Optimal management of apparatus dead space in the anesthetized infant

Effects of apparatus dead space on volumetric capnograms in neonates with healthy lungs: a simulation study

BACKGROUND

Volumetric capnography in healthy ventilated neonates showed deformed waveforms, which are supposedly due to technological limitations of flow and carbon dioxide sensors.

AIMS

This bench study analyzed the role of apparatus dead space on the shape of capnograms in simulated neonates with healthy lungs.

METHODS

We simulated mechanical breaths in neonates of 2, 2.5, and 3 kg of body weight using a neonatal volumetric capnography simulator. The simulator was fed by a fixed amount of carbon dioxide of 6 mL/kg/min. Such simulator was ventilated in a volume control mode using fixed ventilatory settings with a tidal volume of 8 mL/kg and respiratory rates of 40, 35, and 30 breaths per minute for the 2, 2.5 and 3 kg neonates, respectively. We tested the above baseline ventilation with and without an additional apparatus dead space of 4 mL.

RESULTS

Simulations showed that adding the apparatus dead space to baseline ventilation increased the amount of re-inhaled carbon dioxide in all neonates: 0.16 ± 0.01 to 0.32 ± 0.03 mL (2 kg), 0.14 ± 0.02 to 0.39 ± 0.05 mL (2.5 kg), and 0.13 ± 0.01 to 0.36 ± 0.05 mL (3 kg); (p < .001). Apparatus dead space was computed as part of the airway dead space, and therefore, the ratio of airway dead space to tidal volume increased from 0.51 ± 0.04 to 0.68 ± 0.06, from 0.43 ± 0.04 to 0.62 ± 0.01 and from 0.38 ± 0.01 to 0.60 ± 0.02 in the 2, 2.5 and 3 kg simulated neonates, respectively (p < .001). Compared to baseline ventilation, adding apparatus dead space decreased the ratio of the volume of phase III to VT size from 31% to 11% (2 kg), from 40% to 16% (2.5 kg) and from 50% to 18% (3 kg); (p < .001).

CONCLUSIONS

The addition of a small apparatus dead space artificially deformed the volumetric capnograms in simulated neonates with healthy lungs.

Retrospective computed tomography analysis of endotracheal tube constriction and mispositioning in cats and dogs

OBJECTIVE

To discover the prevalence of endotracheal tube (ETT) constriction and rostral and caudal mispositioning in anaesthetized cats and dogs, and to identify associated risk factors.

STUDY DESIGN

Retrospective analysis.

ANIMALS

A total of 146 cats and 670 dogs.

METHODS

Computed tomography images of the head/neck/thorax from orotracheally intubated cats and dogs were visually assessed for constriction or mispositioning of the ETT. If constriction was present, measurements of the cross-sectional area (CSA) of the ETT lumen at constricted and un-constricted locations were compared. Location and cause of constriction were noted and the expected increase in resistance to gas flow was calculated. Animal information was collected from clinical records. Normality of continuous variables was assessed via the Shapiro-Wilk test. Chi-square tests examined associations between variables. Kendall's tau-b test was performed between measured ETT size and degree of constriction.

RESULTS

The ETT extended rostrally beyond incisors in 52% of cases; the connector was within the oral cavity in 19% of cases. The ETT extended beyond the first rib in 25.5% of cases. The prevalence of ETT constriction was 22.7%. Median reduction in CSA was 7.68% (0.14-64.19%). Median increase in resistance assuming laminar and turbulent flow was 16.5% (0.3-680%) and 21% (0.3-1200%), respectively. The most common cause of constriction was the presence of a radiotherapy mouth gag. Significant associations existed between presence of constriction and rostral mispositioning, and caudal mispositioning and extreme brachycephaly. Increased severity of constriction was more likely in smaller ETT.

CONCLUSIONS AND CLINICAL RELEVANCE

Constriction and mispositioning of ETT occurred very commonly in this population. Checking the ETT within the oral cavity for constriction and mispositioning is recommended. Radiotherapy mouth gags increase the risk of ETT compression. Smaller ETT are at greater risk of severe constriction. Brachycephalic dogs are at particular risk of caudal mispositioning.

Alveolar target ventilation and dead space in children under anaesthesia: The proventiped cohort study

INTRODUCTION

Ventilator settings in children under anaesthesia remain difficult because of the changes in the physiology and the high dead space.

OBJECTIVE

To determine the alveolar minute-volume to sustain normocapnia in children under mechanical ventilation.

DESIGN

A prospective observational study.

SETTINGS

This study was performed between May and October 2019 in a tertiary care children's hospital.

