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Year : 2020  |  Volume : 64  |  Issue : 11  |  Page : 992-993  

Heat and moisture exchanger filter in a paediatric patient: A dilemma for anaesthesiologists- to use or not to use?

1 Department of Anesthesiology, AIIMS, Patna, Bihar, India
2 Department of Anatomy, AIIMS, Patna, Bihar, India

Date of Submission04-May-2020
Date of Decision21-Jun-2020
Date of Acceptance11-Oct-2020
Date of Web Publication1-Nov-2020

Correspondence Address:
Dr. Naaz Shagufta
Department of Anesthesiology, AIIMS Patna, Phulwarisharif, Patna, Bihar - 801 507
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ija.IJA_516_20

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How to cite this article:
Shagufta N, Chandni S, Ajeet K, Adil A. Heat and moisture exchanger filter in a paediatric patient: A dilemma for anaesthesiologists- to use or not to use?. Indian J Anaesth 2020;64:992-3

How to cite this URL:
Shagufta N, Chandni S, Ajeet K, Adil A. Heat and moisture exchanger filter in a paediatric patient: A dilemma for anaesthesiologists- to use or not to use?. Indian J Anaesth [serial online] 2020 [cited 2021 Jun 19];64:992-3. Available from: https://www.ijaweb.org/text.asp?2020/64/11/992/299687


Endotracheal intubation bypasses the upper airway leading to loss of heat, humidity and increased chances of infection. Hence, Heat and Moisture Exchanger (HME) is incorporated in the anaesthesia circuit to conserve a part of the patient's exhaled heat and moisture.[1] Adding a filter to the breathing system reduces the transmission of microbes and other particulate matter (together HMEF).[2]

A six-year-old, 20 kg, American Society of Anesthesiologists (ASA) class 1 male child was scheduled for medulloblastoma excision. The standard ASA monitors were attached. Anaesthesia was induced with intravenous fentanyl 40 μg, propofol 50 mg, and vecuronium 2 mg. Tracheal intubation was done with a cuffed endotracheal tube of 5.5 mm internal diameter. After confirming bilateral equal breath sounds on auscultation and normal capnography, surgery was started. The patient was ventilated with a tidal volume (TV) of140 ml, respiratory rate (RR) 14/min, FiO20.5, and inspiratory-expiratory (I:E) ratio of 1:2 using Drager Primus Infinity Kappa anaesthesia workstation. Anaesthesia was maintained with sevoflurane 2-3% in oxygen, and air. After about 30 minutes of surgery, the end-tidal carbon dioxide (EtCO2) started rising. We ruled out one-lung ventilation, bronchospasm, and kinking of the endotracheal tube. Despite adjusting the ventilator settings (respiratory rate to 20, and tidal volume upto 10 ml/kg) and subsequent suctioning of the endotracheal tube, EtCO2 increased to 70 mm Hg. Interventions like changing the sampling line, soda-lime (Dragersorb 800 Plus) and the workstation did not help.

The arterial blood gas (ABG) analysis showed a pH of 7.1 and pCO2 80. Icepacks were applied as there was a rise of 2-degree Celsius in the patient's body temperature. We decided to remove the paediatric HMEF (Medisafe) connected to the Y-piece of the circuit. Subsequently, the EtCO2 decreased to its normal value in half an hour. The temperature and ABG also became normal. Further intraoperative course was uneventful.

Endotracheal tube, Y piece, tube adaptor, and HMEF device add to the apparatus dead space during mechanical ventilation. This increases rebreathing, resistance, and the work of breathing.[3] In children, a vast apparatus dead space volume could be most of the tidal volume, resulting in inadequate ventilation and the development of respiratory acidosis. So, even though the patient might benefit from the addition of the HMEF, some harm might also occur. Kwon MA studied the effect of paediatric HME in healthy patients. They found that HME significantly increased PaCO2. The removal of the HME decreased PaCO2 from 46.1 ± 6.9 mmHg to 37.9 ± 4.3 mmHg (P < 0.001) and increased the pH from 7.32 to 7.37 (P < 0.001). This change was inversely proportional to weight and age.[4]

In healthy adult patients, HME has a low resistance and a relatively small volume (about 75 ml), that does not impair ventilation.[5] However, most paediatric patients are applied with the standard size of HME which has a volume of 20-25 ml.[6] This amounts to about 1/10 of the tidal volume of a 20 kg patient or 1/5 for a 10 kg patient. In our case, HMEF lead to relatively more dead space resulting in ineffective ventilation and accumulation of CO2. There was the buildup of heat and a rise in temperature as well.

In short surgeries, HMEF can be avoided. However, not using an HMEF in prolonged surgeries can lead to hypothermia and metabolic acidosis. Sometimes, the filter may become damp and increase the resistance leading to respiratory acidosis. Hence, further investigations on optimum paediatric HME devices with smaller dead spaces are strongly desirable. Also, various sizes of paediatric filters are now available with reduced dead space: HMEF Paediatric for weight >10 kg and HMEF Neonatal for children <10 kg. Age and weight appropriate filters should be used, with a low threshold for replacing the filter if the EtCO2/pCO2 is persistently high.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Chellam S, Dalal KS, Toal PV. Use of filters in anaesthesia: Is it warranted? Indian J Anaesth 2014;58:475-7.  Back to cited text no. 1
[PUBMED]  [Full text]  
Patwa A, Shah A, Garg R, Divatia JV, Kundra P, Doctor JR, et al. All India difficult airway association (AIDAA) consensus guidelines for airway management in the operating room during the COVID-19 pandemic. Indian J Anaesth 2020;64 (Suppl 2):S107-15.  Back to cited text no. 2
Wilkes AR. Heat and moisture exchangers and breathing system filters: Their use in anaesthesia and intensive care. Part 1–history, principles and efficiency. Anaesthesia 2011;66:31-9.  Back to cited text no. 3
Kwon MA. The effect of a pediatric heat and moisture exchanger on dead space in healthy pediatric anesthesia. Korean J Anesthesiol 2012;62:418-22.  Back to cited text no. 4
Hinkson CR, Benson MS, Stephens LM, Deem S. The effects of apparatus dead space on PaCO2 in patients receiving lung-protective ventilation. Respir Care 2006;51:1140-4.  Back to cited text no. 5
De Robertis E, Servillo G, Tufano R, Jonson B. Aspiration of dead space allows isocapnic low tidal volume ventilation in acute lung injury. Relationships to gas exchange and mechanics. Intensive Care Med 2001;27:1496-503.  Back to cited text no. 6


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