Effects of tidal volume and PEEP on arterial blood gases and pulmonary mechanics during one-lung ventilation

Impact of Lower Tidal Volumes During One-Lung Ventilation: A 2022 Update of the Meta-analysis of Randomized Controlled Trials

OBJECTIVES

To clarify the influence of lower tidal volume (4-7 mL/kg) compared with higher tidal volume (8-15 mL/kg) during one-lung ventilation (OLV) on gas exchange and postoperative clinical outcome.

DESIGN

Meta-analysis of randomized trials.

SETTING

Thoracic surgery.

PARTICIPANTS

Patients receiving OLV.

INTERVENTIONS

Lower tidal volume during OLV.

MEASUREMENTS AND MAIN RESULTS

Primary outcome was PaO2-to-the oxygen fraction (PaO2/FIO2) ratio at the end of the surgery, after the reinstitution of two-lung ventilation. Secondary endpoints included perioperative changes in PaO2/FIO2 ratio and carbon dioxide (PaCO2) tension, airway pressure, the incidence of postoperative pulmonary complications, arrhythmia, and length of hospital stay. Seventeen randomized controlled trials (1,463 patients) were selected. Overall analysis showed that the use of low tidal volume during OLV was associated with a significantly higher PaO2/FIO2 ratio 15 minutes after the start of OLV and at the end of surgery (mean difference 33.7 mmHg [p = 0.02] and mean difference 18.59 mmHg [p < 0.001], respectively). The low tidal volume also was associated with higher PaCO2 values 15 minutes and 60 minutes after the start of OLV and with lower airway pressure, which was maintained during two-lung ventilation after surgery. Moreover, the application of lower tidal volume was associated with fewer postoperative pulmonary complications (odds ratio 0.50; p < 0.001) and arrhythmias (odds ratio 0.58; p = 0.009), with no difference in length of hospital stay.

CONCLUSIONS

The use of lower tidal volume, a component of protective OLV, increases the PaO2/FIO2 ratio, reduces the incidence of postoperative pulmonary complications, and should be considered strongly in daily practice.

A structured narrative review of clinical and experimental studies of the use of different positive end-expiratory pressure levels during thoracic surgery

OBJECTIVES

This study aimed to present a review on the general effects of different positive end-expiratory pressure (PEEP) levels during thoracic surgery by qualitatively categorizing the effects into detrimental, beneficial, and inconclusive.

DATA SOURCE

Literature search of Pubmed, CNKI, and Wanfang was made to find relative articles about PEEP levels during thoracic surgery. We used the following keywords as one-lung ventilation, PEEP, and thoracic surgery.

RESULTS

We divide the non-individualized PEEP value into five grades, that is, less than 5, 5, 5-10, 10, and more than 10 cmH₂ O, among which 5 cmH₂ O is the most commonly used in clinic at present to maintain alveolar dilatation and reduce the shunt fraction and the occurrence of atelectasis, whereas individualized PEEP, adjusted by test titration or imaging method to adapt to patients' personal characteristics, can effectively ameliorate intraoperative oxygenation and obtain optimal pulmonary compliance and better indexes relating to respiratory mechanics.

CONCLUSIONS

Available data suggest that PEEP might play an important role in one-lung ventilation, the understanding of which will help in exploring a simple and economical method to set the appropriate PEEP level.

Effects of Positive End-Expiratory Pressure on Intraocular Pressure during One-Lung Ventilation in the Lateral Decubitus Position-A Prospective Randomized Trial

