RESP 2230 #5

What are three characteristics of monitoring equipment required by the CAS?

required - in continuous use throughout administration of all anaesthetics

exclusively available for each patient - must be available at each work station so they can be applied without delay

immediately available - must be available to be applied without undue delay

What monitors are required by the CAS during anaesthesia?

• Pulse ox 

• BP monitor 

• ECG 

• NMBA monitor in NMBA use 

• Capnography 

• Agent-specific anaesthetic gas monitor 

• Vt/airway pressure monitor 

What equipment should be exclusively available for each patient according to the CAS during anaesthesia?

• stethoscope

• appropriate lighting

• cuff pressure manometer

• thermometer

What equipment should be immediately available according to the CAS during anaesthesia?

invasive hemodynamic monitors

What is the goal of monitoring depth of anaesthesia (DoA)?

• detecting if patient is too light/at risk of awareness

• detecting if patient is too deep/at risk of prolonged recovery

• equipment works the same regardless of patient

• works the same regardless of anaesthetic modality/meds

What are clinical signs to look for when monitoring DoA?

• loss of eyelash/eyelid reflexes (barbiturates)

• pupil reactivity to light - resp pattern (volatile agents)

• reaction to surgical stimulation - HR, BP, EEG

What physical examination may be done while monitoring DoA?

IPPA - inspection, palpation, percussion, auscultation

What should be monitored during DoA?

• neurological function/response

• resp function

• cardiovascular function

• renal function

• neuromuscular function

• body temperature

• fluid management

What is Bispectral Index Monitoring (BIS)?

measures DoA through analyzing a patients EEG and converting it to a number representing their awareness

measured during all three phases of GA, allows for adjustment of DoA

may be subject to artifact

What is the BIS ranking scale of patient awareness?

100: awake

60-90: Sedated, may still be aware

45-60: GA

0: flat line EEG

How should respiratory function be monitored for during anaesthesia?

• rate/depth

• bilateral chest excursion(?)

• irregular respirations/breath-holding/apnea

• hypoxemia/hypercapnia

• ventilatory volumes

• airway pressure

• ABGs, SpO2, Tc monitoring

• O2 analyzers + capnography

In the absence of CO2 rebreathing during anaesthesia, what do ETCO2 values depend on?

• adequacy of alv ventilation

• CO2 production

• state of pulmonary circulation

How should mild hypercapnia (55) during spont ventilation be interpreted during anaesthesia?

central resp depression from anaesthesia medication/oversedation

How should gradual hypercapnia development during MV be interpreted during anaesthesia?

inappropriate vent settings or leaks in system

How should rapid hypercapnia during adequate MV be interpreted during anaesthesia?

metabolic disturbances - check acid-base status, temperature

equipment issues - CO2 absorber?

How should sudden hypercapnia during intra-abdominal insufflation be interpreted during anaesthesia?

CO2 embolism - potentially life threatening

How should mild hypocapnia during MV be interpreted during anaesthesia?

alveolar hyperventilation, metabolic state (hyperthermia, hyperthyroidism)

How should a sudden, unexpected decrease in ETCO2 be interpreted during anaesthesia?

circuit disconnect, cardiac arrest/pulmonary embolism?

What should be monitored cardiovascularly in every patient under anaesthesia?

pulse and BP every 5 min

• indicates DoA

• agents may alter function

What are indications of invasive CV monitoring in patients under anaesthesia?

• major cardiac, thoracic, or neurosurgical procedures

• large fluid shifts are anticipated

• critically ill patients

• inaccurate NIBP

• controlled hypotension

What invasive CV monitoring may be done in patients under anaesthesia?

• Arterial BP

• swan-ganz catheter

• central line

• TEE

What should be monitored to determine renal function in patients under anaesthesia?

• urine output

• stimulation of ADH by opioids and stress

• to be interpreted alongside cardiac function

What should be monitored to determine neuromuscular function in patients under anaesthesia?

