What is the significance of shivering as a sign of carbon dioxide (CO2) retention?

From the Guidelines

Shivering is not a typical sign of CO2 retention, and patients with suspected CO2 retention should be evaluated for symptoms like confusion, headache, and respiratory depression. CO2 retention typically presents with these symptoms, and in severe cases, can lead to respiratory acidosis and potentially life-threatening complications 1. The body retains CO2 when there's inadequate ventilation, which can occur in conditions like COPD, severe asthma, drug overdose, or neuromuscular disorders affecting respiratory muscles.

Key Considerations

• CO2 retention can lead to respiratory acidosis, which is common in clinical practice, especially in patients with COPD 2.
• Monitoring oxygen saturation alone is insufficient to assess CO2 levels, and arterial blood gas analysis is needed for accurate assessment.
• Treatment typically involves addressing the underlying cause, which may include bronchodilators for conditions like COPD, non-invasive ventilation such as BiPAP or CPAP to support breathing, or in severe cases, intubation and mechanical ventilation.
• A saturation target of 88–92% is recommended for acidotic patients, and oxygen therapy should be stepped down to 28% or 35% oxygen from a Venturi mask, or oxygen at 1–2 L/min from nasal cannulae depending on oxygen saturation and blood gas results 3.

Clinical Implications

• Patients with COPD on oxygen therapy with a PO2 >10 kPa (75 mm Hg) are at risk of CO2 retention and may be assumed to have excessive oxygen therapy.
• If a patient is found to have respiratory acidosis due to excessive oxygen therapy, the oxygen therapy should not be discontinued immediately, but rather stepped down to a lower concentration.
• It is essential to prioritize the single most recent and highest quality study, which in this case is the BTS guideline for oxygen use in adults in healthcare and emergency settings 1, to ensure the best possible outcomes for patients with CO2 retention.

From the Research

Co2 Retention and Shivering

• Co2 retention, also known as hypercapnia, is a condition where there is an elevated level of carbon dioxide in the blood [(4, 5, 6)].
• Shivering is not directly mentioned in the provided studies as a symptom or effect of Co2 retention.
• However, hypercapnia can lead to various physiological effects, including changes in breathing patterns, increased dead space ventilation, and decreased alveolar ventilation 7.
• In patients with chronic obstructive pulmonary disease (COPD), hypercapnia can occur due to various mechanisms, including the abolition of 'hypoxic drive', loss of hypoxic vasoconstriction, and absorption atelectasis 4.
• The studies suggest that hypercapnia can have significant clinical implications, including increased risk of mortality, cardiovascular morbidity, and muscle wasting [(8, 5, 6)].

Physiological Mechanisms

• The physiological mechanisms of hypercapnia include a decrease in minute volume, an increase in dead space, or an increase in carbon dioxide production 6.
• In patients with COPD, the pattern of breathing can modulate Co2 retention, with higher respiratory rates and smaller tidal volumes leading to larger dead space ventilation and lower alveolar ventilation 7.
• The studies highlight the importance of understanding the triggers of hypercapnia to provide targeted therapy and avoid complications [(4, 6)].

Clinical Implications

• Hypercapnia is an independent risk factor for mortality in COPD, and its treatment is crucial to improve patient outcomes 5.
• Noninvasive ventilation is a widely used technique to remove carbon dioxide and has been investigated as a treatment option for hypercapnia in COPD 5.
• The studies emphasize the need for careful management of oxygen therapy in patients with COPD to avoid inducing hypercapnia [(4, 8)].