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Respiratory monitoring


Monitoring a patient's respiratory status usually takes place in a hospital setting and may be the primary purpose for a patient being observed or admitted to a medical setting.

The physical signs of respiratory distress may present as a patient appearing short of breath, having an increased work of breathing, use of their accessory muscles, and changes in skin color, general pallor, or partial or complete loss of consciousness.

When the initial efforts of respiratory monitoring show evidence of a patient's inability to adequately oxygenate their blood, the patient may require mechanical ventilation.

It is key to have a good understanding of patient pathophysiology in order to properly interpret medical information.

Measurement of airway pressure (Paw), flow (F) and volume (Vol) during mechanical ventilation assists in the differential diagnosis of respiratory failure. Airway occlusion technique makes possible to carefully characterize the mechanics of the lung, chest wall, and the total respiratory system. Patients with acute respiratory distress syndrome (ARDS) can have a modified elastance due to a stiffer lung or a stiffer chest wall depending in the origin of the disease. Patients with ARDS of pulmonary origin are at greater risk of ventilator lung injury than those of non pulmonary origin.

Recording muscle activity during spontaneous breathing helps differentiate PEEPi caused by dynamic hyperinflation from that caused by expiratory muscles. If the patients PEEPi is caused by dynamic hyperinflation, external PEEP will reduce the patient’s work of breathing. If it is caused by expiratory muscles, it will add an elastic load and it will increase the operating lung volume.

During a weaning trial, esophageal pressure and flow measurement can be used to partition patient’s effort into its resistive, elastic and PEEPi components. The three components are increased in patients that fail the weaning.

Capnometry helps in detecting esophageal intubation. Monitoring flow-volume curves helps in detecting the need for endotracheal suctioning.

Presence of expiratory flow throughout expiration, without reaching zero, suggests the presence of PEEPi. With an occlusion of the expiratory port PEEPi can be measured in a patient in control ventilation.

Monitoring physiologic variables, such as the ratio of respiratory frequency to tidal volume (RR/VT) also called rapid shallow breathing index (RSBI) helps in deciding whether a patient has reasonably likelihood to tolerate discontinuation of mechanical ventilation.


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