General Anesthesia

POS April 14th 2009

Outline

1.Anesthesia Drugs / Monitors.

2. Anesthesia Events in the OR.

3. Anesthesia Consults.

Am I missing something ?

• Miller - 6th ed, 3204 pages (subtract about 800 pages for regional / pain)

• Sabiston – 18th ed, 2353 pages.

Am I missing something ?

• Miller – 6th ed. , 3204 pages.

• Sabiston – 18th ed. , 2353 pages. Takes five years to cover the material

Am I missing something ?

• Miller - 3204 pages. We can cover this in 60 to 90 minutes.

• Sabiston – 18 ed . 2353 pages.

And the POS exam is over !

• I’ll wake you up at the end.

Biggest change for you since 2008?

Biggest change for you since 2008?

• Ask for 2 grams of Cefazolin pre-operatively instead of 1 gram if the patient is > 80 kg.

ANESTHETIC DRUGS / MONITORS

Routine Monitors

• ECG.

• BP.

• Oximetry (use the ear probe in shock).

• End Tidal CO2 .

• Temperature (axillary vs. core).

• Future : Depth of anesthesia - BIS. (Bispectral index EEG) - scale from 0 to 100

March 2008 ,NEJM negative BIS trial.

ETCO2

• Continuous monitor in OR.

• Monitor of position of ETT (after 6 breaths).

• Monitor acute decrease - ↓ Cardiac Output, Embolism.

• Monitor acute rise - for M.H.

Intravenous Drugs

1 .Propofol - less hangover, good anti emetic . Very easily contaminated. Pain on injection,

2 .Pentothal and Propofol - potent anti- convulsants and ICP.

- BP

- resp depressants

3. Ketamine - maintains BP, maintains respiration, but ICP. IM useage.

Neuromuscular Blockers - Succinylcholine

• Can cause excess K+ release in certain conditions -ACUTE neuromuscular disease, burns > 20%.

IOP.• C / I in MH.• 5 minutes to recover from – metabolized by

plasma cholinesterase . Cannot reverse its effect with other drugs

Nitrous Oxide

• MAC - 104%.

• Enlarges air containing closed spaces e.g. obstructed bowel, middle ear, eye with SF6 , pneumothorax, VAE.

• Negative outcomes large studies

• High FIO2 and wound infection

• Not often used - air /oxygen

Vapours

• All C / I in MH.

• Lipid solubility important so awaken quickest from Desflurane.

• Pungency - Sevoflurane least (epiglottitis). For inhalation induction /kids

Toxicity vapours

• Halothane hepatitis (1:10 000)

• Isolated single reports with other vapors.

• Sevoflurane - possible nephrotoxic Fl- ion

• Nitrous Oxide - Possibly rate of spontaneous abortion (RR 1.3) and congenital abnormalities (RR 1.2). ?Recall bias,voluntary response.

Neuromuscular Blockers- Nondepolarizing Drugs

• Cisatracurium, Pavulon, Rocuronium.• Safe in M.H. but can cause anaphylaxis.• Longer acting - 20 mins. to 90 mins.• Monitor with nerve stimulator (train of four)• But clinical testing e.g. head lift is best.• Can reverse action with cholinergic drug e.g.

neostigmine

ANESTHETIC INTRAOPERATIVE EVENTS

ASA Score

1 - Healthy.

2 - Mild systemic disease, no functional limitations.

3 - Severe systemic disease that limits activity.

4 - Incapacitating disease that is a constant threat to life.

5 - Moribund, not expected to survive 24 hrs, with or without surgery.

E - Emergency

ASA Difficult Airway Algorithm

• Not possible to visualize any of the vocal cords = difficult.

• Mallampati score - one of many aspects of airway assessment.

• LMA – rescue device but does not protect vs. aspiration (Can be used as conduit for FFOB).

Failed Intubation

• Management depends on whether can ventilate or not.

• Different blades and smaller tube.

• LMA , Bronchoscope , Bougie, Glidescope

• Cannot intubate , Cannot ventilate - need surgical airway.

Aspiration • Risk factors - Morbid obesity, Pregnancy,

Massive ascites, Diabetes, Pain esp. trauma.

• Prophylaxis – H 2 blockers, Prokinetic agents, Sodium Citrate.

