ABSTRACT
Background:
Overinflation of cuffed endotracheal tubes and transesophageal echocardiography (TEE) probe causes increased intracuff pressure (CP) compromising tracheal perfusion pressure (TPP). Primary objective of the study was to assess CP, TPP on TEE probe insertion and examination during pediatric cardiac surgeries. Secondary objectives were to evaluate the effect of the probe on peak airway pressures (Ppeak), mean airway pressures (Pmean) and to monitor CP, TPP on cardiopulmonary bypass (CPB).
Materials and Methods:
This prospective observational study included fifty patients, aged 1–5 years undergoing cardiac surgeries using CPB. Following induction, TEE probe was introduced. CP, TPP, Ppeak, Pmean were measured before insertion of TEE probe (T1), during probe insertion (T2) and examination at mid-esophageal (T3), transgastric level (T4), and on removing probe (T6). CP, TPP were monitored on CPB (T5). Statistical analysis was done using paired t-test.
Results:
CP, Ppeak and Pmean increased significantly, while TPP decreased significantly from T1 to T2, T3, T4 (P < 0.001). CP, TPP decreased significantly at T5 in comparison to T6 (P < 0.001). In 48% of the patients CP increased above 30 cm H2O at T2.
Conclusion:
TEE probe causes an increase in CP and decreases TPP. Constant monitoring and maintaining CP, TPP in optimum range is recommended.
Keywords: Cuff pressure, endotracheal tube, tracheal perfusion, transesophageal echocardiography
INTRODUCTION
Cuffed endotracheal tubes (cETTs), owing to their improved cuff design and tracheal sealing characteristics, have been increasingly used in pediatric patients including infants and neonates.[1-3] Despite the advantages of cETTs, overinflation of the cuff for a prolonged duration can hamper tracheal perfusion, resulting in tracheal mucosal ischemia and damage to the airway.[4,5] Instantaneous measurement of intracuff pressure (CP) following endotracheal intubation can be done, but CP is a dynamic process during the intraoperative period in pediatric patients undergoing cardiac surgery on cardiopulmonary bypass (CPB) and is affected by various factors like head and neck position, body temperature, and composition of inhaled gases.[6] Tracheal perfusion pressure (TPP) is the difference between mean arterial pressure (MAP) and CP.[6] The changes in hemodynamics and CP affect TPP.[6] Intraoperative hemodynamic instability, excessive CP, and non-pulsatile low perfusion flow on CPB can make these patients prone to airway complications like subglottic edema, stridor, or tracheal stenosis.[7,8]
Transesophageal echocardiography (TEE) has become a standard perioperative diagnostic tool during pediatric cardiac surgeries. TEE probe is placed following induction and endotracheal intubation. Posterior membranous aspect of the trachea is in contact with the esophagus which can lead to compression of the cuff, causing increased CP and reducing TPP.[9] Studies in adults show increased CP following TEE probe placement; however, there are limited studies in pediatric population.[10-13]
The smaller size of pediatric airway in relation to the size of TEE probe can cause airway compression despite proper probe selection. Airways in pediatric patients are more readily compressible than in adults because of the greater pliability of their tracheal and bronchial cartilages and can result in an increase in airway pressures.[14]
Thus, the primary objective of our study was to assess CP and TPP on TEE probe insertion and examination during pediatric cardiac surgeries on CPB. Secondary objectives were to evaluate the effect of the probe on ventilatory parameters like peak airway pressure (Ppeak), and mean airway pressures (Pmean) and also to monitor changes in CP and TPP during CPB.
MATERIAL AND METHODS
This was a prospective observational study, conducted at a single tertiary care center, after obtaining approval from the institute’s ethical committee (EC/Approval/14/C.Anae/13/06/2022) and informed consent from the guardians of the patients. The study is registered with the Clinical Trial Registry of India (CTRI/2022/12/048251) and included fifty pediatric patients, aged 1–5 years weighing more than 5 kg undergoing cardiac surgeries on CPB during a period from September 2022 to December 2022. Patients with pre-existing tracheal or esophageal pathology were excluded from the study.
