Continuous Monitoring of Patients Treated With Opioids for Chronic Pain and Its Impact on Patient Safety. A Feasibility Trial.

Opioids are an effective instrument for patients with acute and chronic pain. Their route of administration ranges from transdermal to subcutaneous application through to Intravenous Patient-Controlled Analgesia (IV-PCA).

The use of IV-PCA-pumps has considerable advantages including decreased delay in the administration of opioids from the time requested, individual dose intervals, self -control of their therapy, rapidity and ease of dose titration . These potential benefits, however are balanced by the need for careful assessment of adverse effects, including decreased quality of life because of the patient's sedation, constipation and possible episodes of bradypnoea and desaturation, eventually leading to respiratory depression (RD) requiring treatment. Often described safety features that help prevent overdosing are PCA bolus dose, delay, and lockout interval.

Even though the risk of serious, potentially life threatening complications by using IV-PCA without a background infusion was described to be very low (0.24%) compared to other methods of opioid delivery , adverse effects like worrying degrees of hypoxemia and bradypnoea do occur and often remain undetected due to the lack of continuous monitoring. One of the possible causes of patient harm are medication errors associated with PCA administration, a common form of PCA errors, which is a significant source of preventable patient morbidity and hospital resource utilization.

The individual patient response to a particular dose of opioids depends on diagnosed or unrecognized comorbidities. Clinical experience has shown that it is not possible to prospectively identify all patients who may be at increased risk.

Conventional opioid monitoring protocol may fail to detect frequent episodes of bradypnoea and desaturation measured by the respiratory rate (RR) and Saturation of Peripheral Oxygen (SpO2) because even at a low respiratory rate SpO2 is usually maintained, so that pulse oxymetry might fail to detect respiratory deterioration, particularly if a patient is receiving supplemental oxygen.

Therefore, continuous monitoring could be considered more sensitive, especially if it contains the measurement of Partial Pressure of Carbon dioxide (PCO2), which is a good parameter for monitoring ventilatory function.

The 'gold standard' method to measure the arterial partial pressure of carbon dioxide (PaCO2) is still the arterial blood gas analysis. But arterial sampling including catheterization or intermittent arterial puncture is invasive and expensive and associated with pain and discomfort for the patient. Therefore cutaneous carbon dioxide tension (PcCO2) measurement was suggested to be used as a non-invasive surrogate measure of PaCO2.

SpO2, and tcPCO2, are important clinical parameters that should be used in conjunction with each other. SpO2 reflects oxygenation, while tcPCO2 reflects ventilation; the first can still be normal while the second may herald early changes in respiratory status. Capnography may provide the earliest indication of opioid-induced respiratory depression. It is important to monitor changes from a baseline tcPCO2 level. As the tcPCO2 level starts to increase, early intervention and changes in medication can be made.

The present study aims to examine combined oxymetry and transcutaneous capnography using a single earlobe sensor (V-Sign™, Sentec AG, Therwil, Switzerland) in chronic pain patients treated with opioids where non-invasive monitoring of ventilation is needed because ventilatory disturbances are suspected. This may, potentially, improve patient's quality of life.