June 22, 2024

Vitavo Yage

Best Health Creates a Happy Life

Medical Care, Surgical Care, Further Inpatient and Outpatient Care

7 min read

Ventilator management and the adjustment of ventilator settings has been the focus of treatment in patients at risk for barotrauma. This approach is based on recognition of the deleterious effects of alveolar overdistention. It follows that avoiding or minimizing alveolar overdistention is key to preventing barotrauma.

Whether this goal is best achieved by using low tidal volumes or by limiting the plateau pressure has been controversial. The two parameters are inextricably linked because in volume ventilation, peak pressures and therefore plateau pressures are dependent variables during mechanical ventilation. Both tidal volume and plateau pressures have been used to titrate ventilator settings, with low tidal volume as the primary variable under study.

The benefits of low-tidal-volume ventilation are demonstrated only in patients with acute respiratory distress syndrome (ARDS). However, clinicians have recognized the hazards of alveolar overdistention in all patients, and lower tidal volumes (in the range of 8-10 mL/kg) have generally been adopted for all patients. Other medical care is focused on treating the underlying condition.

In the ARDS Network trial, ventilation of ARDS patients with a low tidal volume was associated with a 9% absolute reduction in mortality. The low tidal volume was calculated on the basis of predicted body weight (PBW), which clinicians infrequently use. For men, PBW was calculated as 50 + 0.91 (height [cm] – 152.4) or 50 + 2.3 (height [in.] – 60). For women, PBW was calculated as 45.5 + 0.91 (height [cm] – 152.4) or 45.5 + 2.3 (height [in.] – 60).

Low tidal volume was also associated with improvements in ventilator-free days and in the incidence of nonpulmonary organ failure. However, the ARDS Network trial has been somewhat controversial, not because of the results but because of the conduct of the trial and its comparison group. Some have argued that the plateau pressure may be the more appropriate target in adjusting ventilator settings.

In this trial, plateau pressures were limited to less than 30 cm H2O in the low tidal volume group, with further downward adjustment of the tidal volume (to < 6 mL/kg PBW, but no lower than 4 mL/kg) if plateau pressures exceeded that threshold. This area remains under investigation, but several analyses have supported the use of low tidal volumes. It is also worth noting that in this landmark study, the incidence of barotrauma was virtually the same in the low-tidal-volume group as in the high-tidal-volume group.

Post-hoc analyses of patients participating in combined trials of the ARDS Network have focused on the relationship of airway pressures and positive end-expiratory pressure (PEEP) to the development of barotrauma.

In more than 900 patients with a cumulative incidence of barotrauma of 13% over the first 4 study days, no relation was detected between peak airway pressure, plateau pressure, mean airway pressure, or driving pressure (plateau pressure – PEEP) and the development of barotrauma. However, higher concurrent PEEP was consistently associated with barotrauma, with a relative hazard of 1.67 for every increment of 5 cm H2O.

PEEP also may provide a measure of protection against ventilator-induced lung injury (VILI). PEEP is well recognized to increase alveolar recruitment, and a strategy combining PEEP-induced alveolar recruitment with low tidal volumes may minimize this atelectotrauma and confer a clinical benefit in management. Several large multicenter trials have focused on increasing PEEP levels in conjunction with an approach involving low tidal volume and limited plateau pressure.
[20]

Across the differing study protocols, the levels of PEEP used in the higher-PEEP group averaged 13-15 cm H2O, compared with those in the lower-PEEP group, which averaged 6-8 cm H2O. No mortality benefit was found with any of the trials, but improvement was noted in secondary study endpoints in two of the three main trials, with improvement in hypoxemia, acidosis, use of rescue therapies, ventilator-free days, and organ failure–free days in the higher-PEEP group.
[21, 22]

Titrating based on plateau pressures, as opposed to oxygenation, may limit some of the adverse effects seen with higher levels of PEEP. No differences were noted in the incidence of barotrauma between the higher- and lower-PEEP groups, ranging from 5% to 11% in these trials.

In a single-center report of 61 patients, use of esophageal balloon catheters to measure transpulmonary pressure and thereby guide the use of PEEP yielded improvements in oxygenation and respiratory compliance but did not impact mortality. No barotrauma was noted in either group, with average PEEPs of 12 and 18 cm H2O administered in the two groups. Technical issues and limited availability of expertise may limit the use of this approach while the results of larger trials are being awaited.
[23]

In 2017, results were published from the Alveolar Recruitment for ARDS Trial (ART), which was designed to determine whether lung recruitment associated with PEEP titration according to the best respiratory-system compliance decreased 28-day mortality in patients with moderate-to-severe ARDS as compared with a conventional low-PEEP approach.
[24]
 The former strategy was found to increase 28-day all-cause mortality; accordingly, the investigators concluded that routine use of lung recruitment and PEEP titration was not supported in these patients.

