Abstract
Background and Aims:
Using a humidifier in intubated patients is now a standard of care as the humidifying effect of the upper airway is lost. We conducted this study to compare the efficacy of a heated humidifier (HH) with the more commonly used conventional mist nebulizer on overnight intubated and spontaneously breathing post-operative patients.
Material and Methods:
This prospective, randomized control trial included 60 post-operative overnight intubated and spontaneously breathing patients, of which 30 patients were allocated to the HH group and 30 to the mist nebulizer group. The reduction of endotracheal tube (ETT) patency was measured quantitatively by the difference between the pre-intubation and immediate post-extubation ETT volume and compared between the two groups. Also, the characteristics of secretion, the temperature of inspired gas at the Y-piece, and the frequency of refilling the humidifier chamber were recorded and compared.
Results:
The reduction of ETT volume was significantly more in the mist nebulizer group compared to the HH group (P-value 0.00026). The mean temperature of the inspired gas (°C) was higher in the HH group (P-value < 0.0001). More patients in the mist nebulizer group had thicker (P-value 0.057) and drier secretions (P-value 0.005) compared to the HH group. None of the patients in the HH group required refilling of the humidifier chamber while the mean frequency of the refilling was 3.5 times per patient in the mist nebulizer group.
Conclusion:
HH may be preferred over mist nebulizer as the latter requires more frequent refilling which may not be practically possible in a busy recovery room rendering the patient at the risk of inhaling dry gas and consequent thick and dry secretions with decreased ETT patency.
Keywords: Endotracheal tube, heated humidifier, mist nebulizer, secretion, inspired gas, Y-piece
Introduction
Humidification during invasive ventilation is an integral part of care in intubated patients. Various studies have revealed the unfavorable effects of inadequate humidification on the respiratory tract manifested by increased work of breathing, atelectasis, thick and dehydrated secretions, cough and/or bronchospasm, unwanted endotracheal tube (ETT) blockade/reduced patency, and increased resistance to the flow of delivered gases.[1] In an intubated patient, the humidifying effect of the upper airway is lost and the burden of heating and moisturizing inspired gas falls on the lower respiratory tract, which is not well-suited for this purpose resulting in the exposure of the respiratory tract to partially dry and cold gases. The monitoring of humidification is complex. Secretion characteristics, inspection of condensate in tubing, temperature of the inspired gas at Y-piece, and the need for saline instillation have been used as alternate surrogate markers for monitoring of humidification.[2]
In our institution, the post-operative head and neck malignancy patients who are spontaneously breathing and kept intubated overnight are provided humidification through active humidifiers either by mist nebulizer [Figure 1] or heated humidifier [HH; Figure 2]. The mist nebulizer, unlike HH, requires frequent refilling of the humidifier chamber which may not be possible in a busy recovery room, making patients prone to inhale dry, un-humidified gases for a prolonged duration. We hypothesized that HH was a better choice for humidification compared to a mist nebulizer in spontaneously breathing intubated patients.
Figure 1.
Black arrow showing mist the nebulizer mounted to one end of the T-piece
Figure 2.
Image showing (Arrow 1) oxygen tubing connected to the heated humidifier and (Arrow 2) the inspiratory limb carrying the humidified oxygen to the patient
The primary objective of the study was to compare the effects of the mist nebulizer and HH on the extent of ETT blockade. The secondary objectives were to find out the character of secretion (moist or dry, thin or thick), the temperature of the inspired gas, and the number of times the nebulizer or the humidifier chambers were filled that indirectly helped us to assess the workload on the nursing staff.
