Neuro Resus

Basic Science Clinic by Steve Morgan & Sophie Connolly

If you can't explain it simply, you do not understand it well enough.

Albert Einstein

Welcome to Basic Science Clinic Raw Science episode 6. The next step on the oxygen cascade relates to the composition of alveolar gas, how and why it differs from that in the upper respiratory tract and conducting airways. This composition is determined by the components of the alveolar gas equation. We will examine the AGE in more detail in the next podcast, but for now we can take it to be PAO2 = PiO2 – PaCO2/RQ. In this conceptual model the PiO2 describes the gas entering the alveolus and the second half, the minus PaCO2/RQ, is the net gas leaving the alveolus as oxygen is exchanged with CO2 across the alveolar capillary membrane. The PAO2 is therefore the net alveolar oxygen partial pressure reflecting the interaction of these two processes. The composition of PiO2 we ascertained in the last podcast where humidification and warming of inspiratory gas at 1 atm leaves us with ~150 mmHg of oxygen partial pressure at the carina. Before we analyse the gas in the alveolus we are going to examine how it gets there and the factors that affect pulmonary ventilation and respiratory gas flow.

Remember deranged physiology at each transition point on the oxygen cascade may limit the efficacy of oxygen transfer and hence reduce the amount of oxygen delivered to the mitochondria. It is important to understand the ways in which these steps can be disrupted and then systematically consider them all in your assessment of undifferentiated hypoxia. Step 1 is calculating the PiO2, which is FiO2 multiplied by Patm – PH2O. Therefore reduced FiO2, for example when oxygen is consumed in a house fire, or reduced barometric pressure, for example on the peak of mount Everest, are both potential causes in reduced oxygen partial pressure at step 1 and hence are causes of downstream tissue hypoxia.

For step 2 a comprehensive understanding of the complex of interrelated factors that affect respiratory gas flow and the provision of oxygen replete inspired gas to the alveolus is crucial core knowledge for a budding critical care physician. To bear the responsibility of mechanically ventilating a patient's potentially injured lung, it is incumbent on us to be fortified by a high fidelity conceptual model.

In this pod we will cover:

Fluids and Flow

How can you predict the type of flow in a fluid system?

How do you define viscosity?

What about the specifics of gas flow in the airways?

What is ventilation?

So how does the respiratory apparatus generate a pressure differential?

Raw Science Factoids

The total length of the airways running through the two lungs is 1,500 miles or 2,400 kilometers.

The 300-500 million alveoli produce a combined surface area of 50-100 m2, a size roughly equivalent to a tennis court.

The relatively high oxygen content of air means we would only have to breathe once per minute to meet the body's demand for oxygen at rest, the bulk of ventilatory work is for the elimination of carbon dioxide.

For feedback, corrections and suggestions find us on twitter @falconzao and @sophmcon or post on ICN.

Thanks for listening. Next up we'll examine the oppositional forces of respiratory gas flow and the work of breathing.

Effective patient management requires a combination of timely diagnosis, appropriate medical management and application of human factors. Human factors is the study and application of human interaction with the systems around them. It combines engineering and psychology, and a recognition that humans are not machines and subsequently make mistakes. In order for a system to be robust, it needs to take these factors into account.

In other industries, the role of human factors in developing a robust safety culture is well-established. Human factors and non-technical skills are increasingly recognised as a cornerstone of effective management in high stress situations where critical decisions are being made. Nowhere is this more applicable than within critical care.

Closely allied to human factors are non-technical skills. These comprise Communication, Teamwork, Leadership and Situational Awareness - of which Communication is generally regarded as the most vital. These four aspects are vital for effective patient care, particularly in a critical situation. However, for a number of reasons they can become easily compromised - at exactly the time when you need them most. If one fails, there can often be a loss of the other aspects, for example a loss of Situational Awareness in a high-stress situation can result in a failure of Communication, and thus Teamwork. All this can result in poor patient care, or even patient harm.

Using a number of examples, this Podcast discusses some learning points that we can take from both other industries as well as cases of medical error. Strategies to improve the systems we work in are discussed, many of which are now common place in the workplace such as checklists, protocols, standardisation and forcing functions.

So mathematical truth prefers simple words since the language of truth is itself simple.

Tycho Brahe

Welcome to Basic Science Clinic, this is Crit think episode 5. Today our exploration of the mathematical architecture of our most inexact of sciences brings us upon the edifice of logarithms and exponentials. Daunting as it may sound, we will try to tease out their utility and relevance to critical care medicine and even attempt to penetrate the secrets of the mysterious number e.

