Flap Monitoring Using Transcutaneous Oxygen or Carbon Dioxide Measurements

Free tissue transfer is a cornerstone of complex reconstruction. In many cases, it represents the last option available for a patient and their reconstruction. At high-volume centers, the risk of free flap failure is low but its occurrence can be devastating. Currently, the mainstay for flap monitoring is the clinical examination. Though reliable when performed by experienced clinicians, the flap exam is largely subjective, is performed discontinuously, and often results in significant time delay between detection of flap compromise and intervention. Among emerging flap monitoring technologies, the most promising appear to be those that rely on noninvasive transcutaneous oxygen and carbon dioxide measurements, which provide information regarding flap perfusion. In this article, we review and summarize the literature on various techniques but primarily emphasizing those technologies that rely on transcutaneous gas measurements. We also define characteristics for the ideal flap monitoring tool and discuss critical barriers, predominantly cost, preventing more widespread utilization of adjunct monitoring technologies, and their implications.     

Automated Detection of Gastric Luminal Partial Pressure of Carbon Dioxide during Cardiovascular Surgery Using the Tonocap

Background: A new automated system of air tonometry (Tonocap; Datex Ohmeda, Helsinki, Finland) allows for frequent (every 15 min) measurement of gastric luminal partial pressure of carbon dioxide. Its use has not been described in cardiac surgical patients.

Methods: One hundred patients undergoing coronary artery bypass graft or cardiac valve surgery were enrolled in a prospective cohort study. After anesthetic induction and insertion of a TRIP NGS Catheter (Datex Ohmeda), measurements of gastric luminal partial pressure of carbon dioxide were obtained using the Tonocap, and gastric mucosal p H (p Hi) was calculated. The main outcome measure was postoperative complication, defined as either in-hospital death or prolonged postoperative hospitalization (> 14 days).

Results: Four patients (4%) died, all of multiple-system organ failure, one each on postoperative days 9, 26, 46, and 121. Postoperative complication occurred in 18 patients (18%), all of whom exhibited persistent dysfunction of at least one organ system. Perioperatively, an abnormal p Hi (< 7.32) and gastric luminal minus arterial partial pressure of carbon dioxide gap (> 8 mmHg) occurred in 66% and 70% of patients, respectively. Predictors of postoperative complication included postoperative pHi (P = 0.001), gastric luminal partial pressure of carbon dioxide (P = 0.022), and gastric luminal minus arterial partial pressure of carbon dioxide gap (P = 0.013). In contrast, arterial base excess (P > 0.4) and routinely measured hemodynamic variables (e.g., heart rate, blood pressure) were either less predictive compared with Tonocap-derived variables or not predictive.     

A Simple Method of Monitoring Carbon Dioxide Output in Anaesthetized Patients

The mean CO2 output during anaesthesia in paralyzed patients can be monitored by continuous capnographic analysis of the total exhaled gases, the latter being mechanically integrated by pumice canisters. The gas is evacuated from the Hafnia A circuit via an ejector flowmeter. The results are not influenced by the flow rates employed.     

Arterial to End-tidal Carbon Dioxide Pressure Difference during Laparoscopic Surgery in Pregnancy

Background: There is controversy about whether capnography is adequate to monitor pulmonary ventilation to reduce the risk of significant respiratory acidosis in pregnant patients undergoing laparoscopic surgery. In this prospective study, changes in arterial to end-tidal carbon dioxide pressure difference (PaCO2--PetCO2), induced by carbon dioxide pneumoperitoneum, were determined in pregnant patients undergoing laparoscopic cholecystectomy.

Methods: Eight pregnant women underwent general anesthesia at 17-30 weeks of gestation. Carbon dioxide pnueumoperitoneum was initiated after obtaining arterial blood for gas analysis. Pulmonary ventilation was adjusted to maintain PetCO2 around 32 mmHg during the procedure. Arterial blood gas analysis was performed during insufflation, after the termination of insufflation, after extubation, and in the postoperative period.

Results: The mean +/- SD for PaCO2--PetCO2 was 2.4 +/- 1.5 before carbon dioxide pneumoperitoneum, 2.6 +/- 1.2 during, and 1.9 +/- 1.4 mmHg after termination of pneumoperitoneum. PaCO2 and p H during pneumoperitoneum were 35 +/- 1.7 mmHg and 7.41 +/- 0.02, respectively. There were no significant differences in either mean PaCO2--PetCO2 or PaCO2 and p H during various phases of laparoscopy.     

