Slide 21: Primary Findings
Say:
The ARDSNet study’s main findings included a significant decrease in deaths prior to being sent home and an increase in the number of days that patients who used the lower tidal volume strategy were able to breathe on their own. By day 28, there had been a significant increase in the number of patients who could breathe on their own. To be clear, that included individuals who were off the ventilator and did not require continuous or bilevel positive airway pressure.
Between the two groups, there was no difference in the incidence of barotrauma. The number of days without nonpulmonary organ or system failure increased statistically significantly.
Patients with ARDS who used a lower tidal volume strategy had better lung function and were able to stop using the ventilator more quickly, but they also scored better on other organ failure systems. This suggests that the traditional tidal volume strategy’s inflammatory injury to the lungs was affecting not only the lungs but also other organ systems. That makes sense given that we are aware that inflammatory mediators and cytokines don’t stay in the lung. They can circulate throughout the rest of the body. Larger tidal volumes were harming the patient’s body overall by damaging the lungs. All other organ systems benefit from our assistance in preserving the lungs.
This important study fundamentally altered how we treat patients who require mechanical ventilation in many ways. Remember that the ARDSNet trial was restricted to ARDS patients.
Slide 33: Low Tidal Volume Implementation
Say:
The implementation of low tidal volume ventilation techniques in the context of acute care will now be covered.
Initial Ventilator Settings in Various Disease States
In the ED setting, patients frequently require full respiratory support. CMV and A/C are good options for an initial ventilatory mode for the majority of ED patients who are paralyzed as part of rapid-sequence induction. Patients who are not paralyzed and have obstructive airway disease and an intact respiratory effort may tolerate SIMV better. When respiratory effort is intact and respiratory failure is not severe, PSV can be used. [11].
In many cases of severe COPD and CHF, noninvasive ventilation (CPAP, BiPAP) can be used successfully to prevent tracheal intubation. The pulmonary pathophysiology and clinical status of the patient are used to determine the initial ventilator settings. Then, modifications can be made to reduce oxygen toxicity, volutrauma, and barotrauma. CPAP and BiPAP are contraindicated in the presence of facial trauma and demand attentive, cooperative patients who are capable of independently maintaining their airways.
High FiO2 can usually correct hypoxia, but patients who have airway obstruction run the risk of barotrauma, volutrauma, high airway pressures, breath stacking that results in intrinsic PEEP, and other complications. Expiratory flow time should be increased as much as possible, and low tidal volumes and respiratory rates should be used to reduce intrinsic PEEP. [12] With permissive hypercapnia, a low respiratory rate of 6–8 breaths per minute and an elevated I:E ratio of 1:1 are both possible. 5 or 1:2.
PEEP may help some asthmatic patients breathe easier and keep their airways open during expiration, but its effects are unpredictable and require close observation. Patients with asthma and COPD are particularly vulnerable to the complication known as barotraumatic progression to tension pneumothorax, which can initially resemble runaway intrinsic PEEP. By temporarily removing the patient from positive pressure ventilation, these conditions can be distinguished; intrinsic PEEP is the diagnosis if exhaling causes the patient’s pulse or blood pressure to return to normal.
Many COPD patients and some asthmatics will benefit from CPAP and BiPAP. Since these patients are susceptible to respiratory exhaustion, intrinsic PEEP, and hypercarbia, they need to be closely monitored. Nevertheless, a CochraneDatabase Systematic Review analysis of trials including patients with severe COPD exacerbations demonstrated that the use of noninvasive positive-pressure ventilation absolutely reduced the rate of endotracheal intubation by 59% (95% confidence interval [CI] of relative risk [RR]: 0 33-0. 53), the length of hospital stay by 3. 24 days (95% CI: 2. 06-4. 44 days), and the risk of mortality by 48% (95% CI of RR: 0 35-0. 76). [2].
The lungs of people with ARDS are frequently irregularly inflamed and extremely susceptible to atelectasis, barotrauma, and volutrauma. Their compliance is typically reduced, and their dead space increased. The publication of a significant multicenter, randomized trial in 2000 comparing patients with ARDS initially ventilated with either the conventional tidal volume of 12 mL/kg or a lower TV of 6 mL/kg resulted in a significant shift in the standard of care for the ventilatory management of patients with ARDS. Because the lower tidal volume was found to reduce mortality by an absolute 8 percent, this trial was terminated early. 8% (P=. 007). It’s interesting to note that plasma interleukin 6 levels dropped in the low TV group compared to the high TV group (P 001), suggesting a decrease in lung inflammation. [13, 14, 15, 16].