Material and Methods
The study was registered under clinical trial registry “ClinicalTrials.gov Protocol Registration and Result System (PRS)” and commenced after the ethics committee’s approval (IEC/0416/1665/001). Prior written informed consent was taken and all procedures were done in the study following the ethical guidelines of the Declaration of Helsinki. The study was conducted over 1 year from 20.04.2016 to 19.04.2017. This was a pilot, randomized control study. Due to a lack of previously published or non-published data in the literature, this pilot study included a sample size of 30 in each group using a flat rule of thumb. Sixty American Society of Anesthesiologists (ASA) I/II, adult post-operative patients without any underlying cardiac or respiratory diseases who were kept intubated overnight and spontaneously breathing were selected and recruited in the study [Figure 3]. The patients with cardiac diseases (coronary artery disease, valvular heart disease, heart failure, etc.), having lung diseases (chronic obstructive pulmonary disease, bronchiectasis, cystic fibrosis, etc.), smokers (abstinence period less than 3 months), on drugs having sialagogue/anti-sialagogue property were excluded from the study.
Figure 3.
Recruitment algorithm
After taking written informed consent, 30 post-operative patients were supplied humidified oxygen through HH “Fisher and Paykel MR 370” (New Zealand) and 30 through conventional mist nebulizer “Hudson RCI Micro Mist Nebulizer model no. 1885.” Allocation concealment was ensured using sequentially numbered, opaque, sealed envelopes (SNOSE). Randomization was done using a computer-generated list of random numbers. The subjects were allocated to the study groups by the sequential opening of the numbered envelopes containing the random assignment which was done by the recovery room resident doctor.
Pre-operatively size and volume of ETT were calculated and noted. The information regarding the age, sex of the patient, type of surgery, comorbidity if any, duration of humidifier use, and any complications leading to discontinuation of the humidifier were noted. In our set-up, the humidifier chambers are refilled by the nursing staff when the same dry up. We noted down the number of times the humidifier chambers were refilled in each patient. The suctioning of ETT was done once every 2 h by a nurse/doctor/trained personnel. The frequency of additional suctioning and reason for suctioning was also recorded. The reduction of ETT volume caused by secretion was measured immediately following extubation.
The reduction of ETT volume was assessed by the following process:
The bevel end and Murphy’s eye of the ETT were sealed using a sterile insulating tape so that it was water-tight. The tube was gradually filled with a measured amount of sterile fluid using a small volume syringe to increase the accuracy of the measurement. The amount of fluid that the ETT could hold was the actual volume of the tube.
The volume of the extubated tube was measured in a similar way.
The measured volume of the extubated ETT was subtracted from the actual volume.
The result obtained after this subtraction was the volume of the secretion or the volume of ETT that has been blocked.
The characteristics of secretion were also noted, which were subjective and decided by the person measuring the ETT volume after extubation. The characteristics of secretions were defined using the following terms.
Thick secretions: Firm consistency and not flowing freely.
Thin secretions: Watery, flowing freely.
Moist secretions: Somewhat wet or accompanied by moisture.
Dry secretions: Devoid of moisture/encrustations.[2-4]
The temperature of the inspired gas at the Y-piece was measured hourly.
This is an assessor blind study as the participants were aware of the humidifier being used but not the observer. The extubation was done by the ICU resident following which the humidifier was removed from the patient’s side and the measurement of the ETT volume, recording of the temperature of the inspired gas from the monitor, assessment of the characteristics of secretion were done by another doctor/assessor who was blind about the type of humidifier being used.
Two groups were compared in terms of the reduction of ETT volume. The reduction in the volume of ETT of each patient was determined as the percentage of the actual volume and compared between the two groups. The mean temperature of the inspired gas at the Y-end was calculated and compared. The other demographical variables were also measured as mean ± standard deviation and compared between the two groups. The Chi-square test was used for analyzing the categorical variables (such as the characteristics of secretions) and the independent t-test was used to compare the continuous variables (such as temperature at Y-piece, duration of the use of a humidifier, etc.) between the two groups. For non-normally-distributed data as in comparing the reduction of ETT volume between the two groups, the Mann–Whitney U test was used. The P value < 0.05 was considered statistically significant.
