Injury, Poisoning, and the Environment

TL;DR. Roughly 4.4 million people a year die from injury, about 8 percent of all deaths, and injury is the leading cause of death for people between roughly 5 and 45. Unlike almost everything else in this book, these deaths are concentrated in the young, they are sudden, and the interventions that prevent them are engineering and law rather than medicine: seatbelts, speed limits, helmets, pool fencing, smoke alarms, and drink-driving enforcement. The second theme of this chapter is that the first few minutes matter more here than anywhere else in medicine, and the actions that decide the outcome are usually taken by a bystander with no training. Learning four of them takes an afternoon.

Key takeaways

• Injury kills about 4.4 million people a year, and road traffic crashes alone kill roughly 1.2 million, with over 90 percent of deaths in low- and middle-income countries.
• Bystander CPR roughly doubles to triples survival from out-of-hospital cardiac arrest, and compression-only CPR is effective and takes minutes to learn.
• Cool a burn under running water for 20 minutes, and it works up to three hours after the injury. This single action reduces depth, need for grafting, and scarring.
• Paracetamol overdose is a leading cause of acute liver failure, and the antidote works extremely well when given early and poorly when given late.
• Heat stroke is defined by brain dysfunction, not by a thermometer reading alone, and it is a medical emergency where cooling comes before transport.
• Most drownings are silent. The thrashing and shouting of film is not what drowning looks like.

The shape of the problem

In short: Injury is the leading killer of the young, it is concentrated in poorer countries, and the effective interventions are structural.

Two patterns run through all of it. Deaths are heavily concentrated in low- and middle-income countries: over 90 percent of road deaths occur in countries owning a minority of the world's vehicles. And the effective interventions are environmental and legal rather than clinical, which is the injury-prevention field's central finding and the reason it is discussed alongside prevention rather than treatment.

What has actually worked, measurably: seatbelt and child restraint laws, motorcycle helmet laws, drink-driving limits with enforcement, speed limits and traffic calming, separated cycle infrastructure, vehicle crash standards, graduated licensing for young drivers, smoke alarms, lowered water heater temperatures, four-sided pool fencing, child-resistant packaging, blister packs for paracetamol, and bridge barriers. Every one of these produced measurable falls in deaths, and none required anyone to change their beliefs.

Head injury and concussion

In short: Most recover fully; a small proportion have a bleed that is time-critical; and the second injury before recovery is the dangerous one.

Concussion is a functional brain disturbance from a blow to the head or body, with no visible structural damage on ordinary scanning. Symptoms: headache, confusion, feeling dazed, dizziness, nausea, sensitivity to light and noise, and slowed thinking. Loss of consciousness occurs in a minority, so its absence does not exclude concussion.

The red flags that mean an emergency scan, because they suggest bleeding inside the skull:

• Deteriorating consciousness or increasing drowsiness
• Repeated vomiting
• Seizure
• Worsening or severe headache
• Unequal pupils, weakness, numbness, or difficulty speaking
• Clear fluid from nose or ear, or bruising behind the ears or around both eyes
• Any head injury on an anticoagulant, which raises the threshold for scanning substantially
• Age over 65, or a dangerous mechanism such as a fall from height or ejection from a vehicle

A "lucid interval" is the classic trap: with an extradural haematoma, a person can be knocked out, wake up and seem fine for an hour or more, then deteriorate rapidly as the bleed expands. Feeling fine shortly afterwards is not reassurance.

Recovery and return to activity. Most concussions resolve within two weeks in adults and somewhat longer in children. Current guidance is a brief (24 to 48 hour) period of relative rest followed by gradual return to activity as symptoms allow, which is a reversal of older advice to rest in a dark room until completely symptom-free, since prolonged inactivity delays recovery.

