients receiving noninvasive ventilation for prevention of postextubation respiratory failure; both helmets were also compared with the endotracheal tube in place before extubation.

Methods: Fourteen patients underwent 30-min trials in pressure support during invasive ventilation and then with a SH and a NH in a random order. The authors measured comfort, triggering delays, rates of pressurization (airway pressure–time product [PTP] of the first 300 [PTP300-index] and 500 [PTP500-index] ms from the onset of effort, and the first 200 ms from the onset of insufflation [PTP200]), time of synchrony between effort and assistance (Timesynch/Tineu), respiratory drive and frequency, arterial blood gases (ABGs), and rate of asynchrony.

Results: Compared with SH, NH improved comfort (5.5 [5.0 to 6.0] vs. 8.0 [7.8 to 8.0]), respectively, P < 0.001), inspiratory trigger delay (0.31 [0.22 to 0.43] vs. 0.25 [0.18 to 0.31] s, P = 0.007), and pressurization (PTP300-index: 0.8 [0.1 to 1.8] vs. 2.7 [7.1 to 10.0]%; PTP500-index: 4.8 [2.5 to 9.9] vs. 27.3 [16.2 to 34.8]%; PTP200: 13.6 [10.1 to 19.6] vs. 30.4 [24.9 to 38.4] cm H2O/s, P < 0.01 for all comparisons) and Timesynch/Tineu (0.64 [0.48 to 0.72] vs. 0.71 [0.61 to 0.81], P = 0.007). Respiratory drive and frequency, ABGs, and rate of asynchrony were not different between helmets. Endotracheal tube outperformed both helmets with respect to all variables, except for respiratory rate, ABGs, and asynchronies.

Conclusions: Compared with a SH, a NH improved comfort and patient–ventilator interaction.

Abstract

In 14 patients, a novel helmet provided more comfort and faster responses to effort than the standard helmet, but an endotracheal tube enabled the most rapid responses.

What We Already Know about This Topic
  • Mechanical ventilation using a helmet is associated with less discomfort versus commonly used interfaces (i.e., endotracheal tube, face mask). The upward displacement of the standard helmet makes the ventilator less responsive to patients’ breathing effort, while armpit braces contribute to discomfort.

What This Article Tells Us That Is New
  • In 14 patients, a novel helmet provided more comfort and faster responses to effort than the standard helmet, but an endotracheal tube enabled the most rapid responses.

Noninvasive ventilation (NIV) improves gas exchange and unloads the respiratory muscles in patients with acute respiratory failure of different etiologies.1,2  Depending on the several factors including the underlying disease, severity of acute respiratory failure, and associated comorbidities, the duration of NIV application varies from a few hours to several days.3  Both the performance of the interface and the patient’s tolerance may affect NIV outcome.4–7  The helmet is a NIV interface that, compared with the oronasal mask, is better tolerated for prolonged periods and thus allows longer continuous NIV application and fewer interruptions.7–10  Unfortunately, compared with the mask, the helmet is characterized by less-efficient rates of pressurization and triggering function and worsened patient–ventilator synchrony.11,12 
A new helmet (NH; Castar Next, Intersurgical, Italy) was recently introduced into clinical use in Europe and Asia. A NH is characterized by an annular openable ring placed underneath an inflatable cushion that secures the helmet without the need for armpit braces, as opposed to the standard helmet (SH).13  The NH is more effective in delivering NIV by avoiding, or at least reducing to a large extent, the upward displacement of the helmet during ventilator insufflation.13  A NH has shown, compared with a SH, improved performance with respect to pressurization rate and triggering, both during bench study13  and in healthy volunteers.14  However, these encouraging results have not yet been confirmed in intensive care unit (ICU) patients. In addition, no comparison between a NH and a SH regarding patient comfort has been performed in ICU patients.
We designed this study to assess and compare a SH and a NH in patients undergoing NIV to avert the risk of postextubation respiratory failure and reintubation. Our main interest in outcomes was patient’s comfort (primary endpoint) and to the following additional endpoints: triggering performance and rate of pressurization, respiratory rate and drive, arterial blood gases (ABGs), and patient–ventilator synchrony. In addition, NIV delivered with the two helmets was compared with invasive ventilation as delivered immediately before extubation through the endotracheal tube (ET).
Materials and Methods
This prospective crossover randomized controlled trial was performed from April to August 2012 in the ICU of the University Hospital “Maggiore della Carità” (Novara, Italy), in accordance with the principles outlined in the Declaration of Helsinki. The institutional ethics committee (Inter-hospital Ethical Committee, Novara, Italy) approved the study, and patient’s consent was obtained according to the Italian regulations. At the time the study was conducted, trial registration was not mandatory for this type of investigations.
Patients and Protocol
Patients were eligible for the study if they were invasively ventilated for more than 48 h, were awake, and had indications to receive prophylactic NIV after extubation, being at risk of postextubation respiratory failure.15–17  At inclusion, midazolam and propofol had been interrupted for at least 24 and 4 h, respectively, whereas remifentanil was administered up to 0.08 μg·kg−1·min−1, if necessary.18 
Patients were considered at risk of extubation failure when at least one of the following conditions was present: (1) chronic respiratory disorders, (2) chronic heart failure, (3) Paco2 > 45 mmHg during the spontaneous breathing trial, (4) two or more comorbidities, (5) morbid obesity (body mass index ≥ 35 kg/m2),19  and (6) weak cough, as assessed by an Airway Care Score values more than or equal to 8 and less than 12.15  The extubation criteria for the study protocol were those in use for clinical purposes in our ICU. Exclusion criteria were as follows: (1) age less than 18 yr, (2) pregnancy, (3) intracranial bleeding, (4) recent gastric or esophageal surgery, (5) tracheotomy, (6) active upper gastrointestinal bleeding, (7) lack of cooperation, and (8) inclusion in other research protocols.
