Respiratory Emergencies

Respiratory Emergencies


Respiratory depression occurs during every anesthetic episode. Central nervous system (CNS) depression can lead to hypoventilation (increased PaCO2), hypoxemia (decreased PaO2), and apnea. Hypoventilation cannot always be determined by visual inspection of chest wall movements but can be assessed by arterial blood gas analysis or capnography. Although potentially devastating, respiratory depression, if recognized early, is easily treated by establishing a patent airway and providing adequate inflation of the lungs to ensure appropriate gas exchange.

Patterns of respiration

Eupnea: normal rate and rhythm

Tachypnea: increased respiratory rate; caused by fever, hypoxia, hypercapnea, pneumonia, or lesions of the CNS respiratory centers

Bradypnea: slow but regular respirations; caused by sleep, anesthesia, opioids, hypothermia, neoplasia, or respiratory decompensation

Apnea: absence of respiration; may be periodic; caused by drug depression, muscle paralysis, overventilation, obstruction, shock, increased intracranial pressure, or surgical manipulation of vagus and splanchnic nerves

Hyperpnea: large respirations (increased tidal volume); rate normal; caused by excitement, pain, surgical stimulation, hypoxia, hypercarbia, heat, or cold

Cheyne-Stokes respiration: respirations become faster and larger, then slower, followed by an apneic pause; caused by increased intracranial pressure from head trauma or neoplasia, meningitis, renal failure, severe hypoxia, anesthetic drug overdose, or high altitude

Biot’s respiration: respirations that are faster and deeper than normal, with abrupt pauses between them; each breath has approximately the same tidal volume; caused by anesthesia in normal, athletic horses and greyhounds; spinal meningitis; or drugs that cause generalized CNS depression

Kussmaul’s respiration: regular and deep respirations without pauses; animal’s breathing usually sounds labored, with breaths that resemble sighs; caused by renal failure, metabolic acidosis, or diabetic ketoacidosis

Apneustic: prolonged gasping inspiration, followed by extremely short, inefficient expirations; caused by high doses of drugs (e.g., ketamine in cats and horses or excessive doses of guaifenesin in horses) or lesions in the pons and thalamus

General Considerations

Definition: a respiratory emergency is the inability to maintain adequate gas exchange (oxygen [O2]; carbon dioxide [CO2]) such that tissue oxygenation and acid-base status become compromised

II Clinical causes

Potential causes of impaired gas exchange:

1. Hypoventilation caused by preanesthetic or anesthetic drugs

2. Improper placement (e.g., esophageal) of the endotracheal tube

3. Parenchymal pulmonary disease and pulmonary edema (diffusion impairment)

4. Pleural cavity disease (pneumothorax, fractured ribs)

5. Airway obstruction

6. Low inspired oxygen (FiO2)

7. Closed pressure release (“pop-off”) valve

III Species, age, size, and concurrent lung pathology determine respiratory frequency, rate of lung inflation, inflation pressure, and tidal volume to be delivered; larger animals generally require slower inflation rates, lower frequencies of breathing, and larger volumes. Note: Three to 4 minutes of preoxygenation with 100% O2 can markedly prolong the time to hemoglobin desaturation, hypoxemia, and cyanosis.

IV Treating hypoventilation and apnea

If the animal is taking small-volume breaths or is apneic, establish an airway and institute artificial ventilation with room air or O2; O2 is preferred

Control breathing rate if apneic; assist ventilation if breathing

Assist or control ventilation until the animal can maintain adequate tidal breathing and gas (O2; CO2) exchange, normal mucous membrane color, and hemoglobin saturation (SpO2; see monitoring)

Airway Obstruction

Partial airway obstruction may be associated with respiratory disease or obstruction/kinking of the endotracheal tube

II Conditions that predispose animals to airway obstruction

Stenotic nares

Edema of the nasal turbinates

Elongated or displaced soft palate

Collapsing arytenoid cartilages

Everting laryngeal ventricles

Collapsing trachea

Laryngeal paresis or paralysis (“Lar-Par”)

Hypoplasia of the trachea

III Other causes of airway obstruction

Foreign bodies

Nasal disease (e.g., tumor, fungus, parasites)

Mucus or blood in airway or endotracheal tube

Orotracheal device or anesthetic circuit obstruction due to improper setup or kinking

Clinical signs

Sep 6, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Respiratory Emergencies

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