Return to sport follows a graded protocol, and the crucial rule is not returning to contact while symptomatic. A second impact before recovery is disproportionately dangerous, and repeated head impacts over years are associated with chronic traumatic encephalopathy, a neurodegenerative condition found in athletes in contact sports and in military personnel exposed to blast. The relationship between exposure and risk is not yet quantified well enough to give individuals precise numbers, and the direction is clear enough that most sports have changed their rules.

Burns

In short: Twenty minutes of cool running water is the single most effective thing anyone can do, and it works hours after the burn.

Depth determines the outcome:

Painlessness is a sign of severity, not of a minor burn. This is counterintuitive and important.

Extent is estimated by the rule of nines in adults (each arm 9 percent, each leg 18, front of torso 18, back 18, head 9), or by using the patient's own palm including fingers as roughly 1 percent.

First aid, which genuinely changes the outcome

1. Stop the burning. Remove from the source; remove clothing and jewellery unless stuck.
2. Cool with running water at about 15 degrees for 20 minutes. Not ice, which causes further injury by constricting blood supply. This works up to three hours after the burn, so it is still worth doing on the way to help, and studies show it reduces depth, need for grafting, and scarring.
3. Keep the rest of the person warm, particularly children, because cooling a large area causes hypothermia.
4. Cover loosely with cling film (lengthwise, not wrapped circumferentially) or a clean non-fluffy cloth.
5. Do not apply butter, toothpaste, oils, or ice. All are common and all cause harm.

Seek emergency care for: any burn larger than the person's palm, any full-thickness burn, burns to face, hands, feet, genitals, or across a joint, circumferential burns, electrical and chemical burns, and any burn with suspected smoke inhalation.

Smoke inhalation is what usually kills in fires, not the flames: carbon monoxide, cyanide from burning synthetics, and airway swelling. Hoarseness, soot around the mouth or nose, and singed nasal hairs after a fire in an enclosed space mean the airway may swell shut, and it is treated before it does.

Chemical burns need copious prolonged irrigation with water, for far longer than seems necessary. Electrical injury causes damage along the current path that is invisible from outside, and any significant electrical injury needs cardiac monitoring.

Poisoning and overdose

In short: Four exposures account for most of the preventable deaths, and for two of them the antidote is time-critical.

Paracetamol (acetaminophen) is the leading cause of acute liver failure in several countries. The problem is a narrow margin: the maximum daily dose is 4 g in adults, and hepatotoxicity can occur not far above that, particularly with alcohol, malnutrition, or in small adults. Many combination cold and flu remedies contain it without making that prominent, which is a common route to accidental overdose.

The mechanism: paracetamol is mostly metabolised safely, and a small fraction becomes a toxic metabolite that is neutralised by glutathione. In overdose, glutathione is exhausted and the metabolite destroys liver cells. The antidote, acetylcysteine, replenishes glutathione, and it is highly effective within 8 to 10 hours and progressively less effective afterwards.

The critical clinical point: paracetamol overdose causes no symptoms for the first day. People feel fine, do not seek help, and present on day three with liver failure. Any suspected overdose needs assessment immediately, not when symptoms appear. Restricting pack sizes in the UK was followed by measurable reductions in deaths and transplants, which is a clean demonstration of means restriction (Chapter 41).

Carbon monoxide binds haemoglobin roughly 200 to 250 times more tightly than oxygen, so blood carries oxygen poorly while the person appears pink rather than blue and a standard pulse oximeter reads falsely normal. Symptoms are headache, nausea, confusion, and drowsiness, easily mistaken for flu, and the giveaway is that several people or pets in the same building are affected, and symptoms improve away from home. Treatment is high-flow oxygen. Prevention is a CO alarm, which costs very little and is not fitted in most homes.

Opioid overdose causes respiratory depression, pinpoint pupils, and reduced consciousness. Naloxone reverses it within minutes, is available as a nasal spray, works in untrained hands, and has no effect on someone who has not taken opioids (Chapter 43).

