Respiratory acidosis during bronchoscopy-guided percutaneous dilatational tracheostomy: impact of ventilator settings and endotracheal tube size

Abstract

Background: The current study investigates the effect of bronchoscopy-guided percutaneous dilatational tracheostomy (PDT) on the evolution of respiratory acidosis depending on endotracheal tube (ET) sizes. In addition, the impact of increasing tidal volumes during the intervention was investigated.

Methods: Two groups of ICU-patients undergoing bronchoscopy-guided PDT with varying tidal volumes and tube sizes were consecutively investigated: 6 ml/kg (N = 29, mean age 57.4 ± 14.5 years) and 12 ml/kg predicted body weight (N = 34, mean age 59.5 ± 12.8 years).

Results: The mean intervention time during all procedures was 10 ± 3 min. The combination of low tidal volumes and ETs of 7.5 mm internal diameter resulted in the most profound increase in PaCO₂ (32.2 ± 11.6 mmHg) and decrease in pH-value (- 0.18 ± 0.05). In contrast, the combination of high tidal volumes and ETs of 8.5 mm internal diameter resulted in the least profound increase in PaCO₂ (8.8 ± 9.0 mmHg) and decrease of pH (- 0.05 ± 0.04). The intervention-related increase in PaCO₂ was significantly lower when using higher tidal volumes for larger ET: internal diameter 7.5, 8.0 and 8.5: P > 0.05, =0.006 and = 0.002, respectively. Transcutaneous PCO₂ monitoring revealed steadily worsening hypercapnia during the intervention with a high correlation of 0.87 and a low bias of 0.7 ± 9.4 mmHg according to the Bland-Altman analysis when compared to PaCO₂ measurements.

Conclusions: Profound respiratory acidosis following bronchoscopy-guided PDT evolves in a rapid and dynamic process. Increasing the tidal volume from 6 to 12 ml/kg PBW was capable of attenuating the evolution of respiratory acidosis, but this effect was only evident when using larger ETs.

Trial registration: DRKS00011004 . Registered 20th September 2016.

Keywords: Dilatational tracheostomy; Endotracheal tube; Hypercapnia; Respiratory acidosis; Transcutaneous PCO2.

Fig. 1

Typical example of recording transcutaneous PCO₂ during dilatational tracheostomy (endotracheal tube size 7.5 mm ID). Arterial blood gas analysis was measured at the start, the end and the end+ 30 min, respectively

Fig. 2

PaCO₂ during dilatational tracheostomy. Tidal volume was set to 6 ml/kg PBW for the entire period. *p ≤ 0.05, **p ≤ 0.01 and ***p ≤ 0.001. (ET - endotracheal tube, I.D. - internal diameter). Data were analyzed according to the diameter of the tube (a: 7.5mm, b: 8.0mm and c: 8.5mm)

Fig. 3

Increase of PaCO₂ during dilatational tracheostomy. Arterial blood gas analysis was performed at the beginning and end of the procedure. Patients were ventilated with tidal volumes (V_t) of 6 or 12 ml/kg PBW during intervention. *p ≤ 0.05 and **p ≤ 0.01. (ET - endotracheal tube, I.D. - internal diameter). Data were analyzed according to the diameter of the tube (a: 7.5mm, b: 8.0mm and c: 8.5mm)

Fig. 4

Correlation of transcutaneous PCO₂ (PtcCO₂) and arterial PCO₂ (PaCO₂) (a). Corresponding Bland-Altman analysis are given in (b). (r - spearman’s correlation; LoA - Limits of Agreement). Please note that the bias line for the Bland-Altman analysis is not visible due to the observation that the bias was close to zero

Fig. 5

Minute ventilation during dilatational tracheostomy. Tidal volume was set to 6 ml/kg PBW (a, c and e) or 12 ml/kg PBW (b, d and f) for the entire period. *p ≤ 0.05, **p ≤ 0.01 and ***p ≤ 0.001. (ET - endotracheal tube, I.D. - internal diameter)