Tough Anesthesia Cases - VCA Specialty Animal Hospitals

Tough
Anesthesia Cases WINTERFEST 2012
VCA Northwest Veterinary
Specialists
Rochelle Low, DVM,
Medical Director  INTRO IDEAS
 CASES x 4
 Case #1: “FLIPPER”
 Case #2: “MALA”
 Case #3: “LILY”
 Case #4: “HANK”
 2 QUICK CASES …. MABEL + JACKSON
 GENERAL PRINCIPLES
Today’s plan:
 Brachycephalic
 Geriatric
 Pregnant
 Pediatric/small
 Metabolic disease
 Critical patients, polytrauma
 Procedural: thoracotomies, brain tumor removal, shunts, c‐sections
 MRI cases
 Cats
Anesthetic Challenges
Higher risk ….
Higher risk…
WHY ARE THESE CASES MORE CONCERNING?  Decreased reserve to compensate
 Complications more likely, especially hypotension!
 Safety principles essential in these cases : ◦ Pre‐anesthetic exam + workup
◦ Multimodal anesthesia
◦ Monitoring pre, intra + post op Anesthetic challenges …
NORMAL LINE
1
1
2
PATIENTS
2
3
3
DEATH LINE
HASKINS, 2011
Equation for blood pressure? BP = CO X SVR
PRESENTING COMPLAINT: Missing for 24 hours + now limping
ANESTHETIC PROCEDURE/SX: Left stifle injury (cruciate)
CASE #1:
“FLIPPER” : 10 YR FS DSH
Pre‐op:
 Pre‐sx panel – BG 161
 Pre‐op BP + ECG normal, normal chest rads
Anesthetic plan: Wt: 4.2kg
1. Pre‐med: Hydro 0.1 mg/kg IV + Ace 0.025 mg/kg IV
2. Induction: Ketamine 5 mg/kg IV + Diazepam 0.15 mg/kg IV
3. Maintenance: Isoflurane @ 1.5% “FLIPPER”
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Sx induction 11:20am 40 minutes after induction Flipper became cyanotic + stopped breathing Actions:
1. Re‐intubated
2. Stopped Isoflurane
3. Reversed Hydro w/ low dose Naloxone
4. Manual ventilation
 Flipper started breathing on her own, but abdominal distension was noted. A stomach tube was passed + small amount air removed …
“FLIPPER”
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The abdominal distension persisted
Subcutaneous emphysema was noted under Flipper’s chin + along her body wall What’s the most likely problem + what should we do? “FLIPPER”
“Flipper”
TRACHEAL TEAR: 1. SUBCUTANEOUS EMPHYSEMA
2. PNEUMOTHORAX
3. PNEUMORETROPERITONEUM
4. PNEUMOCOLON
“Flipper”
DX:
 Tracheal tear – pneumothorax, subcutaneous emphysema + pneumocolon
TX:  Chest tap: 450 mls of air removed, in O2 in ICU. Buprenorphine 0.01 mg/kg PO for pain.
 Recheck rads 4 hrs later showed marked bilateral pneumoretroperitoneum
“Flipper”
,
OUTCOME: After 48 hours in the ICU with supportive
care, Flipper did well and went home. The
cruciate surgery was performed 1 month
later without complication.
“Flipper”
PRESENTING COMPLAINT: Possible dystocia
ANESTHETIC PROCEDURE/SX: C‐
section CASE #2:
“MALA”: 2 YR F Chihuahua
Pre‐op plan:
Istat – iCa low at 1.07
 Lateral radiograph – 4 fetuses, 1 in birth canal
 BP 120 (systolic)
Anesthesic plan: 3.1 kg (pre), 2.2 kg (post)  *Pre‐oxygenate
 Clip belly prior to induction – speed!
 Pre‐med: 0.005 mg/kg Buprenorphine IV
 Induction: Midazolam 0.1mg/kg IV + Propofol 5‐8 mg IV to effect
 Maintenance: Isoflurane 1%

“Mala”
Dose drugs on lean body weight
Speed from induction to delivery
Do not “swing” pups to revive
Keep Mom stable + pups will be more stable! Puppy survival: 3 of Mala’s pups survived;
1 stuck in canal did not survive. Mala did
well and went home 12 hours after sx …
TIPS:

