Noninvasive mechanical ventilation with average volume assured pressure support (AVAPS) in patients with chronic obstructive pulmonary disease and hypercapnic encephalopathy

Noninvasive mechanical ventilation (NIV) is used in patients with acute respiratory failure for several different etiologies [1]. The heterogeneity of different patient groups leads to varying levels of success, with the best results produced in patients with infectious exacerbations of COPD and congestive heart failure [2‐4]. When NIV is initiated in patients with acute respiratory failure due to infectious exacerbations of COPD, ventilatory parameters are typically determined based on clinical assessment and changes in blood gases. In this manner, NIV support pressures are manually adjusted by an operator [5].

One of the limitations of traditional NIV is altered levels of consciousness. However, under certain circumstances, especially those produced by hypercapnic conditions [6‐8], traditional NIV has produced very favorable results, even in patients with hypercapnic coma [9].

Patients with infectious exacerbations of COPD have obstruction, hyperinflation, air trapping, and increased respiratory effort and central respiratory drive. In particular, blood pCO₂ increases, which, due to its high lipid solubility, readily crosses the blood–brain barrier, provoking acidosis in the cerebrospinal fluid and cerebral interstitial tissue [8‐13].

Previous studies that recommend the use of NIV in patients with altered consciousness report a rapid recovery as soon as the ventilatory strategy is established, and most recommend early intubation and suspension of treatment if consciousness does not quickly normalize [9, 10]. Altered levels of consciousness can be assessed using the Glasgow Coma Scale (GCS) [14, 15], the encephalopathy scoring [16], and the Kelly-Matthay Scale (KMS) [17]. Although KMS is specifically designed to assess patients with neurological disorders on NIV, it is not commonly used in the emergency unit/ICU.

Bilevel positive airway pressure-spontaneous/timed (BiPAP S/T) with average volume assured pressure support (AVAPS) allows for setting a fixed tidal volume, and the system output automatically adjusts based on variations in inspiratory pressure to ensure the predetermined target value. Its long-term benefits have been demonstrated in patients with chronic respiratory failure, obstructive sleep apnea, and alveolar hypoventilation syndrome [18‐20].

We designed this study to assess the use of BiPAP S/T with AVAPS as a ventilatory strategy in patients with chronic obstructive pulmonary disease (COPD) and hypercapnic encephalopathy (GCS < 10) and to compare these results with those from patients treated with BiPAP S/T alone, upon immediate arrival in the emergency department/ICU.

A total of 22 patients were analyzed: 11 in the control group (BiPAP S/T) and 11 in the experimental group (BiPAP S/T with AVAPS). The mean age of all patients was 78.68 ± 10.42 years, mean APACHE II score was 18.50 ± 2.56, 9 patients were women (40.9%) and 13 were men (59.1%). Four patients were diagnosed with COPD with pneumonia (18.2%) and 18 were diagnosed with infectious exacerbations of COPD (81.3%). Sixteen patients (73.8%) received NIV in the emergency and ICU. There were no statistically significant differences between the two groups in terms of BMI, age, APACHE II score, or initial GCS score (Table 1). One patient (4.5%) used a Respironics full face mask, and the other 21 patients (95.5%) used the Mirage IV series (Resmed). In patients undergoing NIV with BiPAP S/T and AVAPS, the programmed tidal volume on AVAPS was 622.73 ± 81.74 ml/kg (range: 500–700), with a programmed Vt/kg of 10.26 ± 2.23 ml (range 7.89- 11,83). The programmed maximum IPAP values (BiPAP S/T with AVAPS) were: 21.36 ± 3.04 cmH₂O (initial), 20.82 ± 3.19 cmH₂O (1 hour), 19.36 ± 3.80 cmH₂O (3 hours), and 19.55 ± 3.45 cmH₂O (12 hours). The ANOVA analysis revealed statistically significant differences in favor of AVAPS for pCO₂ (P = .03), respiratory rate (P = .01), maximum IPAP (P = .005), GCS score (P = .00001) (Figure 1), and EVT (P = .01) (Table 2). However, no significant differences were observed for length of stay (P = .15) or duration of NIV (P = .18) (Table 3).

Our study demonstrates that the addition of AVAPS to BiPAP S/T in patients with encephalopathy and infectious exacerbations of COPD produces a rapid recovery of consciousness (GCS), with early improvement of arterial blood gases as compared to conventional ventilation using solely BiPAP S/T. We observed significantly higher IPAP values in the BIPAP S/T + AVAPS group than in the group of patients treated solely with BIPAP S/T.

No studies exist in the medical literature describing the benefits of using NIV with AVAPS in acute patients. However, in chronic patients with obstructive sleep apnea and alveolar hypoventilation syndrome, authors report a rapid improvement in pCO₂ and sleep quality using this technique [18‐20]. Most studies reported in the literature describing successful use of NIV in hypercapnic encephalopathy indicate an improvement in GCS within only a few hours of initiating NIV, although the vast majority of these are clinical case reports or observational studies [6‐8, 21‐26].