After enrollment, a catheter for detection of electrical activity of the diaphragm (EAdi; Edi catheter, Maquet Critical Care, Sweden) was inserted, and correct positioning was assured.20  Each patient underwent three 30-min trials in pressure support ventilation, first with ET and then, after extubation, with a SH (Castar R, Intersurgical) and a NH, applied according to a computer-generated random sequence. Pressure support ventilation was delivered through the Servo-I ventilator (Maquet Critical Care), set with the following ventilator settings for the entire protocol: positive end-expiratory pressure (PEEP) of 10 cm H2O, inspiratory support of 10 cm H2O, inspiratory flow trigger at 1 l/min, expiratory trigger at 35% of peak inspiratory flow, and the fastest rate of pressurization. Software for air leaks compensation was used during both SH and NH trials. Inspired oxygen fraction (Fio2) was initially set to obtain pulse arterial oxygen saturation (Spo2) ≥ 94 and ≤ 97% and then maintained unmodified throughout the study period.
Predefined criteria for protocol interruption were as follows: (1) need for emergency reintubation; (2) severe acute respiratory acidosis, as defined by Paco2 > 55 mmHg and pH < 7.25; (3) inability to expectorate secretions; (4) hemodynamic instability (i.e., need for continuous infusion of dopamine or dobutamine more than 5 μg·kg−1·min−1, norepinephrine more than 0.1 μg·kg−1·min−1, or vasopressin to maintain mean arterial blood pressure more than 60 mmHg); (5) life-threatening arrhythmias or electrocardiographic signs of ischemia; or (6) loss of 2 or more points of Glasgow Coma Scale score.
Data Acquisition and Measurements
Airflow, airway pressure (Paw), and EAdi were acquired from the ventilator through a RS232 interface at a sampling rate of 100 Hz using dedicated software (NAVA Tracker version 3.0, Maquet Critical Care). Data were recorded and stored on a personal computer; the last minute of each trial was offline analyzed breath by breath, using a customized software.20 
The pressurization performance was assessed with the Paw-time product (PTP) of the first 200 ms computed from the onset of ventilator assistance (PTP200) and with the PTP of the first 300 and 500 ms from the onset of patient effort, indexed to the ideal PTP (PTP300-index and PTP500-index, respectively).13,21  The ideal PTP was computed considering a perfectly squared rectangle on the Paw-time tracing, having the height of the preset inspiratory pressure above PEEP, and the width of the time window considered (i.e., 0.3 and 0.5 s from the onset of the inspiratory effort, assessed from the EAdi tracing, for PTP300 and PTP500, respectively).13,21  The drop in Paw (ΔPtrigger) and the PTP during the triggering phase (PTPt) were computed to evaluate triggering performance.13,21 
Ventilator cycling rate (RRmec) and patient’s neural respiratory rate (RRneu) were calculated on the flow and EAdi tracings, respectively. The neural effort of the patient was evaluated by the EAdi peak value (EAdipeak).22,23  We calculated inspiratory (DelayTR-insp) and expiratory (DelayTR-exp) trigger delays24  and the time of synchrony between diaphragm activity and ventilator assistance, indexed to patient’s own (neural) inspiratory time (Timesynch/Tineu).21  Asynchronies (ineffective efforts, auto and double triggerings) were also assessed and expressed in absolute number and as asynchrony index (AI%), i.e., the total number of asynchronous events divided by the number of triggered and not triggered breaths.25 
At the end of each trial, arterial blood was sampled for gas analysis. At the end of both NIV trials, patient’s comfort was assessed by means of a numeric rating scale (NRS), validated and utilized for assessing pain,26–28  dyspnea,29  and comfort/discomfort,30,31  asking the patient to indicate a number between 0 (worst possible) and 10 (best possible) on an ICU-adapted large print scale including number and descriptors.31  Before protocol initiation, all patients received a detailed explanation about the 11-point NRS, including the manner in which it was going to be administered. The scores obtained were recorded without further indications or comments.
Statistical Analysis
We considered clinically important a 50% increase of the NRS value scored by the patient to indicate his/her comfort with a NH, as opposed to a SH, and accordingly calculated a minimum of 14 patients to be necessary (α risk of 0.05 and a β risk of 0.20). Because of the relatively small number of patients, we analyzed data by nonparametric tests. Data are presented as median and interquartile range (25th to 75th percentile], unless otherwise specified. We used the Wilcoxon signed-rank test for comparison between a SH and a NH. After excluding the presence of treatment–period interaction and carryover effect, we utilized the ANOVA on ranks to compare ET with a SH and a NH; the corrected Bonferroni post hoc test was applied, as indicated. We used the Spearman rank correlation test to determine the correlation between comfort and PTP200, PTP500-index and PTP300-index, and PTPt. We always considered significant P values ≤ 0.05.
Results
We enrolled 15 consecutive patients; 1 patient, however, underwent emergency reintubation because of the lack of airway patency after extubation and was then excluded from the data analysis. A second patient was reintubated 24 h after completion of the study protocol consequent to severe dyspnea and respiratory acidosis. Demographic and anthropometric characteristics of 14 patients are given in table 1. The risk of the carryover effect was ruled out for all data.
Table 1.
Patients’ Characteristics at ICU Admission
Patients’ Characteristics at ICU Admission×
Patients’ Characteristics at ICU Admission
Table 1.