Alcohol poisoning causes vomiting with an impaired gag reflex, hypothermia, hypoglycaemia, and respiratory depression. The single most useful bystander action is putting an unconscious intoxicated person in the recovery position and staying with them, because aspiration of vomit is what kills.

Heat

In short: Two conditions on a spectrum, distinguished by whether the brain is affected, and the second requires cooling before transport.

The distinguishing feature is the brain, not the thermometer. Confusion in a hot person is heat stroke until proven otherwise.

Cooling first is the key principle, and it is the opposite of the usual instinct to transport immediately. Mortality tracks how long the body stays above the critical temperature. Cold water immersion is the most effective method and is standard at endurance events. Otherwise: remove clothing, spray with water and fan continuously, apply ice packs to neck, armpits, and groin.

Who is at risk: older adults (blunted thirst and sweating, and often on diuretics or anticholinergics), infants, outdoor workers, athletes, people with chronic disease, and people on drugs that impair sweating or thermoregulation, including many psychiatric medications.

Humidity is what makes heat lethal. Evaporation of sweat is the only cooling mechanism that works when air temperature exceeds body temperature, and high humidity prevents evaporation. This is why "wet bulb" temperature, which accounts for humidity, matters more than the number on a thermometer, and why heat waves in humid regions are more dangerous at lower temperatures.

This is a growing problem. Heat-related mortality is rising measurably with climate change, and the chronic kidney disease epidemic among agricultural workers in Central America and South Asia is among the first clearly documented occupational disease epidemics attributable in part to heat (Chapter 23).

Cold

In short: Hypothermia kills by stopping the heart, and rewarming has its own dangers.

Hypothermia is a core temperature below 35 degrees Celsius:

Two counterintuitive rules:

• Handle severely hypothermic people gently. A cold heart is electrically irritable and rough movement can trigger a fatal arrhythmia.
• "Not dead until warm and dead." Hypothermia protects the brain, and full neurological recovery has occurred after prolonged cardiac arrest in cold water. Resuscitation is continued during rewarming.

Frostbite is tissue freezing, most often fingers, toes, ears, and nose. Rewarm in water at around 37 to 39 degrees, do not rub, and do not rewarm if there is any chance of refreezing, which causes far worse damage than remaining frozen. Assessment of depth takes days to weeks, so early appearance is a poor guide to eventual loss.

Drowning

In short: Usually silent, fast, and preventable by barriers rather than by supervision alone.

Drowning does not look like it does in films. People who are drowning are usually silent, because the airway is at or below the water and breathing takes priority over calling out. They are upright, head tilted back, arms pressing down at their sides rather than waving, and it typically lasts 20 to 60 seconds before submersion. A large proportion of child drownings occur with an adult present who did not recognise it.

Prevention, in order of effectiveness:

• Four-sided isolation pool fencing reduces drowning substantially and outperforms three-sided fencing that uses the house as the fourth side.
• Swimming lessons for children, which reduce risk although they do not eliminate it.
• Life jackets in and around open water and boats, and not relying on inflatable toys.
• Never swimming alone, and never mixing alcohol with swimming or boating, which is involved in a large share of adult drownings.
• Supervision that is uninterrupted, meaning a designated adult who is not on a phone.

Rescue: the priority is not becoming a second casualty. Reach or throw before you go, and if the person is unresponsive after removal from the water, start rescue breaths and CPR, since drowning is a hypoxic arrest where breaths matter more than in cardiac arrest.

"Dry drowning" and "secondary drowning" are not recognised medical diagnoses, despite recurrent media coverage. Someone who has had a genuine submersion event with breathing difficulty needs assessment, and a child who swallowed water, coughed, and is entirely well afterwards is not going to deteriorate hours later out of nowhere.

Falls

In short: The leading cause of injury death in older adults, and the most preventable thing in geriatric medicine.

Falls cause roughly 700,000 deaths a year and vastly more disability. In older adults, a hip fracture carries a one-year mortality of roughly 20 to 30 percent (Chapter 50).

