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(Chest. 2000;118:18-23.)
© 2000 American College of Chest Physicians

Negative Pressure Ventilation vs External High-Frequency Oscillation During Rigid Bronchoscopy*

A Controlled Randomized Trial

Giuseppe Natalini, MD; Sergio Cavaliere, MD; Veronica Seramondi, MD; Pierfranco Foccoli, MD; Michele Vitacca, MD; Nicolino Ambrosino, MD, FCCP and Andrea Candiani, MD

* From the Department of Anesthesia and Intensive Care (Drs. Natalini, Seramondi, and Candiani), University of Brescia; the Respiratory Endoscopy and Laser-Therapy Center (Drs. Cavaliere and Foccoli), Spedali Civili Brescia; and the Lung Function Unit (Drs. Vitacca and Ambrosino), S. Maugeri Foundation IRCCS, Gussago, Italy.

Correspondence to: Giuseppe Natalini, MD, Terapia Intensiva Polifunzionale, Casa di Cura "Poliambulanza", Via Bissolati 57, 25124 Brescia, Italy; e-mail:newpoli{at}tin.it


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objectives: To compare the effectiveness of two modalities of external ventilation during rigid bronchoscopy: intermittent negative pressure ventilation (INPV) and external high-frequency oscillation (EHFO).

Design: Prospective, controlled, randomized, nonblinded study.

Setting: University-affiliated hospital.

Patients: Seventy patients undergoing interventional rigid bronchoscopy for tracheobronchial lesions were enrolled into the study.

Interventions: Mechanical ventilation was performed by INPV or EHFO. When pulse oximetry was < 90%, manually assisted ventilation was delivered.

Measurements and results: Arterial blood gases were sampled preoperatively and intraoperatively. Most patients in both groups had normal intraoperative PaCO2 (mean, 43.6 ± 11.8 mm Hg under EHFO and 37.4 ± 8.2 mm Hg under INPV; p = 0.012), and acidemia occurred in 9 of 35 patients of EHFO group and in 2 of 35 patients of INPV group (p = 0.049). Hypercapnia (PaCO2 > 50 mm Hg) was observed in 10 patients under EHFO and in 2 with INPV (p = 0.026). Intraoperative mean PaO2 was similar (101.4 ± 52.9 mm Hg with EHFO and 124.2 ± 50.3 mm Hg with INPV; p = 0.07), but O2 supply was different (3.5 ± 2.3 L/min during INPV and 8.5 ± 6.2 L/min during EHFO; p < 0.001). Intraoperative hypoxemia (PaO2 < 60 mm Hg) occurred in five patients with EHFO and two with INPV (p = 0.426). Three EHFO patients required manually assisted ventilation (mean, 0.2 ± 0.9), but no INPV patient did (p = 0.142).

Conclusions: External negative pressure ventilation appears to be a suitable choice during rigid bronchoscopy: both EHFO and INPV ensure effective ventilation and comfortable operating conditions in the majority of patients. Some patients may receive inadequate ventilation with EHFO, developing respiratory acidosis and requiring manually assisted ventilation. In comparison with INPV, EHFO requires a higher fraction of inspired oxygen.

Key Words: anesthesia • bronchoscopy • high-frequency ventilation • respiration, artificial • ventilators, negative-pressure


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Interventional bronchoscopy is an effective approach for the palliation of malignant tracheobronchial lesions, and for the removal of foreign bodies, eradication of carcinomas in situ and benign tumors, and for dilatation of airway stenosis.1 2

The use of a rigid bronchoscope allows laser application, stent positioning, mechanical dilatation, and resection and the drawing of large biopsy specimens. The rigid bronchoscope is also very effective for suction, and serves to control hemorrhagic complications.2 3 On the other hand, the rigid bronchoscope usually requires general anesthesia, and does not permit the use of a cuffed tracheal tube. Intermittent positive pressure ventilation and jet ventilation are the most popular modalities of mechanical ventilation during interventional rigid bronchoscopy (IRB), but neither guarantees effective ventilation and safety, and both can limit surgical options.2 4 5 6 7 Patients can also be managed with spontaneous-assisted ventilation (SAV), but with this method, at least low levels of respiratory acidosis are virtually unavoidable.1 8 9

In previous studies, we showed that, compared to SAV, intermittent negative pressure ventilation (INPV) during IRB prevented intraoperative apnea and respiratory acidosis in nonparalyzed patients.9 In paralyzed patients, it allowed opioid sparing, shortened recovery time, prevented respiratory acidosis, excluded the need for manually assisted ventilation (MAV), and reduced the amount of O2 needed, while maintaining optimal surgical conditions.8 These results suggest that INPV may be useful during IRB.

