2018.1 SAQ 13 Lung Compliance

Define and describe LUNG compliance. Discuss the difference between static and dynamic compliance.

BT_PO 1.11  Define compliance (static, dynamic, specific) and relate this to the elastic properties of the lung
BT_PO 1.12  Discuss ‘fast’ and ‘slow’ alveoli, including the concept of time constants
there are other related LO’s as well

I often observe that clinicians tend not to think much about physiology, until they have a really sick patient, or things aren’t going well. In order to be capable of intelligently managing a patient with very low respiratory compliance (an obese patient having laparoscopic surgery in the head-down position, for example), it is necessary to have a really solid grasp of this area of respiratory physiology.

* although some of the statements below overlap with total respiratory compliance, the SAQ was specifically asking about LUNG compliance only.

T / F  Lung compliance is the change in alveolar pressure for a given change in lung volume.

T / F  Your ventilator screen displays a pressure-volume loop. It tells you the compliance is 50 mL/cmH20. This is LUNG compliance, and is normal for a healthy intubated patient.

T / F  Deriving the compliance from a P-V loop during IPPV is an example of dynamic compliance.

T / F  Static compliance is always higher (better) than dynamic compliance due to the variations in alveolar time constants.

T / F  Increasing PEEP will always improve lung compliance.

T / F  Increasing inspiratory time on the ventilator can improve ventilation of areas of lung with poor compliance, because their time constant will be slower

“Pressure Control-Volume Guarantee” (PC-VG) might be helpful in patients with poor respiratory compliance. Can you explain why? If you need a hint, look at the pressure and flow graphics for this ventilation mode, and try to link this to the concept of time constants.

Apothecaries’ System of Measurement

Australia formally adopted the metric system of measurement in 1971. Before that, the British Imperial system of measurement was in common use, with such units as ounces and pounds for mass; and yards and miles for length. Yet, even prior to 1971, some areas of medicine and science were beginning to adopt metric units, due to the obvious advantage of operating in base 10.

The imperial measurement system falls under a broader system called avoirdupois. Avoirdupois is derived from Old French, meaning “goods of weight”. The first trace of such a system seems to have originated in England circa 1300, and was used for weighing wool. Over the centuries, many variations in measurement systems evolved. These differed between countries (even regions), and industries.

One sub-set of the avoirdupois system, was the Apothecaries’ system of measurement, used in drug dispensing. (Apothecary is an historical term for a person we would now call a pharmacist.)

The Apothecaries’ units of measurement for weight included the – grain, scruple, drachm, ounce, and pound.

The smallest unit – the grain – was based on the mass of an ideal single grain of barley. It was equivalent to 64.79891 mg in the current metric system. Most drug prescriptions were written with grains as the dose unit to be given.

Consider the following pre-medication order, written on an anaesthetic record in 1944. The prescription is morphine 1/6 grain, and atropine 1/100 grain, both to be given IM three quarters of an hour preoperatively. Can you work out the milligram equivalents for the morphine and atropine, based on the conversion factor above?

apothecary

The anaesthetic would have been induced and maintained with ether. Can you think of any advantages and disadvantages of the morphine pre-med? Why do you think the atropine was necessary?

2018.1 SAQ 1

Anatomy of the nose, mouth and larynx

IT_AM 1.1 Describe the basic structural anatomy of the upper airway including the larynx
BT_AM 1.1 Describe the anatomy of the upper airway, larynx and trachea, including its innervation and endoscopic appearance
BT_AM 1.2 Describe the physiology of the airway including airway reflexes

For specialist anaesthetists, the importance of an advanced level of knowledge of airway anatomy hardly needs stating! Your understanding of airway anatomy becomes incredibly important with a difficult intubation, especially when the anatomy is distorted. 

 

T / F  the nasal cavity needs to be cooler than core temperature, in order to function as a heat and moisture exchanger

T / F  Figure 1 shows the nasal turbinates in coronal section on a CT scan. They are abnormally large in size.

T / F  Figure 2 is the view with a fibreoptic scope just inside the LEFT nostril. A = nasal septum, and B = inferior turbinate. The scope should be advanced via X rather than Y.

The following questions all relate to Figure 3.

T / F  A = arytenoid cartilage. Although there is a corniculate cartilage at the apex of the arytenoid, the corniculate is very small, and doesn’t contribute much to the size of the visible “bump”.

T / F  B = posterior commissure. This is the groove formed where the left and right aryepiglottic folds meet posteriorly. With a difficult laryngoscopy, it may be the only visible laryngeal structure.

T / F  C = pyriform fossa. This is commonly the location of foreign bodies (e.g. fish bones), or the place where nasogastric tubes get caught. The pyriform fossae are continuous with the upper oesophagus.