上尿路后腹腔镜手术中不同压力气腹对机体的影响

目的探讨不同压力CO_2气腹在上尿路后腹腔镜手术中对患者机体的影响。方法将2011年09月至2013年12月间在本院行后腹腔镜肾上腺肿瘤切除术和后腹腔镜肾囊肿去顶减压术的68例患者术前随机分为两组,术中气腹压力分别设定为l0mmHg和15mmHg,测定两组气腹前、气腹后30分钟和放气后30分钟的动脉血气;观察手术时间、术中出血量;并记录术后疼痛等并发症的发生率。结果两组手术时间及术中出血量无明显差别;低压力气腹较常规压力气腹对患者PaCO_2、PH的影响更小,术后肩部及上腹部疼痛的发生率更低。结论低压力CO_2气腹相对于常规压力CO_2气腹对患者各系统功能影响较小,在后腹腔镜手术中有一定的应用价值。     

Monitoring Gastric Mucosal Carbon Dioxide Pressure Using Gas Tonometry: In Vitro and in Vivo Validation Studies

Background: Saline gastric tonometry of carbon dioxide has been proposed as a means to assess the adequacy of splanchnic perfusion. However, this technique has several disadvantages, including the long time interval needed for gases to reach equilibrium in saline milieu. Thus the authors evaluated a system that uses a gas-filled instead of a saline-filled gastric balloon.

Methods: In vitro, we simultaneously placed two tonometry catheters in an equilibration water bath maintained at a predetermined and constant pressure of carbon dioxide (PCO2). The first catheter's balloon was filled with air and the second with saline. The performance of gas tonometry was tested by comparing the PCO2 measurements of the bath obtained via gas tonometry (PgCO2) to the PCO2 measurements of direct bath samples (PbathCO2). These results were also compared with the PCO2 measurements obtained simultaneously by saline tonometry (PsCO2). The response time of gas versus saline tonometry was also studied. In vivo, the performance of gas tonometry was tested comparing the measurements of gastric intramucosal PCO2 obtained by gas tonometry (PgCO2) at different equilibration times with those obtained by saline tonometry (PsCO2) using an equilibration time of 30 min. Two nasogastric tonometry catheters were placed simultaneously in seven stable patients in the intensive care unit. The first balloon was filled with air and the second with saline.

Results: In vitro, there was a close correlation between PgCO sub 2 and PbathCO2, for each level of PbathCO2, and for each different gas equilibration time. For an equilibration time of 10 min at a PbathCO2 level of approximately 40 mmHg, the bias of the gas device defined as the mean of the differences between Pbath sub CO2 and PgCO2, and its precision defined as the standard deviation of the bias, were -0.3 mmHg and 0.7 mmHg, respectively. Using the same definitions, the bias and precision of saline tonometry were 11.2 mmHg and 1.4 mmHg, respectively. If the equilibration time-dependent correction factor provided by the catheter manufacturer for saline tonometry was applied, the bias and precision were -6.9 mmHg and 2.9 mmHg, respectively. In vivo, using an equilibration time of 10 min for gas and 30 min for saline tonometry, there was a close correlation between the two techniques (r2 = 0.986). A Bland and Altman analysis revealed a bias (+/- 2 SD) of 0.1 +/- 6.8 mmHg. The correlation between the two methods was not improved if we prolonged the equilibration time of the gas tonometer.     

Method for Continuous Measurement of Carbon Dioxide Output during Anesthesia An Assessment

Employing the Mapleson D circuit, a modified closed-circuit flow-through technique for the continuous measurement of carbon dioxide production (VCO2) was tested for accuracy and precision in a lung model. The recovery of carbon dioxide production was found to be between 90 and 110%, the maximized errors for a single estimate of carbon dioxide production were between +/- 4 and +/- 28%, with the highest errors at high gas flows and low carbon dioxide inputs. Accepting arbitrarily chosen limits of maximized errors of +/- 10%, it could be shown that the system did not work acceptably when the mean carbon dioxide concentration was below 1.5 vol.% within the fresh gas flow rates (2.2--7.7 1 min-1) and the range of minute ventilation (4--10 1 min-1) employed. The half-life of carbon dioxide washout varied between 41 and 138 s, thus limiting the suitability of the system for detecting changes in carbon dioxide output. The method may be used as an approximate monitor of VCO2 in anaesthetized patients, but cannot be regarded as sufficient for research purposes.     

Transcutaneous Monitoring of Blood Gas Tensions in Patients on Intermittent Peritoneal Dialysis

A relative contraindication to intermittent peritoneal dialysis (IPD) is chronic lung disease. To evaluate whether the instillation of 2 L of fluid into the peritoneal cavity affects respiratory function, five IPD patients were studied in the supine position during the first 4 h of a routine IPD session. Blood gas tensions were monitored transcutaneously throughout the study period. At the onset of dialysis, mean transcutaneous blood oxygen tension (PtcO2) was 70.6 +/- 9.1 mm Hg. It decreased to 55 +/- 9.9 mm Hg (22% change from basal values) during the instillation of dialysate. Upon drainage, PtcO2 returned to baseline. This sequence of events repeated itself on subsequent exchanges, although with decreasing decrements of PtcO2 with each consecutive exchange (decrease to 58.6 +/- 7.05, 61 +/- 6.5, 63.8 +/- 5.2 mm Hg corresponding to 16%, 12.7%, and 9.6%, respectively, during the second to fourth exchanges). Transcutaneous blood carbon dioxide tension, PtcCO2, showed a very mild increase during the study (33 +/- 7.1 to 38 +/- 6.0 mm Hg). In two patients, the same study protocol was performed during the last 4 h of an IPD session. In these two patients, there was only a 5% variation of PtcO2 from baseline values. These results suggest that an adaptive response to the hypoxemia induced by dialysate instillation rapidly occurs in IPD patients.     