Patients’ Characteristics at ICU Admission
Patients’ Characteristics at ICU Admission×
×
Comfort
The individual values of the comfort score for all the patients and their median and interquartile range are depicted in figure 1. Comfort was significantly improved while using a NH (8.0 [7.8 to 8.0]), as opposed to a SH (5.5 [5.0 to 6.0] (P < 0.001). Not shown in the figure, the comfort score before extubation was 3.0 (2.0 to 3.7).
Fig. 1.
Hollow circles indicate the individual scores given by the 14 patients on the Numeric Rating Scale for the two helmets. Solid lines depict median and 25th to 75th interquartile values. NH = new helmet; SH = standard helmet.
Hollow circles indicate the individual scores given by the 14 patients on the Numeric Rating Scale for the two helmets. Solid lines depict median and 25th to 75th interquartile values. NH = new helmet; SH = standard helmet.
Fig. 1.
Hollow circles indicate the individual scores given by the 14 patients on the Numeric Rating Scale for the two helmets. Solid lines depict median and 25th to 75th interquartile values. NH = new helmet; SH = standard helmet.
×
Pressurization and Triggering Performance
Figure 2 shows overlapped Paw tracings obtained from one representative subject, corresponding to the last mechanical insufflation with all three interfaces. Even though the rate of pressurization set on the ventilator was the same, the time to achieve the preset pressure differed between interfaces. In fact, the increase in Paw was faster with a NH (dashed line) than with a SH (dotted line), and both were slower than with ET (solid line). As depicted in figure 3, the median values with interquartile range of PTP300-index, PTP500-index, and PTP200 were all improved (i.e., higher) with a NH, as opposed to a SH (P < 0.01 for all comparisons). A NH also improved PTPt compared with a SH (P < 0.01). Compared with both helmets, ET was characterized by better rates of pressurization and triggering performance (P < 0.05 for all comparisons). Comfort was directly correlated with PTP200 (ρ = 0.66, P < 0.001), PTP500-index (ρ = 0.60, P < 0.01), and PTP300-index (ρ = 0.43 P = 0.02) and inversely correlated with PTPt (ρ = −0.55, P < 0.01).
Fig. 2.
Airway pressure profiles of the last mechanical breath during invasive ventilation through ET (solid line), and noninvasive ventilation with NH (dashed line), and SH (dotted line) from one representative patient. ET = endotracheal tube; NH = new helmet; Paw = airway pressure; SH = standard helmet.
Airway pressure profiles of the last mechanical breath during invasive ventilation through ET (solid line), and noninvasive ventilation with NH (dashed line), and SH (dotted line) from one representative patient. ET = endotracheal tube; NH = new helmet; Paw = airway pressure; SH = standard helmet.
Fig. 2.
Airway pressure profiles of the last mechanical breath during invasive ventilation through ET (solid line), and noninvasive ventilation with NH (dashed line), and SH (dotted line) from one representative patient. ET = endotracheal tube; NH = new helmet; Paw = airway pressure; SH = standard helmet.
×
Fig. 3.
PTP300-index (A), PTP500-index (B), PTP200 (C), and PTPt (D) computed during NH, SH, and ET are depicted. The bottom and top of the box indicate the 25th and 75th percentile, the horizontal band near the middle of the box is the median, and the ends of the whiskers represent the 10th and 90th percentile. #P < 0.01 ET versus SH; §P < 0.01 ET versus NH; ^P < 0.05 ET versus NH. ET = endotracheal tube; NH = new helmet; PTP = airway pressure–time product; PTP200 = PTP of the first 200 ms computed from the onset of ventilator assistance; PTP300-index = PTP of the first 300 ms from the onset of patient effort, indexed to the ideal PTP; PTP500-index = PTP of the first 500 ms from the onset of patient effort, indexed to the ideal PTP; PTPt = PTP during the triggering phase; SH = standard helmet.
PTP300-index (A), PTP500-index (B), PTP200 (C), and PTPt (D) computed during NH, SH, and ET are depicted. The bottom and top of the box indicate the 25th and 75th percentile, the horizontal band near the middle of the box is the median, and the ends of the whiskers represent the 10th and 90th percentile. #P < 0.01 ET versus SH; §P < 0.01 ET versus NH; ^P < 0.05 ET versus NH. ET = endotracheal tube; NH = new helmet; PTP = airway pressure–time product; PTP200 = PTP of the first 200 ms computed from the onset of ventilator assistance; PTP300-index = PTP of the first 300 ms from the onset of patient effort, indexed to the ideal PTP; PTP500-index = PTP of the first 500 ms from the onset of patient effort, indexed to the ideal PTP; PTPt = PTP during the triggering phase; SH = standard helmet.
Fig. 3.
PTP300-index (A), PTP500-index (B), PTP200 (C), and PTPt (D) computed during NH, SH, and ET are depicted. The bottom and top of the box indicate the 25th and 75th percentile, the horizontal band near the middle of the box is the median, and the ends of the whiskers represent the 10th and 90th percentile. #P < 0.01 ET versus SH; §P < 0.01 ET versus NH; ^P < 0.05 ET versus NH. ET = endotracheal tube; NH = new helmet; PTP = airway pressure–time product; PTP200 = PTP of the first 200 ms computed from the onset of ventilator assistance; PTP300-index = PTP of the first 300 ms from the onset of patient effort, indexed to the ideal PTP; PTP500-index = PTP of the first 500 ms from the onset of patient effort, indexed to the ideal PTP; PTPt = PTP during the triggering phase; SH = standard helmet.
×
Breathing Pattern
As presented in table 2, RRmec (P = 0.03), whereas not RRneu (P = 0.13), was higher while using a NH, compared with a SH. Moreover, EAdipeak was not significantly different between NH and SH (P = 0.80). When compared with ET, NH (P = 0.03), but not SH (P = 0.65), was characterized by a higher RRmec; on the opposite, RRneu was not different between trials (P = 0.17). EAdipeak was significantly lower with ET compared with both helmets (P < 0.05).
