Washington University Emergency Medicine Journal Club – November 2024
Dr. Brian Cohn
Hello all,
This month at journal club we will be looking at articles evaluating the utility of AVAPS (average volume-assured pressure support) in the management of patients with hypercapnic respiratory failure in COPD. We are holding this at a new venue recommended by several residents so please make every effort to attend.
All four articles will be appraised using the Therapy appraisal form.
Vignette
You’re working a typical shift in TCC one when encounter Mr. B, a 63-year-old male
with a history of hypertension, hyperlipidemia, and COPD. He presents with 3 days
of gradually worsening shortness of breath and cough productive of white sputum.
He woke up this morning in respiratory distress and arrives by EMS on continuous
positive airway pressure (CPAP), which the respiratory therapist quickly transitions
to bilevel positive airway pressure (BiPAP).
You order the patient albuterol/atrovent duonebs, oral steroids, IV magnesium
sulfate, and azithromycin for a presumed COPD exacerbation. His chest x-ray reveals
hyper-expanded lungs with no consolidation or infiltrates and his ECG is nonischemic.
Labs are normal aside from a venous blood gas which reveals a pH of 7.2
and pCO2 of 80. His COVID test is negative.
After two hours on BiPAP, he appears a little more comfortable, but is also a little
more somnolent than he was on arrival, though still awakens and answers questions
appropriately. A repeat blood gas now reveals a pH of 7.15 and a pCO2 of 85. Given
his persistent hypercapneic respiratory failure you are considering intubation when
the respiratory therapist recommends switching over to AVAPS (average volumeassured
pressure support) to improve tidal volumes and hence ventilation. Having
never heard of AVAPS, you decide to trust your RT and look up literature on the
subject after you stabilize your patient…
PICO Question
Population: Adult patients with acute exacerbation of COPD with hypercapnic
respiratory failure
Intervention: Noninvasive mechanical ventilation (NIV) using average volumeassured
pressure support (AVAPS)
Comparison: Tradition fixed pressure bilevel positive airway pressure (BiPAP)
Outcome: Improvements in pH and PaCO2, improvement in mental status, need for
invasive mechanical ventilation, duration of NIV, need for ICU admission, ED length
of stay, hospital length of stay
Search Strategy
PubMed was searched using the terms AVAPS or “average volume-assured pressure
support” which resulted in 84 citations (https://tinyurl.com/4kb865hk). Among
these, the four most relevant articles were chosen.
Article 1: Gö ren NZ, Şancı E, Ercan Coşkun FF, Gü rsoylu D, Bayram B. Comparison of
BPAP S/T and Average Volume-Assured Pressure Support Modes for Hypercapnic
Respiratory Failure in the Emergency Department: A Randomized Controlled Trial.
Balkan Med J. 2021 Sep;38(5):265-271. [Answer Key].
Article 2: Briones Claudett KH, Briones Claudett M, Chung Sang Wong M, et al.
Noninvasive mechanical ventilation with average volume assured pressure support
(AVAPS) in patients with chronic obstructive pulmonary disease and hypercapnic
encephalopathy. BMC Pulm Med. 2013 Mar 12;13:12. [Answer Key].
Article 3: Maheshwari A, Khatri J, Soni G, Saini N. Role of Average Volume Assured
Pressure Support Mode (AVAPS) in the Management of Acute Exacerbation of
Chronic Obstructive Pulmonary Disease With Type 2 Respiratory Failure. Cureus.
2022 Dec 5;14(12):e32200. [Answer Key].
Article 4: Acet Ö ztü rk NA, Aydın Gü çlü Ö , Demirdö ğ en et al. AVAPS-NIV treatment in
hypercapnic respiratory failure with insufficient response to fixed-level PS-NIV.
Tuberk Toraks. 2022 Dec;70(4):324-333. [Answer Key].
Bottom Line
Noninvasive ventilation (NIV) with bilevel positive airway pressure (BiPAP) has been well-studied in the management of acute hypercapnic respiratory failure due to exacerbations of chronic obstructive pulmonary disease (COPD) and has consistently demonstrated to decrease mortality and need for intubation when used in conjunction with usual care (Osadnik 2017). By providing both constant expiratory positive airway pressure (EPAP) and inspiratory positive airway pressure (IPAP) in a spontaneous/timed (S/T) mode, inspiratory muscle work is offloaded, tidal volume and minute ventilation increase, and hypercapnea and arterial pH improve.