PATIENTS

Children between 2 months and 12 years, weighing between 5 and 40 kg, admitted for general anaesthesia.

INTERVENTION

Volumetric capnography was used to estimate the alveolar and dead space volume (Vd).

MAIN OUTCOME MEASURES

Total and alveolar minute ventilation in (ml kg -1  min -1 ) over 100 breaths.

RESULTS

Sixty patients were included comprising 20 per group: 5 to 10 kg (group 1), 10 to 20 kg (group 2), 20 to 40 kg (group 3). Seven patients were excluded for aberrant capnographic curves. After normalisation to weight, the median [IQR] tidal volume per kilogram was similar between the three groups: 6.5 ml kg -1 [6.0 to 7.5 ml kg -1 ], 6.4  ml kg -1 [5.7 to 7.3  ml kg -1 ], 6.4  ml kg -1 [5.3 to 6.8  ml kg -1 ]; P  = 0.3. Total Vd (in ml kg -1 ) was negatively correlated to weight ( r  = -0.62, 95% confidence interval -0.41 to -0.76, P  < 0.001). The total normalised minute ventilation (ml kg -1  min -1 ) to obtain normocapnia was higher in group 1 than in group 2 and in group 3; 203  ml kg -1  min -1 [175 to 219 ml kg -1  min -1 ], 150  ml kg -1  min -1 [139 to 181  ml kg -1  min -1 ] and 128  ml kg -1  min -1 [107 to 157  ml kg -1  min -1 ]; P  < 0.001 (mean ± SD), but (mean ± SD) alveolar minute ventilation was similar between the three groups; 68 ± 21  ml kg -1  min -1 .

CONCLUSION

Total dead space volume (including apparatus dead space) represents a major component of tidal volume in children less than 30 kg, when using large heat and moisture exchanger filters. The total minute ventilation necessary to achieve normocapnia decreased with increasing weight, while the alveolar minute ventilation remained constant.

TRIAL REGISTRATION

ClinicalTrials.gov, identifier: NCT03901599.

Monitoring in Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference

OBJECTIVES

Monitoring is essential to assess changes in the lung condition, to identify heart-lung interactions, and to personalize and improve respiratory support and adjuvant therapies in pediatric acute respiratory distress syndrome (PARDS). The objective of this article is to report the rationale of the revised recommendations/statements on monitoring from the Second Pediatric Acute Lung Injury Consensus Conference (PALICC-2).

DATA SOURCES

MEDLINE (Ovid), Embase (Elsevier), and CINAHL Complete (EBSCOhost).

STUDY SELECTION

We included studies focused on respiratory or cardiovascular monitoring of children less than 18 years old with a diagnosis of PARDS. We excluded studies focused on neonates.

DATA EXTRACTION

Title/abstract review, full-text review, and data extraction using a standardized data collection form.

DATA SYNTHESIS

The Grading of Recommendations Assessment, Development and Evaluation approach was used to identify and summarize evidence and develop recommendations. We identified 342 studies for full-text review. Seventeen good practice statements were generated related to respiratory and cardiovascular monitoring. Four research statements were generated related to respiratory mechanics and imaging monitoring, hemodynamics monitoring, and extubation readiness monitoring.

CONCLUSIONS

PALICC-2 monitoring good practice and research statements were developed to improve the care of patients with PARDS and were based on new knowledge generated in recent years in patients with PARDS, specifically in topics of general monitoring, respiratory system mechanics, gas exchange, weaning considerations, lung imaging, and hemodynamic monitoring.

Historical vignette – The Mapleson G, an original pediatric anesthesia circuit

A previously unpublished pediatric anesthesia circuit is presented here. It was invented and constructed by Dr Bernard-François Gribomont (hence called BFG circuit) around 1965 as a response to the important pediatric case load in the university hospital of Lovanium, near Leopoldville (now Kinshasa, DRC). The original objective was to find a simple solution that would enable the manual ventilation (assisted or controlled) of young children during ENT surgery, remaining very close to the child to reduce dead space while at the same time keeping far enough away from the surgeon in order to avoid obstructing their work. It includes a short coaxial single piece circuit devoid of any mechanical valve connected to an in-line fresh gas ventilation bag; it does not fit into any existing Mapleson category. Hence, the authors propose to classify it in a new Mapleson G class. Its main advantages are conceptual simplicity, inherent safety, very low dead space accounting for minimal rebreathing and thus reduced fresh gas flow, small size and weight, and ease of use even during prolonged manual ventilation in small children. Its main drawback is difficult scavenging of expired gases. For logistical reasons it was abandoned in the nineties but could be of renewed interest in low-income countries.