Table 2.
Arterial Blood Gases and Patient–Ventilator Interactions
Arterial Blood Gases and Patient–Ventilator Interactions×
Arterial Blood Gases and Patient–Ventilator Interactions
Table 2.
Arterial Blood Gases and Patient–Ventilator Interactions
Arterial Blood Gases and Patient–Ventilator Interactions×
×
Patient–Ventilator Synchrony
As also shown in table 2, DelayTR-insp and Timesynch/Tineu were improved with NH, as opposed to SH (P = 0.007 for both variables), whereas DelayTR-exp was similar between helmets (P = 0.31). ET assured better DelayTR-insp and Timesynch/Tineu, compared with both NH (P = 0.04 and P < 0.001, respectively) and SH (P = 0.002 and P < 0.001, respectively). DelayTR-exp was shorter with NH, compared with ET (P = 0.03), whereas not different between SH and ET (P = 0.27).
Four patients had an AI% > 10% during all three trials, with no significant difference among interfaces. In particular, we observed (1) 17 IEs in NH, 31 in SH, and 7 in ET; (2) 4 auto triggerings during both NH and SH and 6 in ET; and (3) 9 double triggerings in NH, 3 in SH, and 1 in ET (fig. 4).
Fig. 4.
Stacked bars indicating the sum of the overall asynchronies observed in all patients during noninvasive ventilation with NH and SH and during invasive ventilation. Ineffective efforts, auto triggerings, and double triggerings are separately indicated in black, gray, and white, respectively. ET = endotracheal tube; NH = new helmet; SH = standard helmet.
Stacked bars indicating the sum of the overall asynchronies observed in all patients during noninvasive ventilation with NH and SH and during invasive ventilation. Ineffective efforts, auto triggerings, and double triggerings are separately indicated in black, gray, and white, respectively. ET = endotracheal tube; NH = new helmet; SH = standard helmet.
Fig. 4.
Stacked bars indicating the sum of the overall asynchronies observed in all patients during noninvasive ventilation with NH and SH and during invasive ventilation. Ineffective efforts, auto triggerings, and double triggerings are separately indicated in black, gray, and white, respectively. ET = endotracheal tube; NH = new helmet; SH = standard helmet.
×
Arterial Blood Gases
As shown in table 2, there was no difference in ABGs between NH and SH; ET was also no different with respect to both helmets.
Discussion
We found that, compared with a SH, a NH (1) improved short term (30′) comfort, (2) improved patient–ventilator interaction (i.e., rate of pressurization, triggering function, and Timesynch/Tineu), (3) did not affect patient respiratory rate and drive, rate of asynchrony, and ABGs. Patient–ventilator interaction was significantly better with ET compared with both helmets, with no significant difference in ABGs and rate of asynchrony. To our knowledge, this is the first comparison between two interfaces for NIV and ET during invasive ventilation.
Patient tolerance of NIV is strongly related to comfort of the interface.6,32  Poor tolerance is a major determinant of NIV failure leading to endotracheal intubation and its related side effects and complications.4  Therefore, interface comfort is an important clinical outcome variable for NIV.32  This is particularly true for the sickest patients who require NIV for a prolonged period of time.4,9  A recent randomized trial in hypoxemic patients comparing standard oxygen therapy with either NIV or heated and humidified high-flow oxygen therapy found the latter to be associated with an increased degree of comfort compared with NIV.33  This may have contributed to the lower intubation rate observed in the most severely hypoxemic patients in the group treated with high-flow oxygen.33 
Comfort depends on different factors such as amount of air leaks, skin pressure sores, pressurization and triggering performance, and quality of patient–ventilator synchrony. Compared with the conventional facial masks, a SH improves patient comfort and enhances NIV tolerance,8,10,34  as indicated by longer time of continuous treatment and fewer interruptions,7–10,34  decreased NIV-related complications,7–10,34  and reduced rate of intubation secondary to intolerance.7–9,34  However, a SH has drawbacks primarily attributable to the armpit braces, which may cause pain and discomfort because of the pressure exerted on the skin of the axillary area,35  and to the highly compliant soft collar, which contributes to the downward movement of the soft collar leading to an upward displacement of helmet during ventilator insufflation.13  An annular openable ring, placed underneath the inflatable cushion surrounding the patient’s neck, constitutes the NH securing system. By replacing the armpit braces, NH overcomes entirely the first problem; in addition, by preventing the displacement of the helmet during insufflation, which affects pressurization and triggering performances, it largely reduces the second limitation.13,14 
This study confirms in ICU patients the findings of previous investigations performed in bench studies13  and healthy volunteers,14  indicating that, compared with a SH, a NH increases the rate of pressurization and improves triggering performance with unmodified ventilator settings. Although the removal of the armpit braces likely also contributed to the better comfort with a NH, as opposed to a SH, the enhanced pressurization and triggering performance were found to significantly correlate with the improvement in comfort achieved by a NH.
In keeping with the findings of studies comparing NIV delivery with different ventilatory modes,36–41  EAdipeak, RRneu, and ABGs were not significantly different between SH and NH and when comparing the two helmets with ET. Even more surprisingly, despite the improvement in patient–ventilator interaction with NH, compared with SH, as indicated by the significant improvement of the rates of pressurization, triggering performance, and Timesynch/Tineu, AI% showed overall no difference between helmets. When considering separately the different asynchronous events, however, we observed that IEs were almost half with NH than with SH, whereas DTs were three times more frequent with the former, as opposed to the latter. During NIV, varying ventilator settings have a quite limited effect on IEs, which are principally reduced by containing air leaks.25  Conversely, DTs depend primarily on a discrepancy between mechanical and patient’s own (neural) inspiratory time, the former being shorter than the latter and is therefore dramatically influenced by the expiratory trigger threshold (i.e., the percent of the peak flow rate at which the ventilator cycles off).42  Accordingly, varying the expiratory trigger threshold with a NH would likely reduce the rate of DTs.
