Acute hyperventilation increases oxygen consumption and decreases peripheral tissue perfusion in critically ill patients

The level of partial pressure of carbon dioxide affects respiratory effort in COVID-19 patients undergoing pressure support ventilation with extracorporeal membrane oxygenation

BACKGROUND

Patients with COVID-19 undergoing pressure support ventilation (PSV) with extracorporeal membrane oxygenation (ECMO) commonly had high respiratory drive, which could cause self-inflicted lung injury. The aim of this study was to evaluate the influence of different levels of partial pressure of carbon dioxide(PaCO2) on respiratory effort in COVID-19 patients undergoing PSV with ECMO.

METHODS

ECMO gas flow was downregulated from baseline (respiratory rate < 25 bpm, peak airway pressure < 25 cm H2O, tidal volume < 6 mL/kg, PaCO2 < 40 mmHg) until PaCO2 increased by 5 - 10 mmHg. The pressure muscle index (PMI) and airway pressure swing during occlusion (ΔPOCC) were used to monitor respiratory effort, and they were measured before and after enforcement of the regulations.

RESULTS

Ten patients with COVID-19 who had undergone ECMO were enrolled in this prospective study. When the PaCO2 increased from 36 (36 - 37) to 42 (41-43) mmHg (p = 0.0020), there was a significant increase in ΔPOCC [from 5.6 (4.7-8.0) to 11.1 (8.5-13.1) cm H2O, p = 0.0020] and PMI [from 3.0 ± 1.4 to 6.5 ± 2.1 cm H2O, p < 0.0001]. Meanwhile, increased inspiratory effort determined by elevated PaCO2 levels led to enhancement of tidal volume from 4.1 ± 1.2 mL/kg to 5.3 ± 1.5 mL/kg (p = 0.0003) and respiratory rate from 13 ± 2 to 15 ± 2 bpm (p = 0.0266). In addition, the increase in PaCO2 was linearly correlated with changes in ΔPOCC and PMI (R2 = 0.7293, p = 0.0003 and R2 = 0.4105, p = 0.0460, respectively).

CONCLUSIONS

In patients with COVID-19 undergoing PSV with ECMO, an increase of PaCO2 could increase the inspiratory effort.

High respiratory effort decreases splanchnic and peripheral perfusion in patients with respiratory failure during mechanical ventilation

PURPOSE

This study aimed to evaluate the effects of high respiratory effort(HRE) on spleen, kidney, intestine, and peripheral perfusion in patients with respiratory failure during mechanical ventilation.

METHODS

HRE was defined as a pressure muscle index (PMI) > 6 cmH₂O and airway pressure swing during occlusion (ΔPOCC) > 10 cmH₂O. Capillary refill time(CRT) and peripheral perfusion index (PPI) were determined when HRE occurred. The resistance indices of the snuffbox, intestine, spleen, and kidney were measured using Doppler ultrasonography simultaneously. These parameters were re-measured when the patients had normal respiratory effort (NRE) following sedation and analgesia.

RESULTS

A total of 33 critically ill patients were enrolled in this prospective observational study. There was a significant increase in CRT (p = 0.0345) and PPI (p < 0.0001) from HRE to NRE; meanwhile, the resistance index of the snuffbox artery decreased (p < 0.0001). Regarding splanchnic perfusion indicators, all resistance indices of the superior mesenteric artery (p = 0.0002), spleen (p < 0.0001), and kidney (p < 0.0001) decreased significantly when the patient changed from HRE status to NRE.

CONCLUSIONS

HRE could decrease perfusion of peripheral tissues and splanchnic organs. The status of HRE should be avoided to protect splanchnic and peripheral organs in mechanically ventilated patients.

Oxygenation Performance of Different Non-Invasive Devices for Treatment of Decompression Illness and Carbon Monoxide Poisoning

Study Objective: Application of high concentrations of oxygen to increase oxygen partial pressure (pO2) is the most important treatment for patients with carbon monoxide intoxication or divers with suspected decompression illness. The aim of this study was to evaluate the oxygenation performance of various non-invasive oxygen systems.

Methods: The effect of different oxygen systems on arterial pO2, pCO2 and pH and their subjective comfort was evaluated in 30 healthy participants. Eight devices were included: nasal cannula, non-rebreather mask, AirLife Open mask, Flow-Safe II CPAP device, SuperNO₂VA nasal PAP device, all operated with 15 L/min constant flow oxygen; nasal high-flow (50 L/min flow, 1.0 FiO2), non-invasive positive pressure ventilation (NPPV, 12 PEEP, 4 ASB, 1.0 FiO2) and a standard diving regulator (operated with pure oxygen).

Results: Diving regulator, SuperNO₂VA, nasal high-flow and NPPV achieved mean arterial pO2 concentrations between 538 and 556 mm Hg within 5 minutes. The AirLife Open mask, the nasal cannula and the non-rebreather mask achieved concentrations of 348–451 mm Hg and the Flow-Safe II device 270 mm Hg. Except for the AirLife open mask, pCO2 decreased and pH increased with all devices. The highest pH values were observed with NPPV, diving regulator, Flow-Safe II and nasal high-flow but apparent hyperventilation was uncommon. The AirLife Open and the non-rebreather mask were the most comfortable, the SuperNO₂VA and the nasal cannula the most uncomfortable devices.

Conclusion: A standard diving regulator and the SuperNO₂VA device were equally effective in providing highest physiologically possible pO2 as compared to nasal high-flow and NPPV.