Effect of arterial puncture on ventilation

BackgroundClinicians 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 PaCO2 and pH near the upper limit of normal as a chronic respiratory acidosis corrected by an acute respiratory alkalosis.ObjectiveDetermine if participants hyperventilate during arterial puncture from pain and anxiety.MethodsWe 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 PCO2 (PETCO2), 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.Results24 participants were recruited (age: 54 ± 12 years; men: 54%). PaCO2 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 PETCO2 during the procedure (35 ± 5) was similar to PETCO2 before the procedure (p = 0.1). The change in PETCO2 and respiratory rate did not correlate with pain, anxiety, or lung function.ConclusionRespiratory rate increased slightly during arterial puncture without any change in PETCO2. Hence, acid-base status must be interpreted without the assumption of procedure induced hyperventilation.