The goal in our study was, the rapid recovery of consciousness in a group of patients undergoing BIPAP S/T + AVAPS (target volume), we scheduled a target volume between (500-700ml) in our patients, with a Vt target average 10.26 ± 2.23 ml (range 7.89 to 11.83), with peak inspiratory pressures during therapy programmed to 26, once the patient achieved clinical stable condition and, in the target Vt our patients were reprogrammed to 6–8 ml/kg/ weight according to manufacturer's specifications. The decision was taken by the expert physician in charge of patient case-dependent (sensory severity scale or measured initial Glasgow).

BIPAP mode S/T + AVAPS delivered pressure changes progressively allowing the patient to conform much better to those pressures while the target tidal volume is reached.

Patients with the acute decompensation of COPD, accompanied by an altered mental status require rapid correction of alveolar hypoventilation which ensure an adequate tidal volume (minute volume) (volume settings between 8–12 ml/kg/weight) for rapid dissemination or carbon monoxide swept cerebrospinal fluid and brain and its sensory recovery as early as possible.

Studies examining the use of NIV in hypercapnic encephalopathy indicate that various ventilatory modes can be employed at different pressure levels. Gonzales et al [6] used BiPAP vision or BiPAP ST-D 30, in which IPAP levels were initially programmed at 12 cmH₂O and increased every 4 hours with an IPAP value in the first hour of 17 + 2 cmH₂O. In our study, patients on BiPAP S/T with AVAPS had an initial IPAP of 19.82, vs 12.36 in the control group. BiPAP S/T with AVAPS achieves the necessary inspiratory pressure level for a predetermined tidal volume, ensuring optimal pressure for the patient and facilitating a suitable inspiratory volume; this also rapidly overcomes alveolar hypoventilation, corrects pCO₂ levels, and decreases CO₂ levels in the brain so as to improve the patient's level of consciousness. Battisti et al. compared manually adjusted pressures with self-adjusting pressure support in patients with acute respiratory failure, which produced a decrease in pCO₂ levels in the latter group [27].

Some studies found favorable results in patients using NIV in hypercapnic encephalopathy reduction in days of mechanical ventilation [26] reduced risk of nosocomial infection [28, 29] and avoid intubation [30]. Recently, a pilot study tested the safety and efficacy of using an endotracheal tube through BiPAP in patients with a mean GCS of 6, a mean pH of 7.1, and poor management of Secretions, with a success rate of 85% (17/20) [31].

In our study, initial GCS and pH values were virtually equal between groups. Secretions were properly managed, which is essential for preventing technique failure and the need for endotracheal intubation. We observed a rapid and significant improvement in arterial blood gases and consciousness (GCS) in both groups; however, patients treated with BiPAP S/T + AVAPS improved much faster than patients treated with the conventional strategy, with a near-complete recovery within 3 hours. The improvement in the BiPAP S/T AVAPS group was probably linked to the rapid improvement in EVT and the fact that, in these patients, IPAP quickly reached the levels needed for maintaining appropriate tidal volume, and hypoventilation was corrected with consequent improvements in alveolar ventilation.

We observed no complications, gastric distention, or facial deformities, probably due to the fact that maximum system pressures did not surpass 20 cmH₂O, which is the threshold associated with damage to the upper esophageal sphincter and facial structures [32, 33].

Our study has certain limitations, including a small number of patients, despite the inclusion of three hospitals. In addition, the study was performed by a single research group with a long-term experience in NIV, which could create problems when extrapolating the results. Finally, it should be emphasized that our patients had a mean pH greater than 7.25, whereas other studies of hypercapnic encephalopathy have reported lower values. Other studies have also reported higher levels of pCO₂ as causing altered levels of consciousness. The lower values of pCO₂ that we observed could be due to several reasons. Firstly, some of our patients live at high altitude places. Gonzalez Garcia et al. [34], showed lower-than-normal pH and pCO₂ values in patients with COPD undergoing effort or exercise [35]. Secondly, some of our patients might have had a very low pH with prolonged base excess and bicarbonate for patients with COPD. The effects of blood volume, diuretic use, height and affecting renal bicarbonate reabsorption have not been assessed [36]. We must also consider that patients in both groups experienced a rapid improvement in GCS of 2 points or more within 3 hours of starting treatment; a lack of improvement of 2 points could be a determining factor for rapid endotracheal intubation, which would obviously constitute an invasive procedure [34]. Finally, our study involved matched case-controls without randomization. Despite these limitations, we believe that this study provides valuable information, as it confirms the usefulness of NIV in hypercapnic encephalopathy, and upholds BiPAP S/T with AVAPS as a strategy that ensures safe and appropriate pressures and tidal volumes, facilitating a rapid correction of arterial blood gases, especially pCO₂, and thus, minimizing the deleterious effects to the brain.

We propose the use of BiPAP S/T with AVAPS as a safe strategy of noninvasive ventilatory treatment in patients with exacerbations of COPD and hypercapnic encephalopathy (GCS < 10), with the caveat that these patients should be treated in units with ample experience and under close surveillance.