• twitching diaphragm, skeletal muscle activity on ECG (consider muscle relaxant)

• return of neuromuscular function is signaled by onset of spont ventilation

What is the purpose of peripheral nerve stimulation in patients under anaesthesia?

• estimates muscle contraction during anaesthesia

• electrical stimulation of ulnar, facial, or lateral popliteal nerve

• supramaximal stimulus applied

• differentiates type of block

• determines block magnitude

• determines degree of recovery

What are the characteristics of the twitch mode of peripheral nerve stimulation?

• square wave stimulus (0.1-0.2 ms)

• apply repeatedly, before and after dose of relaxant

What are the characteristics of the train of four (TOF) mode of peripheral nerve stimulation?

• 4 stimuli at 2hz, applied over 2s

• 3 twitches = 70% block

• 2 = 80%

• 1 = 90%

• none = 100%

What are the characteristics of the tetanus mode of peripheral nerve stimulation?

• most sensitive

• 50-100hz detects minor residual block

• painful when awake

What are the characteristics of the post-tetanus mode of peripheral nerve stimulation?

• assesses deep degrees of block by non-depolarizing agents

• twitch applied, then tetanus, then single twitches until response disappears

How does a non-depolarizing block repond in nerve stimulation?

• lower twitch height, fades gradually

• similar fade in twitch height when TOF is applied

• unsustained response to tetanus stimulus

• transient increase in twitch response during post-tetanus facilitation

How does a depolarizing block repond in nerve stimulation?

• decreased twitch height that does not fade

• no fade with TOF

• sustained tetanus

• no post-tetanus facilitation

What occurs to thermoregulation in patients under GA?

thermoregulation is lost - difference between core and peripheral temp is related to CO and vasoconstriction

What are the 4 mechanisms of heat loss in patients? How do they work?

• radiation - Most common, transfer of heat to surrounding surfaces not in contact with patient (open surgical site)

• conduction - Loss of heat of body to object in contact with body (warm pt on cold operating table) 

• convection - Heat loss due to air currents over the body (warm pt in cold drafty room) 

• evaporation - Loss of heat due to cold dry air entering body (no humidified air in ETT) 

What impact may hypothermia have in patients under GA?

• alteration in drug metabolism

• reduced blood clotting

• cardiac arrhythmias

• decreased LOC

• shivering - increased O2 consumption

What patients are most at risk for hypothermia

• Burn patients 

• Neonates 

• Elderly 

• Long surgery with open abdomen 

• Spinal cord injury 

How can hypothermia be prevented in patients under GA?

• warm room

• cover patient whenever possible

• forced air blankets

• fluid warmers

What is the difference between central and peripheral compartments in accordance with thermoregulation?

central/core: brain and organs, accounts for 2/3 of body heat - maintain within 1C

peripheral: limbs, skin, SC tissue, accounts for 1/3 of body heat - ranges from 2-3C below core but can drop up to 20 below

How does anaesthesia impact the bodies thermoregulation?

• vasoconstriction maintains core to peripheral temp gradient

• anaesthesia induction = loss of vasoconstrictor tone

• vasodilation occurs - heat flows down concentration gradient from core to periphery

• results in mild core hypothermia

How can shivering impact heat production?

increase it up to 60x normal

How do neonates produce heat?

presence of round fat replaces need for shivering

What is the primary cause of heat loss during surgery? What else may impact this?

radiation is most common, but convection and evaporation are also common

How does the body react to a decrease in core temp?

• vasoconstriction, followed by shivering (regulated by hypothalamus)

• shivering normally inhibited by impulses from heat-sensitive area in hypothalamus

• cold impulses exceed a certain rate - excess signals are sent to the spinal cord

• results in increased skeletal muscle tone

How does GA impact thermoregulation?

• increased heat-response thresholds

• decreased cold-response thresholds

mild hypothermia

• initial rapid decrease in core temp (1C in 30min)

• slower, linear decrease to 35-34 over following 2 hours

• core temp plateau

How does RA impact thermoregulation?

