What parameter should be closely monitored when administering morphine?

Respiratory Rate Monitoring is the Critical Parameter When Administering Morphine

When administering morphine, the nurse must give special attention to respiratory rate, as respiratory depression is the most serious and potentially life-threatening complication of opioid administration. 1

Primary Monitoring Parameters

Respiratory Assessment (Most Critical)

• Monitor respiratory rate continuously or at minimum hourly, assessing both rate and depth of respiration without disturbing a sleeping patient 1
• The American Society of Anesthesiologists specifically identifies adequacy of ventilation as the primary monitoring parameter, including respiratory rate and depth of respiration 1
• Respiratory depression can occur at any time but risk is greatest during the first 24-72 hours of therapy or following dose increases 2
• In cases with concerning signs, it is acceptable to awaken a sleeping patient to assess level of consciousness 1

Additional Essential Parameters

• Level of consciousness must be monitored regularly, as decreased alertness identifies patients at increased risk of respiratory depression 1
• Pulse oximetry should be used when appropriate to detect hypoxemia, though continuous pulse oximetry is more effective than periodic monitoring 1
• End-tidal carbon dioxide monitoring (capnography) is more likely to detect hypercapnia and respiratory depression earlier than clinical signs alone 1

Monitoring Frequency Based on Route of Administration

For Neuraxial Morphine (Epidural/Intrathecal)

• Monitor at least once per hour for the first 12 hours after administration 1
• Monitor at least once every 2 hours for hours 12-24 1
• After 24 hours, monitor at least once every 4 hours, with frequency dictated by clinical condition 1
• Monitoring should continue for a minimum of 24 hours after single-injection neuraxial morphine 1

For Intravenous/Oral Morphine

• Monitor closely within the first 24-72 hours of initiating therapy and following any dosage increases 2
• Continuous monitoring reveals that 12% of patients experience desaturation episodes and 41% experience bradypnea lasting 3 minutes or more 3
• The European Society of Cardiology recommends that respiration should be monitored when morphine is administered 1

High-Risk Populations Requiring Increased Monitoring

Intensified monitoring is warranted for patients with: 1

• Unstable medical condition
• Obesity (morbidly obese patients are at greater risk for desaturation) 3
• Obstructive sleep apnea
• Concomitant administration of opioids, sedatives, hypnotics, or benzodiazepines by other routes 2, 4
• Extremes of age (elderly patients over 65 are at greater risk for both desaturation and bradypnea) 3
• Chronic pulmonary disease or significantly decreased respiratory reserve 2

Critical Thresholds and Interventions

Defining Respiratory Depression

• Respiratory rate below 10 breaths/minute is commonly used as a threshold 1, 5
• Some protocols use respiratory rate below 8 breaths/minute or below 12 breaths/minute 5
• Oxygen saturation below 90-95% combined with bradypnea indicates respiratory depression 6

Immediate Management

• Supplemental oxygen should be available and administered to patients with altered consciousness, respiratory depression, or hypoxemia 1
• Continue supplemental oxygen until the patient is alert with no respiratory depression or hypoxemia present 1
• Naloxone should be available for reversal of severe respiratory depression 1
• Appropriate resuscitation should be initiated in cases of severe respiratory depression 1

Common Pitfalls to Avoid

The combination of morphine with benzodiazepines or other CNS depressants profoundly increases the risk of respiratory depression, coma, and death 2, 4

• A case report documented persistent respiratory depression lasting 24 hours requiring intubation when 0.1 mg intrathecal morphine was combined with midazolam 4
• Observational studies demonstrate that concomitant use of opioids and benzodiazepines increases drug-related mortality compared to opioids alone 2

Routine use of supplemental oxygen may mask early detection of respiratory depression 1

• While oxygen should be available, routine prophylactic use may increase the duration of apneic episodes and hinder detection of atelectasis, transient apnea, and hypoventilation 1

Intermittent monitoring is insufficient 3, 5

• Continuous respiratory monitoring is optimal for safe PCA administration, as any respiratory depression event can progress to respiratory arrest if undetected 3
• Clinical monitoring was not performed in 31% of cases for consciousness and 35% for respiratory rate in one multicenter survey, demonstrating the need for standardized protocols 5