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Oxygen Desaturation

(Hypoxia)

By

Cherisse Berry

, MD, New York University School of Medicine

Last full review/revision Nov 2020| Content last modified Nov 2020
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Patients without respiratory disorders who are in the intensive care unit (ICU)—and other patients—may develop hypoxia (oxygen saturation < 90%) during a hospital stay. Hypoxia in patients with known respiratory conditions is discussed under those disorders.

Etiology of Oxygen Desaturation

Evaluation of Oxygen Desaturation

Total fluid volume given during the hospital stay and, in particular, during the previous 24 hours should be ascertained to identify volume overload Volume Overload Volume overload generally refers to expansion of the extracellular fluid (ECF) volume. ECF volume expansion typically occurs in heart failure, kidney failure, nephrotic syndrome, and cirrhosis... read more . Drugs should be reviewed for sedative administration and dosage. In significant hypoxia (oxygen saturation < 85%), treatment begins simultaneously with evaluation.

History

Very sudden onset dyspnea and hypoxia suggest pulmonary embolus Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more Pulmonary Embolism (PE) (PE) or pneumothorax Pneumothorax Pneumothorax is air in the pleural space causing partial or complete lung collapse. Pneumothorax can occur spontaneously or result from trauma or medical procedures. Diagnosis is based on clinical... read more Pneumothorax (mainly in a patient receiving positive pressure ventilation). Fever, chills, and productive cough (or increased secretions) suggest pneumonia Hospital-Acquired Pneumonia Hospital-acquired pneumonia (HAP) develops at least 48 hours after hospital admission. The most common pathogens are gram-negative bacilli and Staphylococcus aureus; antibiotic-resistant organisms... read more . A history of cardiopulmonary disease (eg, asthma Asthma Asthma is a disease of diffuse airway inflammation caused by a variety of triggering stimuli resulting in partially or completely reversible bronchoconstriction. Symptoms and signs include dyspnea... read more , chronic obstructive pulmonary disease Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more Chronic Obstructive Pulmonary Disease (COPD) , heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular failure causes shortness of breath and fatigue, and right ventricular failure causes peripheral and abdominal fluid... read more Heart Failure (HF) ) may indicate an exacerbation of the disease. Symptoms and signs of myocardial infarction may indicate acute valvular insufficiency, pulmonary edema Pulmonary Edema Pulmonary edema is acute, severe left ventricular failure with pulmonary venous hypertension and alveolar flooding. Findings are severe dyspnea, diaphoresis, wheezing, and sometimes blood-tinged... read more Pulmonary Edema , or cardiogenic shock Cardiogenic and obstructive shock Shock is a state of organ hypoperfusion with resultant cellular dysfunction and death. Mechanisms may involve decreased circulating volume, decreased cardiac output, and vasodilation, sometimes... read more . Unilateral extremity pain suggests deep venous thrombosis Deep Venous Thrombosis (DVT) Deep venous thrombosis (DVT) is clotting of blood in a deep vein of an extremity (usually calf or thigh) or the pelvis. DVT is the primary cause of pulmonary embolism. DVT results from conditions... read more Deep Venous Thrombosis (DVT) (DVT) and hence possible PE. Preceding major trauma or sepsis requiring significant resuscitation suggests acute respiratory distress syndrome Acute Hypoxemic Respiratory Failure (AHRF, ARDS) Acute hypoxemic respiratory failure is severe arterial hypoxemia that is refractory to supplemental oxygen. It is caused by intrapulmonary shunting of blood resulting from airspace filling or... read more Acute Hypoxemic Respiratory Failure (AHRF, ARDS) . Preceding chest trauma suggests pulmonary contusion Pulmonary Contusion Pulmonary contusion is trauma-induced lung hemorrhage and edema without laceration. (See also Overview of Thoracic Trauma.) Pulmonary contusion is a common and potentially lethal chest injury... read more .