Our study has some limitations deserving discussion. First, the study was designed as a physiologic comparison and did not consider clinical outcome variables. Very recently, a pilot multicenter randomized control trial enrolling patients with acute on chronic hypercapnic respiratory failure showed NH to be as effective as the oronasal mask in improving ABGs, dyspnea, and respiratory rate and showed no difference with respect to overall tolerance and need for intubation.43  In hypercapnic patients with chronic obstructive pulmonary disease (COPD), compared with the oronasal mask, SH showed reduced efficacy in decreasing Paco28  and inspiratory muscles effort11  and worsened patient–ventilator interaction and synchrony.11  Hence, these findings by Pisani et al.43  indirectly suggest that the physiologic benefit we observed with NH, compared with SH, translate into clinical improvement.
Second, because we powered the study to detect an improvement in comfort corresponding to a 50% increase on the NRS, 14 patients might not be sufficient to ascertain differences regarding other variables. For instance, the median value of EAdipeak with NH was approximately 20% lower than with SH, a difference that could achieve statistical significance when increasing the sample size.
Third, we do not consider in our comparison the oronasal mask, which is the current standard for NIV delivery. Because of our study design, introducing a third group for comparison would have been extremely problematic. As mentioned earlier, previous investigations already separately compared the oronasal mask with either SH or NH.8,9,11,43  In addition, a recent study compared SH, NH, and the oronasal mask in healthy volunteers, showing that, at a PEEP level close to those used in our study, inspiratory effort and patient–ventilator interaction were significantly improved with the oronasal mask, compared with SH, whereas not with NH.14 
Finally, because the evaluation of comfort was done after a relatively short period of evaluation, we cannot exclude that the improvement observed would weaken or even disappear after longer time.
In conclusion, in ICU patients receiving NIV to prevent reintubation due to postextubation respiratory failure, compared with SH, NH improved comfort, rate of pressurization, and triggering performance. This might translate in improved clinical outcome, especially for the most severe patients requiring NIV for prolonged periods of time.
Acknowledgments
The authors thank all physicians and nurses of the intensive care unit of “Maggiore Della Carità” Hospital, Novara, Italy, for their helpful and continuous support. They also thank Jennifer Beck, Ph.D. (Department of Pediatrics, University of Toronto, Toronto, Ontario, Canada), who carefully revised the manuscript.
Intersurgical S.P.A. (Mirandola, Italy) provided the helmets used for the study.
Competing Interests
Drs. Olivieri and Navalesi contributed to the development of the helmet Next, whose license for patent belongs to Intersurgical S.P.A. (Mirandola, Italy) and received royalties for that invention. Dr. Navalesi received equipment and/or grants from MAQUET Critical Care (Solna, Sweden), Intersurgical S.P.A., Draeger Medical GmbH (Lubeck, Germany), Biotest (Dreieich, Germany), and Hillrom (St. Paul, Minnesota). Dr. Navalesi also received honoraria/speaking fees from MAQUET Critical Care, Covidien AG (Dublin, Ireland), Draeger Medical GmbH, Breas (Mölnlycke, Sweden), Hillrom, and Linde AG (Munich, Germany). The other authors declare no competing interests.
Reproducible Science
Full protocol available at: longhini.federico@gmail.com. Raw data available at: longhini.federico@gmail.com.
References
Evans, TW International Consensus Conferences in Intensive Care Medicine: Non-invasive positive pressure ventilation in acute respiratory failure. Organised jointly by the American Thoracic Society, the European Respiratory Society, the European Society of Intensive Care Medicine, and the Société de Réanimation de Langue Française, and approved by the ATS Board of Directors, December 2000.. Intensive Care Med. (2001). 27 166–78 [Article] [PubMed]
Nava, S, Hill, N Non-invasive ventilation in acute respiratory failure.. Lancet. (2009). 374 250–9 [Article] [PubMed]
Nava, S, Navalesi, P, Conti, G Time of non-invasive ventilation.. Intensive Care Med. (2006). 32 361–70 [Article] [PubMed]
Squadrone, E, Frigerio, P, Fogliati, C, Gregoretti, C, Conti, G, Antonelli, M, Costa, R, Baiardi, P, Navalesi, P Noninvasive vs invasive ventilation in COPD patients with severe acute respiratory failure deemed to require ventilatory assistance.. Intensive Care Med. (2004). 30 1303–10 [Article] [PubMed]
Carlucci, A, Richard, JC, Wysocki, M, Lepage, E, Brochard, L SRLF Collaborative Group on Mechanical Ventilation, Noninvasive versus conventional mechanical ventilation. An epidemiologic survey.. Am J Respir Crit Care Med. (2001). 163 874–80 [Article] [PubMed]
