Published in the year 2000, a controlled clinical trial carried out in patients presenting to hospital with AECOPD accompanied by persistent hypercapnia-related acidosis, showed that the application of BiPAP on a respiratory ward in the early stages of treatment, was capable of reducing in-hospital mortality in this cohort by approximately 50% (1). The study extended observations made on AECOPD patients managed with NIV on ICU (2,3). In hospitals with an NIV service, particularly out of hours, generalists often become involved in the care of AECOPD patients on BiPAP. Current published guidelines do not address several key issues arising during the management of these patients. While local guidelines should be followed, this article addresses five key questions which can trouble the generalist.

Abbreviations

AECOPD: acute exacerbation of chronic obstructive pulmonary disease, BiPAP: bilevel positive airway pressure, PaCO₂: arterial partial pressure of carbon dioxide, ERS: European Respiratory Society, ATS: American Thoracic Society, IPAP: inspiratory positive airway pressure, EPAP: expiratory positive airway pressure, bpm: breaths per minute.

First & Foremost

The appropriate target oxygen saturation range in AECOPD is 88% to 92%. Remember, this means that if supplemental oxygen therapy is administered, the SpO₂ must not be allowed to rise above 92%. 92% is the maximum limit of SpO₂ in these cases. It is not a minimum target!

All 5 answers below are subject to modification by clinical judgement. The term ‘considered’ is used below, as, in addition to patient factors, the decision to implement BiPAP will be influenced by the local facilities and expertise available.

When managing a patient with AECOPD

1. Which patients with AECOPD are candidates for BiPAP?

In the absence of a contraindication☥, BiPAP should be considered, if, after one hour of standard medical treatment for AECOPD, the patient has an arterial pH ≤ 7.35^ in association with a PaCO₂ above the normal range (> 45 mmHg) and a respiratory rate above 20 - 24 bpm*(4).

2. What pressures (IPAP and EPAP) are employed in this situation?

There is no international consensus on BiPAP starting pressures and titration protocols in AECOPD. The clinical trial on which the intervention under discussion is based (1), commenced BiPAP with an IPAP of 10 cm H₂O and an EPAP of 4 cm H₂O. In the first hour following the application of BiPAP, the IPAP was titrated upwards in 5 cm H₂0 increments to 20 cm H₂O (or the highest IPAP tolerated by the patient, up to 20 cm H₂O). The patient was then maintained on these pressures.

3. What changes are we targeting during BiPAP?

In the clinical trial referred to above (1), four hours into the study protocol, both the treatment and control groups experienced improvement in key physiological parameters (increased pH, decreased PaCO₂ & decreased respiratory rate). These favourable changes occurred more quickly in the BiPAP group but were similar in magnitude at four hours in both groups. Therefore, it would appear that to achieve the survival benefit imparted by BiPAP in this situation, we are targeting a significant period of time spent on BiPAP rather than marked augmentation of favourable changes in these key physiological variables. We monitor the respiratory rate and repeat the ABG at one hour and at four hours after commencing BiPAP to look for evidence of deterioration in respiratory status. Deterioration may indicate the need for intubation. We monitor the SpO₂ continuously, never allowing this parameter to rise above 92% on oxygen therapy.

4. How long do we keep the patient on BiPAP on day one?

The patient should be kept on BiPAP for as many hours as they can tolerate in the first 24 hours following BiPAP initiation. The patient is allowed breaks from the mask for meals and drug administration.

5. When do we stop BiPAP?

There is no universally accepted protocol for the discontinuation of BiPAP in the clinical scenario under discussion. Again, local guidelines should be followed. In the clinical trial above (1), the time on BiPAP was reduced to 16 hours on day 2 and 12 hours on day 3. This strategy is reasonable (5). On each of these days, an ABG should be carried out 4 hours after stopping BiPAP. If the pH remains normal on the ABG taken four hours after discontinuing BiPAP on day 3, the patient can continue on standard treatment alone.

If not already decided, issues around a ‘ceiling of care’ need to be addressed at the beginning of treatment. ICU should at least be informed that a COPD patient has been started on BiPAP. Failure of BiPAP is indicated by the emergence of indications for intubation.

Opinion: In my experience, the application of BiPAP in AECOPD outside dedicated respiratory units, is frequently suboptimal. However, many of the problems which do arise can be avoided by keeping the SpO₂ on oxygen therapy, at or below 92%.

☥Contraindications to BiPAP: Inability to protect the airway, inability to cooperate, unstable cardiorespiratory status, trauma or burns to the face, apnea, facial or esophageal or gastric surgery

^In the presence of a coexistent metabolic pH disturbance, an algorithmic approach to patient management based on arterial pH is not applicable. The clinician will be guided by their overall clinical assessment of the patient’s need or otherwise for BiPAP.

*(> 23 bpm). Measurement of respiratory rate is subjective; hence this parameter is quoted as a range in the published guidelines.

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