Results
Two study group participants were similar in terms of baseline characteristics like age and sex, ASA status, and the size of ETT used [Table 1]. The post-operative patients with the type of surgery performed are shown in Figure 4. A majority of the patients are a post-operative case of carcinoma tongue (33 out of 60) and carcinoma buccal mucosa (19 out of 60), followed by maxillectomy, surgery for carcinoma alveolus, and carcinoma retromolar trigone. The duration of the humidifier use was 579 ± 102 min in the HH group compared to 573 ± 125 min in the mist nebulizer group. The difference in the reduction of ETT volume between the two groups was statistically significant (P-value 0.00026), the median percentage reduction in the HH group was 6.7%, and that in the mist nebulizer group was 12.25%. The mean temperature of the inspired gas at Y-piece was lower in the mist nebulizer group (24.24 ± 0.87) than the HH group (28.66 ± 1.78), which was statistically significant (P-value < 0.0001). Thick and dry secretions were more prevalent in the patients of the mist nebulizer group compared to the HH group. The mean frequency of refilling of the humidifier chamber in the mist nebulizer group was 3.5 times per patient; however, the humidifier chamber of the HH group did not require any refilling once filled with sterile water [Table 2]. None of the patients in either group required any additional suctioning.
Table 1.
Baseline characteristics
| Heated humidifier | Mist nebulizer | |
|---|---|---|
| Number of patients | 30 | 30 |
| Age of patients in years (Mean±SD) | 48.57±10.34 | 50.60±11.60 |
| Male/Female (n) | 22/8 | 21/9 |
| ASA 1 patients, n (%) | 20 (66.67%) | 17 (56.67%) |
| ASA 2 patients, n (%) | 10 (33.37%) | 13 (43.37%) |
| Patients with ETT No. 7, n (%) | 8 (26.67%) | 12 (40%) |
| Patients with ETT No. 7.5, n (%) | 22 (73.33%) | 18 (60%) |
Figure 4.
Types of surgeries performed in the two groups
Table 2.
Comparison of outcome variables
| Outcome variables | Heated humidifier | Mist nebulizer | P |
|---|---|---|---|
| Percentage reduction of ETT volume (median) | 6.7 | 12.25 | 0.00026 |
| Mean temperature of inspired gas at Y-piece±SD (°C) | 28.66±1.78 | 24.24±0.87 | <0.0001 |
| Mean duration of use of humidifiers±SD (min) | 579±102 | 573±125 | 0.84 |
| Frequency of refilling of humidifier chamber (times/patient) | 0 | 3.5 | |
| Patients with thick secretions n (%) | 20 (66.7%) | 27 (90%) | 0.057 |
| Patients with dry secretions, n (%) | 11 (36.7%) | 25 (83.3%) | 0.0005 |
Discussion
To overcome the ill effects of inspiring dry and un-humidified gas, different types of humidifiers are available for humidification in the intubated and mechanically ventilated patients. In our institute, the head and neck malignancy patients constitute more than 40% of the surgical workload. Such patients require airway protection for a longer period as the bulky flaps used for reconstruction reduce the patency of the upper airway and also prevent coughing. So, it becomes necessary to keep such patients intubated overnight.
In such intubated and spontaneously breathing patients, a mist nebulizer (a type of active humidifier) is commonly used because of its low cost, ease of use, no requirement of electricity, and lightweight. But it has a small chamber of 6 mL capacity which gets emptied soon. Large-volume mist nebulizers (capacity 200–240 mL) are not freely available in our country and are also not a good choice as they are bulky. HH, a type of electrically run active humidifier has the advantage of providing continuous warm and humidified gas. Heat and moisture exchanger (HME) filter is a passive humidifier, which collects the heat and moisture of the patient’s expired air and returns the same during the next inspiration. In the post-operative period, blood and mucus coughed out by such patients may block the HME filter and increase the airflow resistance and work of breathing and so it is not used for this purpose. On literature search, there are studies comparing various other types of humidifiers but no literature has been found comparing HH with the mist nebulizer.