Error traps in pediatric one-lung ventilation

With the advent of thoracoscopic surgery, the benefits of lung isolation in children have been increasingly recognized. However, because of the small airway dimensions, equipment limitations in size and maneuverability, and limited respiratory reserve, one-lung ventilation in children remains challenging. This article highlights some of the most common error traps in the management of pediatric lung isolation and focuses on practical solutions for their management. The error traps discussed are as follows: (1) the failure to take into consideration relevant aspects of tracheobronchial anatomy when selecting the size of the lung isolation device, (2) failure to execute correct placement of the device chosen for lung isolation, (3) failure to maintain lung isolation related to surgical manipulation and isolation device movement, (4) failure to select appropriate ventilator strategies during one-lung ventilation, and (5) failure to appropriately manage and treat hypoxemia in the setting of one-lung ventilation.

Reduction in minute alveolar ventilation causes hypercapnia in ventilated neonates with respiratory distress

Hypercapnia occurs in ventilated infants even if tidal volume (V_T) and minute ventilation (V_E) are maintained. We hypothesised that increased physiological dead space (V_d,phys) caused decreased minute alveolar ventilation (V_A; alveolar ventilation (V_A) × respiratory rate) in well-ventilated infants with hypercapnia. We investigated the relationship between dead space and partial pressure of carbon dioxide (PaCO₂) and assessed V_A. Intubated infants (n = 33; mean birth weight, 2257 ± 641 g; mean gestational age, 35.0 ± 3.3 weeks) were enrolled. We performed volumetric capnography (V_cap), and calculated V_d,phys and V_A when arterial blood sampling was necessary. PaCO₂ was positively correlated with alveolar dead space (V_d,alv) (r = 0.54, p < 0.001) and V_d,phys (r = 0.48, p < 0.001), but not Fowler dead space (r = 0.14, p = 0.12). Normocapnia (82 measurements; 35 mmHg ≤ PaCO₂ < 45 mmHg) and hypercapnia groups (57 measurements; 45 mmHg ≤ PaCO₂) were classified. The hypercapnia group had higher V_d,phys (median 0.57 (IQR, 0.44-0.67)) than the normocapnia group (median V_d,phys/V_T = 0.46 (IQR, 0.37-0.58)], with no difference in V_T. The hypercapnia group had lower V_A (123 (IQR, 87-166) ml/kg/min) than the normocapnia group (151 (IQR, 115-180) ml/kg/min), with no difference in V_E.Conclusion: Reduction of V_A in well-ventilated neonates induces hypercapnia, caused by an increase in V_d,phys. What is Known: • Volumetric capnography based on ventilator graphics and capnograms is a useful tool in determining physiological dead space of ventilated infants and investigating the cause of hypercapnia. What is New: • This study adds evidence that reduction in minute alveolar ventilation causes hypercapnia in ventilated neonates.

Overexpression of phosphoprotein enriched in astrocytes 15 reverses the damage induced by propofol in hippocampal neurons

Propofol is a general anesthetic used in surgical operations. Phosphoprotein enriched in astrocytes 15(PEA15) was initially identified in astrocytes. The present study examined the role of PEA15 in the damage induced by propofol in hippocampal neurons. A model of hippocampal neuron damage was established using 50 µmol/l propofol. Cell viability, proliferation and apoptosis of hippocampal neurons were tested by Cell Counting Kit‑8 and flow cytometry. Western blotting and reverse transcription‑quantitative polymerase chain reaction analysis were performed to measure the expression levels of PEA15, and additional factors involved in apoptosis or in the signaling pathway downstream of PEA15. The present results suggested that propofol significantly decreased PEA15 expression levels in hippocampal neurons. Furthermore, overexpression of PEA15 significantly increased the cell viability and cell proliferation of cells treated with propofol. Additionally, PEA15 overexpression decreased apoptosis, which was promoted by propofol. Treatment with propofol significantly decreased the protein expression levels of pro‑caspase‑3, B‑cell lymphoma-2, phosphorylated extracellular signal‑regulated kinases (ERK)1/2, ribosomal S6 kinase 2 (RSK2) and phosphorylated cAMP responsive element binding protein 1 (CREB1). However, propofol upregulated active caspase‑3 and Bax expression levels. Notably, PEA15 overexpression was able to reverse the effects of propofol. Collectively, overexpression of PEA15 was able to attenuate the neurotoxicity of propofol in rat hippocampal neurons by increasing proliferation and repressing apoptosis via upregulation of the ERK‑CREB‑RSK2 signaling pathway.