Is Less More or Is It a Call for Evidence-Based Guidance?

Experienced intensive care clinicians who reminiscence with rosy nostalgia about the care provided to patients who were critically ill and mechanically ventilated decades ago often highlight the frequent monitoring and handling of almost any airway device for respiratory care. In those years, ventilator circuits, in-line suction catheters, heat and moisture exchangers, and even endotracheal tubes were routinely manipulated and exchanged, based on the flawed perception that changing to a new device was safer, irrespective of the effects of these manipulations. Since then, clinical practice in ICUs worldwide has been greatly transformed,¹ driven by robust evidence in favor of the logic that less may be more.² Indeed, today we allow patients who receive critical care to heal themselves with the lowest level of supportive care to reduce risks of iatrogenic harm and/or unnecessary costs.

We learned that risk of ventilator-associated pneumonia (VAP), a serious complication of patients who are ventilated,^3,4 was unaffected by routine changes of respiratory care devices. In the latest meta-analysis by Han and Liu⁵ of more than 19,000 subjects, a reduced risk of VAP was found as ventilator circuit-change intervals were extended. Likewise, in a study by Thomachot et al,⁶ in which daily change of heat and moisture exchangers was compared with a weekly change, VAP did not differ between the groups. As for the in-line closed suction catheters, soon after introduction of these devices in clinical practice, it was common to frequently change them because of the risks of rapid colonization. These assumptions were challenged by Stoller et al,⁷ who compared, in 2 subsequent periods, daily or weekly changes of in-line catheters. No differences in VAP cases were found between the 2 periods. A 4.5-fold decrease in catheter costs was achieved in the period of prolonged catheter use. In another randomized clinical trial, Kollef et al⁸ evaluated the cost-effectiveness of not routinely changing in-line suction catheters in >500 subjects who required mechanical ventilation. VAP was similar between the groups. Moreover, no differences in other major secondary outcomes were evident, which clearly corroborated the cost-effectiveness of the conservative strategy.

How does the concept of less is more apply to the management of the endotracheal tube, when taking into account the latest technological advancements in this field? In recent years, improvements have been achieved in the design of the tube, primarily aimed at reducing the risk of VAP.⁹ Given the primary role of bacteria-laden subglottic secretions in the pathogenesis of VAP, endotracheal tubes that allow aspiration of subglottic secretions have been developed, with a 50% decrease in VAP incidence in some studies¹⁰ but without consequential improvements in survival. Endotracheal tubes coated with silver¹¹ and cuffs made of innovative materials and/or shapes were reported to have merit¹² but failed to provide conclusive benefits in clinical trials,¹³ which ultimately limits widespread clinical applicability of these innovations.

Another factor in the pathogenesis of VAP is aspiration past the endotracheal tube cuff. Several studies in highly controlled in vitro settings confirmed the role of cuff pressure in preventing aspiration of subglottic secretions.^12,14 Thus, efforts have been made to develop strategies and devices to maintain pressure within the recommended range, specifically 20–30 cm H₂O. As reported by Rello et al,¹⁵ cuff pressure < 20 cm H₂O was a risk factor for the development of VAP. Cuff pressure > 30 cm H₂O may cause tracheal injury by impeding blood flow and causing tissue ischemia.¹⁶ Despite those risks, the appropriate frequency of cuff monitoring is unknown, and health-care providers rely on local hospital policies rather than evidence-based recommendations for routine cuff management. In an Australian survey, significant heterogeneity was reported in the frequency of cuff pressure assessments, which ranged from checks every 4 h to every 24 h.¹⁷ In addition, the providers who were surveyed were also uncertain regarding the most appropriate target cuff pressure.¹⁷

In this issue of Respiratory Care, Letvin et al¹⁸ shed some light on the frequency of cuff pressure monitoring. The study focused on the impact of cuff pressure monitoring frequency on pulmonary complications and found no difference in major outcomes, which suggests the futility of frequent cuff pressure monitoring. Based on this evidence, would it be reasonable to shift to sporadic cuff pressure monitoring, or should we be cautious about interpreting these new findings? Letvin et al¹⁸ used the algorithm for surveillance of ventilator-associated events^19–21 as the primary outcome by using electronic data from the Barnes-Jewish Hospital, where the study was conducted. A ventilator-associated event is defined by a sudden worsening in oxygenation after a period of stability that requires ventilator adjustments. Ventilator-associated events are commonly associated with conditions other than VAP (eg, atelectasis, acute pulmonary edema, ARDS).²¹