Dose all drugs on mom’s body wt. w/out pups

Pain control w/ minimal depression of pups

Protect oxygen delivery to the fetus

Drugs to avoid: Ketamine, Alpha‐2’s, Acepromazine

Length of dystocia leads to complications
“Mala” – C section considerations

Cranial displacement of diaphragm

Increased cardiac output, circulating blood volume (40%), anemia, low BP

Reduced MAC (40%) – do not use mask induction! 
Gastric reflux is common – give all drugs slowly

Increased RR due to progesterone + sens. to CO2
Physiological changes in Mom
during pregnancy

Induction w/ inhalants faster in pregnant animals 
Use lower than normal tidal volumes

Use lower epidural drug doses

Monitor ETCO2 in sx 
*Time from induction to delivery most important element of pup survival C section tips …
Neonatal resuscitation:
 Clear newborn’s airway, gentle physical stim.
 Oxygen Dopram is not recommended
 Warm towels; GV26 accupuncture pt.
Drugs to consider:
 Short acting + reversible (opioids)
 Epidurals (ie. morphine); Reduce dose 25%
 Etomidate?  Slow infusion Propofol  Decrease doses + give slowly!
C-section…
PRESENTING COMPLAINT: Upper airway stridor, chronic upper airway disease
ANESTHETIC PROCEDURE/SX: BAS sx
Case #3:
“LILY” 5YR FS PUG
Pre‐op:  Pre‐op blood/Rads/ECG/BP normal
Anesthetic plan: 1. Premed: Hydro (0.1 mg/kg) + Midazolam (0.1mg/kg)
2. Induction: Midazolam (0.1mg/kg) + Propofol to effect
3. Maintenance: Isoflurane 1.0% + Fentanyl CRI

Acute drop in pulse ox from 98% →74% after moving the patient. Doppler BP normal. Thoughts?
“LILY”
Dx:
 One lung intubation. ET tube moved on transport of patient + slipped into one bronchus. One lung is inflated the other is atelectic (collapsed).
Tx:  Pulled tube back and within 2 minutes the pulse ox was normal. Other considerations? “LILY”
PRESENTING COMPLAINT: Vomiting 3‐4 days, hx of eating socks, presented in shock/ laterally recumbent
ANESTHETIC/SX PROCEDURE: Abdominal explore linear FB, suspect sepsis
Case #4
“HANK” – 4 YEAR OLD M BULL MASTIFF
Pre‐op plan: 
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Attempt to stabilize + correct fluid deficits (PCV 68%/TS 9.0 w/ BP 60)
Start broad spectrum IV antibiotics
Control nausea and pain
CBC/chem, istat, coags, blood type
Chest / abdominal radiographs +/‐ US
ECG – sinus tachycardia
Place 2 IV catheters
“HANK”
Anesthetic plan: 2‐3 hrs after admit
1. Current vitals: Sys. BP of 75, T 98.5, HR 170, RR 40
2. Premed: Hydromorphone CRI 0.01‐0.02 mg/kg/hr
3. Induction: Ketamine 3‐5 mg/kg IV + Diazepam 0.15‐
0.25 mg/kg IV; Astromorph epidural
4. Maintenance w/ micro boluses Ket/Val (vs CRI ie MLK) vs v. low dose ISO (<0.5%)
“HANK”
Equation for blood pressure? BP = CO X SVR
Anesthetic concerns:
 *Hypotension – plan/prepare for it
 Septic patients have minimal CV reserve – use low drug dosages + give to effect
 Monitor BG, istats intra‐op
 Additional possible txs needed: HES, FFP/pRBC’s, Dopamine (started at 7.5‐10 mcg/kg/min)
 Prepare emergency drug sheet
“HANK”
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Hank had 2 enterotomies performed and
an R+A
He was hypotensive (systolic of 75)
throughout surgery
He recovered in ICU over the next 4 days
+ was discharged on day #5 post op
“HANK”
Septic abdomen/critical patient:  Pre‐oxygenate!  Stabilize as much as you can prior to sx
 Speed is essential!
 Avoid drugs that cause/worsen hypotension (inhalants, propofol, acepromazine)  Length of anesthesia (prep/sx) highly correlated to outcome
 Have emergency drugs/fluids ready
“HANK”
 Sig: 7 yr old bulldog
w/ right stifle injury
 Plan: radiographs under sedation, then
surgery
“MABEL”

