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0Egyptian Journal of Anaesthesia (2011) 27, 113-119
Egyptian Society of Anesthesiologists Egyptian Journal of Anaesthesia
www.elsevier.com/locate/egja www.sciencedirect.com
Research Article
Efficiency of the newly introduced ventilatory mode "pressure controlled ventilation-volume guaranteed in thoracic surgery with one lung ventilation
Nermin S. Boules *, Hossam Z. Ghobrial
Department of Anesthesiology and Pain Management, National Cancer Institute, Cairo University, Cairo, Egypt
Received 12 February 2011; revised 14 April 2011; accepted 18 April 2011 Available online 28 May 2011
KEYWORDS
Thoracic surgery; One lung ventilation (OLV); Volume controlled ventilation (VCV);
Pressure controlled ventilation-volume guaranteed (PCV-VG)
Abstract Background: Anesthesia for thoracic surgery routinely involves one lung ventilation (OLV). Volume controlled ventilation (VCV) was and still the most common method of performing OLV. We assumed that pressure controlled ventilation-volume guaranteed (PCV-VG) is a better ventilation strategy for OLV than VCV as regard the inspiratory pressures, oxygenation parameters and post-operative ventilatory outcome.
Methods: Forty patients undergoing elective thoracic surgery in the lateral position requiring at least 1 h of OLV were randomly assigned into two groups. Group VCV: VCV was performed throughout the operation. Group PCV-VG: PCV-VG was performed throughout the operation. Blood gas analysis, peak inspiratory pressure (Ppeak), mean inspiratory pressure (Pmean), plateau inspiratory pressure (Pplateau) were measured: (1) During two lung ventilation (TLV1) 30 min after turning the patient to the lateral decubitus prior the beginning of OLV; (2) 30 min after initiation of OLV(OLV); (3) End of surgery: 30 min after reestablishing TLV (TLV2).
Results: The Ppeak and the Pplateau were significantly lower in PCV-VG compared with VCV in all stages of the study (P value < 0.05). There was significant increase in all pressure values in OLV compared with TLV1 in the two groups (P value < 0.05). There were significant decrease in the mean Pao2 values during OLV and TLV2 compared with TLV1 in the two groups (P value < 0.05).
Corresponding author. Address: 1 Kasr El Aini Street, Fom El Khalig, Cairo, Egypt. Tel.: +20 0123458125. E-mail address: ner1973@yahoo.com (N.S. Boules).
1110-1849 © 2011 Egyptian Society of Anesthesiologists. Production and hosting by Elsevier B.V. All rights reserved.
Peer review under responsibility of Egyptian Society of Anesthesiologists. doi:10.1016/j.egja.2011.04.004
Yet the Pao2 was significantly higher in the PCV-VG group at OLV and TLV2 compared to the OLV and TLV2 in VCV group. Also Pao2 was significantly lower in TLV2 compared with TLV1 in both groups (P value < 0.05).
Conclusion: In patients undergoing thoracic surgery with OLV, pressure controlled volume guaranteed mode of ventilation decreases inspiratory pressure parameters and improve arterial oxygenation better than volume controlled ventilation.
© 2011 Egyptian Society of Anesthesiologists. Production and hosting by Elsevier B.V. All rights reserved.
1. Introduction
Anesthesia for thoracic surgery routinely involves one lung ventilation (OLV) to facilitate surgical exposure, and to isolate and protect the lungs during the procedure. Unfortunately, this practice has been associated with hypoxemia. For many years, arterial hypoxemia during OLV was considered the most important problem for the anesthesiologist. At present, however, there is an increasing concern about the effects of ventilator settings on acute lung injury (ALI) as a consequence of OLV [1].
Volume controlled ventilation (VCV) was and still the most common method of performing one lung ventilation in patients undergoing thoracic surgery. Volume control involves a set tidal volume (VT). The ventilator calculates a flow based on the set tidal volume and the length of the inspiratory time to deliver that tidal volume. A typical volume-controlled pressure waveform increases throughout the entire inspiratory period, and rapidly decreases at the start of expiration, so an increase in the inspiratory pressure is usually observed, and with this excessive amount of inspiratory pressure, the vascular resistance of the dependant lung increases because of compression of intra alveolar vessels [2]. This will counteract hypoxic pulmonary vasoconstriction in the non dependant lung by diverting blood flow away from the ventilated lung, thereby increasing pulmonary shunt fraction [3].
