Replacement of Anesthesia Machines Improves Intraoperative Ventilation Parameters Associated With the Development of Acute Respiratory Distress Syndrome

James M Blum; Victor Davila; Michael J Stentz; Ronald Dechert; Elizabeth Jewell; Milo Engoren

BMC Anesthesiol. 2014;14(44)

Abstract and Introduction

Abstract

Background: The impact of anesthetic equipment on clinical practice parameters associated with development of acute respiratory distress syndrome (ARDS) has not been extensively studied. We hypothesized a change in anesthesia machines would be associated with parameters associated with lower rates of ARDS.

Methods: We performed a retrospective cohort study on a subset of data used to evaluate intraoperative ventilation. Patients included adults receiving a non-cardiac, non-thoracic, non-transplant, non-trauma, general anesthetic between 2/1/05, and 3/31/09 at the University of Michigan. Existing anesthesia machines (Narkomed IIb, Drager) were exchanged for new equipment (Aisys, General Electric). The initial subset compared the characteristics of patients anesthetized between 12/1/06 and 1/31/07 (pre) with those between 4/1/07 and 5/30/07 (post). An extended subset examined cases two years pre and post exchange. Using the standard predicted body weight (PBW), we calculated and compared the tidal volume (total Vt and mL/kg PBW) as well as positive end-expiratory pressure (PEEP), peak inspiratory pressure (PIP), Delta P (PIP-PEEP), and FiO2.

Results: A total of 1,414 patients were included in the 2-month pre group and 1,635 patients included in the post group. Comparison of ventilation characteristics found statistically significant differences in median (pre v post): PIP (26 ± 6 v 21 ± 6 cmH2O, p < .001), Delta P (24 ± 6 v 19 ± 6 cmH2O, p < .001), Vt (588 ± 139 v 562 ± 121 ml, p < 0.001; 9.3 ± 2.2 v 9.0 ± 1.9 ml/kg predicted body weight, p < .001), FiO2 (0.57 ± 0.17 v 0.52 ± 0.18, p < .001). Groups did not differ in age, ASA category, PBW, or BMI. The two year subgroup had similar parameters. Risk adjustment resulted in minimal differences in the analysis. New anesthesia machines were associated with a non-statistically significant reduction in postoperative ARDS.

Conclusions: In this study, a change in ventilator management was associated with an anesthesia machine exchange. The smaller Vt and lower PIP noted in the post group may imply a lower risk of volutrauma and barotrauma, which may be significant in at-risk populations. However, there was not a statistically significant reduction in the incidence of post-operative ARDS.

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Abstract and Introduction
Background
Methods
Results
Discussion
Conclusions
References

Table 1. Preoperative demographics and intraoperative data of patients 2 months before and after ventilator exchange
Preoperative variable	Before vent exchange (n = 1414)	After vent exchange (n = 1635)	p
Age (mean ± SD, yr)	51 ± 16	51 ± 16	0.713
Male (n,%)	628 (44%)	731 (44%)	0.898
Patient ASA 3,4 or 5 (n,%)	443 (31%)	536 (32%)	0.413
Emergent Case (n,%)	46 (3%)	54 (3%)	0.980
Predicted Body Weight (mean ± SD, kg)	64 ± 11	63 ± 10	0.316
Weight (mean ± SD, kg)	85 ± 24	85 ± 24	1
BMI (mean ± SD, kg/m ² )	29 ± 7	29 ± 8	0.517
Smoker
Former (n,%)	247 (18%)	304 (19%)	0.448
Current (n,%)	228 (16%)	267 (16%)	0.917
Lung Disease (n,%)	10 (0.7%)	8 (0.5%)	0.585
Asthma (n,%)	114 (8%)	134 (8%)	0.946
COPD (n,%)	73 (5%)	100 (6%)	0.291
Diabetes (n,%)	178 (13%)	218 (13%)	0.578
Hypertension (n,%)	506 (36%)	616 (38%)	0.297
Coronary Artery Disease (n,%)	93 (7%)	126 (8%)	0.257
Congestive Heart Failure (n,%)	40 (3%)	53 (3%)	0.579
Chronic Kidney Disease (n,%)	76 (5%)	110 (7%)	0.139
Hepatic Disease (n,%)	19 (1%)	33 (2%)	0.195
Alcohol Abuse (n,%)	45 (3%)	47 (3%)	0.697
Current Steroid Therapy (n,%)	46 (3%)	61 (4%)	0.538
Intraoperative variable	Before vent exchange (n = 15,481)	After vent exchange (n = 18,945)	p
Ventilatory Parameters (case medians)
PIP (mean ± SD, cmH ₂ O)	26 ± 6	21 ± 6	< 0.001
PEEP (mean ± SD, cmH ₂ O)	2 ± 1.4	1.6 ± 2.6	< 0.001
ΔP (mean ± SD, cmH ₂ O)	24 ± 6	19 ± 6	< 0.001
RR (mean ± SD, breath per minute)	11 ± 2.5	11 ± 3	< 0.001
Vt (mean ± SD, ml)	588 ± 139	562 ± 121	< 0.001
Vt cc/kg PBW (mean ± SD, ml)	9.3 ± 2.19	9.0 ± 1.88	< 0.001
FiO ₂ (mean ± SD,%)	57.2 ± 0.17	51.8 ± 18	< 0.001
cc/kg PBW ≤ 6 (n,%)	90 (6%)	104 (6%)	1
cc/kg PBW ≤ 8 (n,%)	316 (22%)	433 (27%)	0.009
Epochs of 10 minutes:
PIP > 30 cmH2O	3.5 ± 7.5	1.5 ± 5	< 0.001
Vt > 12 cc/kg PBW	1.8 ± 5	0.9 ± 4	< 0.001
Colloid use (n,%)	198 (14%)	184 (11%)	0.026
Crystalloid volume (median, 25 ^th ,75 ^th , ml)	2000 (1200,3000)	1900 (1000,2700)	< 0.001
Case Length (mean ± SD, minutes)	220 ± 124	208 ± 124	0.005
Transfusion (n,%)	79 (6%)	76 (5%)	0.248
PRBC (n,%)	77 (5%)	73 (5%)	0.244
FFP (n,%)	14 (1%)	17 (1%)	1
Platelets (n,%)	7(0.5%)	8 (0.5%)	0.813

