General anesthesia can induce atelectasis in the dependent regions of the lung due to various factors, including the effect of positive pressure ventilation. Functional residual capacity (FRC) and respiratory system compliance (Crs) decrease1 as the decreased tone of the diaphragm shifts abdominal viscera toward the thorax. These changes may be more pronounced in pediatric patients as the ribcage offers less resistance to lung collapse.2
Laparoscopic procedures are increasingly common in pediatrics. Pneumoperitoneum (PP) causes an upward shift of the diaphragm, decreasing chest wall compliance (Ccw) and lung volumes.3
Electrical impedance tomography (EIT) is a noninvasive technique capable of detecting real-time regional changes in lung ventilation distribution.4
The aim of this study was to describe the variations in regional ventilation distribution and Crs in pediatric patients undergoing laparoscopy at different PEEP levels across ages.
We hypothesized that PP and positive end-expiratory pressure (PEEP) will significantly alter ventilation distribution and Crs in pediatric patients.
METHODS
Prospective, observational study (IRB##2023/ST/099, Comitato Etico Milano Area 1), including patients aged 0–18 years undergoing laparoscopy after written informed consent from a legal guardian and assent for patients ≥5 years. Patients were categorized according to age into 4 categories: Infant/Toddler (0–2 years); Early Childhood (3–6 years); School Age (7–12 years); and Adolescence (13–18 years).
Anesthesia was induced with propofol, fentanyl, and rocuronium and maintained with a continuous infusion of propofol and remifentanil.
Six timepoints (T0–T6) were defined for data collection (Figure A):
- T0: Before induction, spontaneous breathing (SB).
- T1: Mechanical ventilation with PEEP 5 cmH2O.
- T2: PEEP 10 cmH2O.
- T3: Five minutes after PP establishment with PEEP 5 cmH2O.
- T4: Ten minutes after PP establishment with PEEP 10 cmH2O.
- T5: After abdominal deflation.
- T6: SB after extubation.
Volume control mode was used: VT = 8–10 mL·kg− 1, fraction of inspired oxygen (FiO2) adjusted between 0.3 and 0.4 as per institutional protocol to target Spo2 greater than 95%, Inspiratory: Expiratory ratio =1:2, and respiratory rate (RR) adjusted to achieve an end-tidal carbon dioxide (ETCO2) 40 ± 5 mm Hg.
After an inspiratory hold and expiratory hold maneuver, we measured peak inspiratory pressure, plateau pressure, positive end-expiratory pressure (PEEP), delivered VT (mL·kg–1), inspiratory time, RR. Driving pressure (ΔP = PPLAT – tPEEP) and Crs (VT/ΔP, mL·cm H2O–1·kg–1) were calculated.
EIT images were acquired using the EIT monitor (PulmoVista 500, Draeger Medical). The lung region of interest (ROI) was divided into 4 ROIs with equal height. Ventilation distribution of each ROI was expressed as percentage of total Tidal Volume Variation.
Statistical Analysis and Sample Size
Based on a previous study5 conducted in adults that demonstrated changes in Crs during laparoscopy with a sample of 12 patients, we decided to enroll at least 12 patients for each age group. Variations in Crs and ROIs were studied with multilevel mixed linear regression models including a random effect on the subjects and compared across age categories.
Data were analyzed with Stata 18.0 B.E. Two-tailed tests were used. P-values <.05 were considered significant.
RESULTS
Seventy-nine patients were were enrolled (14 Infants/Toddlers; 13 in Early Childhood; 26 in School Age; 26 in Adolescence; Table 1).