Also the high inspiratory pressure may result in barotrau-mas of the dependant lung. In order to avoid high inspiratory
pressures, lower tidal volumes and higher ventilator rates may be used, but lower tidal volumes have been demonstrated to predispose the dependant lung to atelectasis and worsen arterial oxygenation [4].
Pressure controlled ventilation-volume guaranteed (PCV-VG) is a new mode of ventilation in Datex-Omeda Ventilator, it considered a modification of pressure controlled ventilation in which a tidal volume is set and the ventilator delivers that volume using a decelerating flow and a constant pressure. The ventilator will adjust the inspiratory pressure needed to deliver the set tidal volume breath-by-breath so that the lowest pressure is used. The pressure range that the ventilator will use is between the PEEP + 2 cmH2O level on the low end and 5 cmH2O below the maximum pressure on the high end. The inspiratory pressure change between breaths is a maximum of ±3cmH2O [5].
This mode will deliver breaths with the efficiency of pressure controlled ventilation, yet still compensate for changes in the patient's lung characteristics. PCV-VG begins by first delivering a volume breath at the set tidal volume. The patient's compliance is determined from this volume breath and the inspiratory pressure level is then established for the next PCV-VG breath [5].
In our study we assume that PCV-VG is a better ventilation strategy for OLA than VCV as it lead to a decrease in the inspi-ratory pressure parameters and better arterial oxygenation during OLA and may improve post-operative ventilatory outcome.
Table 1 Patient characteristics and operative data.
Variable VCV group n =19 PCV-VG group n =18 P value
Age (year) 34.7 ± 7.6 33.4 ± 6.4 0.562
Wt (kg) 75.6 ± 14.5 71.8 ± 19.7 0.507
Sex (M/F) 12/7 10/8
ASA (I/II/III) 10/6/3 8/6/4
Duration of 75.6 ± 34.7 88.7 ± 42.1 0.308
OLV (min)
Duration of 278 ± 65 295 ± 83 0.745
surgery (min)
Preoperative FVC 76.4 ± 11.3 74.1 ± 14.4 0.547
(% of predicted)
Preoperative FEV1 74.3 ± 12.5 73.4 ± 11.7 0.823
(% of predicted)
Surgical procedure
Metastatectomy 7 5
Lobectomy 5 6
Cr oesophagus 3 4
Mediastinal mass 4 2
Chest wall mass 0 1
Data are mean ± SD.
OLV = one-lung ventilation, VCV = volume control ventilation, PCV-VG = pressure control ventilation-volume guaranteed.
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2. Patients and methods
After approval by the local ethics committee and after obtaining written informed consent from each individual, 40 patients aged 18-45 undergoing elective open thoracic surgery in the lateral position requiring at least 1 h of OLV were enrolled. All patients were ASA physical status I, II and III with normal pulmonary function preoperatively. Patients had a history of obstructive airways disease, bronchial asthma, uncompensated cardiac disease or hemodynamically significant arrhythmias were excluded from the study. Patients with any chest infection (clinically or radiologically) were also excluded.
All patients underwent arterial blood gases; lung spirome-try (forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1)) and chest x-ray prior to surgery. Upon arrival to the operating room, patients were monitored with electrocardiogram and pulse oximetry and noninvasive blood pressure. A 16-gauge IV catheter was inserted in an upper extremity vein and 3 mg midazolam were given, also a 20-gauge catheter was inserted in a radial artery under local anesthesia for invasive arterial pressure monitoring and blood gas analysis. A right internal jugular central venous catheter was inserted under local anesthesia for central venous pressure monitoring. After preoxygenation, anesthesia was induced with fentanyl 2 ig/ kg, propofol 2mg/kg, and atracurium 0.5mg/kg. isoflurane (0.8-1.5% expiratory concentration).
