Intraoperative tPA and Nitroglycerin Dosing During Vascular Procedures
Intraoperative tPA Dosing
For acute thromboembolic complications during vascular procedures, intra-arterial tPA should be administered at 20,000 IU/min of urokinase (mean total dose 975,000 IU, range 450,000-1,300,000 IU) or equivalent recombinant t-PA dosing, with complete or partial recanalization achievable in most cases. 1
Specific Dosing Protocols
Recombinant t-PA can be used interchangeably with urokinase for intra-arterial thrombolysis during endovascular procedures, with both agents demonstrating equal efficacy 1
Prourokinase may be administered at doses of 6-9 mg as an alternative to urokinase or recombinant t-PA for intraoperative thromboembolic events 1
Heparinization during thrombolysis enhances thrombolytic efficacy: administer a heparin bolus of 70 units/kg IV before thrombolysis to maintain ACT between 250-300 seconds 1
Critical Contraindications in High-Risk Patients
In patients with bleeding disorders, recent surgery, or concurrent anticoagulation, tPA is contraindicated and should not be administered. 1
Active bleeding is an absolute contraindication to fibrinolytic therapy 1
Recent surgery (especially intracranial or spinal) requires careful risk-benefit evaluation before any thrombolytic use 1
Recent documented bleeding events preclude tPA administration 1
For patients on direct oral anticoagulants (DOACs), tPA should not routinely be administered; consider endovascular mechanical thrombectomy instead 1
Monitoring and Management
Perform frequent control injections of contrast material or neurological examinations to detect vessel occlusion early 1
Post-thrombolytic heparin is recommended for patients with partial recanalization, arterial dissection, or persistent distal emboli, titrated to maintain aPTT 1.5-2.3 times control values 1
If haematuria or bleeding develops post-thrombolysis, immediately discontinue the infusion and administer tranexamic acid 1000 mg IV over 10 minutes 2
Intraoperative Nitroglycerin Dosing
For intraoperative hypertension during vascular procedures, nitroglycerin should be administered at 0.5-1 mcg/kg/min (typically 32-96 mcg/min total dose), titrated to normalize blood pressure while monitoring for hypotension. 3, 4
Dosing Strategy
Mean effective dose is approximately 80 mcg/min (0.96 mcg/kg/min) for blood pressure control during vascular surgery 3
Start at lower doses (32 mcg/min) and titrate upward in increments (64 mcg/min, then 96 mcg/min) based on hemodynamic response 4
Titrate for a 10 mm Hg decrease in mean arterial blood pressure, with typical therapeutic doses around 1.2 mcg/kg/min 5
Hemodynamic Effects and Monitoring
Nitroglycerin significantly decreases systolic, diastolic, and mean arterial pressures, central venous pressure, pulmonary capillary wedge pressure, and systemic vascular resistance 3
Cardiac index and stroke index typically remain unchanged at therapeutic doses 3
Monitor for the most serious complication: inadvertent systemic hypotension with resulting worsening of myocardial ischemia 6
Special Considerations for Bleeding Risk
Nitroglycerin produces dose-related prolongation of bleeding time that correlates with decreased systolic blood pressure, though this appears related to vasodilation rather than altered platelet function. 7
At therapeutic doses (1.2 mcg/kg/min), nitroglycerin decreases platelet aggregation response to ADP and thrombin by >50% in most patients, with effects reversible within 15 minutes of discontinuation 5
The bleeding time prolongation is due to vasodilation and increased venous capacitance rather than altered vascular-platelet interaction 7
In patients with pre-existing bleeding disorders or on concurrent anticoagulation, use the lowest effective dose and monitor closely for bleeding complications 7
Critical Contraindications
Do not administer nitroglycerin in patients with hypotension, marked bradycardia or tachycardia with relative hypotension 6
Recent use of phosphodiesterase inhibitors is an absolute contraindication 6
Consider hemodynamic effects of other agents being used and intravascular volume status before administration 6
Common Pitfalls to Avoid
Never use nitroglycerin response as a diagnostic test—pain relief does not confirm vascular etiology and has poor specificity 6
Always monitor blood pressure continuously during infusion to prevent dangerous hypotension 6
The venodilating and arterial dilating effects can be potentiated by other medications, leading to dangerous drops in blood pressure 6
In patients at high risk, prophylactic nitroglycerin may lead to cardiovascular decompensation through excessive preload reduction 6