Cecilia M. Acosta, Giovanni Volpicelli, Nadia Rudzik, Nicolás Venturin, Sebastián Gerez, Lila Ricci, Marcela Natal & Gerardo Tusman

The Ultrasound Journal volume 12

Abstract

Background

Pulmonary atelectasis in anesthetized children is easily reverted by lung recruitment maneuvers.

However, the high airways pressure reached during the maneuver could negatively affect hemodynamics.

The aim of this study is to assess the effect and feasibility of a postural lung recruitment maneuver (P-RM); i.e., a new maneuver that opens up the atelectatic lung areas based on changing the child’s body position under constant ventilation with moderated driving pressure (12 cmH₂O) and of positive end-expiratory pressure (PEEP, 10 cmH₂O).

Forty ASA I–II children, aged 6 months to 7 years, subjected to general anesthesia were studied. Patients were ventilated with volume control mode using standard settings with 5 cmH₂O of PEEP.

They were randomized into two groups:

(1) control group (C group, n = 20)—ventilation was turned to pressure control ventilation using a fixed driving pressure of 12 cmH₂O. PEEP was increased from 5 to 10 cmH₂O during 3 min maintaining the supine position.

(2) P-RM group (n = 20)—patients received the same increase in driving pressure and PEEP, but they were placed, respectively, in the left lateral position, in the right lateral position (90 s each), and back again into the supine position after 3 min.

Then, ventilation returned to baseline settings in volume control mode. Lung ultrasound-derived aeration score and respiratory compliance were assessed before (T1) and after (T2) 10 cmH₂O of PEEP was applied.

Results

At baseline ventilation (T1), both groups showed similar aeration score (P-RM group 9.9 ± 1.9 vs C group 10.4 ± 1.9; p = 0.463) and respiratory compliance (P-RM group 15 ± 6 vs C group 14 ± 6 mL/cmH₂O; p = 0.517).

At T2, the aeration score decreased in the P-RM group (1.5 ± 1.6 vs 9.9 ± 2.1; p < 0.001), but remained without changes in the C group (9.9 ± 2.1; p = 0.221). Compliance was higher in the P-RM group (18 ± 6 mL/cmH₂O) when compared with the C group (14 ± 5 mL/cmH₂O; p = 0.001).

Conclusions

Lung aeration and compliance improved only in the group in which a posture change strategy was applied.

Background

Anesthesia-induced atelectasis is a well-known condition in pediatric patients that is related to perioperative episodes of hypoxemia [1, 2].

The incidence of atelectasis is high and commonly appears in the most dependent lung zones where the trans-pulmonary pressure (P_L = airways pressure − pleural pressure) is the lowest [3, 4].

Mechanical ventilation using standard levels of 5 cmH₂O of positive end-expiratory pressure (PEEP) is generally insufficient to reopen those dependent atelectasis in supine pediatric patients [3, 5]. Contrarily, a brief increase in airways pressures with a lung recruitment maneuver (RM) easily revert atelectasis because the opening pressure in these dorsal pulmonary areas is overcome [2, 6].

Many studies in healthy and sick children showed that a brief increase in plateau pressure (Pplat) and PEEP during RM is safe [6,7,8]. However, there are still concerns about the hemodynamic response and the mechanic stress and strain on the lung tissue caused by the maneuver in this population.

In order to avoid these concerns, we have described a postural recruitment maneuver (P-RM), i.e., a ventilatory strategy aimed to obtain a lung recruitment effect by changes in body position under constant driving pressure at a moderate level of PEEP [9].

The P-RM is based on the known gravitational effect on P_L. Two principles explain its rationale [9]: one postulates that dorsal atelectasis can be recruited by placing this lung area in the uppermost position, which increases the local P_L.

The other principle follows the Laplace’s Law, which indicates that, once recruited; a ventral lung area will maintain patency when enough PEEP is applied. Therefore, the proposed P-RM consists to move the patient sequentially in: (1) the left lateral position to recruit atelectasis of the upper right lung; (2) the right lateral position to recruit the left lung atelectasis areas, while keeping open the right lung by applying enough PEEP; and (3) finally back to supine position (Fig. 1).