The authors advise starting A/C ventilation for ARDS patients with a tidal volume of 6 mL/kg, a PEEP of 5, and an initial ventilatory rate of 12 that is titrated up to maintain a pH greater than 7. 25. PEEP greater than 5 cm water is not currently routinely recommended due to a lack of sufficient evidence, but it could be tried under carefully supervised conditions. [17] Patients with ARDS who are receiving high ventilatory rates may develop intrinsic PEEP, which should be kept an eye out for and treated by lowering the rate of ventilation while being closely monitored until plateau pressures drop. Target plateau pressure should be less than 30 cm water, according to the authors. Consideration of a pressure-cycled ventilation trial is reasonable after a patient has been stabilized with adequate tidal volumes at a plateau pressure of less than 30 cm water.
The proportion of alveoli ventilated in ARDS has increased thanks to a number of recruitment strategies. These methods typically try to open collapsed or occluded alveoli by temporarily increasing PEEP or volume. Gattinoni et al, for example, found that among ARDS patients undergoing whole-lung CT, applying 45 cm water PEEP recruited a mean of 13% new lung tissue [18].
In a recent meta-analysis, studies that used the same tidal volume in both the control and intervention arms and compared high versus low levels of PEEP in patients with ALI and ARDS found no difference in mortality before hospital discharge. [17] The authors discovered a decrease in mortality when using a lung-protective ventilation strategy in a later subgroup analysis that compared lung-protective ventilation (low tidal volume, high PEEP) to traditional mechanical ventilation. High levels of PEEP do enhance oxygenation in ALI and ARDS patients, according to the same review.
Guerin et al. recently investigated whether early prone positioning during mechanical ventilation can enhance outcomes in patients with severe ARDS in a prospective, randomized, controlled trial. The authors found that both the 28-day and unadjusted 90-day mortalities in the prone group were significantly lower (16% and 23 6%, respectively) than in the supine group (32. 8% and 41%, respectively). [19] Although they found no difference between the groups with regard to duration of invasive mechanical ventilation or length of stay in the ICU, they found a higher incidence of cardiac arrest in the supine group (31% vs 16% in the prone group)
In the management of patients with ARDS and COPD/asthma who would otherwise need to have dangerously high tidal volumes and airway pressures, permissive hypercapnia has gained particular favor. Permissive hypercapnia has allowed for significantly decreased tidal volumes, airway pressures, and respiratory rates in patients without contraindications like head injury, cerebrovascular accident (CVA), elevated intracranial pressure, or cardiovascular instability, though the evidence for a reduction in mortality rates is insufficient. [20] The typically recommended target pH is 7. 25.
Patients with ARDS have had limited success with noninvasive ventilatory techniques. The authors advise using extreme caution and close supervision when attempting noninvasive positive pressure ventilation (NIPPV) in ARDS patients.
The presence of pneumonia or ARDS was linked to a noticeably higher risk of failure in NIPPV trials in patients with undifferentiated hypoxemia. Although some ARDS patient subgroups may benefit from NIPPV, Antonelli et al found that patients with lower simplified acute physiology scores and higher PaO2/FiO2 ratios responded better to the treatment. [21].
Positive-pressure ventilation, which opens the alveoli and lowers preload, is very effective at treating CHF. An experiment with noninvasive CPAP or BiPAP is beneficial for many CHF patients. Some of these patients’ clinical conditions will improve so quickly that admitting services may ask that noninvasive ventilatory support be stopped. If this is done, though, it must be done with extreme caution because fluid may unexpectedly reaccumulate, leading to hypoxia and respiratory failure.
Intubated patients usually manage to adequately oxygenate. To increase oxygenation and lower preload, PEEP can be raised to an acceptable level. However, in some patients, preload can be especially important for cardiac output, and these patients are more likely to develop postintubation hypotension. A combination of fluid therapy, stopping the use of nitroglycerin or other medications, and, if necessary, interventions for mechanical or medical hemodynamic support are used to treat this common complication. [22].
Traditional management of severe traumatic brain injury included the use of hyperventilation, but recent studies have shown poor outcomes that are thought to be related to excessive cerebral vasoconstriction and decreased cerebral perfusion Although this has not been prospectively validated, retrospective data have shown decreased mortality among traumatic brain injury patients ventilated to PCO2 between 30 and 39 mm Hg. [23, 24].