Download Assessment of the airway

Preoperative Patient Assessment and Care
The objectives of the preoperative visit are:
1. Meet the patient
2. Identify the present problem requiring surgery
3. Identify any previous ongoing illnesses which may influence the anesthetic or surgery, in
particular cardiac and respiratory diseases. Renal, hepatic, gastrointestinal, endocrine,
neurological, and musculoskeletal conditions may also influence perioperative management
4. Elicit any possible concerns about previous anesthetics or any family history of problems
with anesthetics.
5. Any adverse drug reaction and current medications.
6. Examine the patient and in particular assess the airway
7. Review any investigations and order others needed.
8. Plan the anesthetic technique.
9. Provide information for the patient and relatives about the anesthetic and postoperative care
including pain management.
10. Ask the patient to stop smoking.
11. Ensure the patient is NPO for 6 hours for solids and 4 hours for clear fluids.
12. Order any premedications required and all essential routine medications to be
given preoperatively.
13. Ensure adequate postoperative care is available e.g. step down/ ICU.
Assessment of the airway
The incidence of difficult intubation is relatively low (~1:65) with a “failure to intubate”
rate of ~ 1:2000. In an attempt to try and identify those patients who may fall into this
category a variety of tests have been devised. Unfortunately no single test is ideal.
Causes of difficult intubation include:
1) Congenital: e.g. Pierre Robin syndrome.
2) Anatomical: Variants of normal e.g. prominent teeth, small receeding chin, deep
protruding mandible, short thick neck, pregnancy.
3) Acquired: e.g. scarring, swelling, malignancy, rheumatoid arthritis.
At the preoperative visit the anesthesiologist can perform a variety of tests to try and
identify those who may be a difficult intubation. These include:
1. The Mallampati Classification: this involves getting the patient to sit upright, open
their mouth, stick out their tongue and say “Aaah”. The view of the posterior pharyx falls
into four classes:
Class I - The soft palate, tonsillar fauces and uvula are visible.
Class II - The soft palate, tonsillar fauces and part of uvula visible.
Class III - Only the soft palate is visible.
Class IV - Only the hard palate is visible.
Class III and IV are associated with increasing difficulty to intubate.
2. The Thyromental distance: a distance of less than 6.5cm or inability to admit three
fingers associated with more difficult intubation.
The ability to prognath:
Class I: able to move bottom teeth in front of top teeth = normal
Class II: able to align bottom set to top set = some difficulty
Class III: bottom set stays behind top set = difficult to intubate
4. Neck mobility: ability to flex the lower cervical spine and extend the atlanto-occipital
joint (sniffing the morning air position. This position results in axial alignment of the
mouth, pharynx and larynx.
Laboratory Investigations
These tests vary depending on the patient but a few rules can be followed.
1. Complete blood counts should be performed on all patients who show signs of
anemia or have an underlying condition which increases the risk of anemia (e.g. chronic
illness, bleeding disorder, excess alcohol consumption, chemotherapy). It should also
be done when large blood losses are likely during surgery.
It is routine in all women and men over 60yr.
2. Serum Electrolytes should be done on all patients over 40yr, those with renal
disease, hypertension, diuretic therapy including bowel prep., diarrhoea or vomiting.
3. A Coagulation Screen if there is a history of bleeding disorder or on anticoagulation
therapy.
4. An Electrocardiogram should be done on all patients over 40yr, any patient at
increased risk of cardiac disease, have symptoms of cardiac disease, or show signs of
cardiac disease on physical examination.
5. A Chest x-ray is required in all patients with symptomatic pulmonary disease or
underlying malignancy.
6. Urinalysis is required in all patients.
All other investigations are ordered if specific problems are identified on history and
physical examination.
Premedication
These are given to provide amnesia, anxiolysis, antacid prophylaxis,
analgesia, antisialogogue, autonomic control, allergy prophylaxis, and continuation of
specific therapy.
Pre-existing illness:
Certain diseases are especially important during anesthesia. These include
ischemicheart disease, congestive heart failure, hypertension, diabetes mellitus,
reactive airways disease.
1) Ischemic heart disease (IHD)
Five percent of over 35yr olds have asymptomatic heart disease. IHD arises from a
decrease in the supply:demand ratio for myocardial oxygenation. During anesthesia
attempts are made to maximise oxygen supply and limit the oxygen demands of the
heart.
Decreased oxygen supply:
O2 content – anemia?
hypoxia
tachycardia
increased preload
hypotension
Increased oxygen demand:
tachycardia
increased preload
increased afterload
increased contractility
The time of highest risk of a perioperative myocardial ischemic event is not during
surgery but around three days post operatively especially when opioid analgesics are
used without supplemental oxygen therapy.
