Is the helmet different than the face mask in delivering noninvasive ventilation?

Invasive mechanical ventilation, although highly effective in improving gas exchange and reducing the work of breathing, may not sole increase the risk of nosocomial infections on the other hand can also cause discomfort for the patient and barotrauma. (1) greatest in quantity of these complications are related to the endotracheal tube. reciprocally noninvasive positive pressure ventilation (NPPV) defined as any form of ventilatory support applied without the use of an endotracheal tube, presents the potential advantage, in chooseed patients, of avoiding these drawbacks.

NPPV was first applied in the 1930 when Barach and colleagues (2) showed that continuous positive airway compressing could be useful in the treatment of acute pulmonary edema. Subsequently NPPV gained popularity as first-line ventilatory treatment of respiratory failure. sum of two units prospective epidemiologic surveys (3,4) lay the foundation of that NPPV was used in 5 to 15% of patients with respiratory failure; however, the percentage of patients treated with NPPV significantly differed between center ranging from none in eight ICUs to 67% in individual ICU. (4)

NPPV reduc the ne for intubation and mortality in patients with acute cardiogenic pulmonary edema, (5) acute exacerbation of COPD (6) and hypoxemic acute respiratory failure. (7) However, during NPPV up to 40% of patients may require endotracheal intubation and invasive mechanical ventilation, primarily because of poor patient tolerance and the severity of underlying disease. (4) Although the face mask is the greatest in quantity common interface used to deliver NPPV it may be responsible for a certain proportion of NPPV failures. single way of reducing the ne for premature termination of NPPV could be to use a different interface to limit the squeezing necrosis of the skin, air leaks, and discomfort. A plastic "helmet" that overlays the patient's whole head, originally used to deliver an air mixture during hyperbaric oxygen therapy, has now been make knowned for NPPV. The helmet makes no contact with the head, with equal reason it should be more comfortable than the face mask. In patients with acute hypoxemic respiratory failure and cardiogenic pulmonary edema, the helmet improved gas exchange similarly to the face mask on the other hand was more comfortable and permitted longer continuous application. (89)

single of the most important drawbacks of the helmet, owed to its larger inner turn compared to the face mask (ie, a dead space contortion of 8 to 12 L) is carbon dioxide rebreathing, which could limit the efficacy of NPPV (10) Antonelli and colleagues, (11) comparing NPPV using the helmet and face mask in patients with acute exacerbation of COPD fix that after 1 h of NPPV one as well as the other groups had a significant reduction in arterial carbon dioxide horizontals However, the decrease in arterial carbon dioxide was smaller in the helmet clump and this difference was greater in the subgroup of patients who failed NPPV (11)

The helmet comprises a plastic cowl with a soft collar, making for better comfort than the face mask, although it may dissipate the inspiratory crushing delivered by the ventilator. sum of two units studies (12,13) in humans that evaluated the helmet and face mask in healthy subdues during pressure support ventilation base a similar breathing pattern, on the other hand the helmet required greater inspiratory muscle effort and took a longer time to reach the culled level of airway pressure.

In this issue of CHEST (see page 1424) Dr Moerer and colleagues (14) report a bench inquiry of ventilatory performance by simulating spontaneous breathing at the beginning of an inspiratory effort, and compared a helmet and face mask during NPPV at different horizontals of pressure support ventilation and positive end-expiratory squeezing (PEEP). They measured the time delay to activate the ventilatory trigger, the time between the initiation of an inspiratory effort until the preset pule level is reached, and the inspiratory squeezing time product (ie, the muscle inspiratory effort) during these sum of two units periods. The helmet, although presenting a significantly longer time delay, caused a lower compressing time product compared to the face mask. In addition, by the agency of increasing the level of compressing support or PEEP, the helmet furthermore significantly reduc the delay times and compressing time product.

During NPPV the ventilator must first pressurize the interface (face mask or helmet) and then the respiratory combination of parts to form a whole (12) The actual design of the helmet (high compliance) means that it straits higher inspiratory volumes than the face mask to reach the same airway compressing causing a longer delay times. However, the patient can use the higher gas turn inside the helmet at the beginning of an inspiration, thus reducing the initial inspiratory muscle effort.

A practical clinical message from the popular (14) and previous studies (1213) is that the physician should plant higher levels of PEEP and crushing support to reduce inspiratory muscle effort closer to that with the face mask. Although the patient tolerates the helmet better, it straits careful clinical monitoring and setting.