Effects of Intraabdominanlly Insufflated Carbon Dioxide and Elevated Intraabdominal Pressure on Splanchnic Circulation: An Experimental Study in Pigs

Background: Intraabdominally insufflated carbon dioxide (CO2) during laparoscopy may have a specific effect on splanchnic circulation that may be unrelated to the effects of increased intraabdominal pressure alone. Therefore, the influences of insufflation with CO2 versus air on splanchnic circulation were compared.

Methods: Pigs were chronically instrumented for continuous recording of mesenteric artery, portal venous, inferior vena cava, and pulmonary arterial blood flow and portal venous pressure. After induction of anesthesia, CO2 or air was insufflated in 14 and 10 pigs, respectively. With the pigs in the supine position, intraabdominal pressure was increased in steps of 4 mmHg up to 24 mmHg by graded gas insufflation.

Results: During air insufflation, mesenteric artery vascular resistance was unchanged, whereas mesenteric arterial blood flow decreased with increasing intraabdominal pressure. Shortly after CO3 insufflation to an intraabdominal pressure of 4 mmHg, mean arterial pressure, mesenteric arterial blood flow, and mesenteric arterial vascular resistance were increased by 21%, 12% and 9%, respectively. Subsequently, with the onset of CO2 resorption in the third minute, mean arterial pressure declined to baseline values and mesenteric arterial vascular resistance declined to 85% of baseline values, whereas mesenteric arterial blood flow continued to increase to a maximum of 24% higher than baseline values. At steady-state conditions during CO2 insufflation, mesenteric arterial blood flow was increased up to an intraabdominal pressure 相似文献   

左心房压和肺动脉楔压监测在心脏术后的应用

目的评价心脏直视术后合并肺动脉高压患者经颈内静脉安置左心房测压管和肺动脉漂浮导管对于成人心脏外科术后患者监护的可行性、安全性及准确性。方法前瞻性选择2010～2012年于武汉亚洲心脏病医院行心内直视手术的18岁以上患者100例,男43例、女57例,年龄46～65（47±16）岁。将患者分为两组：合并淤血性重度肺动脉高压患者行瓣膜置换术50例（A组）,合并淤血性轻中度肺动脉高压患者行瓣膜置换术50例（B组）。两组患者均经颈内静脉入路置入ARROW5Fr三腔导管,尖端经房间隔穿刺行持续左心房压（LAP）监测;同时经同侧颈内静脉安置ARROW 8Fr高流量鞘管放置肺动脉漂浮导管,入室即监测LAP和肺动脉楔压（PAWP）。观察两组患者中LAP和PAWP的相关性及准确性。结果两组患者均成功行持续LAP及PAWP监测,无严重导管相关并发症发生。A组和B组患者手术时间和体外循环时间差异无统计学意义（P〉0．05）,术后机械通气时间和ICU留置时间差异有统计学意义（P〈O．05）。A组患者平均肺动脉压（PAPMean）、平均左心房压（LAPmean）、平均肺动脉楔压（PAWPmean）、PAWP与LAP差值平均值（PAWP-LAPmean）均显著高于B组（P〈0．01）。两组患者中PAWP与LAP均具有良好相关性,A组患者相关性低于B组,差异有统计学意义（P〈0．01）。结论经颈内静脉入路行LAP监测及肺动脉漂浮导管监测是安全、可行的。PAWP不能准确反映左心室前负荷,在合并淤血性重度肺动脉高压的患者中使用LAP监测对于判断左心室前负荷更准确。     

慢性肾脏病不同分期血二氧化碳结合力的变化及其影响因素分析

目的：调查慢性肾脏病（CKD）患者血二氧化碳结合力（CO2-CP）水平的基础状况。方法：对中山大学附属第三医院肾内科门诊就诊的CKD患者进行为期9个月的前瞻性横断面调查,分析其病例基线特征及各期血CO2水平与代谢性酸中毒的发生率。结果：共有715例CKD病例入选。前4位CKD的病因分别为原发性肾小球疾病、高血压肾病、狼疮肾炎和糖尿病肾病。CKD3期以后,随着CKD分期的进展,血CO2-CP水平逐级显著性降低,代谢性酸中毒的发生率逐级显著性升高。多元回归分析结果显示,血CO2-CP水平和肾小球滤过率呈显著性正相关,血CO2-CP水平和血清钾以及蛋白尿程度呈显著性负相关。结论：对CKD患者血CO2-CP水平单中心横断面调查,将有助于确定CKD患者血CO2-CP水平的变化规律,为进一步综合防治CKD及其并发症奠定基础。