Sedation improves comfort, lowers O 2 consumption, decreases production of CO 2 and protects against barotrauma (14,20,25). Good sedation is totally essential once the decision is made to intubate. If you see hypoxia on the monitor, take it seriously! However, unrecognised hypoxia with an agitated child +/- saturation probes ‘not picking up’ are the cases that die you need to recognise clinically significant hypoxia and react rapidly. Table 1: *Hypoxia, hypercapnia and respiratory distress by themselves are not indicators for ventilation. Increasing hypercapnia* (despite maximal treatment) Hypoxaemia* (despite delivering high concentration of O 2) Very severe respiratory distress & inability to speak* (despite maximal treatment)Īltered mental state/ falling Glasgow Coma Score (GCS) Indicators for mechanically ventilating children with acute severe asthma Unsurprisingly, asthmatics who are intubated have better outcomes if the intubation is done semi-electively, before there is complete collapse or arrest (19).Įxactly when to intubate is a clinical judgement based on various factors (see below) (13,14) and a bit of witchcraft, but the most important thing you are going to do is rapidly escalate management as soon as it is clear that things are going downhill (…in other words, don’t wait for the arrest to make the decision for you). Obviously it’s important to prevent severe hypoxia, but the actual process of intubation itself can cause more bronchoconstriction, worsening airway obstruction and increasing CO 2. We did a literature review based on these searches:ĭeciding to mechanically ventilate an asthmatic is a really big deal. But when it comes to the crunch, we need to know the best strategy for safely ventilating this group of patients. Obviously, we want to prevent asthmatics ever getting to the point of intubation. At this point you are heading towards a doomed spiral around the black hole of respiratory failure. A hyperexpanded chest is not an efficient one, and respiratory muscles soon get tired. This leads to air trapping or ‘breath stacking’. But after huffing and puffing for hours, an asthmatic child just doesn’t have the energy to keep the respiratory muscles working so hard.Īnother issue in severe asthma is dynamic hyperinflation – this is when each expired breath is so prolonged (because of airway resistance) that the next breath ‘interrupts’ the previous one, and so the tidal volume can never be fully expired. not in the acute asthmatic), the respiratory muscles would just work harder to compensate. Air can only flow inwards when this high PEEP is overcome. When there is more resistance to expiration, the end-expiratory pressure in the alveoli shoots up – this is known as auto-PEEP. PaO2 gradually falls with increasing obstruction. As decompensation occurs, the PaCO2 continues rising and pH continues to fall. But even with a prolonged expiratory phase, airway obstruction prevents the alveoli from emptying – that CO 2 is stuck in the alveoli, gets absorbed into the bloodstream and the pH falls.įigure 1: ‘Fish’ diagram showing how pH, PaO2 and PaCO2 change with increasing airway obstruction. Hypoxia and rising CO 2 make you hyperventilate in an attempt to blow off CO 2, which sets off a respiratory alkalosis. Top this off with mucus plugging, and you end up with areas of lung which are perfused normally but no gas exchange is going on – aka V/Q mismatch (4). In severe asthma, the bronchioles are narrower thanks to the combined nasties of bronchoconstriction and mucosal thickening. To really understand ventilation strategies, you need to appreciate some pathophysiology. Ventilation (the last resort in status asthmaticus) is never taken lightly – it can be extremely challenging and comes with major risks (4). Critically unwell asthmatics, not responding to a boat-load of bronchodilators and getting worse before your eyes, are one of the most pant wettingly scary scenarios we see in acute paediatrics. Between 2 – 12% of the population have asthma and every year 12-27 children under the age of 14 die during an acute asthma exacerbation. If you have ever been involved in a case of asthma so severe the child ended up intubated, apologies for any unpleasant flashbacks as you read this.! Despite advances in the understanding and treatment of asthma, it is still a massive public health burden. Dr Seb Gray | Dr Katie Knight | Dr Kim Sykes
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