Chapter 318 - Disorders of Ventilation Flashcards
What is the normal interval for arterial level of carbon dioxide (PaCO2) at the sea level?
37-43mmHg
Describe the equation that represents the relantionship between CO2 production and PaCO2.
PaCO2=(k)(VCO2)/VA, whereas VCO2 represents CO2 production, k is a constant and VA represents fresh gas alveolar ventilattion.
How can one calculate VA (fresh gas alveolar ventilation)?
VA = minute ventilation x (1 -Vd/Vt), wheares Vd/Vt represents the dead space fraction.
What variables might explain PaCO2 disturbances?
“all disturbances of PaCO2 must reflect altered CO2 production, minute ventilation, or dead space fraction.”
Define dead space fraction regarding pulmonary ventilation.
“dead space fraction Vd/Vt represents the portion of tidal breath that remains within the conducting airways at the conclusion of inspiration and so does not contribute to alveolar ventilation.”
Name a lesion in a group of neurons located in the brainstem from which results complete cessation of breathing.
Pre-Bötzinger complex, which is responsible for the generation of avarious forms of inspiratory activity.
Name the afferent and efferent connections related to the Dorsal Respiratory Group (DRG).
The DRG receives information from afferent nerves about PaO2, PaCO2, pH and blood pressure from the carotid and aortic chemoreceptors and baroreceptors. It also receives information from the vagus nerve regarding stretch receptors and juxtapulmonary-capillary receptors in the lung parenchyma and chest wall. The DRG functions as the initial site for integration and, with Ventral Respiratory Column (VRC), they send projections into the contralateral spinal cord to control the phrenic nerve, the upper airway muscle groups and spinal respiratory neurons, and innervate the intercostal and abdominal muscles that participate in normal respiration.
What is the main function of Ventral Respiratory Column (VRC)?
VRC is responsible for the respiratory rythm (also dependendent on pFRG, paraFacial Respiratory Group) and it also includes the Pre-Bötzinger complex.
Name the four categories that include the diseases that reduce minute ventilation or increase dead space.
“parenchymal lung and chest wall disease, sleep-disordered breathing, neuromuscular disease, and respiratory drive disorders.”
Sleep disturbances regarding disorders of ventilation only occurs in the category of sleep-disordered breathing.
True or False?
False.
“Sleep disturbance and orhopnea are also described in neuromuscular disorders.”
Drive respiratory diseases also have sleep disturbances.
How do you explain orthopnea in neuromuscular diseases?
“As neuromuscular weakness progresses, the respiratory muscles, including the diaphragm, are placed at a mechanical disadvantge in the supine position due to the upward movement of the abdominal contents.”
What are the first symptoms/sign of neuromuscular disease?
“More commonly, however, extremity weakness or bulbar symptoms develop prior to sleep disturbance in neuromuscular diseases”
What is the most common sleep disturbance leading to chronic hypoventilation?
Obesity hypoventilation syndrome.
Name the only screening tool validated for Obstructive Sleep Apnea for outpatient primary care setting.
Berlin Questionnaire.
Epworth Sleepiness Scale and STOP-Bang have not been validated in this setting
What is the sensitivity and negative predictive value for STOP-Bang Survery in the preoperative clinic?
93% and 90%, respectively
In drive respiratory diseases there is as increased response to hypoxemia and hypercapnia.
True or False?
False.
“There is an attenuated increase in minute ventilation in response to elevated CO2 and/or low O2 in respiratory drive disorders.”
Drive respiratory diseases are diagnosed by CT or MRI.
True or False?
False.
“Brain imaging (…) can sometimes identify structural abnormalities in the pons or medulla that result in hypoventilation. Chronic narcotic use or significant hypothyroidism can depress the central respiratory drive and lead to chronic hypercapnia as well.”
In neuromuscular diseases, hypercapnia usually precedes muscle weakness.
True or False?
False.
Name the ALS guidelines criteria for the use of Nocturnal noninvasive positive-pressure ventilation (NIPPV).
“ALS guidelines recommend consideration of nocturnal NIPPV if symptoms of hypoventilation existe and one of the following criteria is present: PaCO2 ≥45mmHg; nocturnal oximetry demonstrates oxygen saturation ≤88% for 5 consecutive min; maximal inspiratory pressure [less than] 60mmH2O; FVC [less than] 50% predicted; or snif nasal pressure [less than] 40cmH2O.”
Explain the pH disturbances in chronic hypoventilation.
The retention of CO2 is responsible for respiratory acidosis, which is compensated proportionately with retention of HCO3-, leading to metabolic acidosis.
Is there any surgical option in patients with hypoventilation due to high cervical spinal cord lesions or respiratory drive disorders?
“Phrenic nerve or diaphragm pacing is a potential therapy.”
“small case series suggest that effective diaphragmatic pacing can improve quality of life in these patients.”
What is the definition of Obesity Hypoventilation Syndrome (OHS)?
“The diagnosis of OHS requires body mass index (BMI)≥30Kg/m2 and chronic daytime alveolar hypoventilation, defined as PaCO2≥45mmHg at sea level in the absence of other known causes of hypercapnia.”
How do you define Obstrutive Sleep Apnea Syndrome (OSAS)? How frequent is it?
OSAS is the most frequent form of Obesity Hypoventilation Syndrome, although it might occur without obesity. It is define by an apnea-hypopnea index ≥5 per and daytime sleepiness (or AHI ≥15 without symptoms). It occurs in 3-4% of middle-aged men and 2% of middle-aged women.
What are the main physiopathological mechanisms that might explain hypoventilation in patients with Obesity Hypoventilation Syndrome (OHS)?
“The pathogenesis of hypoventilation in these patients is the result of multiple physiologic variables and conditions including Obstrutive Sleep Apnea, increased work of breathing, respiratory muscle impairment, ventilation-perfusion mismatching, and depressed central ventilatory responsiveness to hypoxemia and hypercapnia.”
