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 Table of Contents  
Year : 2022  |  Volume : 5  |  Issue : 1  |  Page : 13-18

Changes in modified Mallampati class in patients undergoing percutaneous nephrolithotomy in prone position – A prospective observational study

1 Department of Anesthesia, AIIMS, Rishikesh, Uttarakhand, India
2 Department of Anesthesia, SGPGIMS, Lucknow, Uttar Pradesh, India

Date of Submission24-Jul-2021
Date of Decision02-Nov-2021
Date of Acceptance02-Nov-2021
Date of Web Publication17-Jan-2022

Correspondence Address:
Dr. Priyanka Mishra
Department of Anesthesia, AIIMS, Rishikesh, Uttarakhand
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/arwy.arwy_43_21

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Objective: Assessment and evaluation of changes in modified Mallampati class (MMC) in patients undergoing percutaneous nephrolithotomy (PCNL) in the prone position. Patients and Methods: Seventy-one patients undergoing PCNL in prone position who satisfied inclusion criteria were studied and their MMC was assessed preoperatively. The MMC was assessed immediately after surgery and 6 h, 12 h and 24 h postoperatively. The number of attempts for successful intubation, duration of surgery, the quantity of intraoperative fluids and irrigation fluids used, and blood loss was recorded to identify any significant correlation with changes in MMC. Results: MMC changed in 17 patients (23.9%) with the grade increasing by one in all the patients. Among the 17 patients who showed a change in MMC, 8 patients returned to baseline within 6 h, 6 patients at 12 h and the remaining 3 patients at 24 h. Conclusion: MMC worsened by one grade in almost one-quarter of the patients undergoing PCNL in the prone position. This change in MMC had no clinically significant correlation with the number of attempts for successful intubation, duration of surgery, quantity of intraoperative fluids and irrigation fluids used, and blood loss.

Keywords: Airway changes, modified Mallampati class, percutaneous nephrolithotomy, prone position

How to cite this article:
Mishra P, Gupta B, Chandra P, Kumar A. Changes in modified Mallampati class in patients undergoing percutaneous nephrolithotomy in prone position – A prospective observational study. Airway 2022;5:13-8

How to cite this URL:
Mishra P, Gupta B, Chandra P, Kumar A. Changes in modified Mallampati class in patients undergoing percutaneous nephrolithotomy in prone position – A prospective observational study. Airway [serial online] 2022 [cited 2023 May 30];5:13-8. Available from: https://www.arwy.org/text.asp?2022/5/1/13/335892

  Introduction Top

Although the practice of anaesthesia has improved drastically in recent decades, postoperative airway complications still prove a significant challenge.[1] A difficult reintubation after tracheal extubation is challenging and associated with significant morbidity and mortality. Reintubation rates in the postoperative period following elective procedures range from 0.17% to 0.45%.[2],[3] Literature reveals that postoperative airway compromise further increases the incidence of tracheostomy, prolonged hospital or intensive care unit stay, financial burden and mortality.[4] Percutaneous nephrolithotomy (PCNL) is performed in the prone position. Patient position, including prone or prolonged Trendelenburg positions, has been described by the Difficult Airway Society (UK) to be a contributor to airway oedema.[5] In addition, major fluid shifts, surgical duration, prolonged positive pressure ventilation and anaphylaxis can also result in facial and airway oedema. Airway oedema is the most critical cause of extubation failure, postextubation airway catastrophes and subsequent need for reintubation in the postanaesthesia care unit. Patients may show less favourable airway conditions than their preoperative state following surgery in the prone position. The risk of these postoperative changes in the airway increases further in children, elderly, obese and those with preexisting difficult airways. Although airway-related changes are reported during head and neck surgery (e.g., carotid surgery, thyroid surgery), the intraoperative airway changes due to surgery, the underlying condition or the position are less well assessed. Till date, there are very few studies evaluating airway changes and the degree of change during surgeries in the prone position.

