1 / 16

Pulmonary Effects of Volatile Anesthetics

Pulmonary Effects of Volatile Anesthetics. Ravindra Prasad, M.D. Department of Anesthesiology UNC-CH School of Medicine. Basic Concepts. Absorb oxygen (oxygenation), excrete CO 2 (ventilation) Breathing is controlled by medullary ventilatory center MV = RR x TV, PaCO 2. Basic Concepts.

nerea-case
Download Presentation

Pulmonary Effects of Volatile Anesthetics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Pulmonary Effects of Volatile Anesthetics Ravindra Prasad, M.D. Department of Anesthesiology UNC-CH School of Medicine

  2. Basic Concepts • Absorb oxygen (oxygenation), excrete CO2 (ventilation) • Breathing is controlled by medullary ventilatory center • MV = RR x TV, PaCO2

  3. Basic Concepts • Gas exchange is affected by multiple factors (ventilatory drive, muscle function, blood flow to lungs, chest wall compliance, lung disease) • Minimum Alveolar Concentration

  4. Pattern of Breathing • Normal: intermittent deep breaths separated by varying intervals • Anesthetics: dose-dependent increases in RR • Isoflurane - increases RR up to 1 MAC • N2O - increases RR more than others at > 1 MAC • MV decreases: TV decrease > RR increase • GA: Rapid, shallow, regular, rhythmic breathing pattern

  5. Pattern of Breathing: RR

  6. PaCO2 • Measure of adequacy of ventilation • Increases more with enflurane and desflurane than with isoflurane or halothane • N2O - no change in PaCO2 from baseline • Degree of PaCO2 increase due to volatile anesthetics decreases with time (i.e., there is less ventilatory depression after prolonged exposure)

  7. PaCO2

  8. Ventilatory Response to CO2 • Normal (awake) - CO2 increases MV 1-3 L/min for each 1 mmHg increase in PCO2 • Inhaled anesthetics - dose-dependent depression of slope (=decreased sensitivity to the ventilatory stimulant effects of CO2) and rightward shift (=attenuated responsiveness to CO2) of CO2 response curve

  9. Ventilatory Response to CO2

  10. Ventilatory Response to Arterial Hypoxemia • Awake - PaO2 below 60 => increase in MV • Inhaled anesthetics • subanesthetic doses (0.1 MAC) - greatly attenuate ventilatory response to hypoxemia • anesthetic doses (1 MAC) - abolish ventilatory response to hypoxemia • also attenuate the usual synergistic effect of hypoxemia and hypercapnia on stimulation of ventilation

  11. Bronchodilation • Halothane and isoflurane at 1 MAC decrease bronchospasm • Probably due to anesthetic-induced decreases in afferent (vagal) nerve output • Effect is additive with beta-2 agonists

  12. Airway Irritability • Isoflurane and desflurane - modest irritants • coughing • breathholding • production of secretions • Halothane, sevoflurane - well tolerated

  13. Hypoxic Pulmonary Vasoconstriction • A reflex constriction of pulmonary arterioles in areas of atelectasis in attempts to decrease or prevent perfusion of unventilated alveoli • Inhaled anesthetics directly inhibit HPV when studied in isolated lung models • Clinically, no significant effect, presumably due to compensatory mechanisms

  14. Respiratory Muscle Function • Optimal function: descent of diaphragm is coupled with expansion of rib cage due to contraction of intercostal muscles • Inhaled agents produce muscle relaxation (as well as depression of the medullary ventilatory center)

  15. Respiratory Muscle Function • Halothane • preferential suppression of intercostal muscle function, relative sparing of diaphragm • depression of intercostal muscle function • interferes with rib cage expansion in response to hypoxemia/hypercapnia • stabilization of the rib cage is decreased during spontaneous ventilation • descent of diaphragm tends to cause chest to collapse, leading to decreased lung volumes • Effects of other volatile agents on intercostal muscle function have not been reported

  16. Summary • dec MV (inc RR, dec TV) => inc. PCO2 • dec response to CO2 • dec response to hypoxemia • dec synergy between hypoxemia and hypercapnia as ventilatory stimulants • bronchodilation • airway irritation • inhibition of hypoxic pulmonary vasoconstriction • respiratory muscle function interference (Halothane)

More Related