Best Evidence Topics
  • Send this BET as an Email
  • Make a Comment on this BET

Normalisation of pCO2 levels associated with better outcomes in opiate overdose.

Three Part Question

[In adults who present to the emergency department with suspected acute opiate overdose] is [normalisation of pCO2 levels] associated with [a lower incidence of complications – specify……VF, VT aspiration, death]

Clinical Scenario

A 25 year old man is brought into the emergency deparment by his brother who found him unconscious at home. He is pinpoint pupils, a respiratory rate of 6. ABGs show a pH of 7.05 and a pCO2 of 14kPA. In light of the suspected opiate overdose you administer naloxone, but wonder if it would have been beneficial to treat the respiratory acidosis first.

Search Strategy

Medline 1966 to june week 2 2005 using the ovid interface.
Embase 1980 to 2005 week 26.
CINHAL 1982 to june week 3 2005.
The cochrane library.
[{exp NARCOTICS} AND {exp OVERDOSE} AND {exp.respiratory insufficiency}]

Search Outcome

Medline:9 results found, 1 of which was relevant to the question.
Embase:246 results. None of relevance.
CINHAL:4 results. None of relevance.
None found on Cochrane library

Relevant Paper(s)

Author, date and country Patient group Study type (level of evidence) Outcomes Key results Study Weaknesses
Steven a McLaughlin.
United States
Patients in Department of Emergency Medicine, University of New Mexico. No actual number of patients specified.Correspondance referring to case report in the Annals of Emergency Medicine. Reply regarding experience of treating heroin overdose in New Mexico.Predicting and treating hypercapnia in an overdose patient.Mathematical model devised calculates pCO2,HCO3 and pH.As it is a correspondance there is no stated sample size to say how the method was devised and proven to work. No full study means that important points are missing from the evidence. The paper does not mention where treatment with naloxone comes into this management, if, indeed it does. There is not an explanation of the proven advantages of using this method.


This question came about because, when looking into variations in treating heroin overdose, there was an argument regarding not using the antidote naloxone. Instead the patients repiratory acidosis was rectified and the patient stabilized as the effects of the opiates wore off. This avoided potential adverse effects of rapid reversal with Naloxone, such as pulmonary oedema and cardiac dyssrhymthmias,as well as neurological sequelae from prolonged hypoxia and hypercapnia. The original case report stated the protective effects of hypercapnia against ARDS, cardiac and brain ischaemia and by decreasing inflammation.The paper included in this bet states that it is unclear if this is applicable in heroin overdose. The paper has stated that small amounts of supplemental oxygen can result in clinically reassuring SaO2 whilst the patient is suffering severe hypercapnia. In these cases hypoxia is a result of decreased respiratory drive so treatment will not correct hypercapnia. The paper concludes that measurement of end-tidal C02 and interventions for hypoxia should correct the hypoventilation.This is not a practise that occurs in the UK. Whilst this paper does not directly answer the question it does demonstrate the profound acidocisis that can occur in opiate overdose even when the measured SaO2 is normal.

Editor Comment


Clinical Bottom Line

No direct clinical evidence is available. On the basis of pathophysiological argument we advocate that repiratory acidosis is corrected prior to administration of naloxone in an acute opiate overdose.


  1. Steven a McLaughlin. Another perspective on Annals of Emergency Medicine 44(6)pp 670-671