• redistribution of body heat from core to periphery

• plateau phase does not occur due to blocked vasoconstriction

• heat lost continues throughout

What are possible complications of peri-operative hypothermia?

• reduction in BMR

• resp fatigue

• reduced oxygen demand - good in cardiac surgery

• increased risk of wound infection

• platelet function reduces = greater blood loss

• prolonged drug action

• patients will recall being cold

How may peri-operative hypothermia be avoided?

• pre-emptive skin warming - removes gradient of heat loss via skin, 1hr minimum

• insulation with single layer will reduce skin heat loss by 30%

• HMEs

• warmed IV fluids

• forced air warming blankets

What are the characteristics of post-anaesthetic shivering?

• up to 65% of GA patients, 35% of RA

• detectable tremor of the face, jaw, head, trunk, or extremities lasting 15s or longer

• not always a sign of hypothermia, however it is a common cause

• pharmacological treatment

What is the average daily fluid lost in adults?

2.5L

Approximately how much intracellular fluid (ICF) is in an adult body? Extracellular fluid (ECF)?

ICF: 28L

ECF: 14L

What peri-operative fluid considerations should be made?

• pre-existing deficit: pre-op fasting + prep

• maintenance fluid: daily water and electrolyte loss

• third space loss: edema, surgical trauma

• bleeding

How is blood loss estimated during surgery?

• weigh discarded sponges

• measure vol of blood in suction canister

• estimate red cell loss using Hgb

A blood loss of what during surgery will require a blood transfusion?

> 15%

Blood transfusion will depend on the measurement of what?

level of hgb

What fluids may be administered during anaesthesia?

crystalloid

• 0.9% Ringer’s lactate

• dextrose solutions

• hypertonic saline (7% NaCl)

colloid

• starches

• blood products

• albumin

What are the determining factors of a blood transfusion?

• acuity - hgb levels

• potential for ongoing bleeding

• pre-existing medical conditions increase risk of anemia

What are possible complications of blood transfusions?

• disease transmission

• metabolic abnormalities - electrolytes

• coagulopathy

• hypothermia

• transfusion reactions

  • allergic: incompatible plasma proteins

  • febrile: reaction to donor WBCs

  • hemolytic: accidental use of incompatible blood

What is catabolism?

energy resulting from the breakdown of carbs, protein, and fats

breaks down glucose - glycolysis - aerobic process

• anaerobic gycolysis = lactic acid build-ip

What is anabolism?

building-up energy as carbs, protein, and fats

What is the result of carbohydrate metabolism?

glucose, carried across cell membrane with insulin

What are the characteristics of protein metabolism?

• 20-30g/day in absence of protein ingestion (ie. starvation, post-op)

• if carb and fat stores are depleted, can be >100g/day

• results in rapid tissue function decline

What are the characteristics of lipid metabolism?

• lipids: fats, oils, steroids, cholesterol

• major source of energy, provides electrical insulation for nerve conduction

What are the characteristics of lipoproteins?

• comprised of fatty acids broken down in the liver

• byproducts of breakdown go unused = ketone formation

  • diffuse into circulation + used as energy by tissues

  • common conditions: diabetes, starvation alcoholism

  • high ketones = ketoacidosis

How does body temperature impact the BMR?

14% increase per 1C increase

How does GA impact BMR?

Significantly reduces rate

How does RA impact BMR?

Less impact than GA

changes to heat balance and peripheral metabolism

What are the characteristics of the neuroendocrine stress response during surgery?

stimulated by pain, may be diminished during RA, results in metabolism of muscle and fat

• hyperglycemia + insulin intolerance

• impaired wound healing

• fat metabolism = increased fatty acids in blood

• increased myocardial oxygen demand

  • decreased O2 to the heart

• increased blood clotting

• decreased FRC from post-op pain

• reduced GI motility

What are the characteristics of the cytokine stress response during surgery?

resulting from nerve injury to a limb

• inflammation relative to degree of tissue damage

• prolonged wound healing and recovery

  • increased post-op infection risk

How does GA and RA impact the stress response?

