Monitoring IV Cardiovascular Consequences PDF

Monitoring: IV Cardiovascular consequences Blood pressure monitoring and management Goal with ‘cardiopulmonary stability’ = adequate oxygen delivery to tissues...

Monitoring: IV Cardiovascular consequences Blood pressure monitoring and management Goal with ‘cardiopulmonary stability’ = adequate oxygen delivery to tissues Delivery of oxygen to tissues (DO2) = Cardiac output (L/min) x CaO2 Cardiac output (= HR x stroke volume) Nathaniel Kapaldo, DVM, MPH, DACVAA Assistant Professor of Anesthesiology Veterinary Health Center College of Veterinary Medicine Kansas State University Relative Rate Bradycardia definition: HR < 50‐80 in the dog Larger breed dogs: HR < 50‐60 Smaller breed dogs: HR < 70‐80 HR < 110‐120 in the cat *Bradycardia with 2nd degree AV‐block common Allometric scaling  Normal HR not the same for everyone Larger dogs have a lower baseline functional HR Smaller dogs have a higher baseline functional HR Pediatric = SNS still developing Unable to increase contractility/CO or SVR; reliant on HR Not analog (e.g., 2 mo. More developed than 1 mo., > 2 wk) Bradycardia / Bradyarrythmias – when/how to treat When? Hypotensive patients (i.e., to improve CO and thus, blood pressure) Patients with some cardiac diseases (Later lecture) Pediatric patients How? – determine underlying cause! HR lower than expected for breed/species…and hypotensive? Anticholinergic Assess depth of anesthesia, adjust as needed Pop‐off valve closed, open! Drug Dosing/comments Hypoxia – check ETT location, increase FiO2/turn Atropine (A) 0.02‐0.04 mg/kg IV/IM Glycopyrrolate 0.005‐0.01 mg/kg IV/IM O2 flowmeter on, if extubated – ensure not (G) Giving IM increases duration (A: 30‐40 obstructed min; G: 45‐60 min) Hypertension* *Doses can be scaled Hyperkalemia – treat! Relative Rate Tachycardia definition: HR > 140‐180 in the dog Larger breed dogs: HR > 140 Smaller breed dogs: HR > 180 HR > 200‐220 in the cat *smaller breeds tolerate higher HRs than larger breeds **Underlying cardiac disease will reduce tolerance to extremes in heart rate Allometric scaling! A normal HR for one dog, not the same for another! Larger dogs have a lower baseline functional HR = tolerate higher absolute heart rates less well than smaller breed dogs Tachycardia / Tachyarrythmias under GA ‐ treatment First Assess anesthetic depth – alter as needed Ensure adequate analgesia, dosing – re‐administer if suspected cause Hypoventilation?  IPPV to correct EtCO2 (e.g., > 60+ mmHg) If patient is moderately tachycardic but the above are not true or achieved – can tolerate higher heart rate. If patient is moderate‐severely tachycardic and hypotensive – then address rate 1. Suspect hypovolemia/dehydration? Known deficit Disease process leading to volume loss? Fluid bolus (e.g., 10+ ml/kg over 10 min), assess if HR/BP responds 2. Reduce or discontinue sympathomimetic drug (e.g., dobutamine, ephedrine etc.) 3. Beta‐blockers (e.g., esmolol) or opioid Our goal is adequate oxygen delivery to tissues/organs while under general anesthesia Intravascular volume Blood pressure is a result of numerous interdependent variables, but: Organ perfusion/oxygenation is Proportional to CO (↑CO = ↑BP) dependent on: Proportional to VR (↑VR = ↑BP) Cardiac output (CO; L/min) Vascular resistance (VR) Blood pressure is also easy to measure! Blood pressure (BP) Oxygen carrying capacity (CaO2)  Our goal is adequate oxygen delivery to tissues/organs while under general anesthesia Intravascular volume Blood pressure is a result of numerous interdependent variables, but: Proportional to CO (↑CO = ↑BP) Proportional to VR (↑VR = ↑BP) Blood pressure is also easy to measure!  Regional vascular resistance determines organ perfusion = Vasoconstrict will improve BP; however, can impair perfusion in some circumstances Target underlying derangements Hypotension as an Adverse Effect The most common anesthetic‐ related complication reported Hypotension associated complications in people: Acute kidney injury Acute coronary syndrome Increased all‐cause mortality 1 year post anesthetic event Mazzaferro and Wagner 2001; Gaynor et al 2001; Gordan and Wagner 2013; Ruffiato et al. 2015; Monk et al 2005; Son et al 2015 Hypotension as an Adverse Effect Mortality Cats that experienced hypotension under GA had 2.6x increased odds of death AKI in healthy adults MAP beta 1 ml/hr = 0.05 mcg/kg/min per 5 kg agonist) 5 kg cat/dog = 1 ml/hr My recommendation: 10 