The Effect of Ventilation Strategy on Arterial and Cerebral Oxygenation During Laparoscopic Bariatric Surgery

Impact of Altered Airway Pressure on Intracranial Pressure, Perfusion, and Oxygenation: A Narrative Review

OBJECTIVES

A narrative review of the pathophysiology linking altered airway pressure and intracranial pressure and cerebral oxygenation.

DATA SOURCES

Online search of PubMed and manual review of articles (laboratory and patient studies) of the altered airway pressure on intracranial pressure, cerebral perfusion, or cerebral oxygenation.

STUDY SELECTION

Randomized trials, observational and physiologic studies.

DATA EXTRACTION

Our group determined by consensus which resources would best inform this review.

DATA SYNTHESIS

In the normal brain, positive-pressure ventilation does not significantly alter intracranial pressure, cerebral oxygenation, or perfusion. In injured brains, the impact of airway pressure on intracranial pressure is variable and determined by several factors; a cerebral venous Starling resistor explains much of the variability. Negative-pressure ventilation can improve cerebral perfusion and oxygenation and reduce intracranial pressure in experimental models, but data are limited, and mechanisms and clinical benefit remain uncertain.

CONCLUSIONS

The effects of airway pressure and ventilation on cerebral perfusion and oxygenation are increasingly understood, especially in the setting of brain injury. In the face of competing mechanisms and priorities, multimodal monitoring and individualized titration will increasingly be required to optimize care.

Effects of ventilatory strategy on arterial oxygenation and respiratory mechanics in overweight and obese patients undergoing posterior spine surgery

Prolonged inspiratory to expiratory (I:E) ratio ventilation may improve arterial oxygenation or gas exchange and respiratory mechanics in patients with obesity. We performed a randomised study to compare the effects of the conventional ratio ventilation (CRV) of 1:2 and the equal ratio ventilation (ERV) of 1:1 on arterial oxygenation and respiratory mechanics during spine surgery in overweight and obese patients. Fifty adult patients with a body mass index of ≥25 kg/m² were randomly allocated to receive an I:E ratio either l:2 (CRV; n = 25) or 1:1 (ERV; n = 25). Arterial oxygenation and respiratory mechanics were recorded in the supine position, and at 30 minutes and 90 minutes after placement in the prone position. The changes in partial arterial oxygen pressure (PaO₂) over time did not differ between the groups. The changes in partial arterial carbon dioxide pressure over time were significantly different between the two groups (P = 0.040). The changes in mean airway pressure (Pmean) over time were significantly different between the two groups (P = 0.044). Although ERV provided a significantly higher Pmean than CRV during surgery, the changes in PaO₂ did not differ between the two groups.

Effect of prolonged inspiratory time on gas exchange during robot-assisted laparoscopic urologic surgery

BACKGROUND

Gas exchange disturbance may develop during urologic robotic laparoscopic surgery with the patient in a steep Trendelenburg position. This study investigated whether prolonged inspiratory time could mitigate gas exchange disturbances including hypercapnia.

METHODS

In this randomized cross-over trial, 32 patients scheduled for robot-assisted urologic surgery were randomized to receive an inspiratory to expiratory time ratio (I:E) of 1:1 for the first hour of pneumoperitoneum followed by 1:2 for last period of surgery (group A, n = 17) or I:E of 1:2 followed by 1:1 (group B, n = 15). Arterial blood gas analysis, airway pressure and hemodynamic variables were assessed at four time points (T1: 10 min after induction of general anesthesia, T2: 1 h after the initiation of pneumoperitoneum, T3: 1 h after T2 and T4: at skin closure). The carry over effect of initial I:E was also evaluated over the next hour through arterial blood gas analysis.

RESULTS

There was a significant decrease in partial pressure of oxygen in arterial blood (PaO₂) for both groups at T2 and T3 compared to T1 but in group B the PaO₂ at T4 was not decreased from the baseline. Partial pressure of carbon dioxide in arterial blood (PaCO₂) increased with I:E of 1:2 but did not significantly increase with I:E of 1:1; however, there were no differences in PaO₂ and PaCO₂ between the groups.

CONCLUSION

Decreased oxygenation by pneumoperitoneum was improved and PaCO₂ did not increase after 1 h of I:E of 1:1; however, the effect of equal ratio ventilation longer than 1 h remains to be determined. There was no carryover effect of the two different I:E ratios.

