Salbutamol ā When to give the next dose?
Salbutamol is one of the most frequently used medicines in the paediatric pharmacopeia. Most of us can say that itās a short-actingg beta agonist delivered by nebuliser or more commonly via an MDI with spacer. Some might recall that the half-life is between 2.7 and 5.5hrs.
And, most perplexing of all, once weāve used it in the acute situation, how best to use it next? Iām talking here about the post-burst, pre-discharge phase of asthma or an exacerbation of a reactive airway picture.
Pierce is 5yo, he presents at 2300 to your ED. His Mum says he canāt sleep due to the coughing and she thinks his asthma is playing up. He receives a burstĀ and another dose an hour later; he looks like heās coping another hour later. He takes a 2mg/kg dose of Prednisolone. You come to review Pierce and his mum asks āSo, what happens next?ā
Weāre talking here about the frequency of salbutamol usage. If you had asked me this question a month ago, I’d have been certain of my answer. My mental model for how to manage a presentation like this (especially out of hours) was rock solid with experience, but light on evidence.
Iāve had a suspicion I’ve been doing things differently and hence decided to review my practice, first by talking to peers, then looking at some guidelines and finally my reviewing the literature.
My practice, overnight, had been to be quite prescriptive with salbutamol – a slow, regular, wean and then not less than q2h until the sun came up (0500 in the Queensland summer), before aiming for q3h, consultant review if indicated, education and discharge during the morning ward/short-stay round.
This is not the practice of my peers; āYou just wean them and then send them home.ā Or, āJust review them regularly and give it as you need to.ā, were the common answers – hopefully what most folk reading this are thinking – and certainly what I aim to do before the sun goes down.
The RCH Melbourne guidelines suggest only dosing salbutamol when symptoms return.
The experimental literature around this question and reducing the frequency of salbutamol dosing is surprisingly sparse, but here are a few of the highlights:
Chandra A Shim C, Cohen HW, et al. Regular vs ad-lib albuterol for patients hospitalized with acute asthma.Ā Chest. 2005 Sep;128(3):1115-20.
Chandra undertook a small study of 62 adults with the aim compare regular (q4h) salbutamol plus symptomatic versus symptomatic treatment alone. Patients in the pro re nata-only arm used less salbutamol and had less use of salbutamol overall but there was no significant difference in the length of stay or rate of improvement. Patients were randomised 6 hours into their treatment, which seems to expunge most of the external validity for this paper to our clinical question.
Karpel et al. performed an elegant study with 100 adults presenting to NY emergency departments in which the patients were dosed every 30 minutes with salbutamol or placebo inhaler such that the groups essentially became dosed at q30mins or q60mins or q90mins or q120minutes – all after an initial load of 6 puffs of salbutamol. At each time point, FEV1 was recorded. They concluded that q60mins was the optimal dose, with minimal side effects.
This study didn’t utilise a āburstā / salbutamol load, which is now standard (and first described in 1988), and may alter the conclusions, as the outcomes seemed to identifying number of patients who responded well initial dosing, and noted that these early responders benefitted comparably from q30,60 and 120 minutely dosing.
Admittedly, the frequent, regular dosing of salbutamol, once loaded, doesn’t make pharmacological sense; although itās worth noting that only 15% of the dose makes it to the lung surface, whilst the other 85% is swallowed and undergoes first-pass metabolism, there are negligible levels of salbutamol in serum. These of course, are pharmacologic parameters, rather than clinical ones.
On reflection, my prescriptive style required minimal reviews and developed from working jobs as a solo Paeds Reg on nights. The perceived benefits were that with a high patient load and variable nursing experience, I was able to reduce decision making and cognitively offload all whilst keeping patients safe (I’ve not seen salbutamol toxicity from q2h dosing.) I’ve previously suggested other arguments for this, including the predictability for parents, although I’m not so sure about this part.
There are some merits in this shape of care, but itās not āevidence basedā nor āwhat most doctors would do.ā So, is it safe? Is it wrong? How best to change practice?
References
Chandra A Shim C, Cohen HW, et al. Regular vs ad-lib albuterol for patients hospitalized with acute asthma.Ā Chest. 2005 Sep;128(3):1115-20.
