Gas flow rates through transtracheal ventilation catheters

Effect of modified high-flow oxygen therapy on positive end-expiratory pressure and end-expiratory lung volume based on simulated lung platform

Objective

The aim of this study was to assess the effect of modified high-flow oxygen therapy on end-expiratory lung volume (EELV) and positive end-expiratory pressure (PEEP) in tracheotomized patients with normal pulmonary, acute hypoxic respiratory failure (AHRF) or chronic obstructive pulmonary disease (COPD).

Methods

A ventilator and an artificial lung model were used to simulate the normal or strong inspiratory effort state of normal lung, AHRF and COPD patients. The traditional high-flow respiratory humidification therapy device connected with a standard interface (group A), and the modified therapy device added two types of resistance valves (group B, inner diameter 7.7 mm, length 24.0 mm; group C, inner diameter 7.7 mm, length 34.0 mm) to the exhalation end of the standard interface. The changes of end-expiratory lung volume (ΔEELV) and PEEP with the increase of flow rate (10 L/min, 20 L/min, 30 L/min, 40 L/min, 50 L/min, 60 L/min) in the three groups was recorded.

Results

Under simulated conditions of normal lung, AHRF and COPD, as the flow rate increased by using the modified therapy device, the PEEP values in all groups showed an exponential increasing trend, and the ΔEELV also increased accordingly. In addition, under the same flow rate level, the PEEP values of the two modified high-flow oxygen therapies (Group B and Group C) were significantly higher than those of the standard high-flow oxygen therapy (Group A) (p < 0.05). In the normal lung model with normal or strong inspiratory effort, and in the AHRF or COPD model with strong inspiratory effort, when the flow rate was higher than 30 L/min, the PEEP levels of Group B were significantly lower than those of Group C (p < 0.05). In the AHRF model with normal inspiratory effort, when the flow rate was between 10 L/min and 60 L/min, the PEEP levels of Group B were significantly lower than those of Group C (p < 0.05). Moreover, in the COPD model with normal inspiratory effort, the PEEP levels of Group B were significantly lower than that of Group C only when the flow rate was 60 L/min (p < 0.05).

Conclusion

The addition of different types of resistance valves to the high-flow exhalation end may be a feasible solution to improve the clinical efficacy of tracheotomized high-flow oxygen therapy.

Dual-wavelength fiber-optic technique to assist needle cricothyroidotomy

The traditional needle cricothyroidotomy procedure is performed blindly without any medical equipment. Complications including posterior tracheal wall perforation, accidental vessel puncture, and missed tracheal puncture are reported. Therefore, we proposed a dual-wavelength fiber-optic technique based on the technique of near-infrared spectroscopy to assist operators performing needle cricothyroidotomy in a swine model. We embedded optical fibers in a 16-gauge intravenous needle catheter. Real-time data were displayed on an oscilloscope, and we used the program to analyze the data immediately. The change of optical density corresponding to 690-nm and 850-nm wavelengths and hemoglobin parameters (HbO₂ and Hb concentrations) was analyzed immediately using the program in the laptop. Unique and significant optical differences were presented in this experiment. We could easily identify every different tissue by the change of optical density corresponding to 690-nm and 850-nm wavelengths and hemoglobin parameters (HbO₂ and Hb concentrations). Statistical method (Kruskal-Wallis H test) was used to compare differences in tissues at each time-point, respectively. The p values in every tissue in optical density change corresponding to 690 nm and 850 nm were all < 0.001. Furthermore, the p values in every tissue in Hb and HbO₂ were also all < 0.001. The results were statistically significant. This is the first and novel study to introduce a dual-wavelength embedded fibers into a standard cricothyroidotomy needle. This proposed system might be helpful to provide us real-time information of the advanced needle tip to decrease possible complications.

Determination of gas flow through airway exchange catheters: measured and calculated values and dependence on pressure and entrainment

Serious complications have been described during oxygenation of patients with airway exchange catheters, due to catheter malpositioning, accidentally applied high airway pressures or high delivered volumes. In this in-vitro study, we analysed gas flow through various airway exchange catheters and described its dependence on driving pressure and entrainment. We applied driving pressures between 0.5 and 2.5 bar and observed maximal flow rates of 3.6 l.s(-1) . Measured gas flow values differed significantly from values calculated according to the Hagen-Poiseuille equation. Although flow restriction in ventilators and small-bore connectors will limit gas flow, large gas volumes may be unintentionally applied via the airway exchange catheters, leading to serious complications.

Comparison of different methods of ventilation via cannula cricothyroidotomy in a trachea-lung model

BACKGROUND

Cannula cricothyroidotomy is recommended in recent guidelines as a rescue intervention in the 'cannot-intubate cannot-ventilate' scenario. Several methods of providing ventilation via a cannula cricothyroidotomy have been described, but there are no data comparing these methods and using cannulae of differing diameters.

METHODS

Using a bench-top trachea-lung model (comprising a Siemens test lung attached to commercially available breathing system tubing), we compared delivered minute volumes (MVs) for five methods of ventilation administered through cannulae of diameters 20, 16, 14, and 13 G. The ventilation methods were: an ENK oxygen flow modulator, a Manujet, a self-inflating resuscitation bag, the oxygen flush of an anaesthetic machine, and oxygen from a wall-mounted flow meter attached via a three-way tap to the cannula. All experiments were performed with and without a proximal 2.5 mm diameter constriction to simulate partial upper airway obstruction.

RESULTS

MVs increased with increasing cannula diameter. In the absence of a proximal constriction, MVs delivered via a 20 G cannula were <1 litre min(-1) with all devices; only the Manujet delivered MVs >2 litre min(-1), at cannula sizes of >or=16 G. MVs were greater in the presence of a proximal constriction, but did not exceed 4 litre min(-1) using the low-pressure devices.

CONCLUSIONS

Extrapolated to the clinical situation, these data suggest that low-pressure devices will not deliver adequate MVs via a cannula cricothroidotomy and should no longer be advocated. Purpose-made devices should be available in all areas where anaesthesia is administered or airway interventions are performed.