Studies have evaluated airway changes by assessing the worsening of modified Mallampati class (MMC). However, these studies did not evaluate any possible correlation of such changes with airway parameters and intraoperative variables.[5],[6],[7] Airway changes in surgical patients in the prone position were evaluated using MMC based on the hypothesis that prone positioning could cause definable airway oedema. In addition, the duration of surgery and the amount of intravenous fluid administered during surgery were documented as covariates.

The objectives of our study included (a) an assessment of the airway changes in prone position evaluated along a 4-point MMC; (b) exploration of various factors responsible for this change and (c) the time taken for the observed changes to return to the preoperative status.

  Patients and Methods Top

Study design

This prospective observational study was approved by the Institutional Ethical Committee and was registered prospectively on 20 January 2020 at the Clinical Trials Registry-India (CTRI/2020/01/022869). The observational study design followed the STROBE guidelines [Figure 1]. We planned to conduct the study for 6 months but had to extend it to 1 year due to the decrease in the number of cases during the COVID pandemic. After obtaining written informed consent, we included 72 patients aged between 18 and 65 years, weighing 40–80 kg, and belonging to the American Society of Anesthesiologists (ASA) Physical Status I or II. Our study excluded patients with a history of difficult mask ventilation or intubation, inability to open the mouth for performing airway assessment, MMC 4, pregnant patients and those who refused to participate.
Figure 1: STROBE diagram detailing patient flow

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Before surgery, the airway was evaluated using Samsoon and Young's modification of Mallampati class.[8] Evaluation of MMC was done in the semi-upright posture with the head in the neutral position, mouth opened as wide as possible and tongue protruded without phonation. This evaluation was done at 5-time points: Preoperatively (taken as baseline), immediately after surgery, and at 6, 12 and 24 h postoperatively. To eliminate any bias due to position and pain in the postoperative period, all assessments were done with head end of the patient's bed raised to 45° position and the observer's eye at the level of the patient's mouth. The preoperative and postoperative assessments were done independently by two senior anaesthesiologists and no difference was found in their respective evaluations. All subjects received general anaesthesia with monitors including electrocardiography, noninvasive blood pressure, pulse oximeter and end-tidal carbon dioxide. The number of attempts for successful intubation, duration of surgery, quantity of intraoperative fluids and irrigation fluids used, and blood loss was also monitored. Ringer lactate was used as intraoperative fluid replacement in all patients.

The primary outcome was to evaluate any changes in MMC in patients undergoing PCNL in the prone position. Secondary outcomes included the degree of change in MMC, the duration taken for the change to revert to preoperative level and the possible association of various factors with changes in MMC.

A sample size of 71 was determined based on the possible interobserver variability in determining MMC, accompanied by the need of a mean MMC grade change by one grade. We adopted sigma of 1.5 and standard values of 0.05 for alpha error and 0.8 for power. Marginal homogeneity measures were used to equate baseline and postsurgical MMC.

  Results Top

We included 72 patients in our study out of which 1 patient was excluded due to the airway being classified as MMC 4. The demographic data and airway parameters of the patients analysed are shown in [Table 1]. The surgical variables are summarised in [Table 2]. The preoperative baseline MMC was grade 1 in 29 patients, grade 2 in 30 and grade 3 in 12 patients. A change in postoperative MMC was observed in 17 of the 71 patients (23.9%) who completed the study, with the MMC increasing by one grade in all patients. The details of preoperative and postoperative MMC are summarised in [Table 3]. We also assessed the time required for MMC to revert to preoperative status following PCNL in the prone position. Among the 17 patients who showed a change in MMC, 8 patients (47.1%) returned to baseline within 6 h, 6 patients (35.3%) at 12 h and the remaining 3 patients (17.6%) at 24 h. At the 24-h assessment, changes in MMC had reverted to the preoperative state in all 17 patients.
Table 1: Demographics and airway parameters of study patients