Another modality of negative external ventilation, external high-frequency oscillation (EHFO) delivered by means of the Hayek Oscillator (Flexco Medical Instruments AG; Zurich, Switzerland), was used in this setting. Compared with SAV, the use of EHFO reduced the acid-base derangement, O2 need, and the number of MAVs.10 This study was therefore conducted to compare the clinical effectiveness of INPV and EHFO during IRB under general anesthesia.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
The study was approved by the Ethical Committee of Spedali Civili, Brescia, and was conducted according to the Declaration of Helsinki. All patients gave written informed consent to participation in the study.

Patients
Seventy consecutive patients scheduled for IRB for tracheal or bronchial lesions entered the study. Demographics, anthropometrics, diagnoses of lesions, and the American Society of Anesthesiologists (ASA) physical status are shown in Table 1 . In 20 patients (28.5%), IRB was scheduled for treatment of benign tumors or tracheal stenosis; in 50 patients (71.5%), it was a palliative therapy for endoluminal malignant tracheal or bronchial lesions. Tracheotomized or obese patients unable to wear the size 9 cuirass of the Hayek Oscillator were excluded.


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  		Table 1.. Demographic, Anthropometric, and Clinical Characteristics*

 
Measurements and Monitoring
Arterial blood gases were analyzed (ABL 300; Radiometer; Copenhagen, Denmark) on blood samples drawn from the radial artery while patients were breathing room air in supine position before anesthesia, and intraoperatively 20 min after the induction (T1).

The ECG, heart rate, and pulse oximetry (SpO2) were continuously displayed on a ProPaq monitor (Protocol System; Beaverton, OR); BP was measured noninvasively every 5 min by the same monitor. The continuous O2 flow through the rigid bronchoscope was recorded at T1.

The duration of the procedure was defined as the time elapsed from induction to withdrawal of the rigid bronchoscope at the end of the procedure. Recovery time was defined as the time between the removal of the rigid bronchoscope to eye opening in response to a verbal command.

Immediately after the end of the surgical procedure, the bronchoscopist performing the treatment (S. C.) was required to assess the quality of the operating conditions, using a score ranging from 1 (inadequate) to 5 (optimal).

Protocol
The case list was randomly assigned to two groups: (1) ventilation by INPV; and (2) ventilation by EHFO.

Anesthesia: Both groups had the same anesthesia induction: patients breathed 100% O2 for 5 min, and then general anesthesia was induced by fentanyl, 3.5 µg/kg, and propofol, 2 mg/kg. In patients with unstable or poor cardiovascular function, the fentanyl dose was 2 µg/kg, and propofol was slowly titrated until the loss of verbal contact. Before introducing the rigid bronchoscope, 3 to 5 mL of lidocaine 4% was sprayed into the trachea under laryngoscopic control. Anesthesia was maintained by continuous infusion of propofol, 6 to 8 mg/kg/h, and bolus injections of fentanyl, 1 µg/kg, if heart rate and systolic arterial pressure increased >= 20% from baseline. Muscle relaxation was assured by boluses of atracurium besilate, 0.3 mg/kg. At the end of procedures, the neuromuscular blockade was reversed, if necessary, with neostigmine, 0.03 mg/kg, and atropine, 0.015 mg/kg.

INPV Setting: INPV was provided with a poncho-wrap connected to a negative pressure ventilator (Emerson 33 C2; Emerson; Cambridge, MA) as previously described.8 9 The poncho-wrap consists of a vest that fits over a rigid grid encircling the patient’s rib cage and abdomen, and is attached posteriorly by a flat backplate. After intubation with the rigid bronchoscope, the poncho-wrap was tightly sealed at the neck, arms, and legs, and INPV was started. On the basis of our experience,8 9 we set the initial negative pressure (Pneg) at - 25 cm H2O, the respiratory rate (RR) at 15 cycles/min, and the inspiratory/expiratory ratio at 1:1. A continuous O2 flow of 2 L/min was given through the rigid bronchoscope. During the endoscopic procedure, Pneg and O2 flow could be changed in order to maintain a target of 93% < SpO2 < 98%, allowing -35 cm H2O and 15 L/min as maximal levels for Pneg and O2 flow. If SpO2 fell < 90% despite maximal Pneg and O2 flow, MAV with an anesthesia bag at fraction of inspired oxygen (FIO2) of 1 had to be delivered through the rigid bronchoscope.