Navalesi, P, Fanfulla, F, Frigerio, P, Gregoretti, C, Nava, S Physiologic evaluation of noninvasive mechanical ventilation delivered with three types of masks in patients with chronic hypercapnic respiratory failure.. Crit Care Med. (2000). 28 1785–90 [Article] [PubMed]
Antonaglia, V, Ferluga, M, Molino, R, Lucangelo, U, Peratoner, A, Roman-Pognuz, E, De Simoni, L, Zin, WA Comparison of noninvasive ventilation by sequential use of mask and helmet versus mask in acute exacerbation of chronic obstructive pulmonary disease: A preliminary study.. Respiration. (2011). 82 148–54 [Article] [PubMed]
Antonelli, M, Pennisi, MA, Pelosi, P, Gregoretti, C, Squadrone, V, Rocco, M, Cecchini, L, Chiumello, D, Severgnini, P, Proietti, R, Navalesi, P, Conti, G Noninvasive positive pressure ventilation using a helmet in patients with acute exacerbation of chronic obstructive pulmonary disease: A feasibility study.. Anesthesiology. (2004). 100 16–24 [Article] [PubMed]
Antonelli, M, Conti, G, Pelosi, P, Gregoretti, C, Pennisi, MA, Costa, R, Severgnini, P, Chiaranda, M, Proietti, R New treatment of acute hypoxemic respiratory failure: Noninvasive pressure support ventilation delivered by helmet—A pilot controlled trial.. Crit Care Med. (2002). 30 602–8 [Article] [PubMed]
Rocco, M, Dell’Utri, D, Morelli, A, Spadetta, G, Conti, G, Antonelli, M, Pietropaoli, P Noninvasive ventilation by helmet or face mask in immunocompromised patients: A case-control study.. Chest. (2004). 126 1508–15 [Article] [PubMed]
Navalesi, P, Costa, R, Ceriana, P, Carlucci, A, Prinianakis, G, Antonelli, M, Conti, G, Nava, S Non-invasive ventilation in chronic obstructive pulmonary disease patients: Helmet versus facial mask.. Intensive Care Med. (2007). 33 74–81 [Article] [PubMed]
Vargas, F, Thille, A, Lyazidi, A, Campo, FR, Brochard, L Helmet with specific settings versus facemask for noninvasive ventilation.. Crit Care Med. (2009). 37 1921–8 [Article] [PubMed]
Olivieri, C, Costa, R, Spinazzola, G, Ferrone, G, Longhini, F, Cammarota, G, Conti, G, Navalesi, P Bench comparative evaluation of a new generation and standard helmet for delivering non-invasive ventilation.. Intensive Care Med. (2013). 39 734–8 [Article] [PubMed]
Vaschetto, R, De Jong, A, Conseil, M, Galia, F, Mahul, M, Coisel, Y, Prades, A, Navalesi, P, Jaber, S Comparative evaluation of three interfaces for non-invasive ventilation: A randomized cross-over design physiologic study on healthy volunteers.. Crit Care. (2014). 18 R2 [Article] [PubMed]
Nava, S, Gregoretti, C, Fanfulla, F, Squadrone, E, Grassi, M, Carlucci, A, Beltrame, F, Navalesi, P Noninvasive ventilation to prevent respiratory failure after extubation in high-risk patients.. Crit Care Med. (2005). 33 2465–70 [Article] [PubMed]
Ferrer, M, Valencia, M, Nicolas, JM, Bernadich, O, Badia, JR, Torres, A Early noninvasive ventilation averts extubation failure in patients at risk: A randomized trial.. Am J Respir Crit Care Med. (2006). 173 164–70 [Article] [PubMed]
Ferrer, M, Sellarés, J, Valencia, M, Carrillo, A, Gonzalez, G, Badia, JR, Nicolas, JM, Torres, A Non-invasive ventilation after extubation in hypercapnic patients with chronic respiratory disorders: Randomised controlled trial.. Lancet. (2009). 374 1082–8 [Article] [PubMed]
Constantin, JM, Schneider, E, Cayot-Constantin, S, Guerin, R, Bannier, F, Futier, E, Bazin, JE Remifentanil-based sedation to treat noninvasive ventilation failure: A preliminary study.. Intensive Care Med. (2007). 33 82–7 [Article] [PubMed]
El-Solh, AA, Aquilina, A, Pineda, L, Dhanvantri, V, Grant, B, Bouquin, P Noninvasive ventilation for prevention of post-extubation respiratory failure in obese patients.. Eur Respir J. (2006). 28 588–95 [Article] [PubMed]
Colombo, D, Cammarota, G, Bergamaschi, V, De Lucia, M, Corte, FD, Navalesi, P Physiologic response to varying levels of pressure support and neurally adjusted ventilatory assist in patients with acute respiratory failure.. Intensive Care Med. (2008). 34 2010–8 [Article] [PubMed]
Olivieri, C, Costa, R, Conti, G, Navalesi, P Bench studies evaluating devices for non-invasive ventilation: Critical analysis and future perspectives.. Intensive Care Med. (2012). 38 160–7 [Article] [PubMed]
Sinderby, C, Liu, S, Colombo, D, Camarotta, G, Slutsky, AS, Navalesi, P, Beck, J An automated and standardized neural index to quantify patient-ventilator interaction.. Crit Care. (2013). 17 R239 [Article] [PubMed]
Bellani, G, Mauri, T, Coppadoro, A, Grasselli, G, Patroniti, N, Spadaro, S, Sala, V, Foti, G, Pesenti, A Estimation of patient’s inspiratory effort from the electrical activity of the diaphragm.. Crit Care Med. (2013). 41 1483–91 [Article] [PubMed]
Vaschetto, R, Cammarota, G, Colombo, D, Longhini, F, Grossi, F, Giovanniello, A, Della Corte, F, Navalesi, P Effects of propofol on patient-ventilator synchrony and interaction during pressure support ventilation and neurally adjusted ventilatory assist.. Crit Care Med. (2014). 42 74–82 [Article] [PubMed]
