The Effects on Arterial Haemoglobin Oxygen Saturation and on Shunt of Increasing Cardiac Output with Dopamine or Dobutamine during One-lung Ventilation

Dopamine Reverses Lung Function Deterioration After Cardiopulmonary Bypass Without Affecting Gas Exchange

OBJECTIVE

To investigate the effects of dopamine on the adverse pulmonary changes after cardiopulmonary bypass.

DESIGN

A prospective, nonrandomized clinical investigation.

SETTING

A university hospital.

PARTICIPANTS

One hundred fifty-seven patients who underwent elective cardiac surgery that required cardiopulmonary bypass.

INTERVENTIONS

Fifty-two patients were administered intravenous infusion of dopamine (3 µg/kg/min) for five minutes after weaning from cardiopulmonary bypass; no intervention was applied in the other 105 patients.

MEASUREMENTS AND MAIN RESULTS

Measurements were performed under general anesthesia and mechanical ventilation before cardiopulmonary bypass, after cardiopulmonary bypass, and after the intervention. In each protocol stage, forced oscillatory lung impedance was measured to assess airway and tissue mechanical changes. Mainstream capnography was performed to assess ventilation- and/or perfusion-matching by calculating the normalized phase-3 slopes of the time and volumetric capnograms and the physiologic deadspace. Arterial and central venous blood samples were analyzed to characterize lung oxygenation and intrapulmonary shunt. After cardiopulmonary bypass, dopamineinduced marked improvements in airway resistance and tissue damping, with relatively small decreases in lung tissue elastance. These changes were associated with decreases in the normalized phase-3 slopes of the time and volumetric capnograms. The inotrope had no effect on physiologic deadspace, intrapulmonary shunt, or lung oxygenation.

CONCLUSION

Dopamine reversed the complex detrimental lung mechanical changes induced by cardiopulmonary bypass and alleviated ventilation heterogeneities without affecting the physiologic deadspace or intrapulmonary shunt. Therefore, dopamine has a potential benefit on the gas exchange abnormalities after weaning from cardiopulmonary bypass.

One-lung ventilation with use of a double lumen tube in two dogs; when right might be wrong

One-lung ventilation (OLV) is an anaesthetic technique utilised for improved visualisation and access of the surgical field during thoracoscopy. The authors present two cases that underwent OLV with use of a double lumen tube (DLT). The first case was intubated with endoscopic guidance for bronchial port intubation of the right mainstem bronchus. This dog experienced prolonged periods of intraoperative hypoxemia. Upon case review, it was suspected intubation of the mainstem bronchus resulted in occlusion of the right cranial lung lobe. In the second case, the DLT was placed bronchoscopically into the left mainstem bronchus with the aid of computed tomography (CT). Excellent intraoperative oxygenation was achieved. When DLTs are used in dogs, their anatomical differences from humans make them susceptible to additional lung occlusion and pulmonary shunting. Computed tomography is recommended as a fundamental addition to bronchoscopy for correct tube placement.

Effects of a 1:1 inspiratory to expiratory ratio on respiratory mechanics and oxygenation during one-lung ventilation in patients with low diffusion capacity of lung for carbon monoxide: a crossover study

STUDY OBJECTIVE

To investigate the effects of a 1:1 inspiratory-to-expiratory (I:E) ventilation ratio on oxygenation and respiratory mechanics during one-lung ventilation (OLV) in patients with low diffusion capacity of lung for carbon monoxide (DLCO).

DESIGN

Prospective, randomized, crossover study.

SETTING

Operating room, university hospital.

PATIENTS

Twenty-six patients with a preoperative DLCO less than 80% who were scheduled for lung lobectomy requiring OLV under general anesthesia.

INTERVENTIONS

In the first group (n = 13), OLV was begun with a 1:1 I:E ratio, which was switched to a 1:2 I:E ratio after 30 minutes. In the second group (n = 13), the modes of ventilation were performed in the opposite order. Pressure-controlled ventilation with 5 cm H2O of positive end-expiratory pressure and a tidal volume of 5 to 8 mL/kg was applied during OLV.

MEASUREMENTS

Arterial and central venous blood gas analyses were recorded and used to calculate intrapulmonary shunt fraction and physiologic dead space. These measurements were taken at 4 time points: 10 minutes after two-lung ventilation in the lateral decubitus position, 30 minutes after initiation of OLV, 30 minutes after switching the I:E ratio, and 10 minutes after two-lung ventilation was resumed.