The evidence-based prevention package:

The four things worth learning

In short: Four skills, learnable in an afternoon, that decide outcomes before any professional arrives.

1. CPR and defibrillation. For an unresponsive person not breathing normally: call emergency services, push hard and fast in the centre of the chest at about 100 to 120 compressions a minute, and send someone for the nearest defibrillator. Compression-only CPR is effective for adults with a cardiac cause and is what untrained bystanders should do. Defibrillators talk you through themselves and will not shock a heart that should not be shocked. Bystander CPR roughly doubles to triples survival, and survival falls by around 10 percent for every minute without it.

2. The recovery position. For anyone unconscious but breathing normally. Rolling them onto their side keeps the airway open and lets vomit drain. This prevents a large number of avoidable deaths from intoxication, seizure, and overdose.

3. Severe bleeding control. Direct firm pressure on the wound, maintained. For catastrophic limb bleeding, a tourniquet applied high and tight above the wound, tightened until bleeding stops, with the time noted. Public bleeding control training and kits alongside defibrillators are becoming standard in several countries.

4. Choking. Encourage coughing while they can cough. If they cannot, alternate five back blows between the shoulder blades with five abdominal thrusts. For infants, back blows and chest thrusts rather than abdominal thrusts. If they become unresponsive, start CPR.

Add naloxone if you or anyone close to you uses opioids, prescribed or otherwise (Chapter 43), and an adrenaline autoinjector if anyone in the household has anaphylaxis (Chapter 46).

What the person can do

In short: Most of it is fitting things, wearing things, and learning four skills.

• Fit and test smoke alarms and a carbon monoxide alarm. Both are cheap and both prevent deaths that give little warning.
• Wear the seatbelt and the helmet, every time, including short journeys, where most crashes happen.
• Do not drive tired. Seventeen to nineteen hours awake impairs driving comparably to the legal alcohol limit in many countries (Chapter 10).
• Keep medicines and chemicals out of reach and in original containers, and know your local poisons information number.
• Check the paracetamol content of every cold remedy before combining them.
• Fence the pool on all four sides, and supervise without a phone.
• Falls-proof the home of anyone over 70, and get their medications reviewed.
• Learn CPR, the recovery position, bleeding control, and choking management. An afternoon, once, and the skills stay usable for years.

Sources and notes

Global injury mortality figures: WHO injuries and violence fact sheets and Global Burden of Disease estimates (approximately 4.4 million injury deaths annually). Road traffic deaths and their distribution: WHO Global status report on road safety. Burn first aid: 20 minutes of cool running water, effective up to three hours: Wood et al., Annals of Surgery, and Australian and New Zealand Burn Association guidance; Griffin et al., Annals of Emergency Medicine, 2020, on outcomes. Concussion management and graded return: Amsterdam consensus statement on concussion in sport, 2023. Paracetamol overdose and pack size restriction: Hawton et al., BMJ, 2013. Carbon monoxide oximetry limitation: standard toxicology. Heat stroke cooling before transport: Wilderness Medical Society and sports medicine guidance; cold water immersion as the most effective method. Hypothermia management and "not dead until warm and dead": resuscitation council guidance. Drowning presentation ("instinctive drowning response"): Pia, and lifeguard literature; pool fencing effectiveness: Cochrane review. Falls prevention: Sherrington et al., Cochrane review, 2019; high-dose intermittent vitamin D increasing falls: Bischoff-Ferrari et al., JAMA Internal Medicine, 2016. Bystander CPR and survival: multiple registry analyses. "Dry drowning" as a non-diagnosis: position statements from the American Academy of Pediatrics and international drowning research bodies.

Open questions. The dose-response relationship between repeated sub-concussive head impacts and chronic traumatic encephalopathy is not quantified well enough to advise individuals precisely. How much of the rising heat-related mortality can be offset by adaptation rather than emissions reduction is unresolved.

Next, and finally in this part, the population view of who all this happens to. 👉