It could be argued that the primary outcome chosen by Letvin et al¹⁸ was limited in detecting effectiveness of frequent cuff pressure control. Maintaining the cuff pressure within the appropriate range reduces micro-aspiration of colonized subglottic secretions and the incidence of VAP, which was only included as a secondary outcome by the researchers. The concept of ventilator-associated events was never intended as a surrogate of VAP, as clearly described by Klompas and collaborators^19,21 in pivotal studies. As expected, Canadian²² and European²³ studies confirmed inconsistencies between ventilator-associated events and VAP because clinical VAP might occur in only 30% of the ventilator-associated event cases.²³ This raises concerns regarding the methods of the study by Letvin et al¹⁸ because it is possible that many VAP events were overlooked, which reduces the reliability of the chosen measure of effect. Finally, in line with the very low incidence of VAP reported in the latest preventive studies,^11,24 the researchers encountered a lower-than-expected incidence of ventilator-associated events and comparable low numbers of VAP. These low ventilator-associated event/VAP rates raise a question about the overall power of the study in detecting potential differences between groups.

Another point that merits attention concerns the dynamics of endotracheal tube cuff deflation. Little is currently known about how cuffs deflate and the key factors associated with the gradual reduction in internal cuff pressure. These considerations are pertinent to the study by Letvin et al,¹⁸ in which only one endotracheal tube type, the Shiley Hi-Lo (Covidien, Dublin, Ireland), was used for the study. Theoretically, cuff materials and manufacturing features of the cuff pilot balloon may play essential roles in the cuff leakage rate. Thus, the findings by Letvin et al¹⁸ might only pertain to this endotracheal tube, and inferences related to other endotracheal tubes commercially available may not be valid. Along this line of thinking, 2 possibilities might explain the negative findings of this trial. One possibility is that the studied endotracheal tube had exceptional characteristics and was able to maintain the internal cuff pressure within the recommended range, even during infrequent monitoring, which ultimately avoided aspiration. However, previous studies²⁵ that evaluated standard cuff management versus continuous monitoring do not support this argument because recurrent episodes of hypoinflation of the cuff were encountered. The other option is that, irrespective of the significant deflation of the cuff, the resulting deleterious effects on the studied population were negligible due to the implementation of other VAP prevention strategies that could have offset risks associated with pulmonary aspiration.

It is worth noting that comparative studies of standard versus continuous monitoring²⁵ also reported frequent cuff hyperinflations. Unfortunately, the study by Letvin and colleagues¹⁸ does not allow us to extrapolate the risks of hyperinflation associated with sporadic checks of the cuff, but it is important to note that tracheal lesions associated with invasive mechanical ventilation are more common than previously thought and are challenging to diagnose due to subtle clinical signs. A study that evaluated postextubation tracheal lesion through bronchoscopic assessments confirmed that overinflation of a tracheal cuff (>30 cm H₂O) was the main determinant of tracheal lesions.²⁶

In summary, although respiratory care practice has attempted to reduce unnecessary costs while preserving benefits for patients who are mechanically ventilated, it is prudent to not favor sporadic cuff monitoring based on recent findings by Letvin et al¹⁸ but rather to extend the researchers' study rationale and suggest promising areas for further laboratory and clinical investigations. In particular, although the most recent meta-analysis,²⁵ including 543 subjects on the effects of continuous cuff monitoring, reported noteworthy reduction of VAP (hazard ratio 0.47, 95% CI 0.31–0.71) and fewer episodes of cuff underinflation, the reasons for limited implementation of this technology are still elusive, and, in the future, applicability will be further challenged by the continuous decrease in VAP incidence worldwide. Investigators should therefore explore potential hurdles in implementing continuous cuff monitoring and further explore possible benefits to promote pervasive acceptance. Moreover, little is known about the main manufacturing features associated with cuff deflation. Thus, we call attention to this seldom-considered issue and emphasize the importance of comprehensive preclinical and clinical studies to appraise cuff deflation mechanisms. This could ultimately encourage engineering advancements to develop next-generation cuffs less prone to variations in internal pressure. Finally, rather than substantiating the merits of less is more in cuff management, the study by Letvin et al¹⁸ raises awareness about the necessity of developing reliable data in this field, which could be applied by medical organizations to provide guidance on the most proficient cuff management to ensure benefits, while reducing complications and health care costs.

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