ASA = American Society of Anesthesiology Classification, BMI = body mass index, COPD = chronic obstructive pulmonary disease, PIP = peak inspiratory pressure, PEEP = positive end expiratory pressure, RR = respiratory rate, Vt = tidal volume, PBW = predicted body weight, FiO2 = fraction inspired oxygen, PBW = predicted body weight, PRBC = packed red blood cells, FFP = fresh frozen plasma.

Table 2. Preoperative demographics and intraoperative data of patients 2 years before and after ventilator exchange
Preoperative variable	Before vent exchange (n = 15,481)	After vent exchange (n = 18,945)	p
Age (mean ± SD, yr)	50 ± 17	52 ± 16	< 0.001
Male (n,%)	6936 (45%)	8619 (46%)	0.776
Patient ASA 3,4 or 5 (n,%)	4207 (27%)	6259 (33%)	< 0.001
Emergent Case (n,%)	697 (4%)	830 (4%)	0.605
Predicted Body Weight (mean ± SD, kg)	64 ± 11	64 ± 11	0.939
Weight (mean ± SD, kg)	83 ± 22	84 ± 22	< 0.001
BMI (mean ± SD, kg/m ² )	28.6 ± 6.9	29.1 ± 7.3	< 0.001
Smoker
Former (n,%)	2717 (18%)	4009 (21%)	< 0.001
Current (n,%)	2556 (17%)	3024 (16%)	0.174
Lung Disease (n,%)	45 (0.3%)	59 (0.3%)	0.802
Asthma (n,%)	1153 (7%)	1633 (9%)	< 0.001
COPD (n,%)	744 (5%)	1046 (6%)	0.003
Diabetes (n,%)	1758 (11%)	2658 (14%)	< 0.001
Hypertension (n,%)	5055 (33%)	7409 (39%)	< 0.001
Coronary Artery Disease (n,%)	1143 (7%)	1633 (9%)	< 0.001
Congestive Heart Failure (n,%)	378 (2%)	676 (4%)	0.545
Chronic Kidney Disease (n,%)	717 (5%)	1157 (6%)	< 0.001
Hepatic Disease (n,%)	235 (2%)	452 (2%)	< 0.001
Alcohol Abuse (n,%)	535 (4%)	582 (3%)	0.049
Current Steroid Therapy (n,%)	341 (2%)	658 (4%)	< 0.001
Intraoperative variable	Before vent exchange (n = 15,481)	After vent exchange (n = 18,945)	p
Ventilatory Parameters (case medians)
PIP (mean ± SD, cmH ₂ O)	25.4 ± 5.9	20.2 ± 6.1	< 0.001
PEEP (mean ± SD, cmH ₂ O)	1.9 ± 1.2	2.7 ± 2.8	< 0.001
ΔP (mean ± SD, cmH ₂ O)	23.4 ± 5.7	17.5 ± 5.6	< 0.001
RR (mean ± SD, breath per minute)	11.0 ± 2.5	10.7 ± 2.5	< 0.001
Vt (mean ± SD, ml)	587 ± 146	543 ± 118	< 0.001
Vt cc/kg PBW (mean ± SD, ml)	9.35 ± 2.29	8.67 ± 1.95	< 0.001
FiO ₂ (mean ± SD,%)	55.3 ± 16	54.1 ± 19	< 0.001
cc/kg PBW ≤ 6 (n,%)	1221 (8%)	1643 (9%)	< 0.001
cc/kg PBW ≤ 8 (n,%)	3534 (23%)	6465 (34%)	< 0.001
Epochs of 10 minutes:
PIP > 30 cmH2O	3.1 ± 7.1	1.2 ± 4.2	< 0.001
Vt > 12 cc/kg PBW	1.92 ± 4.9	0.8 ± 3.4	< 0.001
Colloid use (n,%)	1585 (10%)	1828 (10%)	0.072
Crystalloid volume (median, 25 ^th ,75 ^th , ml)	2000 (1200,3000)	2200 (1600,3100)	< 0.001
Case Length (mean ± SD, minutes)	214 ± 125	206 ± 122	< 0.001
Transfusion (n,%)	793 (5%)	880 (5%)	0.043
PRBC (n,%)	727 (5%)	810 (4%)	0.064
FFP (n,%)	175 (1%)	159 (1%)	0.007
Platelets (n,%)	91 (0.6%)	104 (0.5%)	0.685