The trachea was intubated with a double lumen tube (Portex Blue Line Endobronchial Tube, Smiths Medical, Mexico) no. 37 for male and no. 35 for female patients. Left double-lumen tubes were chosen as long as there was no contraindication. The position of the tube was confirmed by auscultation before and after turning the patient to the lateral decubitus position. During OLV, the lumen of the nonventilated side was left open to the air. All patients' lungs were ventilated with a Datex-Omeda Ventilator (S/5 Avance-Aisys). Patients were randomly assigned, according to a computer-generated random number table, to one of two groups. Group VCV: VCV was performed throughout the operation as follows: Initially, two lung ventilation (TLV) using a FIO2 of 1.0, VT of 810 mL/kg with inspiratory pause 5% of inspiratory time and a ventilator rate of 12/min, then the rate was adjusted to maintain end-tidal carbon dioxide tension (ETCO2) of 3035 mmHg. An inspiration to expiration ratio of 1:2 was used, and it was unchanged during all the study. No external positive end expiratory pressure (PEEP) was applied. Upon initiation of OLV, (OLV-VCV) we use a VT of 6 mL/kg, and the ventilator rate adjusted to maintain ETCO2 of 30 to 35 mmHg. Group PCV-VG: PCV-VG was performed throughout the operation as follows: Initially, two lung ventilation (TLV) using a FIO2 of 1.0, VT of 8-10 mL/kg with inspiratory pause 5% of inspiratory time and a ventilator rate of 12 min-1, then the rate was adjusted to maintain end-tidal carbon dioxide tension (ETCO2) of 30-35 mmHg. An inspiration to expiration ratio of 1:2 was used. No external positive end expiratory pressure (PEEP) was applied; inspiratory pressure was adjusted (not exceeding 35 cmH2O). Upon initiation of OLV, (OLV-PCV-VG) we use a VT of 6 mL/kg, and the ventilator rate adjusted to maintain ETCO2 of 30-35 mmHg.
Blood gas analysis, peak inspiratory pressure (Ppeak), mean inpiratory pressure (Pmean), plateau inspiratory pressure (Pplateau) were measured and recorded at three stages: (1)
S 20 =
OLV -VCV group
TLV2 PCV-VG group
TLV1= Two lung ventilation, 30 min after turning the patient to the lateral decubitus OLV = One-lung ventilation, 30 min after initiation of OLV TLV2= Two-lung ventilation, 30 min after reestablishing TLV
VCV= volume control ventilation, PCV-VG= pre ssure control ventilation - volume guaranteed
Figure 1 Peak inspiration pressure in the two groups at different stages of the study.
3 postoperatively. Hemodynamic variables were measured every 5 min and recorded at the same points. CVP was measured every 30 min and recorded at the same points.
2.1. Statistical analysis
Data were computerized and analyzed using the Statistical Package for the Social Science (SPSS) Version 13. Normality of the distribution of data was assessed by the Kolmogorov-Smirnov test. Changes in hemodynamic and respiratory parameters during TLV and OLV sequences were analyzed using repeated measures analysis of variance (ANOVA) followed by the Scheffef-test, as appropriate. Otherwise, normally distributed continuous variables were compared using the Student's t-test. To present the results, mean ± SD were used and a P < 0.05 was considered statistically significant.
B- TLV1 OLV TLV2
■ VCV ■ PCV-VG
TLV1= Two lung ventilation, 30 min after turning the patient to the lateral decubitus OLV = One-lung ventilation, 30 min after initiation of OLV TLV2= Two-lung ventilation, 30 min after reestablishing TLV
VCV= volume control ventilation, PCV-VG= pressure control ventilation- volume guaranteed
Figure 2 Pla#132;teau inspiratory pressure in the two groups at different stages of the study.