GA - no impact

RA - reduced/eliminated neuroendocrine response, cytokine response reduced due to limited surgical insicion

What are the most common complications during anaesthesia?

• cardiac arrhythmias

• hypotension

• hypoventilation

• med reactions

What are common causes of anaesthesia complications?

• human error

• equipment failure

• patient condition

What are possible causes of human error during anaesthesia?

• poor working relationships

• varying training levels

• poor working conditions

• fatigue

How can anaesthesia complications be avoided?

• pre-op patient assessment

• pre-op equipment check

• pre-op consultation with personnel

• appropriately trained assisstants

• appropriate monitor use

• documentation

What is the most common respiratory complication during anaesthesia?

partial obstruction during spont or bag-mask ventilation without an OA

What are common causes of laryngospasm during anaesthesia? How might this be treated?

• most common during airway manipulation and higher LOC

  • or surgical + visceral stimulation

treat

• remove stimuli

• 100% O2 and clear airway

• increase anaesthesia depth

• ventilation

What are common causes of bronchospasm during anaesthesia? How might this be treated?

• underlying disease, recent resp infection, smoking hx

• due to: inhalational induction, OA insertion, carina stimulation, beta-blocker use

treat

• prevent hypoxemia

• deepen anaesthesia

• bronchodilators

What are common ventilation complications during anaesthesia?

• hypercapnia

• hypocapnia

• pneumothorax

• atelectasis

What are common causes of hypercapnia during anaesthesia? How might this be treated?

• increased CO2: pyrexia, malignant hyperthermia, shivering, inadequate fresh gas flow, exhausted CO2 absorber

• leads to: tachycardia, sweating, cardiac ectopics, increased ICP

• NEED ADEQUATE VENTILATION

What are common causes of hypocapnia during anaesthesia? How might this be treated?

• mechanical hyperventilation

• leads to: vasoconstriction, decreased cerebral perfusion, decreased CO

  • may have delayed onset of spontaneous respirations until PaCO2 is normalized

• NEED ADEQUATE VENTILATION

What are common causes of pneumothorax during anaesthesia? How might this be treated?

• puncture during CV catheterization, thoracic surgery, nerve block, or high ventilatory pressure

• note: N2O will diffuse into air-filled spaces quicker, rapidly increasing pneumo size

• clinical signs: decreased CO, tachycardia, uneven chest excursion, hypoxia, increased ventilating pressure

• needle decom, chest tube, DISCONTINUE N2O

What are common causes of hypertension during anaesthesia? How might this be treated?

• intraoperative when MAP >25% pre-op value

• due to: inadequate anaesthesia, surgical stimulation, airway manipulation

• at risk for: cerebral ischemia, infarction, or hemorrhage

• manage: pre-op tx, fix causes, meds

What are common causes of hypotension during anaesthesia? How might this be treated?

• common with d/t anaesthesia meds

• increased risk of concerrent hypovolemia and hemorrhage

• treat: fix hypovolemia, IV fluids, alter meds

What are common causes of hypovolemia during anaesthesia? How might this be treated?

• loss of fluids

• treat: fluid, blood/blood product transfusions

What are common causes of hemorrhage during anaesthesia? How might this be treated?

• pre-existing or intraopoerative blood loss

• treat: blood transfusion

What are common cardiovascular complications during anaesthesia?

• bradycardia: increased vagal tone, opioids

• tachycardia: peri-op stress response, burns, sepsis, fever

• arrhythmia: cardio-resp causes, metabolic disturbance, surgical stimulation

What are common causes of thromboembolus during anaesthesia? How might this be treated?