Background and Objectives: The effect of positive end-expiratory pressure (PEEP) on intraocular pressure (IOP) is debatable. There have been no studies investigating the effects of PEEP on IOP during one-lung ventilation (OLV). We aimed to investigate the effects of PEEP on IOP in patients undergoing OLV for video-assisted thoracoscopic surgery (VATs). Materials and Methods: Fifty-two patients undergoing VATs were divided into a zero-PEEP (ZEEP) and a 6 cmH₂O of PEEP (PEEP) groups. IOP, ocular perfusion pressure (OPP), and respiratory and hemodynamic parameters were measured before induction (T1), immediately following endotracheal intubation (T2), 30 min (T3) and 60 min (T4) after a position change to the lateral decubitus position (LDP) and OLV, and 10 min following two-lung ventilation near the end of the surgery (T5). Results: There was no significant difference in IOP and OPP between the two groups. The IOP of the dependent eye was significantly higher than that of the non-dependent eye during LDP in both groups. Peak inspiratory pressure was significantly higher in the PEEP group than in the ZEEP group at T3-T5. Dynamic compliance was significantly higher in the PEEP group than in the ZEEP group at T2-T5. The ratio of arterial oxygen partial pressure to fractional inspired oxygen was significantly higher in the PEEP group than in the ZEEP group at T4. Conclusions: Applying 6 cmH₂O of PEEP did not increase IOP but enhanced dynamic compliance and oxygenation during OLV. These results suggest that 6 cmH₂O of PEEP can be safely applied during OLV in LDP.

[Intraoperative Ventilation Approaches to One-lung Ventilation]

The management of thoracic surgery patients is challenging to the anesthetist, since one-lung ventilation (OLV) includes at least two major conditions: sufficient oxygenation and lung protection. The first is mainly because the ventilation of one lung is stopped while perfusion to that lung continues; the latter is related to the fact that the whole ventilation is applied to only a single lung. Recommendations for maintaining the oxygenation and methods of lung protection may contradict each other (e. g. high vs. low inspiratory oxygen fraction (FiO₂), high vs. low tidal volume, etc.). Therefore, a high degree of pathophysiological understanding and manual skills are required in the management of these patients.In light of recent clinical studies, this review focuses on a current protective strategy for OLV, which includes a possible decrease in FiO₂, lowered V_T, the application of positive end-expiratory pressure (PEEP) to the dependent and continuous positive airway pressure (CPAP) to the non-dependent lung and alveolar recruitment manoeuvres as well. Other approaches such as the choice of anaesthetics, remote ischemic preconditioning, fluid management and pain therapy can support the success of ventilatory strategy. The present work describes new developments that may change the classical approach in this respect.

Repeated intermittent hypoxic stimuli to operative lung reduce hypoxemia during subsequent one-lung ventilation for thoracoscopic surgery: A randomized controlled trial

Background

An intervention to potentiate hypoxic pulmonary vasoconstriction may reduce intrapulmonary shunt and hypoxemia during one-lung ventilation. Previous animal studies reported that repeated intermittent hypoxic stimuli potentiated hypoxic pulmonary vasoconstriction, but no clinical study has examined the effects of this intervention on hypoxemia during one-lung ventilation. We thus performed a single-center, parallel-group, double-blind, randomized controlled trial to investigate whether repeated intermittent hypoxic stimuli to the operative lung reduce hypoxemia during the subsequent one-lung ventilation for thoracoscopic surgery.

Methods

Patients undergoing one-lung ventilation were randomized into two groups (n = 68 each). Before one-lung ventilation, in the intermittent hypoxia group, the nondependent lung was not ventilated for 2 min and then ventilated for 2 min while the dependent lung was continuously ventilated. This was repeated five times. In the continuous normoxia group, both lungs were ventilated for 20 min. We measured SpO₂, PaO₂, FiO₂, PaCO₂, SaO₂, and central venous oxygen saturation during one-lung ventilation. The primary outcome was the number of patients with hypoxemia defined as a SpO₂ <95% during one-lung ventilation, which was analyzed with a chi-squared test.

Results

Hypoxemia was less frequent in the intermittent hypoxia group than in the continuous normoxia group during OLV [6/68 (8.8%) vs 17/68 (25.0%), risk ratio (95% CI) 0.35 (0.15–0.84), p = 0.012]. The PaO₂ (p = 0.008 for 30 min and 0.007 for 60 min) and PaO₂/FiO₂ (p = 0.008 for both) were higher 30 and 60 min after starting one-lung ventilation, and the alveolar-arterial pressure gradient (p = 0.010) and shunt index (p = 0.008) were lower 30 min after starting one-lung ventilation in the intermittent hypoxia group than in the continuous normoxia group. Postoperative adverse events did not differ significantly between groups.