Patients with unstable angina, suboptimally controlled angina, or a myocardial infarction
within the previous 6 months should not undergo elective surgery. Antianginal
medication should continue right up to surgery and can be taken with a sip of water
within an hour of surgery starting. This is especially true of b-blockers where there is a
risk of rebound hypertension if suddenly withdrawn.
2) Congestive Heart Failure
Patients with impaired ventricular function and congestive heart failure do not tolerate
anesthesia and surgery very well. Most anesthetic drugs are negative inotropes and so
decrease the strength of contraction of an already weak muscle. Also the stress of
surgery and fluid shifts that can occur during an operation increases the demands on a
poorly functioning myocardium. No patient should undergo anesthesia in uncontrolled
congestive heart failure.
Hence it is important to recognise these patients preoperatively so their condition can
be optimised.
Symptoms include: orthopnoea, PND, ankle swelling, poor exercise tolerance.
Signs include: raised JVP, pitting odema of legs, tachycardia, basal crackles, S3 or S4
on auscultation.
3) Hypertension
Poorly controlled hypertension increases the anesthetic risk. It results in overeactive
cardiovascular responses, poor left ventricular relaxation, cerebrovascular events,
myocardial ischemia and infarction, and renal failure. Many patients are hypertensive
when first admitted to hospital due to anxiety, so before hypertension is diagnosed a
series of elevated readings are needed whilst the patient is as relaxed as possible.
It is important that antihypertensive medication is continued up until surgery to prevent
the possibility of rebound hypertension.
4) Reactive Airways Disease
Anesthesia can precipitate life theatening bronchospasm in patients with reactive
airways disease (e.g. asthmatics and COPD patients). This can be due to anxiety,
anesthetic drugs, and airway manipulation. Anesthetics also worsen mucus trapping by
drying secretions and impairing cilial function. These patients should have their airways
disease under optimal control prior to elective surgery and should continue their inhalers
and steroids up until the day of surgery. Any patient who has been on steroids in the
previous 6 months will need steroid replacement to cover the stress of surgery since
there may still be a degree of adrenal suppression. If possible these patients should be
done under regional technique (spinal, epidural, peripheral block) to avoid airway
manipulation. Unfortunately this is not always possible. Hence patients with pulmonary
disease need to have their treatment optimised and surgery postponed if there is any
suspicion of infection. Treatment options include stopping smoking, bronchodilator
therapy, physiotherapy to mobilise secretions, and antibiotics where appropriate.
5) Diabetes Mellitus
The first thing to assess in this group of patients is their diabetic control. All except life
saving emergency surgery is delayed until hyperglycemia, dehydration and acidosis are
controlled. This control is aimed at preventing perioperative hypoglycemia /
hyperglycemia. Hyperglycemia can result in delayed wound healing and increased risk
of infection but hypoglycemia can result in irreversible neuronal damage. The risk of
hypoglycemia is increased in those patients on long acting oral hypoglycemic agents or
long acting insulin. The stress of surgery causes a reduction in the body's response to
hypoglycemia (glucagon, epinephrine) and b-blockade can mask the signs of
hypoglycemia. Equally there is a need to prevent hyperglycemia intraoperatively.
The inhalational agents increase the blood sugar levels and the stress of surgery
causes a degree of insulin resistance.
The aim intraoperatively is to maintain control of blood sugar levels in the high normal
range rather than run the risk of a period of hypoglycemia by aggressive control.
Patients on oral hypoglycemic agents should have these held the morning of surgery
and a solution containing 5% dextrose started. This should continue through surgery
with regular monitoring of blood sugars perioperatively. Those taking insulin can be
managed with an insulin and dextrose infusion started prior to surgery. Alternatively
they can take half their intermediate acting insulin the morning of surgery and a solution
of dextrose given throughout the perioperative period. Whichever method is used the
aim is to monitor blood sugar levels and alter management accordingly.
These patients have a multisystem disease and the complications should be looked for.
These include vascular disease, hypertension, cardiomyopathy,
nephropathy,neuropathy, retinopathy, risk of infection, decrease in respiratory function.
Look for associated conditions e.g. thyroid disease, parathyroid disease, obesity,
and pregnancy.
Conduct of Anesthesia
There are three stages to any anesthetic: induction, maintenance and recovery. During
all three stages there is a standard level of monitoring employed: oxygen analyser,
stethoscope, pulse oximeter, non-invasive blood pressure, electrocardiogram, end tidal
carbon dioxide level, inhalation agent concentration, temperature probe. If the patient is
ventilated then additional monitors are needed to read pressures in the airway and the
breathing circuit, tidal volumes delivered and respiratory rate. If the patient is paralyzed
then a peripheral nerve stimulator is used to measure the degree of paralysis.