Average volume-assured pressure support (AVAPS) is a relatively newer modality of NIV that allows for a range of values for IPAP in order to achieve a targeted tidal volume. Using a feedback loop, IPAP is adjusted breath by breath in order to assure that this preset average tidal volume is consistently achieved (Siva Naga 2023). This theoretically should ensure improvements in arterial pH and PaCO2, reducing the risk of failure of NIV and hence need for invasive ventilation.
Two randomized controlled trials comparing NIV using AVAPS with a traditional S/T mode in the management of acute exacerbations of COPD were identified. The first was conducted at a single center in Izmir, Turkey and enrolled 80 subjects between October 2016 and June 2017 (Gören 2021). The only statistically significant differences in outcomes between groups were the median increase in pH between the initial ABG and the one-hour ABG, which was larger in the AVAPS group compared to the S/T group (0.07 vs. 0.03, p = 0.015) and the median decrease in PaCO2 at one hour, which was larger in the AVAPS group (10.20 vs. 4.75, p = 0.033). Length of hospital stay was shorter in the AVAPS group and the risk of intubation in the ED was lower but these differences did not achieve statistical significance.
The second randomized controlled trial included 100 patients seen at two hospitals in Rajasthan, India between January 2021 and December 2021 (Maheshwari 2022). ABG parameters improved in both groups at 3 h after NIV application with no statistically significant difference in changes in pH, PaCO2, PaO2. At 6 and 24 hours, there was statistically significantly better improvement in pH (mean 7.30 vs. 7.28 at 6 hours, p = 0.027; mean 7.33 vs. 7.31 at 24 hours, p = 0.032). Duration of hospital stay was significantly shorter in the AVAPS group (mean 8.54 days vs. 9.90 days; p = 0.003) bu there was no significant difference in the proportion of patients requiring invasive ventilation (8.0% vs. 14.0%; p = 0.338).
Both of these RCTs were limited by an absence of blinding, lack of statistical power to detect potentially clinically significant differences in patient-centered outcomes, and reliance on differences in surrogate outcomes such as pH and PaCO2. Additionally, both studies were conducted outside of the US; ethnic and racial differences could affect disease processes such as COPD. The authors in both studies provide very little information on medical comorbidities in these patients making direct comparison even more difficult (external validity).
A very small prospective, case-control study conducted at 3 hospitals in Guayaquil, Ecuador between February 2009 and September 2011 found similar results to the previous RCTs (Briones 2013). Eleven patients with “infectious exacerbations of COPD” with hypercapnic encephalopathy (GCS < 10) were treated with AVAPS mode and matched with patients treated with S/T mode. At 3 hours GCS improved more in the AVAPS group, rising from a mean of 8.3 to 15 compared with 8.3 to 13 in the S/T group (p = 0.00001). Similarly, PaCO2, showed greater improvement in the AVAPS group (decrease in mean from 63 to 43.6) compared to the S/T group (decrease from 64.8 to 50.1, p = 0.03). There was no statistically significant difference in hospital length of stay or duration of noninvasive ventilation.
A final observational case series included patients with acute exacerbations of COPD admitted to the non-ICU pulmonary ward of the Bursa Uludağ University Hospital in Turkey (Acet Öztürk 2022). Patients with with an arterial pH ≤ 7.35 and PaCO2 > 45 mmHg or a respiratory rate > 24 breaths/minute despite optimal medical treatment received fixed-level pressure support NIV upon admission for 18 hours/day. Among 35 patients, 14 (40%) did not reach clinical and laboratory stability (GCS = 15, respiratory rate < 24, O2 saturation ≥ 90%, and normalized arterial pH with PaCO2 reduction) and were switched to AVAPS mode. Using AVAPS-NIV for a median of 19.5 (9.0–24.0) hours created a significantly better PaCO2 change rate than using PS-NIV for 21.0 (10.0–24.0) hours [-11.4 (-22.0 – -0.5) vs 8.2 (-5.3–19.5), p= 0.02]. The authors found that a higher Charlson comorbidity index and higher PaCO2 upon admission were significantly related to an increased risk of AVAPS-NIV requirement.
While the overall evidence is limited to small, unblinded RCTs and observational studies, AVAPS does appear to be a useful tool in the management of patients with hypercapnic respiratory failure due to exacerbations of COPD. There is no clear evidence of superiority over fixed pressure BiPAP, but AVAPS should at least be considered in patients who fail to respond appropriately to initial management with BiPAP.