Effect of arterial puncture on ventilation.

Background: Clinicians frequently assume that during arterial puncture for measuring arterial blood gases patients hyperventilate from pain and anxiety. This assumption leads clinicians to falsely interpret a PaCO and pH near the upper limit of normal as a chronic respiratory acidosis corrected by an acute respiratory alkalosis.

Objective: Determine if participants hyperventilate during arterial puncture from pain and anxiety.

Methods: We recruited participants from a pulmonary function laboratory referred for arterial blood gas measurement. We excluded those with heart failure and included those with any respiratory condition (COPD, asthma, sleep apnea). We measured end tidal PCO (PCO), respiratory rate, and heart rate 15 min before topical anesthesia, during anesthesia, during arterial puncture, and 15 min later. We assessed generalized anxiety before and measured pain during and after arterial puncture.

Results: 24 participants were recruited (age: 54 ± 12 years; men: 54%). PaCO was 41 ± 5 mmHg. One had acute respiratory alkalosis. Respiratory rate increased from (19 ± 6 breaths per minute (bpm)) before to a maximum (21 ± 6 bpm) during arterial puncture (p = 0.001). Heart rate was stable throughout. The lowest PCO during the procedure (35 ± 5) was similar to PCO before the procedure (p = 0.1). The change in PCO and respiratory rate did not correlate with pain, anxiety, or lung function.

Conclusion: Respiratory rate increased slightly during arterial puncture without any change in PCO. Hence, acid-base status must be interpreted without the assumption of procedure induced hyperventilation.