Acknowledgments
The authors acknowledge the contributions of Drs. Jason Brainard and Clifford Deutschman, who authored a previous edition of this chapter.
The specific indications for endotracheal intubation are difficult to define, in part because large-scale studies examining the question are lacking and in part because clinical practice is evolving. Although a seasoned practitioner is usually able to identify a patient who requires intubation, it is challenging to explain the precise parameters used to arrive at this decision. In addition, advancements in oxygen delivery systems and noninvasive forms of ventilation have changed the decision-making process in recent years. In this chapter, we describe strategies for diagnosing respiratory failure and deciding whether endotracheal intubation is needed for support. We also briefly discuss reasons to avoid endotracheal intubation.
We divide indications for intubation into two broad categories: patients with physiologic compromise currently in need of support (“actual need”) and those at high risk of decompensation (“impending need”). Actual need for intubation occurs when the patient is physiologically unstable as a result of impaired gas exchange (e.g., hypoxic respiratory failure or hypercarbic ventilatory failure). Impending need is present when respiratory compromise can be reasonably anticipated (e.g., impaired consciousness, airway edema). These two general indications are based on accepted practice, with few or no data available to support specific guidelines. This poor evidence base is reflected in Marino’s statement that “…the indication for intubation and mechanical ventilation is thinking of it.”
As with any invasive procedure, informed consent for endotracheal intubation should be obtained from the patient or proxy if possible. Advanced directives should be consulted to ensure that intubation is consistent with the patient’s goals of care, and patients and families should be counseled about the expected duration of mechanical ventilation. Previous intubation records should be reviewed when possible to determine whether difficulty in securing the patient’s airway is likely to occur.
Actual Need for Intubation
Signs and Symptoms
Acute hypoxic respiratory failure results from inadequate exchange of oxygen across the pulmonary alveolar-capillary membrane. This impairment leads to a decrease in arterial oxygen tension (hypoxemia) and insufficient delivery of oxygen to tissues and cells (hypoxia). In addition, because oxygen delivery is the product of arterial oxygen content and cardiac output, hypoxia can also occur secondary to decreased cardiac output, anemia, or abnormal oxygen-hemoglobin binding affinity. In the medical literature, hypoxic respiratory failure is often described as type I failure when hypoxemia is present without hypercarbia. When associated with hypercarbia, this is described as type II respiratory failure.
In contrast, acute ventilatory failure (and subsequent hypercarbia and respiratory acidosis) results from inadequate removal of gas from distal alveoli. Mild ventilatory failure can exist alone or, when impairment is more severe, may be associated with hypoxemia. Ventilatory failure can result from a primary lung process such as chronic obstructive pulmonary disease, or it can occur secondary to disorders in the cardiac, neurologic, metabolic, or other systems.
Both the symptoms and signs of hypoxia and hypercarbia are nonspecific and are noted in Table 6-1 . In addition, the signs and symptoms of hypercarbia also depend on the patient’s baseline Paco 2 (partial pressure of carbon dioxide in arterial blood) the absolute value of Paco 2 , and the rate of change. Unlike hypoxemia, chronic hypercarbia may be well tolerated. Eliciting a history of chronic CO 2 retention and performing careful serial evaluations of arterial pH are essential because hypercarbia with a near-normal pH is a sign of chronic compensation and often does not reflect an acute disorder. Symptoms of acute hypercarbia may include respiratory fatigue and suggest that the patient soon may be unable to achieve the minute ventilation required to maintain a normal pH.
| Hypoxia | Hypercarbia |
|---|---|
| Symptoms | Symptoms |
| Confusion | Confusion |
| Dyspnea ∗ | Dyspnea |
| Exhaustion | Exhaustion |
| Headache | Headache |
| Irritability |
| Signs | Signs |
|---|---|
| Agitation | |
| Central cyanosis | Accessory respiratory muscle use |
| Coma | Cardiovascular collapse |
| Increased work of breathing | Coma |
| Lethargy | Flapping tremor |
| Seizures | Increased work of breathing |
| Somnolence | Lethargy |
| Tachypnea ∗ | Seizures |
| Shallow or small tidal volume breathing | |
| Somnolence | |
| Tachypnea |
∗ May or may not be present depending on the cause of the hypoxia.
Many disease processes can lead to type I failure ( Table 6-2 ) or type II failure ( Table 6-3 ). These processes can be divided into pulmonary and nonpulmonary processes. Although they are presented separately, there is some overlap in these two types of respiratory failure. For the purposes of this chapter, respiratory and cardiac arrest are included as ventilatory (type II) failure.
| Pulmonary Disorders |
| Intrinsic lung disease |
| Lung consolidation (e.g., tumor) |
| Pathophysiologic state |
| Acute respiratory distress syndrome (ARDS) |
| Atelectasis |
| Lung consolidation (e.g., hemorrhage) |
| Noncardiogenic pulmonary edema |
| Pneumonia |
| Transfusion-related acute lung injury (TRALI) |
| Nonpulmonary Disorders |
| Cardiac disorders |
| Cardiogenic pulmonary edema |
| Vascular disorders |
| Pulmonary embolism |
| Toxins |
| Carbon monoxide |
∗ These are causes of type I respiratory failure (hypoxia without hypercarbia).
| Pulmonary Disorders |
| Intrinsic lung diseases |
| Asthma |
| Chronic obstructive pulmonary disease |
| Pathophysiologic state |
| Airway obstruction (functional or mechanical) |
| Obstructive sleep apnea |
| Nonpulmonary Disorders |
| Neurologic disorders |
| Brainstem or medullary stroke |
| Central sleep apnea |
| Critical illness myopathy or polyneuropathy |
| Myasthenia gravis, Guillain-Barré syndrome |
| Obesity-hypoventilation syndrome |
| Opiate or sedative overdose |
| Phrenic nerve dysfunction |
| Cardiac disorders |
| Cardiac arrest |
| Cardiogenic shock |
| Heart failure |
| Vascular disorders |
| Pulmonary embolism |
| Metabolic disorders |
| Hypomagnesemia |
| Hypophosphatemia |
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What Fluids Should I Give to the Critically Ill Patient? What Fluids Should I Avoid?
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