During TLV 30 min after turning the patient to the lateral decubitus position prior the beginning of OLV (TLV1); (2) 30 min after initiation of OLV (OLV); (3) End of surgery: 30 min after reestablishing TLV (TLV2). During the measurement period surgical manipulation of the lung was not allowed. Follow up chest x-ray was performed day 1 and day
3. Results
This was a prospective randomized controlled clinical study that was conducted in National Cancer Institute of Egypt (NCI) between August 2010 and December 2010. Among the 40 patients initially enrolled, only two cases in the PCV-VG group was excluded from the study because of massive blood loss and massive blood transfusion and the need for inotropic support, Also one case of VCV group, shows arterial hypox-emia (Sao2 < 90%) requiring reinflation of the collapsed lung, was excluded. Data were normally distributed. Demographic characteristics, ASA distribution, duration of one-lung anesthesia, duration of surgery, preoperative pulmonary function (FVC and FEV1) and the surgical procedure are summarized in Table 1. There were no statistically significant differences as regard age, weight, duration of one-lung ventilation, duration of surgery, FVC and FEV1.
The peak inspiratory pressures (Ppeak), the plateau inspira-tory pressures (Pplateau) and mean inspiratory pressure (Pmean) were significantly lower in PCV-VG group compared with VCV group in all stages of the study (Table 2). There was significant increase in all pressure values in OLV compared with TLV1 in the two groups (P value < 0.05) (Figs. 1 and 2).
M ty X a
■a •e
TLV1 OLV TLV2
—♦—VCV group — ■- PCV-VG group
TLV1= Two lung ventilation, 30 min after turning the patient to the lateral decubitus,
OLV = One-lung ventilation, 30 min after initiation of OLV,
TLV2= Two-lung ventilation, 30 min after end of one-lung ventilation,
VCV= volume control ventilation, PCV-VG= pressure control ventilation - volume guarante
Figure 3 Arterial oxygen tension in the two groups at different stages of the study.
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There was significant decrease in the mean Pao2 values during OLV compared with TLV1 in the two groups (P value < 0.05). Yet the Pao2 was significantly higher in the PCV-VG group at OLV compared to the OLV in VCV group (Table 3, Fig. 3). The mean Pao2 values increased significantly after lung inflation in the two groups comparably; however it is still significantly higher in PCV-VG group. Also Pao2 was significantly lower in TLV2 than TLV1 in both groups (P value < 0.05) (Table 3).
All hemodynamic variables did not differ significantly at any stage of the study except heart rate which was higher during OLV in both groups (Table 4).
Regarding chest X-ray four patients of VCV group and three of PCV-VG group had basal lung collapse in the first post-operative, all except one patient in PCV-VG group were improved in third post-operative day.
4. Discussion
In our study we found that arterial oxygenation was better during OLV in PCV-VG group when compared to VCV group, we also found highly significant decrease in peak and plateau inspiratory pressures in PCV-VG group compared to VCV group and there was mild change in the mean inspiratory pressure between groups.
These results may be explained by the decelerating flow in the PCV-VG mode that may result in better alveolar ventilation with more homogenous distribution of gases inside the alveoli and better alveolar recruitment reducing intra and post-operative atelectasis. But still some degree of residual ate-lectasis may occur which explain the reduced oxygenation in both groups after lung inflation when compared with data before OLV. Also high inspiratory pressures during OLV in VCV group may lead to barotrauma and an increase in the vascular resistance of the dependent lung. This may increase the shunt flow through nondependent (nonventilated) lung by diverting blood flow to it. The final result of excessive inspiratory pressures in the dependent (ventilated) is to lower arterial oxygenation.
Exposure to elevated inspiratory pressures during OLV has also been identified as strong predictor of ALI in patients undergoing thoracic surgery [6]. However, it is unclear which of the commonly measured pressures is more relevant in the development of complications. The Ppeak is a reflection of the dynamic compliance of the respiratory system and depends on factors such as tidal volume, inspiratory time, endotracheal size, and bronchospasm. In contrast, Pplateau relates to the static compliance of the respiratory system (ie, chest wall and lung compliance) and is considered a better reflection of alveolar pressure so there is a strong correlation between Pplateau and ALI. There does not appear to be a Pplateau level that is truly safe, Pplateau less than 25 cm H2O are achievable in most patients with a well positioned endobronchial tube [7]. On the other hand, Pmean correlates with alveolar ventilation and gas oxygenation [8].