General anesthesia was administered under standard American Society of Anesthesiologists monitoring guidelines. Induction of anesthesia was done with inj. midazolam 0.1 mg/kg, inj. ketamine 1 mg/kg, inj. fentanyl 5 mcg/kg, and inj vecuronium 0.1 mg/kg intravenously. After anesthesia induction, the airway was secured with an appropriate-sized cETT (Avanos Microcuff ETT, Avanos Medical Inc, Alpharetta, GA, USA). The cuff of ETT was slowly inflated using air leak technique, by keeping the stethoscope over the suprasternal notch, along with slow inflation of the cuff, until no air leak was audible while applying continuous positive airway pressure (CPAP) of 20 cm H2O with head and neck in the neutral position. Following inflation of the cuff, CP was continuously monitored using a validated technique.[15,16] For this purpose, transducers for standard invasive pressure monitoring for intra-arterial or central venous pressure were used. Transducer was tightly attached to the pilot balloon of cETT to prevent any air leak [Figure 1]. Measurements were taken after zeroing the transducer to air. Usually, the apparatus used for measuring CP, does not require leveling as it is containing air. However, we kept it at the level of trachea and fixed it at the shoulder. Volume control mode of mechanical ventilation was used with a tidal volume of 6–8 ml/kg of predicted body weight and positive end-expiratory pressure (PEEP) of 4 cm H2O. End-tidal carbon dioxide (EtCO2) of 30–32 mm Hg was targeted by adjusting the respiratory rate. Air-oxygen mixture with sevoflurane was used with an inspired oxygen fraction of 0.5 and an inspiratory/expiratory ratio of 1:2. Changes in peak and mean airway pressures were recorded in various stages.
Figure 1.
(a) Device used to monitor continuous CP (b) Baseline CP before insertion of TEE probe (c) CP during the TEE examination at ME level
The TEE probe (9T-RS GE Vingmed Ultrasound AS, Horten, Norway) was inserted without causing any trauma in the oral cavity of each patient and by applying a jaw-thrust maneuver for a brief duration. CP, MAP and TPP were measured before insertion of TEE probe (T1), during TEE probe insertion (T2), while examining at mid-esophageal (ME) level (T3), transgastric (TG) level (T4), on CPB at point of maximum hypothermia (T5) and while removing the probe (T6). Cuff pressure readings obtained in mm Hg were converted to cm H2O (1 mm Hg = 1.36 cm H2O). TPP was measured by subtracting CP from MAP in mmHg at T1, T2, T3, T4, and T6. Changes in CP were noted and it was optimized between 20 and 25 cm H2O after T4. Ppeak and Pmean were monitored at T1, T2, T3, T4, and T6. No incident of accidental extubation were observed during TEE examination.
Statistical analysis
Statistical analysis was carried out using SPSS version 20.0 software (SPSS Inc, USA). Continuous variables with normal distribution were summarized as means and standard deviation. Statistical analysis was done by comparing CP and TPP at T1 to T2, T3, and T4 via paired t-tests and by comparing Ppeak and Pmean at T1 to T2, T3, T4, and T6 by paired t-tests. T5 and T6 were compared using paired t-tests. A P- value <0.05 was considered significant.
Sample size calculation
The sample size for the study was based on a pilot study of 6 patients conducted in our institute, in which CP was measured at six different time zones from T1 to T6. The mean CP and SD at baseline (T1) and during TEE interrogation at TG level (T4), were used in sample size calculation.
The sample size required in each arm of the study was calculated according to the formula given by Snedecor and Cochran:[17]
Sample size=[2+(Zα + Z 1-β)2 × σ2 ]÷ δ2
Thus, assuming 99% power and 95% confidence interval, the minimum calculated sample size was 30.
RESULTS
This study included 50 patients, ranging in age from 1 year to 5 years and with weight ranging from 5.1 kg to 23.6 kg (11.28 ± 4.92). Demographic data have been mentioned in Table 1. CP, MAP and TPP at T1, T2, T3, T4, T5, and T6 were measured [Table 2 and Figure 2a]. There was a statistically significant increase in CP from T1 to T2, T3, and T4 (P < 0.001), while there was a significant decrease at T5 in comparison to T6. There was a statistically significant decrease in TPP from T1 to T2, T3, and T4 (P < 0.001). There was a statistically significant difference in MAP between T5 and T6 (P < 0.001), and no statistically significant difference in MAP between T1 and the rest of the time points. There was a statistically significant increase in Ppeak and Pmean from T1 to T2, T3, and T4 (P < 0.001), while at T6, there was no significant difference in comparison to T1 [Table 3 and Figure 2b]. In 24 (48%), 18 (36%), and 16 (32%) patients at T2, T3, and T4 respectively, CP increased to more than 30 cm H2O. The magnitude of CP increase among various age groups at different time points has been shown in Table 4.
Table 1.
Demographic characteristics of patients
| Variable | Values |
|---|---|
| Age (Months) | 36.96±19.05 |
| Weight (Kg) | 11.283±4.92 |
| Gender (n) | Males=32 (64%) |
| Females=18 (36%) | |
| Body Surface Area (m2) | 0.488±0.19 |
| Surgery | VSD closure=20 (40%) |
| ICR=18 (36%) | |
| SAM resection=4 (8%) | |
| ASD + VSD | |
| closure=5 (10%) | |
| AVCD repair=3 (6%) | |
| ETT size (mm) [Number] | 4.0[19] |
| 4.5[18] | |
| 5.0[7] | |
| 5.5 [6] | |
| CPB duration (min) | 72.43±19.12 |
| Lowest temperature on CPB (°C) | 32.42±1.51 |
VSD=Ventricular septal defect, ICR=Intracardiac repair, SAM=Subaortic membrane, ASD=Atrial septal defect, AVCD=Atrioventricular canal defect, ETT=Endotracheal tube. Data presented as mean±SD and numbers
Table 2.
