The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts

Measurement of Spontaneous Breathing Parameters in Mechanically Ventilated Patients: Does Resting Period between Measurements Make Difference?

Mauo-Ying Bien MS RPT CRTT, Huei-Guan Shic RT, Shio-Ying Lo RT, Ing-Tiau Kuo MD DrPH, Jia-Horng Wang MD. Veterans General Hospital -- Taipei, Taiwan, R.O.C.

Introduction: Spontaneous breathing parameters such as Pimax, V[dot]E, RR, calculated Vt and RSI are the usual criteria for weaning from mechanical ventilation, but the sequence of these measurements differs. Some clinicians measure Pimax first and then V[dot]E and RR (Method A) to get the highest Pimax. Others measure V[dot]E and RR first (Method B) because this way is easier to perform and less stressful. In whatever sequence, there is conventionally no resting period between two measurements except in case that signs of distress occur. Our previous study found that Method A got higher V[dot]E and RR values and induced fewer adverse reactions than Method B but there was no significant difference in Pimax data*. We doubt whether this difference is due to the absence of resting period between two measurements. Methods: Using Method A and B, 91 sets of spontaneous breathing parameters were measured in 91 adult mechanically ventilated patients who were in stable condition. In randomized choice of sequence, Methods A and B were conducted at least 10 minutes apart to ensure that the patient condition returned to baseline (SaO2: ± 2%, PR: ± 10/min). In each method, between measurements of Pimax and VE/RR, the patient was re-connected to the ventilator until his/her condition returned to baseline and recorded the length of duration. Oxygen saturation, PR and breathing pattern were monitored before, during and after each measurement. Adverse reactions were defined as (1) PVC >= 5/min if patient with EKG monitor, (2) HR increase over 20/min from baseline, (3) HR decrease over 20/min from baseline, and (4) desaturation (SaO2 < = 85%). Paired-t or Wilcoxon signed-ranks test was used to compare the data from different methods. Multiple regression was applied to control the confounding effects. Chi-square test was used to compare the difference in incidence of adverse reactions. A p < 0.05 was considered significant. Results: The medium resting duration for the patient to return to baseline condition was 40 seconds in Method A (range: 0 - 240 sec) and 30 seconds in B (range: 0 - 240 sec). After controlling the confounding effects of age, history of neuromuscular and cardiac diseases, the patient's conscious level significantly influenced all 5 spontaneous breathing parameters, sex influenced V[dot]E and Vt, and with or without COPD influenced RSI. There was no significant difference in any parameter measured by Method A and B. The incidence of adverse reactions differed not much as well (16.48% in A vs 14.29% in B). Conclusions: The results of spontaneous breathing parameters and the incidence of adverse reactions made no difference in whatever sequence they were if adequate resting period was provided between measurements. This finding can persuade the clinicians to modify their techniques in clinical practice.

*Bien MY, Chu CC, Wang JH, Chen JR, Lin IN, Jou SB. Measurement of Spontaneous Breathing Parameters in Mechanically Ventilated Patients: A Comparison of Two Methods. Respir Care 1992;37:1352.

OF-97-167

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