Oxygenation and ventilation characteristics of thoracic surgical patients the night before surgery

Studies of the respiratory effects of perioperative analgesic and anesthetic agents are complicated by evidence that healthy subjects and those with COPD may have abnormalities of oxygenation and ventilation during sleep. This report thus characterizes respiration during sleep preoperatively in a population frequently examined in postoperative analgesia studies. Sixty-two thoracic surgical patients were monitored by continuous respiratory inductive plethysmography, 49 of whom also had continuous pulse oximetry and bi-hourly blood gas measurements. The mean respiratory rate (RR) at each hour during sleep was similar to the awake RR (P > 0.06). The minimum RR during sleep was 7.6 +/- 2.1 (2.6-9.8; median 7.9). At least 1 apnea (tidal volume < 100 mL for > or = 15 sec) occurred in 77% of subjects, and 32% had > or = 1 slow respiratory rate (SRR; 5-min RR < 10 beats/min) episode. The mean SpO2 for hours 2 to 4 was significantly less than while awake (P < 0.0015), but the differences were < or = 1.1%. The minimum SpO2 was 88 +/- 7% (62-97; 89) and 40% of subjects had > or = 1 desaturation (DESAT90; SpO2 < 90% for > or = 15 sec) episode. The pH at hours 2 and 4 was significantly (P < 0.0009) less than while awake, but the differences were only 0.02. Other bi-hourly pH, PaCO2, and PaO2 values were similar to the awake values (P > 0.02). Interpatient variability was high, especially for episodic abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)