Premixed morning insulin: Halve morning dose and omit lunchtime dose; check blood glucose on admission
* lf the patient requires a VRIII then the long-acting background insulin should be continued but at 80% of the dose the patient usually takes when he/she is well.
VRIII, variable-rate intravenous insulin infusion.
Guideline for peri-operative adjustment of oral hypoglycaemic agents (short starvation period – no more than one missed meal). Reproduced with permission from John Wiley and Sons
| Day of surgery | ||||
|---|---|---|---|---|
| Agent | Day before admission | Surgery in the morning | Surgery in the afternoon | Whilst a VRIII is being used |
| Drugs that require omission when fasting owing to risk of hypoglycaemia | ||||
| Meglitinides (e.g. repaglinide, nateglinide) | Take as normal | Omit morning dose if nil by mouth | Give morning dose if eating | Stop until eating and drinking normally |
| Sulphonylurea (e.g. glibenclamide, gliclazide, glipizide) | Take as normal | Omit morning dose (whether taking once or twice daily) | Omit (whether taking once or twice daily) | Stop until eating and drinking normally |
| Drugs that require omission when fasting owing to risk of ketoacidosis | ||||
| SGLT-2 inhibitors* (e.g. dapagliflozin, canagliflozin) | No dose change | Halve the usual morning dose; check blood glucose on admission; leave evening meal dose unchanged | Halve the usual morning dose; check blood glucose on admission; leave the evening meal dose unchanged | Stop until eating and drinking normally |
| Drugs that may be continued when fasting | ||||
| Acarbose | Take as normal | Omit morning dose if nil by mouth | Give morning dose if eating | Stop until eating and drinking normally |
| DPP-IV inhibitors (e.g. sitagliptin, vildagliptin, saxagliptin, alogliptin, linagliptin) | Take as normal | Take as normal | Take as normal | Stop until eating and drinking normally |
| GLP-1 analogues (e.g. exenatide, liraglutide, lixisenatide) | Take as normal | Take as normal | Take as normal | Take as normal |
| Metformin (procedure not requiring use of contrast media†) | Take as normal | Take as normal | Take as normal | Stop until eating and drinking normally |
| Pioglitazone | Take as normal | Take as normal | Take as normal | Stop until eating and drinking normally |
* Also omit the day after surgery.
† If contrast medium is to be used or the estimated glomerular filtration rate is under 60 ml.min−1.1.73 m−2, metformin should be omitted on the day of the procedure and for the following 48 h.
VRIII, variable-rate intravenous insulin infusion; SGLT-2, sodium-glucose co-transporter-2; DPP-IV, dipeptidyl peptidase-IV; GLP-1, glucagon-like peptide-1.
Further reading
Preoperative assessment and preparation for surgery: hypertension guidelines
A 72-year-old man presents on the morning of surgery for transurethral resection of the prostate (TURP) for suspected benign prostatic hypertrophy. He has no additional medical history and is generally fit and well. His blood pressure taken on the morning of surgery is 187/112 mmHg. He was seen in the preoperative assessment clinic where three BP readings were taken, the lowest of which was 170/100 mmHg. There is no documented recording of BP from his GP within the last year.
What is the best course of action?
a) Proceed with the surgery as planned with anaesthesia of your choice, and ensure the patient has his hypertension followed up by his GP
b) Recheck the blood pressure in 30 minutes, and proceed with the surgery only if there is a further drop in blood pressure
c) Postpone the surgery until better blood pressure control can be established
d) Give a dose of metoprolol 200mg orally, and proceed with the surgery when blood pressure has reduced
Answer: a)
This patient has stage 3 hypertension, defined as having a systolic BP 180–209 mmHg or diastolic BP 110–119 mmHg. The guidelines for management of primary hypertension before elective surgery have recently been published. This patient, according to the new guidelines, would be able to undergo elective surgery without further intervention. There is little evidence to suggest that having raised BP prior to planned surgery significantly affects postoperative outcomes, but hypertension still seems to be a common reason for cancellation. Management of hypertension is complex and must balance the risk of delaying the operation for that individual and the risks of anaesthesia without appropriate treatment. Implications for cancelling surgery extend beyond the obvious disappointment; psychological, social and financial factors all play a part.
