Recommendations

Key Recommendations

High-flow oxygen therapy, hyperbaric oxygen, and supportive therapy are the key treatments for CO poisoning. High-flow oxygen therapy should be initiated as soon as the diagnosis is suspected, and should not be discontinued until the diagnosis is ruled out. It is recommended that persistently symptomatic patients are treated with hyperbaric oxygen and re-treated up to a maximum of three times.[2] Depending on where and how the CO poisoning occurred, patients may have multiple other injuries to treat, such as burns, smoke inhalation injury, or overdoses. Contact the Poison Center early for advice on management. America's Poison Centers Opens in new window

Supportive care and monitoring

Remove patient(s) from the CO exposure environment immediately. Resuscitate the patient according to standard guidelines, as needed.[53]

Patients with CO poisoning can be critically ill, and all patients should have close cardiopulmonary and neurologic monitoring throughout treatment, with close attention to fluid balance particularly for hypotensive patients. See Shock.

Patients with altered consciousness should be considered for endotracheal intubation. Seizures and cardiac complications should be treated urgently.

Carboxyhemoglobin (CO-Hb) can be monitored with blood gas CO-oximetry, although levels may be low in patients receiving oxygen for a period of time, or with significant delays to presentation. An ECG and cardiac biomarkers may be monitored to detect evidence of cardiac dysfunction in moderately or severely poisoned patients (based on symptom severity and/or CO-Hb levels of 25% or more), and in those with suspected cardiac involvement.[30] Also consider monitoring lactate to estimate metabolic acidosis, blood glucose to eliminate hypoglycemia as a cause for altered mental status and to check for hyperglycemia, and creatine kinase to monitor for rhabdomyolysis. Fetal monitoring is necessary in pregnant women to detect any evidence of fetal distress or fetal compromise.[16]

Those at highest risk for death are patients with severe metabolic acidosis (low pH on blood gas), those with very high CO-Hb levels (>25%), fire as a source of CO exposure, loss of consciousness or need for mechanical ventilation.[54]

Oxygen

Supplemental 100% oxygen through a non-rebreather mask or high-flow nasal cannula should be given to all patients with CO poisoning regardless of CO-oximetry readings or SaO2 levels (SaO2 alone is not helpful in detecting CO poisoning because it does not distinguish CO-Hb from oxyhemoglobin).[55] Supplemental oxygen reduces hypoxia and increased PaO2 decreases the half-life of CO-Hb through facilitating the elimination of CO in the lungs. Although oxygen therapy is given regardless of arterial PaO2 levels, measuring arterial blood gas can assess acid/base status. Low pH is associated with mortality. Severe acidosis could be considered an indication for hyperbaric oxygen.[16] See Evaluation of metabolic acidosis.

Administering 100% oxygen reduces the half life of carbon monoxide to 85 minutes compared to 4-5 hours in standard room air conditions.[30]​ This can be further reduced to around 20 minutes with hyperbaric oxygen.[30]

Hyperbaric oxygen therapy

Hyperbaric oxygen is 100% oxygen in a pressurized chamber. It is used to enhance clearance of CO-Hb from the body through increasing the PaO2 in the lungs. The therapeutic goal of treatment with hyperbaric oxygen is the prevention of long-term and permanent neurocognitive dysfunction, more than the enhancement of short-term survival rates.[2] Hyperbaric oxygen therapy should be considered in patients with: loss of consciousness, ischemic cardiac changes, neurologic deficits, significant metabolic acidosis, or peak CO-Hb levels ≥25%.[4][27][56][57][58][59] The American College of Emergency Physicians (ACEP) recommends that emergency physicians use either hyperbaric oxygen therapy or high-flow normobaric therapy for acute CO poisoning. The ACEP acknowledges that there is no clear evidence that one approach is more effective than the other in terms of preventing delayed neurocognitive sequelae. The ACEP’s recommendation is intended to support physicians who choose not to refer patients for hyperbaric oxygen therapy owing to, for example, time or geographic constraints.[30]

One systematic review of six clinical trials found no significant benefit to hyperbaric oxygen therapy in preventing delayed neurocognitive deficits.[60] A key limitation of this analysis was the heterogeneity in the trials on primary outcome, the dosage and number of hyperbaric oxygen therapy sessions, and delays to therapy. Negative clinical trials typically used a clinically ineffective dose of hyperbaric oxygen.[59] The only included randomized controlled trial (RCT) that met all Consolidated Standards of Reporting Trials (CONSORT) criteria for assessing quality of RCTs showed a significant benefit from hyperbaric oxygen.[57] The study used the following protocol:

  • First session: 3.0 atmospheres for 60 minutes, followed by 2.0 atmospheres for 60 minutes

  • Second and third sessions: 2.0 atmospheres for 120 minutes.

One subsequent consensus opinion recommended the use of this trial to guide clinical practice until further information from future studies becomes available.[2][4][56][58]

Providers should take this ongoing uncertainty into account when considering hyperbaric oxygen therapy in patients with CO poisoning. Complications from hyperbaric oxygen therapy include pulmonary and ear barotrauma, and seizures.[57]

If hyperbaric oxygen is required, some centers recommend that it should be started within 6 hours and no later than 24 hours.[40] For nonintubated patients, hyperbaric treatments are recommended until signs and symptoms have resolved, or until a clinical plateau has been reached (usually a maximum of three treatments).[59] For intubated patients whose neurologic exam must be abbreviated out of necessity, three treatments are recommended.[61]

Treat hyperglycemia

Hyperglycemia can occur after various types of severe brain injury, regardless of the presence of preexisting diabetes mellitus.[62][63][64] There is evidence that neurologic outcomes are worse in patients with hyperglycemia, although evidence specific to CO poisoning is limited.[33][65][66][67] Treating hyperglycemia with insulin is therefore appropriate. It is critical, however, to avoid dangerously low levels of blood glucose through over-aggressive treatment of hyperglycemia.[68]

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