Anesthesia in the Cardiac Patient. Monitoring Routine Pulse Oximetry PNS Capnography Temperature...
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Transcript of Anesthesia in the Cardiac Patient. Monitoring Routine Pulse Oximetry PNS Capnography Temperature...
Anesthesia in the Cardiac Patient
Monitoring
RoutinePulse OximetryPNSCapnographyTemperature
Core and peripheral
ECGLeads V5 and II
Monitors of Cardiac Performance
Arterial LineStandard of CareSite selection
Pulmonary Artery CatheterProvides means for assessing filling pressuresReliable site for drug administration
Transesophageal Echocardiography
Anesthetic Technique
Goals of Anesthesialoss of conciousnessamnesiaanalgesiasuppression of reflexes (endocrine and autonomic)muscle relaxation
Inhalation Agents
AdvantagesMyocardial oxygen balance altered favorably by
reductions in contractility and afterloadEasily titratableCan be administered via CPB machineRapidly eliminated
Inhalation Agents
DisadvantagesSignificant hemodynamic variabilityMay cause tachycardia or alter sinus node functionPossibility of “coronary steal syndrome”
Coronary Steal
Arteriolar dilation of normal vessels diverts blood away from stenotic areas
Commonly associated with adenosine, dipyridamole, and SNP
Forane causes steal and new ST-T segment depressionMay not be important since Forane reduces SVR,
depresses the myocardium yet maintains CO
Opioids
AdvantagesExcellent analgesiaHemodynamic stabilityBlunt reflexesCan use 100% oxygen
Opioids
DisadvantagesMay not block hemodynamic and hormonal
responses in patients with good LV functionDo not ensure amnesiaChest wall rigidityRespiratory depression
Induction Drugs
BarbituratesBenzodiazepinesKetamineEtomidate
Nitrous Oxide
Rarely used due to:increased PVRdepression of myocardial contractilitymild increase in SVRair expansion
Muscle Relaxants
Used to:Facilitate intubationPrevent shiveringAttenuate skeletal muscle contraction during
defibrillation
Cardiopulmonary Bypass
Basic ComponentsArterial and venous cannulaReservoirPumpOxygenatorHeat exchanger
Cardiopulmonary Bypass
OxygenatorsBubble - most common
Direct contact between blood and fresh gasThe smaller the bubbles the greater the rate of transferPerfusate must be de-foamedAssociated with platelet destruction, microemboli, and
decreased leukocyte counts
Cardiopulmonary Bypass
OxygenatorsMembrane
Blood gas interface separated by semipermeable membrane
No direct mixing of gas and bloodLess trauma to blood
Cardiopulmonary Bypass
CannulationVenous cannula placed into RA, IVC, or SVCArterial cannula into proximal aorta or femoral
arteryAorta cannulated firstSystolic BP reduced to 100 - 110 mm Hg.
Cardiopulmonary Bypass
Complications of CannulationArterial
Hypertension
VenousSupraventricular dysrhythmiasAtrial fibrillation
Cardiopulmonary Bypass
PumpsRoller
positive displacement pump that maintains constant flow when increased resistance is encountered
Impellerwith increased resistance forward flow is reduced
Cardiopulmonary Bypass
Heat ExchangerAdjusts temperature of perfusate to provide
hypothermiaMetabolic requirements are decreased about 8%
per degree of decrease in body temperatureProvides protection during periods of
hypoperfusion and potential tissue ischemia
Cardiopulmonary Bypass
Heparinization300 u/kgACT determines adequacy of anticoagulationACT value greater than 400 sec.
Cardiopulmonary Bypass
Preparation of MachineCrystalloid solution used to “prime pump”Causes a dilution of plasma drug concentrationHgb and HCT are reducedBlood viscosity decreasesMAP drops to 30 -40 mm Hg.
Cardiopulmonary Bypass
Management of Gas ExchangepH statAlpha-Stat
Cardiopulmonary Bypass
Adequacy of PerfusionMAPHematocritMixed venous oxygen saturationBlood lactate levelsCentral and peripheral temperatureUrine output
Cardiopulmonary Bypass
Central Nervous System ProtectionInjury thought to be a consequence of emboliContributing factors
inadequate cerebral perfusionduration of bypassage
Cardiopulmonary Bypass
Rewarming10 degree gradient maintained to reduce gas
bubble formationAwareness may be a problem
Separation from Bypass
Accomplished in three stagesPreparationPartial BypassOff Bypass
Separation from Bypass
PreparationRelease of aortic cross clamp
reestablishes myocardial perfusion and cardiac rhythmOften requires electrical defibrillation
Separation from Bypass
Problems encountered during preparation phaseRecurrent or resistant ventricular fibrillationPersistent left ventricular distentionPersistent asystole
Separation from Bypass
Partial BypassVenous return partially restrictedVenous blood enters the right ventricleLungs inflated and right ventricle ejects blood into
pulmonary arteryModest PA pressure and good systemic pressure
indicate successful separation
Separation from Bypass
Factors contributing to problems during partial bypassunusually low hematocritexcessive vasodilationmarked respiratory or metabolic acidosis
Separation from Bypass
Off BypassComplete occlusion of venous return to machineContinuous assessment of filling pressures
importantvenous blood remaining in reservoir used to
transfuse as necessary
Reversal of Anticoagulation
Protamine administrationMost common method to use standard dose
