Hidden hazards and dangers associated with the use of HME/filters in breathing circuits. Their effect on toxic metabolite production, pulse oximetry and airway resistance

Humidification and the HME filter

The process of intubation and ventilation bypasses both the physiological humidification system and protective filtering processes. Various devices have been developed to aid in providing humidification of medical gasses and to serve as filters to reduce transmission of microbes. The following types of devices are available: * Heat and moisture exchanger without filter (HME) * Electrostatic filter with or without HME * Pleated filter with or without HME

Intraoperative Circuit Leak Likely Caused by Surgical Prep

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Misinterpretation of carbon dioxide monitoring because of deadspace of heat and moisture exchanger with a filter in pediatric anesthesia: A case report

RATIONALE

When patients are intubated and treated with mechanical ventilation, the upper respiratory tract is bypassed by the flow of dry and cold air. To prevent disturbances of airway homeostasis, a heat and moisture exchanger filter (HMEF) has been applied to breathing circuit.

PATIENT CONCERNS

A 4-month-old male infant was ventilated with the pediatric HMEF. We report the impact of ignoring the direct influence of a filter containing deadspace in pediatric mechanical ventilation.

DIAGNOSES

The breathing circuit with HMEF leads to unexpected complications such as mechanical obstructions owing to respiratory secretions, bleeding, inhaled drugs, and moisture. Besides these complications, we generally ignored the deadspace as the internal volume of the filters in breathing circuit for pediatric patients.

INTERVENTIONS

After we noticed the influence of filter deadspace for pediatric patient, we removed the filter for effective respiratory circulation.

OUTCOMES

The operation was completed without any specific incidents and the patient's voluntary breathing was well-maintained. The patient was discharged without any other complications.

LESSONS

The increase in breathing apparatus deadspace should be minimized, and the clinicians should keep in mind that HMEF can causes respiratory acidosis with hypercapnia by apparatus deadspace rebreathing, especially for infants.

Effect of heated humidified ventilation on bronchial mucus transport velocity in general anaesthesia: A randomized trial

Objective

To evaluate the effects of heated humidified ventilation on mucociliary function during general anaesthesia.

Methods

Male patients (ASA physical status 1 or 2), scheduled for elective radical retropubic prostatectomy, were allocated to receive sevoflurane general anaesthesia with conventional or heated humidified ventilation. Bronchial mucus transport velocity was assessed via fibreoptic bronchoscope and methylene blue dye at 3h after induction of anaesthesia.

Results

Median (SE) bronchial mucus transport velocity was significantly higher in the heated humidified group ( n = 26) than the conventional ventilation group ( n = 24) (1.7 [0.3] mm/min vs 0.9 [0.1] mm/min).

Conclusion

Heated humidified ventilation effectively maintains mucociliary clearance of patients during sevoflurane general anaesthesia.

Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. Part 2 - practical use, including problems, and their use with paediatric patients

Heat and moisture exchangers and breathing system filters are intended to replace the normal warming, humidifying and filtering functions of the upper airways. The first part of this review considered the history, principles of operation and efficiency of these devices. The aim of this part of the review is to summarise recent guidelines on the use of these devices and outline the problems that can occur. In particular, the effect of these devices on gas analysis, dead space, resistance to gas flow and blockage of the breathing system is considered. In children, it is important to consider the addition of dead space and resistance to gas flow. A body weight of 2.5 kg is probably the lower weight limit for use with heat and moisture exchangers, and 3 kg for filters. The resistance to gas flow of a heat- and moisture-exchanging filter added to a Mapleson F breathing system can cause a delay in the induction of anaesthesia.

Beware the airway filter: deadspace effect in children under 2 years

BACKGROUND

Filters are increasingly used in breathing circuits as they protect the circuit from contamination and facilitate humidification of inspired gas. The use of filters, however, can augment the anatomical deadspace. This can be significant in children because they have much smaller tidal volumes.

METHODS

Following institutional ethical approval, 20 healthy children <2 years of age who required tracheal intubation were recruited. Ventilation was adjusted to achieve an endtidal carbon dioxide (P(E)CO(2)) of 4.6 kPa (35 mmHg) when sampled at the tracheal tube (TT) adapter. Following a 10-min period of stabilization, an airway filter (22 ml) was introduced into the circuit. The respiratory rate (RR) was then adjusted to return P(E)CO(2) to 4.6 kPa (35 mmHg).

RESULTS

A mean increase in ventilation of 1.42 (0.38) l x min(-1) was required to maintain a normal P(E)CO(2) level. Airway pressure and respiratory rate increased by 7.9 mmHg (4.6) and 19.8 breath x min(-1) (8.7) respectively. The P(E)CO(2) and partial pressure of inspired carbon-di-oxide (PiCO(2)) measured from the TT adapter were higher than measured from the filter port. The mean increase was 3.6 (1.6) mmHg for P(E)CO(2) and 5.9 (3.9) mmHg for PiCO(2).

CONCLUSION

Amplified deadspace from airway filters results in a significant increase in ventilation needed to maintain a normal P((E)CO(2) in children <2 years of age with normal lungs. Sampling of P((E)CO(2) and PiCO(2) from the filter significantly underestimates the effect of increased deadspace. The effect of increased deadspace may be predicted using a proposed mathematical model.