Document Detail

Influences of morphine on the ventilatory response to isocapnic hypoxia.
MedLine Citation:
PMID:  9197304     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: The ventilatory response to hypoxia is composed of the stimulatory activity from peripheral chemoreceptors and a depressant effect from within the central nervous system. Morphine induces respiratory depression by affecting the peripheral and central carbon dioxide chemoreflex loops. There are only few reports on its effect on the hypoxic response. Thus the authors assessed the effect of morphine on the isocapnic ventilatory response to hypoxia in eight cats anesthetized with alpha-chloralose-urethan and on the ventilatory carbon dioxide sensitivities of the central and peripheral chemoreflex loops. METHODS: The steady-state ventilatory responses to six levels of end-tidal oxygen tension (PO2) ranging from 375 to 45 mmHg were measured at constant end-tidal carbon dioxide tension (P[ET]CO2, 41 mmHg) before and after intravenous administration of morphine hydrochloride (0.15 mg/kg). Each oxygen response was fitted to an exponential function characterized by the hypoxic sensitivity and a shape parameter. The hypercapnic ventilatory responses, determined before and after administration of morphine hydrochloride, were separated into a slow central and a fast peripheral component characterized by a carbon dioxide sensitivity and a single offset B (apneic threshold). RESULTS: At constant P(ET)CO2, morphine decreased ventilation during hyperoxia from 1,260 +/- 140 ml/min to 530 +/- 110 ml/ min (P < 0.01). The hypoxic sensitivity and shape parameter did not differ from control. The ventilatory response to carbon dioxide was displaced to higher P(ET)CO2 levels, and the apneic threshold increased by 6 mmHg (P < 0.01). The central and peripheral carbon dioxide sensitivities decreased by about 30% (P < 0.01). Their ratio (peripheral carbon dioxide sensitivity:central carbon dioxide sensitivity) did not differ for the treatments (control = 0.165 +/- 0.105; morphine = 0.161 +/- 0.084). CONCLUSIONS: Morphine depresses ventilation at hyperoxia but does not depress the steady-state increase in ventilation due to hypoxia. The authors speculate that morphine reduces the central depressant effect of hypoxia and the peripheral carbon dioxide sensitivity at hyperoxia.
A Berkenbosch; L J Teppema; C N Olievier; A Dahan
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Anesthesiology     Volume:  86     ISSN:  0003-3022     ISO Abbreviation:  Anesthesiology     Publication Date:  1997 Jun 
Date Detail:
Created Date:  1997-07-17     Completed Date:  1997-07-17     Revised Date:  2003-11-14    
Medline Journal Info:
Nlm Unique ID:  1300217     Medline TA:  Anesthesiology     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1342-9     Citation Subset:  AIM; IM    
Leiden University, The Netherlands.
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MeSH Terms
Analgesics, Opioid / pharmacology*
Anoxia / physiopathology*
Carbon Dioxide / administration & dosage,  physiology*
Morphine / pharmacology*
Oxygen / administration & dosage,  physiology
Partial Pressure
Pulmonary Ventilation / drug effects*,  physiology
Tidal Volume
Reg. No./Substance:
0/Analgesics, Opioid; 124-38-9/Carbon Dioxide; 57-27-2/Morphine; 7782-44-7/Oxygen

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