Mechanical Ventilation

INDICATIONS

Criteria for intubation and mechanical ventilation (MV) include impending respiratory failure, inadequate oxygen delivery, coma, obtundation, inability for the patient to protect the airway, or a need to urgently gather data (e.g., the need for computed tomography [CT] in an uncooperative patient).
Poor air flow, retractions, high respiratory rates, and confusion are useful indicators of the need for MV. A blood gas showing acidosis due to retention of CO₂ or a low Pao[2] despite oxygen therapy can also help in the decision to begin MV.
Noninvasive positive pressure ventilation (NIPPV) may be a viable option for patients with impending respiratory failure or inadequate oxygen delivery who are able to tolerate a tight-fitting mask. Patients who are agitated, confused, or unable to protect their airway are not candidates for NIPPV. Patients whose respiratory distress is due to a rapidly reversible condition (i.e., pulmonary edema or asthma) are the best candidates for NIPPV.
In an emergent setting where a patient is not known to have a “do not resuscitate” (DNR) directive, or the applicability of a DNR directive is in question, intubation and MV should be provided with the knowledge that withdrawal of care remains an option ethically equivalent to withholding initiation of care.

SEDATION AND PARALYSIS

NIPPV is usually well tolerated. Although the mask can be tight fitting and produce anxiety in some patients with respiratory distress, most patients are able to tolerate it without analgesia or sedation. Sedation should be used very cautiously in combination with NIPPV. Some authorities considered sedation contraindicated. A small number of patients may only be able to tolerate NIPPV with a very mild amount of anxiolytic.
MV is uncomfortable. Sedation must be provided for patients who are awake. Neuromuscular blockade will produce the best intubating conditions. Rapid sequence activation is covered extensively in Chapter 2. Once intubated, sedation must be continued. Continuous infusion of benzodiazepines is effective. Chemical paralysis may also need to be continued. See Tables 22-1 and 22-2.

VENTILATOR SETTINGS

For an overview, refer to Table 22-3.

Table 22-1 Sedatives

	Dose (Intravenous)
Sedative	Induction or Bolus (mg/kg)	Drip (μg/kg/min)	Onset (s)	Duration (of Induction/Bolus) (min)
Etomidate (Amidate)	0.2-0.4	100 × 10 min, then 10	15-45	3-12
Fentanyl (Sublimaze)^a	5-10 (μg/kg)	2-10 (μg/kg/h)	60-90	45-60
Ketamine (Ketalar)	1.0-2.0	5-25	45-60	10-20
Lorazepam (Ativan)^b	0.03-0.04	0.25-1.0	60-120	60-120
Midazolam (Versed)^c	0.1-0.4	0.25-1.0	30-90	10-30
Propofol (Diprivan)	1.5-2.5	25-75	15-30	5-10
^aNot an induction agent alone, but useful as an inductive adjunct.
^bNot an induction agent.
^cDrip dosing to be used in concert with opioid analgesia.