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Table 2: Surgical variables

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Table 3: Change of modified Mallampati class in 17 patients

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The volume of intravenous fluids used as well as surgical duration was marginally higher in patients who showed a change in MMC but the difference was neither statistically nor clinically significant [Table 2]. The volume of irrigation fluid used was clinically higher in the patients who developed a change in MMC but the change was not statistically significant. Successful intubation was done in the first attempt in 97.2% of patients. Variables such as body mass index, and airway parameters including thyromental distance, sternomental distance or neck circumference showed no significant association with change in MMC. Complications including hoarseness of voice, sore throat and lip oedema were seen in 3 patients. In our study, no blood transfusion was required for any patient.

  Discussion Top

Oropharyngeal swelling, due to macroglossia, sublingual haematoma and salivary gland inflammation, is a complication that can occur during prolonged surgery in the prone position, especially if the head and neck position is non-neutral. When the neck is fully flexed, kinking and stretching of the salivary ducts, blood vessels and lymphatics can cause congestion and, if persistent, can result in swelling of local structures.[9],[10],[11],[12] These airway changes may exacerbate postoperative complications such as the need for prolonged intubation or reintubation in the recovery period. Among other factors, head and neck surgery, cardiothoracic and airway surgery, emergencies, surgical period > 3 h, preoperative hypoalbuminaemia, renal insufficiency and ASA physical status III are all associated with these complications.[13]

When used correctly, evaluation of the MMC is a simple, repeatable and accurate preanaesthetic airway assessment tool for predicting difficult tracheal intubation. Mallampati et al. created three classes based on the visualisation of faucial pillars, soft palate, and uvula, and compared them with the laryngoscopic view based on the corniculate cartilages, anterior and posterior commissures.[14] In a meta-analysis involving over 34,000 patients, Lee et al. found that MMC was 0.55 sensitive and 0.85 specific in anticipating a difficult laryngoscopy and 0.76 sensitive and 0.77 specific in deciding difficult intubation.[15] Because of its simplicity, relative precision and reproducibility, we chose MMC as an indicator of difficult airway in our study. As per available literature, these changes last well into the postoperative period, with the MMC returning to baseline in the majority of patients within 48 h. The duration of surgery, the amount of intravenous fluids and irrigation fluids used, and blood loss can affect MMC. Since it necessitates the use of significant volumes of irrigation fluids, we chose PCNL procedure for assessing airway changes in the prone position. Since fluid overload can exacerbate airway oedema, we hypothesised that the amount of intraoperative intravenous fluids, as well as the volume of irrigation fluids used during PCNL surgery, may be factors influencing airway oedema and worsening of MMC.

Extravasation of fluid during PCNL may result in systemic absorption of irrigant fluid due to breaches of the renal pelvicalyceal walls and through vessels that open up during tract dilatation. Another route for significant and rapid fluid absorption is through fluid leakage into the peritoneal space. Increased intrapelvic pressure can also induce absorption, which can lead to pyelovenous-lymphatic backflow and pyelotubular backflow.[16],[17] There are various factors that may trigger a change in fluid equilibrium including a) free water redistribution into the dependent interstitial compartments;[18] b) impeded venous drainage from the face; c) secretion of arginine vasopressin that favours free water reabsorption; and d) increased vascular permeability due to the release of inflammatory cytokines as a result of surgical tumescence.[19],[20],[21] Patients undergoing PCNL showed significant fluid absorption with the use of more than 9 L of irrigation fluid.[22] Though MMC changed in 23.9% of the patients in our study, the volume of irrigation fluid used showed no significant correlation with changes in MMC. This is similar to the study by Teo et al. which evaluated airway changes following spine surgery in the prone position. They discovered a major difference in MMC scores before and after surgery. There was a total of 78% of patients who had an increase in MMC (71% of these had a change of one grade, 24% by two grades and 5% by three grades). However, like in our study, they found no correlation between MMC and the amount of intraoperative fluid used or the length of surgery.[7] We also looked at the relationship between airway measurements such as neck circumference, thyromental distance and sternomental distance and found no clinical correlation. Padhy et al. found that MMC worsened in 88% of patients undergoing PCNL surgery in the prone position. The duration of surgery in their study was 120.6 ± 22.83 min (calculated for all 75 patients who were included), which is longer than mean duration in our study for all the 71 patients (102.62 ± 34.99 min). We found that MMC returns to preoperative status in 24 h as contrasted to 48 h reported by Padhy et al.[6] This may be explained by the fact that many patients in their study had a change in MMC by 2 grades, with a possible longer time to return to preoperative status than in our study where the change in MMC observed was only by 1 grade. In contrast to previous research, we have also shown that MMC changes by 1 grade in a smaller number of patients.