EHFO Setting: EHFO was delivered by means of a Hayek Oscillator. This consists of a chest enclosure (cuirass), a power unit, and a control unit. The cuirass is made of clear, flexible, lightweight hollow plastic, and there are 10 different sizes to fit the chest and upper abdomen, from premature neonates to obese adults. The power unit contains a diaphragmatic pump, which can operate over a wide range of frequencies to generate an oscillating pressure. The frequency, inspiratory pressure (PI), and expiratory pressure (PE), and inspiratory/expiratory ratio can be set on the control unit. Since both the inspiratory and expiratory phases are controlled, high frequency can be achieved. Patients were fitted with a cuirass selected among three standard sizes (sizes 7 to 9). The initial setting of the ventilator was as follows: PI, -20 cm H2O; PE, 5 cm H2O; RR, 60 cycles/min; and inspiratory/expiratory ratio, 1:1. On some occasions, the RR had to be reduced because the endoscopist was bothered by the frequent airway movements. On other occasions, large differences between set and measured PI and PE were observed, and attributed to air leaks due to thorax/abdomen disproportion and poor fit of the cuirass. This difference was overcome or reduced by increasing RR. A continuous O2 flow of 2 L/min was supplied through the rigid bronchoscope. The target SpO2 was maintained by adjusting the span between PI and PE, and O2 flow. In any case, PI did not exceed 35 cm H2O. If SpO2 fell < 90% despite maximal PI and O2 flow, MAV had to be performed as in the INPV group.

Statistics
Data are shown as mean ± SD; in Tables, the median and range are added. EHFO and INPV groups were compared using the unpaired t test for parametric data, and the Mann-Whitney test for nonparametric data. Differences between treatments and within treatment were evaluated by analysis of variance (ANOVA) for repeated measures. Differences in frequency were assessed using a {chi}2 comparison of the mean.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
As shown in Table 1 , INPV and EHFO groups were no different in sex, age, weight, type of lesions, physical status evaluated using the ASA score, duration of the surgical procedure, or recovery time. The final settings of the two ventilators are shown in Table 2 . As shown in Table 3 , pharmacologic management of general anesthesia did not differ between groups.


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  		Table 2.. Actual Ventilator Settings*

 

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  		Table 3.. Anesthetic Management*

 
Patients tolerated both procedures well. No major complications or adverse effects were observed perioperatively in either group. Three patients with EHFO but none with INPV group needed MAV; the O2 flow was significantly lower during INPV than during EHFO. The duration of the procedure, recovery time, and the quality of operating conditions as judged by the endoscopist were similar (Table 4) .


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  		Table 4.. MAV, O2 Need, Surgical Comfort, and Duration of Surgery*

 
As shown in Table 5 , baseline arterial blood gas measurements did not differ in the two groups. As expected, given the target SpO2, at T1, PaO2 did not differ in the two groups, whereas intraoperatively mean pH and PaCO2, though in the normal range in both groups, were significantly different. At T1, acidemia (pH < 7.35) occurred in 9 of the 35 patients (26%) in the EHFO group and in 2 patients (6%) in the INPV group (p = 0.049); at least moderate hypercapnia (PaCO2 > 50 mm Hg) was observed in 10 patients (28%) under EHFO and in 2 patients (6%) under INPV (p = 0.026). Intraoperative hypoxemia needing an increase in FIO2 (PaO2 < 60 mm Hg) occurred in five patients in the EHFO and two in the INPV group (p = 0.426).


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  		Table 5.. Arterial Blood Gas Analysis*

 
The time courses of heart rate and BP are shown in Figures 1 2 3 . Preinduction heart rate was similar in both groups (90 ± 17 beats/min in the EHFO group and 90 ± 20 beats/min with INPV). From 5 to 30 min after induction, heart rate in the INPV but not in the EHFO group showed a significant (p = 0.0005, ANOVA) tendency to a reduction, due to the initial drop at 5 min (Fig 1) . Baseline systolic and diastolic arterial pressure did not differ. Both groups showed similar significant reductions in systolic arterial pressure (p = 0.0001, ANOVA), whereas the significant reduction in diastolic arterial pressure (p = 0.0001, ANOVA) was more pronounced in the INPV group (p = 0.03, ANOVA between groups).