Conclusions

Repeated intermittent hypoxic stimuli to the operative lung seemed to potentiate hypoxic pulmonary vasoconstriction, and thus reduced hypoxemia during the subsequent one-lung ventilation.

Effect of ultrasound-guided-pressure-controlled ventilation on intraoperative blood gas and ventilatory parameters during thoracic surgery

Background and Aims:

Identifying an ideal intraoperative ventilation strategy remains an area of research. We evaluated the effect of ultrasound-guided–pressure-controlled ventilation (UG-PCV) on the blood-gas and ventilatory parameters, during both two-lung ventilation (TLV) and one-lung ventilation (OLV) for thoracic surgery of unilateral pulmonary disease, compared with volume-targeted PCV (VT-PCV).

Methods:

In a prospective, parallel-group and double-blinded design, 40 consecutive patients were randomised into two groups. Group A: Received VT-PCV at a tidal volume (TV) of 9 mL/kg for TLV and 5 mL/kg for OLV; group B: Received UG-PCV at an inspiratory pressure (2 cmH₂O increments every 15 s) targeted to achieve the alveolar aeration at the base of the dependent lung (ultrasound-guided), for both TLV/OLV, respectively. Primary outcome included arterial oxygen partial pressure (PaO₂) measured at baseline before anaesthesia induction (T1), at 30 min immediately before conversion from TLV to OLV (T2), at 30 min on OLV (T3) and before terminating OLV at the end of surgery (T4). Statistical tool included Mann-Whitney test.

Results:

The PaO₂ (mmHg) was significantly higher in group B (374.5 ± 25.9, 321.7 ± 35.2 and 357.0 ± 24.7) as compared to group A (353.3 ± 38.1, 272.6 ± 37.9 and 295.3 ± 40.1), at T2, T3 and T4, respectively. The acid-base status remained preserved in group B, while gradual respiratory acidosis was observed in group A. The bicarbonate levels remained uniform in all patients. The TV and airway pressures were marginally higher in group B, with no intraoperative complications.

Conclusion:

The UG-PCV mode offered better oxygenation, homogenous acid-base balance and individualised alveolar ventilation for thoracic surgery.

Effects of small tidal volume and positive end-expiratory pressure on oxygenation in pressure-controlled ventilation-volume guaranteed mode during one-lung ventilation

Background

The purpose of this study was to investigate whether tidal volume (TV) of 8 mL/kg without positive end-expiratory pressure (PEEP) and TV of 6 mL/kg with or without PEEP in pressure-controlled ventilation-volume guaranteed (PCV-VG) mode can maintain arterial oxygenation and decrease inspiratory airway pressure effectively during one-lung ventilation (OLV).

Methods

The study enrolled 27 patients undergoing thoracic surgery. All patients were ventilated with PCV-VG mode. During OLV, patients were initially ventilated with TV 8 mL/kg (group TV8) without PEEP. Ventilation was subsequently changed to TV 6 mL/kg with PEEP (5 cmH₂O; group TV6+PEEP) or without (group TV6) in random sequence. Peak inspiratory pressure (P_peak), mean airway pressure (P_mean), and arterial blood gas analysis were measured 30 min after changing ventilator settings. Ventilation was then changed once more to add or eliminate PEEP (5 cmH₂O), while maintaining TV 6 mL/kg. Thirty min after changing ventilator settings, the same parameters were measured once more.

Results

The P_peak was significantly lower in group TV6 (19.3±3.3 cmH₂O) than in group TV8 (21.8±3.1 cmH₂O) and group TV6+PEEP (20.1±3.4 cmH₂O). PaO₂ was significantly higher in group TV8 (242.5±111.4 mmHg) than in group TV6 (202.1±101.3 mmHg) (p=0.044). There was no significant difference in PaO₂ between group TV8 and group TV6+PEEP (226.8±121.1 mmHg). However, three patients in group TV6 were dropped from the study because PaO₂ was lower than 80 mmHg after ventilation.