MAIN RESULTS

There was no difference in arterial oxygen tension during OLV between the 2 groups (P = .429). Arterial carbon dioxide tension and peak airway pressure were lower in the 1:1 group than in the 1:2 group (P = .003; P = .008). Physiologic dead space was also decreased in the 1:1 I:E ratio group (P = .003). Mean airway pressure and dynamic compliance were higher in the 1:1 group (P = .003; P = .007).

CONCLUSIONS

Pressure-controlled ventilation with a 1:1 I:E ventilation ratio did not improve oxygenation in patients with low DLCO during OLV compared with a 1:2 I:E ventilation ratio. However, it did provide benefits in terms of respiratory mechanics and increased the efficiency of alveolar ventilation during OLV.

Managing hypoxemia during minimally invasive thoracic surgery

An ever-increasing number of thoracic procedures are being performed through minimally invasive techniques. Although the incidence of hypoxemia during one-lung ventilation (OLV) has decreased over the years, it remains an issue in roughly 10% of cases. Algorithms for the management of OLV hypoxemia have to be adapted to the thoracoscopic approach, in particular the need for optimal surgical exposure. With appropriate planning and caution, most of the treatment modalities for OLV hypoxemia can be applied to the thoracoscopy setting, with some modifications.

Effects of a 1:1 inspiratory to expiratory ratio on respiratory mechanics and oxygenation during one-lung ventilation in the lateral decubitus position

Prolonged inspiratory to expiratory (I:E) ratio ventilation may have both positive and negative effects on respiratory mechanics and oxygenation during one-lung ventilation (OLV), but definitive information is currently lacking. We therefore compared the effects of volume-controlled ventilation with I:E ratios of 1:1 and 1:2 on respiratory mechanics and oxygenation during OLV. Fifty-six patients undergoing thoracoscopic lobectomy were randomly assigned volume-controlled ventilation with an I:E ratio of 1:1 (group 1:1, n=28) or 1:2 (group 1:2, n=28) during OLV. Arterial and central venous blood gas analyses and respiratory variables were recorded 15 minutes into two-lung ventilation, at 30 and 60 minutes during OLV, and 15 minutes after two-lung ventilation was re-initiated. Peak and plateau airway pressures in cmH2O [standard deviation] during OLV were significantly lower in group 1:1 than in group 1:2 (P <0.01) (19 [3] and 23 [4]; 16 [3] and 19 [5], respectively). The arterial to end-tidal carbon dioxide tension difference was significantly lower in group 1:1 than in group 1:2 (P <0.01), (0.5 [0.3] and 1.1 [0.5]). There were no significant differences in PaO2 during OLV between the two groups (OLV30, P=0.856; OLV60, P=0.473). In summary, volume-controlled ventilation with an I:E ratio of 1:1 reduced peak and plateau airway pressures improved dynamic compliance and efficiency of alveolar ventilation, but it did not improve arterial oxygenation in a substantial manner. Furthermore, the associated increase in mean airway pressure might have reduced cardiac output, resulting in a lower central venous oxygen saturation.

Anesthesia for Tracheobronchial Surgery

The airway is a crucial dynamic structure that spans different anatomical zones, including the intrathoracic, extrathoracic, tracheal, bronchial, and alveolar zones. Because of its vital role as the sole oxygen-conducting pathway to the alveoli, and hence to the human body, surgery involving any portion requires careful and specific planning by both the surgeon and the anesthesiologist. The review covers essential management points for proximal and distal tracheal procedures, including a discussion of tracheal stenting and tracheoplasty.

The effects of dobutamine and dopamine on intrapulmonary shunt and gas exchange in healthy humans

The development of intrapulmonary shunts with increased cardiac output during exercise in healthy humans has been reported in several recent studies, but mechanisms governing their recruitment remain unclear. Dobutamine and dopamine are inotropes commonly used to augment cardiac output; however, both can increase venous admixture/shunt fraction (Qs/Qt). It is possible that, as with exercise, intrapulmonary shunts are recruited with increased cardiac output during dobutamine and/or dopamine infusion that may contribute to the observed increase in Qs/Qt. The purpose of this study was to examine how dobutamine and dopamine affect intrapulmonary shunt and gas exchange. Nine resting healthy subjects received serial infusions of dobutamine and dopamine at incremental doses under normoxic and hyperoxic (inspired O(2) fraction = 1.0) conditions. At each step, alveolar-to-arterial Po(2) difference (A-aDo(2)) and Qs/Qt were calculated from arterial blood gas samples, intrapulmonary shunt was evaluated using contrast echocardiography, and cardiac output was calculated by Doppler echocardiography. Both dobutamine and dopamine increased cardiac output and Qs/Qt. Intrapulmonary shunt developed in most subjects with both drugs and paralleled the increase in Qs/Qt. A-aDo(2) was unchanged due to a concurrent rise in mixed venous oxygen content. Hyperoxia consistently eliminated intrapulmonary shunt. These findings contribute to our present understanding of the mechanisms governing recruitment of these intrapulmonary shunts as well as their impact on gas exchange. In addition, given the deleterious effect on Qs/Qt and the risk of neurological complications with intrapulmonary shunts, these findings could have important implications for use of dobutamine and dopamine in the clinical setting.

