Respiratory issues are some of the most common and challenging problems encountered in a Post-Anesthesia Care Unit (PACU). Anesthesia and surgical manipulation disrupt normal pulmonary physiology and can also exacerbate underlying pulmonary pathophysiology. Changes in respiratory rate, such as tachypnea or hypopnea, can herald the onset of major physiological derangement. In the PACU, respiratory compromise may also present as cardiac or neurological dysfunction, making expeditious recognition and treatment paramount.

Respiratory function is largely controlled by subcortical structures on the unconscious level. The brainstem is responsible for basic respiratory function, with the medulla oblongata acting as the “pacemaker” for respiration and the pons housing the pneumotaxic and apneustic centers which control the depth of inspiration.^[1] Higher cortical centers may adjust respiration in response to information received from peripheral chemoreceptors, peripheral stretch receptors, and central nervous system receptors. Chemoreceptors, found in the carotid and aortic bodies, trigger changes in respiration due to fluctuations in PaO₂ and PaCO₂. In general, derangements in respiratory rate are due to conscious effort by the patient, physiological disturbance, or pharmacologic effect.^[1] This chapter will review the commonly encountered causes of tachypnea and hypopnea in the PACU.

Tachypnea

Tachypnea means “rapid breathing.” In an adult this can be defined as a respiratory rate above 20 breaths/min.^[1] Young children have a much higher resting respiratory rate, especially during the first three years of life.^[2] The initial evaluation of the tachypneic postoperative patient should always include an immediate assessment of all vital signs and a focused history and physical exam, with attention to surgical procedure, type of anesthetic, and anesthetic course. Causes of tachypnea can be divided into two main categories, hypoxic and non-hypoxic (see Tables 11.1 and 11.2). When evaluating a postoperative patient, it is important to make this distinction rapidly. A decreased pulse oximetry reading (less than 90%) is probably the most efficient method of determining whether or not hypoxia is the cause.

Table 11.1 Hypoxic causes of tachypnea

Cause	Additional signs and symptoms	Diagnostic tests	Initial treatment
Atelectasis	Decreased breath sounds, crackles, wheezes, narrowed intercostal spaces	Chest X-ray	Deep breathing exercises, incentive spirometry, analgesics if incisional pain contributing to hypoventilation
Pulmonary embolism	Chest pain, hypoxia, sinus tachycardia, right heart strain on electrocardiogram (ECG)	Spiral computed tomography scan, ventilation–perfusion scan	Systemic anticoagulation
Pneumothorax	Chest pain, cyanosis, confusion, hypotension, diminished breath sounds, hyperresonance to chest percussion, tracheal deviation, subcutaneous emphysema, narrowed pulse pressure	Chest X-ray, arterial blood gas	Increase FiO2, immediate needle decompression prior to imaging if tension pneumothorax is suspected, consult surgical service for chest tube placement, use caution with positive pressure ventilation
Hemothorax	Chest pain, cyanosis, confusion, hypotension, diminished breath sounds, tracheal deviation, narrowed pulse pressure	Chest X-ray, arterial blood gas, complete blood count, coagulation studies	Consult surgical service for chest tube placement, search for and treat underlying cause of hemorrhage
CO poisoning	Lightheadedness, confusion, headache, vertigo	Blood spectrophotometry or chromatography	Deliver 100% FiO2, may consider hyperbaric O2 in extreme cases
Congestive heart failure (fluid overload, transfusion-associated circulatory overload)	Respiratory distress, rales and crackles, gallop rhythm, peripheral edema, jugular venous distention, cyanosis, dullness to percussion	ECG, chest X-ray, arterial blood gas	Discontinue IV fluids, administer diuretics
Transfusion-related acute lung injury (TRALI)	Hypoxia, hypotension, pulmonary edema, recent (within 6 hours) transfusion	Chest X-ray	Supplemental oxygen, mechanical ventilation, supportive care, avoid diuresis
Asthma	Wheezing, coughing, bronchospasm, use of accessory muscles, chest tightness	Arterial blood gas	Administer β2-agonist via nebulizer such as albuterol, consider adrenergic agonist such as epinephrine and emergent intubation in extreme cases
Acute coronary syndrome	Chest pain, jaw pain, chest pressure, nausea, diaphoresis, feeling of impending doom	ECG, complete blood count, cardiac enzymes, chest roentgenogram, urine drug screen	Morphine, oxygen, nitroglycerin, aspirin, immediate cardiology consultation
Anemia	Weakness, fatigue, malaise, dyspnea, palpitations, chest pain	Hemoglobin and hematocrit, blood glucose	Transfusion of packed red blood cells for acute symptomatic anemia

Table 11.2 Non-hypoxic causes of tachypnea

Cause	Additional signs and symptoms	Diagnostic tests	Initial treatment
Pain	Tachycardia, hypertension, agitation, delirium, diaphoresis	Pain score assessment	Analgesics
Anxiety	Tachycardia, hypertension, agitation, delirium, diaphoresis	Pain score assessment	Anxiolytics (e.g. benzodiazepines)
Dehydration	Tachycardia, hypotension, pulse pressure variation on pulse oximeter/arterial line, decreased urinary output	Hemoglobin and hematocrit	Fluid bolus, reassess for improved hemodynamics and urine output, search for underlying cause
Acidosis	Confusion, lethargy, hyperventilation (compensatory in metabolic acidosis) in response to hypercarbia or hypoventilation (respiratory acidosis)	Arterial blood gas	Determine underlying cause as respiratory or metabolic in nature and treat accordingly
Malignant hyperthermia	Increased temperature, tachycardia, muscle rigidity	Arterial blood gas, assess for hyperkalemia and acidemia	Dantrolene

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