CP, MAP and TPP before and after insertion of TEE probe
| T1 (Baseline) | T2 (During insertion of TEE probe) | T3 (During TEE examination at ME level) | T4 (During TEE interrogation at TG level) | T5 (on CPB) | T6 (After TEE probe removal) | P (Paired t-test) | ||||
|---|---|---|---|---|---|---|---|---|---|---|
|
| ||||||||||
| T1 vs T2 | T1 vs T3 | T1 vs T4 | T5 vs T6 | |||||||
| CP | 22.98±2.22 | 33.16±10.57 | 30.19±8.36 | 29.81±8.15 | 15.8±3.07 | 21.95±3.49 | <0.001 | <0.001 | <0.001 | <0.001 |
| MAP | 64.54±9.76 | 64.28±10.19 | 63.68±8.62 | 61.48±7.32 | 42.86±6.67 | 61.16±7.51 | 0.691 | 0.454 | 0.077 | <0.001 |
| TPP | 47.64±9.78 | 39.9±13.01 | 41.49±8.2 | 39.56±9.19 | 31.24±7.09 | 44.78±7.23 | <0.001 | <0.001 | <0.001 | <0.001 |
TEE=Transesophageal echocardiography, CP=Intracuff pressure, MAP=Mean arterial pressure, TPP=Tracheal perfusion pressure. Data shown as mean±SD. CP in cm H2O, MAP and TPP in mm Hg
Figure 2.
(a) Graphical representation of CP, MAP, and TPP (b) Graphical representation of Ppeak and Pmean
Table 3.
Peak and mean airway pressures before and after insertion of TEE probe
| T1 (Baseline) | T2 (During insertion of TEE probe) | T3 (During TEE examination at ME level) | T4 (During TEE interrogation at TG level) | T6 (After TEE probe removal) | P (Paired t-test) | ||||
|---|---|---|---|---|---|---|---|---|---|
|
| |||||||||
| T1 vs T2 | T1 vs T3 | T1 vs T4 | T1 vs T6 | ||||||
| P peak | 11.94±2.11 | 13.02±2.6 | 12.92±2.46 | 12.74±2.38 | 11.64±2.15 | <0.001 | <0.001 | <0.001 | 0.482 |
| P mean | 5.9±1.5 | 6.66±1.36 | 6.52±1.26 | 6.54±1.31 | 6.06±1.4 | <0.001 | <0.001 | <0.001 | 0.298 |
Ppeak=Peak airway pressure, Pmean=Mean airway pressure. Data shown as mean±SD. Values shown in cm H2O
Table 4.
Magnitude of CP increase across the age groups
| Age group | Number of patients with CP >30 cm H2O during TEE probe insertion | Difference of CP between baseline and during TEE Probe Insertion (cm H2O) | Difference of CP between baseline and during TEE probe interrogation at ME level (cm H2O) | Difference of CP between baseline and during TEE probe interrogation at TG level (cm H2O) |
|---|---|---|---|---|
| 1–2 years | 11 (64.7%)* | 10.35 | 7.35 | 6.96 |
| 2–3 years | 06 (60%)* | 10.25 | 7.30 | 6.85 |
| 3–4 years | 01 (11.1%)* | 9.10 | 6.57 | 6.23 |
| 4–5 years | 06 (42.8%)* | 9 | 6.72 | 6.24 |
*Percentage of patients with CP >30 cm H2O during TEE probe insertion in the above mentioned age groups
DISCUSSION
Pediatric patients with congenital heart disease (CHD) are prone to the development of airway complications due to the anomalous relationships between the cardiovascular system and the tracheobronchial tree.[7] High CP of ETT can result in complications like sore throat, hoarseness, tracheal stenosis, and even rupture.[18] Mossad et al.[8] reported that younger age and prolonged postoperative ventilation are significant risk factors for subglottic stenosis.
There was a significant increase in CP on TEE insertion and interrogation at ME and TG levels, while TPP decreased significantly from baseline in our study. Kamata et al.[13] observed a significant increase in CP during the insertion of the TEE probe, in a study conducted on 80 pediatric patients, aged 6 days to 18.4 years, a finding, similar to our study. But CP returned to baseline when the probe was advanced into the stomach, while we observed significantly higher CP at T4 (at TG level) in comparison to baseline CP at T1. TPP measurement was not done in their study.