Vignaux, L, Vargas, F, Roeseler, J, Tassaux, D, Thille, AW, Kossowsky, MP, Brochard, L, Jolliet, P Patient-ventilator asynchrony during non-invasive ventilation for acute respiratory failure: A multicenter study.. Intensive Care Med. (2009). 35 840–6 [Article] [PubMed]
Paice, JA, Cohen, FL Validity of a verbally administered numeric rating scale to measure cancer pain intensity.. Cancer Nurs. (1997). 20 88–93 [Article] [PubMed]
Gerbershagen, HJ, Rothaug, J, Kalkman, CJ, Meissner, W Determination of moderate-to-severe postoperative pain on the numeric rating scale: A cut-off point analysis applying four different methods.. Br J Anaesth. (2011). 107 619–26 [Article] [PubMed]
Gagliese, L, Weizblit, N, Ellis, W, Chan, VW The measurement of postoperative pain: A comparison of intensity scales in younger and older surgical patients.. Pain. (2005). 117 412–20 [Article] [PubMed]
Gift, AG, Narsavage, G Validity of the numeric rating scale as a measure of dyspnea.. Am J Crit Care. (1998). 7 200–4 [PubMed]
Chooi, CS, White, AM, Tan, SG, Dowling, K, Cyna, AM Pain vs comfort scores after Caesarean section: A randomized trial.. Br J Anaesth. (2013). 110 780–7 [Article] [PubMed]
Maggiore, SM, Idone, FA, Vaschetto, R, Festa, R, Cataldo, A, Antonicelli, F, Montini, L, De Gaetano, A, Navalesi, P, Antonelli, M Nasal high-flow versus Venturi mask oxygen therapy after extubation. Effects on oxygenation, comfort, and clinical outcome.. Am J Respir Crit Care Med. (2014). 190 282–8 [Article] [PubMed]
Elliott, MW The interface: Crucial for successful noninvasive ventilation.. Eur Respir J. (2004). 23 7–8 [Article] [PubMed]
Frat, JP, Thille, AW, Mercat, A, Girault, C, Ragot, S, Perbet, S, Prat, G, Boulain, T, Morawiec, E, Cottereau, A, Devaquet, J, Nseir, S, Razazi, K, Mira, JP, Argaud, L, Chakarian, JC, Ricard, JD, Wittebole, X, Chevalier, S, Herbland, A, Fartoukh, M, Constantin, JM, Tonnelier, JM, Pierrot, M, Mathonnet, A, Béduneau, G, Delétage-Métreau, C, Richard, JC, Brochard, L, Robert, R FLORALI Study Group; REVA Network, High-flow oxygen through nasal cannula in acute hypoxemic respiratory failure.. N Engl J Med. (2015). 372 2185–96 [Article] [PubMed]
Principi, T, Pantanetti, S, Catani, F, Elisei, D, Gabbanelli, V, Pelaia, P, Leoni, P Noninvasive continuous positive airway pressure delivered by helmet in hematological malignancy patients with hypoxemic acute respiratory failure.. Intensive Care Med. (2004). 30 147–50 [Article] [PubMed]
Lucchini, A, Valsecchi, D, Elli, S, Doni, V, Corsaro, P, Tundo, P, Re, R, Foti, G, Manici, M [The comfort of patients ventilated with the Helmet bundle].. Assist Inferm Ric. (2010). 29 174–83 [PubMed]
Cammarota, G, Olivieri, C, Costa, R, Vaschetto, R, Colombo, D, Turucz, E, Longhini, F, Della Corte, F, Conti, G, Navalesi, P Noninvasive ventilation through a helmet in postextubation hypoxemic patients: Physiologic comparison between neurally adjusted ventilatory assist and pressure support ventilation.. Intensive Care Med. (2011). 37 1943–50 [Article] [PubMed]
Piquilloud, L, Tassaux, D, Bialais, E, Lambermont, B, Sottiaux, T, Roeseler, J, Laterre, PF, Jolliet, P, Revelly, JP Neurally adjusted ventilatory assist (NAVA) improves patient-ventilator interaction during non-invasive ventilation delivered by face mask.. Intensive Care Med. (2012). 38 1624–31 [Article] [PubMed]
Schmidt, M, Demoule, A, Cracco, C, Gharbi, A, Fiamma, MN, Straus, C, Duguet, A, Gottfried, SB, Similowski, T Neurally adjusted ventilatory assist increases respiratory variability and complexity in acute respiratory failure.. Anesthesiology. (2010). 112 670–81 [Article] [PubMed]
Wysocki, M, Richard, JC, Meshaka, P Noninvasive proportional assist ventilation compared with noninvasive pressure support ventilation in hypercapnic acute respiratory failure.. Crit Care Med. (2002). 30 323–9 [Article] [PubMed]
Poggi, R, Appendini, L, Polese, G, Colombo, R, Donner, CF, Rossi, A Noninvasive proportional assist ventilation and pressure support ventilation during arm elevation in patients with chronic respiratory failure. A preliminary, physiologic study.. Respir Med. (2006). 100 972–9 [Article] [PubMed]
Winck, JC, Vitacca, M, Morais, A, Barbano, L, Porta, R, Teixeira-Pinto, A, Ambrosino, N Tolerance and physiologic effects of nocturnal mask pressure support vs proportional assist ventilation in chronic ventilatory failure.. Chest. (2004). 126 382–8 [Article] [PubMed]
Mauri, T, Bellani, G, Grasselli, G, Confalonieri, A, Rona, R, Patroniti, N, Pesenti, A Patient-ventilator interaction in ARDS patients with extremely low compliance undergoing ECMO: A novel approach based on diaphragm electrical activity.. Intensive Care Med. (2013). 39 282–91 [Article] [PubMed]
Pisani, L, Mega, C, Vaschetto, R, Bellone, A, Scala, R, Cosentini, R, Musti, M, Del Forno, M, Grassi, M, Fasano, L, Navalesi, P, Nava, S Oronasal mask versus helmet in acute hypercapnic respiratory failure.. Eur Respir J. (2015). 45 691–9 [Article] [PubMed]
Fig. 1.