What is the proper ventilation strategy during laparoscopic surgery?

The main stream of intraabdominal surgery has changed from laparotomy to laparoscopy, but anesthetic care for laparoscopic surgery is challenging for clinicians, because pneumoperitoneum might aggravate respiratory mechanics and arterial oxygenation. The authors reviewed the literature regarding ventilation strategies that reduce deleterious pulmonary physiologic changes during pneumoperitoneum for laparoscopic surgery under general anesthesia and make appropriate recommendations.

Effect of general anesthesia on serum β-amyloid protein and regional cerebral oxygen saturation of elderly patients after subtotal gastrectomy

The aim of the present study was to investigate the influence of general anesthesia on serum β-amyloid protein (Aβ) and regional cerebral oxygen saturation (rSO₂) of elderly patients after subtotal gastrectomy. From June, 2014 to December, 2015, among 168 patients undergoing subtotal gastrectomy, the Mini-Mental State Examination and Montreal Cognitive Assessment was administered the day prior to surgery and the second and ninth days after the operation. In addition, we administered the tests to 168 healthy adult volunteers (healthy controls) who were treated in our hospital medical center in the same period. Near-infrared spectroscopy technology was used for continuous monitoring of the intraoperative rSO₂, and the mean of intraoperative rSO₂ was then calculated. Of the 168 patients, 28 developed postoperative cognitive dysfunction (POCD) and the remaining 140 patients were normal (control). The ELISA method was used to test the expression levels of serum Aβ in the three groups and statistical analyses were conducted. Serum Aβ level in the POCD group was significantly higher than that in the control and healthy control groups, and the difference was statistically significant (P<0.05). The rSO₂ level in the patients with POCD was significantly lower than the control group (P<0.05). The correlation analysis with Aβ as an independent variable and other factors as dependent variables revealed that the serum Aβ level negatively correlated with rSO₂ (r=-1.6749, P<0.05). The combined Aβ and rSO₂ may be useful for the diagnosis and prevention of POCD after subtotal gastrectomy under general anesthesia.

Effect of the Prolonged Inspiratory to Expiratory Ratio on Oxygenation and Respiratory Mechanics During Surgical Procedures

Prolonged inspiratory to expiratory (I:E) ratio ventilation has been researched to reduce lung injury and improve oxygenation in surgical patients with one-lung ventilation (OLV) or carbon dioxide (CO2) pneumoperitoneum. We aimed to confirm the efficacy of the 1:1 equal ratio ventilation (ERV) compared with the 1:2 conventional ratio ventilation (CRV) during surgical procedures. Electronic databases, including PubMed, Embase, Cochrane Central Register of Controlled Trials, Web of Science, and Google Scholar were searched.Prospective interventional trials that assessed the effects of prolonged I:E ratio of 1:1 during surgical procedures. Adult patients undergoing OLV or CO2 pneumoperitoneum as specific interventions depending on surgical procedures. The included studies were examined with the Cochrane Collaboration's tool. The data regarding intraoperative oxygenation and respiratory mechanics were extracted, and then pooled with standardized mean difference (SMD) using the method of Hedges. Seven trials (498 total patients, 274 with ERV) were included. From overall analysis, ERV did not improve oxygenation at 20 or 30 minutes after specific interventions (SMD 0.193, 95% confidence interval (CI): -0.094 to 0.481, P = 0.188). From subgroup analyses, ERV provided significantly improved oxygenation only with laparoscopy (SMD 0.425, 95% CI: 0.167-0.682, P = 0.001). At 60 minutes after the specific interventions, ERV improved oxygenation significantly in the overall analysis (SMD 0.447, 95% CI: 0.209-0.685, P < 0.001) as well as in the subgroup analyses with OLV (SMD 0.328, 95% CI: 0.011-0.644, P = 0.042) and laparoscopy (SMD 0.668, 95% CI: 0.052-1.285, P = 0.034). ERV provided lower peak airway pressure (Ppeak) and plateau airway pressure (Pplat) than CRV, regardless of the type of intervention. The relatively small number of the included articles and their heterogeneity could be the main limitations. ERV improved oxygenation at all of the assessment points during laparoscopy. In OLV, oxygenation improvement with ERV was observed 1 hour after application. ERV could be beneficial to reduce the Ppeak and Pplat.