There is currently no clear evidence that lowering BP preoperatively affects the rate of cardiac events beyond those expected in a month in primary care. Indeed, BP readings may be more accurate with the GP. There is little guidance on a ‘safe’ BP for planned anaesthesia and surgery. However, it does seem that those with stage 1 or 2 hypertension (without evidence of end organ damage) are not at an increased perioperative cardiovascular risk.
When referring a patient for elective surgery, they should ideally have documented BP readings from their GP within the past 12 months. These should be requested as soon as possible. Surgery can proceed if the BP in primary care is <160/100 mmHg. If this is not the case, BP may be measured in the preoperative assessment clinic up to three times. If the lowest reading is SBP <180 mmHg and DBP <110 mmHg, surgery may proceed. Otherwise, the patient warrants referral back to the GP for treatment. Here, the elevated reading on the morning of surgery would not be a reason for cancellation and there is no evidence that acutely lowering BP with β-blockers is in the patient’s interest.
Perioperative β-blockers were used in the POISE trial, and although this was associated with a reduction in cardiac morbidity, there was an overall increase in mortality. The study does not support the routine use of perioperative β-blockers, but they may have a role to play in patients with risk factors for ischaemic heart disease.
Further reading
Preoperative assessment and preparation for surgery: recent myocardial infarction and stents
A 65-year-old man is seen in a preoperative assessment clinic. He is listed for a craniotomy for an astrocytoma in 2 weeks. His past medical history includes an ST-elevation myocardial infarction 6 months ago which was treated with a drug-eluting stent to his left main stem coronary artery. He is currently taking aspirin 75 mg OD and clopidogrel 75 mg OD.
Regarding the management of his antiplatelet medication, which ONE option would be most suitable?
a) Continue both aspirin and clopidogrel throughout
b) Stop both aspirin and clopidogrel 10 days preoperatively
c) Stop clopidogrel 5 days preoperatively and continue the aspirin throughout
d) Stop aspirin and clopidogrel the day before surgery and start bridging therapy
e) Continue aspirin throughout, stop clopidogrel 5 days pre-op and start bridging therapy
Answer: e)
Percutaneous coronary intervention (PCI) is a common and effective method of coronary revascularization. The vast majority of PCIs involve placement of one or more stents. There are two types of coronary stents used; bare-metal stents (BMS) and drug-eluting stents (DES). DES are coated with a material which slowly releases an anti-proliferative drug; this inhibits smooth muscle proliferation, thus preventing the formation of a neo-intima which can cause stent re-stenosis. Re-endothelialization is consequently slowed down compared with BMS.
Stent thrombosis is a rare but catastrophic complication resulting in myocardial ischaemia or death. The majority occur before re-endothelialization is complete; dual antiplatelet therapy (DAPT) is therefore recommended during this time (6–12 weeks for BMS and at least 12 months for DES). DAPT commonly consists of aspirin and clopidogrel. These both irreversibly inhibit platelet function. Stopping clopidogrel during this time results in a 30-fold increased risk of stent thrombosis.
Wherever possible, elective surgery should be postponed until DAPT is no longer required. Essential surgery will require careful management and a multidisciplinary team approach. For the majority of operations, aspirin is not associated with an increased risk of surgical bleeding, unlike clopidogrel. Careful discussion of the risks of surgical bleeding versus stent thrombosis should be made in collaboration with anaesthetists, surgeons, and cardiologists. Continuing DAPT is often the safest option and is recommended in cases of low/intermediate surgical bleeding risk. This category includes visceral surgery, major orthopaedic surgery, ENT, cardiac surgery, etc. However, continuing DAPT is not appropriate where there is a high risk of surgical bleeding (or serious consequences of this bleeding, e.g. neurosurgery, spinal surgery and posterior eye surgery). In these situations, clopidogrel should be stopped 5 days preoperatively, and bridging therapy started the following day.