The overall conduct of any anesthetic is a balance between analgesia, anesthesia, and
muscle relaxation.
Anesthetic agents used
Inhalational agents -halothane, enflurane, isoflurane,sevoflurane, desflurane, nitrous
oxide Intravenous agents -pentothal, propofol, ketamine.
Adjuncts to anesthetic agents
There are a variety of drugs used to supplement the anesthetic agents.
Benzodiazepines
– e.g. midazolam. Used as a sedative to decrease the intravenous induction agent and
minimize its side effects. Also acts as an amnesic.
Narcotics
– e.g. fentanyl, morphine, sufentanil. Analgesics which also help in reducing anxiety
preoperatively, decrease the cardiovascular response at intubation, decrease the
amount of agent neede to maintain anesthesia.
Muscle relaxants
– these are in two groups: depolarizing relaxants (succinylcholine), and nondepolarizing relaxants ( rocuronium, vecuronium, cis-atracurium, pancuronium).
They are used in anesthesia for a variety of purposes:
a) facilitate endotracheal intubation
b) facilitate surgery on the abdomen or thorax, and make surgical access easier
c) to prevent reflex patient movements during anesthesia.
MUSCLE RELAXANTS SHOULD NEVER BE USED UNLESS THE PERSON
ADMINISTERING IT HAS THE SKILL AND EQUIPMENT AVAILABLE TO
ESTABLISH AND MAINTAIN AN AIRWAY.
Induction can be either via an intravenous or inhalational technique. Inhalation
induction is usually done on very young children who may be difficult to get an
intravenous in awake, and in certain airway conditions where it is important that the
patient maintains spontaneous respiration. The inhalation agents used are halothane
and sevoflurane since they smell nice, are relatively non-irritant, and, in the case of
sevoflurane, quick. Intravenous induction is the more usual technique as it is fast,
controlled and pleasant for the patient. The agents commonly used are pentothal and
propofol.
Maintenance of anesthesia is usually by administering inhalational agents and in
particular a mixture of nitrous oxide and oxygen with one of the following volatileagents:
halothane, enflurane, isoflurane, sevoflurane, desflurane. Nitrous oxide is a very weak
anesthetic but adding it to the mixture means that less of the volatile is needed and so
decreases the likelihood of side-effects.
These side effects include hypotension and arrythmias. Alternatively it is possible to use
a continuous intravenous infusion technique. The agent used for this is propofol and it is
a technique most frequently employed in patients who are sensitive to the volatile
agents. This sensitivity is known as malignant hyperthermia and as the name implies it
causes anincrease in body temperature. As well as the rise in body temperature
symptoms include muscle rigidity, tachycardia, hypoxia, hypercarbia, acidosis. Without
treatment there is a 70% mortality rate; with treatment it is 2-3%. The treatment is
dantrolene and supportive measures.
Recovery commences once surgery has finished and involves stopping the nitrous
oxide and volatile agents and increasing the oxygen to 100%. The agents will diffuse
out of the body down a concentration gradient. With the decrease in concentration the
patient begins to waken. If the patient has been paralysed for surgery then this will need
to be reversed before waking the patient.
This is done using an acetylcholinesterase inhibitor such as neostigmine and
edrophonium wich increase the concentration of acetylcholine at the receptor. This
reverses the competitive inhibition of the muscle relaxant at the receptor and so
reverses the paralysis. These drugs can cause a bradycardia and so are usually given
with either atropine or glycopyrrollate. If succinylcholine is the only muscle relaxant used
then there is no need for using a reversal agent. This drug loses its effect through
metabolism by cholinesterase. Normally this is not a problem but occasionally a patient
will have abnormal cholinesterase and the effect of succinylcholine will be prolonged.
This condition is known as “sux apnoea”. When the patient is breathing spontaneously,
maintaining their airway, and cardiovascularly
stable the patient is moved to the recovery room. In the recovery room the patients vital
signs are monitored. When the patient is awake, protecting their airway adequately,
cardiovascularly stable, and comfortable they are transferred to the floor.
