The effects of ventilation on left-to-right shunt and regional cerebral oxygen saturation: a self-controlled trial

BACKGROUND

Increase of pulmonary vascular resistance (PVR) is an efficient method of modulating pulmonary and systemic blood flows (Qp/Qs) for patients with left-to-right (L-R) shunt, and is also closely associated with insufficient oxygen exchange for pulmonary hypoperfusion. So that it might be a preferred regime of maintaining arterial partial pressure of carbon dioxide tension (PaCO₂) within an optimal boundary via ventilation management in congenital heart disease (CHD) patients for the inconvenient measure of the PVR and Qp/Qs. However, the appropriate range of PaCO₂ and patient-specific mechanical ventilation settings remain controversial for CHD children with L-R shunt.

METHODS

Thirty-one pediatric patients with L-R shunt, 1-6 yr of age, were included in this observation study. Patients were ventilated with tidal volume (V_T) of 10, 8 and 6 ml/kg in sequence, and 15 min stabilization period for individual V_T. The velocity time integral (VTI) of L-R shunt, pulmonary artery (PA) and descending aorta (DA) were measured with transesophageal echocardiography (TEE) after an initial 15 min stabilization period for each V_T, with arterial blood gas analysis. Near-infrared spectroscopy sensor were positioned on the surface of the bilateral temporal artery to monitor the change in regional cerebral oxygen saturation (rScO₂).

RESULTS

PaCO₂ was 31.51 ± 0.65 mmHg at V_T 10 ml/kg vs. 37.15 ± 0.75 mmHg at V_T 8 ml/kg (P < 0.03), with 44.24 ± 0.99 mmHg at V_T 6 ml/kg significantly higher than 37.15 ± 0.75 mmHg at V_T 8 ml/kg. However, PaO₂ at a V_T of 6 ml/kg was lower than that at a V_T of 10 ml/kg (P = 0.05). Meanwhile, 72% (22/31) patients had PaCO₂ in the range of 40-50 mmHg at V_T 6 ml/kg. VTI of L-R shunt and PA at V_T 6 ml/kg were lower than that at V_T of 8 and 10 ml/kg (P < 0.05). rScO₂ at a V_T of 6 ml/kg was higher than that at a V_T of 8 and 10 ml/kg (P < 0.05), with a significantly correlation between rScO₂ and PaCO₂ (r = 0.53). VTI of PA in patients with defect diameter > 10 mm was higher that that in patients with defect diameter ≤ 10 mm.

CONCLUSIONS

Maintaining PaCO₂ in the boundary of 40-50 mmHg with V_T 6 ml/kg might be a feasible ventilation regime to achieve better oxygenation for patients with L-R shunt. Continue raising PaCO₂ should be careful.

TRAIL REGISTRATION

Clinical Trial Registry of China (http://www.chictr.org.cn) identifier: ChiCTR-OOC-17011338 , prospectively registered on May 9, 2017.

Effects of carbon dioxide insufflation on anastomosis remodeling at a carotid artery site in rabbits

Introduction

Use of carbon dioxide (CO₂) insufflation (CDI) on the surgical field during heart surgery has become widespread, and in some units routine.

Aim

To assess the effects of CDI on endothelial dysfunction in a carotid artery model in rabbits.

Material and methods

Twelve randomly selected rabbits were divided into two groups. Right carotid arteries of the animals were transected and sutured with running suture technique. Then, 1 l/min CO₂ insufflation was initiated with a 45° angle. In the control group, the anastomotic field was irrigated with 0.1 ml/s flow of 0.9% saline. At day 28, the carotid artery segments were removed and prepared for histological specimens.

Results

In the cross-sections of the control group vessel samples, thickening of the tunica intima was observed. Scoring the quantity of endothelial nitric oxide synthase (e-NOS) and α-smooth muscle actin (α-SMA) positive staining revealed a nonsignificant difference between the experimental groups (p = 0.07). In the CO₂ group, the intimal hyperplasia (p = 0.2) and the thickness of the tunica media (p = 0.2) were indistinguishable when compared to the control group. The mean luminal diameters and luminal areas of the experimental groups were all evaluated by histomorphometry and a significant differences was found between luminal areas (p = 0.016). On the other hand, no significant difference was found between mean luminal diameters (p = 0.055).

Conclusions

Our study indicated that CDI can affect endothelial cell damage and the mean luminal diameters.

A validation method for near-infrared spectroscopy based tissue oximeters for cerebral and somatic tissue oxygen saturation measurements

We describe the validation methodology for the NIRS based FORE-SIGHT ELITE^® (CAS Medical Systems, Inc., Branford, CT, USA) tissue oximeter for cerebral and somatic tissue oxygen saturation (StO₂) measurements for adult subjects submitted to the United States Food and Drug Administration (FDA) to obtain clearance for clinical use. This validation methodology evolved from a history of NIRS validations in the literature and FDA recommended use of Deming regression and bootstrapping statistical validation methods. For cerebral validation, forehead cerebral StO₂ measurements were compared to a weighted 70:30 reference (REF CX_B) of co-oximeter internal jugular venous and arterial blood saturation of healthy adult subjects during a controlled hypoxia sequence, with a sensor placed on the forehead. For somatic validation, somatic StO₂ measurements were compared to a weighted 70:30 reference (REF CX_S) of co-oximetry central venous and arterial saturation values following a similar protocol, with sensors place on the flank, quadriceps muscle, and calf muscle. With informed consent, 25 subjects successfully completed the cerebral validation study. The bias and precision (1 SD) of cerebral StO₂ compared to REF CX_B was −0.14 ± 3.07%. With informed consent, 24 subjects successfully completed the somatic validation study. The bias and precision of somatic StO₂ compared to REF CX_S was 0.04 ± 4.22% from the average of flank, quadriceps, and calf StO₂ measurements to best represent the global whole body REF CX_S. The NIRS validation methods presented potentially provide a reliable means to test NIRS monitors and qualify them for clinical use.