| Infant/toddler | Early childhood | School age | Adolescence | Total | |
|---|---|---|---|---|---|
| n (%) | 14 (18%) | 13 (17%) | 26 (33%) | 26 (36%) | 79 (100.0%) |
| Age, years | 1.0 (0.5; 1.3) | 6.0 (5.0; 6.0) | 9.0 (8.0; 11.0) | 14.0 (14.0; 15.5) | 9.0 (5.0; 14.0) |
| Height, m | 0.75 (0.6; 0.82) | 1.150 (1.1; 1.2) | 1.4 (1.3; 1.5) | 1.7 (1.6; 1.8) | 1.4 (1.1; 1.65) |
| Weight, kg | 9.1 (6.0; 10.0) | 20.0 (18.0; 23.0) | 31.0 (26.0; 39.0) | 56.0 (49.0; 70.0) | 30.0 (20.0; 51.0) |
| BMI, kg/m-2 | 17.0 (15.1; 18.3) | 15.1 (14.5; 17.4) | 16.1 (14.7; 19.9) | 18.4 (17.7; 20.7) | 17.5 (14.9; 19.8) |
| Tv, ml | 94 (60; 100) | 180(144; 230) | 300 (250; 360) | 500 (470; 560) | 290 (170; 490) |
| Tv/kg (IBW) | 9.4 (8.3; 10.0) | 9.2 (7.2; 10.0) | 9.0 (7.7; 11.1) | 9.0 (7.6; 9.1) | 9.0 (7.7; 10.0) |
| Crs, ml•cmH20-1• kg-1 | 1.00 (0.855 1.072) | 1.03 (0.93; 1.21) | 1.15 (1.01; 1.31) | 1.13 (1.04; 1.21) | 1.11 (1.00; 1.24) |
| PIP, cmH2O | 19.5 (19.0; 21.0) | 22.0 (18.0; 25.0) | 21.0 (19.0; 22.0) | 18.5 (17.0; 19.5) | 19.0 (18.0; 22.0) |
| PPLAT, cmH2O | 11.3 (11.0; 15.0) | 11.0(8.0; 12.1) | 10.3 (9.0; 12.0) | 9.0(8.0; 9.0) | 10.0 (8.7; 12.0) |
| ΔP, cmH2O | 6.1 (6.0; 9.0) | 6.0 (3.0; 7.1) | 4.8 (4.0; 7.0) | 4.0 (3.0; 4.0) | 4.8(3.6; 7.0) |
During transition from SB to PPV, ROI 1 increased significantly (Coefficient: 4.66; 95% confidence interval [CI], 3.74–5.58; P < .001) while ROI3 decreased (Coefficient: −2.84; 95% CI, −4.23 to −1.45; P < .001) and so did ROI 4 (Coefficient: −0.81; 95% CI, −1.5 to −0.12; P = .021; Table 2).
| T0 SB pre induction |
T1 PPV PEEP 5 |
T2 PPV PEEP 10 |
T3 PP PEEP 5 |
T4 PP PEEP 10 |
T5 Post PP |
T6 SB post |
|
|---|---|---|---|---|---|---|---|
| ROI 1, % | 12.67 (±3.40) | 18.21(±3.78) | 16.265(±3.49) | 20.03 (±5.78) | 19.67 (±5.90) | 17.74 (±4.09) | 12.27 (±3.60) |
| ROI 2, % | 37.70 (±6.83) | 41.24 (±5.55) | 42.16 (±4.34) | 31.75(±8.59) | 31.46 (±7.50) | 40.66 (±5.27) | 36.62 (±5.79) |
| ROI 3, % | 39.65(±6.64) | 33.53 (±5.64) | 34.43 (±4.84) | 38.00 (±8.71) | 38.82 (±8.79) | 34.56 (±5.58) | 41.50 (±5.15) |
| ROI 4, % | 9.87 (±3.70) | 7.12 (±2.80) | 7.164 (±2.15) | 10.22 (±4.65) | 10.20 (±4.46) | 6.92 (±1.97) | 9.65 (±4.20) |
Overall, PEEP reduced ROI 1 ventilation with no significant effect in the other ROIs (Table 3). Age-specific changes in ROI ventilation are presented in Table 3. PP increased ROI4 ventilation in all ages, but at the smallest in infants/toddlers.
