Single-breath measurements of pulmonary oxygen uptake and gas flow rates for ventilator management in ARDS

Development of a Breath Analyzer for O2 and CO2 Measurement

Background:

Breath analysis can be used to screen disease and detect physical conditions. Many research studies have investigated various sensors or techniques that were used to detect gas concentrations and temperature. However, the studies were less concerned about the performance of sensors.

Methods:

In this study, we developed and tested a portable breath analyzer for exhaled gas measurement. We detected air flow rate, temperature, humidity, CO2 and O2 concentrations. Commercial sensing elements were used to assemble this breath analyzer. All sensors were calibrated to ensure their accuracy. The response times of different sensors were considered. We analyzed breath during three states; 1) seating and resting for 5 min, 2) walking for 5 min and 3) running for 5 min in test participants. Fifteen students 20 to 34 years of age were the test participants.

Results:

Heat, humidity and CO2 production and O2 consumption were calculated from these measured data and were used to assess the performance of the analyzer. The Respiratory Quotient (RQ) were estimated by the ratio of VCO2 to VO2. The RQ values for resting, walking and running states were 0.899, 0.865 and 0.785, respectively. Walking and running significantly increased the heat and humidity production of the human body, corresponding to the human physiological function.

Conclusion:

The RQ value is usually in the range of 0.8 to 0.85. The measurement results for our exhaled analyzer were close to this range. From the respiratory quotient values, the performance of this breath analyzer was reasonable.

Respiratory oxygen uptake is associated with survival in a cohort of ventilated trauma and burn patients

BACKGROUND

Little data is available in the literature about the role of end tidal oxygen in critically ill patients. We sought to identify the association between the level of respiratory oxygen and clinical outcomes in critically-ill ventilated trauma and burn patients.

METHODS

A retrospective cohort of 55 trauma and burn patients from 2010 to 2016 was collected. Exposures of interest included a) expiratory end tidal oxygen (ETO2) and b) the difference between FiO₂ and ETO2 (uptake). Associations of clinical characteristics with ETO2 and oxygen uptake were examined using a Spearman correlation. The relationships between discharge status, demographics, injury type, severity, and clinical characteristics were examined using chi-square (or Fisher's exact) tests and two-sample t-tests. Multivariable analyses using linear and logistic regression were performed to determine whether expiratory end tidal oxygen or oxygen uptake was an independent predictor of clinical outcomes.

RESULTS

Mean age for the patients was 46.3±18.2years with 41 (74.6%) male and 34 (61.8%) white. In the cohort, 27 (49.1%) of patients had burns and 28 (50.9%) blunt trauma. Oxygen uptake was negatively correlated with lactic acid, minute ventilation, total ICU days, and ventilator days (p<0.05). Patients who died demonstrated lower oxygen uptake than those alive, oxygen uptake remained significantly associated with discharge status after adjusting for potential confounders (p=0.028).

CONCLUSION

A narrowed difference between ETO₂ and inspiratory oxygen is associated with increased mortality in a cohort of ventilated trauma and burn patients. Future research is needed to further elucidate the role of respiratory oxygen level in larger, prospective studies.

Mechanical ventilation in acute respiratory distress syndrome

The acute respiratory distress syndrome occurs commonly in critical care. There is an increasing volume of clinical and experimental evidence that poor ventilatory technique that is injurious to the lungs can propagate the systemic inflammatory response and adversely affect mortality. Many ventilatory techniques have been hypothesized to 'protect' the lungs during mechanical ventilation, including tidal volume limitation, high positive end-expiratory pressure, pressure-controlled inverse ratio ventilation, and prone positioning. Experimental techniques include liquid ventilation, surfactant administration and extracorporeal gas exchange. Despite excellent rationale for their use, few techniques, apart from tidal volume limitation, have been shown to improve survival in randomized controlled trials.

Monitoring pulmonary function with superimposed pulmonary gas exchange curves from standard analyzers

OBJECTIVE

A repetitive graphic display of the single breath pulmonary function can indicate changes in cardiac and pulmonary physiology brought on by clinical events. Parallel advances in computer technology and monitoring make real-time, single breath pulmonary function clinically practicable. We describe a system built from a commercially available airway gas monitor and off the shelf computer and data-acquisition hardware.

METHODS

Analog data for gas flow rate, O2, and CO2 concentrations are introduced into a computer through an analog-to-digital conversion board. Oxygen uptake (VO2) and carbon dioxide output (VCO2) are calculated for each breath. Inspired minus expired concentrations for O2 and CO2 are displayed simultaneously with the expired gas flow rate curve for each breath. Dead-space and alveolar ventilation are calculated for each breath and readily appreciated from the display.

RESULTS

Graphs illustrating the function of the system are presented for the following clinical scenarios; upper airway obstruction, bronchospasm, bronchopleural fistula, pulmonary perfusion changes and inadequate oxygen delivery.

CONCLUSIONS

This paper describes a real-time, single breath pulmonary monitoring system that displays three parameters graphed against time: expired flow rate, oxygen uptake and carbon dioxide production. This system allows for early and rapid recognition of treatable conditions that may lead to adverse events without any additional patient measurements or invasive procedures. Monitoring systems similar to the one described in this paper may lead to a higher level of patient safety without any additional patient risk.