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  		Figure 1.. Heart rate (mean and SD) during the first 30 min of anesthesia. Open squares: EHFO group; solid circles: INPV group; time "0": preoperative value.

 


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  		Figure 2.. Systolic arterial pressure (mean and SD) during the first 30 min of anesthesia. Open squares: EHFO group; solid circles: INPV group; time "0": preoperative value.

 


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  		Figure 3.. Diastolic arterial pressure (mean and SD) during the first 30 min of anesthesia. Open squares: EHFO group; solid circles: INPV group; time "0": preoperative value.

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
This study shows that both EHFO and INPV can be safely used during IRB. However, EHFO required higher FIO2 to maintain the targeted SpO2, and 8.5% of EHFO patients required MAV to ensure adequate oxygenation. Furthermore, at least 25% of patients under EHFO showed respiratory acidosis in comparison to 6% of patients under INPV.

The main application of INPV is in the treatment of acute on chronic respiratory failure.11 12 In previous studies, we showed it was effective to sustain ventilation during IRB.8 9 Consequently, we were confident that other modalities of external ventilation could be useful in this setting, and we demonstrated in a pilot study that EHFO successfully ventilated patients undergoing IRB.10

To the best of our knowledge, there are no controlled randomized trials comparing INPV and EHFO during IRB or other conditions. The Hayek Oscillator achieves an EHFO by creating a negative PI and a positive PE around the thorax; unlike INPV, EHFO controls both phases of ventilation. Previous studies showed that EHFO, used without a tracheal tube, reduced PaCO2 in patients with severe COPD13 and sustained ventilation in patients undergoing microlaryngeal surgery under general anesthesia.14 In intubated patients, EHFO has been proposed also in the treatment of acute respiratory failure.15

Different INPV and EHFO settings might have influenced the results of this study. INPV and EHFO cannot be set to the same values, because the parameters and the operative modalities of the devices are different. Moreover, during IRB, the tidal volume measurement and capnometry are not available, requiring a "clinical" approach to the ventilation of the patient. As a consequence, this study did not compare INPV and EHFO per se, but their application in a specific surgical field, ie IRB.

The initial setting and the intraoperative changes in ventilatory parameters during INPV and EHFO were based on our previous experience8 9 10 and on published data.13 15 16 RR was different between INPV and EHFO. During INPV, RR remained fixed at the initial set value (15 cycles/min) in most patients, requiring only occasional small changes, whereas EHFO required frequent changes in RR. In line with our previous experience10 and with the literature,15 16 we started with a RR of 60 cycles/min. In some patients, this had to be reduced because the endoscopist complained it was causing too frequent airway movements; whether the high RR was troublesome for the endoscopist depended on the individual patient and on the procedure. During laser application, the lesion must be focused precisely, so rapid movements are disturbing; mechanical resection or dilatation are not influenced so much by this problem.

In other patients, large differences were observed between set and measured PI and PE and attributed to air leaks from the cuirass. Leakage occurred when the thorax and the abdomen were different sizes and the cuirass did not fit well around one or the other. The clinical effect of these air leaks was reduced and sometimes even eliminated by raising the RR, thus increasing the delivered minute ventilation.

The inspiratory driving pressure is due to Pneg during INPV and to the difference between PI and PE during EHFO. We selected PI in EHFO similar to that in the published data,13 16 and it showed greater variability than Pneg in INPV to reach our target in ventilation (Table 2) . In our opinion, it was simpler to set one variable (Pneg in INPV) than two (PI and PE in EHFO).

The quality of the operating conditions was judged to be optimal with both ventilators, even though the operator (the same for all patients) occasionally complained of rapid airway movements during EHFO. This was solved by slowing the RR.

Despite the statistical differences, the mean pH and PaCO2 remained in the normal range in both conditions. Mean PaO2 was higher than normal in both groups (Table 5) . Individual arterial blood gases indicated a greater prevalence of hypercapnia in EHFO than in INPV. The lower need of O2 supply in the INPV group may be useful. Indeed, IRB is frequently used in laser therapy, which exposes the patient to the risk of combustion related to FIO2.17 Consequently, at least theoretically, INPV may be safer than EHFO during airway laser therapy.

