Healthy appearing patient with afib s/p ablation and returning for repeat ablation for recurrent afib. Anesthesia induced normally and patient VSS. 3 minutes after a request of a heparin bolus, patient dropped their SBP into the upper 40s, lower 50s. Patient recovered well after small bolus of epinephrine. ICE used to rule out pericardial effusion as well as confirm normal LVEF and RVEF.
What does an angiotensin receptor blocker (ARB) do?
Angiotensin II receptor blockers (ARBs) represent a newer class of effective and well tolerated antihypertensive agents 1. Several clinical studies have indicated the beneficial effects of ARBs in hypertensive patients such as reduction of left ventricular hypertrophy, decrease in ventricular arrhythmias, and improved diastolic function 1. Inhibitors of the renin-angiotensin system (RAS), either angiotensin converting enzyme (ACE) inhibitors or ARBs, mediate vasodilation and consequently decrease blood-pressure by different mechanisms 1. ARBs specifically inhibit angiotensin II from binding to its receptor, the Angiotensin-1 (AT 1) receptor on vascular smooth muscle cells. This blockade results in increased angiotensin II and normal bradykinin plasma levels. ARBs were developed to overcome several deficiencies of ACE inhibitors, which, by comparison, lead to decreased angiotensin II, but increased bradykinin levels. Hence, the key advantage of ARBs over ACE inhibitors is their lack of adverse effects related to bradykinin potentiation. ARBs have been shown to reduce morbidity and mortality associated with hypertension, and therefore, it is not surprising that an increasing number of patients scheduled for surgery are chronically treated with ARBs 2. However, RAS blockade increases the risk of severe hypotension during and after anesthetic induction. ACE-inhibitors are well known for inducing severe circulatory side effects during anesthesia, which led to the general recommendation to withhold the drug on the day of surgery 3.
Chronic AT 1 blockade also reduces the vasoconstrictor response to α 1 receptors activated by norepinephrine, which explains why ARB-induced hypotension can be so resistant to phenylephrine, ephedrine and norepinephrine 2, 8 Clinical studies have shown significant vasoconstrictor effects of vasopressin and increased cardiac filling during echocardiographic measurements 2.
Vasopressin or its synthetic analogues can restore the sympathetic response and may be useful pressors in cases of refractory hypotension during anaphylaxis 9 and septic shock 10 as well as in patients on RAS inhibitors, although norepinephrine has been reported to have a more favorable effect on splanchnic perfusion and oxygen delivery 11.
When conventional therapies such as: decreasing the anesthetic agent, volume expansion, phenylephrine, ephedrine, norepinephrine, and epinephrine are not effective, exogenous vasopressin may improve hypotension. To date, at least 5 clinical trials have demonstrated that patients on chronic ACEI/ARB undergoing general anesthesia, respond to exogenous vasopressin derivatives with an increase in blood pressure and fewer hypotensive episodes.6,7 Typically, a 0.5-1 unit bolus of AVP is administered to achieve a rise in mean arterial pressure.4 The subsequent recommended infusion dose is 0.03U/min for AVP and 1-2 mcg/kg/h for terlipressin. Caution should be used as V1 agonists have been associated with the following deleterious effects: reduction in cardiac output and systemic oxygen delivery, decreased platelet count, increased serum aminotransferases and bilirubin, hyponatremia, increased pulmonary vascular resistance, decrease in renal blood flow, increase in renal oxygen consumption, and splanchnic vasoconstriction.
Studies involving cardiac surgical patients suggest that MB treatment for patients with VS may reduce morbidity and mortality.5 It has also been suggested that the early use (preoperative use in patients at risk for VS) of MB in patients undergoing coronary artery bypass grafting may reduce the incidence of VS.5,9A bolus dose of 1-2mg/kg over 10-20 minutes followed by an infusion of 0.25mg/kg/hr for 48-72 hours is typically utilized in clinical practice and trials (with a maximum dose of 7 mg/kg).10 Side effects include cardiac arrhythmias (transient), coronary vasoconstriction, increased pulmonary vascular resistance, decreased cardiac output, and decreased renal and mesenteric blood flow.1 Both pulse and cerebral oximeter readings may not be reliable during MB administration due to wavelength interference.11,12 The use of MB is absolutely contraindicated in patients with severe renal impairment because it is primarily eliminated by the kidney.13 It may also cause methemoglobinemia and hemolysis.13 At high doses, neurotoxicity may occur secondary to the generation of oxygen free radicals. Neurologic dysfunction may be more severe in patients receiving serotoninergic agents such as: tramadol, ethanol, antidepressants, dopamine agonists and linezolid. Recommended doses for VS ranging from 1-3 mg/kg do not typically cause neurologic dysfunction.14 However, recent reports suggest that MB in doses even ≤ 1mg/kg in patients taking serotonin reuptake inhibitors (SSRIs) may lead to serotonin toxicity due to its monoamine oxidase (MAO) inhibitor property.15
Over the years, our hospital has been using Amicar… until there was a drug shortage. With that drug shortage came a different drug called tranexamic acid. We’ve been using it for awhile and I can’t seem to tell a difference in coagulation between the two drugs. Let’s break down each one and also discuss cost-effectiveness.