Pre op : BP, ECG, Pre-sx panel wnl

Sedation for Mabel:
Hydro 0.1 mg/kg IV + Diazepam 0.15
mg/kg IV

6 minutes after sedation Mabel became
acutely bradycardic (HR 40)

Tx?
“MABEL”
 Sig: 2 year old collie
with bite wounds
 Plan: sedation for wound cleaning + repair “JACKSON”
 Pre‐op: BP, ECG normal
 Sedation: Buprenorphine 0.015 mg/kg IV + Dexdomitor 4 mcg/kg IV  5 mins after sedation = acute sinus bradycardia w/ HR 30, sys BP 80
 TX options: a) Atropine or Glyco + IV fluid bolus
b) Partial reversal Dexdomitor w/ Antisedan + IVF sup
c) Reverse buprenorphine w/ Naloxone
“JACKSON”
Teaching points …
Why do animals do poorly? 
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1. Overanesthetization**
2. Hypotension
3. Poor tissue perfusion
4. Hypoventilation
5. Hypoxemia
6. Hypothermia
7. Arrhythmias
*CRITICAL + HIGH RISK PATIENTS ARE MORE LIKELY TO SUFFER FROM THESE PROBLEMS AS THEY HAVE LESS PHYSIOLOGIC RESERVE
CARDIOVASCULAR EFFECTS OF ANESTHETIC AGENTS:
DRUG
HEART
RATE
OPIOID
CARDIAC
OUTPUT
SVR
BP
↓ or NC
↓ or NC
↓
↓
↓
+/-
PROPOFOL
NC
↓
VALIUM
NC
NC
INHALANT
NC
↓
↓
↓
+/- ↑
↓
↓
↓
NC or ↓
↑
↓
+/- ↑
↑
↑
↑
ACEPROMAZINE
+/- ↑
∂-2
AGONIST
KETAMINE
NC= No change
↓
NC
NC
NORMAL LINE
1
1
2
PATIENTS
2
3
3
DEATH LINE
HASKINS, 2011
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Higher risk patients = more potential for anesthetic complications
If a patient was stable under anesthesia + this acutely changes = check the patient + check the machine!
Pre‐op workup, vigilant monitoring + post‐op care is critical
Pre‐oxygenate + minimize stress
Drug choice, drug administration speed/timing
Always dose drugs based on lean body weight Teaching points …
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Be prepared for complications! Have vasopressors, HES, emergency drug doses ready Give drugs slowly! Many anesthetic complications occur on induction
Careful when moving the anesthetized patient –
increased vagal sensitivity in brachycephalics , protect airway …
Start at the low end of the dosing range – you can always give more!
Teaching points …
 Mask induction is not “safer”. Why? 1. Increased patient stress
2. Staff exposure
3. Time to induction is longer
4. Unsecured airway
5. High concentrations of anesthetics required
Teaching points…
QUESTIONS?
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Perioperative risk factors for puppies delivered by c‐section. JAVMA 2000, Moon et al. Results of the confidential enquiry into perioperative small animal fatalities regarding risk factors for anesthetic related deaths in dogs. JAVMA 2008, Boradbelt D. et al
VECCS proceedings 2010: Anesthesia + Analgesia in pregnant animals; Brock, DACVA
Small Animal Critical Care Medicine; Hopper. Chapter 140 – Dystocia + Obstetrics; Chapter 148 Post‐thoracotomy management; Chapter 162 Sedation of the Critically Ill Patient
Bench to bedside review: Permissive Hypercapnia. Critical care 2005. O’Croinin et al. Traumatic Diaphragmatic Hernia: Pathophysiology and Management. Compendium 2005. Worth et al.
How Anesthetics Harm Patients. Haskins, 2011
Anesthesia for the Critical Care Patient. Brainard, 2010
References…
ADDENDUM 1-4
Tip: Dose all drugs
and fluids based on
lean body weight of
the patient!
