Situation: A 68-year-old man with chronic obstructive pulmonary disease (COPD) and a 45 pack-year smoking history is admitted to the medical ward with an exacerbation: 3 days of increased breathlessness and more purulent sputum. His records show chronic carbon dioxide retention. On room air, his oxygen saturation by pulse oximetry (SpO2) is 84%. The physician orders controlled oxygen titrated to an SpO2 of 88% to 92%. Thirty minutes after a Venturi mask set at 24% is applied, his SpO2 is 85%. He is alert and oriented, and his respiratory rate is 26/min. What should the nurse do?

His SpO2 of 85% is below the prescribed 88% to 92% target, and he is alert, so oxygen must be increased, not withheld. The controlled step is to raise the Venturi setting to the next level and recheck within minutes, titrating toward the target. High-concentration devices would overshoot the target and risk worsening hypercapnia.

Clinical situation and immediate priority

This patient is in an acute COPD exacerbation with chronic carbon dioxide retention. The physician prescribed a controlled oxygen target of 88% to 92%, but after 30 minutes on a Venturi mask at 24%, the SpO2 remains 85%. The patient is alert and oriented with a respiratory rate of 26/min. The priority is to correct the persistent hypoxemia while avoiding excessive oxygen delivery that could worsen hypercapnia.

Because the SpO2 is below the prescribed target and the patient is alert, oxygen delivery must be increased in a controlled, stepwise manner rather than withheld or escalated abruptly. The correct action is to move to the next Venturi setting, 28%, and recheck the saturation within minutes.

Why controlled titration matters in COPD with CO2 retention

Patients with chronic CO2 retention have a blunted central respiratory drive that depends less on hypercapnia and more on hypoxemia to stimulate breathing. When high-concentration oxygen is delivered, the hypoxic drive can be suppressed, leading to progressive hypoventilation, further CO2 retention, and potentially CO2 narcosis. This is the central danger behind options 2 and 3.

Titrated oxygen therapy to maintain SpO2 between 88% and 92% is the standard recommended by professional guidelines for acute COPD exacerbations ^[1][3][4]. A pre-hospital randomized controlled trial showed that high-concentration oxygen therapy was associated with a 2.4-fold increased risk of mortality compared with titrated oxygen to the 88–92% target range ^[1]. This finding underscores that more oxygen is not safer in this population.

Stepwise escalation with a Venturi mask

A Venturi mask delivers a fixed, precise fraction of inspired oxygen (FiO2) regardless of the patient’s respiratory pattern, which makes it the preferred device for controlled oxygen therapy in COPD exacerbations ^[3]. The settings typically progress from 24% to 28%, then 31%, 35%, and 40%. Each step should be followed by reassessment of SpO2 and clinical status within a short interval.

In this case, the patient remains hypoxemic on 24%, so increasing to 28% is the logical next step. The goal is to reach the target range without overshooting. Key point! A partial rebreather or nonrebreather mask delivers high and variable FiO2, which can rapidly push SpO2 well above 92% and suppress respiratory drive in a CO2 retainer.

Why the other options are incorrect

Option	Device and flow	Problem
2. Partial rebreather mask at 8 L/min	High-concentration, variable FiO2	Risk of overshooting the target and worsening hypercapnia; not a controlled device
3. Nonrebreather mask at 15 L/min	Very high FiO2, near 100%	Greatest risk of suppressing hypoxic drive and causing CO2 narcosis; contraindicated for controlled titration
4. Keep 24% and recheck in 1 hour	No change in oxygen delivery	Leaves the patient hypoxemic below target for an unnecessarily long time; SpO2 of 85% requires prompt intervention

Monitoring and reassessment

After increasing the Venturi mask to 28%, the nurse should recheck SpO2 within a few minutes, not wait an hour. The respiratory rate, level of consciousness, and work of breathing must be monitored alongside pulse oximetry. Watch out! Pulse oximetry is a surrogate and has limitations in patients with poor perfusion, abnormal hemoglobins, or skin pigmentation; arterial blood gas analysis remains the standard for assessing gas exchange in COPD exacerbations ^[3]. If the SpO2 does not improve on 28%, further stepwise increases or an arterial blood gas should be considered, but abrupt high-flow oxygen is never the first escalation.

The patient’s alert mental status is a reassuring sign. Drowsiness, confusion, or a falling respiratory rate after oxygen escalation would suggest CO2 retention and require immediate reevaluation of the oxygen strategy ^[4].