Table 3. Preoperative demographics and intraoperative data of patients 2 months before and after ventilator exchange after risk matching
Preoperative variable	Before vent exchange (n = 864)	After vent exchange (n = 864)	p
Age (mean ± SD, yr)	49 ± 16	48 ± 16	0.656
Male (n,%)	358 (41%)	362 (42%)	0.884
Patient ASA 3,4 or 5 (n,%)	198 (23%)	188 (22%)	0.603
Emergent Case (n,%)	24 (3%)	16 (2%)	0.263
Predicted Body Weight (mean ± SD, kg)	64 ± 10.5	63 ± 10.5	0.294
Weight (mean ± SD, kg)	84 ± 23.5	84 ± 22.8	0.658
BMI (mean ± SD, kg/m ² )	28.9 ± 7.4	29.0 ± 7.3	0.854
Smoker
Former (n,%)	141 (16%)	134 (16%)	0.693
Current (n,%)	138 (16%)	132 (15%)	0.74
Lung Disease (n,%)	3 (0.3%)	5 (0.6%)	0.726
Asthma (n,%)	71 (8%)	72 (8%)	1
COPD (n,%)	20 (2%)	19 (2%)	1
Diabetes (n,%)	86 (10%)	73 (8%)	0.381
Hypertension (n,%)	250 (29%)	230 (27%)	0.308
Coronary Artery Disease (n,%)	23 (3%)	18 (2%)	.527
Congestive Heart Failure (n,%)	12 (1%)	12 (1%)	1
Chronic Kidney Disease (n,%)	21 (2%)	20 (2%)	1
Hepatic Disease (n,%)	11 (1%)	11 (1%)	1
Alcohol Abuse (n,%)	27 (3%)	21 (2%)	0.464
Current Steroid Therapy (n,%)	24 (3%)	25 (3%)	1
Intraoperative variable	Before vent exchange (n = 864)	After vent exchange (n = 864)	p
Ventilatory Parameters (case medians)
PIP (mean ± SD, cmH ₂ O)	25.3 ± 5.7	20.3 ± 6.2	< 0.001
PEEP (mean ± SD, cmH ₂ O)	2.0 ± 1.3	1.5 ± 2.5	< 0.001
ΔP (mean ± SD, cmH ₂ O)	23.3 ± 5.4	18.8 ± 5.6	< 0.001
RR (mean ± SD, breath per minute)	11.0 ± 2.3	10.5 ± 2.2	< 0.001
Vt (mean ± SD, ml)	587 ± 146	559 ± 125	< 0.001
Vt cc/kg PBW (mean ± SD, ml)	9.33 ± 2.22	8.98 ± 1.94	< 0.001
FiO ₂ (mean ± SD,%)	55.5 ± 16	51.2 ± 18	< 0.001
cc/kg PBW ≤ 6 (n,%)	62 (7%)	63 (7%)	1
cc/kg PBW ≤ 8 (n,%)	188 (22%)	219 (34%)	0.089
Epochs of 10 minutes:
PIP > 30 cmH2O	2.9 ± 6.4	1.4 ± 4.5	< 0.001
Vt > 12 cc/kg PBW	1.7 ± 4.3	0.9 ± 3.6	< 0.001
Colloid use (n,%)	51 (5.9%)	47 (5.4%)	0.755
Crystalloid volume (median, 25 ^th ,75 ^th , ml)	1950 (1100, 2700)	1900 (1000,2500)	0.111
Case Length (mean ± SD, minutes)	198 ± 103	195 ± 104	0.531
Transfusion (n,%)	17 (2%)	15 (2%)	0.858
PRBC (n,%)	16 (2%)	15 (5%)	1
FFP (n,%)	2 (0.2%)	4 (0.5%)	0.683
Platelets (n,%)	2 (0.2%)	1 (0.1%)	1