Reversal for Opioids:
1. Naloxone 0.01‐0.02 mg/kg IV or IM
2. Low dose Naloxone 0.001‐0.004 mg/kg IV (reverses
dysphoria, not analgesia) Reversal for Benzodiazepenes (Diazepam + Midazolam):
Flumazenil 0.1‐1.0 mg/kg IV
Reversal for Dexmedetomidine: Antisedan 0.1 mg/kg (IM, SQ or ½ IV + ½ IM)
Addendum 1: Drug reversals
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“Maintenance”: Dogs 65 mls x BW (kg)/ 24 hrs, Cats 45 mls x BW (kgs)/24 hrs
“Shock”: 90 mls/kg (dog), 60 mls/kg (cat). Give ¼ shock then re‐evaluate.
Crystalloid bolus for acute hypotension while under anesthesia: Cats 2.5‐5 mls/kg, Dogs 5‐10 mls/kg
Surgical fluid rate: Dogs 10 mls/kg/hr, Cats 5 mls/kg/hr. For patients with cardiac disease decrease rate by 50%.
Hetastarch: 2‐5 mls/kg shock/bolus (give over 5‐10 mins)
pRBC’s: 5‐7.5 mls/kg over 4 hours
Addendum 2: Useful fluid doses
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Fentanyl CRI : 1‐7 mcg/kg/hr
Hydromorphone CRI : 0.01‐0.03 mg/kg/hr
Ketamine CRI (pain) : 2 mcg/kg/min
Diazepam CRI : 0.1‐0.4 mg/kg/hr
(* May lead to accumulation of drug + slow recovery)
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Dexmedetomidine CRI : 1‐2 mcg/kg/hr (anxiety)
Lidocaine CRI for pain: 20‐30 mcg/kg/min
Lidocaine CRI for arrhythmias: 50‐75 mcg/kg/min (after 1.5‐2 mg/kg bolus)
Propofol CRI : 2‐4 mg/kg/hr for sedation
Hetastarch CRI : 5‐20 mls/kg/24 hours
Addendum 3: Common CRI doses
Anesthesia + metabolic disease – some tips
ADDENDUM #4
Example cases:
Pulmonary contusions, Lung tumor, Pleural effusion
 Starlings forces!
 Limited fluid strategy ensuring euvolemia
 Avoid overperfusion (more prone to fluid overload, conservative use of colloids)
 Ensure tissue perfusion (monitor BP, lactate, extremity warmth, pre‐op bloods)
 Pre‐oxygenate! Keep them warm!
 Evacuate chest of air, fluid etc prior
to induction
 Conservative tidal volume Pulmonary Disease
Example cases:
Patients w/ murmurs, patients w/ hypertension, patients w/
known cardiac disease (HCM, DCM, valvular disease)
 Conservative anesthetic plan + fluid therapy
 Avoid Ketamine, + only use low levels inhalants
 In critical patients w/ cardiac disease consider Etomidiate
 If not in CHF, fluid rates: Cats 2.5‐3 mls/kg/hr + Dogs 5 mls/kg/hr 
Conservative use of colloids as
prone to fluid overload
Cardiovascular disease
Example cases:
Dental procedure in cat w/ CRF, Azotemia in hemorrhagic shock
trauma case, Cruciate repair in dog w/ PLN
 Renal autoregulation 80‐180 mmHg
 Renal perfusion may be more linear in damaged kidneys
 During sx/anesthesia must maintain BP!
 Kidneys primarily responsible
for clearance of drugs through excretion
 Avoid Ketamine in cats w/renal disease
 Use lower doses of drugs
 +/‐ Increase dosing interval
Renal Disease
Example cases: Biliary mucocele, Fracture repair in patient w/chronic liver
Disease, Trauma case with elevated LES
 Metabolism of drugs! Increased duration of action of drugs –
altered metabolism by p450 enzyme system, decreased PBP’s and decreased biliary excretion
 Use lower doses of anesthetic drugs
 Some opioids (Morphine) = increased ½ life w/ liver disease. Fentanyl is not affected by liver compromise
 Diazepam/Midazolam – delayed excretion
Liver disease