Preoperative Patient Assessment and Care

The objectives of the preoperative visit are:

  1. Meet the patient
  1. Identify the present problem requiring surgery
  1. 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
  1. Elicit any possible concerns about previous anesthetics or any family history of problems with anesthetics.
  1. Any adverse drug reaction and current medications.
  1. Examine the patient and in particular assess the airway
  1. Review any investigations and order others needed.
  1. Plan the anesthetic technique.
  1. Provide information for the patient and relatives about the anesthetic and postoperative care including pain management.
  1. Ask the patient to stop smoking.
  1. Ensure the patient is NPO for 6 hours for solids and 4 hours for clear fluids.
  1. 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 non-depolarizing 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.