T / F  the sensory innervation of X is the same as for the vocal cords

airway SAQ pics

Anticonvulsants

BT_PO 1.99  Outline the pharmacology of anti-depressant, anti-psychotic, anti-convulsant, anti-parkinsonian, and anti-migraine medication

 

T / F   in the ampoule, phenytoin is formulated in alcohol and ethylene glycol, making it prone to cause thrombophlebitis

T / F   phenytoin has very high oral bioavailability, so the IV and oral doses are similar

T / F   both phenytoin and levetiracetam require blood level monitoring

T / F   levetiracetam causes a “voltage dependent” block of voltage gated sodium channels

T / F   levetiracetam is only available as an oral medication

Ventilation / Perfusion (V/Q) Relationships

BT_PO 1.26 Discuss normal ventilation-perfusion matching

BT_PO 1.29 Discuss ventilation-perfusion inequalities, venous admixture and the effect on oxygenation and carbon dioxide elimination

 

T / F   the V/Q ratio at the base of the upright lung is about 0.6, because there is more perfusion than ventilation

T / F   a V/Q ratio of infinity is alveolar shunt

T / F   in a conscious patient with left lower lobe collapse, hypoxaemia would be WORSE when lying on their left side

T / F   in an intubated ventilated patient with left lower lobe collapse, hypoxaemia would be WORSE when lying on their left side

T / F   hypoxic pulmonary vasoconstriction can reduce the degree of hypoxaemia caused by V/Q mismatch – HPV is mediated by BOTH alveolar and mixed venous PO2

LLL

Some patients have very little room to move with gas exchange! Here is the CXR of a very sick patient with LLL collapse and L pleural effusion. If lateral positioning was required, you should be able to anticipate the effect that this would have on V/Q mismatch.

Medical Gas Cylinders

BT_SQ 1.10 Describe the supply of medical gases (bulk supply and cylinder) and features to ensure supply safety including pressure valves, regulators and connection systems

 

T / F   nitrous oxide cylinders have a blue body, and blue shoulders

T / F   a medical gas cylinder with a single pin index hole would contain carbon dioxide

T / F   a full C-size oxygen cylinder at 20 degrees C would contain 490 L of oxygen, at 400 kPa

T / F   an Entonox cylinder contains 50% liquid nitrous oxide and 50% gaseous oxygen

T / F   the fitting which couples to the cylinder neck is known as a Schrader valve

 

Drug Metabolism

BT_GS 1.11  Describe the mechanisms of hepatic and non-hepatic metabolism of drugs….

 

T / F   a phase 1 reaction exposes a polar group on the parent molecule, rendering it more water soluble

T / F  all phase 1 reactions are catalysed by the CYP450 enzymes

T / F  adding (conjugating) glucuronide to the parent molecule is an example of a phase 2 reaction

T / F  phase 2 reactions decrease the activity of the parent compound

T / F  CYP2D6 metabolises codeine to morphine – this enzyme is absent in 1% of caucasians

 

Is pharmacogenetic testing the “new frontier” of pharmacology? Your patients might have seen websites like this one from the Mayo clinic. Some patients are already coming to hospital with their “genetic printout” stating which drugs they should have!

Ketones

BT_PO 1.82a  Outline basic cellular physiology, in particular …. energy production by metabolic processes in cells

BT_PO 1.83  Describe the physiological consequences of starvation

 

T / F  ketones are produced from the oxidation of free fatty acids

T / F  the important role of ketones is as an alternative fuel source to glucose for the brain – this decreases the protein catabolism which occurs via gluconeogenesis

T / F  lipolysis is stimulated by insulin, adrenaline, and cortisol

T / F  ketones provide a source of acetyl-CoA for use directly in the TCA cycle (structurally, ketones consist of actetyl groups)

T / F  in poorly nourished patients (frail elderly, alcoholics etc), a short period of fasting can induce starvation ketoacidosis

ketones.jpg

I’m not sure that taking ketone pills is a good idea!!

Now that you have thought about ketones….
i) find out if any of the glucometers in your hospital can also measure ketones (if not, how else could you diagnose ketosis?) 
ii) how would you treat starvation ketoacidosis in a non-diabetic?

 

IV Fluids – Crystalloids

IT_GS 1.5   Describe the chemical composition of crystalloids and colloids used in clinical practice and their effects when used in volume replacement

salt

salt being produced at Shark Bay, Western Australia

 

T / F   the osmolarity of Hartmann’s solution is 255 mOsm/L, which is slightly lower than plasma

T / F   lactate is included in Hartmann’s because it gets metabolised to bicarbonate in the liver

T / F   5% glucose is a way of giving free water without causing haemolysis

T / F   5% glucose and “4% and a fifth” are iso-osmolar but hypo-tonic

T / F   if one litre of 0.9% saline is given rapidly IV, half of it will remain in the intravascular space after 4 hours

IV Fluids – Albumex

IT_GS 1.5   Describe the chemical composition of crystalloids and colloids used in clinical practice and their effects when used in volume replacement

stiff peaks2

The word albumin is derived from the Latin albus, meaning “white” (in reference to the white of an egg). Albumin is the most abundant egg white protein (although it’s ovalbumin – not quite the same as human serum albumin). Ever wondered why you can get “stiff peaks” to form when you beat egg whites? Click here to find out.

T / F   “Albumex 4” contains 4 g/L of albumin

T / F   Albumex is not a human blood product, because it is manufactured by recombinant DNA techniques

T / F   Albumex contains 150 mmol/L Na+ and 150 mmol/L Cl-

T / F   Albumex is rendered free of possible virus transmission by pasteurisation (heating to 60 degrees C for 10 hours)

T / F   the half life of albumin in the circulation is 48 hours