Breathing pattern and blood gases during remifentanil infusion in patients with respiratory distress
Introduction
The rapid shallow breathing is a common finding in patients with fatigue of the respiratory muscles due to increased ventilatory workload. This breathing pattern begins a vicious circle often ending to the ventilatory failure. Opioids reduces the respiratory rate (RR) and, at higher doses, the tidal volume (VT) (1). Aim of this study was to evaluate the impact on the breathing pattern and arterial blood gases of low-dosage remifentanil infusion in patients with rapid shallow breathing.
Material and methods
We studied ten consecutive patients showing a RR higher than 30/min and a RR/VT higher than 100. Study population was 63±17 years old, the body weight was 61±13 kg, the PaO2/FIO2 was 209±68; six patients had acute lung injury due to pneumonia, two had post-operative respiratory failure and two cardiogenic pulmonary oedema. One patient was intubated, one tracheotomised and eight underwent to non-invasive mechanical ventilation (NIMV). Four patients had pressure support ventilation and six continuous positive airway pressure. Remifentanil infusion was delivered at the rate of 0.1 mcg*kg-1*min-1 for 30 minutes in all patients. Arterial blood gas analysis, RR, VT, heart rate (HR), arterial pressure (AP), sedation (Ramsey score) were evaluated before the remifentanil infusion (T0), after the 30’ of infusion (T1) and 30’ after the stop of the drug administration (T2). During the study the ventilator setting remained unchanged. Data are presented as mean ± sd. Differences between groups were analysed by the Friedman test (Ramsey score) and with the ANOVA for repeated measurements. Differences between groups were isolated by the Student-Newman-Keuls test.
Results
|
|
Ramsey |
HR beat/min |
Mean AP mmHg |
RR breath/min |
VT litres |
pH |
PaCO2 mmHg |
PaO2 mmHg |
|
T0 |
1.9±0.6 |
102±14 |
99±10 |
37±4 |
0.34±0.08 |
7.46±0.04 |
39±3 |
85±26 |
|
T1 |
2.4±0.5 |
99±16 |
90±11 |
24±3 |
0.31±0.09 |
7.43±0.03 |
42±4 |
92±29 |
|
T2 |
2.3±0.5 |
103±16 |
99+±9 |
36±5 |
0.35±0.07 |
7.45±0.03 |
39±3 |
82±24 |
|
p |
> 0.05 |
0.132 |
0.059 |
0.000* |
0.538 |
0.000* |
0.002* |
0.009* |
*p<0.05 between T1 and T0 and between T1 andT2
Discussion
The remifentanil infusion rate of 0.1 mcg*kg-1*min-1 in patients with rapid shallow breathing reduces significantly RR without affect VT. VT measurement have to be cautionary evaluated in the eight patients undergoing NIMV. The increase in PaCO2 and the drop in pH were clinically negligible and no patients showed respiratory acidosis. The oxygen cost of breathing during mechanical ventilation is 20 % of the total oxygen consumption, with occasionally much higher values (2): the reduced RR could reduce significantly the O2 consumption. The decreased CO2 production and the reduced dead space ventilation could explain the small increase in PaCO2 despite the wide decrease in minute ventilation. The measured variables returned at the baseline 30’ after the stop of the infusion, stressing the dependence of the results to the remifentanil infusion.
Conclusion
The low-rate infusion of remifentanil could be useful in the medical management of patients with respiratory distress due to its ability to favourably modify the breathing pattern. Moreover the fast kinetic can facilitate an accurate titration of the drug.
References
1. Bailey P, Egan T. Fentanyl and congeners. In: White PF. Textbook of intravenous anaesthesia. Baltimore, Williams and Wilkins 1997, 213-245
2. Fitting JW. Diagnosing the adequacy of neural stimulation. In: Marini JJ, Roussos C. (Eds) Ventilatory failure. Berlin Heidelberg, Springer Verlag 1991, 49-61