We suggested that PCV-VG have advantages on both VCV and PCV as the ventilator controls peak inspiratory pressure, within preset limits, to achieve the target VT. In this fashion, the ventilator automatically compensates for changes in lung mechanics to maintain the set TV. This approach effectively combines advantages of volume-controlled and
Table 4 Hemodynamic variables in the two groups
Variable VCV group (n = 19) PCV-VG group (n = 18)
Set time points TLV1 OLV TLV2 TLV1 OLV TLV2
MAP (mmHg) HR (b/min) CVP (cmH2O) 89.45 ± 22.34 75.24 ± 15.36 9.4 ± 2.3 91.24 ± 19.75 95.35 ± 14.27 (P < 0.001)* 10.1 ± 2.7 88.43 ± 24.36 77.62 ± 18.27 8.6 ± 2.2 89.46 ± 18.75 75.42 ± 13.86 9.1 ± 1.7 87.95 ± 23.47 96.26 ± 8.67 (P < 0.001)* 9.6 ± 1.4 93.16 ± 31.45 78.04 ± 12.84 9.1 ± 2.1
Data are presented as mean ± SD.
TLV1 = two lung ventilation, 30 min after turning the patient to the lateral decubitus position. OLV = one-lung ventilation, 30 min after initiation of OLV. TLV2 = two-lung ventilation, 30 min after reestablishing TLV. MAP = mean arterial pressure, HR = heart rate, CVP = central venous pressure. VCV = volume control ventilation, PCV-VG = pressure control ventilation-volume guaranteed. P value < 0.05 compared with two-lung ventilationl (TLV1) in the same group (within group comparison)
pressure-limited ventilation, and ensures that the minimal pressure necessary to achieve the desired TV is used. So the potential beneficial effects of PCV-VG during OLV are the use of lower inspiratory pressure and a decelerated flow that could reduce the lung damage and might improve recruitment and the distribution of inspired gas.
Up to our knowledge there were no studies comparing PCV-VG with VCV; however there were many literatures concerning the comparative effects of PCV and VCV on intraoperative inspiratory pressures and arterial oxygenation during OLV which showing inconsistent results.
Regarding comparison between PCV and VCV Tugrul et al. found a statistically significant decrease in Ppeak and Pplateau and improved oxygenation and intrapulmonary shunt with PVC compared to VCV in patients undergoing thoracot-omy using a VT of 10 mL/kg during TLV and OLV. The findings were more relevant in subjects who had poor preoperative lung function [9]. In a subsequent study, Senturk and colleagues showed that PCV with a PEEP of 4 cmH2O was associated with an improvement in oxygenation compared to VCV and zero PEEP[10].
On the contrary, Unzueta et al. [11] who found that PCV offered no advantage over VCV for improving oxygenation during OLV in patients with normal preoperative lung function. These results are consistent with those recorded by Heimberg et al. [12] in patients undergoing cardiac surgery with OLV periods. Similarly, the study performed by Pardos et al. [13] revealed no differences in intraoperative arterial oxygenation, inspiratory plateau pressure and mean pressure. Again, the only difference between VCV and PCV was the peak inspi-ratory pressure that was lower in the later.
Moreover, Choi et al. [14] compared PCV vs. VCV during OLV in the prone position for robot-assisted esophagectomy. There were no differences in arterial oxygen tension, inspira-tory pressures, dynamic lung compliance or physiological dead space during OLV between PCV and VCV in the prone position. Finally, Montes and colleagues found that in patients without severe lung disease undergoing thoracic surgery with OLV, lung protective strategies using ''low VT'' combined with PEEP was safe and effective and PCV (vs. VCV) decreases peak inspiratory pressure maintaining similar blood oxygenation indices [15].
Limitations of our study were the small sample size, and lack of a more informative CT chest for assessment and follow up of post-operative lung atelectasis.
5. Conclusion
In conclusion, in patients undergoing thoracic surgery with OLV, pressure controlled volume guaranteed mode of ventilation seemed to be a better approach compared to volume controlled ventilation. Further studies is required to evaluate the effect of addition of positive end expiratory pressure to the pressure controlled volume guaranteed mode to prevent the occurrence of atelectasis during one lung ventilation.
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