Table 4. Preoperative demographics and intraoperative data of patients 2 years before and after ventilator exchange after risk matching
Preoperative variable	Before vent exchange (n = 13,250)	After vent exchange (n = 13,250)	p
Age (mean ± SD, yr)	51 ± 16	50 ± 16	< 0.001
Male (n,%)	5932 (45%)	5956 (45%)	0.776
Patient ASA 3,4 or 5 (n,%)	3788 (28.6%)	3604 (27.2%)	0.012
Emergent Case (n,%)	591 (4.5%)	588 (4.4%)	0.952
Predicted Body Weight (mean ± SD, kg)	63 ± 10.6	64 ± 10.6	0.247
Weight (mean ± SD, kg)	83 ± 22	83 ± 22	0.568
BMI (mean ± SD, kg/m ² )	29 ± 7	29 ± 7	0.906
Smoker
Former (n,%)	2410 (18.2%)	2637 (19.9%)	< 0.001
Current (n,%)	2182 (16.5%)	2195 (16.6%)	0.843
Lung Disease (n,%)	37 (0.3%)	33 (0.2%)	0.72
Asthma (n,%)	1054 (8%)	998 (7.5%)	0.206
COPD (n,%)	664 (5%)	643 (4.9%)	0.57
Diabetes (n,%)	1531 (12%)	1477 (11%)	0.305
Hypertension (n,%)	4670 (35%)	4366 (33%)	< 0.001
Coronary Artery Disease (n,%)	1028 (8%)	989 (7%)	0.379
Congestive Heart Failure (n,%)	307 (2%)	323 (2%)	0.545
Chronic Kidney Disease (n,%)	616 (5%)	605 (5%)	0.77
Hepatic Disease (n,%)	212 (2%)	277 (2%)	0.003
Alcohol Abuse (n,%)	467 (4%)	396 (3%)	0.015
Current Steroid Therapy (n,%)	304 (2%)	415 (3%)	< 0.001
Intraoperative Variable	Before vent exchange (n = 13,250)	After vent exchange (n = 13,250)	p
Ventilatory Parameters (case medians)
PIP (mean ± SD, cmH ₂ O)	25.5 ± 6	20 ± 6	< 0.001
PEEP (mean ± SD, cmH ₂ O)	1.9 ± 1.2	2.7 ± 2.8	0.257
ΔP (mean ± SD, cmH ₂ O)	23.6 ± 6	17.3 ± 6	< 0.001
RR (mean ± SD, breath per minute)	11 ± 2.5	11 ± 2.5	< 0.001
Vt (mean ± SD, ml)	590 ± 144	541 ± 120	< 0.001
Vt cc/kg PBW (mean ± SD, ml)	9.41 ± 2.26	8.62 ± 1.96	< 0.001
FiO ₂ (mean ± SD)	55 ± 16	54 ± 19	< 0.001
cc/kg PBW ≤ 6 (n,%)	953 (7%)	1223 (9%)	< 0.001
cc/kg PBW ≤ 8 (n,%)	2915 (22%)	4584 (35%)	< 0.001
Epochs of 10 minutes:
PIP > 30 cmH2O	3.2 ± 7.1	1.1 ± 4	< 0.001
Vt > 12 cc/kg PBW	2 ± 4.8	0.7 ± 3.1	< 0.001
Colloid use (n,%)	1202 (9%)	1157 (9%)	0.343
Crystalloid volume (median, 25 ^th ,75 ^th , ml)	2000 (1300,3000)	2000 (1500,3000)	< 0.001
Case Length (mean ± SD, minutes)	215 ± 122	197 ± 116	< 0.001
Transfusion (n,%)	560 (4%)	554 (4%)	0.878
PRBC (n,%)	509 (4%)	513 (4%)	0.924
FFP (n,%)	103 (0.8%)	91 (0.7%)	0.428
Platelets (n,%)	64 (<0.5%)	60 (<0.5%)	0.787