Introduction to Ventilator Management

ventilator Machine

Intubation, with subsequent mechanical ventilation, is a common life-saving intervention in the emergency department (ED). Given the increasing length of stay of ventilated patients in EDs, it is necessary for emergency practitioners to have a good understanding of techniques to optimize mechanical ventilation and minimize complications.
Many different strategies of positive-pressure ventilation are available; these are based on various permutations of triggered volume-cycled and pressure-cycled ventilations and are delivered at a range of rates, volumes, and pressures.
Poor ventilatory management can inflict serious pulmonary and extrapulmonary damage that may not be immediately apparent.
Because many of the effects of ventilator-induced lung injury are delayed and not seen while patients are in the ED, much of our understanding of the adverse consequences of volutrauma, air-trapping, barotrauma, and oxygen toxicity has come from the critical care literature. While the fundamental principles underlying mechanical ventilatory support have changed little over the decades, much progress has been made in our understanding of the secondary pathophysiologic changes associated with positive-pressure ventilation.

  Indications For Mechanical Ventilation

The principal indications for mechanical ventilation are airway protection and respiratory failure. A compromised airway, or an airway at risk of compromise, may be identified by physical examination and ancillary testing.
Respiratory failure in the ED is almost always and most appropriately a clinical diagnosis. The decision to intubate and mechanically ventilate or to institute noninvasive ventilation support is generally made purely on clinical grounds without delay for laboratory evaluation.
Respiratory failure may also be easily identified with laboratory or pulmonary function data. Obtaining a PaCO₂ is useful to confirm respiratory failure when a broader differential diagnosis exists for example, obtunded patients who may be hypercarbic but might have a reversible metabolic or toxicological etiology for their conditions but adequate stabilization and ventilation of these patients should not be delayed to wait for laboratory results.
Mechanical ventilation is indicated for both hypercapnic respiratory failure and hypoxemic respiratory failure. It is also indicated for treatment of certain critical conditions such as correction of life-threatening acidemia in the setting of salicylate intoxication, for intentional hyperventilation in the setting of major head injury with elevated intracranial pressure, for suspicion of clinical brain herniation from any cause, or for a patient in critical condition with cyclic antidepressant toxicity.

Laboratory criteria

Laboratory Criteria for Mechanical Ventilation
Blood gases	PaO2 < 55 mm Hg
	PaCO2 >50 mm Hg and pH < 7.32
Pulmonary function tests	Vital capacity < 10 mL/kg
	Negative inspiratory force < 25 cm H2 O
	FEV1 < 10 mL/kg

Blood gases : PaO₂ < 55 mm Hg

                       PaCO₂ >50 mm Hg and pH < 7.32

Pulmonary function tests : Vital capacity < 10 mL/kg

                                          Negative inspiratory force < 25 cm H₂ O

                                          EV₁ < 10 mL/kg

Clinical criteria
1. Apnea or hypopnea
2. Respiratory distress with altered mentation
3. Clinically apparent increasing work of breathing unrelieved by other interventions
4. Obtundation and need for airway protection

Other criteria
1. Controlled hyperventilation (eg, in head injury).
2. Severe circulatory shock

No absolute contraindications exist to mechanical ventilation. The need for mechanical ventilation is best made early on clinical grounds. A good rule of thumb is if the practitioner is thinking that mechanical ventilation is needed, then it probably is. Waiting for return of laboratory values can result in unnecessary morbidity or mortality.