Biomedical subjects

Carole Hamilton

Publications and source records attributed to Carole Hamilton.

3 recordsLinked to original sources

PubMed2006

Testing of heat exchangers in membrane oxygenators using air pressure.

All heat exchangers (HE) in membrane oxygenators are tested by the manufacturer for water leaks during the production phase. However, for safety reasons, it is highly recommended that HEs be tested again before clinical use. The most common method is to attach the heater-cooler to the HE and allow the water to recirculate for at least 10 min, during which time a water leak should be evident. To improve the detection of water leaks, a test was devised using a pressure manometer with an integrated bulb used to pressurize the HE with air. The cardiopulmonary bypass system is set up as per protocol. A pressure manometer adapted to a 1/2" tubing is connected to the water inlet side of the oxygenator. The water outlet side is blocked with a short piece of 1/2" deadend tubing. The HE is pressurized with 250 mmHg for at least 30 sec and observed for any drop. Over the last 2 years, only one oxygenator has been detected with a water leak in which the air-method leaktest was performed. This unit was sent back to the manufacturer who confirmed the failure. Even though the incidence of water leaks is very low, it does occur and it is, therefore, important that all HEs are tested before they are used clinically. This method of using a pressure manometer offers many advantages, as the HE can be tested outside of the operating room (OR), allowing earlier testing of the oxygenator, no water contact is necessary, and it is simple, easy and quick to perform.

Air Pressure↗

PubMed2005

Improved outcome in thoracoabdominal aortic aneurysm repair: the role of cerebrospinal fluid drainage.

INTRODUCTION: To evaluate the protective effect and the optimum duration of cerebrospinal fluid drainage (CSFD) during and after thoracoabdominal aortic aneurysm (TAAA) repair. METHODS: From April 2001 to October 2003, we retrospectively compared 17 (n = 17) consecutive patients who have been electively operated on by Martin Grabenwoger for left heart bypass and selective perfusion of the visceral and renal organs. RESULTS: The first 7 patients had CSFD for 72 hours; the duration of CSFD was increased to 100 hours in the remaining 10 patients. Median drained cerebrospinal fluid (CSF) volume was 680 milliliters in the 72-hour group versus 1441 milliliters in the 100-hour group. A characteristic increase in CSF volume was noted between POD No. 2 and POD No. 4 indicating persistent spinal cord edema. Univariate and multivariate analysis demonstrated that CSFD for 100 hours is a significant predictor for decreased incidence of late onset paraplegia (p < 0.001). The overall incidence of postoperative neurological deficit was 17.6% (3 of 17). There was one patient (6%) who developed permanent paraplegia and two patients (12%) with transient paraplegia. These patients sustained late-onset paraplegia 72 hours after surgery for removal of a CSFD device. Complete motor function could be restored after re-insertion of a CSFD device. In one patient, permanent paraplegia was evident after awakening from anesthesia. Because of technical difficulties, only two intercostal arteries could be re-implanted, which was obviously not sufficient to restore spinal cord perfusion. In contrast, no neurological deficit occurred in patients in whom a CSFD instrument was left for 100 hours. CONCLUSION: The extended duration of CSFD may lower the risk of late-onset paraplegia and could improve outcome in patients undergoing thoracoabdominal aortic surgery.

Aged↗

PubMed2004

The oxygen dissociation curve: quantifying the shift.

An oxyhaemoglobin dissociation curve (ODC) quantifies the most important function of red blood cells and that is the affinity for oxygen and its delivery to the tissues. Oxygen affinity for haemoglobin plays a critical role in the delivery of oxygen to the tissues and is changed by shifting to the left or right. A shift to the left implies an increased oxygen affinity and, hence, tighter binding due to the higher oxygen saturation in relation to the pO2. On the other hand, a shift to the right corresponds to a decreased oxygen affinity and easier release of oxygen to the tissues. It is well known that the ODC shifts in response to changes in pH, pCO2 and 2,3 diphosphoglycerate. However, how much the ODC shifts has never been quantified. Arterial and venous blood gases were taken during cardiopulmonary bypass and two indices were used to quantify the shift of the ODC; the p50 shift and the SO2 difference. Arterial blood shifted to the right by 4 +/- 0.1 mmHg at a pH of 7.24 and shifted to the left by -3.5 +/- 0.05 mmHg at a pH of 7.51. The change in arterial saturation was minimal, rising by 0.8% and dropping by -5% and did not correlate to p50 shifting and changes in pH, but demonstrated changes dependent on the concentration of dyshaemoglobins. The venous blood exhibited a greater range of p50 shifting at each pH value. At a pH of 7.24, the p50 shifted to the right by 4.8 +/- 2 mmHg and at a pH of 7.51 the p50 shifted to the left by -4 +/- 1.8 mmHg. Unlike the arterial blood, the change in saturation correlated well to p50 shifting. It is shown here for the first time how much the curve shifts with changes in pH and how this may be used to evaluate treatment strategies.

Arteries↗