Asthma and Invasive mechanical ventilation strategies:point_left:
Status asthmaticus is reversible small airway obstruction refractory to sympathomimetic and anti-inflammatory agents that may progress to respiratory failure without prompt and aggressive intervention.
Pathophysiology:
The key pathophysiologic feature of status asthmaticus is:
inflammation of small airways leading to increased airway resistance, dramatically extending the time required for full exhalation
premature airway closure lower pulmonary elastic recoil in children with asthma result in:
Auto-PEEP: increases the inspiratory load and can induce respiratory muscle fatigue.
the dynamic hyperinflation: elevate intrathoracic pressure can lead to barotrauma and hemodynamic compromise from impaired preload.
All patients with status asthmaticus must be monitored closely in a pediatric ICU, with serial physical exams being supplemented with continuous cardiorespiratory monitoring and intermittent arterial blood gas sampling.
Status asthmaticus, intubation and invasive M.V:
Mechanical ventilation is reserved for patients with continued progression toward respiratory failure despite maximal medical therapy.
the goal of mechanical ventilation is to maintain adequate oxygenation and ventilation
with the least amount of barotrauma until other therapies become effective.
Indications for intubation:
●Hypoxemia despite provision of high concentrations of oxygen or noninvasive positive pressure ventilation (NPPV; partial pressure of oxygen [pO2] <60 on 100 percent oxygen or NPPV)
●Severe and unremitting increased work of breathing (eg, inability to speak)
●Altered mental status
●Respiratory or cardiac arrest
Hypercarbia alone is not an indication for intubation However, intubation is warranted if a patient demonstrates a progressively rising arterial partial pressure of carbon dioxide (PaCO2) despite maximal medical therapy and/or NPPV and if hypercarbia is causing profound acidosis or altered mental status.
Goals — The goals of endotracheal intubation and mechanical ventilation for children with status asthmaticus and respiratory failure are :
●To take over the work of breathing from the exhausted patient and allow respiratory muscle rest
●To ensure adequate oxygenation
●To ensure sufficient, although still abnormal, gas exchange (initial hypercarbia is tolerated) until airway obstruction can be reversed. Strategies for Intubation:
A cuffed endotracheal tube with the largest diameter appropriate
for the age of the child should be used.
Rapid sequence intubation technique is the preferred method of intubation in children with acute asthma. (Photo attached) with most experience doctor should perform intubation. Strategies for Mechanical Ventilation:
Successful mechanical ventilation in patients with asthma depends upon limiting the risk of hyperinflation and barotrauma.
Hyperinflation:
reduced by decreasing the minute volume(peak pressure,
rate, tidal volume) and permitting adequate time for complete exhalation before the next inhalation is initiated. This is accomplished by slowing the RR and increasing the expiratory time while keeping a normal inspiratory time, thereby decreasing the ratio of inspiratory to expiratory time (I:E ratio).
Barotrauma:
Decreased by minimizing hyperinflation and peak inspiratory pressures (PIP).
SO,
Initial Ventilator Settings:
Mode: pressure-regulated volume control modes can provide a guaranteed tidal volume with a decelerating gas flow and combine some of the advantages of both pressure-limited (preset peak pressure) and volume-limited ventilations (consistent minute ventilation). there is no evidence to support one mode over another.
Tidal Volume: 6-8 ml/kg ideal body weight
Enough to move the chest.
Expiratory Time: (Long expiratory time)
Inspiratory:Expiratory ratio may be 1:4, but can be as high as 1:8
Goal is to allow exhalation and avoid stacking breaths with barotrauma.
Resp Rate: 8-15 /min. Below physiologic rate for age.(half rate for age) .
Controlled Hypoventilation has been shown to be safe .
PEEP: zero or close to intrinsic(auto) PEEP measured by expiratory pause maneuver or from vent graphics (photo attached) (in acute phase. PEEP used once improving and weaning starts).
Permissive hypercapnia with pH (7.2-7.3) was found to be well tolerated (alleviates risk of hyperinflation & barotrauma whilst allowing acceptable gas exchange).
FiO2: can start at 100%, but titrate to keep sats >90%.
Keep the child adequately sedated:
Avoid patient-ventilator asynchrony.
Also helps decrease CO2 production.
Ketamine is a useful med to consider.
It is best to avoid prolonged neuromuscular paralysis if you are able to.
Keep Plateau Pressures <30 cmH20
Increased risk of barotrauma above this level.
Measured by an end-inspiratory pause of several seconds in a system without leaks (hence, the cuffed ETT)
Complication:
Associated with ETT:
Desaturation, bradycardia, hypotension, aspiration pneumonia.
Associated with m.v:
Pneumothorax, pneumomediastinum, hypotension, arrhythmia, VAP, ETT Displacement.
Rogers PICU book
UPTodate 2018
Pediatric and neonatal mechanical ventilation book