Comparison of airway pressures and expired gas washout for nasal high flow versus CPAP in child airway replicas

Background For children and adults, the standard treatment for obstructive sleep apnea is the delivery of continuous positive airway pressure (CPAP). Though effective, CPAP masks can be uncomfortable to patients, contributing to adherence concerns. Recently, nasal high flow (NHF) therapy has been investigated as an alternative, especially in CPAP-intolerant children. The present study aimed to compare and contrast the positive airway pressures and expired gas washout generated by NHF versus CPAP in child nasal airway replicas. Methods NHF therapy was investigated at a flow rate of 20 L/min and compared to CPAP at 5 cmH2O and 10 cmH2O for 10 nasal airway replicas, built from computed tomography scans of children aged 4–8 years. NHF was delivered with three different high flow nasal cannula models provided by the same manufacturer, and CPAP was delivered with a sealed nasal mask. Tidal breathing through each replica was imposed using a lung simulator, and airway pressure at the trachea was recorded over time. For expired gas washout measurements, carbon dioxide was injected at the lung simulator, and end-tidal carbon dioxide (EtCO2) was measured at the trachea. Changes in EtCO2 compared to baseline values (no intervention) were assessed. Results NHF therapy generated an average positive end-expiratory pressure (PEEP) of 5.17 ± 2.09 cmH2O (mean ± SD, n = 10), similar to PEEP of 4.95 ± 0.03 cmH2O generated by nominally 5 cmH2O CPAP. Variation in tracheal pressure was higher between airway replicas for NHF compared to CPAP. EtCO2 decreased from baseline during administration of NHF, whereas it increased during CPAP. No statistical difference in tracheal pressure nor EtCO2 was found between the three high flow nasal cannulas. Conclusion In child airway replicas, NHF at 20 L/min generated average PEEP similar to CPAP at 5 cm H2O. Variation in tracheal pressure was higher between airway replicas for NHF than for CPAP. The delivery of NHF yielded expired gas washout, whereas CPAP impeded expired gas washout due to the increased dead space of the sealed mask.

An Unusual Cause of High Airway Pressures Using an Oesophageal Calibration Bougie in Bariatric Surgery- A Case Report

Background: Bariatric anaesthesia poses various challenges for the anaesthesiologist. We report a case of high airway pressures from the presence of the calibration bougie used in sleeve gastrectomy. This is the first time we have encountered raised airway pressures with the use of a calibration bougie. This underlines the need to be vigilant and consider the calibration bougie as a causative factor for raised airway pressures. Case presentation: The patient had a high Body Mass Index of 44 and no comorbid conditions. High airway pressures were noted on insertion of the calibration bougie by the anaesthesiologist. The common causes for intraoperative high airway pressures were ruled out and a fresh endotracheal tube was reinserted without any problems. After the second endotracheal tube was placed and the bougie was reinserted, the recurrence of the problem alerted us to the possibility of the bougie being the causative factor. With a change in ventilatory settings, the problem was circumvented and the procedure completed without any further problems. Conclusion: Bariatric anaesthetists should be aware that the calibration tube can lead to high airway pressures. This could be exacerbated especially if there are any unidentified underlying tracheal abnormalities. It is imperative to rule out the more common causes of high airway pressures. In retrospect it might have been useful to have used a reinforced endotracheal tube to determine if the problem recurred. Keywords: Calibration Bougie, Bariatric surgery, High airway pressure, Sleeve Gastrectomy

The respiratory system

The respiratory system is key to the management of patients with respiratory, as well as haemodynamic, compromise and should be monitored. The ventilator is more than just a machine that delivers gas; it is a true respiratory system monitoring device, allowing the measurement of airway pressures and intrinsic positive end-expiratory pressure and the plotting of pressure/volume curves. For effective and reliable monitoring, it is necessary to keep in mind the physiology such as the alveolar gas equation, heart–lung interactions, the equation of movement, etc. Monitoring the respiratory system enables adaptation of not only respiratory management, but also haemodynamic management.

High-CPAP Does Not Impede Cardiovascular Changes at Birth in Preterm Sheep

Objective: Continuous positive airway pressures (CPAP) used to assist preterm infants at birth are limited to 4–8 cmH2O due to concerns that high-CPAP may cause pulmonary overexpansion and adversely affect the cardiovascular system. We investigated the effects of high-CPAP on pulmonary (PBF) and cerebral (CBF) blood flows and jugular vein pressure (JVP) after birth in preterm lambs.Methods: Preterm lambs instrumented with flow probes and catheters were delivered at 133/146 days gestation. Lambs received low-CPAP (LCPAP: 5 cmH2O), high-CPAP (HCPAP: 15 cmH2O) or dynamic HCPAP (15 decreasing to 8 cmH2O at ~2 cmH2O/min) for up to 30 min after birth.Results: Mean PBF was lower in the LCPAP [median (Q1–Q3); 202 (48–277) mL/min, p = 0.002] compared to HCPAP [315 (221–365) mL/min] and dynamic HCPAP [327 (269–376) mL/min] lambs. CBF was similar in LCPAP [65 (37–78) mL/min], HCPAP [73 (41–106) mL/min], and dynamic HCPAP [66 (52–81) mL/min, p = 0.174] lambs. JVP was similar at CPAPs of 5 [8.0 (5.1–12.4) mmHg], 8 [9.4 (5.3–13.4) mmHg], and 15 cmH2O [8.6 (6.9–10.5) mmHg, p = 0.909]. Heart rate was lower in the LCPAP [134 (101–174) bpm; p = 0.028] compared to the HCPAP [173 (139–205)] and dynamic HCPAP [188 (161–207) bpm] groups. Ventilation or additional caffeine was required in 5/6 LCPAP, 1/6 HCPAP, and 5/7 dynamic HCPAP lambs (p = 0.082), whereas 3/6 LCPAP, but no HCPAP lambs required intubation (p = 0.041), and 1/6 LCPAP, but no HCPAP lambs developed a pneumothorax (p = 0.632).Conclusion: High-CPAP did not impede the increase in PBF at birth and supported preterm lambs without affecting CBF and JVP.