Perioperative Fluid Management:
A knowledge of fluid and electrolyte physiology is required before fluid management can
be approached.
the average adult is composed of:
~60% water –of this 2/3 is intracellular and 1/3 is extracellular
-extracellular fluid consists of intravascular and interstitial fluid
-the blood volume (intravascular volume) is ~ 70ml/kg
This can be shown as:
Total body water 42 litres
Intracellular fluid 8 litres
Extracellular fluid 14 litres
Plasma Volume 3 litres
Interstitial fluid 11 litres
Sodium is the major extracellular cation and potassium the major intracellular cation
-cells are impermeable to sodium but there is free movement of water and sodium
between the interstitial space and plasma
-water moves freely across cell membranes to maintain osmotic equilibrium between
the intracellular and extracellular compartments
Types of fluid:
The following is a guide to the commonly available fluids for intravenous administration:
Isotonic crystalloids
-normal saline-154 mol Na,154 mmol Cl osmolality 308 mosm/l
-Ringers lactate-130 mmol Na 109 mmol Cl 28 mmol lactate 4 mmol K
1.5 mmol Ca osmolality 272 mosm/l
These solutions have approximately the same osmolality as plasma and contain sodium
as the major cation. When given intravenously they distribute throughout the
extracellular space (75% interstitial, 25% intravascular. They do not move intracellularly.
Hypotonic crystalloids
- 5% dextrose-no electrolytes –essentially water so distributes throughout all
compartments –osmolality 252 mosm/l
- 5% dextrose/ 0.45% saline-77 mmol Na –77 mmol Cl –osmolality *** mosm/l
- 2/3 and 1/3-3.3% dextrose and 0.3 saline –51 mmol Na –51 mmol Cl osmolality - 269
mosm/l
The electrolyte concentration in these solutions is less than plasma. These solutions
contain dextrose to maintain the overall osmolality near to that of plasma. This is
because hypotonic solutions alone will cause the red blood cells at the site of injection
to swell and burst. However once in the body the dextrose is metabolised and only the
electrolytes and water remain for distribution. Since there is more free water then more
of the solution goes intracellularly. The electrolytes again remain extracellularly.
Colloids
- pentaspan, hetastarch, 5% albumin, fresh frozen plasma
These solutions contain high molecular weight substances which cannot diffuse out of
the intravascular space. They also contain electrolytes similar to plasma. The overall
oncotic pressure they exert in the plasma maintains the fluid in the intravascular space
and prevents the fluid leaking into the interstitial space. The solutions contain either
synthetic compounds in the form of large molecular weight carbohydrates or biological
protein.
The main objective during anesthesia and surgery is to maintain intravascular volume.
During surgery there can be large shifts in fluid out of the intravascular space. This can
be due to blood loss but also due to increase in fluid shifts into the interstitial space as a
result of trauma to tissue. This is sometimes referred to as third space fluid.
There are 4 components to fluid requirements during surgery;
1) maintenance fluids
2) replacing existing fluid losses from preop. fasting etc
3) replacing third space fluid loss
4) replacing blood lost
Maintenance fluids:
4:2:1 rule
4ml/kg for first 10 kg,
2ml/kg for next 10 kg,
1ml/kg for each additional 10 kg
thus a 4 kg baby needs 16ml/hr and a 70 kg man needs 110ml/hr
Fluid deficits:
Patients fasted for surgery need compensating for fluid not taken. Hence if they have
been starved for 10 hours then they will need 10x their hourly maintenance fluid during
the surgical procedure. Other deficits must also be replaced e.g. those patients who
have had bowel preps or have bowel obstruction.
Third space losses:
This is proportional to the extent of surgery i.e.
Minor (appendectomy)~2ml/kg/hr
Intermediate (cholecystectomy)~ 4ml/kg/hr
Extensive (AP resection)~6ml/kg/hr
Very extensive(aortic aneurysm)~ 10-12ml/kg/hr
This type of loss contains electrolytes so it is important to replace them accordingly
using isotonic crystalloids.
Blood losses:
Patients do not require small amounts of blood loss to be replaced with blood. Initially
it is the volume itself and not the hemoglobin that must be replaced. Isotonic crystalloids
up to 4 times the blood loss will maintain intravascular volume ( this is because only
25% of the solution will remain intravascularly). Replacing the hemoglobin itself will
depend on the individual patient and weighing up the risk:benefit of giving blood
products. Hence the hemoglobin level at which you would transfuse an elderly patient
with ischemic heart disease will be much higher than a fit, healthy young adult. If there
is any possibility of the patient needing a transfusion this must be discussed beforehand
and the patients consent obtained. If the patient makes an informed choice not to be
given blood under any circumstances then this must be respected whatever the
outcome. Anything else would be assault.
Whenever fluids are given do not rely solely on formulae; look at the patient and assess
their vital signs. These signs include heart rate, blood pressure, peripheral perfusion,
urine output. Once fluid has been given these parameters need to be reassessed and
management altered accordingly.