In summary, using low tidal volumes
[25]
and limiting plateau pressures remain the preferred approach in ventilator management, and this, in turn, reduces the risk for barotrauma. It appears best to use the ARDS Network lung-protective thresholds in management, which are tidal volumes at 6 mL/kg PBW and plateau pressures less than 30 cm H2O. No mortality benefit has been conclusively demonstrated with higher PEEP
[26, 27]
(though one meta-analysis did find a benefit in a subset of patients
[28]
), and the optimal approach to PEEP remains to be determined. The ARDS Network has formulated a useful mechanical ventilation protocol (see the image below).

Acute Respiratory Distress Syndrome Network refere


Acute Respiratory Distress Syndrome Network reference summarizing the mechanical ventilation protocol.

Clinicians should be aware that the low-tidal-volume approach may result in relative hypoventilation. This translates into hypercapnia, and patients may develop hypercapnic respiratory acidosis. Patients generally tolerate hypercapnia and respiratory acidosis well, and adjustments in the ventilator settings are not usually required. A respiratory acidosis with a pH in the range of 7.20-7.25 is not uncommon with low-tidal-volume ventilation, but lower pH levels have prompted some to increase the tidal volume or treat with bicarbonate.

During mechanical ventilation, most patients require some sedation, which may also contribute to hypercapnia. The need for and the dose of intravenous (IV) sedation should be assessed on a daily basis. Sedation is obviously essential for patient comfort, but also to minimize adverse effects that may occur with patient agitation and patient-ventilator dyssynchrony.

Along that line, neuromuscular blockade could virtually eliminate patient-ventilator dyssynchrony and its adverse effects, while maximizing efficient airflow and improving oxygenation. This, in turn, would be another method to reduce exposure to high airway pressures, whether in the form of peak airway pressures, plateau pressures, mean airway pressure, or driving pressures.

In a randomized investigation assessing neuromuscular blockade with 48 hours of cisatracurium against placebo (N = 340), there was a statistically lower proportion with barotrauma in the treatment group (5% vs 11.7%).
[10]
 No increase was noted in plateau pressure readings prior to the episode of barotrauma (primarily pneumothoraces), but patients with barotrauma did have higher minute ventilation than control subjects did.

Pneumothoraces also occurred earlier in the course of this study,
[10]
which may provide further support for the barotrauma-protective effects with early use of cisatracurium. A mortality benefit for cisatracurium was suggested, but statistical significance was not achieved. There was no increased in neuromuscular weakness associated with cisatracurium use.

The findings from this study notwithstanding, the potential for adverse effects with neuromuscular blockade has given rise to uncertainty regarding the minimally effective duration of such blockade and the concentration of benefit among those with the most severe ARDS (PaO2/FIO2 < 120). A meta-analysis of 431 patients, all from the same study group, also noted a reduction in barotrauma (5% vs 9.7%).
[29]
 A subsequent meta-analysis of 1598 ARDS patients reported a significant decrease in the incidence of barotrauma with the use of neuromuscular blockade.
[30]

There remains a need for additional confirmatory investigations before neuromuscular blockade can be endorsed for routine use in this setting.

Other medical approaches may help reduce the risk for barotrauma. Early nutritional support facilitates recovery. However, no pharmacologic agents are effective in the prevention or treatment of acute lung injury (ALI), ARDS, or barotrauma.

Pharmacotherapy includes diuretics to decrease lung water and pulmonary edema, sedatives to facilitate patient-ventilator synchrony, and bronchodilators to decrease airway resistance and possibly improve oxygenation and ventilation. These therapies are part of the general supportive care of patients receiving mechanical ventilation, and they are not specific to the management of barotrauma.

Medical therapies that were once promising but that failed to improve outcomes include surfactant replacement, nitric oxide, ketoconazole, and glucocorticosteroids. Therapies under investigation include beta-agonists to reduce alveolar fluid and anticoagulation with biologically engineered compounds.

In patients with ALI or ARDS, corticosteroids have been an intriguing option because of their potential to reduce associated inflammation and lung destruction. However, results from prospective randomized trials of corticosteroids in the 2000s were generally disappointing.
[31, 32]
 No mortality difference was demonstrated, and the possibility of increased adverse events in patients treated with corticosteroids late (>14 days) into the course was suggested. However, a multicenter randomized controlled study from 2020 found that early administration of dexamethasone reduced the duration of mechanical ventilation and overall mortality in patients with moderate-to-severe ARDS.
[33]

Additionally, corticosteroids are known to adversely increase hyperglycemia and impair wound healing. However, patients treated within 7 days appear to have increased resolution of gas exchange abnormalities and quicker discontinuance of mechanical ventilation.

No data support the proposition that corticosteroid therapy reduces barotrauma. However, a small study in which corticosteroids were administered 3 days after the onset of ALI or ARDS documented a definite, albeit nonsignificant, decrease in the incidence of pneumothorax in the control group (8% vs 21%). Further studies are required to validate this potential benefit of corticosteroids.

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