Various regimes for bridging therapy have been suggested, including unfractionated heparin, low molecular weight heparin (LMWH), and more commonly glycoprotein (GP)IIb/IIIa inhibitors such as tirofiban. The bridging therapy is then stopped pre-op (4 hours pre-op for tirofiban), and restarted post-op until clopidogrel is reloaded. Aspirin should be continued throughout. Thromboelastography (TEG) can be used to titrate the dosing of GPIIb/IIIa inhibitors.
Emergency surgery in the presence of DAPT can be challenging and requires expert management; major uncontrolled haemorrhage may warrant platelet transfusion to reverse the antiplatelet agents.
Further reading
Preoperative assessment and preparation for surgery: anaesthetic machine check
You are anaesthetizing for an ENT list.
Which one of the following statements regarding the anaesthetic machine check is true?
a) A full machine check should be completed before each patient
b) The anaesthetist is primarily responsible for checking the anaesthetic machine and equipment
c) The ODP is responsible for documentation of each check
d) There is no need to perform a check straight after it has been serviced
e) Training on any new equipment can take place during the first case
Answer: b)
The pre-use check of anaesthetic equipment is essential to maintain patient safety. It is the primary responsibility of the anaesthetist and forms part of the World Health Organization (WHO) Surgical Safety Checklist. The AAGBI has produced guidelines and an abbreviated checklist that are suitable for all modern anaesthetic workstations. These should be available in laminated form.
The anaesthetist has a responsibility to ensure that they are familiar with all the equipment; formal training and induction should be given for any new or unfamiliar equipment. At the start of every operating session a full check should be carried out. Further specific checks should be performed before every new patient or after a change in equipment. Checks should be documented in a record kept with the anaesthetic machine and in the patient’s notes. The first user check after servicing is particularly important and must be documented.
The pre-use check starts with ensuring the availability of a self-inflating bag – a potentially life-saving alternative means of ventilation. The manufacturer’s machine check should then be performed; this usually occurs automatically on start-up. The power supply should be checked. An adequate gas supply should be confirmed; a pipeline tug test is now recommended to avoid potential Schrader socket and probe failure. A reserve cylinder of oxygen must be present and adequately filled. The flowmeters, hypoxic guard, emergency oxygen bypass control (oxygen flush) and suction should be working.
The breathing system should then be checked. After visual inspection and checking of connections, a pressure leak test checks the adjustable-pressure limiting (APL) valve. The vaporizers must be adequately filled, siting correctly, plugged in and leak free. The contents, connections and colour of the soda lime should be checked. Any alternative breathing systems should be checked. The correct gas outlet should be selected; this is especially relevant during lists where the breathing systems are regularly changed. The ventilator, scavenging, and monitors must be checked and the settings selected, including audible alarms.
The two-bag test is performed after the breathing system, vaporizer and ventilator have been checked, checking for patency of the breathing system, the function of the unidirectional and APL valves and any leaks. Finally the airway equipment should be checked, including the availability of difficult airway equipment.
The checks to be performed prior to every new patient include those of the breathing system, ventilator, airway equipment and suction.
Despite satisfactory pre-use checks, equipment faults can develop or manifest during anaesthesia. A logical, stepwise approach to checking the equipment during anaesthesia should be adopted in the event of a critical incident.
Further reading
Advanced patient monitoring techniques: cardiac output monitoring
An 82-year-old lady is undergoing emergency laparotomy for bowel obstruction.