Tranexamic acid acts by reversibly blocking the lysine binding sites of plasminogen, thus preventing plasmin activation and, as a result, the lysis of polymerised fibrin.12 Tranexamic acid is frequently utilised to enhance haemostasis, particularly when fibrinolysis contributes to bleeding. In clinical practice, tranexamic acid has been used to treat menorrhagia, trauma-associated bleeding and to prevent perioperative bleeding associated with orthopaedic and cardiac surgery.13–16 Importantly, the use of tranexamic acid is not without adverse effects. Tranexamic acid has been associated with seizures,17 18 as well as concerns of possible increased thromboembolic events, including stroke which to date have not been demonstrated in randomised controlled trials.
Fibrinolysis is the mechanism of clot breakdown and involves a cascade of interactions between zymogens and enzymes that act in concert with clot formation to maintain blood flow.25 During extracorporeal circulation, such as cardiopulmonary bypass used in cardiac surgery, multiplex changes in haemostasis arise that include accelerated thrombin generation, platelet dysfunction and enhanced fibrinolysis.26 Tranexamic acid inhibits fibrinolysis, a putative mechanism of bleeding after cardiopulmonary bypass, by forming a reversible complex with plasminogen.
In summary, we found no evidence that tranexamic acid increases the risk of death and thrombotic complications after coronary-artery surgery. Tranexamic acid was associated with a lower risk of bleeding complications than placebo but also with a higher risk of postoperative seizures.
The study used a high-dose regimen, in which either 50 mg/kg or 100 mg/kg of TXA was delivered for each patient. There is a possibility that lower dose of TXA can be equally effective while causing less adverse effects. In fact, TXA plasma concentrations required to suppress fibrinolysis and plasmin-induced platelet activation are merely 10 and 16 μg/ml, respectively [7, 8]. This relatively low plasma concentration can be reached in cardiac surgery when 10 mg/kg of TXA is administered as a bolus then followed by continuous infusion of 1 mg kg/h and 1 mg/kg in CPB [9]. But another potential mechanism of TXA action might be the increase in thrombin formation, which requires concentrations more than 126 μg/ml to be effective [10, 11]. 30 mg/kg of TXA administered as a bolus followed by 16 mg/kg/h and 2 mg/kg in CPB prime solution was able to maintain the plasma concentration above 114 μg/ml [9].
Using their model-based meta-analysis, the authors conclude that low-dose tranexamic acid (total dose of 20 mg/kg of actual body weight) provides the best balance between reduction in postoperative blood loss and red blood cell transfusion and the risk of clinical seizure. The use of higher doses would only marginally improve the clinical effect at the cost of an increased risk of seizure.
Low-risk group received a single 50 mg/kg TXA bolus after induction of anesthesia. The high-risk group received Blood Conservation Using Anti-fibrinolytics Trial (BART) TXA regimen, consisting of 30 mg/kg bolus infused over 15 minutes after induction, followed by 16 mg/kg/h infusion until chest closure with a 2 mg/kg load within the pump prime.
Risk of seizure is dose-dependent, with the greatest risk at higher doses of tranexamic acid. We conclude that, in general, patients with a high risk of bleeding should receive high-dose tranexamic acid, while those at low risk of bleeding should receive low-dose tranexamic acid with consideration given to potential dose-related seizure risk. We recommend the regimens of high-dose (30 mg kg−1 bolus + 16 mg kg−1 h−1 + 2 mg kg−1 priming) and low-dose (10 mg kg−1 bolus + 1 mg kg−1 h−1 + 1 mg kg−1 priming) tranexamic acid, as these are well established in terms of safety profile and have the strongest evidence for efficacy.
The exposure value with the low-dose tranexamic acid regimen proposed by Horrow et al. (10 mg/kg followed by 1 mg/kg/h over 12 h) was close to the 80% effective concentration for postoperative blood loss and above the 80% effective concentration for erythrocyte transfusion. Compared to this regimen, a fivefold increase in total dose (100 mg/kg) achieved only a 58 ml (95% credible interval,54 to 65 ml) increment in the reduction of postoperative blood loss, up to 48 h postsurgery, with a decrease in erythrocyte transfusion rate from 46% to 44%.