Conclusion

It is postulated that TV 8 mL/kg without PEEP or TV 6 mL/kg with 5 cmH₂O PEEP in PCV-VG mode during OLV can safely maintain adequate oxygenation.

Intraoperative use of low volume ventilation to decrease postoperative mortality, mechanical ventilation, lengths of stay and lung injury in adults without acute lung injury

BACKGROUND

Since the 2000s, there has been a trend towards decreasing tidal volumes for positive pressure ventilation during surgery. This an update of a review first published in 2015, trying to determine if lower tidal volumes are beneficial or harmful for patients.

OBJECTIVES

To assess the benefit of intraoperative use of low tidal volume ventilation (less than 10 mL/kg of predicted body weight) compared with high tidal volumes (10 mL/kg or greater) to decrease postoperative complications in adults without acute lung injury.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2017, Issue 5), MEDLINE (OvidSP) (from 1946 to 19 May 2017), Embase (OvidSP) (from 1974 to 19 May 2017) and six trial registries. We screened the reference lists of all studies retained and of recent meta-analysis related to the topic during data extraction. We also screened conference proceedings of anaesthesiology societies, published in two major anaesthesiology journals. The search was rerun 3 January 2018.

SELECTION CRITERIA

We included all parallel randomized controlled trials (RCTs) that evaluated the effect of low tidal volumes (defined as less than 10 mL/kg) on any of our selected outcomes in adults undergoing any type of surgery. We did not retain studies with participants requiring one-lung ventilation.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the quality of the retained studies with the Cochrane 'Risk of bias' tool. We analysed data with both fixed-effect (I² statistic less than 25%) or random-effects (I² statistic greater than 25%) models based on the degree of heterogeneity. When there was an effect, we calculated a number needed to treat for an additional beneficial outcome (NNTB) using the odds ratio. When there was no effect, we calculated the optimum information size.

MAIN RESULTS

We included seven new RCTs (536 participants) in the update.In total, we included 19 studies in the review (776 participants in the low tidal volume group and 772 in the high volume group). There are four studies awaiting classification and three are ongoing. All included studies were at some risk of bias. Participants were scheduled for abdominal surgery, heart surgery, pulmonary thromboendarterectomy, spinal surgery and knee surgery. Low tidal volumes used in the studies varied from 6 mL/kg to 8.1 mL/kg while high tidal volumes varied from 10 mL/kg to 12 mL/kg.Based on 12 studies including 1207 participants, the effects of low volume ventilation on 0- to 30-day mortality were uncertain (risk ratio (RR) 0.80, 95% confidence interval (CI) 0.42 to 1.53; I² = 0%; low-quality evidence). Based on seven studies including 778 participants, lower tidal volumes probably reduced postoperative pneumonia (RR 0.45, 95% CI 0.25 to 0.82; I² = 0%; moderate-quality evidence; NNTB 24, 95% CI 16 to 160), and it probably reduced the need for non-invasive postoperative ventilatory support based on three studies including 506 participants (RR 0.31, 95% CI 0.15 to 0.64; moderate-quality evidence; NNTB 13, 95% CI 11 to 24). Based on 11 studies including 957 participants, low tidal volumes during surgery probably decreased the need for postoperative invasive ventilatory support (RR 0.33, 95% CI 0.14 to 0.77; I² = 0%; NNTB 39, 95% CI 30 to 166; moderate-quality evidence). Based on five studies including 898 participants, there may be little or no difference in the intensive care unit length of stay (standardized mean difference (SMD) -0.06, 95% CI -0.22 to 0.10; I² = 33%; low-quality evidence). Based on 14 studies including 1297 participants, low tidal volumes may have reduced hospital length of stay by about 0.8 days (SMD -0.15, 95% CI -0.29 to 0.00; I² = 27%; low-quality evidence). Based on five studies including 708 participants, the effects of low volume ventilation on barotrauma (pneumothorax) were uncertain (RR 1.77, 95% CI 0.52 to 5.99; I² = 0%; very low-quality evidence).