• Rapid Sequence Induction (RSI).• Presents as desaturation or wheezing.• Guidelines : 6 hrs for light meal (clear fluid and

toast) to 8 hrs. (meat) and 2 hours for clear fluids.

Malignant Hyperthermia

• Triggered by vapours and Succinylcholine.

• Hypermetabolic state of muscles. ET CO2 , tachycardia (metabolic storm).

• Arrhythmias from K+ release – VT,VF

• Muscle rigidity and temp -LATE signs.

• Rx- Dantrolene (2,5mg/kg up to 10mg/kg),

Airway fire

1. Ignition source — cautery, laser, flammable ointment alcohol based prep solution.

2. Fuel – drapes , PVC ETT.

3. Oxidizer near surgical site — Oxygen or Nitrous Oxide.

• Laser surgery, Tracheotomy.

• Disconnect patient from machine, extubate and extinguish with saline,ventilate or reintubate, evaluate airway damage (rigid bronchoscopy).

Gas Embolism

• Air, Helium, CO 2 .

• Operative site above heart, low CVP.• Presents as ETCO2, SaO2, millwheel

murmur, BP, PA pressures.• Rx - D/C Nitrous, Trendelenburg, flood field,

aspirate from CVP catheter, left side down (airlock RV), consider hyperbaric oxygen.

Latex Allergy

• Multiple procedures, health care esp. dental workers, spina bifida, food sensitivity.

• Prevent - glass syringes, remove top of vial, 1st case of day, premed optional.

• Onset after 20 - 60 minutes.

• Airway and 100% O2.

• Volume.

• Epinephrine - 0,1 micrograms / kg boluses

Massive Transfusion

• All complications of 1 unit -TRALI, Immunosuppression.

• Hypothermia.

• Hypocalcemia from citrate.

• K + abnormalities (> 120 ml/ min).

• Dilutional coagulopathy.

ABO Transfusion Reaction

• Minimal signs under GA.

• Hypotension.

• Hemoglobinuria.

• DIC ( “oozy” NYD ).

• Blood for re XM and hemolysis workup.

• Die from DIC and ARF.

Autologous donation

• EPO and Iron supplementation.

• Clerical error (1: 100 000).

• Yersinia enterocolitica contamination.

• May not be enough blood.

• Anemia.

Hypothermia

• Core and peripheral component ,with tonic constriction normally.

• 1st hour – rapid drop 1,5 °C – vasodilation.• 2nd stage - slow linear decrease for 2 -4 hours of

1,5 -2,5 ºC as heat loss exceeds metabolic heat gain . (radiation*,convection, evaporation, conduction)

• 3rd stage - plateau after 2- 4 hours

Adverse Effect Hypothermia

• Cardiac - RCT 35.4°C vs. 36.7C in 300 patients undergoing abdo, vascular, thoracic (JAMA April 9 1127, 1997 ).

• Postop morbid cardiac events: 1,4%vs 6,3%

• VT : 2% vs. 8%.

• Infection - RCT 200 patients undergoing colorectal surgery 34,7° vs. 36,6°- 3 x risk wound infection (NEJM 1996 334, 1209).

Adverse effects hypothermia

• Blood loss - 500 ml greater 35,5C vs. 36,6C in THA ( Lancet 1996 347 289)

• Coagulopathy - platelet dysfunction and sequestration in liver, false negative normal PTT as lab always warms blood to 37.

• 1 litre fluid or 1 unit blood temp 0,25C.

• Forced air warming best method ($10)

Positional Injuries

• Ulnar - commonest (male, >4hrs, BMI<20 or >40). 27% used extra padding.Often delayed onset, at day 3. Occurs in regional anesthesia also.

• Brachial plexus- median sternotomy, steep Trendelenburg with shoulder braces,prone esp. head to opposite side (females)

Positioning

• Arms < 90° when supine.

• At side, neutral position.

• On arm board – supinate.

• Chest roll risk brachial neuropathy.

DNR

• Patient or SDM. – 3 choices for OR:

1.DNR intact.

2. DNR partially rescinded .

3. DNR rescinded completely

• Discuss specifics and goals - chest compressions, pacing, defib, vasoactive drugs, postop ventilation, postop ICU ( time limited).

