Mechanical Effects of Cardiovascular Drugs and Devices
Michel R. Labrosse in Cardiovascular Mechanics, 2018
Bench testing of CPB components requires a mock circulatory loop of bovine blood that uses a large venous reservoir and a second oxygenator for the simulated patient. The second oxygenator uses a mixture of nitrogen and carbon dioxide as the gas to deoxygenate the blood. Following the recommendations in the guidance document, the oxygenator must be investigated for leaks, toxicity, loss of gas transfer efficiency, gas embolism, thromboembolism, and blood damage. The circuit components should be tested at a blood flow rate of 5 L/min for 6 hours. Operating specifications for CPB oxygenators include an inflow oxygen transfer requirement of 250 mL/min and an outflow carbon dioxide elimination of 200 mL/min at a blood flow rate of 5 L/min.18 Most oxygenators also serve as heat exchangers and must be characterized for safety and performance. The heat-exchange performance factor is calculated from the difference in blood temperature across the oxygenator, divided by the difference between water and blood temperature at the oxygenator inlet. The water side pressure difference should be monitored. The arterial line filter must be evaluated for hemolysis separately from the oxygenator, and platelet functionality must be characterized. Excessive pressure drop across the filter over the time of use may result in inadequate blood flow and should be measured. The filtration efficiency measures the ability of the device to remove solid and gaseous emboli by using a bubble generator and detector in the circuit. Standard hemocompatibility and sterility testing are also expected.
Cardiac surgery
Brian J Pollard, Gareth Kitchen in Handbook of Clinical Anaesthesia, 2017
This is shown diagrammatically in Figure 16.1. Venous cannulae are inserted into the right atrium, the venae cavae, or (more rarely) the femoral vein or pulmonary artery. The large-bore venous return line drains blood, under gravity, from the patient on the operating table to the reservoir of the bypass machine on the floor. The reservoir is either a rigid casing or a bag (soft-cell). Blood is then pumped through the oxygenator, where it is oxygenated and carbon dioxide is removed. In addition, a heat exchanger allows heating and cooling of the blood. The pumps driving the flow may be compression roller devices or use centrifugal force (centrifugal pumps). The blood is returned to the body via an aortic or (more rarely) a femoral cannula after passing through a filter. The arterial cannula is always inserted first and is the last to be removed. There are a number of scenarios where femoral venous and arterial cannulation is the site of choice:
Cardiac surgery
Roy Palmer, Diana Wetherill in Medicine for Lawyers, 2020
After anticoagulation with heparin, venous blood is drained by cannulae in the right atrium through plastic tubing into a reservoir from which it is pumped into an oxygenator, where oxygen is absorbed and carbon dioxide is given off. The earliest oxygenators allowed direct contact between blood and gas, but this was shown to cause harmful changes to the blood and to the patient. Since the 1970s, oxygenators have imitated the human lung by separating blood from gas by a diffusible membrane. From the oxygenator the now oxygen-rich, arterialized blood passes through a heater/cooler and a micropore filter before returning to the patient through a cannula placed in the ascending aorta. Since the heart and lungs have now been bypassed, the heart can be excluded from the circulation by cross-clamping the ascending aorta below the cannula. The heart is then arrested and protected from the ischaemia produced by the cross-clamp by the infusion of a ‘cardioplegic’ solution of potassium-enriched arterial blood into the aortic root or directly into the coronary arteries through an incision in the aorta. The heart is thus rendered motionless, flaccid and empty of blood, providing the surgeon with ideal operating conditions.
Dexmedetomidine improves postoperative neurocognitive disorder after cardiopulmonary bypass in rats
Published in Neurological Research, 2021
Zhiwei Gao, Zhengfen Li, Rui Deng, Qing Liu, Qiuxia Xiao, Jiang Han, Cuixia Pu, Ying Zhang
After 8 hours of fasting, rats were intraperitoneally injected with 50 mg/kg pentobarbital, and the operation began once the rats lost their righting reflex. The surgical area was shaved and disinfected. The skin on the right neck of the rats was cut longitudinally and the external jugular vein was exposed. A 24G indwelling needle was used to puncture the external jugular vein towards the heart, sutured, and firmly fixed in position. The ventral median skin of the rat tail was cut longitudinally and the caudal median artery was exposed. Heparin 125 u was injected into the external jugular vein to drain blood to the blood collector. A peristaltic pump was used to push the blood flow forward into the rat oxygenator (xijing medical supplies co., LTD.). The blood was oxygenated by the oxygenator and input into the tail artery. The entire CBP process took 90 minutes. Furosemide (2 mg/kg) and protamine (1.5 mg/kg) were intravenously administered after the operation. The rats were warmed by placing them near a heat lamp until they were awake.
The Moral Relevance of ECMO Bridge Maintenance
Published in The American Journal of Bioethics, 2023
When an oxygenator or circuit fails or begins to fail, the medical team is obligated to assess whether the patient is a candidate for replacement. As with the initial decision to cannulate for ECMO, this requires a discussion about the risks and benefits of the procedure, the likelihood of recovery, and the presence of factors that would make the patient prohibitively high risk for intervention. Here, demonstrated failure to recover or become eligible for transplant despite ECMO support, as well as other complications that may have developed during the ECMO bridge such as recurrent pulmonary infections, renal insufficiency, malnutrition, or skin breakdown, should be taken into consideration. If, as Childress et al. note, not all patients have a right to ECMO, a patient who develops a contraindication to ECMO does not have a right to ECMO maintenance when the circuit fails.
Postoperative delirium after coronary artery bypass graft surgery: Dexmedetomidine infusion alone or with the addition of oral melatonin
Published in Egyptian Journal of Anaesthesia, 2021
Ramy Mahrose, Heba ElSerwi, Alfred Maurice, Mayar Elsersi
Midazolam was used before surgery with a maximum of 0.03 mg/kg. Induction of anesthesia was with incremental doses of fentanyl up to 10–12 ug/kg and incremental doses of propofol 0.5–2 mg/kg. Muscle relaxation was achieved by 0.6 mg/kg rocuronium followed by top-up doses during the surgery guided by the nerve stimulator. Maintenance of anesthesia was done using isoflurane 0.5–2%. Blood pressure and heart rate were maintained at around 20% of baseline values. Heparin was used for anticoagulation and maintenance of activated clotting time more than 480 s. The cardiopulmonary bypass circuit was primed with 1 L of Ringer’s Lactate and 250 ml of 20% mannitol. Membrane oxygenator (Medtronic Affinity NT) was used. During CPB temperature was lowered to 30–32°C and maintained at the same level, the pump flow rate 2.4–2.8 l/min/m2, and mean perfusion pressure was targeted between 60 and 80 mmHg. Increments of morphine and propofol were used to maintain anesthesia during CPB. Hematocrit was maintained within 25–35%, fractional concentration of inspired oxygen adjusted to keep oxygen partial pressure within 150–250 mmHg, and gas flow was adjusted to maintain arterial carbon dioxide tension within 35–40 mmHg. Intermittent antegrade and occasionally retrograde blood cardioplegia was given for myocardial protection. Rewarming to 36º-37°C was done before separation from CPB. Protamine sulfate 1 mg/100 U heparin was given after separation from CPB to reach activated clotting time within 10% of baseline. After surgery all patients were transferred to ICU.