AUTHORS' CONCLUSIONS

We found moderate-quality evidence that low tidal volumes (defined as less than 10 mL/kg) decreases pneumonia and the need for postoperative ventilatory support (invasive and non-invasive). We found no difference in the risk of barotrauma (pneumothorax), but the number of participants included does not allow us to make definitive statement on this. The four studies in 'Studies awaiting classification' may alter the conclusions of the review once assessed.

The Society for Translational Medicine: clinical practice guidelines for mechanical ventilation management for patients undergoing lobectomy

Patients undergoing lobectomy are at significantly increased risk of lung injury. One-lung ventilation is the most commonly used technique to maintain ventilation and oxygenation during the operation. It is a challenge to choose an appropriate mechanical ventilation strategy to minimize the lung injury and other adverse clinical outcomes. In order to understand the available evidence, a systematic review was conducted including the following topics: (I) protective ventilation (PV); (II) mode of mechanical ventilation [e.g., volume controlled (VCV) versus pressure controlled (PCV)]; (III) use of therapeutic hypercapnia; (IV) use of alveolar recruitment (open-lung) strategy; (V) pre-and post-operative application of positive end expiratory pressure (PEEP); (VI) Inspired Oxygen concentration; (VII) Non-intubated thoracoscopic lobectomy; and (VIII) adjuvant pharmacologic options. The recommendations of class II are non-intubated thoracoscopic lobectomy may be an alternative to conventional one-lung ventilation in selected patients. The recommendations of class IIa are: (I) Therapeutic hypercapnia to maintain a partial pressure of carbon dioxide at 50-70 mmHg is reasonable for patients undergoing pulmonary lobectomy with one-lung ventilation; (II) PV with a tidal volume of 6 mL/kg and PEEP of 5 cmH₂O are reasonable methods, based on current evidence; (III) alveolar recruitment [open lung ventilation (OLV)] may be beneficial in patients undergoing lobectomy with one-lung ventilation; (IV) PCV is recommended over VCV for patients undergoing lung resection; (V) pre- and post-operative CPAP can improve short-term oxygenation in patients undergoing lobectomy with one-lung ventilation; (VI) controlled mechanical ventilation with I:E ratio of 1:1 is reasonable in patients undergoing one-lung ventilation; (VII) use of lowest inspired oxygen concentration to maintain satisfactory arterial oxygen saturation is reasonable based on physiologic principles; (VIII) Adjuvant drugs such as nebulized budesonide, intravenous sivelestat and ulinastatin are reasonable and can be used to attenuate inflammatory response.

Intraoperative use of low volume ventilation to decrease postoperative mortality, mechanical ventilation, lengths of stay and lung injury in patients without acute lung injury

BACKGROUND

During the last decade, there has been a trend towards decreasing tidal volumes for positive pressure ventilation during surgery. It is not known whether this new trend is beneficial or harmful for patients.

OBJECTIVES

To assess the benefit of intraoperative use of low tidal volume ventilation (< 10 mL/kg of predicted body weight) to decrease postoperative complications.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2014, Issue 9), MEDLINE (OvidSP) (from 1946 to 5 September 2014) and EMBASE (OvidSP) (from 1974 to 5 September 2014).

SELECTION CRITERIA

We included all parallel randomized controlled trials (RCTs) that evaluated the effect of low tidal volumes (defined as < 10 mL/kg) on any of our selected outcomes in adult participants undergoing any type of surgery. We did not retain studies with participants requiring one-lung ventilation.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the quality of the retained studies with the Cochrane 'Risk of bias' tool. We analysed data with both fixed-effect (I(2) statistic < 25%) or random-effects (I(2) statistic > 25%) models based on the degree of heterogeneity. When there was an effect, we calculated a number needed to treat for an additional beneficial outcome (NNTB) using the odds ratio. When there was no effect, we calculated the optimal size information.

