Perioperative evaluation of respiratory impedance using the forced oscillation technique: a prospective observational study

Abstract

BackgroundIntravascular fluid shifts, mechanical ventilation and inhalational anesthetic drugs may contribute to intraoperative lung injury. This prospective observational study measured the changes in respiratory impedance resulting from inhalational anesthesia and mechanical ventilation in adults undergoing transurethral resection of bladder tumors. The components of respiratory impedance (resistance and reactance) were measured using the forced oscillation technique (FOT).MethodsRespiratory resistance at 5 Hz (R5) and 20 Hz (R20), respiratory reactance at 5 Hz (X5), resonant frequency (Fres) and area of low reactance (ALX) were measured before and immediately after surgery in 30 adults. In addition, preoperative vital capacity (VC), forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1.0) were evaluated using spirometry. All patients were intubated with an endotracheal tube and were mechanically ventilated, with anesthesia maintained with sevoflurane. Pre- and postoperative FOT measurements were compared using Wilcoxon paired rank tests, and the relationships between FOT measurements and preoperative spirometry findings were determined by Spearman’s rank correlation analysis.ResultsTwenty-six patients were included in the final analysis: postoperative FOT could not be performed in four because of postoperative restlessness or nausea. The mean duration of surgery was 47 min. All components of respiratory resistance deteriorated significantly over the course of surgery, with median increases in R5, R20, and R5–R20 of 1.67 cmH2O/L/s (p < 0.0001), 1.28 cmH2O/L/s (p < 0.0001) and 0.46 cmH2O/L/s (p = 0.0004), respectively. The components of respiratory reactance also deteriorated significantly, with X5 decreasing 1.7 cmH2O/L/s (p < 0.0001), Fres increasing 5.57 Hz (p < 0.0001) and ALX increasing 10.51 cmH2O/L/s (p < 0.0001). There were statistically significant and directly proportional relationships between pre- and postoperative X5 and %VC, %FEV1.0 and %FVC, with inverse relationships between pre- and postoperative Fres and ALX.ConclusionsAll components measured by FOT deteriorated significantly after a relatively short period of general anesthesia and mechanical ventilation. All components of resistance increased. Of the reactance components, X5 decreased and Fres and ALX increased. Pre- and postoperative respiratory reactance correlated with parameters measured by spirometry.Trial registration JMA-IIA00136.

Factors Causing Post-Anesthetic High Respiratory Resistance in Patients Undergoing Transurethral Resection of Bladder Tumors

“…Spirometry, an established measurement to evaluate respiratory function, is used to evaluate respiratory function in many studies; however, we suggest that patients’ postoperative condition affects the spirometry results in any kind of surgery because spirometry requires a patient’s maximum for inspiration and expiration. Although patients are forced to breathe through a mouthpiece while wearing a nose clip during the FOT, patients only breathe normally in the sitting position ( 24 ). The FOT is a more reliable method to evaluate the comparison between pre- and post-operative status.…”

Lung function and CT lung densitometry in 37- to 39-year-old individuals with alpha-1-antitrypsin deficiency

“…Respiratory system resistance at 5 Hz (R5Hz) (kPa/(L/s)) and 20 Hz (R20Hz) (kPa/(L/s)), the resistance in the small airways (R5Hz–R20Hz) (kPa/(L/s)), respiratory system reactance at 5 Hz (X5Hz) (kPa/(L/s)), resonant frequency (Fres) (Hz), and the area of low reactance (Alx) (kPa/L) were measured. 8 – 10 , 19 …”

“…IOS/FOT is reported to be a good complementary diagnostic tool for the management and monitoring of asthma and COPD. 8 – 11 Computed tomography (CT) with CT densitometry is considered to be more accurate to assess the progression of emphysema than PFTs. 12 , 13 …”

Eine Alternative zur COPD-Diagnostik mit Spirometrie bei Betagten?

“…So bietet sich die FOT, wie sie auch in der Anästhesie perioperativ teilweise verwendet wird, als Funktionsuntersuchung bei besonderen Bedingungen an [3]. Zwar muss berücksichtigt werden, dass die Studie überwiegend mit männlichen Chinesen gemacht wurde und daher die Aussagekraft ein wenig eingeschränkt ist, jedoch konnten die Autoren zeigen, dass die FOT bei geriatrischen Patienten eine Ergänzung/Alternative zur konventionellen Spirometrie ist.…”