[Hemodynamic monitoring in one-lung ventilation]

One-lung ventilation causes adverse effects in pulmonary gas exchange and cardiocirculatory function. These adverse effects become particularly important for patients with underlying cardiopulmonary comorbidities. Alterations in pulmonary gas exchange have been investigated in several experimental and clinical trials. However, the hemodynamic consequences of one-lung ventilation are to a great extent unknown. Furthermore, no conclusive recommendations exist as to which kind of hemodynamic monitoring should be preferred in the situation of one-lung ventilation. Many issues regarding hemodynamic monitoring in one-lung ventilation remain unacknowledged. This article will review the current literature on hemodynamic monitoring in one-lung ventilation in order to derive recommendations for the application of hemodynamic monitoring in this specific peri-operative situation.

Arterial oxygenation and one-lung anesthesia

PURPOSE OF REVIEW

In the presence of the obligatory shunt during one-lung ventilation, arterial oxygenation is determined by the magnitude of the shunt in addition to the oxygen content of the mixed venous blood coursing through that shunt. The present discussion aims to heighten awareness of factors determining arterial oxygenation during one-lung anesthesia, other than the magnitude of the shunt and dependent lung low-ventilation perfusion units.

RECENT FINDINGS

A convenient way to increase mixed venous and thereby arterial oxygenation is to raise cardiac output. While this approach has achieved some success when increasing cardiac output from low levels, other studies have highlighted limitations of this approach when cardiac output attains very high levels. The effect of anesthesia techniques on the relationship between oxygen consumption and cardiac output could also explain unanswered questions regarding the pathophysiology of arterial oxygenation during one-lung anesthesia.

SUMMARY

The effects of anesthesia techniques on oxygen consumption, cardiac output and therefore mixed venous oxygenation can significantly affect arterial oxygenation during one-lung anesthesia. While pursuing increases in cardiac output may, under limited circumstances, benefit arterial oxygenation during one-lung ventilation, this approach is not a panacea and does not obviate the necessity to optimize dependent lung volume.

Effects of Arginine Vasopressin on Oxygenation and Haemodynamics during One-Lung Ventilation in an Animal Model

In a case of arterial hypotension during one-lung ventilation, haemodynamic support may be required to maintain adequate mean arterial pressure. Arginine vasopressin, a potent systemic vasoconstrictor with limited effects on the pulmonary artery pressure, has not been studied in this setting. Twelve female pigs were anaesthetised and ventilated and arterial, central venous and pulmonary artery catheters were inserted. A left-sided double lumen tube was placed via tracheostomy and one-lung ventilation was initiated. The animals were in the left lateral position, with the left lung ventilated and right lung collapsed. Respiratory and haemodynamic values were recorded before and during a continuous infusion of arginine vasopressin sufficient to double the mean arterial pressure. The arginine vasopressin caused a decrease in cardiac output (3.8±1.1 vs. 2.7±0.7 l/min, P <0.001) and mixed-venous oxygen tension (39.1±5.8 vs. 34.4±5 mmHg, P=0.003). Pulmonary artery pressure was unchanged (24±2 vs. 24±3 mmHg, P=0.682). There was no effect of the arginine vasopressin on arterial oxygen tension (226±106 vs. 231±118 mmHg, P=0.745). However, there was a significant decrease in shunt fraction (28.3±6.2 vs. 24.3±7.8%, P=0.043) and a significant proportional increase in perfusion of the ventilated lung (78.8±9.5 vs. 85.5±7.9%, P=0.036). In our animal model of one-lung ventilation, doubling mean arterial pressure by infusion of arginine vasopressin significantly affected global haemodynamics, but had no influence on systemic arterial oxygen tension.

Atemwegsmanagement bei der Ein-Lungen-Ventilation

The progress in sophisticated and complex operating methods for intrathoracic procedures demands reliable lung separation with the possibility of one-lung ventilation. Patients with thoracic traumas and pulmonary emergencies can confront any anaesthesiologist with the need for lung separating procedures. This review describes the contemporary procedures for lung separation. The special aspects of difficult airway management during one-lung ventilation and the indications for one-lung ventilation are described in detail. The pathophysiological changes during one-lung ventilation and strategies to avoid hypoxemia and to preserve adequate oxygenation are discussed.