Logarithmic transformations permeate pharmacokinetic, biological and physiological modelling. Exponentials are the inverse function of the logarithm, and the special properties of explosive exponential change in quantities has implications for ventilation, pharmacotherapy and beyond.

Euler's number, e, represents the idea that all continually growing systems are scaled versions of a common rate. Describing e as a constant approximating 2.718 is like calling pi an irrational number approximating 3.141. It's true but it totally misses the point. Pi is the ratio between the circumference and diameter of every circle. It is a fundamental ratio and therefore impacts any calculation involving circumference, area, volume and surface area for all circles, spheres and cylinders. e is not just a number it is about the fundamental relationship between all growth rates.

Thanks for listening. From The Happy Prince by Oscar Wilde: "I am so clever that sometimes I do not understand a single word of what I am saying."

Word of the day: evanescent

Literary: soon passing out of sight, memory, or existence; quickly fading or disappearing.

Physics: denoting a field or wave which extends into a region where it cannot propagate and whose amplitude therefore decreases with distance.

For feedback, corrections and suggestions you can contact us on the twitter handles @falconzao and @sophmconnolly or post on Intensive Care Network.

Next up is the last in this Crit Think: You Do the Math(s) series and we will examine the mathematics behind clinical measurement.

Dr Andrew Davies, Intensivist at Frankston Hospital in Melbourne discusses how Intensive Care Specialists can better care for themselves, including avoiding burnout, eating well, exercising, escaping work, and meditation. This talk was recorded at the ICN Victoria meeting in December 2015.

Basic Science Clinic by Steve Morgan & Sophie Connolly

"…water is the driving force of all nature….without it, nothing retains its form."

Leonardo Da Vinci

Welcome to Basic Science Clinic Raw Science episode 5. Let's get down to business and accompany oxygen on its relentless tumble from nasopharynx to mitochondria down the partial pressure staircase that explains how 160 mmHg of inspired oxygen partial pressure becomes 20 mmHg in the inner mitochondrial matrix. In this pod we will examine step one of this cascade and the science of the humidification of dry, inspired atmospheric gas, whilst paying deference to dihydrogen oxide.

Water is pretty amazing stuff. It is the solvent of life characterized by anomalous idiosyncrasies without which biology wouldn't even be a thing. It is the only substance found concurrently in 3 phases on Earth's surface and is a byproduct of the outpouring of stellar gas and dust produced when a star is born. NASA recently discovered a water vapour cloud surrounding a quasar 12 billion light years away, a celestial snapshot capturing the antiquity of water in the universe.

What to expect:

• What makes water so special?
• What is water's role in the first step of the oxygen cascade?
• What is the difference between a gas and a vapour?
• How do you define humidity?

Raw Science Factoids

The length of the side of a cube that could hold all of Earth's water is 1150 km, containing 1.5 billion km3 or 800 trillion Olympic swimming pools.

Everywhere there is liquid water on Earth there is life inspite of temperatures of 100s of degrees or searing acidity.

All of Earth's water likely arrived on carbonaceous meteorites that can be up to 20% water as ice, between 4.5-3.8 billion years ago during the late heavy bombardment.

Thanks for listening. For feedback, corrections and suggestions find us on twitter @falconzao and @sophmcon or post on ICN. Next up we'll scrutinize respiratory gas flow.

"Isaac Newton was not the first of the age of reason. He was the last of the magicians."

John Maynard Keynes

Welcome to Basic Science Clinic, Crit Think episode 4, in which we will discuss The Calculus. One of the crowning intellectual achievements of humanity, Calculus is the foundational mathematical concept of modern science. Almost usurped by a publication entitled the Complete History of Fishes released only months earlier, through his development of the fundamental theorem, Newton (or was it Leibniz?) has provided us with the tools to successfully land a rover on the surface of Mars.

Calculus delineates the dynamic system. It is the lens through which we may focus our perception of bedside numbers and observations to comprehend the beat to beat physiology of the critically unwell.

In this pod we'll cover:

- Newton and Leibniz and the development of the fundamental theorem of calculus

- Differentiation and pressure-volume relationships

- Integration and area under the curve

Word of the day:

Propinquity: the physical or psychological proximity between people.

Basic Science Clinic by Steve Morgan & Sophie Connolly

We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology.