Padhy et al. and Teo et al. have shown a larger number of patients demonstrating increase in MMC grade postoperatively. However, no correlation was found between quantity of intravenous fluids administered and the worsening of MMC. We also did not find any significant correlation between the quantity of intravenous fluids administered and the change in MMC. More research is warranted to evaluate the relationship between the amount of intravenous fluids used and the occurrence of airway oedema or worsening of MMC.

We also investigated any possible correlation between the number of attempts for successful intubation and the postoperative airway changes. This aspect has not been assessed in any of the previous studies.[6],[7] Currently available literature has established that an increase in the number of attempts for intubation directly correlates with an increase in airway-related complications including airway oedema.[23],[24] The comparatively lesser proportion of patients showing the change in MMC in our study compared to others can also be explained by the fact that the majority of our patients (97.2%) were intubated at the first attempt. As this criterion has not been documented by other investigators, further research needs to be done to explore the correlation between the number of attempts for successful intubation and its effect on postoperative MMC grades.

The change in MMC did not show any statistical significance when compared with the amount of irrigation fluid used (P = 0.072). Extravasation of fluid because of perforation of the collecting system during PCNL can lead to systemic fluid absorption through the vessels which open up during tract dilatation. Although the irrigation fluid used in patients showing a change in MMC in our study (25.06 ± 15.96 L) was clinically greater than those showing no change (17.11 ± 9.05 L), it was not statistically significant.

The significance of our study lies in its importance to clinical practice. Patients undergoing surgery in prone position and requiring reintubation in the immediate postoperative period are more likely to present with worsened airway conditions than their preoperative status. Our study also looked at various factors and their association to airway changes occurring in prone position which could further guide our anaesthetic practice in anticipating and managing postoperative consequences. Airway catastrophes, particularly postextubation, can be caused by a variety of factors, including changes occurring during the perioperative period. MMC can worsen dramatically from the baseline during surgery in the prone position. This does not appear to be related to the duration of surgery or the amount of intravenous fluid received. Even though the cause of change of MMC grade is unclear, extra caution should be exercised when extubating a patient at the end of surgery performed in the prone position, regardless of the duration of the surgery or the volume of fluid infused. Patients who need reintubation shortly after surgery in the prone position may have less favourable airway conditions than were present before surgery. More research is needed for better evaluation of the airway status in patients who require reintubation and the time course of airway changes following prone surgery.

Our study has the limitation that an element of observer bias could have been introduced in airway assessment. Despite the deterioration in MMC grades due to oropharyngeal oedema, none of our patients presented with difficulty in extubation or needed reintubation.

  Conclusion Top

Our study suggests that PCNL done in the prone position is associated with postoperative changes in MMC grades. Such changes do not correlate with the amount of irrigation fluids, intravenous fluids or duration of surgery. Airway changes (such as a worsening of MMC) return to baseline within 24 h in all patients. We believe that further large group studies and a probable meta-analysis need to be performed on this topic to conclusively establish the relationship of various factors with change in MMC grades following surgeries in the prone position.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1]

  [Table 1], [Table 2], [Table 3]


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