Antonio Messina

New versus Conventional Helmet for Delivering Noninvasive Ventilation: A Physiologic, Crossover Randomized Study in Critically Ill Patients.

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.

New Setting of Neurally Adjusted Ventilatory Assist during Noninvasive Ventilation through a Helmet

Background:Compared to pneumatically controlled pressure support (PSP), neurally adjusted ventilatory assist (NAVA) was proved to improve patient–ventilator interactions, while not affecting comfort, diaphragm electrical activity (EAdi), and arterial blood gases (ABGs). This study compares neurally controlled pressure support (PSN) with PSP and NAVA, delivered through two different helmets, in hypoxemic patients receiving noninvasive ventilation for prevention of extubation failure. Methods:Fifteen patients underwent three (PSP, NAVA, and PSN) 30-min trials in random order with both helmets. Positive end-expiratory pressure was always set at 10 cm H2O. In PSP, the inspiratory support was set at 10 cm H2O above positive end-expiratory pressure. NAVA was adjusted to match peak EAdi (EAdipeak) during PSP. In PSN, the NAVA level was set at maximum matching the pressure delivered during PSP by limiting the upper pressure. The authors assessed patient comfort, EAdipeak, rates of pressurization (i.e., airway pressure-time product [PTP] of the first 300 and 500 ms after the initiation of patient effort, indexed to the ideal pressure–time products), and measured ABGs. Results:PSN significantly increased comfort to (median [25 to 75% interquartile range]) 8 [7 to 8] and 9 [8 to 9] with standard and new helmets, respectively, as opposed to both PSP (5 [5 to 6] and 7 [6 to 7]) and NAVA (6 [5 to 7] and 7 [6 to 8]; P < 0.01 for all comparisons). Regardless of the interface, PSN also decreased EAdipeak (P < 0.01), while increasing PTP of the first 300 ms from the onset of patient effort, indexed to the ideal PTP (P < 0.01) and PTP of the first 500 ms from the onset of patient effort, indexed to the ideal PTP (P < 0.001). ABGs were not different among trials. Conclusions:When delivering noninvasive ventilation by helmet, compared to PSP and NAVA, PSN improves comfort and patient–ventilator interactions, while not ABGs. (Anesthesiology 2016; 125:1181-9)

Patient-ventilator asynchrony affects pulse pressure variation prediction of fluid responsiveness.

PURPOSE During partial ventilatory support, pulse pressure variation (PPV) fails to adequately predict fluid responsiveness. This prospective study aims to investigate whether patient-ventilator asynchrony affects PPV prediction of fluid responsiveness during pressure support ventilation (PSV). MATERIALS AND METHODS This is an observational physiological study evaluating the response to a 500-mL fluid challenge in 54 patients receiving PSV, 27 without (Synch) and 27 with asynchronies (Asynch), as assessed by visual inspection of ventilator waveforms by 2 skilled blinded physicians. RESULTS The area under the curve was 0.71 (confidence interval, 0.57-0.83) for the overall population, 0.86 (confidence interval, 0.68-0.96) in the Synch group, and 0.53 (confidence interval, 0.33-0.73) in the Asynch group (P = .018). Sensitivity and specificity of PPV were 78% and 89% in the Synch group and 36% and 46% in the Asynch group. Logistic regression showed that the PPV prediction was influenced by patient-ventilator asynchrony (odds ratio, 8.8 [2.0-38.0]; P < .003). Of the 27 patients without asynchronies, 12 had a tidal volume greater than or equal to 8 mL/kg; in this subgroup, the rate of correct classification was 100%. CONCLUSIONS Patient-ventilator asynchrony affects PPV performance during partial ventilatory support influencing its efficacy in predicting fluid responsiveness.

Use of the Fluid Challenge in Critically Ill Adult Patients: A Systematic Review.

The fluid challenge (FC) aims at identifying patients in whom fluid administration improves hemodynamics. Although the FC has been extensively studied, the implementation and definition of improvement are not standardized. This systematic review of studies published between January 1, 1994 and December 31, 2014 characterizes these key components of the FC for critically ill adult patients, as described in the medical literature in the last 20 years. A literature search was performed using MEDLINE, Embase, and Cochrane. For each study, data were collected on study design, study size, study setting, patient population, and how the FC was administered. Eligibility criteria for FC were (1) the infusion of a definite quantity of fluid, (2) of a specific type, (3) in a fixed time period (expressed as either span or infusion rate), (4) with a defined hemodynamic variable as the target, and (5) for a predetermined threshold. One hundred fifty-seven full-text manuscripts were extracted from 870 potentially relevant studies. The inclusion criteria were met by 71 studies including 3617 patients. Sixty-six studies were from a single center and 45 were prospective observational in format. The most common amount infused was 500 cc, used by 55 (77.5%) studies. The most commonly infused fluids were colloids (62.0%). In 43 (60.5%) studies, the FC was administered between 20 and 30 minutes. A positive response to fluid administration was defined as an increase ≥15% of cardiac index or cardiac output in 44 (62.6%) studies. Static or dynamic physiologic indices were utilized in a minority of studies (16.9%) and safety limits for interrupting the FC are adopted in 4 (5.6%) studies only. This systematic review indicates that the FC most commonly consists in infusing 500 mL of crystalloids or colloids in 20–30 minutes, and considered an increase in cardiac index ≥15% as a positive response. However, definite standards for FC administration and evaluation remain undefined.