| C | ROI1 | ROI2 | ROI3 | ROI4 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Coeff. | P>z | 95% CI | Coeff. | P>z | 95% CI | Coeff. | P>z | 95% CI | Coeff. | P>z | 95% CI | ||
| All ages | PEEP | -1.205 | .004 | -2,025; -0,385 | 0.160 | .757 | -0,854; 1,174 | 0,926 | .155 | -0,350; 2,202 | 0,077 | .798 | -0,515; 0,669 |
| PP | 2.247 | .000 | 1,367; 3,127 | -10,481 | .000 | -11,567; -9,395 | 4,935 | .000 | 3,567; 6,303 | 3,248 | .000 | 2,614; 3,883 | |
| Infants | PEEP | -0.57 | .545 | -2.42; 1.28 | -0.2 | .854 | -2.28; 1.88 | 0.68 | .61 | -1.93; 3.29 | 0.00 | .995 | -0.87; 0.87 |
| PP | 3.24 | <.001 | 1.46; 5.03 | -4.64 | <.001 | -6.64;-2.63 | -0.04 | .976 | -2.56; 2.48 | 1.47 | .001 | 0.63; 2.31 | |
| _cons | 16 | <.001 | 13; 19 | 43.41 | <.001 | 39.67; 47.14 | 33.88 | <.001 | 29.86; 37.89 | 6.55 | <.001 | 5.01; 8.08 | |
| Early Child hood |
PEEP | -1.05 | .254 | -2.86; 0.76 | 0.32 | .829 | -2.55; 3.18 | 1.65 | .338 | -1.73; 5.04 | -0.80 | .141 | -1.87; 0.26 |
| PP | -0.38 | .687 | -2.21; 1.45 | -10.06 | <.001 | -12.97; -7.16 | 7.83 | <.001 | 4.41; 11.25 | 2.46 | <.001 | 1.38; 3.54 | |
| _cons | 20.94 | <.001 | 17.94; 23.94 | 40.88 | <.001 | 35.88; 45.87 | 30.01 | <.001 | 24.6; 35.41 | 8.12 | <.001 | 6.36; 9.89 | |
| School Age |
PEEP | -1.1 | .102 | -2.41; 0.22 | 0.37 | .601 | -1.02; 1.76 | 1.03 | .26 | -0.76; 2.81 | -0.16 | .752 | -1.18; 0.85 |
| PP | 2.09 | .002 | 0.76; 3.42 | -10.65 | <.001 | -12.05; -9.25 | 4.64 | <.001 | 2.85; 6.44 | 4.05 | <.001 | 3.03; 5.06 | |
| _cons | 19.17 | <.001 | 16.88; 21.47 | 40.95 | <.001 | 38.37; 43.53 | 32.33 | <.001 | 29.31; 35.35 | 7.3 | <.001 | 5.45; 9.14 | |
| Adolescence | PEEP | -2.34 | .008 | -4.07; -0.6 | 0.3 | .794 | -1.93; 2.52 | 1.11 | .435 | -1.68; 3.9 | 0.81 | .246 | -0.56; 2.17 |
| PP | 3.28 | <.001 | 1.52; 5.04 | -12.26 | <.001 | -14.52; -10 | 5.37 | <.001 | 2.54; 8.19 | 3.54 | <.001 | 2.16; 4.92 | |
| _cons | 20.76 | <.001 | 17.99; 23.53 | 41.8 | <.001 | 38.17; 45.43 | 31.63 | <.001 | 27.28; 35.99 | 6.15 | <.001 | 4.02; 8.27 | |
Crs was associated with body mass index (BMI) before PP institution (Coeff: 0.01; 95% CI, 0.001–0.021; P = .026) but not during PP (Coeff: 0.004; 95% CI, −0.009 to 0.018; P = .561), and it was negatively associated with all ROIs except ROI2 (Figure).
DISCUSSION
Our findings can be summarized as follows: (1) there is a significant variation in regional volume distribution from SB to PPV; (2) there is a relationship of Crs with BMI in the absence of PP, but no relationship during PP; (3) PEEP and PP have significant relationships with each ROI’s ventilation; and (4) regional ventilation distribution is also related to Crs and age.
In the transition from SB to PPV we described an increase in the anterior lung regions’ ventilation (ROI1), and a decrease in the middle and posterior ones (ROI3-4). We attributed this to the cephalad displacement of the diaphragm due to lost muscular tone and the creation of atelectatic zones in the dependent regions, typical of anesthesia and PPV,6,7 coupled with the low pediatric Ccw in the anterior area.8
During spontaneous breathing, the dorsal part of the diaphragm is more “stretched” by the upward pressure of the abdominal contents but this advantage is lost with the switch to positive pressure ventilation, creating posterior atelectasis.8
With PEEP, alveoli are kept open, redistributing ventilation to more dependent lung regions,3 reducing anterior ventilation and increasing Crs, also during PP.
Crs was positively associated with BMI before but not during PP. During PP, we found increased ROI 1 and 4 ventilation and attributed these changes to the dome-shaped displacement of the diaphragm9, which, under increased IAP, affected the central areas of the lung more than the peripheral ones. In fact, infants and toddlers, who have a flatter diaphragm shape10 compared to older children, showed a relatively smaller increase in the posterior areas and a more pronounced increase in the anterior ROI, due to low Ccw in this lung region.2 This translates clinically to higher risk for postoperative atelectasis in the youngest.
Although limited by the lack of a perfusion study, we could show different behaviors of regional lung ventilation across different pediatric ages during laparoscopy. Future research should explore tailored ventilatory approaches in this population and relative perfusion changes.
REFERENCES