Our preliminary data showed that P-RM using 10 cmH₂O of PEEP and 22 cmH₂O of Pplat was enough to open up atelectasis during anesthesia in children [9].

Diagram of the protocol. Ventilation was switched to pressure control mode using 12 cmH₂O of driving pressure (DP). PEEP was increased from 5 to 10 cmH₂O during 3 min. The control group (C group) remained supine along the protocol while children in the postural recruitment group (P-RM group) were turned to the left lateral position (LL) during 90 s and then to the right lateral (RL) for another 90 s, to finally reach the supine position again. T1 analysis 5 min after anesthesia induction, T2 analysis 5 min after treatment, LUS lung ultrasound images

We hypothesized that the P-RM can re-aerate lung collapse without the need of reaching the high airways pressures obtained in standard RM. The objective of this study was to study the effect and feasibility of P-RM in anesthetized children.

Main end-points of the study were lung aeration and respiratory mechanics.

The primary outcome was to compare lung aeration assessed by lung ultrasound exams (LUS) between groups. The secondary outcome was to compare respiratory mechanics determined by airways resistance and dynamic respiratory compliance between groups.

Methods

This randomized and controlled trial was performed in the operating theater of a Community Hospital. Ethical approval for this study (IRB #2919/1457/2017) was provided by the Ethical Committee of the Hospital Privado de Comunidad, Mar del Plata, Argentina (ClinicalTrials.gov NCT03141515). Written informed consent was obtained from parents of all subjects participating in the trial.

The study started 20 April 2017 and ended 5 January 2018.

Patient’s eligibility criteria

We sequentially recruited patients aged 6 months to 5 years undergoing programmed surgeries. Conditions for enrollment were: need for general anesthesia and mechanical ventilator support, American Physical Status Classification (ASA) I–II and baseline pulse oximetry saturation (SpO₂) while breathing room air ≥ 97%.

We excluded patients undergoing emergency and thoracic surgeries and patients with pre-existing pulmonary, cardiac or chest wall diseases. After this first selection, we then excluded those patients without LUS evidence of atelectasis after anesthesia induction.

Anesthesia, ventilatory treatment and monitoring

Anesthesia was induced with sevoflurane using a circular system of the GE Aespire workstation (GE Healthcare, Madison, WI, US). Boluses of fentanyl 2 μg kg⁻¹ and vecuronium 0.1 mg kg⁻¹ were added before tracheal intubation with a cuffed endotracheal tube. Anesthesia was maintained with sevoflurane 0.7 minimum alveolar concentration and remifentanyl 0.3–0.5 μg kg⁻¹ min.

The lungs were ventilated with a volume control mode using a tidal volume (VT) of 6 mL kg⁻¹, respiratory rate between 20 and 25 bpm, inspiratory-to-expiratory ratio of 1:1.5, 10% of inspiratory pause, PEEP of 5 cmH₂O and a FIO₂ of 0.5.

Standard EKG, non-invasive mean systemic arterial pressure (MAP), capnography, pulse oximetry and respiratory mechanics were monitored with the S5 device (GE Healthcare/Datex-Ohmeda, Helsinki, Finland). Respiratory flow and pressure signals were obtained by a pediatric mainstream gadget placed at the airways opening, from which peak airways pressure (Pip), dynamic respiratory compliance (Cdyn) and respiratory airways resistance (Rrs) were obtained.

Gas exchange evaluated by the Air-test

Arterial oxygenation was evaluated after anesthesia induction with the Air–test using a pediatric pulse oximeter placed at the thumb (MightySat Rx, Masimo Corporation, Irvine, CA, USA) and decreasing FIO₂ from 0.5 to 0.21 during 5 min [10, 11]. Reference SpO₂ values breathing air in healthy patients are ≥ 97% and correspond to the anatomical shunt (~ 5–8% of the cardiac output). Any value below 97% is a marker of an additional shunt, presumably due to atelectasis, in those patients who presented baseline SpO₂ values ≥ 97% breathing air before anesthesia induction [12].