calculated on original dose of Heparin1 mg Protamine per 100 u Heparin
Protamine Reactions
Three TypesHypotensive (Type I) - Transient hypotension
occuring with rapid administration of ProtamineAnaphylactic/ Anaphylactoid (Type II) - True
allergic reaction or response to release of vasoactive mediators
Catastrophic Pulmonary Vasoconstriction (Type III) - systemic hypotension and elevated PAP
Hemodynamic Goals Post-Bypass
Heart RateMust provide adequate cardiac output70 -90 bpmRhythm should be sinusVentricular dysrhythmiasSupraventricular dysrhythmias
Ventricular Dysrhythmias
Cause must be identified rapidly and treatment instituted
V tach and V fib treated with internal defibrillation
V tachydysrhythmias treated with:Lidocaine ProcainamideBretylium EsmololMagnesium
Supraventricular Dysrhythmias
Atrial fib and tachycardia treated with synchronized internal cardioversion
Need to look at blood gases, acid-base status, and electrolytes
Assume ischemia - use NTGOther treatments;
Digoxin Esmolol Verapamil AdenosineEdrophonium Procainamide
Hemodynamic Goals Post-Bypass
PreloadEnough to support CO but avoid distentionVolume may be administered from CPB machineExcessive preload may be relieved with NTG or
diuretic
Hemodynamic Goals Post-Bypass
AfterloadReduction advantageous to the post-bypass patientDecreased wall stress lowers MVO2Favors forward flow
Hemodynamic Goals Post-Bypass
ContractilityOptimize to maintain COMay be augmented with inotropic supportChoice of agent depends on:
severity of ventricular dysfunctionheart rateafterloadpersonal preference
Inotropic Drugs
Dopamine 2-20 ug/kg/min
Increased RBF Mild vasocanstriction
Tachycardia, dysrhythmias
Dobutamine 2-20 ug/kg/min
Vasodilation Tachycardia, dysrhythmias
Epinephrine Bolus 5-10mcg
Common Problems Post-Bypass
Left Ventricular FailureCauses
IschemiaValve failureHypoxemiaInadequate PreloadVolume OverloadDecreased contractility
Common Problems Post-Bypass
Left Ventricular FailureTreatment
NitroglycerineInotropesTransfusionTreat any acid-base/electrolyte abnormalities
Common Problems Post-Bypass
Right Ventricular FailureCauses
Same as LV failureRV ischemia or infarctionPulmonary HTNCOPDMechanical ventilationProtamine reactionPulmonary embolus
Common Problems Post-Bypass
Right Ventricular FailureTreatment
Ischemia treated with NTG to decrease preload and improve coronary flow
Control Preload Pulmonary vascular resistance
Mechanical Assist Devices
Intraaortic Balloon Pump (IABP)Indications for use
Intractable cardiac failurePreop stabilization of angina or LV failureComplications of MI refractory to pharmacologic
support
Mechanical Assist Devices
IABPPlaced percutaneously or via cutdown through
femoral arteryBalloon inflates at beginning of diastole augmenting
coronary blood flowBalloon deflates at beginning of systole reducing
afterloadTriggered by ECG or arterial pressure waveform
Mechanical Assist Devices
Ventricular Assist DevicesDesigned to augment either R or L ventricular
functionGoal is to decrease MVO2Three types available
Roller pumpsCentrifugal pumpsPneumatic pulsatile pumps
Common Problems Post-Bypass
CoagulopathyPulmonary Complications
Pump lungBroncho spasm
Postoperative predictors
Ischemia does occur most commonly in the postoperative period
Persists for 48 hours or longer following non-cardiac surgery
Predictor value is unknown
Goldman, L., (1983) Cardiac Risk and Complications of noncardiac surgery, Annals of Internal Medicine. 98:504-513
Nonadrenergic Cardiovascular Drugs
Nonadrenergic CV drugsNonadrenergic CV drugs
• Direct-Acting VasodilatorsDirect-Acting Vasodilators– Hydralazine (Apresoline)Hydralazine (Apresoline)• Arterial dilatorArterial dilator
– Diazoxide (Hyperstat)Diazoxide (Hyperstat)• Arterial dilator (can cause hyperglycemic coma)Arterial dilator (can cause hyperglycemic coma)
– NitroglycerinNitroglycerin• VenodilatorVenodilator
– Nitroprusside (Nipride)Nitroprusside (Nipride)• Arterial and venous dilatorArterial and venous dilator
Nonadrenergic CV drugsNonadrenergic CV drugs
• Calcium Channel BlockersCalcium Channel Blockers– VerapamilVerapamil• Arterial dilator and decreases heart rateArterial dilator and decreases heart rate
– DiltiazemDiltiazem• Arterial dilator and decreases heart rateArterial dilator and decreases heart rate
– Nifedipine (Procardia)Nifedipine (Procardia)• Arterial dilator (causes reflex increase in heart rate)Arterial dilator (causes reflex increase in heart rate)
Nonadrenergic CV drugsNonadrenergic CV drugs
• Angiotensin Converting Enzyme InhibitorAngiotensin Converting Enzyme Inhibitor– Captopril (Capoten)Captopril (Capoten)• Arterial dilatorArterial dilator
– Enalapril (Vasotec)Enalapril (Vasotec)• Arterial dilatorArterial dilator
Nonadrenergic CV drugsNonadrenergic CV drugs
• Phosphodiesterase (PDE) Inhibitors Phosphodiesterase (PDE) Inhibitors (Positive Inotropes)(Positive Inotropes)– Inamrinone (Inocor)Inamrinone (Inocor)– Milrinone (Primacor)Milrinone (Primacor)• Block breakdown of cAMPBlock breakdown of cAMP• Increase myocardial contractilityIncrease myocardial contractility• Decrease SVR (relaxes smooth muscle)Decrease SVR (relaxes smooth muscle)