1. What devices are available to monitor her cardiac output perioperatively?
2. What are the advantages and disadvantages of each device?
Normal values
| Cardiac output (CO) | HR × SV/1000 | 4–8 l/min |
| Cardiac index (CI) | CO/BSA | 2.5–4 l/min/m2 |
| Stroke volume (SV) | CO/HR × 1000 | 60–100 ml/beat |
| Stroke volume index (SVI) | SV/BSA | 33–47 ml/beat/m2 |
| Systemic vascular resistance (SVR) | 80 × (MAP – CVP)/CO | 800–1200 dynes/s/cm−5 |
| Systemic vascular resistance index | SVR/BSA | 1970–2390 dynes/s/cm−5/m2 |
BSA = body surface area; CVP = central venous pressure; MAP = mean arterial pressure.
Cardiac output monitors
| Cardiac output monitor | Principle | Advantages | Disadvantages |
|---|---|---|---|
| Pulmonary artery flotation catheter | Thermodilution: a change in blood temperature is measured by a thermistor in the pulmonary artery following injection of a known volume of cold saline into the right atrium. This allows calculation of right heart CO | Gold standard Automated system now available to give continuous readings of CO | Invasive Risk of damage to cardiac valves with prolonged use, catheter knotting, pulmonary artery rupture and pulmonary infarction |
| Pulse contour analysis PiCCO [TMPulsion Medical Systems, Munich, Germany] FloTrac/Vigileo [TMEdwards Lifesciences, Irvine, CA, USA] | Pulse contour analysis of the aortic waveform: CO is proportional to arterial pulse pressure, therefore the contour of the systolic portion of the arterial pressure waveform can be related to SV and SVR | Continuous Less invasive and useful in both conscious and unconscious patients. The FloTrac/Vigileo system only requires an existing arterial line and does not require external calibration Provides SVV measurements: SVV is the change in SV over the respiratory cycle caused by alterations in preload as intrathoracic pressure changes. SVV can be used as an indicator of fluid responsiveness. Patients with an SVV > 15% are likely to benefit from fluids | PiCCO requires a specific thermistor-tipped arterial line in a proximal artery and a CVC to calibrate the system using a transpulmonary thermodilution technique which measures left heart CO Less accurate for absolute measurement if uncalibrated FloTrac/Vigileo system but useful for trends |
| Pulse power analysis LiDCO [TMLiDCO, Cambridge, UK] | Lithium dilution and pulse power analysis: uses lithium dilution for initial calibration followed by a pulse power algorithm to determine beat to beat SV from a mathematical analysis of the peripheral arterial waveform | Only requires standard arterial catheterization Continuous Useful in conscious and unconscious patients Can be calibrated using lithium dilution or used uncalibrated to monitor trends Measures SVV | Non-depolarizing muscle relaxants may interfere with the lithium ion sensing electrode Contraindicated with concurrent lithium use or in first trimester of pregnancy. If using lithium dilution |
| Oesophageal Doppler monitor | Doppler shift: the frequency of reflected ultrasound waves changes with the velocity of flow. This change in frequency is proportional to flow and when the cross-sectional area of flow is known CO can be calculated. The oesophageal Doppler measures flow in the descending aorta | Minimally invasive Continuous measurement | Probes uncomfortable in awake patients Contraindicated in patients with severe oesophageal pathology A correction factor is required to take account of the fact that it measures CO to the lower body. Alternatively CO is calculated from a nomogram using aortic blood velocity, height, weight and age |
| Supra-sternal Doppler | Doppler shift: a probe in the jugular notch is used to measure blood velocity in the ascending aorta. Measurement of the cross-sectional area of the aortic outflow tract is used to calculate SV and CO | Non-invasive alternative to oesophageal Doppler Measurements are taken from the aortic root and therefore unaffected by distribution of CO to upper and lower body | May be difficult to identity aortic root in some subjects May have greater interobserver variability than other methods |
Transoesophageal echocardiography (TOE) also uses the principles of Doppler shift to measure CO. Other methods of measuring CO using pulmonary gas clearance and electrical impedance are available but are less often used in clinical practice.
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