As shown in Table 3 , three patients in EHFO needed MAV despite the attempt to achieve optimal ventilator settings and maximal continuous O2 flow through the rigid bronchoscope. All these patients had disproportion between the thorax and the abdomen size. The fact that it was impossible to maintain SpO2 > 90% reflected the ventilation problem caused by the poor fit between the cuirass and the thorax and abdomen, as demonstrated by the fact that all these patients were hypercarbic at T1. MAV should be avoided during IRB because it slackens or interrupts the procedure, and the endoscopist might lose sight of the operatory field; in case of hemorrhagic complications, this could be dangerous.

Despite a similar anesthesiologic schedule and mean arterial blood gases, EHFO patients showed higher intraoperative heart rate and diastolic arterial pressure compared to INPV patients. These differences were unexpected and intriguing. However, comparison of cardiovascular impact of EHFO and INPV goes beyond the aim of this study.

In the present study, interventional bronchoscopy was carried out with laser application, mechanical resection, and/or stent positioning. Nonetheless, other therapeutic modalities, such as cryotherapy or electrocautery, could be equally as effective as laser therapy for the treatment of endoluminal lesions. Further studies should be performed to evaluate the feasibility and the safety of the external negative pressure ventilations in these settings; at least theoretically, there are no specific concerns caused by using these techniques during EHFO or INPV. Future studies could look at whether patients who failed with one technique could be switched over to and adequately ventilated and oxygenated with the other technique.

In conclusion, external negative pressure ventilation appears to be a suitable choice during IRB: both EHFO and INPV provide effective ventilation and comfortable operating conditions in the majority of patients undergoing IRB. Some patients with thorax/abdomen disproportion may be inadequately ventilated with EHFO and may need MAV. INPV achieves good oxygenation with lower O2 supply than EHFO, reducing the potential risk of combustion during laser applications.


   Footnotes
 
Abbreviations: ANOVA = analysis of variance; ASA = American Society of Anesthesiologists; EHFO = external high-frequency oscillation; FIO2 = fraction of inspired oxygen; INPV = intermittent negative pressure ventilation; IRB = interventional rigid bronchoscopy; MAV = manually assisted ventilation; PE = expiratory pressure; PI = inspiratory pressure; Pneg = negative pressure; RR = respiratory rate; SAV = spontaneous-assisted ventilation; SpO2 = pulse oximetry; T1 = after induction

Received for publication September 21, 1999. Accepted for publication January 26, 2000.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Cavaliere, S, Venuta, F, Foccoli, P, et al (1996) Endoscopic treatment of malignant airway obstructions in 2,008 patients. Chest 110,1536-1542[Abstract/Free Full Text]
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  4. Conacher, ID, Paes, ML, Morritt, GN (1985) Anesthesia for carbon dioxide laser surgery on the trachea: taking turns in the airway. Br J Anaesth 57,448-450[Abstract/Free Full Text]
  5. Schlenkhoff, D, Droste, H, Sciezka, S, et al (1986) The use of high-frequency jet-ventilation in operative bronchoscopy. Endoscopy 18,192-194[ISI][Medline]
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  9. Vitacca, M, Natalini, G, Cavaliere, S, et al (1997) Breathing pattern and arterial blood gases during Nd-YAG laser photoresection of endobronchial lesions under general anaesthesia: use of negative pressure ventilation; a preliminary study. Chest 112,1466-1473[Abstract/Free Full Text]
  10. Natalini, G, Vitacca, M, Cavaliere, S, et al (1997) Use of Hayek oscillator during rigid bronchoscopy under general anaesthesia [abstract]. Br J Anaesth 78(Suppl1),23
  11. Corrado A, Gorini M, Villella G, et al. Negative pressure ventilation in the treatment of acute respiratory failure: an old noninvasive technique reconsidered. Eur Respir J 1996; 1531–1544
  12. Corrado, A, De Paola, E, Gorini, M, et al (1996) Intermittent negative pressure ventilation in the treatment of hypoxic hypercapnic coma in chronic respiratory insufficiency. Thorax 51,1077-1082[Abstract]
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  16. Hardinge, FM, Davies, RJO, Stradling, JR (1995) Effects of short term high frequency negative pressure ventilation on gas exchange using the Hayek oscillator in normal subjects. Thorax 50,44-49[Abstract]
  17. Dumon, JF, Shapshay, S, Bourcereau, J, et al (1984) Principles for safety in application of Neodymium-YAG laser in bronchology. Chest 86,163-168[Abstract/Free Full Text]




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