Looking for the Grail, Finding Traces on the Way.

Critical Care Medicine www.ccmjournal.org 1237 The ventilator yellow alarm rings (Peak airways pressure limit? Low tidal volume? High minute volume? High/ low respiratory rate?). This event may occur several times per patient each ICU shift. What is creating the antagonism between patient and ventilator? From the patient side, troubles might develop from lung (i.e., dynamic hypeinflation/ intrinsic positive end-expiratory pressure [PEEP], resistance, and elastance), from muscles function (respiratory muscle deficit or weakness) or from central nervous system (respiratory drive), the latter being influenced by mechanical and chemical feedbacks, as well as over-/undertitration of sedatives and opiates (1, 2). From the ventilator side, it is even more problematic, i.e., trigger (both inspiratory and expiratory), cycling criteria, modality of ventilation, support, and PEEP all intertwined over a respiratory cycle (3). Sometimes it seems that “this marriage cannot take place.” Due to the increasing interest in patient-ventilator interaction (PVi) (4), several studies in the past decade reported strategies to improve (5), or better recognize PVi (6, 7), including the study of techniques able to provide assistance proportionally to patient’s effort (i.e., proportionally assisted ventilation plus [PAV+] [8, 9] and neurally adjusted ventilator assist [9, 10]). These articles often show superiority of the new technique in terms of patient-machine coordination, but without clear-cut benefit on patient’s outcome. However, most of these studies are small clinical trials with a limited number of patients enrolled and are not specifically designed to assess outcome endpoints. In this issue of Critical Care Medicine, Bosma et al (11) aim to assess PSV and PAV+ in terms of patient outcome. The study is well conducted, and the number of patients enrolled is appropriate. In this protocol, only patients with more than 36 hours of mechanical ventilation before the screening were enrolled; it is likely the first randomized clinical trial (RCT) with PAV+ with a study period longer than 48 hours, as opposed to previous shorter term physiologic studies. The authors not only demonstrated the feasibility and safety of the protocol (primary endpoint) but also found a reduction of the ICU length of stay (LOS) in PAV+ group when compared with the PSV one. This encouraging result (as secondary endpoint) rises a question: Is it really possible to modify ICU mortality or LOS adjusting only a single variable? This is a fascinating hypothesis, the Grail for a researcher. Technical progress in the last 30–40 years has made a difference in ICU setting, increasing (12), or maintaining (13) the rate of survival despite the admission of more severe and older patients (13). The complexity of an ICU patient with multidisciplinary treatments and numbers of specialists coordinated by the intensivist make it harder and harder to identify the direct cause-effect relationship of a new technique or drug application on patient outcome. In this complex environment, other nonmedical factors might influence patient outcome, including organizational issues (14). It is important to take all variables into account when the targets of the research are LOS, ICU mortality, or an analogous surrogate. Not surprisingly, in recent years, RCTs targeting clinical outcome, based on the promising results of physiological studies, failed to demonstrate clinical benefit (15–17). When comparing a novel but infrequently used technique with a traditional one, it is well known that the expertise of the treatment team is crucial and may heavily influence the results in both directions. On the one hand, if the team is uncomfortable with the new technique, the results might underestimate the benefit. On the other hand, if the team is well trained, results might be influenced by the great ability of the personnel to handle the new technique. Bosma et al (11) worked in a single-center environment, and the good result might rely, once again, on their experience with PAV+. Reproducibility is a cornerstone of the scientific method and, from this perspective, if a broad application of a technique is unable to replicate the positive results, we have “a real-world” problem. Whether subsequent multicenter RCTs that will follow will be positive or negative is yet to be seen, but looking for the Grail, we should remember that the journey is more important than the destination and that even small traces, such the ones left by Bosma et al (11), might indicate the right direction on the way.

THE MINI-SIGH TEST: A NEW HAEMODYNAMIC TEST OF FLUID RESPONSIVENESS IN ICU PATIENTS UNDERGOING PRESSURE SUPPORT VENTILATION

Dynamic predictors of fluid responsiveness (FR) perform poorly in ICU patients receiving partial ventilatory assistance. Because these modes of partial support are increasingly used, FR dynamic indexes are applicable only in a few ICU patients [1]. To overcome these limitations, novel approaches for testing FR in ICU have been proposed, such as the passive leg raising and the end-expiratory occlusion. These tests, however, may not always be applicable [2]. During controlled mechanical ventilation, Pulse Pressure (PP) and left ventricle stroke volume are coupled; their variations are due to the reduction of right ventricle stroke volume consequent to ventilator insufflation and are either proportional to the tidal volume and closely related to preload dependence.