Concentrations close to 80% effective concentration can be achieved at the end of surgery with a low-dose regimen administered either as a preoperative bolus plus infusion (10mg/kg followed by 1mg/kg/h) or as a single preoperative loading dose of 20mg/kg (fig. 6). Postoperative administration of tranexamic acid appears unnecessary because tranexamic acid concentrations will decrease but nevertheless remain sufficient (greater than or equal to EC50) up to the end of the drug’s contribution to blood loss reduction (8 h after the start of surgery).
The type of surgery and the duration of CPB both affected the risk of seizure. Open-chamber surgery resulted in a 5.5-fold increase in the risk of seizure compared to closed-chamber procedures (95% credible interval, 3.2 to 10). Each additional hour of CPB doubled the risk of seizure (2.0;95% credible interval, 1.2 to 3.2).
Ortho/Spine
OB
Trauma
Currently at our hospital (June 2022):
TXA DOSING AND ADMINISTRATION OVERVIEW
How supplied from Pharmacy
TXA 1000mg/10mL vials Will not provide premade bags like with Amicar; Amicar is a more complex mixture than TXA Will take feedback on this after go-live and reassess
There are a number of dosing strategies in the literature. What I recommend for maximal safety and efficacy is taken from Zuffery, et al. Anesthesiology 2021 meta-analysis and is practiced at Scripps Mercy.
~ 20 mg/kg total dose recommended in this meta-analysis.
Two dosing strategies they report that were as effective as high-dose but with lower seizure risk than high dose:
Patients with ACS will usually be critically ill and unable to provide history and symptoms. On physical exam, patients present with a distended abdomen. However, palpation and abdominal circumference are not reliable for the diagnosis of ACS[25].
A prospective study in postoperative ICU patients showed physicians have less than a 50% chance to identify IAH by clinical examination[25]. The clinical abdominal exam as IAP assessment has an estimated sensitivity of 56%-60% and specificity of 80%-87%[25,26].
Signs of ACS will present as the end-organ effect from the physiologic changes (Table (Table2).2). The most notorious signs are usually abdominal distention, oliguria, high ventilatory pressures, diminished cardiac output, and metabolic acidosis[26].
The more commonly used method is an indirect measurement such as intravesicular catheter pressures (e.g., Foley catheter), which has become the gold standard due to its widespread availability and limited invasiveness. The trans-bladder technique involves using aseptic clamping the drainage tubing of the Foley then connecting the Foley to a three-way stop tap adjusted to the level of the mid-axillary line at the iliac crest to zero transducers follow by injecting 25 cc of sterile saline into the bladder. Measurements should be taken at end-expiration and complete supine position and expressed in mmHg. Bladder pressures below 5 mm Hg are expected in healthy patients. Pressures between 10 to 15 mm Hg can be expected following abdominal surgery and in obese patients. Bladder pressures over 25 mm Hg are highly suspicious of abdominal compartment syndrome and should be correlated clinically. It is recommended that pressure measurements be trended to show and recognize the worsening of intra-abdominal hypertension.
Contraindications to using bladder pressures include bladder trauma, neurogenic bladder, BPH, and pelvic hematoma. Bladder pressures may be inaccurate if the patient is not sedated or lying flat.[9][10]
The primary treatment for ACS is surgical decompression. However, the early use of non-surgical interventions may prevent the progression of IAH to ACS. Early recognition involves supportive care to include keeping patients comfortable with pain well-controlled. Decompressive procedures such as NG tube placement for gastric decompression, rectal tube placement for colonic decompression, and percutaneous drainage of abscesses, ascites, or fluid from the abdominal compartment. The neuromuscular blockade has been described to be used as a brief trial in an attempt to relax the abdominal musculature, leading to a significant decrease in abdominal compartment pressures in the ventilated ICU patient. If conservative and medical management does not resolve the IAH and further organ damage is noted, surgical decompression using emergent laparotomy may be considered. [11][2]
After surgical laparotomy for compartment syndrome, the abdominal fascia may be closed using temporary closure devices such as (vacs, meshes, and zippers). The fascia can be appropriately closed after 5 to 7 days after the compartment pressures and swelling have decreased.
0.2 mg/kg of methadone (based on ideal body weight, up to a maximal dose of 20 mg)250 mg of ketamine was added to the dextrose 5% in water bag (total volume 500 ml). 500 ml bags were connected to a pump that was programed to deliver an infusion of ketamine dosed at ideal body weight (or an equal volume of dextrose 5% in water) at a rate of 0.3 mg · kg−1 · h−1 from induction of anesthesia until surgical closure, at which time the infusion was decreased to 0.1 mg · kg−1 · h−1. The infusion was maintained at a rate of 0.1 mg · kg−1 · h−1 in the postanesthesia care unit (PACU) and for the next 48 postoperative hours. Dosing of ketamine was based on recommendations in the literature17,18 and from clinical experience at our institution.
Sleepy Time 