Regarding invasive ventilation of a patient with severe life-threatening asthma, all of the following statements are correct EXCEPT:
Answer: D: Dynamic hyperinflation in a patient with severe asthma can cause barotrauma to the lung and severely compromise venous return to the heart. As a result marked hypotension may develop. Hence, after intubation, the patient should be carefully manually ventilated with a slow breath rate not exceeding 6–8/min. This allows adequate time for exhalation of air from the lungs. Patients should be clinically assessed to determine the degree of bronchospasm, the time taken for full expiration and the degree of gas trapping. Once the above are determined the patient can be connected to the ventilator circuit with carefully selected ventilator settings. Generally a ventilator rate of 6–8 breaths/min and a tidal volume of 5–6 mL/kg are recommended. A long expiratory time should be set with an I:E ratio > 1:2. Full expiration before the next breath should be confirmed clinically by observing the patient’s chest rise and fall. In addition, this should be confirmed on the ventilator graph. Moderate hypercarbia and acidosis is well tolerated but hypercarbia may be detrimental in patients with myocardial depression. During pressure-controlled ventilation, tidal volume may fluctuate and this may cause significant hypoventilation. Therefore, pressure-controlled ventilation may not be the ideal mode and volume-controlled ventilation is usually preferred.
References:
Regarding the management of acute asthma in adults, which ONE of the following is TRUE?
Answer: A: The principles of ventilation include small tidal volumes, a long expiratory time and a slow respiratory rate. The high-inspiratory flow rate is an important component of allowing long expiratory times. The peak inspiratory pressure (PIP) is likely to be high with these settings, but there does not appear to be a correlation between high PIPs and barotrauma in ventilated patients with asthma. Dynamic hyperinflation can be assessed by measuring the plateau airway pressure by occluding the expiratory valve at the end of inspiration and recording the pressure after a 5-second pause. This is the most easily measured estimate of alveolar pressure at the end of inspiration and is affected by the degree of hyperinflation. Ideally this should be maintained at <25 cm H2O. There is a paucity of randomized trial data regarding the use of NIV in asthma. Some case series suggest benefit. There are as yet no clear guidelines for the use of NIV in severe asthma. A trial of NIV is reasonable once patients are screened for contraindications and are willing to cooperate.
Similarly, there is a paucity of good evidence regarding the use of IV salbutamol. However, IV β-agonists should be considered if there is no response to nebulized bronchodilator therapy. Increasing airway obstruction may prevent nebulized drug delivery and some studies have demonstrated improved response when intravenous β-agonist is used. Salbutamol (e.g. 250 mcg) may also be given IV to non-intubated patients with severe asthma.
Reference:
A young adult male was intubated in the ED for a near-fatal asthma episode. A few minutes after connecting to the ventilator, significant oxygen desaturation was observed on the monitor. If the ventilator, ventilator circuit, oxygen delivery and tube placement are found to be functioning well and correct, which ONE of the following statements is TRUE regarding the patient’s hypoxaemia?
Answer: D Emergency clinicians should be vigilant about the possibility of desaturation after intubation. This is a complication that may occur in the severe asthmatic. The ‘DOPE’ mnemonic describes the practical drill that should be adopted during such a scenario (it does not describe the order of the drill).
Although a supine CXR may occasionally miss a pneumothorax, in most situations in a ventilated patient a pneumothorax that is significant enough to cause hypoxaemia can be detected by a supine CXR. Dynamic hyperinflation of the lungs may be contributory to desaturation due to hypoxaemia. Mucus plugging is a major concern and this may be due to drying and thickening of secretions. A mucus plug may cause collapse of one or more segments of the lung, causing severe desaturation. To dislodge the mucus plug adequate suctioning through the endotracheal tube (ETT) with assistance from physiotherapy is required and sometimes may need to proceed to bronchoscopic lavage. Adequate humidification of inspired gas is recommended to prevent mucus plugging in ventilated asthmatics.
DOPE:
Regarding the treatment of acute asthma in children, which ONE of the following is TRUE?
Answer: B: Salbutamol is commonly used for bronchodilator therapy in acute asthma. Evidence suggests that salbutamol administration via MDI and spacer is not only more effective but is also associated with fewer side effects such as tachycardia, vomiting and hypoxia, as compared with administration via nebulizer. However, in a lifethreatening exacerbation of asthma, continuous nebulized salbutamol should be used. If the initial response to nebulized salbutamol is inadequate, salbutamol can be administered via the intravenous route at a dose of 15 mcg/kg over 10 minutes followed by a maintenance infusion of 1 mcg/kg/min. However, the role of intravenous bronchodilators in addition to nebulized treatment remains unclear. The referenced guidelines vary in their recommendations. Aminophyllin can be considered in children with severe and life-threatening attacks unresponsive to maximal other therapies. It has been shown to have an effect on the outcome (intubation). Recommendations in guidelines vary, however, and it remains a controversial area.
There is a paucity of evidence to clarify the role of NIV in acute severe paediatric asthma. NIV has had some success in adults with restrictive lung conditions and it has been used in acute adult asthma. None of the current paediatric guidelines recommend the use of NIV.
In select patients, NIV may avoid the need for intubation. For a child who is alert and cooperative and who does not have increased airway secretions, NIV may be considered in the following situations at experienced hands:
Regarding the management of acute severe exacerbation of COPD, all of the following statements are correct EXCEPT:
Answer: B: Spirometry is indicated in all patients presenting with acute exacerbations of COPD except rare occasions of altered level of consciousness. FEV 1.0 manoeuvre can be performed by even unwell COPD patients with a normal conscious state. When FEV 1.0 is <1 L or <40% predicated, it usually indicates a severe exacerbation in a patient with mild to moderate disease.
In a patient with advanced disease (severe COPD), worsening hypoxaemia, acute hypercapnoea, acute/ chronic hypercapnoea or acidosis indicates severe exacerbation. ABG should be obtained in all patients with severe exacerbations of COPD and with suspected respiratory failure or cor pulmonale. Hypercapnoea may occur during acute exacerbations in both patients with normal CO2 levels and chronically elevated CO2 levels. Excessive oxygen administration may worsen this hypercapnoea. Several mechanisms promote CO2 retention including reduced ventilation due to reduced hypoxic drive and increased ventilation–perfusion mismatch due to hypoxic pulmonary vasoconstriction. Early identification of a patient who is in hypercapnoeic respiratory failure will alert against excessive oxygen administration. Excessive oxygen administration has been shown to increase length of hospital stay, increased rate of admission to the high dependency unit (HDU) and increased use of NIV. Excessive oxygen administration is rarely required to treat hypoxia in COPD and ideally should be treated with Venturi mask at 24% or 28%. Although nasal prongs provide variable amounts of oxygen, at a rate of 0.5–2 L/min is less likely to cause CO2 retention.
Oxygen saturation (SpO2) should be maintained at 88–92%. SpO2 >92% does not provide additional advantages. Between 8 and 10 puffs of a 100 mcg MDI salbutamol provides an equivalent dose to 5 mg nebulized salbutamol and may be used in patients with acute exacerbations.
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