A ventilation strategy during general anaesthesia to reduce postoperative atelectasis

Figures & data

Figure 1. Summary of study design with the ventilatory strategy during anaesthesia from start of preoxygenation to emergence, including the oxygen level during transport and completion of CT. n = 10 at all time points (minutes) both in the control and intervention groups.

Table I. Demographic and physiologic data (median and range) for study groups.

	Control group: FIO2 1.0, ZEEP	Intervention group: FIO2 1.0; 6 cmH2O CPAP/PEEP	Intervention group: FIO2 0.8; 6 cmH2O CPAP/PEEP
Patients (n)	10	10	10
Male/ female	5/ 5	6/ 4	4/ 6
Age (years)	61; 31–65	60; 39–62	58; 42–72
Height (cm)	171; 164–186	175; 159–187	170; 165–180
Weight (kg)	70; 54–96	86; 60–98	69; 45–85
IBW (kg)	63; 56–76	67; 53–77	61; 50–72
BMI (kg/m^2)	25.4; 19.8–30.3	26.4; 23.1–29.6	23.4; 19–29.4
ASA I, II, III (n)	n = 5, 3, 2	n = 5, 5, 0	n = 3, 5, 1
Haemoglobin (g/L)	136; 124–155	145; 118–162	133; 117–160
Midazolam (n)	n = 6/10	n = 5/10	n = 5/10
Smoking habit	9/ 1/ 0	8/ 2/ 0	3/ 5/ 2
Smoking, pack years	10	25, 18; Σ43	40, 30, 43, 35, 18, 3, 20; Σ189

Definition of smoking habits: Never smoked/ stopped smoking/ smoking. With the exception of smoking habits, demographic and physiologic data did not differ significantly between groups, p > 0.05.

ASA = physical status according to the American Society of Anesthesiologists; BMI = body mass index, calculated as weight/height in metres squared; CPAP = continuous positive airway pressure; F_IO₂ = fraction of inspired oxygen; IBW = ideal body weight (7); PEEP = positive end-expiratory pressure; ZEEP = zero end-expiratory pressure.

Table II. Time data for special events during anaesthesia (median and range) in study groups.

	Control group: FIO2 1.0, ZEEP	Intervention group: FIO2 1.0; 6 cmH2O CPAP/PEEP	Intervention group: FIO2 0.8; 6 cmH2O CPAP/PEEP
From starting preoxygenation to start of intubation (seconds)	394; 378–467	401; 375–560	419; 377–588
From starting intubation to restart of ventilation (seconds)	52; 35–68	49; 35–120	44; 35–127
From starting postoxygenation to extubation (seconds)	900; 260–1350	565; 138–1291	455; 190–1249
Duration of mask ventilation after extubation (seconds)	240; 84–280	230; 83–780	120; 59–540
From end of mask ventilation to completion of CT scan (minutes)	25; 18–57	21; 13–25	20; 16–35
Duration of anaesthesia (minutes)	136; 43–248	141; 84–183	107; 42–178

Time data for any of the events did not differ significantly between groups, p > 0.05.

CPAP = continuous positive airway pressure; CT scan = computed tomography scanning; F_IO₂ = fraction of inspired oxygen; PEEP = positive end-expiratory pressure; ZEEP = zero end-expiratory pressure.

Table III. Ventilatory data with controlled ventilation during maintenance of anaesthesia (median and range) in study groups.

	Control group: FIO2 1.0, ZEEP	Intervention group: FIO2 1.0; 6 cmH2O CPAP/PEEP	Intervention group: FIO2 0.8; 6 cmH2O CPAP/PEEP
ETCO2 (%)	4.8; 4.5–5.3	5.1; 4.6–5.4	4.9; 4.6–5.3
Tidal volume (TV) (mL)	435; 350–550	465; 350–540	450; 370–500
TV/IBW (mL/kg)	6.5	6	7
Respiratory rate (breaths/minute)	9; 8–11	8; 8–10	9; 8–10

Ventilatory data did not differ significantly between groups, p > 0.05.

CPAP = continuous positive airway pressure; _ETCO₂ = end-tidal concentration of carbon dioxide; F_IO₂ = fraction of inspired oxygen; IBW = ideal body weight (7); PEEP = positive end-expiratory pressure; ZEEP = zero end-expiratory pressure.

Figure 2. Area of postoperative atelectasis 1 cm above the dome of the right diaphragm in the control and intervention group given F_IO₂ 1.0, unadjusted (raw data) and adjusted for age and BMI. Boxes represent the first to the third quartile. The dark line is the median. Extended bars represent the range. *p = 0.016 (Mann–Whitney U test).

Table IV. Peripheral oxygen saturation (SpO₂) (median and range) in study groups measured with F_IO₂ 0.21.

	Control group: FIO2 1.0, ZEEP	Intervention group: FIO2 1.0; 6 cmH2O CPAP/PEEP	Intervention group: FIO2 0.8; 6 cmH2O CPAP/PEEP
SpO2 preoperatively	99%	98%	99%
SpO2 test 1	96%^a	96%^a	95%^a
SpO2 test 2	96%^a	95%^a	95%^a
SpO2 postoperatively	9/10 ≥ 94%	9/10 ≥ 94%	9/10 ≥ 94%
SpO2 at CT	All ≥ 94%	All ≥ 94%	All ≥ 94%

^ap < 0.025, Wilcoxon signed rank test (limit due to Bonferroni correction), comparing the median differences for patients in the three groups respectively, between awake before anaesthesia and controlled ventilation during anaesthesia, SpO₂ did not differ significantly between groups, p > 0.05.

CPAP = continuous positive airway pressure; CT = computed tomography scanning; F_IO₂ = fraction of inspired oxygen; PEEP = positive end-expiratory pressure; ZEEP = zero end-expiratory pressure.

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