• typically post-op risk due to DVT of legs/pelvis

• risk factors: immobilization, pelvic/limb surgery, venous stasis/trauma, smoking

• treat: risks pre-op, compression stockings

  • during surgery: 100% O2, bronchodilation, inotropes, thrombolytic tx

What are common causes of gas embolus during anaesthesia?

• gas enters via surgical opening, venous catehter, laparascopic surgery

• enters RA and blocks circulation

• clinically: sudden decreased ETCO2 then hypoxemia, increased pulm art pressure, ECG changes

  • depends on vol of gas and rate of entry

What are common causes of fat embolus during anaesthesia? How might this be treated?

• dislodged from long bones, can onset up to 48h post-op

• clinically: SOB, hypoexemia, hemogynamic changes

What are common causes of awareness during anaesthesia? How might this be treated?

• inadequate anaesthesia depth

• risk factors: emergency surgery, paralysis, hypotensive periods IV agents

• clinically: sweating, tachycardia, tears, pupil reactivity

What are common causes of CNS ischemia during anaesthesia? How might this be treated?

• disrupted oxygenation and perfusion = ischemia/infarction

• risk factors: pre-existing cerebrovascular disease

What are common causes of hypothermia during anaesthesia?

• prolonged procedures

• extensive incisions

• blood loss

What are the characteristics of malignant hyperthermia during anaesthesia?

• hypermetabolic state induced by volatile anaesthesia and succinylcholine = rhabdomyosis

  • inherited disorder, more common in pediatrics

• up to 80% mortality

What is the pathophysiology of malignant hyperthermia?

• Ca2 channel receptor mutations on sarcoplasmic reticulum of skeletal muscle is present

  • abnormal Ca2 release and re-uptake by sarcoplasmic reticulum

• chain of events:

  • muscle contraction

  • ATP depletion

  • increased O2 consumption and CO2 production

  • metabolic acidosis

  • heat production

  • cell breakdown

What are the signs of a malignant hyperthermia crisis?

in order:

1. increased HR

2. tachypnea

3. increased ETCO2

4. muscle rigidity

5. mottling/cyanosis

6. hyperthermia

additionally:

• cardiac arrhythmia = K release

• severe combined acidosis

• coagulopathy

• Acute Renal Failure (due to rhabdo, myoglobin leaks into bloodstream and obstructs tubules)

How can a malignant hyperthermia crisis be managed during anaesthesia?

• d/c all volatile agents, 100% O2

• maintain IV anaesthesia

  • administer Dantrolene - reduce muscle tone and metabolism

• active cooling, monitor core temp

How should malignant hyperthermia be tested for?

caffeine-halothane contracture test (CHCT)

• compares fresh muscle tissue when exposed to c-h against non-MH muscle response

  • if fresh tissue is higher - positive

• all first-degree relatives of a patient with MH

How should a patient with known malignant hyperthermia be managed in surgery?

• IV/RA anaesthesia

• ventilate with:

  • specially reserved MH anaesthetic machine

  • machine with vaporizers removed and flushed with 100% O2 for several hours

What are the characteristics of the “recovery period” of anaesthesia?

• begins as soon as patient leaves operating table

• patient may still be unconscious/semi-conscious

• patient may still have:

  • reduced CO and BP

  • hypovolemia

  • hypertension as consciousness is regained

  • hypoventilation from residual anaesthesia

  • N/V

What is typically monitored post-op?

• vitals

• urine output (major surgery)

• wounds/drainage

What should be reported by anaesthetist to recovery room staff?

• pre-existing medical problems

• nature/extent of surgical procedure

• anaesthetic techinique, meds, regional block

• fluids, blood loss + replacement

• any unexpected events

What factors may impact patient regaining consciousness?

• meds used

• pain - more pain = faster recoveru

• hypoxemia, hypercapnia

• hypotension

• hypothermia

• hyperglycemia

• cerebral damage

• confusion

Respiratory post-op complications are related to what?

• FRC reduction

• surgical site

• patient condition: age, ASA classification