Physical examination

Patency of the airway and strength and adequacy of respirations should be assessed immediately. For patients on mechanical ventilation, it is important to determine that the endotracheal tube is not obstructed or dislodged. Findings are suggestive as follows:

Testing

Hypoxia is generally recognized initially by pulse oximetry. Patients should have the following:

  • A chest x-ray (eg, to assess for pneumonia, pleural effusion, pneumothorax, or atelectasis)

  • ECG (to assess for arrhythmia or ischemia)

  • Arterial blood gases (ABGs), to confirm hypoxia and evaluate adequacy of ventilation

Bedside echocardiography done by an intensivist may be used to assess for hemodynamically significant pericardial effusion or reduced global left ventricular or right ventricular function until formal echocardiography can be done. Elevated serum levels of brain (B-type) natriuretic peptide (BNP) may help differentiate heart failure from other causes of hypoxia. If diagnosis remains unclear after these tests, testing for PE Diagnosis Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more Diagnosis should be considered. Bronchoscopy may be done in intubated patients to rule out (and remove) a tracheobronchial plug.

Treatment of Oxygen Desaturation

Identified causes are treated as discussed elsewhere in THE MANUAL. If hypoventilation persists, mechanical ventilation Overview of Mechanical Ventilation Mechanical ventilation can be Noninvasive, involving various types of face masks Invasive, involving endotracheal intubation Selection and use of appropriate techniques require an understanding... read more via noninvasive positive pressure ventilation or endotracheal intubation is necessary. Persistent hypoxia requires supplemental oxygen.

Oxygen therapy

The amount of oxygen given is guided by arterial blood gasses (ABG) or pulse oximetry to maintain PaO2 between 60 and 80 mm Hg (ie, 92 to 100% saturation) without causing oxygen toxicity. This level provides satisfactory tissue oxygen delivery; because the oxyhemoglobin dissociation curve is sigmoidal, increasing PaO2 to > 80 mm Hg increases oxygen delivery very little and is not necessary. The lowest fractional inspired oxygen (FIO2) that provides an acceptable PaO2 should be provided. Oxygen toxicity is

  • Concentration-dependent

  • Time-dependent

Sustained elevations in FIO2 > 60% result in inflammatory changes, alveolar infiltration, and, eventually, pulmonary fibrosis. An FIO2 > 60% should be avoided unless necessary for survival. An FIO2 < 60% is well tolerated for long periods.

An FIO2 < 40% can be given via nasal cannula or simple face mask. A nasal cannula uses an oxygen flow of 1 to 6 L/minute. Because 6 L/minute is sufficient to fill the nasopharynx, higher flow rates are of no benefit. Simple face masks and nasal cannulas do not deliver a precise FIO2 because of inconsistent admixture of oxygen with room air from leakage and mouth breathing. However, Venturi-type masks can deliver very accurate oxygen concentrations.

An FIO2 > 40% requires use of an oxygen mask with a reservoir that is inflated by oxygen from the supply. In the typical nonrebreather mask, the patient inhales 100% oxygen from the reservoir, but during exhalation, a rubber flap valve diverts exhaled breath to the environment, preventing admixture of carbon dioxide and water vapor with the inspired oxygen. Nonetheless, because of leakage, such masks deliver an FIO2 of at most 80 to 90%.

Refractory hypoxia may require neuromuscular blockade, recruitment maneuvers, prone ventilation, or extracorporeal membrane oxygenation (ECMO).

Key Points

  • Hypoxia can be caused by disorders of ventilation and/or oxygenation and is usually first recognized by pulse oximetry.

  • Patients should have a chest x-ray, ECG, and arterial blood gas measurements (to confirm hypoxia and evaluate adequacy of ventilation); if diagnosis remains unclear, consider testing for pulmonary embolus.

  • Give oxygen as needed to maintain PaO2 between 60 and 80 mm Hg (ie, 92 to 100% saturation) and treat the cause.

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