Awareness

• MAC. – 50% don’t respond in to pain in a “grossly purposeful” manner. Use surgical incision as stimulus.

• Sandin – 18 / 11785 ( 0,15%). Trauma, OB, CV surgery.B – Aware trial . 2 vs. 11 cases using BIS

(bispectral index)

Laparoscopic Physiology

• CVS - Trendelenburg or reverse

- tachycardia from venous return,CO2

- bradycardia from insufflation

• Resp - PCO 2 , atelectasis, subcutaneous emphysema, pneumothorax, CO2 embolus,venous stasis

Laparoscopy

• Hypothermia

• Impaired renal flow ICP

PONV

• Risk factors – female, nonsmoker, volatile agents, nitrous oxide, opioids, laparoscopy, middle ear, strabismus, breast surgery.

• Prophylaxis – Serotonin antagonists e.g. Ondansetron.

- Dexamethasone 4 - 8 mg IV.

- Dimenhydrinate.

Anesthesia Consults

Risks of Anesthesia

CEPOD - Mortality rate total contribution :

1. Patient factors 1: 870.

2. Surgical factors 1: 2860.

3. Anesthesia 1: 185,056 totally.

Anesthesia partially 1: 1430.

Fleisher - 564 267 outpatient , ASC , Office. Had a

mortality of 25 -50 / 100 000.

Newland - intraop arrest – 1/14 000.( 1/10 000)

Myocardial ischemia

• Risk of surgery - High ,intermediate and low.

• > 4 Mets.• Beta blockade preoperatively- Atenolol,

200 patients - Noncardiac surgery. NEJM 1996 335, 1713.

• Bisoprolol in vascular patients - NEJM 1999, 341, 1789.

POISE Trial

• Beta blockers decreased myocardial infarction , but increased stroke rate and overall mortality likely from decreasing blood pressure.

• Risk / Benefit now much more uncertain

AHA guidelines

• Five risk factors (Lee or RCRI):

- History CAD

- History heart failure

- History of CVA

- Renal insufficiency

- Diabetes

Stents and elective surgery

• Bare metal – minimum safe Plavix duration before discontinuation is 30 days.

• Drug Eluting - only safe to stop Plavix after 365 days

Respiratory Disease

• GA - FRC

• GA - Diaphragmatic function

• Shapiro score

• Po2 on room air <50, Pco2 45

• Active wheezing

• Site of surgery especially upper abdomen and thorax

Respiratory disease

• Quit smoking > 8 weeks does resp complications (14.5% vs. 33% in 200 ACB) (Prospective, Mayo Clinic Proc 1989 ,64 609).

• <48 hrs COHB levels and ciliary activity.

• 1-2 Weeks to sputum.

• PFT- only to diagnose,not prognosticate.

AJRCCM Mar 1 2005.

Respiratory disease

• Laparoscopic approach- better ABG’s, PFT.

• Epidural may be better- Meta analysis showed less atelectasis.

• Lung expansion manoevres postop work

Herbal remedies

• CVS - Ginseng, Ephedra, St. Johns Wort, dietary hyperadrenergic

• Bleeding - Ginko, Vit E, Ginger

• Hepato and nephro toxic

• Natural herb CPS

• www.herbnet. com

OSA

• 3 Scoring factors:

1. Severity - AHI (6-20, 21-40, >40).

2. Invasiveness surgery.

3. Narcotic needs postoperatively.

• CPAP use or not?

• Ward, ward with 24 hr oximetry, Step-down

Summary

• Think ICU post-op especially for the emergency list patients (sepsis).

• Consult for multiple Lee cardiac risk factors.

• OSA – beware need for step-down bed.• Being available and in the OR at the

beginning and end of the case is greatly appreciated and noticed.

Sickle Disease

• Hb AS -Trait - <40% S -only sickle at extremes of O2 and temp, not anemic

• Hb SC - 50%S -eye, hip , pregnancy borderline anemia

• Hb SS Disease > 80 %S, anemic

• Get HBS < 40%

• Keep warm and hydrated and oxygenated

MaVs Trial

• 496 patients for vascular surgery receive metoprolol or placebo 2 hrs preoperatively and for 5 days.

• Blinded.

• No difference in CV deaths or nonfatal MI

• CJA 2004 51 .

Ann Int Med Nov 2001