In our study, a decrease in the ETT patency was more in the mist nebulizer group compared to the HH group (P-value 0.00026). Jaber et al. found in their study that progressive reduction in ETT patency was more in the HME group compared to the HH group. And the study was conducted on the patients who were ventilated for more than 48 h.[3]
The reduction in the ETT patency increases the airflow resistance. Jaber et al. also found that the reduction in the ETT patency in the HME group, compared to the HH group, was associated with a reciprocal increase in the ETT resistance. They measured the volume of ETT by using the “acoustic reflection” method and calculated airflow resistance by applying the “Blasius formula.”[5] In some instances, the increase in airway resistance may necessitate a change of ETT. There are case reports where patients developed cardiac arrests due to blocked tubes.[6] In our study, none of the patients in any group required a change of tube. Doyle et al.[7] reported a 5.7% incidence of ETT occlusion in the HME group compared to no occlusion in the HH group in their study. The patients who were intubated for more than 24 h were only included in their study. Thus, both the studies indicated HH as a better alternative in terms of ETT blockade and airway resistance.
We also looked at the temperature of the inspired gas at Y-piece as an indirect marker of the adequacy of humidification in our study and found that the temperature in the HH group was more compared to the mist nebulizer group which was statistically significant. However, the mean temperature of the inspired gas measured at the Y-piece in the HH group (28.65°C) was lesser than the temperature that was set at the heater plate (32°C). This difference in the temperature of the heater plate and Y-piece (~4°C) could be the result of heat dissipation based on ambient temperature. Davies et al.[8] found in their study that the magnitude of the temperature difference could be related to the length of the inspiratory tube exposed to ambient temperature.
The ambient temperature of our recovery room is maintained at around 21–22°C and the whole length of the inspiratory limb used in the HH group was exposed to this ambient temperature. Decreasing the inspiratory limb length or setting the heater plate temperature to 36°C may help reduce this temperature drop. However, Solomita et al.[9] found in their study that maintaining the temperature at one point in the inspiratory circuit does not ensure adequate water vapor delivery.
We found a higher incidence of thick and dry secretions in the mist nebulizer group in comparison to the HH group suggesting inadequate humidification, as the unconditioned dry gas reaching the lower respiratory tract drew moisture from the mucus and made them dry and thick. Similarly, Misset et al.[10] found HH to be superior to HME in terms of the characteristics of tracheal secretion and ETT occlusion.
In our study, the mean frequency of refilling was 3.5 times per patient in the mist nebulizer group compared to no refilling in the HH group. The mist nebulizer chamber with a capacity of 6 mL gets emptied at the end of 45 min on the O2 flow rate of 5 L/min. Since the mean duration of the use of mist nebulizer was 573 min, the mean frequency of refilling should have been 12.7 times per patient to provide continuous humidification. So, it implies that in the mist nebulizer group, with a mean frequency of refilling of 3.5 times per patient, the chamber was empty for a mean duration of 370.5 min (which is 64.66% of the mean duration of humidifier use in the mist nebulizer group). This interruption in the continuous supply of humidified gas made the secretions thick and dry, and thus, causing more reduction of ETT patency in the mist nebulizer group compared to the HH group.
Inadequate refilling of the mist nebulizer chamber could be the result of increased workload on the nursing staff in a busy recovery room. The humidifier chamber of HH with a capacity of 300 mL gets emptied at the end of ~ 12 h on the O2 flow rate of 5 L/min thus requiring no refilling in any of the patients in the HH group.
Single-centric trial and the small sample size is the limitation of our study. Future multicentric trials involving a larger number of subjects may be done to justify our present findings.
It may be concluded that the use of HH in overnight intubated and spontaneously ventilated patients is associated with a decreased incidence of unwanted reduction in the ETT patency by thick and dry secretions compared to the mist nebulizer. HH may be a reliable choice to provide continuous humidification which will also decrease the workload on the nursing staff.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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