A Chat with An Anaesthetist About What Happens when you’re ‘under’


I was lucky enough to chat to an anaesthetist recently and ask him all the questions I’ve always wanted to know, like how cold is a patient when they’re under anaesthetic? What drugs are being given? The risks of DVT? Plus a whole lot more …. This has been one of my favourite interviews, so many questions I wanted to know.

Trish: When people are under anaesthetic, can they feel the cold? And can you explain to us a little bit about what happens to the body when you’re under anaesthetic and why if someone’s having a breast lift, the nipples don’t get sensitised or anything like that?

Anesthetist: Yeah, sure. The drugs that we use to induce or maintain anaesthesia impair the body’s ability to regulate temperature. It’s all the normal mechanisms that the body uses to maintain the body warmth, like peripheral vasodilation, directing all blood flow away from the skin so that in cold temperature you don’t lose a lot of heat radiating from the skin. It doesn’t work properly. So the anaesthetic drugs that we use for maintenance inhibit all of the bodies ways that it uses to maintain temperature. So a person won’t have any active methods of heat generation – like shivering, people don’t shiver when they’re asleep. And operating theatres are cold and patients are normally in the middle of the procedure room under the air conditioning, which is high flow and there’s a specific way that the air flows around the operating theatres and that’s to minimise the chance of airborne pathogens landing in the surgical field and causing infection.


But it means that fresh cold air is blowing directly from the ceiling above the patient and onto the patient and then circulates outwards from the patient. And the amount of air in the operating theatres changed over a number of times. At least 20 times an hour, is what it’s supposed to be. And so patients have got a constant flow of really cold air to help maintain or try to minimise the risk of infection. So they lose their ability to thermo-regulate. We’re essentially putting them under like high flow cold air conditioned air. People get really cold, and if patients are hypothermic intraoperatively and postoperatively, then it increases their risk of postoperative wound infection. It can delay healing. This obviously slowed cognitive responses in severe hypothermia, drug metabolism is affected, patient’s coagulation is dramatically impaired when they’re hypothermic. So patients don’t clot properly, which means they probably more at risk of hematoma development and things like that. There are a whole bunch of things that we do to try and keep patients warm, in terms of active warming.

What you’re saying about other things like nipple changes and things like that. That’s all, again, just the muscles that ’cause pilli erection, it makes your little hairs on your arms and legs stand up when you’re cold. And the body’s way of forming goosebumps, which is associated with that. It lifts up all the hairs and that’s supposed to decrease air flow right across the skin. All of that’s impaired under anaesthetic. And so it doesn’t occur. Patients don’t shiver, they don’t get goosebumps. They don’t get shrunken nipples like you would if you dived into a cold pool. And you don’t get any of the vaso-constriction, which means instead of the body conserving its warmth – Just like the body thinking that it’s in a nice warm environment – You’ve got a lot of blood flow right to the skin, which means that patients radiate a lot of heat.

It just means that they’re at risk of developing hypothermia, which is why we need to use forced air warmers and under patient heating blankets.

Trish: What’s that plate that the patients on that keeps them warm?

Anaesthetist: Different hospitals have got different devices used to what we call “active warming”. At one facility there’s a device that the patients lay on which is like an electric warming blanket. That direct contact with that helps them stay warm. We use forced air warmers, which is like a perforated double layered blanket that blows hot air through the blanket, and again we position them and stick them across areas of the body that we have access to. Obviously it depends on the type of surgery that a patient’s having. If we’re doing something on the upper body, then we’re able to use a forced air warmer on the lower body, and we can use warm fluids and a warming coil on the fluids so that instead of giving cold, intravenous fluids, we give warm intravenous fluids. Some of these devices and techniques are used preoperatively so that patients don’t come in already a little bit hypothermic and then we can use more of them in recovery.

Trish: We were talking before about a particular patient and she has had a DVT before or something like that. Can you tell us a little bit about like what the anaesthetist does in the case of that sort of situation?

Anesthetist: Patients are inherently at a higher risk of developing DVT peri-operatively and postoperatively, that’s one of the risk factors. The effect of surgery and the way it changes, I guess the way our blood clots along with other risk factors like being female and being on hormone replacement therapy or being on the oral contraceptive pill or being a cigarette smoker or going on long flights or being a cancer patient. Those are all risk factors to develop deep venous thrombosis. For some of the procedures that we do, some of them, they’re pretty prolonged, and so we’ve got mechanical methods of DVT Prophylaxis and then we can give chemical DVT prophylaxis so that we give drugs that decrease the risk or decrease the body’s propensity to form DVT’s. So for that particular patient, she has got a venous “Thrombo Embolism Deterrent” – TED stockings and we’re using sequential compression devices, which is a machine that inflates a sock – or stocking I guess, over patients either calves or over their calves and thighs and it inflates and deflates intermittently every minute or so. It acts as like a pressure pump to keep blood flowing through the veins in their legs.