Carl Sagan

Welcome to Basic Science Clinic Raw Science episode 4. We are close to embarking on the descent down the oxygen cascade, en route we will examine the key contributors to these stepwise decrements in oxygen partial pressure that coax the gas down to the level of the mitochondria. To grasp the concepts essential to the physiology of this pathway you need to understand the fundamentals of gas behaviour, enter the gas laws.

In this pod we will cover:

Boyle's, Charles', Guy-lussac's laws

Avogadro's number

Dalton's and Henry's laws

Saturated vapour pressure & boiling point

The concept of in vivo partial pressures

Raw Science Factoids

Increasing ambient pressure from 1 to 2 atm will decrease the volume of 1L water by

At an oceanic depth of 40m an FiO2 0.21 results in a PiO2 > 400 mmHg and FiO2 1.0 gives PiO2 > 2000 mmHg, resulting in tissue hyperoxia.

Opening a soda can drops the pressure of the CO2 gas above the liquid that has set up an equilibrium in accordance with Henry's law. This results in CO2 rushing out of solution to reach a new equilibrium with ambient, atmospheric CO2 partial pressure.

Basic Science Clinic by Steve Morgan & Sophie Connolly

If you would be a real seeker after truth, you must at least once in your life doubt, as far as possible, all things.

Rene Descartes

Welcome to Basic Science Clinic, this is the 3rd Crit Think podcast on mathematics. Having examined the origin of maths and its influence on the enlightenment explosion of rationality and empiricism, we now turn our attention to extracting the ways maths turns up in our critical care practice.

Is it essential to know the maths? Thou doth protest too much methinks. Think of these relationships as the grammatical fibre to your conceptual fabric. It's like totally, you know like, easy to make yourself understood without no grammar, do ya know wanna I mean…like? However, understanding maths as the language of science with grammatical and linguistic accuracy changes your perception of the relationships between the physiological variables that you are attempting to dial up in your practice. Go deeper, understand better, effortlessly recall.

In this pod we'll cover:

Basic mathematical relationships

Relations Vs Functions

Classification of mathematical models

Important relations in critical care

Word of the Day: Peripatetic; 1. adjective; itinerant, walking or traveling about; 2. noun; an adherent of Aristotelianism.

Equipped with his five senses, man explores the universe around him and calls the adventure Science.

– Edwin Hubble

Welcome to the third podcast in the Basic Science Clinic Raw Science series. Following our investigation of the how and why of oxygen, you may be eagerly anticipating the gas' entry into the respiratory system, prompting a discussion of gas flow, partial pressures and similarly patient-based physiology. Think again. Resisting the urge to dive down the trachea, we need to describe some foundational concepts to fine tune the resolution of your understanding. Enter atmospheric physics. Remember physiology is functional biology, biology is effectively applied chemistry, and chemistry is applied physics.

This week we discuss the physics of atmospheric gas in the biosphere. Such a topic raises discussion of fluid and gauge pressure, heat and temperature, the SI units and clearly, why the sky is blue.

Feedback, requests and corrections are always welcome.

Raw Science Factoids

• The atmosphere has a total mass of 5 x 1018kg, or 5 quintillion kg or 5 zettagrams (1021), which is 5 sextillion grams.
• Every square metre of Earth has 10 tonnes of atmosphere pressing down on it.
• The average temperature of the universe is 2.73K, which is -270.42°C.

Basic Science Clinic by Steve Morgan & Sophie Connolly

"As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain they do not refer to reality."

- Albert Einstein

Welcome to the second podcast in the Crit Think series from the Basic Science Clinic. Remember, this is about stimulating insights into the machinations of your mind to assist able deployment of the knowledge you are rapidly assembling, to be a better scientist. Having discussed the evolution of mathematics and the concept of number in our first podcast, we move now to examine the relationship of maths and science. The debatable definition of maths as a science is one thing, but its contribution to science in its performance and explication, and also in informing the development of the method itself, is unquestionable and worthy of acknowledgement.

Addressing a subject that entire degrees are dedicated to escaped the confines of our usual length, but we hope you can hang in there with us. Continuing our trend of celebrating the inner geek, we couldn't resist delving deep into the mathematical origins and historical path of the scientific method to illuminate the intellectual inventory of evidence based medicine as we use it today. Thanks for coming back for more.

In this pod we'll cover:

• What is science and does maths qualify?
• What is the scientific method?
• How did the method develop and where does maths fit in?

Pulchritudinous: Having great physical beauty.