Lung ultrasound

LUS was performed with the ultrasound MyLab Gamma device (Esaote, Genova, Italy) using a high-frequency linear probe of 6–12 MHz. Each hemithorax was segmented into six regions using the longitudinal parasternal, anterior and posterior axillary lines and two axial lines, one above the diaphragm and the other 1 cm above the nipples [13].

The ultrasound probe was placed perpendicular to the ribs looking for the standard LUS view, where the pleura and the ventilated lung are visualized between two adjacent ribs (the bat sign) [13]. The probe was placed in the oblique position (along the intercostal spaces between ribs) in the areas where the typical atelectatic consolidations were detected. In general, the posterior zones of the lungs are those with the highest incidence of anesthesia-induced atelectasis [3, 4].

A LUS imaging based aeration score was calculated as previously described for children [6]. Briefly, this score is based on four LUS patterns [13,14,15] investigated in each of the 12 scanned thoracic areas:

1. Normal aeration (N): presence of the respiratory movement of the lung image relative to the chest wall (lung sliding) and the horizontal artifacts generated by repetition of the linear image of the pleura at regular intervals (A lines), with absence of sub-pleural ultrasound parenchymal signs (B-lines or consolidations).
2. Moderate loss of lung aeration (B1): presence of vertical dynamic lines, originating from the pleural line or from small sub-pleural consolidations, reaching the lowest edge of the screen (B-lines).
3. Severe loss of lung aeration (B2): multiple coalescent B-lines giving the aspect of a “white lung”, when the B-lines are so intense and numerous to occupy the whole image.
4. Complete loss of aeration (C): atelectasis, defined as localized sonographic consolidation, i.e., sub-pleural images with a tissue-like or hypoechoic pattern. Air bronchograms may be observed as bright echogenic branching structures within the consolidated area.

For a given thoracic area, points were allocated to the worst LUS pattern observed: N = 0, B1 = 1, B2 = 2 and C = 3. The LUS aeration score was calculated by the sum of points obtained in all the 12 lung areas, thus ranging from 0 to 36. Progressive increase of the score corresponds to loss of lung aeration.

Protocol

After tracheal intubation atelectasis areas were diagnosed by LUS examination, consequences on arterial oxygenation were assessed by performing the Air-test (Fig. 1, T1). Patients without LUS evidence of atelectasis were excluded. Patients with atelectasis were randomized into two groups using a computerized randomization table (StatsDirect v 2.7.2; Altrincham, Cheshire, United Kingdom) by an independent and blinded operator:

• Control group (C group, n = 20). Ventilation was turned to pressure control ventilation using a fixed driving pressure of 12 cmH₂O. PEEP was increased from 5 to 10 cmH₂O along 3 min maintaining the supine position during the whole protocol time.
• Postural–recruitment maneuver group (P-RM group, n = 20). Ventilation was turned to pressure control ventilation using a driving pressure of 12 cmH₂O and PEEP of 10 cmH₂O, but they were immediately and sequentially placed: (1) in the left lateral position (90 s), (2) in the right lateral position (other 90 s), (3) back to the supine position (Fig. 1).

After 3′ maneuver, both groups returned to baseline ventilation adding 8 cmH₂O of PEEP to maintain eventually the recruitment effect. Five minutes later patients were evaluated by LUS at T2 (Fig. 1). The same investigator non-blinded to treatment groups repeated LUS at each step. Respiratory data and hemodynamic parameters were collected at each protocol step.

Statistical analysis

The null hypothesis was that lung aeration score would be similar between groups. Considering a beta-power of 80% and an alpha-error of 5% the statistical power to reject this hypothesis was calculated assuming that atelectasis would be present in 90% of patients in the C group and in only 45% of patients in the RM group [6]. A sample size of 20 patients per group was estimated. Univariate comparisons were performed between and within groups applying the Student’s t test.

Multiple linear mixed models were adjusted to explain changes in LUS, respiratory and hemodynamic variables related to six predictive factors: age, gender, weight, surgery duration, Air-test and treatment group (fixed effects). The main factor to be analyzed was the proposed treatment.

Data are presented as n (%) for proportions and mean ± SD or median for continuous variables. A p-value < 0.05 was considered statistically significant. All calculations were performed using the R statistical package (R Core Team, 2015, Foundation for Statistical Computing, Vienna, Austria).

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