Lecture 10: Asthma Theraputics Flashcards
What features are suggestive of a severe asthma attack (and therefore immediate action is required)?
- -Severe breathlessness and wheeze.
- -Agitation
- -Tachypnoeic (respiratory rate 34 breaths/minute),
- -Only able to talk in words rather than sentences
- -Hunched over and use of respiratory accessory muscles.
- -Reduced skin turgor suggesting dehydration due to fluid loss with panting.
- -Tachycardia 130/minute.
- -Pulsus paradoxus - systolic BP varied with respiration (130 mm Hg during inspiration and 160 mm Hg during expiration).
- -Silent chest indicates very poor air entry to the alveoli
what is the pulsus paradoxus?
An abnormally large decrease in systolic blood pressure and pulse wave amplitude during inspiration. The normal fall in pressure is less than 10 mmHg. When the drop is more than 10mmHg, it is referred to as pulsus paradoxus
what is the mechanism of pulsus paradoxus
An exaggeration of the normal variation of BP with respiration. Normally during inspiration, systolic blood pressure decreases ≤10 mmHg, and pulse rate goes up slightly. This is because the intra-thoracic pressure becomes more negative relative to atmospheric pressure. This increases systemic venous return, so more blood flows into the right side of the heart. However, the decrease in intra-thoracic pressure also expands the compliant pulmonary vasculature. This increase in pulmonary blood capacity pools the blood in the lungs, and decreases pulmonary venous return, so flow is reduced to the left side of the heart. Also the increased systemic venous return to the right side of the heart expands the right heart and directly compromises filling of the left side of the heart. Reduced left-heart filling leads to a reduced stroke volume which manifests as a decrease in systolic blood pressure.
what are the causes of pulsus paradoxus?
- -Constrictive pericarditis
- -Cardiac tamponade
- -Superior vena cava syndrome
- -Severe obstructive airway disease (asthma, COPD)
- -Obstructive sleep apnea
- -Tension pneumothorax
- -Croup
What investigations would you immediately organize as the casualty officer?
1) Oxygen saturation
2) Arterial blood gases
3) Peak expiratory flow rate (PEFR) or FEV1
4) Chest X-ray to out-rule pneumothorax, and to check for infection and or lobar/segmental collapse.
5) Urea, Electrolytes, Creatinine – potassium, in particular, can be affected by anti-asthma therapy.
6) Full Blood Count – to check for evidence of infection.
What therapies are available for a severe asthma attack?
–High concentration oxygen (>60% oxygen if possible via face mask (aim O2 saturation > 95%)
–Nebulised b2 agonists (salbutamol via oxygen driven nebulizer)
–Nebulised muscarinic antagonist (ipratropium via oxygen driven nebulizer)
–IV hydrocortisone
–Correct fluid and electrolytes
If life-threatening consider
–Magnesium sulfate 2gm IV over 20 mins
–IV aminophylline or salbutamol (not usually if high dose –nebulized b2 agonists used)
–Intubation and Ventilation (ICU)
do you need to administer antibiotics in all severe asthma attacks?
No
in the absence of evidence of infection, empiric antibiotics not recommended
what is the role of MgSo4 in an asthma attack?
Current evidence does not support routine use of intravenous magnesium sulfate in all patients with acute asthma presenting to the emergency department. Magnesium sulfate appears to be safe and beneficial in patients who present with severe acute asthma.
what is the role of aminophylline in a severe asthma attack?
Starting intravenous aminophylline may be reasonable in patients who do not respond to medical treatment with bronchodilators, oxygen, corticosteroids, and intravenous fluids within 24 hours.
Data suggest that aminophylline may have an anti-inflammatory effect in addition to its bronchodilator properties.
Indications for intubation and mechanical ventilation include…
- -Apnea or respiratory arrest
- -Diminishing level of consciousness
- -Impending respiratory failure marked by significantly rising PCO2 with fatigue, decreased air movement, and altered level of consciousness
- -Significant hypoxemia that is poorly responsive or unresponsive to supplemental oxygen therapy alone
- -Numbers not improving after initial therapy
1) If O2 saturation remained below 90%
2) If PEFR or FEV1 remained <50% of expected
3) If PCO2 climbed to >42 mm Hg.
does noninvasive ventilation can replace mechanical ventilation?
No
- -Supplemental oxygen and/or helium-oxygen mixture (heliox)
- -Noninvasive ventilation (NIV)
1) Bilevel positive airway pressure (BiPAP) provides greater support.
2) Maintains airways open → decreases airways resistance → reduces auto-PEEP → reduces work of breathing - -Use for 1–2 hours in cooperative patients not responding to medical therapy.
- -Do not delay intubation when it is indicated.
how does aminophylline work?
Aminophylline is a drug combination of theophylline and ethylenediamine in a ratio of 2 to 1. It is FDA approved for relieving symptoms of reversible airway obstruction due to asthma or other chronic lung diseases like chronic bronchitis and emphysema. It is also used to prevent apnea in preterm infants.
- -competitive nonselective phosphodiesterase inhibitor which raises intracellular cAMP, activates PKA, inhibits TNF-alpha and leukotriene synthesis, and reduces inflammation and innate immunity and
- -nonselective adenosine receptor antagonist.
what is the beclometasone?
inhaled sterioid
reduces transcription of inflammatory enzymes & cytokines
how MgSo4 works?
Effects on intracellular calcium levels, smooth muscle cell relaxation, stabilization of T cells & mast cells, inhibition of acetylcholine release, and stimulation of nitric oxide & prostacyclin synthesis
Inhibition of 5-Lipoxygenase describes
zileuton