kg dog = 2 ml/hr 15 kg dog = 3 ml/hr; etc. Invest in a syringe driver; create charge for its use Start at 0.05 mcg/kg/min, double q 3‐5 min until E.g., $1000‐1,500 investment; 20$/use = 50‐75 patients the normotensive pump has been paid for Epinephrine Mix 0.25 ml (250 mcg) into 250 ml 0.9 NaCl bag Create protocol for norepinephrine (beta/alpha = 1 mcg/ml solution agonist) 0.1 mcg/kg IV q 5‐10min Call me or other anesthesiologist for help 10 kg dog = 1 ml protocolizing your anesthetic practices 5 kg cat = 0.5 ml  Case Example 1 yr FI Golden (26 kg) is presented to you for elective OHE. On presentation – Overtly healthy with normal physical examination; vitals normal (HR 108, RR panting/excited, Temp 101, hydration status normal. Demeanor is relatively excitable. Premedication: 1 mg/kg maropitant, then 0.02 mg/kg acepromazine with 0.1 mg/kg hydromorphone IM. Produced mild sedation. Induction of general anesthesia with propofol titrated to effect; required 3.1 mg/kg. 4 minutes post induction 1st Oscillometric BP 109/60 (71) mmHg; HR 77; RR 7‐9 bpm and ISO vaporizer is at 1.6%. Depth is on lighter side since just induced and only just on circuit with inhalant (O2 inhalant on 3 L/min for now to increase circuit partial pressure faster). Assessment?  Case Example 20 minutes later, BP trending down – 4th BP: 96/47 (61) mmHg; Depth is adequate (not too deep) with vaporizer now at 1.5% (O2 flow had been turned down to 0.75 L/min) Assessment? Treated with ephedrine 0.1 mg/kg IV once, 3 min later  HR relatively unchanged (72 bpm) but BP increased: 104/64 (73) mmHg 5 minutes later, BP decreased again to 100/50 (64), HR remains 65‐70 Now what, options? Repeated Ephedrine boluses OK Ephedrine CRI OK NE CRI OK Increase HR probably not needed but OK; increase HR probably not needed but OK Acepromazine and hypotension Dexmedetomidine and hypotension Acepromazine molecule = Dexmed = alpha‐2 agonist  analog to catecholamines receptors present peripherally & (structurally similar) centrally Peripheral effects – Binds to alpha‐1 adrenergic vasoconstriction/ reflex bradycardia receptors, but does not agonize Central effects— them (i.e., competitive reduced sympathetic tone = antagonist) reduced HR, reduced vascular tone, reduced contractility Majority of alpha‐1 receptors Both occur simultaneously; but on venous side  exacerbates peripheral effects only last 20‐30 blood volume shift (reduces min, then continued central effects preload, thus CO, and BP) = vasodilation, continued bradycardia  Review / Questions Blood pressure is the only global assessment we can easily measure to ensure adequacy of cardiovascular system in anesthetized patients. Minimum blood pressure for adequate end‐organ perfusion is SBP ≥ 90mmHg or MAP ≥ 60mmHg; however, measurement techniques used underestimate hypotension, which alters treatment thresholds Hypotension is the most common reported complication from GA in dogs and cats. Maintenance IVF do not mitigate or prevent hypotension. Fluid boluses should be reserved for patients who demonstrate or are suspected of having a deficit. Approaching blood pressure is straight forward but should be individualized (e.g., patient’s age, comorbidities, etc.). Interventions should progress logically/expeditiously and will be most effective when targeting primary cause of the hypotension.  Constant rate infusions E.g.,: Norepinephrine CRI in syringe pump 0.1 mcg/kg/min = 5 ml/hr 0.1 mcg/kg/min x 26 kg = 2.6 mcg/min x 60 min = 156 mcg/hr  will make 4 hr worth; 156mcg/hr x 4 hr = 624 mcg NE (which is 1 mg/ml)  0.62 ml NE 4 hours worth at 5 ml/hr = 20 ml total infusion volume = simply add 0.62 ml NE to ~20 ml NaCl  administer at 5 ml/hr (which will = 0.1 mcg/kg/min) So if patient hypotensive, begin infusion; 5 min later patient still hypotensive?  double CRI rate (e.g., 10 ml/hr = 0.2 mcg/kg/min); Patient blood pressure responds? Perfect, leave it, or turn down as needed every few minutes if BP elevated significantly  Volume Deficits Example: 20 kg dog, est. 7% dehydrated on PE Under GA for OHE due to pyometra; on 10 ml/kg/hr due to deficit; however, currently hypotensive, tachycardic, but at an adequate plane of anesthesia What is this patient’s free water deficit? 7% deficit = 1.4 L free water deficit Treatment? Begin with 20 ml/kg (400 ml) over 10‐15 min  Re‐assess, BP improved? Great. BP improved but again declines later? Consider another 10‐20 ml/kg bolus, otherwise vasopressor likely indicated