Trish: You don’t do this with everyone do you? It’s just ’cause she’s had a pre existing DVT is that right, or do you do it with everyone?

Anesthetist: We’d use it, unless we were doing a very short surgery or ambulatory surgery where the risk of DVT is much less. We certainly use mechanical methods like that for all prolonged surgery. It’s just even more important in her to make sure that it’s on and that it’s working correctly. She’s also had some chemical VTE prophylaxis, so she’s had some subcutaneous Heparin during the case and that decreases the chance of her developing DVT and she’ll have postoperative chemical VTE prophylaxis.

Trish: I know that this was a very long surgery, so when she comes out – sometimes when you come of anaesthetic that you can feel nauseous and in a lot of pain or whatever. What’s the stuff that you gave to kind of stop that – to make us feel good when we come out of surgery so we don’t want to just – you know – kill ourselves (jokes)?

Anesthetist: I’m sure if you surveyed a hundred patients – And I’m sure it’s been done, I couldn’t tell you – And you asked people about things that negatively impacted their day surgery or their elective procedure, pain would definitely be an issue. Pain and discomfort, obviously, because it’s surgery and pain is inherent, but one of the other big things is patients having postoperative nausea or vomiting. That can make people feel miserable, and the incidence of postoperative nausea and vomiting is pretty high in terms of you know – compared to other complications of anaesthesia and surgery. And the incidence, depending on your risk factors of postoperative nausea or vomiting might be anywhere from a few percent to 20%, which is high – if 1 in 5, or 1 in 10 patients suffer nausea or vomiting postoperatively, then there are a whole bunch of things that we can do to try and minimise the chance of it occurring. And it just so happens that in plastic surgery a lot of our patients are inherently at high risk of suffering postoperative nausea and vomiting. There are risk factors like being female, being a nonsmoker.

Trish: Does that mean if you smoke you’d be alright?

Anaesthetist: Oddly enough, yes. Smokers have got a decreased chance of suffering nausea and vomiting postoperatively. It’s definitely not a reason to take up cigarette smoking, because that’s another big conversation, and there are some terrible complications associated with perioperative smoking. But so I mean, being female, being a nonsmoker, being young, having particular types of surgery like laparoscopic surgery or gynaecological surgery or breast surgery or ear, nose, and throat maxillofacial surgery; all of those types of surgeries we know have got a high baseline incidence of post operative nausea and vomiting compared to an orthopaedic procedure on an ankle, for example.

Previously having postoperative nausea and vomiting is a huge risk factor. So if you’ve been sick with previous surgeries – Again, the chance of that happening is very high.

Trish: I’ve had surgery sometimes where I haven’t had any nausea where I’ve felt fine afterwards, and other times where I’ve just been violently ill. Is there different types of anaesthetic?

Anaesthetist: There is. There are different drugs that we use for induction and for maintenance of anaesthesia, and there are different drugs that we can give as prophylaxis to try and minimise the chance of someone waking up and having nausea or vomiting in the recovery room. Like with anything in anaesthesia, all of the drugs that we have, have got benefits. They also have disadvantages or side effects, and it really comes down to, I guess, a tailored approach for antiemetic prophylaxis in patients; talking to them and discovering what potential risk factors they have, and then deciding on a regime of drugs that we can give as prophylaxis intra-operatively to try and minimise the chance of PONV, which is postoperative nausea and vomiting, even occurring. And so we could give a single drug as PONV prophylaxis, or if someone was at very high risk, we could give multiple drugs as PONV prophylaxis. And then there are different drugs we can give in recovery as rescue therapy, or we can give someone to take home.

I mean, it’s unfortunate that some of the stronger pain relief medication that we have – of the opioid analgesic drugs, all have nausea and vomiting as a side effect. It’s very common for people to feel sick if they need to have opioids to treat strong pain. But at the same time, if we ignore PONV prophylaxis, most people would say it’s pretty miserable having nausea or vomiting in the recovery area. Certainly if we’re doing a body lift or abdominoplasty, the last thing you want is to be actively heaving or dry retching in recovery.

This interview was cut short, BUT there were many more questions to ask, but we will continue with this Series on Anaesthesia in the future ….

Further Reading Related to Preparation for Surgery