Hollow circles indicate the individual scores given by the 14 patients on the Numeric Rating Scale for the two helmets. Solid lines depict median and 25th to 75th interquartile values. NH = new helmet; SH = standard helmet.
Hollow circles indicate the individual scores given by the 14 patients on the Numeric Rating Scale for the two helmets. Solid lines depict median and 25th to 75th interquartile values. NH = new helmet; SH = standard helmet.
Fig. 1.
Hollow circles indicate the individual scores given by the 14 patients on the Numeric Rating Scale for the two helmets. Solid lines depict median and 25th to 75th interquartile values. NH = new helmet; SH = standard helmet.
×
Fig. 2.
Airway pressure profiles of the last mechanical breath during invasive ventilation through ET (solid line), and noninvasive ventilation with NH (dashed line), and SH (dotted line) from one representative patient. ET = endotracheal tube; NH = new helmet; Paw = airway pressure; SH = standard helmet.
Airway pressure profiles of the last mechanical breath during invasive ventilation through ET (solid line), and noninvasive ventilation with NH (dashed line), and SH (dotted line) from one representative patient. ET = endotracheal tube; NH = new helmet; Paw = airway pressure; SH = standard helmet.
Fig. 2.
Airway pressure profiles of the last mechanical breath during invasive ventilation through ET (solid line), and noninvasive ventilation with NH (dashed line), and SH (dotted line) from one representative patient. ET = endotracheal tube; NH = new helmet; Paw = airway pressure; SH = standard helmet.
×
Fig. 3.
PTP300-index (A), PTP500-index (B), PTP200 (C), and PTPt (D) computed during NH, SH, and ET are depicted. The bottom and top of the box indicate the 25th and 75th percentile, the horizontal band near the middle of the box is the median, and the ends of the whiskers represent the 10th and 90th percentile. #P < 0.01 ET versus SH; §P < 0.01 ET versus NH; ^P < 0.05 ET versus NH. ET = endotracheal tube; NH = new helmet; PTP = airway pressure–time product; PTP200 = PTP of the first 200 ms computed from the onset of ventilator assistance; PTP300-index = PTP of the first 300 ms from the onset of patient effort, indexed to the ideal PTP; PTP500-index = PTP of the first 500 ms from the onset of patient effort, indexed to the ideal PTP; PTPt = PTP during the triggering phase; SH = standard helmet.
PTP300-index (A), PTP500-index (B), PTP200 (C), and PTPt (D) computed during NH, SH, and ET are depicted. The bottom and top of the box indicate the 25th and 75th percentile, the horizontal band near the middle of the box is the median, and the ends of the whiskers represent the 10th and 90th percentile. #P < 0.01 ET versus SH; §P < 0.01 ET versus NH; ^P < 0.05 ET versus NH. ET = endotracheal tube; NH = new helmet; PTP = airway pressure–time product; PTP200 = PTP of the first 200 ms computed from the onset of ventilator assistance; PTP300-index = PTP of the first 300 ms from the onset of patient effort, indexed to the ideal PTP; PTP500-index = PTP of the first 500 ms from the onset of patient effort, indexed to the ideal PTP; PTPt = PTP during the triggering phase; SH = standard helmet.
Fig. 3.
PTP300-index (A), PTP500-index (B), PTP200 (C), and PTPt (D) computed during NH, SH, and ET are depicted. The bottom and top of the box indicate the 25th and 75th percentile, the horizontal band near the middle of the box is the median, and the ends of the whiskers represent the 10th and 90th percentile. #P < 0.01 ET versus SH; §P < 0.01 ET versus NH; ^P < 0.05 ET versus NH. ET = endotracheal tube; NH = new helmet; PTP = airway pressure–time product; PTP200 = PTP of the first 200 ms computed from the onset of ventilator assistance; PTP300-index = PTP of the first 300 ms from the onset of patient effort, indexed to the ideal PTP; PTP500-index = PTP of the first 500 ms from the onset of patient effort, indexed to the ideal PTP; PTPt = PTP during the triggering phase; SH = standard helmet.
×
Fig. 4.
Stacked bars indicating the sum of the overall asynchronies observed in all patients during noninvasive ventilation with NH and SH and during invasive ventilation. Ineffective efforts, auto triggerings, and double triggerings are separately indicated in black, gray, and white, respectively. ET = endotracheal tube; NH = new helmet; SH = standard helmet.
Stacked bars indicating the sum of the overall asynchronies observed in all patients during noninvasive ventilation with NH and SH and during invasive ventilation. Ineffective efforts, auto triggerings, and double triggerings are separately indicated in black, gray, and white, respectively. ET = endotracheal tube; NH = new helmet; SH = standard helmet.
Fig. 4.
Stacked bars indicating the sum of the overall asynchronies observed in all patients during noninvasive ventilation with NH and SH and during invasive ventilation. Ineffective efforts, auto triggerings, and double triggerings are separately indicated in black, gray, and white, respectively. ET = endotracheal tube; NH = new helmet; SH = standard helmet.
×
Table 1.
Patients’ Characteristics at ICU Admission
Patients’ Characteristics at ICU Admission×
Patients’ Characteristics at ICU Admission
Table 1.
Patients’ Characteristics at ICU Admission
Patients’ Characteristics at ICU Admission×
×
Table 2.
Arterial Blood Gases and Patient–Ventilator Interactions
Arterial Blood Gases and Patient–Ventilator Interactions×
Arterial Blood Gases and Patient–Ventilator Interactions
Table 2.
Arterial Blood Gases and Patient–Ventilator Interactions
Arterial Blood Gases and Patient–Ventilator Interactions×
×