An increase in CP has also been observed following TEE probe placement in studies done in adult patients. In a study done by Tan et al.,[19] 28 adult patients underwent cardiac surgery. CP was measured 1 min after TEE probe insertion and baseline CP was adjusted to 25–30 cm H2O using a manometer. CP increased significantly from 27.7 to 36.2 cm H2O and in 45% of the patients, it was more than 35 cm H2O. In our study, CP increased to more than 30 cm H2O in 48% of patients during TEE probe insertion and 36% of patients during TEE interrogation at the ME level. Kim et al.[10] and Borde et al.[11] reported similar findings in their study.
Maddali et al.[20] similarly reported a significant increase in CP on TEE probe insertion and examination at ME and TG levels in comparison to baseline CP, in a study conducted on 34 adult patients undergoing cardiac surgery. They also reported a significant increase in peak airway pressure on TEE probe insertion and interrogation at ME and TG levels. We also observed an increase in peak and mean airway pressures at T2, T3, T4 in comparison to the baseline at T1.
Compression of the membranous trachea by TEE probe in pediatric patients can increase airway pressures.[1] We observed an increase in peak and mean airway pressure on TEE probe insertion and examination.
In a study on 27 patients, aged 1 month to 15.3 years by Kako et al.[6] CP decreased significantly from baseline with the onset of CPB and hypothermia. With rewarming, CP increased backward toward the baseline. While TPP did not decrease significantly during the institution of CPB, due to a decrease in CP despite MAP reduction during hypothermic CPB. In the current study, CP was allowed to increase without any intervention until the TEE examination was completed, to observe the range to which CP may rise during TEE interrogation. But after the TEE examination was completed, CP was optimized in patients where it exceeded 30 cm H2O. Then, we observed the changes in CP and TPP on CPB. CP, MAP, and TPP decreased significantly in hypothermic CPB in our study.
Non-pulsatile flow and MAP lower than patient’s baseline MAP may compromise tracheal mucosal perfusion on CPB. Hemodilution, lower plasma oncotic pressure and inflammatory response can lead to tracheal mucosal edema, which can compromise effective tracheal mucosal perfusion. Inada et al.[21] reported a decrease in CP on hypothermic CPB in adult patients undergoing cardiac surgery. Similarly, we observed a decrease in CP on CPB in our study, which could help maintain TPP during low MAP on CPB, but lower CP may have a risk of silent aspiration. Souza Neto et al.,[22] compared the CPs in adult patients subjected to normothermic and hypothermic CPB and found that the CP was lower in patients undergoing hypothermic CPB. Kako H et al.[6] monitored the CP continuously in infants and children subjected to CPB during surgery for CHD and found a significant decrease which coincided with the onset and progression of hypothermia. Alteration in the temperature would affect the volume of air in closed spaces, for example, cuff air and can lead to changes in cuff pressure. The effect of change in the volume of air within the cuff with the temperature change would likely explain the decrease in CP observed during the CPB in our study. Pan et al.[12] in a study conducted on 58 patients, of all age groups including 22 infants, reported a significant increase in CP while TEE probe insertion and CP remained elevated even when the probe tip advanced into the stomach, a finding similar to our study. They, however, observed that the magnitude of the increase in CP was significantly smaller for infants when compared with the increase in CP for adolescents and adults. Their study reported postoperative extubation failure in five patients (9%) and all of them were infants (25% of infants). TPP did not differ significantly between infants extubated successfully and those with failed postoperative extubation, but the duration of CPB was more in patients with failed extubation in comparison to the patients with successful extubation. We included exclusively pediatric patients, of age 1–5 years, undergoing cardiac surgery in our study, so no comparison between pediatric and adult patients, regarding the magnitude of increase in CP and decrease in TPP could be made; however, we did not follow up on patients in the postoperative period.
Limitations
We monitored CP, TPP intraoperatively and no monitoring in the postoperative period was done. Patients were not followed up in the postoperative period for airway complications. Another limitation is that TPP was indirectly derived from MAP and CP since direct objective measurement of TPP was not possible.
CONCLUSION
Continuous monitoring of CP and TPP is not standard practice during pediatric cardiac surgery. CP increases with insertion and examination of the TEE probe, while TPP decreases, which may lead to airway complications. CP, TPP falls on hypothermic CPB, which again can compromise the blood supply to tracheal mucosa, causing temporary and permanent tracheal damage. Ppeak and Pmean are increased during the period of TEE probe insertion and interrogation. The findings of the current study suggest that intraoperative continuous objective monitoring of CP during TEE examination and CPB should be practiced. Monitoring of TPP and CP may help patients with hemodynamic instability or airway anomalies and are prone to tracheal hypoperfusion.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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