MAIN RESULTS

We included 12 studies in the review. In total these studies detailed 1012 participants (499 participants in the low tidal volume group and 513 in the high volume group). All studies included were at risk of bias as defined by the Cochrane tool. Based on nine studies including 899 participants, we found no difference in 0- to 30-day mortality between low and high tidal volume groups (risk ratio (RR) 0.79, 95% confidence interval (CI) 0.40 to 1.54; I(2) statistic 0%; low quality evidence). Based on four studies including 601 participants undergoing abdominal or spinal surgery, we found a lower incidence of postoperative pneumonia in the lower tidal volume group (RR 0.44, 95% CI 0.20 to 0.99; I(2) statistic 19%; moderate quality evidence; NNTB 19, 95% CI 14 to 169). Based on two studies including 428 participants, low tidal volumes decreased the need for non-invasive postoperative ventilatory support (RR 0.31, 95% CI 0.15 to 0.64; moderate quality evidence; NNTB 11, 95% CI 9 to 19). Based on eight studies including 814 participants, low tidal volumes during surgery decreased the need for postoperative invasive ventilatory support (RR 0.33, 95% CI 0.14 to 0.80; I(2) statistic 0%; NNTB 36, 95% CI 27 to 202; moderate quality evidence). Based on three studies including 650 participants, we found no difference in the intensive care unit length of stay (standardized mean difference (SMD) -0.01, 95% CI -0.22 to 0.20; I(2) statistic = 42%; moderate quality evidence). Based on eight studies including 846 participants, we did not find a difference in hospital length of stay (SMD -0.16, 95% CI -0.40 to 0.07; I(2) statistic 52%; moderate quality evidence). A meta-regression showed that the effect size increased proportionally to the peak pressure measured at the end of surgery in the high volume group. We did not find a difference in the risk of pneumothorax (RR 2.01, 95% CI 0.51 to 7.95; I(2) statistic 0%; low quality evidence).

AUTHORS' CONCLUSIONS

Low tidal volumes (defined as < 10 mL/kg) should be used preferentially during surgery. They decrease the need for postoperative ventilatory support (invasive and non-invasive). Further research is required to determine the maximum peak pressure of ventilation that should be allowed during surgery.

Effects of a preemptive alveolar recruitment strategy on arterial oxygenation during one-lung ventilation with different tidal volumes in patients with normal pulmonary function test

BACKGROUND

Hypoxemia during one-lung ventilation (OLV) remains a major concern. The present study compared the effect of alveolar recruitment strategy (ARS) on arterial oxygenation during OLV at varying tidal volumes (Vt) with or without positive end-expiratory pressure (PEEP).

METHODS

In total, 120 patients undergoing wedge resection by video assisted thoracostomy were randomized into four groups comprising 30 patients each: those administered a 10 ml/kg tidal volume with or without preemptive ARS (Group H and Group H-ARS, respectively) and those administered a 6 ml/kg tidal volume and a 8 cmH2O PEEP with or without preemptive ARS (Group L and Group L-ARS, respectively). ARS was performed using pressure-controlled ventilation with a 40 cmH2O plateau airway pressure and a 15 cmH2O PEEP for at least 10 breaths until OLV began.

RESULTS

Preemptive ARS significantly improved the PaO2/FiO2 ratio compared to the groups that did not receive ARS (P < 0.05). The H-ARS group showed a highest PaO2/FiO2 ratio during OLV, the L-ARS and H groups showed similarly improved arterial oxygenation, which was significantly higher than in group L (P < 0.05). The plateau airway pressure in group H-ARS was significantly higher than in group L-ARS (P < 0.05).

CONCLUSIONS

Preemptive ARS can improve arterial oxygenation during OLV. Furthermore, a 6 ml/kg tidal volume combined with 8 cmH2O PEEP after preemptive ARS may reduce the risk of pulmonary injury caused by high tidal volume during one-lung ventilation in patients with normal pulmonary function.